Kemija u Industriji (Dec 2004)
Monolitni katalizatori i reaktori: osnovne značajke, priprava i primjena (Monolith catalysts and reactors: preparation and applications)
Abstract
Monolithic (honeycomb) catalysts are continuous unitary structures containing many narrow, parallel and usually straight channels (or passages). Catalytically active components are dispersed uniformly over the whole porous ceramic monolith structure (so-called incorporated monolithic catalysts) or are in a layer of porous material that is deposited on the walls of channels in the monolith's structure (washcoated monolithic catalysts). The material of the main monolithic construction is not limited to ceramics but includes metals, as well. Monolithic catalysts are commonly used in gas phase catalytic processes, such as treatment of automotive exhaust gases, selective catalytic reduction of nitrogen oxides, catalytic removal of volatile organic compounds from industrial processes, etc. Monoliths continue to be the preferred support for environmental applications due to their high geometric surface area, different design options, low pressure drop, high temperature durability, mechanical strength, ease of orientation in a reactor and effectiveness as a support for a catalytic washcoat. As known, monolithic catalysts belong to the class of the structured catalysts and/or reactors (in some cases the distinction between "catalyst" and "reactor" has vanished). Structured catalysts can greatly intensify chemical processes, resulting in smaller, safer, cleaner and more energy efficient technologies. Monolith reactors can be considered as multifunctional reactors, in which chemical conversion is advantageously integrated with another unit operation, such as separation, heat exchange, a secondary reaction, etc. Finally, structured catalysts and/or reactors appear to be one of the most significant and promising developments in the field of heterogeneous catalysis and chemical engineering of the recent years. This paper gives a description of the background and perspectives for application and development of monolithic materials. Different methods and techniques used in the preparation of monolithic catalysts are described. Several commercial applications of monolithic catalysts are presented. New applications and the associated technical challenges for the monolithic catalyst and reactors are discussed as well.
