Selective Oxidation Of Methanol To Dimethoxymethane Over Bifunctional Vanadium And Molybdenum Catalysts

Dimethoxymethane (DMM) is an important intermediate, and has been widelyused as diesel fuel additive and organic synthesis reagent. It has been also utilized asan excellent solvent in pharmaceutical and perfume industries due to its low toxicity.The direct slecitive oxidation of methanol to DMM has been received much attentionbecause of the green and environmental friendly synthesis process. Bi-functionalvanadium molybdenum catalysts for selective oxidation of methanol to DMM arestudied in this paper, which describes the design and application of V2O5-MoO3/Al2O3and V2O5/TiO2-Al2O3catalysts for the selective oxidation of methanol to DMM.The V2O5-MoO3/Al2O3catalysts exhibit superior performance for DMM yieldthan the corresponding samples with V and Mo species only, even at relativity lowtemperatures. The origin of high DMM yield of the V2O5-MoO3/Al2O3catalysts isexplored and attributed to the synergistic effect of V and Mo mixed oxides presentedon the surface of the catalyst. The synergism can be ascribed to (i) the completion of aredox cycle and (ii) the enrichment of weak Br nsted acidic sites. The redox cycle ofV-Mo-O oxides could be completed through electron transfer between lattice oxygenand metal cations. The V species exhibits a superior performance in the adsorptionand activation of gaseous oxygen, as well as enhanced capability to restore the latticeoxygen and suppress the aggregation of Mo species. The enrichment of weakBr nsted acidic sites is attributed to the addition of MoO3and the increase of partiallyreduced V and Mo species, respectively, which is critical to increasing the DMM yield.By adjusting the content of V2O5and MoO3, we have obtained a14V2O5-14MoO3/Al2O3catalyst with the optimized amounts of redox sites and acidicsites, which exhibits a54%methanol conversion with a DMM selectivity of92%at393K.From the comparison of V2O5/TiO2-Al2O3catalytic performance with differentpreparation methods, we find that the sol-gol method and ball-miling method exhibitbetter performance than others. These catalysts prepared by these two methods havesuperior redox ability, which is helpful to improve methanol conversion. Meanwhile,the interation of Ti and Al species destroyed the original structure of Al2O3andaltered the acidic properties by restraining its strong acid sites and produce moreweak acidic sites, which could increase the yield of DMM. Furthermore, theball-miling method could decrese the particle diameter of V2O5/TiO2-Al2O3catalyst and enable the Ti species to incorporate into the lattice of alumina oxide, whichcould induce more oxygen vacancies and enhance the electron transfer ability,improving the redox ability of the catalyst.