Mechanistic Aspects of the Role of K Promotion on Cu–Fe-Based Catalysts for Higher Alcohol Synthesis from CO₂ Hydrogenation

Abstract

Direct CO2 hydrogenation to higher alcohols (HAs) is a promising way to achieve the conversion of CO2 to high-value chemicals. Alkali metals as promoters are generally crucial for Cu–Fe-based catalysts, but their critical role in higher alcohol synthesis (HAS) is still far from clear. Here, we report the regulating effect of a potassium (K) promoter from a reactant activation perspective on Cu–Fe-based catalysts for HAS from CO2 hydrogenation using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemisorption methods. The optimized catalyst denoted as 4.6K-CMZF with a moderate K content exhibits the highest HA space time yield (STY) in a fixed-bed reactor. It is found that the K can promote reverse water gas shift (RWGS) reaction and tailor the ratio of nondissociated CO to dissociated CO by strengthening linear CO adsorption and weakening bridging CO adsorption. A proper amount of K can balance the nondissociated and dissociated activation of CO, thus providing an adequate *CHx and *CO species to take part in *CHx–*CO coupling reaction. The K promoter can also suppress H2 activation, thereby inhibiting alkylation reaction. The promoting effect of K can be attributed to the balance of surface *CHx, *CO, and *H species by regulating CO activation and H2 activation, thus favoring HA synthesis via *CHx–*CO coupling and hydrogenation reactions.