Unraveling the roles of Cu0 and Cu+ in CuZnAl catalyst for CO hydrogenation to higher alcohols.

The valence states of Cu site are regarded as an important factor affecting the performance of syngas to higher alcohols (C 2+ OH). Regrettably, the role of Cu0 and Cu+ in CO hydrogenation to higher alcohols remains controversial due to the complexity of the reaction. In this study, Cu0 and Cu 2 O powders are directly added as the precursors to adjust the ratios of Cu+/(Cu0+Cu+) and Cu particle sizes in CuZnAl catalysts by a complete liquid-phase (CLP) technology. The CAT-Cu0 catalyst with higher Cu0 content shows the highest CO conversion (>15%) ascribing to the biggest S Cu , but is also accompanied by the highest CO 2 selectivity (>40%), while the CAT-Cu+ catalysts with higher Cu+ content displays relative better C 2+ OH selectivity (>60%) and stability due to a higher probability of CO insertion. In-situ DRIFTS experiments reveal that a synergy between larger Cu particle sizes (30～40 nm) and surface Cu+ sites, in which larger Cu sizes enhances the probability of bridge CO adsorption, thereby favoring the C–O bond dissociation for CH x formation. Meanwhile, Cu+ active sites provide a higher probability for CO/CHO insertion to form CH 3 CHO*/CH 2 CO* intermediates. This study further deepens our understanding of the critical controlling factors for highly selective synthesis of C 2+ OH from syngas over Cu-based catalysts. • Catalytic performance was strongly related to Cu+/(Cu0+Cu+) ratios. • Cu + active site provided a higher probability for CO insertion. • Cu0 was more active than Cu + for water-gas shift reaction. • Larger Cu particles size favored the formation of CH x. [ABSTRACT FROM AUTHOR]