Kinetic Modeling of Spillover and Temperature-Programmed
Oxidation of Oxy-Carbon Surface Species on Pt/Al<sub>2</sub>O<sub>3</sub>
Casey
P. O’Brien
Ivan C. Lee
10.1021/acs.jpcc.7b03858.s001
https://acs.figshare.com/articles/journal_contribution/Kinetic_Modeling_of_Spillover_and_Temperature-Programmed_Oxidation_of_Oxy-Carbon_Surface_Species_on_Pt_Al_sub_2_sub_O_sub_3_sub_/5035886
During propane oxidation
over Pt/Al<sub>2</sub>O<sub>3</sub> in
the 200–300 °C temperature range, many different oxygenated
carbonaceous (oxy-carbon) surface species spillover from the platinum
nanoparticles and grow on the Al<sub>2</sub>O<sub>3</sub> support.
The rate of oxy-carbon species growth on the Pt/Al<sub>2</sub>O<sub>3</sub> surface is consistent with a diffusion-limited process where
the rate of oxy-carbon species diffusion on the Al<sub>2</sub>O<sub>3</sub> support is the rate-determining step. A model based on Fick’s
second law for two-dimensional radial diffusion is used to analyze
the kinetics of oxy-carbon species spillover on the Al<sub>2</sub>O<sub>3</sub> support. An Arrhenius expression describing the rate
of oxy-carbon species diffusion on the Al<sub>2</sub>O<sub>3</sub> support, which has a pre-exponential factor of 7.9 × 10<sup>–14</sup> cm<sup>2</sup>/s and an activation barrier of 24
kJ/mol, was extracted from the kinetic analysis. Following propane
oxidation, the oxy-carbon surface species were completely oxidized
to CO<sub>2</sub> during temperature-programmed oxidation (TPO). During
TPO of the oxy-carbon species, diffusion of the oxy-carbon species
on the Al<sub>2</sub>O<sub>3</sub> support is relatively fast, and
a surface reaction on the platinum nanoparticles is the rate-determining
step. TPO of oxy-carbon surface species was simulated using surface
reaction rate expressions with three different reaction orders with
respect to the surface carbon concentration (first-order, second-order,
and power-law). The kinetics of TPO of the oxy-carbon surface species
is most accurately represented by second-order kinetic rate expressions
with activation barriers of 147 kJ/mol for oxidation of acetate species
and 112 kJ/mol for oxidation of higher reactivity enolate, aliphatic
ester, and acetone species. Formation of platinum oxides during propane
oxidation increase the activity of the catalyst for TPO of the oxy-carbon
species. This work reveals quantitative mechanistic insights into
both the carbon growth and burnoff processes, which is important for
designing efficient hydrocarbon conversion processes.
2017-05-10 00:00:00
oxy-carbon surface species
oxy-carbon species diffusion
oxy-carbon species
oxy-carbon species growth
Al 2 O 3 support
oxy-carbon species spillover
propane oxidation increase
hydrocarbon conversion processes
rate-determining step
surface carbon concentration
CO
Oxy-Carbon Surface Species
propane oxidation
surface reaction rate expressions
TPO
surface species spillover
platinum nanoparticles