Low temperature steam reforming of methane: A combined isotopic and microkinetic study

•Ni and Rh on La2O3-CeO2-ZrO2 low temperature CH4 steam reforming kinetics studied.•Kinetic isotope effects during CH4 steam reforming and decomposition measured.•CH bond activation kinetically limiting over Ni and Rh with no steam participation.•Microkinetic modelling identifies CH3* dehydrogenation as the rate determining step.•Binding energies of key surface species help discriminate catalysts' performance.

Low temperature steam reforming in combination with hydrogen selective membranes presents great potential of intensifying the classical industrial hydrogen production process via natural gas. This concept can lead to significant environmental and process benefits, such as reduced energy needs, milder material stability requirements and considerably simplified process layouts via e.g. avoiding the use of downstream WGS reactors. Ni and Rh based catalysts supported on La2O3-CeO2-ZrO2, already identified as active and stable at these conditions, are further investigated in the current work aiming at the elucidation of reaction kinetics. Temperature programmed experiments of methane conversion in steam reforming and decomposition modes in conjunction with isotopic investigations using CD4 are carried out, showing that cleavage of a CH bond participates in the rate determine step, whereas steam derived intermediates do not. A thermodynamically consistent microkinetic model considering a comprehensive set of surface pathways is also developed. The model describes correctly experimental trends, predicting surface CH3 dehydrogenation to be rate limiting. Estimated model parameters further help elucidate the different catalysts' activities. The combined approach presented shows potential to accelerate catalyst and process design efforts for the promising low temperature steam reforming hydrogen production process.

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