K-promoted NiMo catalysts supported on activated carbon for the hydrogenation reaction of CO to higher alcohols: Effect of support and active metal

This study investigates the effect of active metal and the nature and pre-treatment of the support in a series of K-promoted NiMo catalysts supported on activated carbon (AC) for the hydrogenation reaction of CO. The Ni-Mo synergistic effect was found to be essential for the activation of CO. The use of activated carbon as support led to a three-fold increase in the selectivity toward higher alcohols, compared to the unsupported material, probably due to a reduction in the crystallinity of the active NiMoO4 phase and its partial transformation from alpha to beta form. Pre-treatment of the activated carbon prior to its use as support with HNO3 aqueous solution led to significant increase in CO conversion, related to the lower amount of ash and the much higher acidity of the acid treated sample. The use of a higher surface area acid-treated support also increases activity, with the K-NiMo/AC2a catalyst exhibiting a 45% higher conversion at 280 degrees C compared to K-NiMo/AC1a. The improvement in activity can be ascribed to better dispersion of the active phase on the higher surface area AC support and therefore higher exposure of active Ni-O-Mo sites. Overall, the K-NiMo/AC2a catalyst exhibited the optimum performance, with high CO conversion (25% at 280 degrees C) and high production of oxygenates, with a space time yield to oxygenates of 141.5 mg/g(catalyst)/h at 280 degrees C. A clear tendency of increasing higher alcohol production with decreasing acidity was evidenced for all K-promoted bimetallic NiMo catalysts. (C) 2014 Elsevier B.V. All rights reserved.