Research On The The Gas-solid Phase Catalytic Oxidation Of 2-methyl Naphthalene To 2-naphthaldehyde By Vanadiumtitanium-based Catalyst

Gas-solid phase catalytic oxidation of 2-methyl naphthalene to 2-naphthaldehyde is a green,efficient and easy to industrial production process.However,due to the complexity of the reaction,how to adjust the physicochemical properties of the catalyst to obtain a higher yield of 2-naphthaldehyde is an urgent problem to be solved.In this paper,vanadium-titanium-based catalyst was used to prepare 2-naphthaldehyde by catalytic oxidation of 2-methylnaphthalene.The influence of the size effect of the support particles and the pore structure of the catalyst on the catalytic performance was investigated.On this basis,the physicochemical properties of the catalyst were modulated by doping gallium element further.The optimum reaction conditions were determined for the preferred catalyst and the reaction kinetics were studied.The vanadium-titanium-based catalyst was prepared by incipient wetness impregnation with VO_x as the main active component and anatase Ti O₂ as the support.The effects of primary particle size of support（In the following text,it is referred to as particle size）,heating rate of calcination and pore reamer on catalytic performance were investigated.The results showed that when anatase Ti O₂ with grain size of 14.7nm was selected as the support and the heating rate of calcination was controlled at5℃/min,the yield of 2-naphthaldehyde was the highest.The continuous growth of T₁support grain during the calcination process,on the one hand,optimized the pore structure of the catalyst,reduced the diffusion resistance of reactants,products and reaction intermediates,and on the other hand,decreased the specific surface area of the catalyst,and increased the proportion of polymerized active VO_x species with higher selectivity for 2-naphthaldehyde.The low temperature performance of the catalyst can be improved by using urea or PEG400 as pore reamer,but the yield of 2-naphthaldehyde is not improved.The performance of vanadium-titanium-based catalyst was further improved by gallium doping.The activity evaluation experiment showed that the suitable doping amount of gallium was 1 wt.%.The enhancement mechanism of gallium doping was studied by XRD,BET,SEM,XPS,FT-IR,Raman and H₂-TPR.The results show that the introduced gallium element exists on the substrate and surface of Ti O₂（named as framework gallium species or surface gallium species）,and the superior performance of vanadium-titanium-based catalysts doped with 1 wt.%gallium comes from the synergistic promotion of these two gallium species.The framework Ga species increases the proportion of surface chemically adsorbed oxygen species and improves the reaction activity.The surface Ga species can promote the formation of two-dimensional surface VO_x species and increase the ratio of dehydrogenation centers(V⁴⁺)to oxygen supply centers(V⁵⁺),all of which are favorable for the increment of the selectivity.For the vanadium-titanium-based catalysts doped with 1 wt.%gallium,the influence of process conditions on the reaction was investigated by single factor experiment and orthogonal experiment in a fixed-bed reactor.The optimal process conditions were determined as follows:temperature:380℃,flow rate:5.3×10^-4 mol·h^-1,space velocity:12500 h^-1.Under these conditions,the yield of 2-naphthaldehyde is35.08%,and the catalyst activity is stable after continuous operation for 180 h.The kinetics of gas-solid phase oxidation of 2-methylnaphthalene over the vanadium-titanium-based catalysts doped with 1 wt.%gallium was investigated.Using2-methylnaphthalene（A）,2-naphthaldehyde（B）,phthalic anhydride（C）,2-methyl-1,4-naphthoquinone（D）and 4-methylbenzene anhydride（E）as system components,the reaction network was simplified,and the rate equation was obtained by optimizing the kinetic parameters using Matlab programming:...