High pressure microreactor for minute amounts of catalyst on planar supports: A case study of CO₂ hydrogenation over Pd_0.25Zn_0.75O_x nanoclusters

High-pressure studies of well-defined catalysts, deposited on planar supports in ultra-high vacuum using physical methods, may bridge the gap between surface science and applied catalysis approaches in order to develop better catalysts for crucial reactions such as CO₂ hydrogenation. However, the chemical reactors necessary for such investigations, typically involving catalyst quantities down to a few hundred nanograms, are lacking. We present the novel design and evaluation of a 50 µL rectangular microchannel reactor capable of testing small quantities of catalyst at pressures up to 40 bar and temperatures up to 240 °C. To evaluate the microreactor performance, Pd_0.25Zn_0.75O_x nanoclusters soft-landed on SiO₂-coated mica sheets using the cluster beam deposition technique, were tested for CO₂ hydrogenation via the reverse water–gas shift reaction through a series of kinetic experiments. Experimental results, combined with computational fluid dynamics and mass transport analysis, demonstrate that the proposed microreactor setup allows for testing minute quantities of catalysts with very high sensitivity at industrially relevant temperatures and pressures. Although not restricted to a particular catalyst preparation method, the setup is an excellent platform for conducting catalytic tests on composition-controlled, mass-selected, gas-phase nanoparticles deposited on planar substrates, facilitating the determination of reliable structure–activity relationships and enabling a more rational design of catalysts.