Palladium-based catalysts for the synthesis of alcohols

Abstract

The present work intends to illustrate the effects of precursor and support composition on the structure and performance of Pd-based catalysts for the synthesis of methanol and higher oxygenated compounds. The power of the XRD technique and the reaction itself, as characterisation tools, was evidenced. The hydrogenation of carbon monoxide has been studied over palladium supported on ZnO, Zr(OH)4 and ZrO2 using PdCl2 and Pd(NO3)2 as salt precursors. Catalysts were characterised by XRD and Raman spectroscopy. The results show that activity and selectivity are strongly dependent on the salt precursor and on the acid–basic properties of the support. As seen from the CH3OH/DME ratio, the order of acidity of the supports is: Zr(OH)4 > ZrO2 > ZnO independently of the salt precursor used. The Pd(NO3)2/ZnO catalyst shown the highest methanol selectivity which was related to the presence of large particles of a PdZn alloy. A double bifunctionality on the catalysts for the production of higher oxygenated seems evident. On the one hand, an acid–base bifunctionality of the support seems to be needed for the formation, stabilisation, chain growth and further reactivity of intermediates such as formate, as well as for the dissociative adsorption of CO, and on the other hand, a metal-support bifunctionality, where the palladium metal particles would play the role of hydrogenating the intermediates and possibly adsorb non-dissociatively the CO.