溶胶-凝胶法制备Ni-SiO2催化剂的表征与性能

以正硅酸乙酯和硝酸镍为原料,采用溶胶-凝胶法,将硝酸镍分别溶于水和乙醇制得凝胶,分别经超临界干燥和常规干燥制备了一系列Ni-SiO2气凝胶和干凝胶催化剂,运用BET、XRD、TPR、IR、H2-TPD和活性评价等方法对催化剂的物理化学性质和催化间二硝基苯加氢性能进行研究.结果表明,Ni-SiO2气凝胶催化剂均具有较高的比表面积,但由于金属镍烧结导致活性比表面积较小,加氢性能较差;以乙醇为溶剂制备的干凝胶催化剂的镍物种分散度较高,但镍与载体之间的相互作用过强,致使催化剂的还原度降低,活性组分利用率下降;以水为溶剂制备的干凝胶催化剂具有较高的活性比表面积,表现出很高的催化活性和选择性.

Sol-gel Preparation,Characterization and Hydrogenation Property of Silica Supported Ni Catalyst

A series of Ni-SiO2 aerogel and xerogel catalysts were prepared by sol-gel supercritical drying (SCD) and general drying methods using tetraethylorthosilicate (TEOS) as a precursor of silica and nickel nitrate as starting material of nickel. Water or alcohol was used as solvent. Based on the experimental results of nitrogen adsorption-desorption, XRD, temperature-programmed reduction (TPR), IR, temperature-programmed desorption of hydrogen (H2-TPD) and activity evaluation, the physical and chemical properties and catalytic performance of the catalysts for hydrogenation of m-dinitrobenzene to m-phenylenediamine were investigated. Both the Ni-SiO2 aerogel catalysts had high specific surface areas, but their catalytic activity and selectivity were low due to their small active surface areas caused by sintering of nickel crystallite. For the Ni-SiO2 xerogel catalyst that used alcohol as solvent, well-dispersed nickel particles were formed, but the strong interaction between nickel and the support made the catalyst difficult to be reduced, thus resulting in lower degree of the utilization of metal. However, the xerogel catalyst that made use of water solution exhibited the highest catalytic activity and selectivity for m-phenylenediamine attributed to its higher surface area of active nickel, over which the conversion of m-dinitrobenzene and the yield of m-phenylenediamine were up to 92. 6% and 88. 4% , respectively, under the conditions of 2. 6 MPa and 373 K after reaction for 1 h.