Synthesis Of Tungsten Based Nanomaterials And Its Application In Catalytic Hydrogenation Of Cellulose

Biomass energy has attracted the attention of researchers due to its characteristics of renewable,abundant reserves and wide distribution.The current direct hydrogenolysis of cellulose into low molecular polyols is of remarkable achievements,particularly in ethylene glycol?EG?.The process of hydrogenolysis of cellulose to EG is controlled by two processes of both hydrolysis of cellulose and retro-aldol condensation of hydrolyzed products.It has been found that acidic tungsten-based catalysts can effectively promote the hydrolysis of cellulose and retro-aldol condensation of oligosaccharides.Therefore,it attracted great interest from researchers.However,there are few reports on the catalytic effect of the microcrystalline surface properties of tungsten catalysts on the hydrolysis of cellulose.In this paper,template-free hydrothermal methods had been successfully used to synthesize hexagonal,orthorhombic,and monoclinic tungsten trioxide?WO₃?.The hexagonal and monoclinic WO₃ had regular nanorod and nanosheet morphology,and exposed specific?100?and?002?crystal planes,respectively.At the same time,the surface morphology,crystal planes,surface-bound water and surface acid sites of the hexagonal and monoclinic WO₃nanocrystals were systematically studied and applied to the process of hydrogenolysis of cellulose to prepare EG.The corresponding relationship between surface microscopic properties and catalytic activity was further evaluated.Results showed that the highest EG yield reaches 77.5%by a combination of loading 1 wt%Ru on the hexagonal WO₃ catalyst.In addition,the relationship between the catalytic effect and characteristics of different crystalline WO₃ after calcination was also investigated.It was found that the specific surface area of WO₃decreased after calcining and the number of acid sites decreased,resulting in poor performance of EG yield.The excellent catalytic effect of the hexagonal WO₃ is dependent on the WO₃-H₂O crystal structure formed by the surface-bound water and unique?100?active crystal plane.Moreover,the higher active?100?crystal plane in the hexagonal WO₃ was conducive to the transformation of W⁶⁺to W⁵⁺,finally prompted the formation of H_?WO₃-H₂O active center.This structure provided more Lewis acid sites,can promote cellulose hydrolysis and the retro-aldol condensation of oligosaccharides.On this basis,a new type of catalytic activity center?H_?WO₃-H₂O?was proposed,and the high-efficient hydrogenolysis mechanism of cellulose under the synergistic effect of hydrogen bonding was explained.This work not only deepened the understanding of the selective hydrogenolysis process of cellulose,but also provided an alternative control method of crystal plane for the rational design of more efficient tungsten-based catalysts.