金属助剂对Ni/SiO_2催化剂苯甲醚加氢脱氧性能的影响

Influence of metallic promoters on the performance of Ni/SiO_2 catalyst in the hydrodeoxygenation of anisole

采用等体积浸渍法制备了Ni/SiO_2及Ni与金属助剂M(M=Fe、Co、Cu、Zn及Ga)物质的量比为30的Ni基双金属催化剂(记作Ni_(30)M/SiO_2),利用H_2-TPR、XRD、H_2化学吸附、NH_3-TPD以及N_2物理吸附-脱附等手段对催化剂进行了结构表征,研究了不同助剂对催化剂结构与苯甲醚加氢脱氧性能影响。结果发现,金属助剂影响了催化剂前驱体中镍物种的还原性能,表明金属助剂及镍之间存在一定相互作用。Ni_(30)M/SiO_2中Ni-M双金属晶粒粒径和Ni/SiO_2中金属Ni晶粒粒径相近。由于表面张力较低的金属会在双金属晶粒表面富集,Ni_(30)M/SiO_2的H_2化学吸附量不同程度地低于Ni/SiO_2。另外,Ni_(30)M/SiO_2催化剂的酸量(尤其较弱酸中心酸量)高于Ni/SiO_2。在300℃、常压、苯甲醚质量空速1.0 h^(-1)及H_2与苯甲醚物质的量比为25∶1条件下考察了各催化剂苯甲醚的加氢脱氧性能。Ni_(30)M/SiO_2上苯甲醚转化率不同程度低于Ni/SiO_2,原因在于Ni_(30)M/SiO_2催化剂H_2化学吸附量较低。Ga及Zn改性催化剂上三苯(包括苯、甲苯及二甲苯)选择性分别为81.7%和76.8%,高于Ni/SiO_2(71.5%),且Ni_(30)Ga/SiO_2及Ni_(30)Zn/SiO_2上三苯收率(分别为65.0%及63.8%)高于或接近于Ni/SiO_2(63.7%)。Ni/SiO_2及Ni_(30)M/SiO_2催化剂中,Ni_(30)Zn/SiO_2具有较高甲基转移能力及较低C-C键氢解活性。从提高碳收率、降低耗氢量角度而言,Ni_(30)Zn/SiO_2具有较佳的加氢脱氧性能,与Ni和Zn之间作用及Zn亲氧性高于Ni有关。

Ni/SiO2 and Ni-based bimetallic Ni（30）M/SiO2 catalysts（with a Ni/Matomic ratio of 30; M= Fe,Co,Cu,Zn and Ga） were prepared by the impregnation method and characterized by the means of H2-TPR,XRD,H2 chemisorption,NH3-TPD and N2 sorption; the effect of Mpromoters on the structure and performance Ni-based catalysts in the hydrodeoxygenation of anisole was investigated.The results indicated that the metallic promoters have a significant influence on the reducibility of nickel species,due to the interaction between Mand Ni species,although the sizes of Ni-Mbimetallic crystallites in Ni（30）M/SiO2 are similar to that of Ni crystallite in Ni/SiO2.Because of the interaction between Ni and Mand the enrichment of certain Mpromoters on the surface of Ni-Mbimetallic particles,the adsorption quantity of H2 on Ni（30）M/SiO2 is lower than that on Ni/SiO2.In addition,the Ni（30）M/SiO2 catalysts also have more acid sites（especially the weak ones） than Ni/SiO2.For the hydrodeoxygenation of anisole under 300 ℃,0.1 MPa,weight hourly space velocity（WHSV） of anisole of1.0 h-1 and H2/anisole molar ratio of 25,the Ni（30）M/SiO2 catalysts exhibit lower anisole conversion than Ni/SiO2,probably due to the lower H2 uptakes on the bimetallic catalysts.However,Ni（30）Ga/SiO2 and Ni（30）Zn/SiO2 give much higher selectivities to BTX（benzene,toluene and xylene）（81.7% and 76.8%,respectively） than Ni/SiO2（71.5%）.Meanwhile,Ni（30）Zn/SiO2 exhibits higher activity in methyl transfer and lower activity in C-C bond hydrogenolysis than other catalysts; owing to the high oxophilicity of Zn,from the aspects of increasing carbon yield and reducing H2 consumption,Ni（30）Zn/SiO2 is probably an appropriate catalyst in hydrodeoxygenation.