Multivariate analysis of the role of preparation conditions on the intrinsic properties of a Co-Ni/Al2O3 steam-reforming catalyst

The effect of major preparation variables on the innate characteristics of an alumina-supported Co-Ni catalyst system has been examined via a factorial design. Both calcination temperature and time have statistically significant (negative) effects on the Brunauer-Emmett-Teller surface area, with variation in the heating rate registering little or no influence. Similarly, the acid-site strength and concentration were unaffected by variations in the three preparation variables. However, the heating rate was a strong determinant of the metal particle size, dispersion, and metal surface area. Even so, analysis of the calcination kinetics revealed that a high rate of metal aluminate formation was associated with poor dispersion, low metal surface area, and large crystallite size especially for low-temperature calcination. The solid-state metal nitrate decomposition implicated an Avrami-Erofeev kinetics with an activation energy of 82.6 kJ mol(-1). H-2 temperature-programmed reduction and X-ray diffraction revealed the existence of multiple oxide phases, namely, Co3O4, NiO, NiCo2O4, Ni2O3, and Ni(Co)Al2O4, whose magnitude and stability depended on the calcination heating rate. Phase changes during reduction were supported by scanning electron microscopy and transmission electron microscopy images as well as surface elemental profiles.