Nickel containing MCM-41 and AlMCM-41 mesoporous molecular sieves: Characteristics and activity in the hydrogenation of benzene

Abstract

Pure siliceous and aluminosilicate mesoporous molecular sieves of MCM-41 type have been used as matrices for nickel incorporation (1.7–5%, w/w) via wet impregnation. Moreover, the AlMCM-41-32 material was modified by the cation-exchange method. The properties of the prepared catalysts were studied by means of XRD, XPS, N 2-adsorption, H 2-TPR, H 2-adsorption and TPD. The reaction of gas-phase benzene hydrogenation was carried out on the prepared catalysts. The hydrogen spillover effect in this reaction was also studied using 3% Ni/MCM-41 and 3% Ni/AlMCM-41-32 catalysts diluted by MCM-41 and AlMCM-41-32, respectively. NiSiO 3 and Ni 2O 3 species in the calcined precursor were shown by H 2-TPR and XPS techniques. The presence of metallic aluminium is shown in the Ni/AlMCM-41-32 reduced materials. The reducibility of the catalyst is strongly influenced by the nature of the matrix and the method of preparation. The kinetic study of benzene hydrogenation on 1.7% Ni catalysts demonstrated various partial orders in hydrogen and benzene ascribed to the existence of several surface chemical processes. Investigations on the hydrogen spillover effect showed a maximum of activity for the diluted catalyst. The intensity of hydrogen spillover is strongly decreased in the presence of Al. The kinetic study with the mechanical mixtures suggested changes in the surface reactions due to the contribution of the support to the chemical processes. Moreover, the results strongly indicated that the migration of hydrogen atoms from the metal phase onto the support oxide is assisted by the aromatic hydrocarbon.