Preparation of high loading silica supported nickel catalyst: simultaneous analysis of the precipitation and aging steps

Abstract

The precipitation and aging steps used for the preparation of high loading silica supported nickel catalysts were simultaneously analyzed with the aid of statistical design of experiments. Empirical models relating catalyst final properties and preparation variables were developed. It was found that the precipitation step determines the final catalyst nickel content, and that at low nickel concentrations high metallic area per gram of reduced nickel may be attained with the precipitated precursor without performing the aging step. When it is performed, the aging step has a strong influence on final catalyst properties, such as specific surface area, metallic area per gram of nickel and degree of reduction. Therefore, catalyst aging may be an effective method to control dispersion, reducibility and active phase accessibility. The importance of the aging step was shown to increase with the aging temperature, which is linked to the larger rates of silicate formation at high temperatures. A semi-empirical model was developed to describe the final catalyst specific surface area as a function of the rate of silicate formation. This model is able to describe changes of the catalyst surface area fairly well and allow the proper manipulation of preparation conditions in order to maximize the catalyst specific area, leading to maximum catalyst activities.