Features of the Formation of Catalysts on the Basis of γ-Al2O3 Modified with Ca2+ and Ni2+ Ions Highly Active and Resistant to Carbonization in the Dry Reforming of Methane into Synthesis Gas: Relationship between Physicochemical and Catalytic Properties
摘要
It has been shown that, in the NixCa1 – xAl2O4 (x = 0.1–0.5) catalysts prepared by coprecipitation after calcination in air at a temperature of 700°C, an oxide compound with a defective structure of γ-Al2O3, in which Ni2+ and Ca2+ ions are stabilized, is formed along with highly dispersed NiAl2O4 and NiO moieties. During reduction in hydrogen at the pretreatment stage and further operation in the reaction medium, nickel is partially reduced to a metallic state and leaves the structure of the compound to form highly dispersed Ni0 particles of 3–15 nm in size on the surface. Calcium is stabilized in the structure of γ-Al2O3 and on its surface. The introduction of Ca leads to a significant increase in the concentration of not very stable surface and bulk carbonates and hydrocarbonates to promote the oxidation of C-containing intermediate compounds formed on Ni0 sites. In addition, the modification of Ca leads to a decrease in the concentration of strong acid sites on the surface, the formation of a weaker CO2 bond under reaction conditions, and the complete disappearance of signals from CO complexes with strong Lewis acid sites (LAS), which significantly reduces the amount of carbon formed at the stage of deposition on the surface. The obtained catalysts exhbit high activity and stable operation over a long period of time in the reaction of dry methane reforming (DMR).