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Abstract: This paper reports a direct route for the preparation of cyclic styrene carbonate from styrene, which avoids the preliminary synthesis and isolation of styrene oxide. A catalyst system consisting of Au/SiO2, zinc bromide, and tetrabutylammonium bromide (Bu4NBr) has been applied to the one-pot synthesis of styrene carbonate from styrene, organic peroxide, and CO2. Au/SiO2 is active for the epoxidation of styrene, and zinc bromide and Bu4NBr cooperatively catalyze the subsequent CO2 cycloaddition to epoxide. The influence of various reaction parameters, such as CO2 pressure, reaction temperature, reaction time, catalyst amount, ratio of oxidant to styrene, and oxidant type, has been investigated in detail. [Copyright &y& Elsevier]

Abstract: TiO2-supported Pd–Au catalysts were prepared with Pd (0.5 wt%) by impregnation and then Au (1.0 wt%) by deposition–precipitation (Au/Pd/TiO2) and vice versa (Pd/Au/TiO2). For the former sample, the state of dispersion of Pd on TiO2 changed during the loading of Au, resulting in the formation of small Au–Pd alloy particles and thus changing the electronic properties of Pd species. The alloy formation was not clearly detected on the Pd/Au/TiO2, and the electronic properties of Pd were not so different from those of monometallic Pd/TiO2. All the catalysts were selective to 1-heptene (>95%) until close to the complete conversion of 1-heptyne. However, the selectivity of 1-heptene drastically decreased to 0% (which was further hydrogenated to heptane) in 120min for the Au/Pd/TiO2 while it still remained >60% for the Pd/Au/TiO2 similar to the monometallic Pd/TiO2 catalyst. The rate of 1-heptene hydrogenation (in the second step) did not depend on the Pd dispersion but was found to be greatly enhanced as the Pd species became electron-rich in the Au–Pd alloy particles. The modification of Pd species by Au was less significant for the first step of hydrogenation of 1-heptyne to 1-heptene. [Copyright &y& Elsevier]

Abstract: The selective hydrogenation of citral was studied with various TiO2-supported monometallic and bimetallic Pd and Au catalysts and their physical mixtures in supercritical CO2 (scCO2). Significant synergistic effects appeared when active Pd species was chemically or physically mixed with less active Au species. The total rate of conversion was greatly enhanced and the selectivity to citronellal (CAL) was improved. The physical properties of those catalysts were characterized by TEM, HRTEM-EDS, XPS, and UV/Vis and their features of H2 desorption were examined by TPD. The physical and chemical characterization results were used to discuss the reasons for the unexpected synergistic effects observed. The same selective hydrogenation was also conducted in a conventional non-polar organic solvent of n-hexane to examine the roles of scCO2. The use of scCO2 was effective for accelerating the hydrogenation of citral and improving the selectivity to CAL. [Copyright &y& Elsevier]

Abstract: Liquid-phase semihydrogenation of phenylacetylene under mild conditions has been investigated on a series of solvothermal-derived nano-TiO2 supported Pd catalysts with various TiO2 crystallite sizes in the range of 9–23 nm. As revealed by CO chemisorption and transmission electron microscopy, all the catalysts exhibited strong metal–support interaction (SMSI) when reduced at 500 °C. The catalysts with SMSI show remarkably high catalytic performance in terms of both hydrogenation activities (turnover frequencies (TOFs) 9.1–21.4 s−1) and moderate-high selectivities to styrene (86–90%) at complete conversion of phenylacetylene. Without SMSI effect (the catalysts reduced at 40 °C), styrene selectivity and catalytic activity depended largely on the Pd particle size in which small Pd particles (formed on small crystallite size TiO2 supports) exhibited lower phenylacetylene conversion and poor styrene selectivity. Moreover, the TOF values of the non-SMSI catalysts were similar to those reported in the literature for other supported Pd catalysts in liquid-phase semihydrogenation of phenylacetylene under mild conditions (TOFs 1.3–2.8 s−1). [Copyright &y& Elsevier]