Effects on Resistance to Deactivation

After finding that sulfite reduced the catalytic activity of Pd/alumina, Schuth investigated the effects of support on deactivation. Applying sulfite as the model poison and 1,2 dichlorobenzene as a model substrate, batch tests were conducted with a variety of zeolite supports loaded with 1%o Pd by weight. The results indicate that pore size and hydrophobicity must both be considered for optimal catalyst performance. Larger pore sizes allowed faster diffusion of the substrate to the active Pd sites and therefore faster reaction; however, the larger pore sizes also allowed more access to the poison sulfite, which resulted in faster catalyst deactivation. The optimal pore size was one which was large enough to allow the substrate molecule to enter the zeolite pores, but small enough to limit sulfite access to the Pd. When this optimal pore size was used in conjunction with a hydrophobic support, the overall catalyst activity was maximized. (Schuth et al. 1998; Schuth and Reinhard 1997)

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