Oxidative bromination of methane on silica-supported non-noble metal oxide catalysts

Oxidative bromination of methane, mediated by HBr/H2O (solution), provides an original route for the production of oxygenates and gasoline directly from natural gas. However, the reported catalysts for this reaction all involved noble metals. From the consideration of replacing noble metal catalysts with cheaper oxides, various silica-supported oxide catalysts were surveyed. It was found that the redox ability of different metals had a strong impact on the product distribution. On the catalysts with metals that lack facile redox ability, such as BaO/SiO2, both CH3Br and CO were main products. Otherwise, deep oxidation proceeded. Moreover, methanol was firstly reported in this system. In order to obtain a molar ratio of (CH3OH + CH3Br): CO = 1, which can provide a perfect feedstock for the synthesis of acetic acid, the process variables were optimized on BaO/SiO2. It was demonstrated that 44.0% methane conversion and 95% total selectivity of CH3Br, CH3OH and CO could be achieved at 620 °C, and the molar ratio of (CH3Br + CH3OH): CO was close to 1. Time-on-stream tests showed declined catalytic performance after 30 h. The results from N2-adsorption, XRF and XRD implied that aggregation of barium particles occurred, making the metathesis between BaO and BaBr2 difficult. The functions of BaO were also proposed. Additionally, the activity data were compared with those of noble metal catalysts.

Various silica-supported non-noble metal oxide catalysts were investigated for the oxidative bromination of methane, mediated by HBr/H2O. BaO/SiO2 showed good activity for its lack of facile redox capacity, but suffered deactivation after 30 h. The characterization results implied that aggregation of barium particles occurred, which made the metathesis between BaO and BaBr2 difficult. Figure optionsDownload as PowerPoint slide