山田 泰弘

Vapor-phase intramolecular aldol condensation of 2,5-hexanedione (2,5-HD) to 3-methyl-2-cyclopentenone (MCP) was performed over several rare-earth zirconate catalysts, with yttrium zirconate (YZrO) emerged as the most efficient catalyst. Several parameters, such as Y content, calcination temperature, reaction temperature, and contact time, highly influenced the catalytic performance of the YZrO catalyst: YZrO calcined at 700 °C exhibited the highest catalytic activity but still suffered from catalyst deactivation due to coke formation. Modifying the YZrO with Ag and employing the modified catalyst in an H2 flow effectively reduced the coke accumulation, thus improving the catalytic stability during the aldol condensation of 2,5-HD at 350 °C. The poisoning experiment with the co-fed of acidic CO2 gas and basic molecules of 2,6-, and 3,5-dimethylpyridine suggested that the aldol condensation proceeded via an acid-base concerted mechanism.

Silica-supported Cu (Cu/SiO2) prepared by using an organic additive-assisted impregnation method was employed as a catalyst for the dehydrogenation of 3-methyl-2-butanol (3M2BO) to 3-methyl-2-butanone (methyl isopropyl ketone, MIPK). The utilization of organic additives, especially mannitol, during the impregnation protocol has led to the generation of a Cu/SiO2 catalyst containing highly dispersed Cu nanoparticles, i.e. high Cu surface area (SACu). These properties contributed to the high activity of the mannitol-assisted Cu/SiO2 catalyst, in which the activity was limited only by the equilibrium nature of the reaction. The proportional relationship between the formation rate of the MIPK with the SACu confirmed the benefits of the utilization of organic additives. In addition, the improvement in the SACu of Cu/SiO2 prepared using mannitol only gave a negligible side product originating from the dehydration of 3M2BO; thus, the equilibrium MIPK yield of 99.5% was achieved even at 300 °C.

A highly efficient and stable Cu/SiO2 catalyst was prepared via 12-crown-4-ether (12C4)-assisted impregnation and used in the vapor-phase conversion of glycerol to 1,2-propanediol (propylene glycol, PG) via acetol formation in an ambient hydrogen flow. The 12C4-Cu/SiO2 catalyst gave a PG yield of >97% due to a low rate of C-C cleavage to generate ethylene glycol. Under optimum conditions, the high catalytic performance was maintained for 98 h of time on stream.