REARRANGEMENT AND DISPROPORTIONATION OF TOLUENE OVER LA1-XSRXNIO3 CATALYSTS

The gas-phase oxidation of toluene over La1−xSrxBO3 (B = Mn, Fe, Co, Ni) catalysts was studied with the aid of a GC/MS. Unlike the products resulting from the use of Mn-, Fe-, and Co-series or LaNiO3 catalysts, when La1−xSrxNiO3 (x > 0) was employed, bicyclo-[2.2.1.]-hept-2,5-diene and 2-propenylidene cyclobutene were formed by the rearrangement of toluene, while o-xylene, m-xylene, p-xylene, and ethyl benzene were produced by the disproportionation of toluene. It is believed that the rearrangement and disproportionation of toluene on the perovskite catalysts are due to the NiO- and La2NiO4-phases. The amount of NiO- and La2NiO4-phases in the La1−xSrxNiO3 (x > 0) catalysts was found to increase with x, and hence affected toluene oxidation activity as well. The disproportionation products were formed when either NiO, the mixture of NiO (50%) and LaNiO3 or the mixture of La2NiO4 · NiO (50%) and LaNiO3 as the catalysts were used. It is shown that the disproportionation of toluene is due to the NiO- and La2NiO4-phases. A change in the carrier gas from nitrogen to helium showed that nitrogen gas can react with the adsorbed oxygen and the lattice oxygen on the catalyst surface, leading to a decrease in the oxidation and disproportionation reaction rates of toluene. Substituting benzene for toluene revealed that the rearraneement of toluene starts at the methyl group. The mechanisms for the rearrangement and disproportionation of toluene were based on the GC/MS analysis for the products. © 1993 Academic Press, Inc.