Effect of Support and Promoter on Activity and Selectivity of Gold Nanoparticles in Propanol Synthesis from CO₂, C₂H₄, and H₂

Direct propanol synthesis from CO₂, H₂, and C₂H₄ was investigated over TiO₂- and SiO₂-based catalysts doped with K and possessing Au nanoparticles (NPs). The catalysts were characterized by scanning transmission electron microscopy and temperature-programmed reduction of adsorbed CO₂. Mechanistic aspects of CO₂ and C₂H₄ interaction with the catalysts were elucidated by means of temporal analysis of products with microsecond time resolution. CO₂, which is activated on the support, is reduced to CO by hydrogen surface species formed from gas-phase H₂ on Au NPs. C₂H₄ adsorption also occurs on these sites. In comparison with TiO₂-based catalysts, the promoter in the K–Au/SiO₂ catalysts was found to increase CO₂ conversion and propanol production, whereas Au-related turnover frequency of C₂H₄ hydrogenation to C₂H₆ decreased with rising K loading. The latter reason was linked to the effect of the support on the ability of Au NPs for activation of C₂H₄ and H₂. The positive effect of K on CO₂ conversion was explained by partial dissolution of potassium in silica with formation of surface potassium silicate layer thus inhibiting formation of potassium carbonate, which binds CO₂ stronger and therefore hinders its reduction to CO