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Supported Pt catalysts were prepared using several kinds of TiO supports different in the crystallite size in the range of 10-500 nm and their catalytic activity was tested for the liquid-phase hydrogenation of 3-nitrostyrene, nitrobenzene, and styrene. With Pt on smaller TiO crystallites (nanocrystals), the selectivity to vinylaniline was improved in the hydrogenation of 3-nitrostyrene (regioselective hydrogenation) and the selectivity to aniline was promoted in the hydrogenation of a mixture of nitrobenzene and styrene (chemoselective hydrogenation). The effects of TiO crystallite size were discussed on the basis of the results of turnover frequency and FTIR of CO adsorbed on dispersed Pt particles. Low coordinated and/or electron-rich Pt sites should be formed on the surface of nanocrystal TiO supports. Nanocrystal TiO support is an important factor for controlling and improving the catalytic performance of dispersed Pt particles. Graphical Abstract: Smaller TiO crystallites give rougher Pt crystal planes on the surface of Pt particles, beneficial for the hydrogenation of nitro group than vinyl group.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: The present work has studied the influence of CO2 pressurization on the hydrogenation of nitrostyrene (NS) using Pt/TiO2. With CO2 pressurization up to 12MPa (CO2-dissolved expanded liquid (CXL) phase), the over-all reaction rate and the selectivity to aminostyrene (AS) increased. At higher CO2 pressures where all NS dissolved in scCO2 (scCO2-homogeneous phase), both of them decreased with increasing the CO2 pressure. The phase behavior was an important factor for the present reaction system. It was also found that the presence of pressurized CO2 gave higher selectivity to AS than in its absence at any conversion level. This was ascribed to retardation effects of dense phase CO2 on the hydrogenation of AS to ethylaniline. Competitive adsorption of nitro and vinyl groups was suggested to determine the product selectivity. FTIR measurements showed that the pressurized CO2 lowers the reactivity of the nitro group, and this effect is stronger in scCO2-homogeneous phase than in CXL phase, resulting in the lower AS selectivity in the former phase. Lower Pt loadings and higher catalyst reduction temperatures gave Pt/TiO2 catalysts more selective for the AS formation. FTIR measurements of adsorbed CO over the catalysts suggested that the presence of less-coordinated Pt atoms on edge, corner and kink sites was significant for the selective hydrogenation of NS to AS. [Copyright &y& Elsevier]

Abstract: A catalyst system of ZnBr2/n-Bu4NI is reported for the first time as a highly efficient binary catalyst for the synthesis of styrene carbonate (SC) from styrene oxide and carbon dioxide under supercritical conditions. In a very short reaction time (30min) and even at a mild reaction temperature (80°C), 100% selectivity and nearly 100% yield of SC have been obtained; the TOF value obtained is 46 times larger than those so far reported under similar conditions. The effects of the ZnBr2/n-Bu4NI ratio, types of cation and anion, and other reaction conditions on the reaction were investigated. On the basis of the results, a reaction mechanism has been proposed. [Copyright &y& Elsevier]

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]

Styrene carbonate is synthesized by a direct benign route in the presence of tetrabutylammonium bromide (TBAB) from styrene, compressed CO2 and tert-butyl hydroperoxide (TBHP) as oxidant, in which two sequential reactions of epoxidation and cycloaddition are coupled for a one-pot synthesis. Various reaction parameters, such as CO2 pressure, reaction temperature and time, TBAB concentration, molar ratio of TBHP to styrene and oxidant types, were investigated. CO2 pressure was found to play a crucial role in achieving the high yield of styrene carbonate. A plausible reaction mechanism was also proposed. [Copyright &y& Elsevier]

Styrene carbonate is synthesized by a direct benign route from styrene and compressed CO2 in the presence of ionic liquid, in which two sequential reactions of epoxidation and cycloaddition are coupled for a one-pot synthesis. The structure of ionic liquids and the nucleophilicity of anions strongly affect the yield of styrene carbonate formed and tetrabutylammonium bromide (TBAB) is the most effective catalyst. Other reaction parameters such as CO2 pressure, reaction temperature, time, and TBAB concentration have also been investigated and a plausible reaction mechanism is proposed. [Copyright &y& Elsevier]

The liquid-phase selective hydrogenation of 3-nitrostyrene (NS) was investigated over nanocrystalline Pt/TiO 2 catalysts synthesized by the single-step flame spray pyrolysis (FSP) method. The obtained powder was characterized by N 2 physisorption, X-ray diffraction (XRD), CO pulse chemisorption, transmission electron spectroscopy (TEM), temperature-programmed reduction (TPR), and infrared spectroscopy of adsorbed CO (CO-IR). High dispersion of small Pt particles ( d P 1.2 nm) on high anatase/rutile TiO 2 was obtained by the FSP method. The catalyst performances of the FSP-made catalysts (F-Pt/Ti) in terms of both hydrogenation activity and selectivity to vinylaniline (VA) improved from 61 to 66% and from 40 to 73% by reduction at high temperature. Compared to F-Pt/Ti, Pt/TiO 2 obtained by conventional impregnation (I-Pt/Ti) on a sol–gel TiO 2 contained higher amount of rutile phase composition and exhibited much lower Pt dispersion and hydrogenation activity (5% after reduction at 200 °C and 50% at 500 °C). The TOFs for NS hydrogenation were calculated to be 22–113 s −1 . Complete transformation of anatase TiO 2 to rutile occurred after reduction at 600 and 700 °C for the I-Pt/Ti and F-Pt/Ti, respectively, leading to excessive decoration of Pt by the reducible TiO x species and poor catalytic performances. [ABSTRACT FROM AUTHOR]

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]