Preparation, Characterization And Catalytic Performance Of Ni/CCA Catalyst

The Ni/Al2O3catalyst is widely used in many chemical processes. The γ-Al2O3is belonged to a defect spinelle structure. During the process of catalyst preparation, Ni was preferentially inserted into the crystal defect to form some Ni species having strong interaction with the support. This makes the reduction of the catalyst must be done under a higher temperature. However, the high reduction temperature may casue sintering of the active component and influences the catalytic performance. While the catalyst was used in the hydrogenation of compounds containing multi-unsaturated bonds, the surface defect sites may attend the process of adsorption and activation of reactant. It even has a strong interaction with one of the unsaturated bonds, inhibiting the hydrogenation of this unsatureated bond and decreasing the catalystic activity.Recently, the carbon covered alumina support (CCA) was reported. The CCA support retains the structure and physical characteristics of alumina, simultaneously have surface properties similar to carbon. The altering of surface properties of CCA support will undoubtedly change the exisiting state and chemical environment of active component Ni. Consequently, the reduction performance, dispersion, electronic configuration and catalystic performance will be greatly affected. However, it is scarely researched about the effect of carbon on the Ni/γ-Al2O3structure, texture and catalytic performance.In the present work, the influencees of carbon source, support calcination temperature, Ni loading and reduction temperature on the structure, texture and active metal statement in Ni/CCA catalyst were systematically researched. Moreover, the Ni/CCA catalyst was used in the hydrogenation of MA. The main results were obtained as follows:1. The carbon source and support calcination temperature have great influence on the nature of CCA. The carbon content was significant different with the various carbon sources. When the sucrose was empolyed as carboneous source, the CCA showed the highest carbon content. The calcination temperature influence on the statement of surface carbon. When CCA support was calcined at600℃, the surface carbon existed as stable graphitized carbon form.2. The introduction of C prevented the insertion of Ni into the surface tetrahedron and octahedron site of Al2O3, which improve the effective availability of the Ni. Meanwhile, the intermediate species which was harmful for the hydrogenation of C=O was also inhibited. The Ni/CCA showed superior carbonyl hydrogenation performance than the Ni/y-Al2O3.3. The Ni loading and reduction temperature had significant effect on the structure and MA hydrogenation poformance of Ni/CCA. With the increase of Ni content, the Ni dispersion decreased slightly, but it still remained high active surface area. The catalyst showed excellent C=O hydrogenation performance. For the reduction temperature, low reduction temperature can not make the NiO reduced completely; the high reduction temperature is easy to lead to the sintering of the active component. When the reduction temperature was450℃, the catalyst showed the highest Ni effective availability and the highest hydrogenation activity.