S. Monteverdi

Nickel Nanoparticles Supported on Silica of Low Surface Area. Hydrogen Chemisorption and TPD and Catalytic Properties

Nickel metal nanoparticles supported on silica of low surface area (15 m2 g-1) were prepared by reduction of nickel acetate by hydrazine in aqueous medium. Their gas-phase stability and surface properties depended on thermal pre-treatment under H2 or air atmosphere. Small nickel particles (<10 nm), in oxidized or reduced state, are strongly resistant to reductive or oxidative treatment respectively. For H2-treated catalysts, H2 chemisorption and TPD results suggested the occurrence of spillover hydrogen between the metal nickel phase and silica. For air then H2 treated catalysts, hydrogen spillover seemed to involve the NiO phase. The activity of the catalysts in gas-phase benzene hydrogenation also depended on the thermal pre-treatment. Pre-calcined then reduced catalysts exhibited higher TOFs than non pre-calcined catalysts, suggesting that the presence of NiO phase may have influenced the hydrogenation process.

Physicochemical and catalytic properties of iron-doped silica—the effect of preparation and pretreatment methods

Chemical vapor deposition (1wt% of iron) and wet and wetness impregnations (both giving Fe loading of 1.6 and 2.9 wt%) have been applied for the formation of iron-doped silica. The obtained materials were characterized by means of low-temperature N2 adsorption, XRD, TEM, H2-TPR, ESR, and chemisorption of CO and O2. Their catalytic activity was tested in isopropanol decomposition and oxidation of methanol to formaldehyde. Depending on the preparation procedure various levels and strengths of Fe–silica interactions were observed. The activation conditions determine the nature of the Fe species formed. Fe3+ isolated species are active in isopropanol dehydration whereas Fe–oxide centers exhibit very high selectivity in methanol oxidation to methylformate and formaldehyde.

Acetylene cyclotrimerization over Ni/SiO2 catalysts in hydrogen atmosphere

Abstract Non-conventional Ni catalysts supported on low surface area SiO 2 were prepared by reduction of nickel acetate by aqueous hydrazine, characterized by XRD and H 2 chemisorption properties or TPSR and tested in acetylene cyclotrimerization in the presence of hydrogen. Their performances were compared with those of classical catalysts supported on silica of low or high surface area. Hydrogen TPD profiles exhibited the presence of active sites involving nickel or nickel in interaction with the support. Hydrogen storage increased for non-classical catalysts or low surface area support. Under the reaction conditions used, no cyclotrimerization of acetylene was observed in the absence of hydrogen, probably as a result of strong adsorption of benzene precursor species. In the presence of hydrogen, benzene and ethylene were the main products in the low reaction temperature regime ( 2 and C 4 hydrogenation products at the expense of cyclotrimerization to benzene. Increasing the partial pressure of acetylene strongly deactivated the catalyst but favoured selectivity of both benzene and ethylene. The presence of both water vapour and hydrogen improved cylotrimerization to benzene at the expense of hydrogenation products, notably at low reaction temperatures. The effect of the different parameters on the sorptive and catalytic properties of the nickel catalysts prepared are discussed, notably the role of hydrogen and water in the determination of activity and reaction paths.

Colloidal nanometric particles of nickel deposited on γ-alumina: characteristics and catalytic properties

The present paper deals with supported nanoparticles of metallic nickel prepared by impregnation of an organometallic colloidal precursor (NiRC complex) on γ-alumina. The obtained supported materials (NiRCS complex) were characterized by STEM, EELS, XRD and TGA and tested in the hydrogenation reaction of benzene and styrene both in the gas and liquid phases. EELS and STEM studies showed that the metallic nickel nanoparticles of the NiRC precursor were well dispersed (1–3 nm) on the support, without size variation during the impregnation step. However, particle growth in NiRCS was observed in samples used after reaction tests. On the other hand, TGA experiments showed that the nickel phase was inserted in an organic matrix which remained in the supported material after impregnation. This organic matrix should be partly removed or totally decomposed by washing with an appropriate solvent or thermal treatment above about 250°C under N2, H2 or air atmosphere respectively. The supported nickel particles were active in the gas phase hydrogenation of benzene in the temperature range of 150–200°C and their activity was enhanced by partial removal of the organic matrix with an organic solvent (e.g. ethanol) or by its total thermal decomposition. They were also found very active in the gas phase hydrogenation of styrene at room temperature. Finally, the supported nickel particles exhibited good hydrogen reservoir properties in organic solvent media.

Adsorption du trichlorure d'azote gazeux sur charbon actif

In a wet atmosphere, gaseous nitrogen trichloride is dissociatively adsorbed on active carbon through the formation of gaseous dinitrogen and chloride surface species irreversibly bound. The rate law of the surface coverage is as follows: θ=1−exp(-k [NCl3] t). Active carbon could adsorb more than 13 % (w/w) of nitrogen trichloride. Doping the active carbon with KI increased the adsorption properties (+15 %), whereas adding Na2CO3 decreased them (−25 % ). Strikingly, in the absence of water vapour in the gaseous effluent, the adsorption of NCl3 was strongly inhibited (divided by a factor of 30-40).