Magnetic characterization of semi‐amorphous nickel catalysis and their methanation activity

Commercial catalysts (A) and (B) containing 43 and 67% wt. Ni supported on alumina have been successfully characterized by using magnetization (σ) versus H (to 20 k Oe) and T (77−600°K) type curves and by electron microscopy. Hysteresis curves yielded coercive force, remanence and σ (saturation following heat treatment of the catalysts between (440−700°C. These parameters are interpreted in terms of the following properties of constituent particles: (a) superparamagnetic (b) single‐domain‐anisotropic and (c) multi‐domain. Needlelike ’b’ and ’c’ type particles are formed when A is heated to about 600° and above 650°C respectively. The formation of ’c’ type particles coincides with a decrease in the catalytic activity of A for the reaction CO+3H2→CH4+H2O. B consisted of a larger fraction of ’a’ type particles which on heat treatment increased Hc and σ (sat) as expected, but was more thermally resistant to the formation of ’c’ type particles. Unlike A, catalyst B did not show a significant decrease in cataly...