Insight into the structural sensitivity of CuZnAl catalysts for CO hydrogenation to alcohols

The catalytic conversion of CO hydrogenation is a structure-sensitive reaction over Cu-based catalyst. It is very important to distinguish the structural differentiation and possible reaction pathway of Cu-based catalysts in methanol synthesis and ethanol/C2+OH synthesis. Herein, the activity of four types of CuZnAl catalysts is evaluated, and their structural differentiation is investigated. The CuZnAl catalyst (CZA) prepared by a complete liquid-phase (CLP) method after solid-liquid separation directly applied in the fixed bed reactor also shows the ability to synthesize ethanol and higher alcohols (C2+OH), with the selectivity of C2+OH in liquid product reaching up to 31.6% at the CO conversion of 10.6%. However, commercial methanol synthesis catalyst (CMC) displays the highest CO conversion (28.2%) and the poorest C2+OH selectivity (7.8%). After characterized by ICP, XRD, CO-TPD, N2O adsorption, XPS, SEM, TEM and in-situ DRIFTS techniques, it is discovered that the dispersion of Cu and the exposed Cu surface area significantly influences CO conversion. The selectivity of ethanol and C2+OH is related to the size and distribution of Cu, the architectural feature, and the chemical environment of Cu and Al. In-situ DRIFTS indicates that CHxO* species can be formed over different CuZnAl catalysts. However, the formed CHxO* species will be rapidly hydrogenated to produce methanol on CMC catalyst, while the step is inhibited on CZA catalyst. Additionally, a bridge-type adsorbed CO is only observed on CZA catalyst, which is beneficial for the formation of CHx intermediates, leading to the formation of ethanol and higher alcohols.

Automated summary

The dispersion of Cu and the exposed Cu surface area significantly influence CO conversion, while the selectivity of ethanol and C2+OH is related to the size and distribution of Cu, the architectural feature, and the chemical environment of Cu and Al. Through evaluating the activity and structural differences of four CuZnAl catalysts, it is discovered that the selectivity of products is highly dependent on the structural characteristics and chemical properties of the catalysts.