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Abstract

Mo_xC/CNT catalysts were prepared through carburization of an oxidic molybdenum precursor impregnated on multiwalled carbon nanotubes (CNTs). The effects of different carburization atmospheres, heating rates, and molybdenum loadings were tested. The catalysts were characterized by using CO temperature-programmed desorption, XRD, N₂ physisorption, SEM, and TEM. The catalytic performance in the steam reforming of methanol was used as a sensitive probe to indicate changes in the catalyst surface during the catalytic action. Contrary to the bulk Mo_xC catalysts, the heating rate during carburization has no effect on the catalysts. Instead, molybdenum loading and carburization atmosphere are the key factors for catalyst structure and performance. The molybdenum-based activity decreases at loadings >10 wt % at a constant product selectivity. The CO₂/CH₄ product ratio indicates changes in the catalyst properties at the loadings <20 wt %, at which the activity is constant. Carburization in 20 % CH₄/H₂ yields 2 nm sized crystallites of cubic α-MoC. Carburization in pure H₂ and He yields hexagonal β-Mo₂C with a larger particle size. Both phases show different catalytic performances in terms of activity and CO₂/CH₄ selectivity. Thus, a multiparameter toolbox for fine-tuning of catalyst properties is presented.