Diversity in the operation of a monolith reactor

Apart from the specific applications of microreactors as devices for screening and catalyst testing, measurement of the intrinsic kinetics in a system with the advantages previously mentioned is highly desirable. Their improved mass and heat transfer properties at uniform temperature are beneficial, to avoid falsification of the observed kinetics. The following characteristics should be also mentioned  

Several kinetic studies in microreactors/monoliths are available in the literature over a wide range of conditions. In particular, measurements under severe conditions are attractive for a number of reasons. We mention some examples in the following. 

McCarty [125] used an annular reactor to evaluate kinetics of methane combustion over PdO-supported catalysts. The design of the apparatus had a small gap between cylinders (0.1-0.3 mm) and a thin coating (10 pm). Using high flow rates and dilute methane and oxygen in helium, the author claims to have measured the intrinsic rate of methane oxidation up to 900°C, without contributions from gas-phase reactions. Groppi et al. 

The suitability of the structured annular reactor for very fast catalytic combustion reactions was confirmed, since it allowed measurement of kinetic data under conditions closer to the ones in the commercial applications (at higher GHSV and temperature). Extrapolation from lab-scale results can therefore be avoided, as changes in the reaction mechanism may occur 

A related topic is the evaluation of internal diffusion limitations in catalyst coatings supported on microchannels. Experimentally, the two most common tests are variation of temperature and catalyst layer thickness. Both quantities are sometimes given as criteria for the chemical regime (specification of a temperature or thickness below which kinetics controls). For example, some authors [127, 131] consider internal diffusion neghgible for t 50pm. Kapteijn et al. [132] concluded that washcoat layers thicker than this would lead to mass transfer control in the washcoat, when testing square channel 

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