**Part 5**

**Application of Chemical Kinetics** 

322 Chemical Kinetics

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**15** 

Pfeifer Peter

*Germany* 

**Application of Catalysts to** 

 **Metal Microreactor Systems** 

*Institute for Micro Process Engineering, Karlsruhe Institute of Technology,* 

Applying microsystems for heterogeneously catalyzed processes means that the surface of tiny channels or structures has to be functionalized. Considering the surface-to-volume ratio of microchannels, volume specific surfaces of microchannels in the order of 105 up to 106 m2/m3 can be obtained. However, when combining the channels to reactors the entire fabrication technique and the necessary connection to conventional equipment lowers the overall surface-to-volume ratio to roughly 2\*103 up to 2\*104 m2/m3 and thus increases costs for materials and manufacture. Taking into account the demand of catalysis, i.e. the necessary "edges and corners" of the active species and the surface area of conventional catalyst support materials of 107 up to 109 m2/m3, the surface-to-volume ratio of the microsystems is not necessarily sufficient. Reviewing the literature only few cases are reported, where the geometric surface of the microsystem, e.g. channels made in copper or silver metal, is high enough ensuring cost competitive micro process engineering equipment. The reaction rates per surface site need to be very high, so that the volume specific heat flux is in a range that the advantage of microsystems, i.e. the high heat transfer rates, can be utilized for improving chemical processes in terms of process

Two approaches are often applied for increasing the geometric surface, the application of a micro fixed bed, also often called "packed bed microreactors", or the surface coating with support material and catalytically active species. Regarding the process requirements it is obvious that both approaches have Pros and Cons. So for example, commercial catalyst can directly be applied for the packed bed system while catalyst coating may take a serious time for its development. Catalysts can be removed in packed bed arrangements whereas the coating may only be removed with the whole microreactor. On the other hand coating technology provides new insights into catalysis due to quasi isothermal conditions so that

This book chapter will give information on interplay between reaction engineering aspects, material science and microfabrication which have to be considered when developing a specific heterogeneously catalysed microreactor process. A brief introduction in the individual coating approaches and exemplarily in new coating

much higher activity of the catalysts can be applied or obtained.

**1. Introduction** 

intensification.

developments will be given.
