Reverse water-gas shift chemistry inside a supersonic molecular beam nozzle

Resistive heating of the metal surface of a supersonic molecular beam nozzle is shown to be very effective in converting CO2 diluted in H-2 to CO and H2O via the reverse water-gas shift (RWGS) reaction at temperatures that preclude simple pyrolysis. The conversion of CO2 to CO, referred to herein as "RWGS yield," exceeds 80% at nozzle temperature above 1000 K, with a detectable methane byproduct. The stainless-steel surface of the nozzle appears to facilitate the reaction as a heterogeneous catalyst. Reaction yield is observed to increase with nozzle temperature and, when the gas mixture contains a significant excess of H-2, decrease with increasing in nozzle stagnation pressure. The inverse dependence of the reaction on stagnation pressure is used to propose a reaction mechanism. Additional kinetic control over the mechanism is afforded by adjusting reactant partial pressures and residence times inside the nozzle reactor, highlighting this method's utility in screening heterogeneous catalysis reactions with fine control over mass flow rates, pressure, and temperature. The results of this study, therefore, present a route to efficient, high pressure, inline catalysis as well as a method to rapidly assess the viability of new catalysts in development.