Multifunctional catalysts are developed for converting CO2 with C2H4 and H2 into propanol. Au nanoparticles (NP) supported on TiO2 are found to facilitate this reaction. The activity and selectivity strongly depend on NP size, which can be tuned by the method of Au deposition and by promoting with K. The promoter improves the selectivity to propanol. Under optimized reaction conditions (2 MPa, 473 K, and CO2/H2/C2H4=1:1:1), CO2 is continuously converted into propanol with a near-to-100% selectivity. Catalytic tests as well as mechanistic studies by in situ FTIR and temporal analysis of products with isotopic tracers allow the overall reaction scheme to be determined. Propanol is formed through a sequence of reactions starting with reverse water-gas shift to reduce CO2 to CO, which is further consumed in the hydroformylation of ethylene to propanal. The latter is finally hydrogenated to propanol, while propanol hydrogenation to propane is suppressed.

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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.

Combining catalytic and characterisation studies with statistical data analysis for elucidating factors determining CO2 conversion to propanol with H2 and C2H4.