catalysts

Article
A Study on the Pyrolysis Behavior and Product Evolution of
Typical Wood Biomass to Hydrogen-Rich Gas Catalyzed by the
Ni-Fe/HZSM-5 Catalyst
Xueqin Li 1,2 , Yan Lu 1 , Peng Liu 1, *, Zhiwei Wang 3,4 , Taoli Huhe 1 , Zhuo Chen 5 , Youqing Wu 2 and Tingzhou Lei 1, *

1 Changzhou Key Laboratory of Biomass Green, Safe & High Value Utilization Technology, National-Local Joint
Engineering Research Center of Biomass Refining and High-Quality Utilization, Institute of Urban and Rural
Mining, Changzhou University, Changzhou 213164, China; lxq88889@126.com (X.L.);
luyan6667@163.com (Y.L.); hhtaoli@cczu.edu.cn (T.H.)
2 Department of Chemical Engineering for Energy Resources, School of Resources and Environmental
Engineering, East China University of Science and Technology, Shanghai 200237, China; wyq@ecust.edu.cn
3 School of Environmental Engineering, Henan University of Technology, Zhengzhou 450001, China;
zw.wang@gaut.edu.cn
4 Institute for Carbon Neutrality, Henan University of Technology, Zhengzhou 450001, China
5 School of Management and Economics, North China University of Water Resources and Electric Power,
Zhengzhou 450046, China; chenzhuo@ncwu.edu.cn
* Correspondence: liupeng@cczu.edu.cn (P.L.); ltz@cczu.edu.cn or china_newenergy@163.com (T.L.)

Abstract: The thermo-chemical conversion of biomass wastes is a practical approach for the value-
added reclamation of bioenergy in large quantities, and pyrolysis plays a core role in this process.
In this work, poplar (PR) and cedar (CR) were used as staple wood biomasses to investigate the
apparent kinetics of TG/DTG at different heating rates. Secondly, miscellaneous wood chips (MWC),
in which PR and CR were mixed in equal proportion, were subjected to comprehensive investigations
on their pyrolysis behavior and product evolution in a fixed bed reactor with pyrolysis temperature,
catalyst, and the flow rate H2 O steam as influencing factors. The results demonstrated that both
Citation: Li, X.; Lu, Y.; Liu, P.; Wang, PR and CR underwent three consecutive pyrolysis stages, the TG/DTG curves shifted to higher
Z.; Huhe, T.; Chen, Z.; Wu, Y.; Lei, T. A temperatures, and the peak temperature intervals also enhanced as the heating rate increased. The
Study on the Pyrolysis Behavior and kinetic compensation effect expression and apparent reaction kinetic model of CR and PR pyrolysis
Product Evolution of Typical Wood were obtained based on the law of mass action and the Arrhenius equation; the reaction kinetic
Biomass to Hydrogen-Rich Gas
parameter averages of Ea and A of its were almost the same, which were about 72.38 kJ/mol
Catalyzed by the Ni-Fe/HZSM-5
and 72.36 kJ/mol and 1147.11 min−1 and 1144.39 min−1 , respectively. The high temperature was
Catalyst. Catalysts 2024, 14, 200.
beneficial for the promotion of the pyrolysis of biomass, increased pyrolysis gas yield, and reduced
https://doi.org/10.3390/
tar yield. This process was strengthened in the presence of the catalyst, thus significantly increasing
catal14030200
the yield of hydrogen-rich gas to 117.9 mL/g-biomass . It was observed that H2 O steam was the
Academic Editor: Anna Maria most effective activator for providing a hydrogen source for the whole reaction process, promoted
Raspolli Galletti
the reaction to proceed in the opposite direction of H2 O steam participation, and was beneficial
Received: 1 February 2024 to the production of H2 and other hydrocarbons. In particular, when the flow rate of H2 O steam
Revised: 8 March 2024 was 1 mL/min, the gas yield and hydrogen conversion were 76.94% and 15.90%, and the H2 /CO
Accepted: 14 March 2024 was 2.07. The yields of H2 , CO, and CO2 in the gas formation were significantly increased to
Published: 19 March 2024 107.35 mL/g-biomass , 53.70 mL/g-biomass, and 99.31 mL/g-biomass , respectively. Therefore, H2 was
the most dominant species among gas products, followed by C-O bond-containing species, which
provides a method for the production of hydrogen-rich gas and also provides ideas for compensating
or partially replacing the fossil raw material for hydrogen production.
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
Keywords: wood biomass; Ni-Fe/HZSM-5 catalyst; pyrolysis behavior; products evolution; gaseous
distributed under the terms and products
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).

Catalysts 2024, 14, 200. https://doi.org/10.3390/catal14030200 https://www.mdpi.com/journal/catalysts

Catalysts 2024, 14, 200 2 of 20

1. Introduction
Pyrolysis technology plays a significant role in the sectors of petrochemicals, chemi-
cals, and energy and is responsible for the production of various energy products [1]. In
response to the changing global energy security situation and the increasing emphasis on
environmental protection, enterprises in the petrochemical, chemical, and energy produc-
tion sectors are actively exploring new pyrolysis technologies. As one of the important
thermochemical conversion technologies, biomass pyrolysis refers to the process of heating
and degrading biomass raw materials to combustible gas, liquid bio-oil, and solid biochar
under anaerobic or anoxic conditions [2]. In the process of pyrolysis, biomass raw materials
would incur a series of physical (heat transfer and material transfer during the heating
process, etc.) and chemical changes (primary, secondary, and even multi-level chemical
reactions) by controlling the conditions of the pyrolysis process (raw material types and
compositions, reaction temperatures, heating rate, residence times and reactor types, etc.),
resulting in different types of products [3]. The technology and principle of the traditional
pyrolysis of biomass are shown in Figure 1, and the research status of pyrolysis and gasifica-
tion reactors nationally and globally is shown in Table 1. Among them, the fixed bed reactor
is an internal thermal coupling process, which can be divided into updraft, downdraft,
and transverse fixed bed reactors according to the movement direction of airflow in the
furnace. That is, gas is used as a heat carrier to make contact with raw materials and, in turn,
provide heat. The structure is relatively simple and has many advantages, such as a wide
adaptability of raw materials, simple manufacturing, low costs, few moving parts, simple
operation, and the high thermal efficiency of the system. However, fixed bed pyrolysis has
certain requirements on the particle size, ash content, and ash melting point of biomass,
and to maintain the autothermal reaction system, air should be used as a gasifying agent.
Thus, the resulting gas is easy to dilute with N2 and CO2 , reducing the content of effective
components such as H2 and CO, and the content of by-products such as tar is high, which
is not conducive to the production of hydrogen-rich gas. At the same time, according to the
structure, the pyrolysis process of the fluidized bed is divided into a bubbling fluidized
bed gasifier, circulating fluidized bed gasifier, airflow bed gasifier, conical fluidized bed
gasifier, etc., which have the advantages of high heat and mass transfer efficiency, high
production capacity, and uniform reaction temperature. However, the dust entrainment
is serious, the gas–solid residence time is short, and the carbon conversion rate is low. In
addition, the pyrolysis process of the airflow bed uses oxygen as a gasifying agent, and the
operating environment of high temperature and high pressure is dangerous. Therefore, it
is urgent to solve the various problems caused by controlling the sub-processes of biomass
pyrolysis and gasification. It is also urgent to reform and solve the various problems that
arise in different chemical reactions caused by the mutual shackles of thermodynamics
and kinetics. In particular, tar is an important by-product; it is difficult to achieve selective
regulation and the efficient removal of the reaction process.
By analyzing the thermogravimetric (TGA), derivative thermogravimetric (DTG), and
pyrolysis characteristics of biomass, we may explore whether hydrogen-rich gas can be
prepared by the catalytic pyrolysis of biomass. The TGA and DTG data obtained from
thermogravimetric balances are widely used to determine the intrinsic kinetics of pyrolysis.
Kinetic parameters such as the apparent activation energy and pre-exponential factor are
primarily estimated by either the model-based method or the model-free method [4]. Tan
et al. [5] found an increase in temperature was found to elevate the CO, CH4 , and mono-
cyclic aromatic hydrocarbon content, whereas it decreased the contents of phenols, acids,
aldehydes, and other oxygenates. In addition, the catalytic pyrolysis process effectively
inhibited the production of acids, phenols, and furans in the liquid.
 University of Laval Vacuum fluidized bed Canada 50
NREL Ablation rotating cone America 30
RTI Fluidized bed Canada 30
VET/Ensym Circulating fluidized bed Finland 30
Catalysts 2024, 14, 200 CRES Circulating fluidized bed Greece 20 3 of 20
University of Waterloo Fluidized bed Canada 4

(a) Fixed bed reactor

Biomass Biomass Biomass (b) Fluidized bed reactor
Gas Gas
Gas

Drying Drying Drying

Pyrolysis
Bubbing Circulating
Pyrolysis
Biomass Gasification agent

Combustion
Reduction Air Air
Combustion (d) Entrained flow reactor (e) Plasma reactor
Combustion Biomass
Air
Gas
Air Reduction Gas
Ash
Gasificat
Gas ion agent
Ash Gas Biomass

Updraft Downdraft Crossdraft

Gasification agent
Biomass (c) Rotary kiln reactor
Gas
Plasma torch

Slag
Residual materials
Slag

Figure 1.
Figure 1. Schematic
Schematic view
view of
of different
different types
types of
of reactors.
reactors.

Table By analyzing
1. Research theofthermogravimetric
status pyrolysis/gasification(TGA),
reactor. derivative thermogravimetric (DTG),
and pyrolysis characteristics of biomass, we may explore whether hydrogen-rich gas can
beResearch
prepared Organization Pyrolytic Technique
by the catalytic pyrolysis of biomass. The TGA Country Sale (kg/h)
and DTG data obtained from
thermogravimetric
Dynamotive balances are Fluidized
widely used bed to determine the Canada intrinsic kinetics 1500
of pyroly-
sis. Red Arrom/Emsyn
Kinetic parameters such Circulating fluidizedactivation
as the apparent bed America
energy and pre-exponential1250 factor
Red Arrom/Emsyn Circulating fluidized bed America 1000
are primarily estimated by either the model-based method or the model-free method [4].
ENEL/Emsym Circulating fluidized bed Italy 625
Tan et al. [5] found an increaseRotating
BTC/kara
in temperature
cone
was found to elevate the CO, 200
Netherlands
CH4, and
monocyclic aromatic hydrocarbon
Uniom Feboea/Waterloo content,
Fluidized bedwhereas it decreased Spain the contents of200 phenols,
acids, aldehydes,
Ensym and otherCirculating
oxygenates. In addition,
fluidized bed the catalytic
Canada pyrolysis process 100 effec-
BTC the production of
tively inhibited Rotating
acids, cone
phenols, and furans Netherlands
in the liquid. 50
University
Catalyticof Hamburg Fluidized
pyrolysis is an efficient bed of biomass Germany
method thermal conversion. Under 50 the
University of Laval Vacuum fluidized bed Canada 50
action of a catalyst, pyrolysis products can be cracked into short-chain intermediate prod-
NREL Ablation rotating cone America 30
ucts by the RTI
dehydration or decarboxylation
Fluidized bedof long-chain bio-oilCanada molecules and inhibit
30 the
occurrence of
VET/Ensym secondary cracking reactions; thus,
Circulating fluidized bed high-quality
Finland target products can
30 be ob-
tained by directional
CRES conversion [6]. Recently,
Circulating catalytic pyrolysis
fluidized bed Greecehas attracted substantial
20
University
research andofcommercialization
Waterloo Fluidized
attention,bedwith over 15,000 Canadajournal articles and4 patents
published in the past decade alone. Wang et al. [7] overviewed the catalytic reaction
routes, reactionpyrolysis
Catalytic types, and keyefficient
is an steps involved
methodinofthe selective
biomass preparation
thermal of various
conversion. Underim-
portant products from lignocellulose and put forward the rational design
the action of a catalyst, pyrolysis products can be cracked into short-chain intermediate methods of ac-
tive and robust heterogeneous catalysts. Eliseo et al. [8] analyze the main
products by the dehydration or decarboxylation of long-chain bio-oil molecules and inhibit kinetic features
of biomass
the pyrolysis,
occurrence devolatilization,
of secondary and the gas
cracking reactions; phase
thus, reactions of
high-quality the released
target productsspecies.
can be
Wang et by
obtained al. [9] comprehensively
directional conversionreviewed recent
[6]. Recently, advances
catalytic in bothhas
pyrolysis theattracted
fundamental stud-
substantial
ies and technological
research applications
and commercialization of biomass
attention, withpyrolysis.
over 15,000 Therefore,
journal the overall
articles andpyrolysis
patents
process of in
published biomass
the pastcandecade
be considered
alone. Wang the decomposition of polymer
et al. [7] overviewed the chains in reaction
catalytic biomass
routes, reaction types, and key steps involved in the selective preparation of various
important products from lignocellulose and put forward the rational design methods
of active and robust heterogeneous catalysts. Eliseo et al. [8] analyze the main kinetic
features of biomass pyrolysis, devolatilization, and the gas phase reactions of the released
species. Wang et al. [9] comprehensively reviewed recent advances in both the fundamental
studies and technological applications of biomass pyrolysis. Therefore, the overall pyrolysis
process of biomass can be considered the decomposition of polymer chains in biomass
Catalysts 2024, 14, 200 4 of 20

macromolecules to produce condensable volatiles (bio-oil), no condensable gases, and

biochar via externally supplied heat under an inert atmosphere. But the outcomes of
biomass pyrolysis are heavily dependent on its reaction conditions. However, at present,
the research on the pyrolysis mechanism of biomass pyrolysis is mostly based on the
structure of biomass raw materials and pyrolysis products to deduce the possible reaction
path in the process of pyrolysis or to speculate the possible evolution path of product
functional groups by a method of theoretical calculation. More importantly, obtaining high-
quality hydrogen-rich gas by improving and optimizing reaction conditions not only serves
as one of the important paths toward the development of biomass pyrolysis technology,
but it also provides an important theoretical basis for promoting the utilization of biomass
pyrolysis gas.
Based on the structure of the chemicals of biomass and their components and relying
on thermogravimetric behavior and pyrolysis kinetics, this study explored and optimized
the process of the catalytic pyrolysis of wood biomass to hydrogen-rich gas in a fixed-bed
reactor with pyrolysis temperature, catalysts, and H2 O steam as influencing factors; this
was to determine the reaction path and mechanism of catalytic pyrolysis and provides a
theoretical basis for the pyrolysis process of biomass. This study also paves the way for a
greener and more sustainable low-carbon future.

2. Results and Discussion

2.1. Pyrolysis Kinetics of Wood Biomass
2.1.1. TG/DTG Analysis
The TG and corresponding DTG curves of PR and CR at the heating rates of 10, 20, 30,
and 40 ◦ C/min are shown in Figure 2. The higher the peak value, the faster the reaction rate
at this temperature. As shown in Figure 2, it is quite clear that the whole decomposition
process can be categorized into three successive stages, i.e., drying, rapid pyrolysis, and
carbonization. In the drying stage (before 200 ◦ C), the biomass samples were preheated,
and the external moisture gradually evaporated and was removed from light volatile
matter. Since biomass is a complex polymer, structural evolutions, like depolymerization,
reorganization, and glass transition, would take place in this stage, that is, the modification
of raw biomass materials [10]. The rapid pyrolysis stage (200~600 ◦ C) was the major weight
loss stage, in which a great number of volatile substances were continuously generated
due to the thermal decompositions of weak bonds between cellulose and hemicellulose
as well as the linkages between lignin monomers. Additionally, it was observed that the
temperature ranges during the pyrolysis of PR and CR were similar, which was 200–550 ◦ C
at different heating rates, which is the maximum decomposition rate of both hemicellulose
and cellulose. In particular, more components of CR and PR were decomposed or trans-
formed before 400 ◦ C. The maximum mass loss rate (~50%) was about 330~390 ◦ C, and
the corresponding maximum weight loss temperatures were located at 365 ◦ C and 370 ◦ C,
respectively, with a heating rate of 30 ◦ C/min. So, the order of their thermal stability was
CR > PR. In other words, the range of the pyrolysis interval for PR was similar to that of
CR, indicating that a similar pyrolysis reaction was shown in the pyrolysis process of wood
biomass. In the carbonization stage (600–900 ◦ C), the rest of the lignin fractions with high
bond energies tended to aggregate, forming char structures (fixed carbon) and presenting
slow variations in weight loss. Among the three major components in biomass, lignin is the
only polymer that has an aromatic structure, including various branches and strengthened
bonds [11], which gives it high thermal stability. Thus, thermal decomposition takes place
over a wider temperature range and covers the whole pyrolysis process. Meanwhile, the
TG/DTG curves were roughly close to a straight line until the end of the pyrolysis reaction.
Catalysts 2024,2024,
Catalysts 14, x 14,
FOR PEER REVIEW
200 5 of 20
5 of 20

110 -1.2 110 -0.8

(a) PR 40mL/min 40mL/min
Ti (b) CR
100 30mL/min 100 30mL/min -0.7
-1.0 Ti
20mL/min 20mL/min
90
10mL/min 90 10mL/min -0.6
80 -0.8
Tm 80 -0.5
Weight loss(%)

Weight loss(%)
Tm

DTG(%/min)

DTG(%/min)
70
-0.6 70 -0.4
60
-0.4 60 -0.3
50
50 -0.2
40 -0.2
40 Tt -0.1
30 Tt
0.0
20 30 0.0

10 0.2 20 0.1
100 200 300 400 500 600 700 800 900 100 200 300 400 500 600 700 800 900
Temperature(℃) Temperature(℃)

Figure 2. TG/DTG
Figure curvecurve
2. TG/DTG of wood biomass
of wood at different
biomass heating
at different rates.rates.
heating

The The
DTG DTG peakpeakshowsshows thethe overall
overall degradationrate
degradation rateofofall
allreactions
reactions combined [12]. [12]. ItItwas
wasalso
alsoobserved
observedfrom fromFigure
Figure22thatthatDTG
DTGcurves
curvesshowed
showedsimilarsimilarvariation
variationtrends
trendsininaddition
ad-
dition to the acceleration of pyrolysis rates with an increase in heating rates. In compari-there
to the acceleration of pyrolysis rates with an increase in heating rates. In comparison,
son,was
therea difference in the position
was a difference and height
in the position of the of
and height peak,
the which is consistent
peak, which with the
is consistent study
with
of Garima et al. [13]. As the heating rate increased from 10 ◦ C/min to 40 ◦ C/min, the initial
the study of Garima et al. [13]. As the heating rate increased from 10 °C/min to 40 °C/min,
and final
the initial andtemperatures all shifted
final temperatures all slightly
shifted to a higher
slightly to temperature range, andrange,
a higher temperature the maximum
and
the weight
maximum lossweight
temperature and pyrolysis
loss temperature andinterval alsointerval
pyrolysis increased.alsoThe above situation
increased. The above might
situation might be attributed to (1) the increase in heat rate during pyrolysis leading toheat
be attributed to (1) the increase in heat rate during pyrolysis leading to the decrease in
transfer efficiency
the decrease or (2) the
in heat transfer higher heating
efficiency or (2) therate stimulated
higher heating byrate
augmented
stimulatedthermal energy
by aug-
promoting the proceeding pyrolysis reactions, thus increasing
mented thermal energy promoting the proceeding pyrolysis reactions, thus increasing the the maximum value of the
maximum value of the pyrolysis rate. The pyrolysis characteristic parameters of PR andrates
pyrolysis rate. The pyrolysis characteristic parameters of PR and CR at four heating
CR atarefour
shown in Table
heating rates2. Among
are shownthem in are x = 2.
Table 0.99, n = 1, them
Among and Rare = 8.31. Therefore,
x = 0.99, n = 1,the
andpyrolysis
R=
of wood biomass is mainly a process of carbon enrichment,
8.31. Therefore, the pyrolysis of wood biomass is mainly a process of carbon enrichment, and the depolarity functional
andgroup of organic
the depolarity components
functional group andofthe pyrolysis
organic reactionand
components are facilitated
the pyrolysis at areaction
higher heating
are
facilitated at a higher heating rate. The pyrolysis of cellulose, hemicellulose, andThe
rate. The pyrolysis of cellulose, hemicellulose, and lignin is interactive [14]. existence
lignin is
of lignin inhibits the thermal polymerization of polysaccharides in cellulose, promotes
interactive [14]. The existence of lignin inhibits the thermal polymerization of polysaccha-
the formation of medium- and low-molecular-weight products in cellulose, and reduces
rides in cellulose, promotes the formation of medium- and low-molecular-weight prod-
the content of char. The existence of cellulose inhibits the formation of char in lignin and
ucts in cellulose, and reduces the content of char. The existence of cellulose inhibits the
promotes the formation of lignin derivatives. In comparison, the reaction between cellulose
formation of char in lignin and promotes the formation of lignin derivatives. In compari-
and lignin is more obvious in the process of pyrolysis.
son, the reaction between cellulose and lignin is more obvious in the process of pyrolysis.
Table 2. Pyrolysis characteristic parameters of PR and CR at different heating rates.
Table 2. Pyrolysis characteristic parameters of PR and CR at different heating rates.
Sample β (mL/min)
Sample β (mL/min) m0 (mg)
m0 (mg) m (mg)
m (mg) m∞ (mg)
m∞ (mg) t (min)
t (min) T (K)T (K) RT RT
10 10 12.66
12.66 1.41 1.41 1.27 1.27 146.00
146.00 1123.15
1123.15 9337.87
9337.87
20 20 12.11
12.11 1.61 1.61 1.52 1.52 104.50
104.50 1123.50
1123.50 9340.78
9340.78
PR PR
30 30 12.69
12.69 1.69 1.69 1.62 1.62 92.1892.18 1123.33
1123.33 9339.32
9339.32
40 40 12.41
12.41
1.63 1.63 1.56 1.56 85.7685.76 1123.33
1123.33
9339.32
9339.32
10 17.41 3.31 3.15 142.00 1123.15 9337.87
10 17.41 3.31 3.15 142.00 1123.15 9337.87
20 15.98 3.08 2.97 104.50 1123.50 9340.78
CR 20 15.98 3.08 2.97 104.50 1123.50 9340.78
CR 30 16.16 3.18 3.06 92.18 1123.33 9339.32
40 30 16.16
16.07 3.15 3.18 3.05 3.06 85.7692.18 1123.33
1123.33 9339.32
9339.32
40 16.07 3.15 3.05 85.76 1123.33 9339.32
2.1.2. Analysis of Apparent Kinetics
The kinetic parameters, including the activation energy (Ea) and preexponential fac-
tor (A), of two wood biomasses were calculated according to the law of mass action and
the Arrhenius equation based on TG analysis. The Ea and A data are shown in Table 3. It
Catalysts 2024, 14, 200 6 of 20

2.1.2. Analysis of Apparent Kinetics

The kinetic parameters, including the activation energy (Ea) and preexponential factor
(A), of two wood biomasses were calculated according to the law of mass action and the
Arrhenius equation based on TG analysis. The Ea and A data are shown in Table 3. It can
be seen in Table 3 that there are some differences in Ea and A at different heating rates. In
general, the increase in Ea is accompanied by the increase in A. However, as the shape of
the curve in the TG method is related to the heating rate and other test conditions, it is
necessary to introduce the corresponding kinetic compensation effect. According to the
research of relevant scholars [15], there is a relationship between kinetic parameters A and
Ea as follows: ln(A) = aEa + b. Furthermore, the data points in Table 3 are linearly fitted to
obtain the expression of the kinetic compensation effect of CR and PR pyrolysis, as shown
in Equations (1) and (2).
ln(A) = 0.09583Ea + 0.12230 (1)
ln(A) = 0.09548Ea − 0.1470 (2)

Table 3. Kinetic parameters of biomass pyrolysis under different heating rates.

PR CR
β(mL/min)
Ea (kJ/mol) A (min−1 ) Ea (kJ/mol) A (min−1 )
10 73.89 1341.81 73.04 1237.76
20 72.22 1144.56 72.27 1150.18
30 71.69 1091.38 72.44 1169.72
40 71.63 1084.02 71.77 1099.88

The Ea obtained at different heating rates was averaged, and the A was obtained by
using the kinetic compensation effect expression. The apparent reaction kinetic model of
wood biomass was obtained, as shown in Equations (3) and (4).
 
dx 1147.11 72, 380
= exp − (1 − x ) n (3)
dT β 8.314T
 
dx 1144.39 72, 360
= exp − (1 − x ) n (4)
dT β 8.314T
It was obvious from Table 4 that there was little difference in the pyrolysis kinetic
parameters of the two wood biomasses, and the Ea of their pyrolysis reactions was about
72 kJ/mol. This was mainly due to the small difference in the composition of cellulose,
hemicellulose, and lignin, which led to little difference in the thermal reaction path, trans-
formation direction, and difficulty degree of transformation in the heated state. This slight
difference was mainly due to the different degrees of decomposition of the three com-
ponents at different temperature levels and the different durations of pyrolysis with the
continuous increase in temperature. Specifically, cellulose produced a small amount of
carbon after rapid pyrolysis between 325 ◦ C and 375 ◦ C, lignin slowly pyrolyzed to form
more carbon between 250 ◦ C and 500 ◦ C, and hemicellulose decomposed rapidly between
225 ◦ C and 325 ◦ C [16]. The pyrolysis of three components produced different products,
which promoted/inhibited each other. Therefore, the complex heat and mass transfer in
the pyrolysis process and many factors lead to the difference in the kinetic behavior of
the pyrolysis process of biomass. Additionally, the greater the Ea, the more difficult the
pyrolysis reaction at the same temperature [17]. The Ea difference between CR and PR
was very small, indicating that the difficulty of pyrolysis at the same temperature was the
same. At the same time, other types of raw materials with higher Ea need to consume more
external energy to achieve the same conversion effect under the same conditions. Therefore,
it is necessary to optimize the pyrolysis reaction conditions, improve the heat and mass
Catalysts 2024, 14, 200 7 of 20

transfer conditions of the pyrolysis process, and grasp the pyrolysis reaction path to obtain
specific target products.

Table 4. Reaction kinetic parameters of pyrolysis of wood biomass.

Sample Ea (kJ/mol) A (min−1 )

CR 72.38 1147.11
PR 72.36 1144.39

2.2. Effect of Pyrolysis Temperature on the Product Distribution from Catalytic Pyrolysis of MWC
2.2.1. Product Distribution and Release Rate of Pyrolysis Gas
Under the action of the Ni-Fe/HZSM-5 catalyst, the heating rate of 20 ◦ C /min rose
from 200 ◦ C to 900 ◦ C and was kept at this temperature for 30 min to explore the main
product distribution law of the pyrolysis of MWC. The reaction formula for the catalytic
pyrolysis of MWC is Equation (5). Figure 3 exhibits the released law analysis of gases
from the catalytic pyrolysis of MWC at 200–900 ◦ C. The analysis showed that H2 was the
most dominant gaseous product during the pyrolysis process; in addition, the gaseous
products also comprised some small molecule gases, such as CO, CO2 , and CH4 . The
effect mechanism of pyrolysis temperature on the release rate of each component was
different. In particular, when the pyrolysis temperature reached 700 ◦ C, the H2 release rate
reached the maximum (14.79 mL/min). This was because continuous heating promoted the
bond-breaking transformation of macromolecules and strengthened the ability of hydrogen
evolution. With the continued increase in temperature, the release rate of H2 began to
decrease, which was due to the complex reforming reaction (Equations (6)–(8)) between
gases [18], indicating that the reaction before 700 ◦ C was the process of releasing H2 by
the catalytic pyrolysis of MWC and the consumption process of H2 in the reaction system
occurred after 700 ◦ C. Correspondingly, the release rate of CH4 reached its maximum at
500 ◦ C, which is beneficial to promote the effective cracking of intermediate products to
achieve the best effect of hydrogen release. With the continued increase in temperature,
the release rate of CH4 began to decrease until it reached an equilibrium, indicating that
the catalytic pyrolysis of MWC before 500 ◦ C produced CH4 , and the reduction reaction
of hydrogen and C to produce CH4 (Equation (6)) occurred after 500 ◦ C. When the CH4
release rate began to equalize, the reduction reaction of CO2 and H2 (Equation (7)) and the
gasification reaction of carbon deposition (Equation (8)) became the main reactions. The
release rates of CO and CO2 reached the highest at 400 ◦ C, which were 14.41 mL/min and
23.56 mL/min, respectively, indicating that the maximum loss of the catalytic pyrolysis of
MWC was delayed from 365 ◦ C to 400 ◦ C under the action of Ni-Fe/HZSM-5 catalyst.

CX HY OZ N (MWC) → H2 + CH4 + CO + CO2 + H2 O + Cm Hn (tar) + C (char) ∆H > 0 (5)

C + H2 → CH4 ∆H = −75 kJ/mol (6)
CO2 + H2 → CO + H2 O ∆H = +41 kJ/mol (7)
C + CO2 → 2CO ∆H = +172 kJ/mol (8)
The product distribution of the catalytic pyrolysis of MWC at different pyrolysis
temperatures is shown in Figure 3b. The analysis showed that the gas yield increased to
the maximum (51.22%) as the temperature increased from 400 ◦ C to 700 ◦ C. When the
temperature continuously increased to 800 ◦ C, the gas yield decreased obviously, which
was mainly because the high temperature not only promoted the catalytic pyrolysis of
MWC but also promoted the secondary cracking of by-products and the intermolecular
polymerization of pyrolysis gas [19,20]. Thus, the highest tar yield was obtained at 800 ◦ C
(37.5%). When the temperature was further increased to 900 ◦ C, the yield of char and tar
decreased obviously, and the gas yield increased, indicating that the high temperature
promoted the cracking of macromolecular substances, and the main reaction was the tar
 Catalysts 2024, 14, 200 8 of 20

cracking/reforming reaction [21]. Significantly, the tar yield appeared in the lowest range
between 600 ◦ C and 700 ◦ C, the char yield showed a gradual downward trend and was
24, 14, x FOR PEER REVIEW 8 of 20
16.09% at 700 ◦ C, and the total gas yield was 117.9 mL/g-biomass at this same temperature.
Therefore, the pyrolysis temperature is an important factor in reducing tar yield and
increasing gas yield.
25 70
(b) Gas Char Tar
H2 65
(a) CH4
20 60
CO
55
Gas release rate(mL/min)

CO2
50
15
45

Weight(%)
40
10
35
30
5
25
20
0 15
10
0 10 20 30 40 50 60 70 400 500 600 700 800 900
Pyrolysis time(min) Pyrolysis temperature(℃）

Figure 3. Effect of pyrolysis temperature on the release rate (a) and distribution of pyrolysis
products
Figure 3. Effect (b).
of pyrolysis temperature on the release rate (a) and distribution of pyrolysis prod-
ucts (b). 2.2.2. Formation Process and Composition Distribution of Tar
The ion chromatography of tar and the serial numbers of corresponding substances
The product distribution
from the of the catalytic
catalytic pyrolysis of MWCpyrolysis
at 400–900of◦ CMWC at different
are shown pyrolysis
in Figure tem-
4 and Table S1.
peratures is The
shown in Figure
distribution 3b. The
of liquid analysis
products showed
at different that the gas
temperatures yield in
is shown increased to the
Table 5. From the
maximum (51.22%) as of
distribution thecompounds
temperature in tarincreased
composition, from 400 °C to 700
the composition °C.
is the sameWhen the 400
between tem- ◦C
◦
and 800 C, increased
mainly including
perature continuously to 800 aldehydes
°C, the gas (AL),
yieldacids (AC), alcohols
decreased (ALc), which
obviously, ketoneswas(KE),
phenols (PH), furans (FU), esters (ES), and a small number
mainly because the high temperature not only promoted the catalytic pyrolysis of of hydrocarbons. However,
MWC the
content of the same substance varied greatly at different temperatures. At 400 ◦ C, the AC
but also promoted the secondary cracking of by-products and the intermolecular
substances were mainly acetic acid (6.99%), and the KE substances were acetone, butanone,
polymerization of pyrolysis
pentanone, gasderivatives,
and their [19,20]. Thus,withthe highest
a content of tar yieldThe
70.27%. was ALobtained
substancesatincluded
800 °C
(37.5%). When the temperature was further increased to 900 °C, the yield
succinaldehyde, furfural, carboxylic aldehyde, and their derivatives, with a content of char and tarof
decreased obviously,
4.42%. The and the gas yield
ALc substances increased,
included butanediol, indicating
methanol, that the high
alcohol, temperature
and their derivatives,
promoted the cracking of macromolecular substances, and the main reaction wasand
with a content of 12.25%. The PH substances included methoxy, vinyl phenol, the their
tar
derivatives, with a content of 1.04%. The FU substances were
cracking/reforming reaction [21]. Significantly, the tar yield appeared in the lowest range acetyl furan benzofurans
and their derivatives, with a content of 1.22%. The ES substances were phenyl carbamates,
between 600 °C and 700 °C, the char yield showed a gradual downward trend and was
butyrolactone, and their derivatives, with a content of 2.69%. The ALk substances were
16.09% at 700 °C, and
propane the totalwith
derivatives, gasayield
content was 117.9Furfural,
of 1.13%. mL/g-biomass at this same temperature.
5-hydroxymethylfurfural, and acetic
Therefore, the
acid were the main products in the pyrolysis of hemicellulose, while tar
pyrolysis temperature is an important factor in reducing yield
vinyl phenolandandin-L-
creasing gas glucan
yield. are representative products in the pyrolysis of lignin and cellulose [22], respectively.
Therefore, the three components in MWC had different degrees of pyrolysis at ≤400 ◦ C.
2.2.2. Formation Process and Composition Distribution of Tar
The ion chromatography of tar and the serial numbers of corresponding substances
from the catalytic pyrolysis of MWC at 400–900 °C are shown in Figure 4 and Table S1.
The distribution of liquid products at different temperatures is shown in Table 5. From
the distribution of compounds in tar composition, the composition is the same between
400 °C and 800 °C, mainly including aldehydes (AL), acids (AC), alcohols (ALc), ketones
(KE), phenols (PH), furans (FU), esters (ES), and a small number of hydrocarbons. How-
ever, the content of the same substance varied greatly at different temperatures. At 400
°C, the AC substances were mainly acetic acid (6.99%), and the KE substances were ace-
tone, butanone, pentanone, and their derivatives, with a content of 70.27%. The AL sub-
stances included succinaldehyde, furfural, carboxylic aldehyde, and their derivatives,
with a content of 4.42%. The ALc substances included butanediol, methanol, alcohol, and
 rolysis of biomass is summarized in Figure 5; the increase in temperature prom
formation of phenols and alcohols. The ketone compounds are not much affected
perature, but the presence of ketones can effectively reduce the viscosity of tar. It
Catalysts 2024, 14, 200 reduce the thermal stability and chemical stability of tar, so it is necessary
9 of 20 to inh
formation of ketones in the process of improving the pyrolysis of biomass.

18 1920 7 22 28 900 ℃
2 3 24 12 25 26 27
21 23
1 3 56
7 8 11
4 9 10 800 ℃
12 13
1 6 7 11
5
Intensity(a.u.)
3 8 9 15 16 700 ℃
4 10 15 12 13 14 17
6 7 11
1 3 5 8 9 15 16 600 ℃
2 4 10 15 12 13 14 17
1 67 11
3 5 500 ℃
4 8 10 15
12 13 14 16
1 3 6 7 11
5
8
4 10 15 12 13 400 ℃

2 4 6 8 10 12 14
Time(time)
Figure Effect
Figure4.4. of pyrolysis
Effect temperature
of pyrolysis on the liquid
temperature products
on the liquidofproducts
catalytic pyrolysis of MWC.
of catalytic pyrolysis of M

Table 5. Distribution of liquid products by the catalytic pyrolysis of MWC at different

pyrolysis temperatures.

Percent Proportion (%)

Type Name
400 ◦ C 500 ◦ C 600 ◦ C 700 ◦ C 800 ◦ C 900 ◦ C
Acetic acid 3.96 36.01 24.50 23.74 42.91
Acetic acid, (acetyloxy)- 1.61
AC
Propanoic acid 2.61 2.67 2.44
Dodecanoic acid, 3-hydroxy- 3.03 4.42 1.05 2.71
2-Propanone, 1-hydroxy- 66.28 6.53 3.30 5.04 5.53 9.86
1-Hydroxy-2-butanone 0.90 0.99 0.70 2.40
1-Hydroxy-2-pentanone 1.80

KE 2-Cyclopenten-1-one 2.32 2.65 2.02 1.65 2.07 1.62

2-Propanone, 1-(acetyloxy)- 0.77 3.74 6.15
2-Cyclopenten-1-one, 2-hydroxy-
2-Cyclopenten-1-one,
6.16
2-hydroxy-3-methyl-
Succindialdehyde 1.40
3-Furaldehyde 1.19 10.43 7.68 9.06 1.74
AL 2-Furancarboxaldehyde, 5-methyl- 3.23 2.50 3.13 6.91
Furfural 9.03
5-Hydroxymethylfurfural 20.32 15.26 16.82
2,3-Butanediol 4.24 4.16 33.02 3.38 2.49
2-Furanmethanol 2.40 1.95 1.47 1.18 2.91
ALc
Creosol 12.27
2-Propyl-tetrahydropyran-3-ol 5.60 6.06 6.00 64.83 4.75
Catalysts 2024, 14, 200 10 of 20

Table 5. Cont.

Percent Proportion (%)

Type Name
400 ◦ C 500 ◦ C 600 ◦ C 700 ◦ C 800 ◦ C 900 ◦ C
ALk Propanal, 2,3-dihydroxy-, (S)- 1.13 1.34
Phenol, 2-methoxy- 1.04 1.04 0.77 0.91 2.25 14.06
Phenol, 4-ethyl-2-methoxy- 9.39
Phenol, 2,6-dimethoxy- 2.03 1.76
PH
Phenol, 2-methoxy-5-(1-propenyl)-, (E)- 3.13
Phenol, 2-methoxy-4-(1-propenyl)- 9.25
2-Methoxy-4-vinylphenol 9.43
Ethanone, 1-(2-furanyl)- 1.22 0.91 0.72 0.79 1.46
FU
Benzofuran, 2,3-dihydro- 2.09 2.25 2.65
Carbamic acid, methyl-, phenyl ester 1.19 0.90 0.90 2.01
ES
Butyrolactone 1.49 18.60 1.55 1.55 1.90

With the pyrolysis temperature increase to 500 ◦ C, the contents of AC, AL, FU, and
ES substances increased significantly to 40.43%, 20.32%, 3%, and 18.60%, respectively.
The KE substances content decreased significantly to 13.91%, and the contents of ALk,
ALC, and PH substances were not significantly changed, indicating that the appropriate
increase in temperature promoted the complete pyrolysis of three components from MWC.
When the pyrolysis temperature increased to 600 ◦ C, the AC substance content decreased
to 25.55%. In particular, the acetic acid content decreased significantly, and propionic
acid appeared; the contents of KE, AL, and ES substances further decreased to 5.31%,
25.45%, and 2.45%, respectively. But the contents of PH and ES substances increased
significantly to 2.79% and 20.32%, indicating that an increasing temperature was beneficial
to increasing the length of the carbon chain and promoting the pyrolysis of KE substances
to produce gas. However, when the pyrolysis temperature reached 700 ◦ C, the vinyl phenol
appeared in PH substances, and the content of ALc substances increased significantly to
69.39%; the content of ALc substances also increased by 18.4%, indicating that 700 ◦ C was
beneficial for the complete pyrolysis of lignin. Furthermore, when the pyrolysis temperature
was further increased to 800 ◦ C, the AC substances content increased again, indicating
that the high temperature promoted the polymerization and depolymerization of small
oxygen-containing molecular substances to form acids. The dehydration of alcohols and
decarboxylation of carboxylic acids were typical deoxidization reactions to produce H2 O
and CO2 [23], significantly decreasing the contents of ALc and AL substances to 10.16%
and 8.65%. There are some macromolecular oxygen-containing substances in AL, PH, and
KE substances at 900 ◦ C, which may be due to the ketonization initiated by the catalyst;
that is, the conversion of carboxyl and acid into ketones leads to a significant increase in
the content of KE substances [24–26]. The distribution law of the catalytic pyrolysis of
biomass is summarized in Figure 5; the increase in temperature promotes the formation
of phenols and alcohols. The ketone compounds are not much affected by temperature,
but the presence of ketones can effectively reduce the viscosity of tar. It can also reduce the
thermal stability and chemical stability of tar, so it is necessary to inhibit the formation of
ketones in the process of improving the pyrolysis of biomass.
OR PEER REVIEW 11 of 20
Catalysts 2024, 14, 200 11 of 20

Figure 5. Product distribution of catalyzing

Figure 5. Product pyrolysis
distribution of biomass.
of catalyzing pyrolysis of biomass.

2.3. Enhanced Catalytic Pyrolysis of Wood Biomass under H2 O Steam Atmosphere

2.3. Enhanced Catalytic Pyrolysis of Wood Biomass under H2O Steam Atmosphere
The effect of H2 O steam and its flow rate (0.5 mL/min, 1 mL/min, 1.5 mL/min,
The effect of H22O steamon
mL/min) and its flowpyrolysis
the catalytic rate (0.5 mL/min,
of MWC 1 mL/min,The
was investigated. 1.5product
mL/min, 2
distribution
and gaspyrolysis
mL/min) on the catalytic yield are shown
of MWC in Figure
was6. investigated.
The analysis showed The that the additional
product introduction
distribution
of H2 O steam promoted the catalytic pyrolysis process of MWC. In particular, when the
and gas yield are shown in Figure 6. The analysis showed that the additional introduction
flow rate of H2 O steam increased to 1 mL/min, the gas yield and H conversion ratio
of H2O steam promoted the obviously
increased catalytictopyrolysis process
76.94%, 15.90%, and H of /CO
MWC. ratioIn particular,
to 2.07. In the gaswhen the com-
production
2
flow rate of H2O steam increased
position, the yields toof1HmL/min,
2 , CO, and the
CO2 gaswereyield and Hincreased
significantly conversion ratio
to 107.35 mL/g in--biomass ,
creased obviously to 76.94%, 15.90%,
53.70 mL/g -biomass and H2/CO ratio
, and 99.31 mL/g to 2.07. In the gas production com-
-biomass , respectively. This indicated that the addi-
tional introduction
position, the yields of H2, CO, and CO2 were of H 2 O steam
significantly increased to 107.35 mL/g-biomassreaction
could provide a hydrogen source for the whole ,
process and significantly enhance the char gasification reaction (Equation (9)) and water
53.70 mL/g-biomass, and 99.31 mL/g -biomass, respectively. This indicated that the additional in-
vapor shift reaction (Equation (10)), which is beneficial to the production of H2 and other
troduction of H2O steam could provide
hydrocarbons [27]. a hydrogen source for the whole reaction process
and significantly enhance the char gasification C + H2 O → reaction ∆H = +131(9))
CO + H2(Equation and water vapor (9)
kJ/mol
shift reaction (Equation (10)), which is CH beneficial to the production of H2 and other hydro- (10)
4 + H2 O → CO + 3H2 ∆H = +206 kJ/mol
carbons [27].
Figure 7 shows the release rate of main gases at different flow rates of H2 O steam.
Obviously,
C+H as2the
O→ flow
COrate
+H of 2H2 OΔH
steam= +increased to 2 mL/min, the gas yield decreased,
131 kJ/mol (9)
and the tar yield decreased to a certain extent and then began to maintain equilibrium. This
was because the tar had a self-reforming reaction with H2 O and CO2 , indicating that the
additional H2O → COof+H3H
CH4 +introduction 2 ΔH = + 206 kJ/mol (10)
2 O steam would shorten the residence time of tar-containing
gas in the reforming reactor. Thus, the cracking/reforming reaction of tar was inhibited and
consumed a lot of energy, which can be explained by Figure 8. As can be seen from Figure 8,
300 2.25
the degree of carbon deposition
CO on (b)the surface of the catalyst increased with the increase
Char
in H2 O steam flow rate, indicating
CO2 that too much H2 O steam reduced the conversion
Gas
of tar, resulting 250
in the accumulation of a large number of macromolecular substances to
CH4 2.00
18 form carbon deposition and cover the surface of the catalyst. Therefore, the additional
16
H
H2
Gas yield(mL/g-biomass)

C introduction of H2 O steam promotes the steam gasification reaction of char and water–gas
Conversion rate of H/C in the gas(%)

14 200
change reaction but avoids the introduction of excessive H2 O steam.
12
1.75
H2/CO

10

8 150
6

4 1.50
2 100
0
0 0.5 1 1.5 2
H2O flow rate(mL/min)
1.25
 shift reaction (Equation (10)), which is beneficial to the production of H2 and other hydro-
carbons [27].
C + H2O → CO + H2 ΔH = + 131 kJ/mol (9)
Catalysts 2024, 14, 200 12 of 20
CH4 + H2O → CO + 3H2 ΔH = + 206 kJ/mol (10)
Catalysts 2024, 14, x FOR PEER REVIEW 12 of 20

80 300 2.25
(a) CO (b)
70 Char CO
Figure 6. Effect of H2O Gas
steam flow rate on250the distribution of pyrolysis products of catalytic MWC,
2

18
CH4 H2/CO.
(a) distribution of pyrolysisi product, (b) gas yield and 2.00
60
16
H
H2

Gas yield(mL/g-biomass)
C
Conversion rate of H/C in the gas(%)

Figure 7 shows the release rate200

14
50 of main gases at different flow rates of H2O steam.
12
1.75
Weight(%)

Obviously, as the flow rate of H2O steam increased to 2 mL/min, the gas yield decreased,

H2/CO
10

40 8
and the tar yield decreased to a certain 150 extent and then began to maintain equilibrium.
6

30 4
This was because the tar had a self-reforming reaction with H2O and CO2, indicating that 1.50
2 the additional introduction of H2O steam 100 would shorten the residence time of tar-contain-
0
20 0 ing gas in the reforming reactor. Thus, the cracking/reforming reaction of tar was inhibited
0.5 1
H O flow rate(mL/min)
2
1.5 2

1.25
and consumed a lot of energy, which50can be explained by Figure 8. As can be seen from
10
Figure 8, the degree of carbon deposition on the surface of the catalyst increased with the
0 increase in H2O steam flow rate, indicating 0 that too much H2O steam reduced the conver- 1.00
0.0 0.5 sion of1.0 tar, 1.5 in the
resulting 2.0accumulation of a0 large number 0.5 of 1 1.5
macromolecular 2
substances
H2O flow rate(mL/min) H2O flow rate(mL/min)
to form carbon deposition and cover the surface of the catalyst. Therefore, the additional
introduction Figure 6. ofEffect
H2O of steam promotes
H2 O steam the on
flow rate steam gasification
the distribution reaction products
of pyrolysis of char of
and water–
catalytic MWC,
gas change reaction but
(a) distribution avoids the
of pyrolysisi introduction
product, of excessive
(b) gas yield and H2 /CO. H2O steam.

25 5
0 mL/min 0 mL/min
(a) (b)
0.5 mL/min 0.5 mL/min
20 4 1 mL/min
1 mL/min
1.5 mL/min
CH4 release rate(mL/min)

1.5 mL/min
H2 release rate(mL/min)

2 mL/min 2 mL/min
15 3

10 2

5 1

0 0

0 5 10 15 20 25 30 35 40 45 50 55 60 0 10 20 30 40 50 60
Pyrolysis time(min) Pyrolysis time(min)
16 25
(c) (d)
14 0 mL/min 0 mL/min
0.5 mL/min 20 0.5 mL/min
12 1 mL/min
1 mL/min
CO2 release rate(mL/min)
CO release rate(mL/min)

1.5 mL/min 1.5 mL/min

10
2 mL/min 15 2 mL/min
8

6 10

4
5
2

0 0

-2
0 10 20 30 40 50 60 0 10 20 30 40 50 60
Pyrolysis time(min) Pyrolysis time(min)

Figure 7. Effect7.ofEffect
Figure H2O offlow rate
H2 O on rate
flow the gas release
on the from catalytic
gas release pyrolysis
from catalytic of MWC,
pyrolysis (a) H2(a)
of MWC, release
H2 release
rate, (b) CH4 release rate, (c) CO release rate, and (d) CO2 release rate.
rate, (b) CH4 release rate, (c) CO release rate, and (d) CO2 release rate.
Catalysts 2024, 14, x FOR PEER REVIEW 13 of 20

Catalysts
Catalysts 14, 200
2024,2024, 14, x FOR PEER REVIEW 13 of 20 20
13 of

Figure 8. SEM of reacted catalysts by the catalytic pyrolysis of MWC at different H2O steam flow
rates. Figure 8. SEM of reacted catalysts by the catalytic pyrolysis of MWC at different H2O steam flow
Figure 8. SEM of reacted catalysts by the catalytic pyrolysis of MWC at different H2 O steam flow rates.
rates.
Furthermore, the pore
Furthermore, thecharacteristics of the reacted
pore characteristics catalystcatalyst
of the reacted at different flow rates
at different flow rates
were analyzed, Furthermore,
as shown the pore9characteristics of the reacted
withcatalyst at different flow
ringratesthe
were analyzed, as in Figure
shown and Table
in Figure 6. Compared
9 and Table 6. Compared fresh with
catalysts,
freshthecatalysts,
ofwere
degreering the analyzed, as
hysteresis
degree of theloop
shown
frominthe
hysteresis
Figure
loopNfrom
9 and Table 6. Compared
2 adsorption/desorption
withof
curve
the N2 adsorption/desorption
fresh catalysts,
thecurve
reacted the ring
cat-
of the reacted
degree
alyst varied of the
obviously hysteresis loop
at different from the
flow rates N 2 adsorption/desorption curve of the reacted cat-
H2O steam.
of rates
catalyst varied obviously at different flow of H2 OThe pore
steam. size
The varied
pore size greatly
varied greatly
alyst varied
in the range obviously at different rates of H2O specific
flowenlarged steam. The pore area
size and
varied greatly
in theofrange
0–5 nm. In addition,
of 0–5 H2O steam
nm. In addition, H O steamthe enlarged thesurface
specific surface pore
area and
in the range of 0–5 nm. In addition, H2O2steam enlarged the specific surface area and pore
volumeporeof the catalyst
volume in varying
of the catalyst degrees.
in varying Indegrees.
particular, the pore characteristic
In particular, of the re- of the
the pore characteristic
volume of the catalyst in varying degrees. In particular, the pore characteristic of the re-
acted catalyst
reacted under
catalyst1 mL/min
under 1 2O steamH
HmL/min was
2 O better,
steam which
was was
better, consistent
which was with the anal-
consistent with the
acted catalyst under 1 mL/min H2O steam was better, which was consistent with the anal-
ysis of analysis
the experimental
of the results.
experimental results.
ysis of the experimental results.
130 0.10
130 0.5mL/min H2O reacted catalyst desorption 0.10
(a) 0.5mL/min H2O reacted catalyst desorption (b)
(a)
0.5mL/min H2O reacted catalyst adsorption (b)
Quantity adsorbed/desorption(cm3/g STP)

0.5mL/min H2O reacted catalyst adsorption

120
Quantity adsorbed/desorption(cm3/g STP)

0.5mL/min H2O reacted catalyst

120 1mL/min H2O reacted catalyst desorption
1mL/min H2O reacted catalyst desorption 0.5mL/min H2O reacted catalyst
1mL/min H2O reacted 1mL/min H 2O reacted
H2Ocatalyst
1mL/mincatalyst adsorption
H2O reacted catalyst adsorption 0.08 0.08
1mL/min reacted catalyst
1.5mL/min1.5mL/min
H2O reacted
H2Ocatalyst
110 110 1.5mL/min H2O1.5mL/min
reacted catalyst desorption
H2O reacted catalyst desorption reacted catalyst
Pore Volume (cm3/g)

Pore Volume (cm3/g)

1.5mL/min H2O1.5mL/min
reacted catalyst adsorption 2mL/min H 2O reacted
2mL/min H Ocatalyst
reacted catalyst
H2O reacted catalyst adsorption 2

100 2mL/min H2O reacted

2mL/mincatalyst desorption
H2O reacted catalyst desorption
100 0.06 0.06
2mL/min H2O reacted
2mL/mincatalyst adsorption
H2O reacted catalyst adsorption

90 90

0.04 0.04
80 80

70 70
0.02 0.02

60 60
0
0.0 0.0
0.2 0.2 0.4
0.4 Relation0.6 0.6
0.8 0.8
1.0 1.0 0 5 10 515 1020 1525 20Pore
30 25width(nm)
35 30 4035 4540 5045 5550 55
pressure(P/Po) Pore width(nm)
Relation pressure(P/Po)
Figure 9. N2 adsorption/desorption isotherms and pore distribution of reacted catalysts, (a) quan-
Figure 9. N2 adsorption/desorption
Figure isotherms
9. N2 adsorption/desorption and pore
isotherms anddistribution
porevolume. of reacted
distribution catalysts,
of reacted (a) quan-
catalysts, (a) quantity
tity adsorbed/desorption, and (b) distribution of pore
tity adsorbed/desorption, and (b) distribution of pore volume.
adsorbed/desorption, and (b) distribution of pore volume.
Table 6. Effect of H2O flow rate on the pore characteristics of catalyst.
Table 6. Effect of H2O flow rate on the pore characteristics of catalyst.
Table 6. Effect of H2 O flow rate on the pore characteristics of catalyst.
BET Surface t-Plot Micropore Total Pore Vol- Pore Size Average Nanoparti-
Sample BET Surface t-Plot Micropore Total Pore Vol- Pore Size(nm) Average Nanoparti-
Sample BET Surface Area (m²/g) Area
t-Plot Micropore(m²/g) Total ume
Pore(cm³/g) cle (nm)
Average
Sample Area (m²/g) Area (m²/g) ume (cm³/g) Pore Size (nm) cle (nm)
(nm)
Reacted catalyst under 0.5 mL/minArea H2(m²/g)
O 227.56 Area (m²/g) 157.86 Volume (cm³/g) 0.17 2.93 Nanoparticle
26.37 (nm)
Reacted catalyst under
Reacted 0.5 mL/min
catalyst under 1HmL/min
2O
H227.56
O 229.30 157.86 157.15 0.17 0.18 2.93 3.21 26.37 26.17
Reacted catalyst under 2
Reacted catalyst under 1 mL/min H2mL/min
O 227.56
229.30 157.86 0.17 3.21 2.93 26.37
Reacted catalyst
0.5 mL/min Hunder
2O 1.5 H 2O 224.82 157.15 171.25 0.18 0.16 2.82 26.17 26.16
Reacted catalyst under
Reacted 1.5 mL/min
catalyst under 2HmL/min
2O H224.82
2O 224.35 171.25 174.34 0.16 0.17 2.82 3.11 26.16 26.74
Reacted catalyst under
Reacted catalyst under 2 mL/min H2O 229.30
224.35 157.15
174.34 0.18
0.17 3.11 3.21 26.74 26.17
1 mL/min H2 O
Table 7 listed the related studies on the production of hydrogen-rich gas by the cata-
Reacted catalyst under
Table 7224.82
listed
lytic the related
pyrolysis studies
of biomass on theyears
in recent
171.25 production
[27–40],of
0.16 inhydrogen-rich
which the gas type,
2.82catalyst by the cata-
type
26.16 of raw
1.5 mL/min H2 O
material,
lytic pyrolysis gas composition,
of biomass in recentand
yearsyield were in
[27–40], taken as indicators.
which the catalyst In type,
contrast,
typeinofthis
rawstudy,
Reacted catalyst under
material, the
gas pyrolysis temperature
composition, and andwere
yield flow taken
rate ofasHindicators.
2O steam had In a3.11
great influence
contrast, in this on the cata-
study,
224.35 174.34 0.17 26.74
2 mL/min H2 O lytic temperature
pyrolysis law andof wood
the pyrolysis flowbiomass.
rate of HIn2Oparticular,
steam had a suitable
a great temperature
influence onguarantees
the cata- the
complete
lytic pyrolysis lawconversion of wood In
of wood biomass. biomass and catalyst
particular, stability,
a suitable and the type
temperature of catalyst
guarantees theis the
basis of
complete conversion the resistance
of wood
Table 7 listed to carbon
the biomass deposition
and catalyst
related studies and hydrogen
stability,
on the production
and the
production oftype by the directional
of catalyst isgas
hydrogen-rich theby the
pyrolysis
basis ofcatalytic
the of wood
resistance
pyrolysis ofbiomass.
to carbon However,
deposition
biomass in recent the
and residence
hydrogen
years [27–40],time of pyrolysis
production
in which by the
the gasdirectional
is limited,
catalyst type, typeand of
pyrolysis
rawofmaterial,
wood biomass. However, the
gas composition, andresidence time
yield were of pyrolysis
taken gas is limited,
as indicators. and in this
In contrast,
study, the pyrolysis temperature and flow rate of H2 O steam had a great influence on the
Catalysts 2024, 14, 200 14 of 20

catalytic pyrolysis law of wood biomass. In particular, a suitable temperature guarantees

the complete conversion of wood biomass and catalyst stability, and the type of catalyst is
the basis of the resistance to carbon deposition and hydrogen production by the directional
pyrolysis of wood biomass. However, the residence time of pyrolysis gas is limited, and
the contact condition between tar-containing gas and bed material is poor, leading to
insufficient conversion of tar and polymerization to form heavy components, which affects
the conversion and utilization efficiency of wood biomass. At the same time, biomass tar
often contain a variety of oxygenated compounds, which can compromise their usefulness
as a fuel [41]. Therefore, effectively controlling the formation of tar from the pyrolysis
source and prolonging the contact time between tar-containing gas and bed material is an
important condition to achieve effective tar removal.

Table 7. Comparison of the effects of catalytic pyrolysis of biomass.

Gas Production Composition (vol%)

Catalyst Raw Material Temperature (◦ C)
H2 CH4 CO CO2
40%wtCaCO3 Rice straw 750 11.8 14.5 15
K2 CO3 /Ni-Al2 O3 Coking coal 560 61.4 0 1.9 36.6
Ni-based catalyst Apricot pit 850 88.74 9.15
biocarbon 800 34.53 10.71 30.37
Corn straw
650 79.1
Dolomite
Pine 900 70.5
Ni-Mo/Al2 O3 Sawdust 600 52.82 3.8 33.68 8.63
SiO2 Sawdust 600 0.45 9.31 3.65 0.75
Ni-Al2 O3 -Ca Pine 500 0.04 0.36 3.27 3.38
Pine 31.31 1.8 49.83 16.4
Ni-based catalyst Wood biomass 700 46.03 0.79 39.03 14.15
Cellulose 34.67 1.08 47.36 16.83
Ni-CaO catalyst Pine 750 60.23 6.74 18.44 13.18
1.8Ni/Al2 O3 Pine 900 29.78 15.55 39.97 10.20
W-Ni0.65 Beech wood 600 0.58 0.9 10 16.6
RM800-40%Fe2 O3 Corn straw 900 22.98 29.8 36.6 10.6
5%SiO2 Wheat straw 600 20.7 7.89 25.86 45.6
BFeCo Bamboo 850 32.6 7.96 27.97 28.76

3. Materials and Method

3.1. Raw Materials
Two kinds of feedstock (poplar, PR, and cedar, CR) from the wood processing plant
were crushed and ground to obtain particles less than <40 mm by a grinder and stored in
a desiccator for analysis of apparent kinetics. The proximate analysis was monitored ac-
cording to standard methods shown in our previous paper [42,43]. The elemental analyzer
(Elementar Vario Micro Cube, Shanghai, China) was used to analyze elements of C, H, N,
and S, and the O element was calculated by mass difference. Cellulose, hemicellulose, and
lignin contents were determined by the classical method proposed by Van Soest [44]. The
results of proximate analysis, ultimate analysis, and fiber analysis of two wood biomass
samples are shown in Table 8. The mixture of PR and CR in equal proportion was used
as the samples of the catalytic pyrolysis experiment, which is called miscellaneous wood
chips (MWC).
The catalyst was synthesized according to the method shown in our previous pa-
per [45], used HZSM-5 (H-type zeolite molecular sieve-5) with a SiO2 /Al2 O3 ratio of 25 as
support, and impregnated by a 0.17 mol/L solution of Ni(NO3 )2 ·6H2 O, and the Ni loading
was 8 wt.%. Fe (NO3 )3 ·9H2 O was used as a precursor of the promoter Fe, and the loading
of Fe was 4 wt.% (relative to the amount of Ni). After impregnation, the mixture was dried
overnight, followed by calcination at 550 ◦ C for 3 h, marked Ni-Fe/HZSM-5. The surface
properties and pore structures of catalysts were determined by surface area and porosity
instrument (Tristar II 3020, MICRO cube, USA), shown in Table 9. The micromorphology of
Catalysts 2024, 14, 200 15 of 20

catalysts was analyzed by scanning electron microscope (SUPRA55, ZEISS, Oberkochen,

Germany), shown in Figure 10. Interaction of Ni and Fe was characterized by XPS technique
(K-Alpha, Thermo Scientific, Waltham, MA, USA) with the excitation source of Al Kα ray,
as shown in Figure 10.

Table 8. Proximate, ultimate, and fiber analyses of PR and CR.

Catalysts 2024, 14, x FOR PEER REVIEW 15 of 20

Proximate Analysis/%
Sample QG (MJ/Kg)
Mad Aad Vad FCad
PR 0.48 53.51 7.27 0.04 38.70 1.63 0.54
PR 9.70 1.30 83.65 16.35 16.62
CR 0.76 51.88 7.51 0.04 36.21 1.62 0.49
CR 10.57 5.35 80.04 Fiber analysis (dry)/%
19.96 16.40
Sample Ultimate analysis (dry)/%
Hemicellulose Cellulose Lignin Extractable
Sample
PR N 19.56 C 53.20
H S 18.96
O# H/C 8.28 O/C
CR
PR 0.48 17.71 53.51 39.45
7.27 0.04 27.62
38.70 1.63 15.22 0.54
CR 0.76 Note: 51.88
ad, air dry free; d, dry free; daf, dry
7.51 0.04ash free; #, By36.21
difference. 1.62 0.49
Fiber analysis(dry)/%
Sample The catalyst was synthesized according to the method shown in our previous paper
Hemicellulose [45], used Cellulose
HZSM-5 (H-type zeolite molecular Lignin sieve-5) with a SiO2/Al Extractable
2O3 ratio of 25 as

PR 19.56 support, and53.20impregnated by a 0.17 mol/L18.96 solution of Ni(NO3)2·6H2O, and the Ni loading
8.28
CR 17.71 was 8 wt.%. 39.45
Fe (NO3)3·9H2O was used as a27.62 precursor of the promoter Fe,15.22 and the loading
of Fe was 4 wt.% (relative to the amount of Ni). After impregnation, the mixture was dried
Note: ad, air dry free; d, dry free; daf, dry ash free; #, By difference.
overnight, followed by calcination at 550 °C for 3 h, marked Ni-Fe/HZSM-5. The surface
properties
Table and pore
9. Physical structures
properties and pore of catalysts
distribution were determined
of fresh by surface
Ni-Fe/HZSM-5 area and porosity
catalyst.
instrument (Tristar II 3020, MICRO cube, USA), shown in Table 9. The micromorphology
BET Surface of catalysts
t-Plot Micropore was analyzed by scanning
t-Plot External electron microscope (SUPRA55, ZEISS,
Total Pore Volume Oberkochen,
Pore Size
Area (m²/g) Germany),
Area (m²/g) shown in SurfaceFigure 10.Area Interaction
(m²/g) of Ni and(cm³/g)
Fe was characterized by (nm)XPS tech-
219.50 nique (K-Alpha,
133.02 Thermo Scientific,
84.48 Waltham, MA, USA)0.17with the excitation source
3.11 of Al
Kα ray, as shown in Figure 10.

XPS

O1s
CKL1
CKL1 Ni LM8
Ni LM2 C1s
Ni 2p Al 2s
Si 2p

Fe 2p Si 2s
Ni LM5 Al 2p
O 2p

1400 1200 1000 800 600 400 200 0

Binging energy(eV)

Figure 10.
Figure 10. The
The morphology and crystalline-phase
morphology and crystalline-phase structure
structure of
of fresh
fresh Ni-Fe/HZSM-5
Ni-Fe/HZSM-5 catalyst.
catalyst.

Table
3.2. 9. Physical
Pyrolysis properties and pore distribution of fresh Ni-Fe/HZSM-5 catalyst.
Method
3.2.1. Pyrolysis in TG
BET Surface Area t-Plot Micropore Area t-Plot External Surface Area Total Pore Volume Pore Size
(m²/g) The thermogravimetric behavior
(m²/g) (m²/g) of wood biomass was tested on a Pyris 1 (nm)
(cm³/g) TGA from
219.50 PerkinElmer,
133.02 Waltham, MA, USA. A
84.48 total of 15 mg samples were
0.17 uniformly spread
3.11 in an
◦
alumina crucible to heat from ambient temperature to 100 C at the rate of 10 C/min ◦

for 1 h to remove free water. Then, non-isothermal thermogravimetric experiments were

3.2. Pyrolysis Method
carried out in 99.999% helium (He) from 100 ◦ C to 900 ◦ C with heating rates of 10 ◦ C/min,
3.2.1.
20 Pyrolysis
◦ C/min, 30 ◦in TG and 40 ◦ C/min, respectively, to calculate apparent kinetic parame-
C/min,
thermogravimetric
ters. The terminal weight lossbehavior
(wt.) andofmaximum
wood biomass
weightwas
losstested on a Pyris 1 TGA
rate temperature from
(Tm) were
PerkinElmer,
read from TG Waltham,
curves andMA,DTGUSA. A total
curves, of 15 mgThe
respectively. samples were uniformly
thermochemical spread
properties ofin an
sam-
alumina crucible to heat from ambient temperature to 100 °C at the rate of 10 °C/min for
1 h to remove free water. Then, non-isothermal thermogravimetric experiments were car-
ried out in 99.999% helium (He) from 100 °C to 900 °C with heating rates of 10 °C/min, 20
°C/min, 30 °C/min, and 40 °C/min, respectively, to calculate apparent kinetic parameters.
The terminal weight loss (wt.) and maximum weight loss rate temperature (Tm) were read
Catalysts 2024, 14, 200 16 of 20

Catalysts 2024, 14, x FOR PEER REVIEW 16 of 20

ples were analyzed by thermogravimetric experiment, and the characteristic temperature
point was combined with the analysis of subsequent pyrolysis products.
3.2.2. Catalytic Pyrolysis in a Fixed Bed Reactor
3.2.2. Catalytic Pyrolysis in a Fixed Bed Reactor
Catalytic pyrolysis of wood biomass was carried out in a vertical quartz tubular re-
Catalytic pyrolysis of wood biomass was carried out in a vertical quartz tubular reactor
actor to further analyze the pyrolysis behavior and product evolution, and the reaction
to further analyze the pyrolysis behavior and product evolution, and the reaction system is
system is shown in Figure 11, which mainly includes pyrolysis reaction device, gas collec-
shown in Figure 11, which mainly includes pyrolysis reaction device, gas collection device,
tion device, condensation and collection device of tar. Ni-Fe/HZSM-5 was used as catalyst
condensation and collection device of tar. Ni-Fe/HZSM-5 was used as catalyst with 5 g.
with 5 g. Before the start of the experiment, 5 g Ni-Fe/HZSM-5 catalyst was evenly mixed
Before the start of the experiment, 5 g Ni-Fe/HZSM-5 catalyst was evenly mixed with wood
with wood biomass samples and placed in the reaction tube. The gas–liquid separator was
biomass samples and placed in the reaction tube. The gas–liquid separator was connected
connected with the reactor at the bottom through ground glass by two levels of conden-
with the reactor at the bottom through ground glass by two levels of condensation with the
sation with the ice water bath. Before the start of each experiment, 5 g samples were placed
ice water bath. Before the start of each experiment, 5 g samples were placed in the mid-
in the mid-reactor and heated to a set temperature at a heating rate of 10 °C/min and kept
reactor and heated to a set temperature at a heating rate of 10 ◦ C/min and kept going for a
going for a while. N2 was placed into the reactor at a flow rate of 90 mL/min for an inert
while. N2 was placed into the reactor at a flow rate of 90 mL/min for an inert environment
environment
and swept the and swept the high-temperature
high-temperature pyrolysis
pyrolysis gas out. Pyrolysisgas
gasout.
wasPyrolysis
collectedgas was
every 50col-
◦C
lected every 50 °C into sampling bags through the cooling
◦ system from 200
into sampling bags through the cooling system from 200 C. Before sampling, the gas °C. Before
sampling,bag
sampling the shall
gas sampling bag shall
be vacuumed be vacuumed
and purified manyand purified many times.
times.

P
Gas flowmeter Sample (5g Ni-Fe/HZSM-5 catalyst was
evenly mixed with wood biomass)
Thermocouple
Electric heating
furnace

N2
Quartz reaction tube

Temperature control box

Sampling bags
Cooling system

Figure 11.
Figure 11. Primary
Primary high-temperature
high-temperature fixed
fixed bed
bedreaction
reactiondevice.
device.

3.3.
3.3. Analysis
Analysis of
of Samples
Samples and
and Products
Products
3.3.1. Analysis of Pyrolysis Products
3.3.1. Analysis of Pyrolysis Products
The gas products (H2 , CH4 , CO, and CO2 ) were determined by gas chromatograph
The gas products (H2, CH4, CO, and CO2) were determined by gas chromatograph
(Panna GC-A91), and the liquid products collected by the cooling system were analyzed
(Panna GC-A91), and the liquid products collected by the cooling system were analyzed
by gas chromatography–mass spectrometer (GC-MS, Clarus 680-SQ 8 T, PerkinElmer,
by gas chromatography–mass spectrometer (GC-MS, Clarus 680-SQ 8 T, PerkinElmer,
Waltham, MA, USA) with an Agilent DB-17MS capillary column, and the morphology
USA) with an Agilent DB-17MS capillary column, and the morphology characterized of
characterized of solid products was by SEM. Determination of component content of gas by
solid products
internal standardwas by SEM.gas
method, Determination of component
release rate, and yield werecontent of gas
calculated byby internal
nitrogen stand-
balance
ard method, gas release rate, and yield were calculated
method. The index parameters involved are calculated as follows: by nitrogen balance method. The
index parameters involved are calculated as follows:
90 × v×i
γi = 𝛾 = (i =
(i =H,H,CH CO22))
CH44,, CO, CO (11)
(11)
v N2 × m×b

Yi = ∑∑γ𝛾i ××t 𝑡
𝑌 = (12)
(12)
Tar yield (%) =
Tar yield mTar
(%) =m(g)/m Biomass
Tar (g)/m
(g) × 100%
Biomass (g) × 100%
(13)
(13)
Char yield (%) = mChar (g)/mBiomass (g) × 100% (14)
Char yield (%) =mChar (g)/mBiomass (g) × 100% (14)
Gas yield (%) = 1 − Char yield (%) − Tar yield (%) (15)
Gas yield (%) =1 − Char yield (%) − Tar yield (%) (15)
Catalysts 2024, 14, 200 17 of 20

nh i o
H conversion rate (%) = n(H2 ) + n(CH4 ) /nbiomass−H × 100% (16)

In Equation (11), γi is the release rate of gas i, mL/min; vN2 is the flow of N2 ,
90 mL/min; vi is the volume percentage of gas i (i represents H2 , CH4 , CO, CO2 ), %;
vN2 is the volume percentage of N2 in the tail gas from fixed bed reactor, %; mb is the mass
of biomass by dry and free ash basis. In Equation (12), Yi is the yield of gas i, mL/g-biomass ; t
is the gas reception time, 5 min. In Equations (13)–(15), mx is the quality of the x component
(x represents tar, char, biomass), g. In Equation (16), n(y) is the total H moles in the y
fraction (y represents H2 , CH4 , biomass), moL.

3.3.2. Surface Characteristics of the Reacted Catalyst

The specific surface area, pore size, and pore volume of the reacted catalyst were
measured by automatic specific surface area and porosity instrument (Tristar II 3020,
MICRO cube, USA). Before the test, all the samples were treated in a high vacuum at 120 ◦ C
for 6 h. The specific surface area and pore size distribution of samples were measured by
the N2 adsorption method at liquid nitrogen temperature −196 ◦ C, and the specific surface
area was calculated by the crystal phase of the N2 adsorption curve by the multi-point BET
method, and the single-point pore volume at relative pressure P/P0 = 0.995.

3.4. Apparent Kinetic Model

The visualization of reaction kinetics is the main research direction and also a general
method to study the reaction kinetics of pyrolysis process of biomass in recent years.
According to the law of mass action and Arrhenius equation, the kinetic relationship
between reaction rate and reaction temperature was established. The kinetic parameters in
the relationship were determined by thermogravimetric test data and the kinetic model
to describe the reaction process. Usually, the kinetic analysis is the most severe stage of
biomass weight loss; that is, the process of temperature drops from Ti to Tt . The sample
with initial mass M0 decomposes under programmed temperature. If the mass changes to
m at a certain time, the decomposition rate can be expressed as shown in Equation (17) [46].
In Equation (17), Ea is the activation energy of the reaction, kJ·mol−1 ; A is frequency
factor, min−1 ; T is the absolute temperature, K; β is the heating rate, ◦ C/min; n is the
reaction series. Most researchers approximately set the thermal decomposition of ligno-
cellulosic materials as the first-order reaction [47,48], so n = 1. x is the conversion rate, %,
which is defined as shown in Equation (18).
In Equation (18), m0 , m∞ , and m are the mass of the sample at initial, final, and time
t, respectively, g. Take logarithms on both sides of the Equation (17), and the equation is
expressed as shown in Equation (19).
 
dx A Ea
= exp − (1 − x ) n (17)
dT β RT

m0 − m
x= (18)
m0 − m ∞
   
dx A Ea
ln − n ln(1 − x ) = ln − (19)
dT β RT
Thus, there is a linear relationship between the left side of Equation (19) and 1/T; the
form is Y = ax + b form, the line slope is −Ea/R and the intercept is ln(A/β).
Finally, the main reaction section of pyrolysis is analyzed and calculated according
to the Equation (19) and combined with the data of TG/DTG. The kinetic parameters
of pyrolysis process of biomass are obtained. Then, the reaction kinetic model can be
established by Equation (17), and the kinetics of pyrolysis process of biomass was analyzed.
Catalysts 2024, 14, 200 18 of 20

4. Conclusions
The apparent kinetic of PR and CR was investigated under four diverse heating rates
by TG/DTG. Both PR and CR exhibited three consecutive stages of weight loss and the
TG/DTG curves. The characteristic parameters shifted to a higher temperature as the
heating rate rose. The activation energies and preexponential factor obtained from the law
of mass action and Arrhenius equation for CR were 72.38 kJ/mol and 1147.11 min−1 and
located in 72.36 kJ/mol and 1144.36 min−1 for PR. The pyrolysis mechanisms of wood
biomass were mainly the process of carbon enrichment and depolarity functional group
of organic components. H2 was the most dominant gaseous product during the pyrolysis
process, followed by C–O bond-containing species (CO, CO2 ), while CH4 was abundant
in pyrolysis gas. The high temperature was beneficial for promoting the pyrolysis of
biomass, increasing pyrolysis gas yield, and reducing tar yield. In the presence of the
Ni-Fe/HZSM-5 catalyst, the gas yield significantly increased to 117.9 mL/g-biomass at the
pyrolysis temperature of 700 ◦ C. The catalytic pyrolysis of MWC could generate larger
amounts of oxygenated product. In particular, more hydrocarbons like AL, AC, ALc, KE,
PH, FU, and ES were observed in the liquid products. Furthermore, the H2 O steam had
more effect on the product evolution and yield of gaseous products. However, too much
H2 O inhibits the cracking/reforming reaction of tar and also consumes a lot of energy.
In particular, the gas yield and hydrogen conversion were 76.94% and 15.90%, and the
H2 /CO was 2.07 under the H2 O steam flow rate of 1 mL/min. The yields of H2 , CO, and
CO2 were 107.35 mL/g-biomass, 53.70 mL/g-biomass , and 99.31 mL/g-biomass , respectively.
The pyrolysis mechanism and product distribution of wood biomass were demonstrated
through different indexes. It was concluded that wood biomass has great advantages in
pyrolysis for producing hydrogen-rich gas, and it has a good application prospect as the raw
material of alternative fuel. However, understanding how to carry out deep purification
and the efficient utilization of high-temperature pyrolysis gas is an important direction for
promoting the development of biomass technology.

Supplementary Materials: The following supporting information can be downloaded at: https://
www.mdpi.com/article/10.3390/catal14030200/s1, Table S1. Numbers of liquid products.
Author Contributions: Conceptualization, Y.W. and T.L.; methodology, X.L.; software, X.L. and T.H.;
validation, Y.L.; formal analysis, X.L. and P.L.; investigation, X.L. and Z.C.; resources, Y.W., T.L. and
P.L.; data curation, X.L. and Z.W.; writing—original draft preparation, X.L. and P.L.; writing—review
and editing, Y.W. and T.L.; visualization, X.L. and P.L.; supervision, Y.W. and T.L.; funding acquisition,
T.L., P.L. and Z.C. All authors have read and agreed to the published version of the manuscript.
Funding: This study was funded by the National Key R&D Program of China (2022YFB4201901),
a Special scientific research project for civil aircraft in 2020-EU China Sustainable Aviation Fuel
(MJ-2020-D-09), Changzhou Sci & Tech Program (CE20222034, CJ20220246 and CJ20220138), and Key
R&D Program Project in Henan Province (Soft Science) (232400411019).
Data Availability Statement: The data presented in this study are available upon request from the
corresponding author.
Conflicts of Interest: The authors declare no conflicts of interest.

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