A Study Of Preparation And Performance Of Pd/TiO₂ Nanocatalysts For The Selective Hydrogenation Of Bio-Derived Phenolics In Aqueous Phase

With the severe social problems including energy crisis and environmental pollution,people pay more and more attention to development and utilization of biomass.Lignin is one of the most important compounds in lignocellulosic biomass,thanks to abundant benzene ring and low proportion of oxygen,which is similar to petroleum in structure and composition.Generally,lignin can be converted into aromatics and phenols by some methods such as hydrolysis and pyrolysis,nevertheless,more valuable oxygen-containing chemicals cannot be obtained by these methods only.Phenol is often used as the platform molecule to research the hydrogenation of phenols.Cyclohexanone and cyclohexanol are the main productions of phenol hydrogenation,and the latter is used to produce the former in industry,because cyclohexanone is a key raw material to produce nylon-6 and nylon-66.Cyclohexanol is the thermodynamically favorable product comparing with cyclohexanone,therefore,it is vital to design and synthesize efficient catalysis system to control hydrogenation process and inhibit further hydrogenation to cyclohexanol.In order to solve the problem above,a novel TiO2 nanowire,named as TiO2 NW was prepared by Hydrothermal-Ionexchange-Calcination methods using commercial TiO2(.Degussa P25,anatase 79%,rutile 21%)as raw material.As catalyst support,TiO2 NW contained both Lewis acid sites and Lewis basic sites,derived from Ti4+ and ox.ygen vacancies respectively,which were important functional sites for selective hydrogenation of phenol.Pd/TiO2 NW catalyst was synthesized by photochemical route subsequently,ultrasmall Pd Nanoparticles with hybrid species were constructed for precise synthesis of cyclohexanone with high yield(>98%)in hydrogenation of phenol.Particularly,the selectivity of cyclohexanone was not affected by the mass of catalyst,stirring rate,reaction temperature or hydrogen pressure,thus reaction conditions could be adjusted to meet the need of industry,meanwhile,the general activity of Pd/TiO2 NW was demonstrated by selective hydrogenation of phenol derivatives,which was more flexible and had potential of practical application.The mechanism was explored by a series of characterizations and experiments:it was the synergistic effect of both the highly dispersed noble metal with hybrid species and the novel support being rich in acid-base sites that created the excellent performance of Pd/TiO2 NW catalyst.