Interdependence of Point Defects and Reaction Kinetics: CO and CH4 Oxidation on Ceria and Zirconia

Maximilian Schaube,Rotraut Merkle,Joachim Maier

doi:10.1021/acs.jpcc.0c03256

Maximilian Schaube, Rotraut Merkle + Show 1 more

Open Access

https://doi.org/10.1021/acs.jpcc.0c03256

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Abstract

The rate of CO and CH4 oxidation is measured on systematically Pr , Gd , or Nb–doped ceria, and Y– or Pr–doped zirconia to investigate the impact of point defects on heterogeneously catalyzed oxida...

Highlights

Oxidation reactions represent an important class of heterogeneously catalyzed reactions
This is in fair agreement with the experimental results. (The partial pressure dependencies of 9CO in Figure 4, as well as those of p(O2)eff in Figure 9b,c, are measured under comparably low conversion such that, in first approximation, gradients of the p(CO)/p(O2) ratio over the extension of the reactor bed and their effect on p(O2)eff can be neglected.) This discussion emphasizes the importance of appropriate consideration of the modified oxygen activity within the oxide catalyst particles (p(O2)eff); neglecting it would lead to incorrect predictions of the partial pressure dependencies of 9CO
CO and CH4 oxidation kinetics were studied on systematically Pr, Gd, Nb-doped ceria, and Y- or Pr-doped zirconia

Summary

INTRODUCTION

Oxidation reactions represent an important class of heterogeneously catalyzed reactions. The reductant oxidation at the surface comprises two processes, one of which is usually considered to be rate-determining (Figure 1): (i) The reoxidation branch (blue arrow) describes the oxygen exchange reaction If this branch is the ratedetermining step (rds), it is expected that the overall reaction rate follows similar dependencies on oxygen partial pressure p(O2), dopant type, and concentrations as found for oxygen exchange in pure oxygen atmosphere (cf ref 13). If this is rate-determining (i.e., the reoxidation is fast compared to the CO/CH4 branch), the dependencies of the reaction rate may differ strongly from those found for oxygen exchange In the latter case (ii), the oxygen activity within the catalyst oxide particles will always be in equilibrium with the gas-phase oxygen activity. Its variation with the reductant molecule (CO vs CH4) is studied

EXPERIMENTAL SECTION

TAILORING BULK DEFECT CHEMISTRY BY DOPING

RESULTS AND DISCUSSION

Decreased Oxygen Activity Inside the Catalyst

CONCLUSIONS

■ REFERENCES