Kinetic Aspects of Catalyst Deactivation

In this book, the authors summarize the groundwork developed by various researchers in concern of the kinetics of reactions accompanied by catalyst deactivation, and expound some concepts and approaches which we developed with the aim to extend the knowledge in this area. A new approach is suggested providing opportunities to prognosticate the rate of deactivation according to the reaction mechanism and the current conversion degree. Various deactivation types are distinguished, and the corresponding kinetic descriptions are specified. On this basis, it is proposed to extend the trivial classification for deactivation mechanism patterns leading to different evolution of the catalyst activity. The analysis performed points conversion. Analysis performed to clarify the joint effects of coke formation and mass transfer covers a broad variety of regularities characterizing typical mechanisms when coke originates from constituent participants in the basic process. Shown it is that for certain reaction mechanisms in a domain of operation conditions the efficient rate of the process under diffusion control may exceed the rate in the kinetic region. These results show a possibility to prolong the catalyst lifetime on the account of leading the process on grains of appropriate size, thus reducing the deterioration of catalyst activity. A model is suggested interpreting the kinetic features of processes occurring in narrow zeolite pores with regard to the probabilistic regularities determining phenomena within zeolite structures. An original approach is suggested distinguishing different types of active sites responsible for different routes of processes on multi-functional catalysts. The derived models assume non-uniform vulnerability of active sites, depending on their location, structure, adsorption properties. For avoiding discrepancy with the Langmuir kinetics, the developed approach considers the catalyst surface as containing co-existing ideal adsorbed layers, each of which is characterized by private individual parameters. Problems concerning the relation of the active phase dispersion with process selectivity are discussed. The effect of coke formation on the contribution of different site types to the evolution of activity is put to analysis. The authors hope that the ideas developed can be of use to researchers investigating various problems of kinetics and catalysis. The book can be used by university professors and students for education activities in the field of general chemistry, kinetics, chemical engineering, process design. The authors are grateful to the National Science Fund of Bulgarian Ministry of Education and Science for the financial support through the project DO 02-295/008. The authors acknowledge the financial support of SABIC Chair in Catalysis, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia for publishing this book.