Toshiaki Sodesawa

Ni/SiO2 catalyst with hierarchical pore structure prepared by phase separation in sol–gel process

Silica-supported nickel catalysts with both macropores and mesopores were prepared in an alkoxide-derived sol–gel process in the presence of poly(ethylene oxide) (PEO) with an average molecular weight of 100000. In this process, the interconnected macroporous morphology is formed when transitional structures of spinodal decomposition are frozen by the sol–gel transition of silica. The addition of nickel into a silica–PEO system has negligible effect on the morphology formation suggesting that phase separation in the nickel-containing system proceeds by repulsive interaction between the solvent and PEO adsorbed on the silica, as observed in the system without nickel. In gel formation, it was found that the Ni was distributed selectively in mesopores in the silica gel skeleton as fine particles rather than aggregated in macropores. It is considered that PEO interacts with both silica and nickel cations. The interaction between PEO and Ni makes nickel distribute in the silica phase and keeps Ni from aggregation during drying, resulting in a high dispersion of Ni.

Pore size control of mesoporous SnO2 prepared by using stearic acid

Abstract Mesoporous SnO 2 with controlled pore size was prepared by calcination of the precursors containing stearic acid (STA). The vaporization of STA promoted the crystallization of SnO 2 at low temperature. Crystallization accompanied with the vaporization of STA at low temperature allowed SnO 2 crystallites to aggregate loosely to form mesopores. The SnO 2 consisted of the aggregates of crystallites, and the mesopores were located at intercrystallites. The pore size and crystallite size of the mesoporous SnO 2 increased with increasing calcination temperature ( T c ). The specific surface area decreased with increasing T c , while the pore volume showed little change in the range of T c . The crystal growth of SnO 2 during calcination at high T c provided large mesopores at interparticles.

Mesoporous MgO and Ni–MgO prepared by using carboxylic acids

MgO and NiO–MgO with large mesopores were prepared by using the corresponding nitrates and carboxylic acids. Their pore structures were characterized by N2 adsorption, and reduced Ni–MgO samples were used in the liquid-phase hydrogenation of ketone. The mesopore size of MgO was controllable with the alkyl-chain length of the carboxylic acid in the range between 13 and 38 nm. The mesopores are located at the MgO interparticles. In the hydrogenation of 4-heptanone to 4-heptanol, the catalytic activity of the Ni–MgO, which had mesopores at 11 nm, prepared using dodecanoic acid was higher than that of a commercial Raney Ni with mesopores around 4 nm, while the Ni surface of the Ni–MgO was lower than that of a Raney Ni catalyst. At an optimum regulated size of mesopores, the Ni–MgO catalyst would show high catalytic activity satisfying both rapid mass transfer of the reactants and high dispersion of Ni metals on the catalyst surface.

Diffusion coefficient of ketones in liquid media within mesopores

The liquid-phase diffusion coefficient of several ketones within mesopores was estimated by measuring the change in UV absorbance of mesoporous plates immersed in a solvent. Monolithic plates of silica gel with different mesopore sizes at ca. 4 and 10 nm were used for the measurement after their pore surface had been modified with trimethylsilyl groups. In the modified silica plates, the diffusion coefficient of ketones, Dp, decreases with increasing the molecular size of the solvent, whereas little dependence is observed on the molecular size of solutes. This indicates that diffusivity of the solute in the mesopores is determined by the diffusivity of the solvent. A zigzag tendency (i.e. the Dp in alkane solvents with an odd number of carbons is larger than those with an even number of carbons) was observed in the small pores with a diameter of ca. 4 nm. The zigzag in Dp can explain a similar zigzag trend in the reaction rate observed only in the small mesopores of the Raney nickel catalyst with a diameter of 3.8 nm in the hydrogenation of several ketones.