(617fr) Transient Kinetic Screening of Active Sites and Their Consumption: Pt on Molybdenum Carbide Nanotubes | AIChE

(617fr) Transient Kinetic Screening of Active Sites and Their Consumption: Pt on Molybdenum Carbide Nanotubes

Authors 

Fushimi, R. - Presenter, Idaho National Laboratory
Wang, L., Idaho National Laboratory
Gleaves, J. T., Washington University in Saint Louis
Yablonsky, G. S., Washington University in Saint Louis
Tan, S., University of Wyoming
Li, D., University of Wyoming














Transient
kinetic pulse response experiments were used to characterize reaction
pathways and active sites in platinum catalysts prepared via atomic
layer deposition on a Mo
2C
nanotube support. CO multiplulse TAP (Temporal Analysis of Products)
experiments combined with slow temperature programming revealed a
complex dependence of CO surface storage and CO
2
release. The primary kinetic characteristics were calculated
directly from experimentally measured exit-flow moments without
a
priori

assumption of a kinetic mechanism using the theoretical methodology
developed by Shekhtman and Yablonsky [1]. This ‘model-free’
approach allows one to compare materials based on intrinsic rate
constants and regulation between the surface and gas phase. A
variety of kinetic models are then imposed and rate constants of
elementary steps presented.

The
CO/CO
2
transient kinetic results presented here, combined with detailed
structural characterization presented separately, suggest that Pt
particles in the unique size range (<2.7 nm) present an additional
high temperature pathway for CO
2
formation. A detailed analysis of the temperature dependence allowed
active sites to be distinguished kinetically as their consumption
incrementally progressed and the material transitioned from one
dominant site to another. A rate/rate coherency technique was used
to distinguish reaction pathways observed on pure support and
Pt-modified materials. These results present a new experimental
strategy for identifying and distinguishing pathways and kinetic
regimes in complex catalytic materials.

[1]
S.O. Shekhtman, G.S. Yablonsky, J.T. Gleaves, R. Fushimi, “State
defining” experiment in chemical kinetics—primary
characterization of catalyst activity in a TAP experiment, Chem. Eng.
Sci. 58 (2003) 4843-4859.