(600as) Effects of Support Shape and Size On the Metal Distribution of Supported Catalysts

Supported catalysts are essential components in a variety of industrial processes, ranging from catalytic converters to production of new drugs. They are generally required because of their high surface area and high mechanical and thermal stabilities. The performance of a catalytic process is intimately related to the catalyst design - uniform, egg-yolk, egg-shell and egg-white metal profiles. Although catalyst preparation and catalytic processing have been investigated for many years, many aspects of catalyst manufacturing are still not fully understood and in industry the design of catalysts is usually based on trial and error, which is expensive and time-consuming, and does not offer assurances on the final results.

It is generally believed that the metal profile is controlled by the conditions that are applied during impregnation where the metal contacts the solid support for the first time. However, experiments have shown that drying may also significantly impact the metal distribution within the support. Therefore, to achieve a desired metal profile we need to understand both impregnation and drying. Controlling the impregnation and drying conditions can enhance catalyst performance, and minimize the production of useless batches that have to be disposed, or recycled.

In this work we have examined the effects of support shape and size on the metal distribution of Ni/Alumina catalysts. The cylindrical pellets with diameter 1mm, 3mm and 4mm are tested to examine the impact of support size. In general, egg-shell profiles can be enhanced with an increase in the support size. This is because drying is much faster for small supports so the metal precursor doesn’t have enough time to migrate during the process. The impact of support shape is examined by testing four high surface area γ-alumina carriers, including rings with 7.9mm diameter, cylinders with 3.2mm diameter, spheres with 3mm diameter and trilobes with 2.5mm diameter. Asymmetric metal profiles are found in triblobes. We have also developed theoretical models to simulate the impregnation and drying processes of Ni/Alumina systems. The initial input of the drying model comes from the results from the impregnation simulations. Therefore, we can combine impregnation and drying together to analyze their effects on the preparation of supported catalysts. We have compared simulation predictions and experimental results based on cylindrical catalysts.

Our simulations and experiments have allowed us to better understand the fundamental mechanisms that occur during impregnation and drying, and to develop a strategy that can generate desired metal profiles. The models used in the present work can capture the essential physics of impregnation and drying while still maintaining a level of generality. Although the results presented are based on a particular metal/support system, they serve to provide physical insight into the fundamentals of the impregnation and drying processes.