Study On Performance Of Ni/SiO₂ Catalysts Modified By Metal Promoters For Hydrodeoxygenation Of Anisole

SiO₂ supported Ni-M（Fe,Co,Cu,Zn,Ga,In,Mo）bimetallic catalysts were prepared and investigated for the hydrodeoxygenation（HDO）of anisole.Their physicochemical properties were characterized by means of H₂-TPR,H₂ chemisortion,XRD,NH₃-TPD,XPS,TEM and N₂ sorption,and their activities were tested on a quartz fixed-bed reactor under the reaction condition of 300 ^oC,atmospheric pressure,H₂/anisole of 25,anisole WHSV of 0.4 or 1.0 h^-1.The relationship between catalyst structure and performance is discussed.Firstly,the Ni/SiO₂ catalysts modified with metal In were prepared by the incipient impregnation and temperature-programmed reduction（TPR）method.The effects of Ni content and Ni/In ratio on the structure and HDO activities of Ni-In bimetal catalysts were studied.It was found that Ni-In alloy formed in SiO₂ supported Ni-In bimetal catalysts.While Ni-In alloy crystallite sizes were similar to metallic Ni one at the same Ni content,the bimetallic Ni-In catalysts possessed much lower H₂uptake than the metallic Ni ones due to the dilution of Ni atoms by In ones.A charge transfer from In to Ni was also found in bimetallic Ni-In catalysts.All results indicate an intimate contact between metal Ni and In atoms.In hydrodeoxygenation of anisole,while bimetallic Ni-In catalysts showed lower anisole conversion than metallic Ni one,they had higher TOFs,indicative of a synergetic effect between metallic Ni and In.Also,they gave higher selectivity to BTX and lower activity for C–C bond hydrogenolysis and methanation,which is very interesting for enhancing carbon yield and reducing H₂ consumption.And the lower the Ni/In ratio was,the more remarkable the effect of In on catalyst performance.The selectivity to BTX is primarily determined by the Ni/In ratio and scarcely affected by the nickel content.We suggest that the performance of Ni-In bimetallic catalysts is ascribed to the dilution and high electron density of Ni atoms as well as oxophlicity of metallic In,which might change the adsorption configuration of anisole.Secondly,SiO₂ supported Ni-M（M=Fe,Co,Cu,Zn,Ga,In,Mo）catalysts with the Ni/M molar ratio of 30 and Ni mass content of 30 wt.%were also prepared by the impregnation method.A small amount of metal Cu and Fe promoted the reduction of Ni species in catalyst precursors,while metal Co,Ga and In obviously suppressed the reduction of Ni species.The introduction of metal Fe,Cu and In decreased the H₂uptakes dramatically.Ni₃₀M/SiO₂(expect Ni₃₀In/SiO₂)had higher total acid amount than Ni/SiO₂.The acid strength on Ni₃₀Fe/SiO₂ and Ni₃₀Mo/SiO₂ were much weaker than the others.In the HDO of anisole(WHSV of 1.0 h^-1),Ni30M/SiO2 catalysts gave lower conversion of anisole than Ni/SiO₂ due to lower H₂ uptakes.However,Ni₃₀Ga/SiO₂ and Ni₃₀Zn/SiO₂ had higher selectivities to BTX（including benzene,toluene and xylene）（respectively 81.7%and 76.8%）than Ni/SiO₂（71.5%）,and gave comparable BTX yields（respectively 65.0%and 63.8%）to Ni/SiO₂（63.7%）.Additionally,Zn benefited the process of methyl transfer.Metal In played an excellent performance on suppressing hydrogenation and C-C bond hydrogenolysis and CO methanation.The performance of Ni-M bimetallic catalysts is probably related to the formation of alloy,where there are the geometric and electronic effects of metal promoters.