The hydrogenation of CO2 on Rh/Al2O3 catalysts modified with Ni and K was studied by in situ and operando DRIFTS spectroscopy comprising transient and isotopic exchange experiments to study the influence of this modification on the catalytic performance in CO and methane formation at 250–350 °C and to gain mechanistic insight. Catalytic testing and spectroscopic studies revealed that the modification with particularly K promotes the formation of CO being the highest over Rh, K, Ni/Al2O3, whereas methane formation is preferred over the unmodified catalyst. It was found that CO2 does not dissociatively adsorb but is adsorbed at the support, forming mainly hydrogen carbonate, and in the presence of K, also carbonate species. The dissociative adsorption of H2 proceeds on Rh. The activated H2 reacts mainly with the hydrogen carbonate species forming CO adsorbed on Rh and formate (F1) species stably adsorbed on the support. On the K-containing catalysts, an additional formate species (F2) was identified as more reactive than F1 formate and can act as a reaction intermediate in the CO formation pathway. Furthermore, adsorbed formyl species were detected, which are assumed to be intermediates in the methanation reaction. The modifying additives change the surroundings of the Rh particles. This influences the strength of CO adsorption and the activation ability of Rh for H2 dissociation. Thus, desorption of the formed CO from the catalyst surface is favored, and the methanation of CO is hindered. The modification with K enhances the ability for CO2 fixation by formation of additional carbonate species which cover adsorption sites for unreactive F1 formate species and favors the formation of reactive F2 formate species.

Au/TiO2 and Au/SiO2 catalysts containing 2 wt % Au and different amounts of K or Cs were tested for alcohol synthesis from CO2, H2, and C2H4/C3H6. 1‐Propanol or 1‐butanol/isobutanol were obtained in the presence of C2H4 or C3H6. Higher yields of the corresponding alcohols were obtained over TiO2‐based catalysts in comparison with their SiO2‐based counterparts. This is caused by an enhanced ability of the TiO2‐based catalysts for CO2 activation, as concluded from in situ fourier‐transform infrared (FTIR) spectroscopy and temporal analysis of products (TAP) studies. The synthesized carbonate and formate species adsorbed on the support do not hamper CO2 conversion into CO and the hydroformylation reaction. The transformation of Auδ+ to active Au0 sites proceeds during an activation procedure. As reflected by CO adsorption and scanning transmission electron microscopy, the accessible Au0 sites are influenced by the amount of alkali dopants and the support. FTIR data and TAP tests reveal a very weak interaction of C2H4 with the catalyst, suggesting its quick reaction with CO and H2 after activation on Au0 sites to form propanol and propane.

The Cover Feature shows the direct synthesis of 1‐propanol from CO2, H2, and ethene. This process includes two steps: the hydrogenation of CO2 to CO by reverse water‐gas shift reaction and subsequent hyroformylation of ethene with the formed CO and hydrogen. Gold nanoparticles together with alkali dopants are responsible for reactant activation. More information can be found in the Full Paper by Heyl et al. on page 651 in Issue 3, 2019 (DOI: 10.1002/cssc.201801937).

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