Er composition (X)-mediated catalytic properties of Ce_1-XEr_XVO₄ surfaces for selective catalytic NO_X reduction with NH₃ at elevated temperatures

Catalytic rare earth metal vanadates have shown promise for efficiently converting NO_X to N₂ at elevated temperatures (NH₃-SCR) (e.g., CeVO₄, ErVO₄, and TbVO₄). However, these vanadates have limitations as catalytic sites because of three major issues such as weak hydro-thermal stability, low N₂ selectivity, and limited numbers of major active (Lewis acid) sites. As an efficient way to circumvent these constraints, this study showcases a means of structurally modifying vanadate with additional rare earth metals to generate bimetallic vanadates with variable metal compositions. While selecting Ce and Er as metal constituents, a series of Ce_1-XEr_XVO₄ solid solutions were deposited onto WO₃-promoted TiO₂ supports (WO₃-TiO₂) to form Er_X catalysts, whereas a control simulating a commercial catalyst (V) was also synthesized using WO₃-TiO₂ for comparison. Bimetallic Ce_1-XEr_XVO₄ (X = 0.25, 0.5, and 0.75) showed enhanced redox features, improved the quantities of Lewis/Brönsted acid sites and defects, and increased resistance to hydro-thermal aging relative to their monometallic analogues (X = 0 and 1). The optimal Er composition of Ce_1-XEr_XVO₄ studied was found to be X = 0.5. This was because Er_0.5 provided the best redox character, the largest number of active sites with the desired Lewis acid strength, and the greatest hydro-thermal stability among all the Er_X and V catalysts studied. This led to the best catalytic consequence of Er_0.5 in the selective NH₃ oxidation and the NH₃-SCR reactions, both of which should achieve high N₂ productivities at elevated temperatures. In addition, Er_0.5 subjected to hydro-thermal aging also extended its best NH₃-SCR performance among all aged catalysts studied even to low temperature regime of < 300 °C. This paper remarks the proper combination of rare earth metals used to construct bimetallic vanadates can be adaptable to create high-performance NH₃-SCR catalysts for use at elevated temperatures.