Kinetics of catalyst coking in heptane reforming over Pt-Re/Al2O3

Previous studies have shown that five-membered ring naphthenes (C5N) are the key source of coke in n-heptane (nC(7)) reforming on a Pt-Re/Al2O3 catalyst. Using methylcyclopentane (MCP) as a model C5N compound, we develop a kinetic model that predicts its coking rate on the basis of the data obtained from a vibrational microbalance and a fixed-bed reactor. This rate, with an apparent activation energy of 39.7 kcal/mol, decays exponentially in coke-on-catalyst and is first order in MCP partial pressure. Its dependence on H-2 is a combination of negative first and second orders. The model considers that coke deposits randomly on both clean and coked sites-a feature that permits the distinction between monolayer and multilayer coke buildup. The model correctly predicts the coking rates of ethylcyclopentane and of nC(7). Moreover, it predicts the observed coke profile generated from nC(7) reforming in the integral fixed-bed reactor under conditions quite different from those used in the microbalance. As such, the model may be used for probing the state of coking in a reformer and for guiding catalyst-accelerated aging studies.