Porous catalyst systems monolithic

Fig. 1. Two cases which have to be distinguished for heat transfer limitation a strictly cooled system (left) and a monolithic system (right). The different directions of heat flux and the temperature profiles are indicated (porous catalyst = shaded, microreactor wall = black).

Catalysts can be metals, oxides, sulfides, carbides, nitrides, acids, salts, virtually any type of material. Solid catalysts also come in a multitude of forms and can be loose particles, or small particles on a support. The support can be a porous powder, such as aluminium oxide particles, or a large monolithic structure, such as the ceramics used in the exhaust systems of cars. Clays and zeolites can also be solid catalysts. 

The most general case of catalyst-membrane systems are systems containing a conventional granulated catalyst and a membrane catalyst. Two varieties of such systems are possible (1) a pellet catalyst with a monolithic membrane or (2) a pellet catalyst with a porous (sometimes composite) membrane. The inorganic membrane reactors with or without selective permeability are discussed in Chapter 17 of this book. Examples of applications of systems of selective metal-containing membrane and granulated catalyst are presented in Table 5. 

Porous and thermally stable washcoating layer on mechanically strong support is an important component in both oxidative and three-way catalysts used for car exhaust gas cleaning. The washcoat provides a high and stable surface area for dispersion of the active component of the catalysts consisting of platinum and /or paladium. Usually for the preparation of this layer aluminas modified by La, Ce, Zr, Si etc. are used [1-3]. As it was shown in [4-6] the properties of modified aluminas depend on the method of introduction of the additives In this work we present the results on the preparation and study of model alumina systems modified by La, Ce and Zr as well as of monolith supports washcoated by optimal compositions of alumina and additives. 

Monolith reactor model—For validation purposes, the kinetic models of the SCR catalyst [6] and of the PGM catalyst [18] were used to simulate catalytic activity runs over honeycomb monoliths coated with the SCR and the PGM component, respectively, of the studied ASC system. In the case of the SCR catalyst, the kinetics were implemented in a heterogeneous dynamic ID -I- ID model of a single monolith channel, accounting both for external (gas-solid) and internal (intra-porous) mass transfer resistances [12, 25, 26]. Model simulations... 

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