Synthesis Of WO₃ Nanomaterials And Its Application In Catalytic Hydrogenation Of Cellulose

The rapid development of the world economy leads to the rapid growth of fossil energy consumption.More and more people are concerned with the utilization of clean,renewable energy because of finite reserves and unrenewable nature of fossil fuel and environmental pollution caused by it.Biomass energy is the only carbon-fixed energy among all the renewable energy(wind energy,solar energy and geothermal energy)on the earth.Cellulose is the most important component of biomass.Although cellulose had been used for long time,such as paper,artificial fibers,etc,it has become study as an energy source just in recent years.It is generally divided in to two steps in the traditional method of producing polyols from cellulose.The first step is hydrolysis of cellulose to form glucose and cellobiose;the second step is the catalytic hydrogenation of glucose to poyols.Such reaction process is complicated and time consuming.So to develop new catalysts and synthesis technology to catalyze cellulose to produce polyols in a simple one step is of great importance.This paper introduces one-pot conversion and transfer hydrogenation of cellulose to poyols with Ru/WO3 catalyst in high temperature,high pressure and water conditions.Tungsten-based catalyst was chosen in the experiment of catalyst preparation.In the present work,we synthesize WO3 nanosheets with square corners and high crystallinity via an organic-additive-free hydrothermal method.The deposition of transition metals on WO3 via reduction of the metals salt precursor by NaBH4,and we also synthesis Ru supported three-dimensional WO3 by the same method.The catalysts were characterized by XRD?Raman?TEM?XPS and H2-TPR to explore the effect of catalysts on the transfer hydrogenation liquefaction of cellulose.The results showed that Ru/W03 has better stability and a better catalytic activity because of the uniformity of Ru at such a method.Direct liquefaction of cellulose over transition metals/WO3 catalysthas been carried out in a reaction vessel,the conversion rate of cellulose and the yield of EG as the target.A series of experiments have been conducted to investigate the influence of metal content,reaction temperature,reaction time and reaction pressure.The optimum conditions and best economic conditions have been achieved through single-factor tests.The results showed that the optimal conditions are reaction temperature 240?,reaction time 2h and reaction pressure 4MPa.1%Ru/WO3 was found to be the optimal promoter with a complete conversion of cellulose and highest EG yield of 76.3%.In order to investigate the reusability of the composite catalyst,the 1%Ru/WO3 catalyst was reused five times.The results demonstrate that the WO3 nanosheet supported Ru catalysts could be stable and reusable under the current reaction conditions.The liquefaction mechanism has been studied preliminary by the means of GC.The results showed that sorbitol and mannitol are the main liquid products of cellulose without catalyst in water,while EG is the main products of cellulose with Ru/WO3.Using several physicochemical methods indicates that the high yield of EG depends on the collective manufacture of crystallinity,the nature of the ruthenium particles,and the electronic interactions between tungsten oxide(WO3 and WO3-x).and Ru metallic sites.In addition,the presence of RuOx?+ is responsible for the generation of protons and metallic Ru is favorable for the reduction of WO3 to WO3-x,and proposed the mechanism of the glucose retro-aldol condensation reaction.Finally,a possible catalytic reaction mechanism for the conversion of cellulose into EG over Ru/WO3 catalyst was proposed.