Use of the methanol decomposition reaction for identifying surface species in Cu/Co-based catalysts

Abstract

Methanol decomposition was used as test reaction for characterizing Cu/Co-based catalysts. Three Cu/Co/Al ternary catalysts containing Co/ (Cu + Co) molar ratios of 0.34, 0.49, and 0.67, respectively, were prepared. Two binary reference samples containing Co/Al and Cu/Al, respectively, were also prepared. Methanol decomposition on binary Co/Al sample gave predominantly CO, CH 4, and higher hydrocarbons; the active sites were metallic Co crystallites, the Co n+ ions being almost inactive. Main products on binary Cu/Al sample were methyl formate, CO, and CO 2. Both, Cu 0 and Cu n+ sites were active. The methanol decomposition mechanism was interpreted in terms of a reaction scheme based on the initial dehydrogenation of methanol to formaldehyde and the consecutive decomposition of the formaldehyde intermediate to different products according to the nature of the Cu or Co active site involved. The test reaction was specifically used to investigate the effect of both the chemical composition and the calcination temperature on the generation of surface species of ternary Cu/Co/Al samples. Good agreement was found between the conclusions obtained from catalytic testing and those from sample characterization by means of bulk and surface techniques (X-ray diffraction, temperature programmed reduction, and X-ray photoelectron spectroscopy). Methanol decomposition proved to be a useful test reaction for discriminating between Cu and Co sites on Cu/Co-based catalysts.