Sulfur promoted low-temperature oxidation of methane over ceria supported platinum catalysts

The influence of sulfur dioxide on methane oxidation over ceria supported platinum catalysts under lean conditions has been studied by transient flow reactor and in situ Fourier transform infrared spectroscopy experiments. The results show that sulfur dioxide can promote the oxidation of methane, here between 300 and 450 °C, although, as a function of time on stream, the promoting effect diminish and instead the methane oxidation becomes inhibited. We suggest that sulfate formation on ceria creates oxygen vacancies in the ceria that govern oxygen spillover leading to a lowering of detrimental oxygen coverage of platinum and/or decomposition of platinum oxide facilitating the dissociative methane adsorption. Eventually the ceria becomes saturated with sulfates and the oxygen dynamics in the platinum–ceria system settles. As a consequence, the system regresses towards highly oxidized platinum and/or otherwise active sites on the ceria or platinum–ceria boundary become blocked, which may explain the long-term inhibiting effect by SO2 exposure.

Graphical abstractMethane oxidation over Pt/CeO2 which is initially promoted by SO2 pulsing, leading to formation of sulfates that facilitate oxygen spill-over and/or special sites at the platinum–ceria boundary for enhanced methane dissociation, and as a function of time on stream becomes gradually inhibited by sulfur exposure.Figure optionsDownload full-size imageDownload high-quality image (123 K)Download as PowerPoint slideHighlights► Mechanisms of sulfur promoted methane oxidation. ► Role of metal–support interactions, boundary sites and spill-over processes. ► Transient in situ FTIR spectroscopic analysis.