Effect of Surface Oxides on Pt-Catalysed Nh3 Oxidation Kinetics: Transient Response Measurements and Modelling

Abstract

The correct description of the kinetics of NH3 oxidation over Pt are crucial for the optimal catalyst design. In this work, we apply a novel kinetic analysis to this process, reconciling experimentally and theoretically derived activation energies. We developed a Transient Response Measurement protocol which allowed to measure the intrinsic kinetics, observing an activation energy of 39 kJ/mol, close to theory, and then the following Pt oxide formation/decomposition. By combining the two phenomena, we obtained a model describing the experimental light-offs and their high apparent activation energy (>100 kJ/mol). This is explained by the Pt-oxide decomposition evolving concurrently with the heating ramp. This leads to a gradual enhancement of the catalytic activity beyond the increase related to the low intrinsic activation energy. Furthermore, our model explains previously observed effects, i.e. the NH3 conversion hysteresis during light-up/light-down, and the O2 inhibition on NH3 light-offs. The work paves the way for a more fundamental understanding of a wide range of NH3 conversion/abatement catalytic systems.

Keywords: NH3 Oxidation, Platinum, Kinetic Analysis, Catalytic Modelling, Pt Oxides, Transient Response Measurements