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Carbon based materials are some of the most commonly studied catalysts for the conversion of cellulose to polyols. The catalytic performance of these materials, however, is typically limited by the access of the substrate to the active sites, which is governed by the poor solubility of cellulose in aqueous solutions. In an attempt to resolve this, we presented a novel hierarchical carbon material which was synthesized by a dual-templating method. Transmission electron microscopy and porosity measurements confirmed that the resultant materials consisted of both spherical macropores and well-defined mesoporous channels. Additional characterisation of this material revealed that it has an exceptionally high surface area (＞1110 m2 g−1) and a high concentration of acidic sites, which are considered to be crucial for the hydrolysis of cellulose. Ni nanoparticles were subsequently immobilised onto this material and some additional carbon supports. It was determined that the high surface area and porosity of the synthesised carbon material assisted with the dispersion of the Ni nanoparticles. This Ni catalyst was found to be highly efficient for the one-pot conversion of cellulose to polyols, which is proposed to be a consequence of both the high number of acid sites and excellent Ni dispersion. This approach to catalyst design, offers a novel method for the valorisation of cellulose. [ABSTRACT FROM AUTHOR]

Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O–compressed CO2 system at 35–50 °C 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. [ABSTRACT FROM AUTHOR]

We prepared a series of mesostructured Ni/TiO 2 –SiO 2 (Et) hybrid catalysts with highly dispersed Ni nanoparticles and incorporated ethane-bridged organosilica moieties. Ni/TiO 2 –SiO 2 (Et) showed high activity in the hydrogenation of nitrobenzene in water, and it could be recycled for several times with a constant activity and selectivity. It was confirmed that Ni/TiO 2 –SiO 2 (Et) catalyst is of hydrophobicity as the ethane-bridged organosilica fragments were incorporated into the mesoporous framework, and so the Ni active species was protected without contacting with water to form the inactive Ni species. In particularly, the Ni/TiO 2 –SiO 2 (Et) catalyst was air-stable, it could remain good activity after being exposed to air for a week. Accordingly, this work developed a kind of hydrophobic Ni catalyst with high stability to water and air, which is expected to have a wide application in the hydrogenation reactions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hexitols were produced over Ni/ZSM-5 with a high yield of 82%. [•] Hexitols yield depended on the hydrogenation/dehydrogenation activity of catalyst. [•] The activation energy of hydrogenation and dehydrogenation was estimated. [•] The synergistic effect of Ni and acid–base sites of support was confirmed. [•] Mechanism of cellulose conversion was discussed based on the basic step reactions. [ABSTRACT FROM AUTHOR]

Highlights: [•] The addition of CO2 remarkably affected the reaction rate and product selectivity. [•] The decreased reaction rate is due to the formation of solid carbamate in the presence of CO2. [•] The yield of benzylamine was increased to >94.4% in the presence of CO2. [•] The presence of CO2 could prohibit the formation of dibenzylamine in organic solvents. [•] The acidic nature of H2O–CO2 benefited the elimination of NH3. [Copyright &y& Elsevier]

Highlights: [•] The activity of Ni–Ir/TiO2 catalyst was four times as high as that of the Ni/TiO2 catalyst. [•] The reducibility of Ni was improved as addition of tiny amount of Ir. [•] The hydrogen spillover from Ir to Ni occurred in Ni–Ir/TiO2 catalyst. [•] The electronic structure of the surface Ni atoms was modified upon the addition of Ir. [ABSTRACT FROM AUTHOR]

Abstract: Water as a green solvent to replace the conventional organic solvent presents many advantages in the organic synthesis. The hydrogenation of nitrobenzene in water has been investigated by using Ni/TiO2 catalyst in this work, and our main purpose was focused on the Ni/TiO2 catalyst activity and its stability improvement. The experimental results and analysis from the data of XRD, XPS, ICP revealed that the formation of nickel hydroxide from metallic nickel reacting with water caused a rapid deactivation of Ni/TiO2 catalyst. Based on these, we designed a catalyst with hydrophobic property to prevent the nickel active species to contact with water; thus, a hydrophobic carbon layer was coated on the surface of Ni/TiO2. As expected, the hydrophobic carbon was successfully coated on Ni/TiO2 catalysts by a hydrothermal method and they presented higher reactivity and improved stability in the present aqueous reaction system; nickel hydroxide was not detected on the used and water treated carbon-coated Ni/TiO2 samples. The improved abilities were attributed to the increased hydrophobicity of catalysts modified by carbon, which not only prevents water to contact with nickel catalytic species, but also protects the metallic nickel to be oxidized as it exposed to air. [Copyright &y& Elsevier]

Abstract: The hydrogenation of chloronitrobenzene to chloroaniline was investigated over Ni/TiO2 at 35°C in supercritical CO2 (scCO2), ethanol, and n-hexane. The reaction rate followed the order of scCO2 > n-hexane>ethanol. In scCO2, the selectivity to chloroaniline and to aniline over Ni/TiO2 were 97–99.5% and <1%, respectively, in the conversion range of 9–100%. The high chemoselectivity to chloroaniline cannot be achieved over Ni/TiO2 in ethanol and n-hexane. In situ high-pressure Fourier transform infrared measurements were made to study the molecular interactions of CO2 with the following reactant and reaction intermediates: chloronitrobenzene, chloronitrosobenzene, and N-chlorophenylhydroxylamine. The molecular interaction modifies the reactivity of each species and accordingly the reaction rate and the selectivity. The influence of Cl substituent on the interaction modes of CO2 with these reacting species is discussed. Possible reaction pathways for the hydrogenation of chloronitrobenzene in scCO2 over Ni/TiO2 are also proposed. [Copyright &y& Elsevier]