Comparison of Catalyst Preparation In Microreactors: Atomic Layer Deposition Vs. Impregnation

Comparison of Catalyst Preparation in Microreactors:

Atomic Layer Deposition vs. Impregnation

Huiliang Shi, XuliZhai, DayongTian, Weixiong Pan and Yi Cheng

Department of Chemical Engineering, Tsinghua University, Beijing 100084, China

Microreactors have great potential for fast heterogeneously catalyzed gas phase reactions under high temperature due to their superior mass and heat transfer properties. However, two fundamental challenges remain before we could fully exploit the kinetic potential of catalyst in microreactors. Firstly, traditional catalyst preparation methods, such as impregnation, would result in poor dispersion of active species on reactor walls. Secondly, severe catalyst fall-off tends to take place at high temperature due to the thermal expansion difference between the metallic substrate and the catalyst layer, which would hinder the practical applications of microreactors.

In the present study, a new method called "pre-heated thermal spraying" was adopted to enhance the binding force between the catalyst layer and the metallic substrate of the catalytic plates. As a result, the prepared catalyst by this means had a fall-off rate that could be neglected during high-temperature reaction and vigorous ultrasonic treatment. This method has been successfully applied in hydrogen production from steam reforming of methane in microreactors at our lab. Besides, we also employed atomic layer deposition (ALD) to prepare catalyst nanoparticles on the support of catalytic plates. Using ALD we were able to obtain smaller catalyst particles with a narrower size distribution so that the dispersion of active species could be improved. The differences in catalytic performances (i.e. activity and selectivity) using the two preparation methods, ALD and impregnation, were investigated by evaluating the model reactions: ethane/propane oxidative dehydrogenation (ODH). Besides, the differences in appearances (i.e. size and valence) of active species between fresh and used catalysts were also analyzed. These results revealed that it is possible to use ALD for catalyst preparation in microreactors with high performance in catalytic activity and selectivity.