One-pot Conversion Of Cellulose To Hexitols Over Bi-functional Ru-supported Solid Acid Catalysts

A series of Ru-supported solid acid bi-functional catalysts were prepared and the catalytic activities for one-pot conversion of cellulose to hexitols were studied.Acid zeolites HY, Hbeta and HZSM-5 were used as the supports to load Ru nanoparticles and catalyzed the conversion of cellulose. Compared to HY-Ru and Hbeta-Ru, higher conversion of cellulose and yield of hexitols were obtained over HZSM-5-Ru. However, according to characterization results, the catalytic activities of Ru-supported acid zeolites were limited by the microporous structures.Ru-loaded sulfonated carbon catalysts were prepared with different carbon resources. The capability of stablizing the –SO3H groups was dependent on the carbon precursor: active carbon and mesoporous carbon material CMK-3 had higher abilities than the cellulose derived carbon, resulting in higher S contents of catalysts. SAC-Ru and SCMK-3-Ru catalysts demonstrated higer activities and selectivities to hexitols than ScellAC-Ru and the highest selectivity(84.0%) was reached by SCMK-3-RuN150.Mesoporous Ru-supported ZrO2-SiO2 catalysts were prepared by precipitation, one-pot synthesis and post synthesis, respectively. The post-synthesis catalysts loaded on SBA-15 retained the long-range order mesoporous structures, which could be partly destroyed or blocked by the increasing Zr content. Weak acid sites and moderate acid sites were dominated on the surface of catalysts, which might be the reason for the low activities. Given the same molar ratio of Zr/Si, catalyst with large surface area provided more accessible acid sites; the concentration of acid sites of the catalysts synthesized by the same method increased with the raising Zr content. The catalytic activity was in the order of ZrO2-SiO2-Ru<OZSBA-15-Ru<PZSBA-15-Ru. Reaction temperature gave a remarkable influence on the selectivity. Elevating temperature caused the degradation of hexitols and increased the yield of unkown soluble organics. A 36.1% yield of hexitols with a 51.2% conversion of cellulose was achieved over PZSBA-15-Ru(0.5).Ru-supported sulfated zirconia catalysts were prepared by precipitation method and the catalytic activities were studied. There were chemical bonds between the SO42- and ZrO2 so that strong acid sits could be formed and acidity was enhanced through sulfation. The catalyst calcined at 500℃ was composed of pure tetragonal phase ZrO2 and showed the highest activity. This result indicates that the tetragonal phase of zirconia is the active phase for the conversion of cellulose and the formation of hexitols. Doping with a proper amount of Si increased the ratio of Br?nsted to Lewis acid sites on the surface of catalyst and elevated the [B]/[L] value of the catalyst; however, transformation of C5~C6 alcohols into the soluble unkown degradation products was accelerated by the increased portion of Br?nsted acid sites and resulted in low yields. A 58.1% yield of hexitols with a 71.0% conversion of cellulose was achieved over SZ-Si-Ru(100:15).