Preparation,Characterization And Catalytic Performance Of Selective Oxidation Of Methane Over Cu,V And B/M-SiO₂ Catalysts

Due to the exhaustion of oil and coal resources and environmental problems,the researchers pay more and more attention to the utilization of clean energy.Therefore,the efficient utilization of clean energy（natural gas,shale gas and combustible ice）becomes inevitable.Methane is the main component of these clean energy sources,and it can be directly converted into more value of chemical products for making practical economic significance.Selective oxidation of methane has become a key research in the field of catalysis in recent years because of its advantages such as a low energy consumption and the low carbon accumulation.Transition metals（V,Cu）are the excellent active components for activating methane molecules owing to the existence of d electrons and the strong oxidation-reduction ability.The m-SiO₂@TiO₂ support with core-shell structure could make up for the deficiency of the single material itself thanks to the inertness,large specific surface area,mesopore structure of SiO₂ spheres and weak acidity of TiO₂.In addition,the active species in the nonmetallic B oxides could activate and convert the C-H bond of low carbon alkanes,which have become a new type catalyst for the selective oxidation of low carbon alkanes in recent years.In this paper,Cu or B/m-SiO₂@TiO₂ and V-m-SiO₂ catalysts were prepared,and the relationship between the selective oxidation performance of methane and the structure of these catalysts were studied.The main contents of this paper are as follows:1.Cu/m-SiO₂@TiO₂-x catalysts were successfully synthesized by a grafting method,and the performance of selective oxidation of methane were investigated.The results showed that the best catalytic performance was obtained over 1%Cu/SiO₂@TiO₂-1 catalyst under these reaction conditions(T=675 ^oC,F_total=60 m L·min^-1 and CH₄:O₂=3:1),the selectivity and yield of formaldehyde were 37%and 1.1%,respectively.2.V-m-SiO₂ catalysts with different V loadings were prepared by a pH-modified method,and the catalytic performance of the selective oxidation of methane to formaldehyde were also studied.By screening catalysts and optimizing reaction conditions,the following conclusions were obtained:When the V loading was 0.75%,the selectivity of formaldehyde over V-SiO₂ catalyst was31.2%,and the HCHO yield was 1.8%(reaction conditions:T=650 ^oC,F_total=60 m L·min^-1 and CH₄:O₂=3:1).3.B₂O₃/SiO₂@TiO₂-2 catalysts were successfully prepared by a sol-gel method,and the influence of B loading,space velocity and reaction temperature on the catalytic performance of selective oxidation of methane to formaldehyde were investigated.When B load was 15%,the selectivity of formaldehyde was 59.5%at 600 ^oC.Moreover,the catalytic performance over the bifunctional catalysts were also studied.The methane conversion was significantly improved by adding a small amount of Ni O catalyst into the catalyst bed.