Supported Boron Oxide Catalysts for Selective and Low-Temperature Oxidative Dehydrogenation of Propane

Abstract

Oxidative dehydrogenation (ODH) of light alkanes catalyzed by metal oxides is considered to be a thermodynamically favorable process for olefin production. The strong interaction between the unoccupied d-orbital of metal atom and the π-electrons of olefins, however, leads to deep oxidation of olefin to CO2, especially at elevated temperatures. The challenge lies in the development of selective and low-temperature active catalysts to avoid such unwanted deep oxidation. Here, we report unambiguous evidence on properly prepared mesoporous silica-supported boron oxide catalysts showing high selectivity for ODH of propane. The catalysts are active at a temperature as low as 405 °C, showing a propane conversion of 2.8% and a propene selectivity of 84.1% (C2–3=: 94.6%). Upon raising the temperature to 450 °C, a propane conversion of 14.8% can be achieved, with a selectivity of 73.3% toward propene or 87.4% for both propene and ethene (C2–3=). Both experimental and theoretical studies indicate tricoordinated boroxol and hydroxylated linear boron species are the active sites for the ODH of propane. In addition, the oxophilicity of boron sites is responsible for suppressing deep oxidation by eliminating the alkoxyl species, leading to high selectivity toward olefin products.