IN SITU METHODS OF CATALYST
CHARACTERIZATION
Deepak Pandey
14514013
Submitted to:
Dr. Prateek Jha
Assistant Professor
IIT ROORKEE
BACKGROUND
catalyst under action
Catalyst undergoes many changes when in
action
These changes may lead to change in catalytic
properties that we are interested in.
Characterization involves determination of
parameters like porosity, surface area ,density,
selectivity etc.
X-RAY DIFFRACTION
Governed by Braggs law
X ray have wavelength of same order of inter
atomic spacing , hence can be used for
diffraction
Different diffraction pattern
- single crystal
- more than one crystal
-mixture of crystals (PXRD)
XRPD patterns, diffraction cones
Random orientation of crystals ,so powdered
sample generates cones instead of single spots
Cones intersect strip of photographic film to
produce characteristic sets of arcs.
Detector converts this signal into count rate
versus 2 plot.
Plot compared with reference data available for
different materials
More information
Diffraction peak broadening may contain info
about sample microstructure
Peak position can be used to calculate unit cell
dimensions.
CASE STUDY-1
Discusses about importance of XRPD
Zn/Cr oxides are well known catalysts for
synthesis of methanol from syn-gas
For long time its active component was
considered to be ZnO.
XRPD revealed active species nonstoichiometric spinel-like phase of ZnCr2O4
Earlier it was known that Zn ion occupy
tetrahedral while Cr ions octahedral spaces
Residual ZnO is expected when Zn/Cr above 0.5
But XRPD showed pure spinel- phase existence
at least up to Zn/Cr =1 due to nonstoichiometric
spinel- where Zn ions occupy some octahedral
sites randomly with Cr ions.
Common catalysts for WGS reaction are CuMoO4,
NiMoO4 , CuO-ZnO .XRD studies have been done
before
XRD studies of CuFe2O4 inverse spinel structure
Contains both octahedral and tetrahedral sites ,Cu ion
sits on octahedral while iron on both.
CuFe2O4 is cubic at elevated temp(>400) and
tetragonal at room temp.
As temperature was raised , tetragonal diffraction
lines disappeared at 380 ,only cubic lines left
200 no WGS activity
200-300 CO attacks oxide and partial reduction leads
to metallic Cu ,onset of WGS activity
At 35o active WGS catalyst mixture of Cu,CuFe5O8
and Fe3O4
These XRD results point to metallic copper as an
active species for the WGS.
References :
[1] Giovanni Perego, Characterization of heterogeneous catalysts by Xray diffraction techniques, catalysis today(1998)
[2] Jose A. Rodriguez , Jonathan C. Hanson , Wen Wen, Xianqin
Wang, Joaqun L. Brito , Arturo Martnez-Arias , Marcos FernandezGarc, In-situ characterization of watergas shift catalysts using timeresolved X-ray diffraction,catalysis today (2009)
[3]Scott A Speakman, Introduction to X-Ray Powder Diffraction, Data
Analysis, Centre for Materials Science and Engineering at MIT.
[4] Andrew M. Beale , Eli Stavitski, Bert M. Weckhuysen,
Characterization of catalysts : Surface and In-situ methods, Department
of Chemistry, Utrecht university, The Netherlands
