Bromine-mediated conversion of methane to C1 oxygenates over Zn-MCM-41 supported mercuric oxide

Abstract

The structure mobility of the zigzag mercuric oxide chains and the strong preference of mercuric (II) cation sites for bromine lead to a novel bromine-mediated partial methane oxidation at relatively low reaction temperature (220 °C). Zn-MCM-41 supported mercuric oxide nanophases were used as the model catalyst to investigate the role of bromine in the catalytic cycle. The introduction of bromine to feed gas consisting of CH4/O2/Ar (3:1:6) leads to a sharp increase in the methane conversion. Meanwhile, a transient high product selectivity to C1 oxygenates was observed. Two bromine-mediated routes can be identified: MeHgBrn as the intermediate species and mercuric hypobromite as the active agent for methane oxidation, which occur simultaneously in the methane conversion. The controlling mechanism transfers from the former to the latter with the gradual fixation of bromine into mercuric oxide lattice. The catalyst was characterized detailedly by XRD, XPS, and N2 sorption. The chemical composite changes of active species were detected by XPS, which provide some direct information about the mediator role of bromine in the catalytic cycle.