Novel perovskite catalysts for CO2 utilization - Exsolution enhanced reverse water-gas shift activity

Abstract

Reverse Water-Gas Shift (rWGS) is among the reactions with the highest readiness level for technological implementation of CO2 utilization as an abundant and renewable carbon source, and its transformation for instance into synthetic fuels. Hence, great efforts are made in terms of further development and comprehension of novel catalyst materials. To achieve excellent catalytic performance, catalytically active (nano)particles that are evenly distributed on (and ideally embedded in) an active support are crucial. An extremely versatile material class that exhibits the desired properties are perovskite-type oxides due to the fact that they can easily be doped with highly active elements. Upon controlled reduction or during reaction, these dopants leave the perovskite lattice and diffuse through the material to form nanoparticles at the surface (by exsolution) where they can greatly enhance the activity. Here, six perovskites were studied and their exsolution capabilities as well as rWGS performance were explored. Nanoparticle exsolution significantly enhanced the rWGS activity, with the catalytic activity being in the order Nd0.6Ca0.4Fe0.9Co0.1O3-δ > Nd0.6Ca0.4Fe0.9Ni0.1O3-δ > Nd0.9Ca0.1FeO3-δ > Nd0.6Ca0.4FeO3-δ > La0.6Ca0.4FeO3-δ > La0.9Ca0.1FeO3-δ > La0.6Sr0.4FeO3-δ(benchmark). Moreover, it could be shown that nanoparticles formed due to exsolution are stable at high reaction temperatures. In this paper, the flexibility of the investigated perovskite materials is demonstrated, on the one hand facilitating a material design approach enabling control over size and composition of exsolved nanoparticles. On the other hand, the studied perovskites offer a tuneable host lattice providing oxygen vacancies for efficient CO2 adsorption, activation, and resulting interface boundaries with the ability to enhance the catalytic activity.