Influence of support material on Ni catalysts for propane dry reforming to synthesis gas

Abstract

Ni/SiO2 and Ni/Mg(Al)O catalysts with difference metal loadings have been prepared. The activity, selectivity and stability of supported Ni catalysts for propane dry reforming to syngas reaction were investigated by catalytic testing at 600 ºC, C3H8:CO2:H2:N2 (in vol.%) = 10:30:10:50. Ni particle size was investigated by Transmission electron microscopy (TEM). Turn-over frequencies for Ni/SiO2 catalysts were calculated as a guideline to the relationship between catalytic activity and Ni particle size. The best performances including a low selectivity to methane was observed on 1.0 wt% Ni/SiO2, which has relative small nickel particle size. Mechanistic investigations including isotopic tracer study and temperature-programmed deuteration of a used catalyst were also performed to elucidate the rate limiting step of the dry reforming to synthesis gas reaction over a Ni/SiO2 catalyst. Partial pressure variation experiments gave reaction orders of 0.75 and 0.77 respect to propane and CO2 respectively, indicating a high surface coverage under the test condition. Isotopic tracer studies showed that the reverse water-gas shift reaction approaches equilibrium unde the applied test conditions, demonstrating that CO2 activation is fast and can not be the rate determining step for the title reaction. The experiments further showed that propane dissociation followed by hydrogenation is the main route to methane formation. Temperature-programmed deuteration of a used catalyst showed that C3 species dominate among the hydrocarbon species on the catalyst surface. Together, the above results led to the conclusion that C-C bond rupture is the rate-limiting step of reaction. Based on the results presented above, a reaction sequence has been proposed for the propane reaction over a Ni/SiO2 catalyst.