371826 Impact of Support Size, Shape and Pore Structure 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.
In this work we have examined the effects of support shape, size, and pore sturcture 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. In order to examine the impact of support pore size, we have tested five alumina supports, where SA1 (sphere, 75μm, 0.05m2/g) and SA2 (cylinder, 3μm, 0.18m2/g) are low surface area supports with large pore structures, SA3 (cylinder, 1.2μm, 12m2/g) and SA4 (cylinder, 20/230 nm, 75m2/g) are moderate surface area supports with moderate pore sizes, SA5 (cylinder, 7/500 nm, 257m2/g) are high surface area supports with small pore sizes. In general, for low concentrations, such as 0.1M and 0.2M, egg-shell distribution is enhanced by increasing the support pore size. The most significant egg-shell distribution was observed in SA1 and SA2 samples. This trend becomes opposite when we extended our studies to high metal loading conditions, such as 1M and 2M. Under these situations, a W shape distribution was observed in SA2 samples. Detailed explanation will be given in the poster.
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.
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