Ru Supported Aluminum-silicon Composites For The Hydrogenation Of Aryl Carboxylic Acids And Their Derivatives In Water

The hydrogenation products of aryl carboxylic acids and their derivatives,cyclohexanedicarboxylic acids and cyclohexane diester,can be widely used in polyester,coatings,fibers and rubber fields.The traditional catalysts for the hydrogenation of aryl carboxylic acids and their derivatives require a series of conditions such as the high temperature and pressure,organic solvent,and high loading precious metals due to the stability of the benzene ring and the conjugation effect between the benzene ring and the carbonyl group.These disadvantages result in the catalyst not being widely used in industry.In this paper,sol-gel and hydrothermal methods were used to synthesize aluminum-silicon composites with abundant acid sites on the surface.After loading highly dispersed ruthenium nanoparticles,they were applied for the hydrogenation of aryl carboxylic acids and their derivatives under mild conditions in water.Through the characterization of composites,the performance evaluation of catalysts,and the preliminary exploration of reaction mechanism,the following conclusions were obtained:?1?The catalysts Ru/S-AS-x?x refers to the Si/Al molar ratio in the raw materials?,ruthenium nanoparticles supported onto the aluminum-silicon composites synthesized by sol-gel method,showed good catalytic performance for the hydrogenation of terephthalic acid in water,and its catalytic conversion rate and cis-selectivity of the product were up to 92.6% and 84.9% at 80 °C?H₂ pressure,5 MPa?,respectively.However,the framework dealumination and ruthenium nanoparticles leaching during the catalyst recycling resulted in the relatively poor stability of these catalysts.?2?The aluminum-silicon composites prepared by hydrothermal method supported ruthenium nanoparticles catalysts Ru/H-AS-x showed good catalytic performance for the hydrogenation of aryl carboxylic acids and their derivatives in water.Ru/H-AS-x exhibited ordered mesoporous structure and the properties of Lewis acid sites.And the catalyst Ru/H-AS-3 showed the ordered mesoprous structure,highly dispersed ruthenium nanoparticles,and highest total acid amount and strong acid amount.Ru/H-AS-3 catalyst could obtain 100% conversion and 84% cis-isomer selectivity for the hydrogenation of terephthalic acid in water at 80 °C?H₂ pressure,5 MPa?.Meanwhile,this catalyst also showed excellent stability,it could still achieve 90.2% conversion and 83.3% cis-isomer selectivity after reusing 14 times.The comprehensive characterization and catalytic results showed that the catalytic performance for hydrogenation of terephthalic acid in water was determined by the ordered structure of catalyst,specific surface area,and the strong Lewis acid sites amount.In addition,water and hydrogen provided equivalent hydrogen atoms for the hydrogenation reaction,and therefrom a possible reaction path for the hydrogenation of terephthalic acid in water was proposed.?3?Ru/H-AS-3 catalyst was also able to completely hydrogenate phthalic acid,isophthalic acid,dimethyl phthalate,dimethyl isophthalate,dimethyl terephthalate and trimellitic anhydride under mild condition in water.Among them,the cis-isomer selectivity of dimethyl phthalate could reach 100%.In addition,this catalyst could achieve 95.1% conversion for the hydrogenation of trimellitic anhydride in water.