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Solvent effects were investigated for selective hydrogenation of acetophenone (AP) with commercial 5% Pd/Al2O3 and 5% Pd/C catalysts using polar and nonpolar solvents. The rate of AP hydrogenation varied with the solvents used in different ways depending on the catalysts used. The highest AP conversion was achieved with water for the two catalysts and the AP conversion was correlated with hydrogen-bond-acceptance (HBA) capability (beta) for Pd/Al2O3 and hydrogen-bond-donation (HBD) capability (alpha) for Pd/C. These trends were the same as the corresponding solvent effects obtained previously with Rh/ Al2O3 and Rh/C catalysts, respectively (Green Chem., 2015, 17, 1877-1883). The influence of solvents on the rate of AP hydrogenation depends on the support materials and not on the metal species. Furthermore, AP hydrogenation was conducted with the four supported noble metal catalysts in different solvents pressurized by CO2 (CO2-dissolved expanded solvents). The influence of CO2 pressurization on the rate of reaction, the product selectivity, and the catalyst life was investigated to know whether or not CO2 molecules could function as a reaction promoter in heterogeneous AP hydrogenation reactions with supported Pd and Rh catalysts in different solvents.

Liquid-phase hydrogenation of phenylacetylene was investigated with Pd and PdZn alloy catalysts in toluene compressed by CO2. The influence of alloying and dense phase CO2 on the rate of conversion and the product selectivity was examined. With either Pd or PdZn the partially hydrogenated product of styrene was produced in high selectivity but the selectivity to styrene obtained with the latter was larger than that with the former when compared at the same conversion level. After the initial substrate was fully consumed, the styrene was fully hydrogenated to ethylbenzene for both catalysts but more slowly with the PdZn alloy catalyst. The presence of a dense phase of CO2 (1.5 MPa) enhanced the rate of phenylacetylene hydrogenation and the selectivity to styrene for the Pd and PdZn catalysts. Possible reasons for the positive effects of alloying and dense phase CO2 on the partial hydrogenation of phenylacetylene to styrene are discussed.

A series of magnesium containing mesoporous smectites has been prepared with and without incorporation of alkali hydroxide ( NaOH, KOH or LiOH) and employed for the reaction of CO2 with aminobenzonitrile to produce quinazoline-2,4(1H,3H)-dione. The effects of the quantity and kind of the incorporated alkali atoms on the catalytic properties of the smectites were investigated. Characterization of the smectites has shown that the incorporation of alkali atoms reduces their surface area and total pore volume but enhances the amount and strength of their basic sites. The product yield increases with the amount of alkali atoms incorporated. The incorporation of Li was less effective than that of Na and K for the enhancement of the yield. It has been suggested that weak and/or moderate base sites are responsible for the reaction. The active sites should be alkali hydroxide particles existing between the smectite layers for the alkali incorporated smectites, while for the un-incorporated smectite, the active sites should be the Mg atoms and/or the neighboring O atoms. The Na incorporated smectite was deactivated by repeated catalyst recycling, while such deactivation was not observed with the un-incorporated smectite. The reason for the deactivation was discussed in connection with the structures of the active sites and the actions of the reaction intermediate.

The catalytic hydrogenation of 2,4-dinitroaniline using a 0.5 wt% Pt/TiO2 catalyst was investigated in a multiphase medium of tetrahydrofuran (THF) pressurized by CO2 at different pressures and at 323 K. When CO2 pressure was increased, the overall rate of hydrogenation simply decreased but the selectivity to the desired product of 4-nitro-1,2-phenylenediamine increased. The noticeable enhancement of the selectivity to 4-nitro-1,2-phenylenediamine can be explained by chemical reactivities of CO2 molecules. In situ high-pressure FTIR and molecular simulations demonstrate that the dissolved CO2 molecules may interact with amino groups of the substrate and weaken the intra-hydrogen bonding between the amino and 2-nitro groups, which results in the change in the relative reactivity of the two nitro groups, yielding the desired product in a higher selectivity. The change in the intra-and inter-molecular interactions between the substrate and CO2 molecules was theoretically examined by DFT calculations.

A series of magnesium containing mesoporous smectites has been prepared with and without incorporation of alkali hydroxide ( NaOH, KOH or LiOH) and employed for the reaction of CO2 with aminobenzonitrile to produce quinazoline-2,4(1H,3H)-dione. The effects of the quantity and kind of the incorporated alkali atoms on the catalytic properties of the smectites were investigated. Characterization of the smectites has shown that the incorporation of alkali atoms reduces their surface area and total pore volume but enhances the amount and strength of their basic sites. The product yield increases with the amount of alkali atoms incorporated. The incorporation of Li was less effective than that of Na and K for the enhancement of the yield. It has been suggested that weak and/or moderate base sites are responsible for the reaction. The active sites should be alkali hydroxide particles existing between the smectite layers for the alkali incorporated smectites, while for the un-incorporated smectite, the active sites should be the Mg atoms and/or the neighboring O atoms. The Na incorporated smectite was deactivated by repeated catalyst recycling, while such deactivation was not observed with the un-incorporated smectite. The reason for the deactivation was discussed in connection with the structures of the active sites and the actions of the reaction intermediate.

The formation and adsorption of CO from CO2 and H2 at high pressures were studied over alumina-supported noble metal catalysts (Pt, Pd, Rh, Ru) by in situ FTIR measurements. To examine the effects of surface structure of supported metal particles and water vapor on the CO adsorption, FTIR spectra were collected at 323 K with untreated and heat (673 K) treated catalysts in the absence and presence of water (H2O, D2O). It was observed that the adsorption of CO occurred on all the metal catalysts at high pressures, some CO species still remained adsorbed under ambient conditions after the high pressure FTIR measurements, and the frequencies of the adsorbed CO species were lower either for the heat treated samples or in the presence of water vapor. It is assumed that the CO absorption bands on atomically smoother surfaces appear at lower frequencies and that water molecules are adsorbed more preferentially on atomically rough surfaces rather than CO species.

The photocatalytic H2 production from water with TiO2 can be noticeably enhanced by the presence of both dense phase CO2 and a surfactant of sodium dodecyl sulfate, being larger by more than one order of magnitude than that from water with TiO2 alone. The surface of TiO2 may be modified by the accumulation of CO2 molecules assisted by the TiO2- and CO2-philic surfactant, changing its photocatalytic activity.

The formation and adsorption of CO from CO2 and H2 at high pressures were studied over alumina-supported noble metal catalysts (Pt, Pd, Rh, Ru) by in situ FTIR measurements. To examine the effects of surface structure of supported metal particles and water vapor on the CO adsorption, FTIR spectra were collected at 323 K with untreated and heat (673 K) treated catalysts in the absence and presence of water (H2O, D2O). It was observed that the adsorption of CO occurred on all the metal catalysts at high pressures, some CO species still remained adsorbed under ambient conditions after the high pressure FTIR measurements, and the frequencies of the adsorbed CO species were lower either for the heat treated samples or in the presence of water vapor. It is assumed that the CO absorption bands on atomically smoother surfaces appear at lower frequencies and that water molecules are adsorbed more preferentially on atomically rough surfaces rather than CO species.

Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O-compressed CO2 system at 35-50℃ without using any environmentally harmful solvent. The effective CO2 pressure is much lower than the critical pressure of CO2. The hydrogenation of nitro group should be the rate-determining step.