Synthesis And Mechanism Investigation On High Efficient Catalysts For Methanol One-step Oxidation To DMM

In recent years,methanol productivity increased greatly through the conversion of syngas,which can come from coal,natural gas and biomass.It's extremely urgent to develop dowmstreams for methanol.Among these methanol downstreams,dimethoxymethane?DMM?,a good oil additives and environmentally friendly solvent,has attracted much attention.In this paper,V₂O₅-TiO₂-SO₄^2-?VTiS?synthesized by co-precipitation route was selected as the catalyst for methanol oxidation to DMM.The catalyst activity and DMM selectivity were optimized by adjusting the ratio of active components,adding surfactants and hydrophobic reagents.The structure,textual data and the dispersion of the active components were investigated by kinds of characterization techniques such as XRD,XPS,Raman spectra and TEM to reveal the relationship between the physic-chemical properties and methanol to DMM performance.It was found that the acidity of catalyst increased after vanadium was partly substituted by molybdenum.The 20%molybdenum-substituted catalyst showed a methanol conversion of 52%and a DMM selectivity of 79%at 155?.When CTAB was used during the co-precipitation process,the agglomeration of catalyst particles was effectively alleviated,and the particle size was reduced from 19 nm to 7 nm,as a result,an increase in the catalyst specific surface area and a decrease in the pore size and pore volume was found.Furthermore,both the dispersion of the vanadium species on the surface of catalysts and its acidity was increased after CTAB addition,as confirmed by the disappearance of V₂O₅ crystal peak in the Raman analysis.The reaction of the methanol oxidation to DMM showed that methanol conversion and DMM selectivity were promoted at relatively low temperature on the CTAB-modified catalyst,and the temperature for the highest DMM yield decreased from 140? to 125?.By optimizing the reaction conditions,a 47⁵5%methanol conversion and a 87⁹2%DMM selectivity with a prolonged lifetime of at least 700h were achieved at GHSV of 549 h^-1,methanol:O₂:N₂ of 8.3:2:8 and 115¹20?.After further treatment with hydrophobic reagents,the water contact angle of catalyst was increased from 15°to 136°,but the methanol conversion of the catalysts was reduced for the large steric hindrance of the hydrophobic group and the reduced acidity of the catalyst.However,DMM selectivity higher than 90%was still observed even at 160?.