Electron promoted ZnO for catalytic synthesis of higher alcohols from syngas

Abstract

Direct conversion of syngas from those non-petroleum carbon resources to higher alcohols are very attractive due to the process simplicity with low energy consumption. However, the reaction always suffers from low yield as well as low selectivity. Herein, effective increase of higher alcohols proportion in the product is realized by direct conversion of syngas over electronically-modulated ZnO semiconductor via Cu doping. It is considered that the lower Fermi level and narrower band gap of catalysts by embedding Cu2+ into ZnO lattice could facilitate donor reaction by boosting the process for the reactants to obtain electrons on the catalyst surface for the formation of CHx species and carbon chain growth, in which the Cu doping on ZnO lattice play important role in the promotion of CO adsorption. As a result, 4 mol% Cu doped ZnO exhibits a highest C2+OH/ROH fraction of 48.1%. Selectivity of catalysts from straight chain alcohol is better than from branch chain alcohol, which is different from promoted Cu/ZnO based catalyst. However, over-doping of Cu (7 mol%) on ZnO results in the aggregation Cu species on ZnO surface, leading to a sharp decrease of higher alcohols proportion to 3.2%. The results shed light on the nature that a direct correlation between semiconductor Fermi level and synthesis of higher alcohols, and the semiconductor-based catalysts mainly accelerate the hydrogenation reactions by enhancing thermally excited electron transfer.