Alcohol Synthesis from CO2 , H2 , and Olefins over Alkali-Promoted Au Catalysts-A Catalytic and In situ FTIR Spectroscopic Study

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 C₂ H₄ /C₃ H₆ . 1-Propanol or 1-butanol/isobutanol were obtained in the presence of C₂ H₄ or C₃ H₆ . 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 Au^δ+ 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 C₂ H₄ with the catalyst, suggesting its quick reaction with CO and H₂ after activation on Au⁰ sites to form propanol and propane.

Potassium and Water Coadsorption on TiO2(110): OH-Induced Anchoring of Potassium and the Generation of Single-Site Catalysts

Potassium deposition on TiO₂(110) results in reduction of the substrate and formation of loosely bound potassium species that can move easily on the oxide surface to promote catalytic activity. The results of density functional calculations predict a large adsorption energy (∼3.2 eV) with a small barrier (∼0.25 eV) for diffusion on the oxide surface. In scanning tunneling microscopy images, the adsorbed alkali atoms lose their mobility when in contact with surface OH groups. Furthermore, K adatoms facilitate the dissociation of water on the titania surface. The K-(OH) species generated are good sites for the binding of gold clusters on the TiO₂(110) surface, producing Au/K/TiO₂(110) systems with high activity for the water-gas shift.