The role of sulfur sinks and micro-structured supports on the performance of sulfur-sensitive non-PGM catalysts

Abstract

The presence of traces of sulfur dioxide (i.e. 1–10 ppmV) alongside residual methane emissions induces the rapid deactivation of typical methane abatement catalysts. As a result, sulfur-induced poisoning is the main challenge faced by after-treatment technologies for residual methane abatement. The aim of this study was to synthesise a series of cobalt and molybdenum catalysts and assess their performance under realistic after-treatment conditions. The series of catalysts was characterised by BET, XRD, XPS, TPR, TGA under air flow, SEM, EDX and in situ DRIFTS. In addition, the performance of Co100 supported on an alumina hollow fibre was assessed under similar reaction conditions and characterised by SEM and EDX. It was found that the catalytic activity of the series of cobalt and molybdenum catalysts decreased in the following order: Co100 > Co80Mo20 > Co60Mo40. In addition, it was discovered that the other two catalysts (i.e. Co25Mo75 and Mo100) were inactive at 450 °C due to the lack of highly active Co3+ species. Among the active catalysts, Co100 and Co80Mo20 experienced an initial activation followed by a gradual deactivation whereas Co60Mo40 experienced a 1 h interval with stable methane conversion levels in between the activation and deactivation. The delay in poisoning of the active cobalt (II,III) oxide phase of Co60Mo40 was attributed to the sulfur sink-properties of the cobalt molybdenum oxide present in this catalyst (i.e. 44 wt%). Finally, Co100 supported on an alumina hollow fibre achieved the highest methane conversion per unit mass of catalyst and its performance was stable for a duration of 2.5 h. The high activity was attributed to the large surface area provided by the geometry of the support while the higher resistance to sulfur poisoning was credited to the sulfur sink-properties of the alumina, which delayed the poisoning of the active phase.