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Three supported Ir/TiO2 catalysts, containing anatase TiO2 nanocrystals with predominantly exposed {101}, {100}, and {001} planes, were subjected to various pre-treatments (H2 reduction at different temperatures and O2 re-oxidation) and then tested in the vapor phase selective hydrogenation of crotonaldehyde. The pre-treatments significantly altered the Ir-TiOx interactions, including the morphologies and electronic properties of the Ir species and their surface acidity. These interactions were also closely related to the crystal planes of TiO2, which further supported the observed reaction behaviors of the various Ir/TiO2 catalysts. The best performance was obtained using the Ir/TiO2-{101} catalyst pre-reduced at 300 °C, owing to its higher Ir0 surface concentration and moderate surface acidity compared to the other catalysts. Moreover, these findings indicated the synergistic role of the Ir-TiOx interface in the reaction, as the interfacial sites were responsible for the adsorption/activation of H2 and the C=O bond in the crotonaldehyde molecule. However, pre-reduction at 400 °C resulted in partial encapsulation of the Ir particles by TiOx via strong metal-support interactions, which is unfavorable for the catalytic reaction owing to the loss of Ir-TiOx interfacial sites.

The Cu-based catalysts have been widely employed in the hydrogenation of CO2-derived ethylene carbonate (EC) to methanol (MeOH) and ethylene glycol (EG), but still suffered from some problems such as excess hydrogen/ester ratio, unsatisfactory MeOH selectivity and catalyst stability & deactivation. Herein, a MoOx-promoted Cu/SiO2 catalyst, which was prepared via a one-pot modified hydrothermal method and derived from copper phyllosilicate precursors, exhibited superior catalytic performance (89% MeOH yield and 99% EG yield) and good stability (>150 h) at a H2/EC ratio (20). Remarkably, the turnover frequency (TOF) and space time yield of MeOH (STYMeOH) reached up to 17.5 h−1 and 0.207 g⋅gcat−1⋅h−1, respectively, which are among the highest values in the literature data. The characterization results and kinetic studies revealed that modification of Cu species by MoOx obviously changed the electronic properties of Cu species, reduced the activation energy and enhanced the Cu+/(Cu0 + Cu+) ratios. Such modification may lead to possible formation of Cu-O-Mo bond between Cu species and MoOx species located on the periphery of Cu-MoOx interface, which might strengthen the adsorption and activation of EC, stabilize the Cu nanoparticles, and thus improve the selectivity to MeOH and catalyst stability. In addition, MoOx decoration had obvious effect on the strength and quantity of the surface acid sites.

Supported Ir/TiO2 catalysts with the anatase TiO2 nanocrystals exposing {1 0 1}, {1 0 0} and {0 0 1} planes were tested for selective hydrogenation of crotonaldehyde. The Ir/TiO2-{1 0 1} catalyst dominantly exposing {1 0 1} plane gave a initial reaction rate of 166.1 μmol gIr-1 s−1 at 80 °C and a turnover frequency of crotyl alcohol formation of 0.022 s−1, which is 5 and 7 times respectively higher than those obtained on the Ir/TiO2-{0 0 1} catalyst dominantly exposing {0 0 1} plane even though they have similar Ir particle sizes (ca. 1.3 nm). The reaction behaviors were related to the surface oxygen vacancy, which served as surface acid sites and provide adsorption sites for C O bond in the CRAL molecule. Therefore, the higher concentration of oxygen vacancy in the Ir/TiO2-{1 0 1} accounted for the improved performance compared to the Ir/TiO2-{0 0 1}. However, strong adsorption of crotonaldehyde and/or products on the catalyst surface, as well as the CO poisoning via decarbonylation of crotonaldehyde, were the main reasons for the catalyst deactivation.

Indirect CO2 conversion to ethylene glycol (EG) and methanol (ME) via CO2-derived ethylene carbonate (EC) as the intermediate is an attractive and promising approach. Cu-Based catalysts have been regarded as effective catalysts for the hydrogenation of EC to yield ME and EG. In this work, we prepared Cu/SiO2 catalysts through different methods for the hydrogenation of EC to yield ME and EG. The results show that Cu/SiO2-AE catalysts prepared by an ammonia evaporation (AE) method are superior to Cu/SiO2-DP catalysts prepared by a deposition–precipitation (DP) method. After modification using glucose with an optimal amount, the Cu8G1/SiO2-AE catalysts showed enhanced catalytic performance, furnishing 86% selectivity to ME and 99% selectivity to EG at almost full conversion of EC, with a TOF value for ME formation reaching about 39 h−1. A series of techniques such as N2 sorption, ICP-AES, FT-IR, H2-TPR, H2-TPD, TEM, and XPS were adopted to characterize the physicochemical properties of relevant catalysts. It was found that the Cu/SiO2-AE catalyst had a smaller Cu particle size. After modification with glucose, the Cu8G1/SiO2-AE catalyst had the smallest Cu particle size, the highest hydrogen adsorption ability, and the strongest interaction of Cu with SiO2 so that the highest Cu+/(Cu0 + Cu+) molar ratio was detected. In addition, upon investigation of catalyst stability and reusability, it was found that glucose modification for the Cu/SiO2-AE catalyst can also alleviate the deactivation distinctly.