N2O Pulse Titration of Ni/α-Al2O3 Catalysts: A New Technique Applicable to Nickel Surface-Area Determination of Nickel-Based Catalysts

Transmission electron microscopy (TEM), CO pulse, and N2O pulse titration were applied to measuring Ni particle sizes on Ni/alpha-Al2O3 catalysts. It was clarified for the first time that the N2O pulse titration could estimate the size at titration temperature between 50 and 100 degrees C, which was confirmed by TEM observation. This agreement in the Ni particle sizes by N2O titration and TEM observation means that the Ni surface was fully covered with the monolayer of oxygen formed by N2O decomposition and the adsorption of N-2 and N2O on the catalysts was negligible. The Ni particle sizes estimated from the CO pulse technique were larger than those measured by the TEM observations. This is because the stoichiometry of CO to Ni was assumed to be one despite the complicated adsorption states of CO on Ni surface. On the contrary, the stoichiometry of oxygen to Ni using N2O pulse titration was one, which indicates that the stoichiometry measurements were not required for this method.