Modulation of Oxygen Vacancies on Cu/ZnO by Promoter for Higher Alcohol Synthesis From Syngas

The influence of promoters on oxygen vacancies (Ovs) within CuZn catalysts is crucial for optimizing CO hydrogenation to higher alcohols (C₂₊OH). The CuZn catalysts were successfully prepared with controlled Ovs concentrations via a fully liquid-phase technique through the incorporation of various promoters (Cr, Al, Ga). Additional metal atoms were introduced at ZnO tetrahedral sites of Al³⁺- and Ga³⁺-doped CuZn catalysts, facilitating the formation of Ovs within the lattice. Conversely, Cr formed a CuCr₂ bimetallic phase mixture in the Cr-doped CuZn, which thwarted the promotional effect of Cr³⁺ in the precursor and inhibited the generation of ZnO defects. Enhanced Ovs facilitated the transport of electrons from ZnO to Cu, increasing the CuZn interaction and promoting the formation of additional Cu⁰ and Zn^δ+ defects. The CO dissociative intermediates (CH_x*) were formed at Cu⁰ sites, while nondissociative intermediates (CO* and CH_xO*) were formed at Cu⁺ or Ovs sites. These intermediates then participated in CC coupling at Zn^δ+ sites and subsequent hydrogenation to form C₂₊OH. The Ga-doped CuZn catalyst showed optimal performance, yielding 17.22% CO conversion with 60.22% ethanol and 71.90% C₂₊OH proportions in the alcohol products.