Catalysis and Reaction Kinetics of a Model Reaction

Abstract

The development of new and the improvement of existing reactor concepts is diffi cult without understanding the reaction mechanism and -if a catalyst is used -its operation principles. In the ideal case an accurate kinetic model with detailed structure -activity relations would be available. However, in industrial practice in general only simplifi ed strategies are applied in order to minimize experimental effort and to reduce the complexity of the corresponding mathematical expressions. Often simplifi ed kinetic models of the power law type are used to describe reaction rates and catalytic performance for a limited parameter range. Nevertheless, for the understanding and the correct prediction of the performance of alternative reactor concepts, as the membrane reactors treated in this book, a more detailed understanding of the kinetic relations is essential. In membrane reactors the concentration profi les of the reactants and the contact time profi les in the catalyst bed are infl uenced simultaneously. A reliable kinetic model has to describe also the reaction behavior for conditions which are far from those present in conventional packed -bed reactors.In order to deliver reliable data for the comparison between conventional and membrane reactors on the one hand, and between different membrane reactor concepts on the other, it is important to study the same reaction system and to apply the same catalyst. In this and the following chapters, the focus is set on the catalyzed oxidative dehydrogenation of ethane ( ODHE ). Although this reaction is currently far from a wide industrial application, it has several advantages for the purpose of this conceptual study:• The expected reaction network is limited to a rather low number of main products and byproducts, which facilitates mechanistic as well as kinetic studies.• There are no condensable products under reaction conditions, which is benefi cial for monitoring the reactor performance with high accuracy.

Establishing the Role of Graphite as a Shaping Agent of Vanadium–Aluminum Mixed (Hydr)oxides and Their Physicochemical Properties and Catalytic Functionalities

“…The widening of the two bands of graphite has been recurrently observed when the degree of disorder of its structure augments because of an amorphization of the graphite structure. Nevertheless, both the D- and G -bands result from vibration of the sp 2 sites of the carbon–carbon structure; more specifically, the D -band is caused by breathing modes of sp 2 atoms in rings and G -band is the product of the stretching of pairs of the sp 2 atoms in both rings and chains …”

Selective oxidation of H2S over V2O5 supported on CeO2-intercalated Laponite clay catalysts

“…The reduction can be attributed to the weakening of the vanadyl group, which is caused by the significant interaction of vanadium species with cerium species. 27 Meanwhile, the new peak shifts towards higher temperature with the rise of V 2 O 5 loading. This can be explained by the fact that with the rise of V 2 O 5 loading, more surface vanadium atoms interact with the internal vanadium layer and increase the bond strength of the vanadyl group.…”

Oxidative dehydrogenation of propane over low-loaded vanadia catalysts: Impact of the support material on kinetics and selectivity

“…Recent studies of Klose et al, however, suggested a new structural model for vanadium surface species on alumina supported vanadium catalysts [42]. In their work a trimeric surface species, containing V 5+ and V…”