Issue 2, 1987

CH bond activation and radical–surface reactions for propylene and methane over α-Bi2O3

Abstract

A molecular-orbital study has been made of CH activation in methane and the methyl group of propylene by an α-Bi2O3 surface. Three oxidation states of the surface bismuth cations were modelled: II(reduced), III(normal) and V(oxidized). It was found that barriers to the formation of surface OH and gas-phase methyl and allyl radicals decrease as the bismuth oxidation state increases. This is because the radical electron from hydrogen is promoted by σ-bond formation to successively lower-energy bismuth 6s, 6p lone-pair or surface-state dangling bond orbitals as the state of bismuth oxidation increases. Experimental results in the literature also show this trend for forming gas-phase allyl radicals: in an oxidizing environment with O2 in the gas stream the barrier is lower than in a reducing environment with no oxygen. We found a similar trend for stabilities of heterolytically adsorbed dissociation products and for homolytic adsorption on oxygen. The increased stability with increasing bismuth oxidation state is the result of reducing lower-lying surface orbitals. We found heterolytic adsorption, H on O2– and CH3 or C3H5 on Bi, most stable for the BiIII and BiV surfaces and we predict that the BiII surface is unreactive.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans. 1, 1987,83, 463-475

CH bond activation and radical–surface reactions for propylene and methane over α-Bi2O3

S. P. Mehandru, A. B. Anderson and J. F. Brazdil, J. Chem. Soc., Faraday Trans. 1, 1987, 83, 463 DOI: 10.1039/F19878300463

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