Mesoporous TiO₂ Comprising Small, Highly Crystalline Nanoparticles for Efficient CO₂ Reduction by H₂O

The conversion of CO₂ into hydrocarbon fuels with H₂O using low-cost photocatalysts can offer a sustainable route to meet some of our energy needs, besides being able to contribute to the solutions of global warming. In this work, a series of highly crystalline mesoporous titanium dioxide (TiO₂) photocatalysts are synthesized via a simple template-free synthetic method. The synthesis involves preparation of titanium glycolate microspheres (TGMs), then hydrolysis of the TGMs in boiling water under ambient pressure, and finally calcination of the products in air. The hydrolysis step is found to play a crucial role in the formation of TiO₂ microspheres comprising a network of small anatase grains. The hydrolysis of the TGMs is also found to considerably inhibit the possible phase transformation of anatase to rutile during the subsequent high-temperature crystallization process. The resulting materials have good crystallinity and efficient charge carrier separation capabilities, as well as large specific surface areas, and thus large density of accessible catalytically active sites. These unique structural features enable these materials to exhibit high photocatalytic activities for the conversion of CO₂ with H₂O into hydrocarbon fuels (CH₄) and to show much better catalytic activities than that of the commercial photocatalyst Degussa P25 TiO₂

Influence of the Molecular Structure on the Electrocatalytic Hydrogenation of Carbonyl Groups and H₂ Evolution on Pd

We investigated the electrocatalytic hydrogenation (ECH) of model aldehydes and ketones over carbon-supported Pd in the aqueous phase. We propose reaction mechanisms based on kinetic measurements and on spectroscopic and electrochemical characterization of the working catalyst. The reaction rates of ECH and of the H2 evolution reaction (HER) vary with the applied electric potential following trends that strongly depend on the organic substrate. The intrinsic rates of hydrogenation and H2 evolution are influenced, in opposing ways, by the sorption of the reacting organic substrate. Strong interactions, that is, higher standard free energies of adsorption of the organic compound, induce high hydrogenation rates. The fast hydrogenation kinetics produces a hydrogen-depleted environment that kinetically hinders the HER and the bulk phase transition of Pd to a H-rich bulk Pd hydride, which is triggered by the applied potential in the absence of reacting organic compounds. As a consequence of strong organic–metal interactions, hydrogenation dominates at low overpotential. However, the coverages of organic substrates on the metal surface decrease, and the rates of H2 evolution surpass those of hydrogenation with increasingly negative electric potential. We determined the range of electric potential favoring hydrogenation on Pd and quantitatively deconvoluted the effects of the sorption of the organic compound, and of the rates of proton-coupled electron transfers, on the kinetics of both ECH and HER. The results indicate that electrocatalysis offers hydrogenation pathways for polar molecules which are different and, in some cases, faster than those dominating in the absence of an external electric potential