Abstract

VILLARROEL, Marlin et al. Thermal decomposition of nickel catalysts supported on silica synthesized by impregnation and by the ammonium method. Rev. Soc. Quím. Perú [online]. 2009, vol.75, n.3, pp.281-292. ISSN 1810-634X.

Nickel catalysts supported on silica synthesized by impregnation (acid, pH = 5,6) and by the ammonium method (basic, pH = 13,0) were characterized by X-Ray Diffraction (XRD) and temperature-programmed reduction (TPR) to establish the influence of pH and temperature on the chemical and structural composition of the synthesized solids. Thermal decomposition of the catalysts and their precursors were studied, alone and treated with ammonia solution simultaneously by different methods of thermal analysis: Thermogravimetry (TGA), Differential Scanning Calorimetry (DSC), and Differential Thermal Analysis (DTA), conducted in air atmosphere (100ml/min) at different heating rates (5, 10, 15 and 20° C). Results suggest that an acidic environment favors formation of superficial low-temperature metallic phases (NiO), while in a basic environment nickel interacts strongly with silica to form nickel phyllosilicates reducible at high temperatures (780°C). In both cases, part of the nickel forms an intermediate temperature phase (430°C) which may consist of metal silicates. Results obtained by TGA and XRD suggest that during decomposition of the catalysts, stable nickel oxides are formed. General chemical reactions are proposed for decomposition of solids. Enthalpy values were determined by DSC and activation energy by the Kissinger method, besides other kinetic parameters that govern each process of decomposition. The decomposition patterns of these solids were compared, to verify that during preparation of the catalyst by the ammonium-modified method, acuoamino nickel complexes are formed that bind tightly to the silica to form catalysts of the phyllosilicate nickel type.

Keywords : temperature-Programmed Reduction (RTP); Study Thermal (TG-DSC and DTA); nickel; silica.

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