Thermal decomposition study of silica-supported nickel catalyst synthesized by the ammonia method

Abstract

Silica-supported nickel catalyst synthesized by the ammonia method and their precursors treated and untreated with ammonia solution were studied by temperature-programmed reduction (TPR), scanning electron microscopy (SEM), and simultaneous thermogravimetry, differential scanning calorimetry and differential thermal analysis (TGA–DSC–DTA) carried out in nitrogen atmosphere (100 ml/min) at different heating rates (5, 10, 15 and 20 K/min). Temperature effect on the catalyst structural composition was studied by X-ray diffraction (XRD). The results indicated that synthesized catalyst shows mainly a higher temperature metal phase (973 K), constituted by a superposition of bi-dimensional sheets similar to nickel phyllosilicate, resulting from the strong metal–support interaction (SMSI) between nickel aqua ammine complex and silica surface. At high temperature, such a compound degrades to stable silica-supported nickel catalyst. Activation energies and kinetic parameters for each decomposition process were calculated by Kissinger's method. Enthalpy values were determined from differential scanning calorimetric profiles. The activity tests of such a catalyst to methane steam reforming indicated that deactivation process caused by carbon deposition was less pronounced than deactivation of a similar nickel content catalyst prepared by impregnation.