(169b) 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.