In对Ni/SiO2催化剂苯甲醚加氢脱氧性能的影响:苯环加氢及 C-C键氢解的抑制作用

由可再生木质素基生物质油加氢脱氧制三苯(苯、甲苯及二甲苯)及燃油可减少对化石能源依赖、缓解环境问题,加氢脱氧催化剂的研究开发为众多学者密切关注.我们以低成本金属Ni为加氢脱氧活性组分,采用金属In对金属Ni催化剂进行改性,旨在增加以苯甲醚为模型反应物加氢脱氧中的三苯收率、降低金属Ni的C-C键氢解及甲烷化活性,提高反应过程中碳收率、降低耗氢量.采用等体积浸渍-程序升温还原法制备了Ni/SiO2及Ni-In/SiO2催化剂,研究了Ni/In比及Ni含量对In改性Ni/SiO2催化剂结构和苯甲醚加氢脱氧性能的影响,利用H2-TPR,H2化学吸附,XRD,NH3-TPD,XPS,TEM及N2物理吸附-脱附等手段对催化剂及其前驱体进行了表征,采用石英管固定床反应器在300°C、常压、H2/苯甲醚摩尔比25及苯甲醚重时空速0.4 h-1的反应条件下考察了催化剂苯甲醚加氢脱氧性能,分析了催化剂结构与性能之间的关系.H2-TPR结果显示,金属In的加入抑制了催化剂前驱体中Ni物种的还原.XRD,H2化学吸附,HAADF-STEM-EDS及XPS等结果表明,经450°C还原制备的Ni-In/SiO2双金属催化剂中Ni和In接触紧密.In的加入明显降低了催化剂表面金属Ni的活性位数量;并且,Ni/In比越低Ni-In/SiO2催化剂H2化学吸附量越小.XPS结果还显示,Ni-In/SiO2催化剂中存在金属In向Ni转移电子.上述结果说明,在Ni-In/SiO2催化剂中金属Ni与In存在较强的相互作用.在苯甲醚加氢脱氧反应中,与Ni/SiO2催化剂相比,Ni-In/SiO2催化剂虽因表面Ni密度较低而具有较低苯甲醚转化率,但其苯环加氢、C-C键氢解及CO甲烷化活性较低,因而具有较高的三苯及环己烷选择性;并且,随Ni/In比的降低(即In含量的增加),Ni-In/SiO2催化剂的加氢、氢解及甲烷化能力呈减弱趋势.随Ni质量含量提高,Ni-In/SiO2双金属催化剂上苯甲醚转化率提高,但对三苯选择性及C-C键氢解能力影响不明显.经分析认为,与Ni/SiO2相比,Ni-In/SiO2催化剂较低的苯加氢及C-C键氢解活性与In对表面连续Ni位隔离作用及金属镍位电子云密度提高有关.在优化的反应条件下,Ni质量含量为40%、Ni/In比为40的Ni-In/SiO2催化剂上三苯收率为60.4%,高于相同Ni质量含量Ni/SiO2催化剂上三苯收率(51.6%).

Effects of indium on Ni/SiO2 catalytic performance in hydrodeoxygenation of anisole as model bio-oil compound:Suppression of benzene ring hydrogenation and C-C bond hydrogenolysis

SiO2-supported monometallic Ni and bimetallic Ni-In catalysts were prepared and used for hydro-deoxygenation of anisole, which was used as a model bio-oil compound, for BTX (benzene, toluene, and xylene) production. The effects of the Ni/In ratio and Ni content on the structures and perfor-mances of the catalysts were investigated. The results show that In atoms were incorporated into the Ni metal lattice. Although the Ni-In bimetallic crystallites were similar in size to those of mono-metallic Ni at the same Ni content, H2 uptake by the bimetallic Ni-In catalyst was much lower than that by monometallic Ni because of dilution of Ni atoms by In atoms. Charge transfer from In to Ni was observed for the bimetallic Ni-In catalysts. All the results indicate intimate contact between Ni and In atoms, and the In atoms geometrically and electronically modified the Ni atoms. In the hy-drodeoxygenation of anisole, although the activities of the Ni-In bimetallic catalysts in the conver-sion of anisole were lower than that of the monometallic Ni catalyst, they gave higher selectivities for BTX and cyclohexane as a result of suppression of benzene ring hydrogenation and C-C bond hydrogenolysis. They also showed lower methanation activity. These results will be useful for en-hancing carbon yields and reducing H2 consumption. In addition, the lower the Ni/In ratio was, the greater was the effect of In on the catalytic performance. The selectivity for BTX was primarily de-termined by the Ni/In ratio and was little affected by the Ni content. We suggest that the perfor-mance of the Ni-In bimetallic catalyst can be ascribed to the geometric and electronic effects of In.