Er composition (X)-mediated catalytic properties of Ce1-XErXVO4 surfaces for selective catalytic NOX reduction with NH3 at elevated temperatures

Abstract

Catalytic rare earth metal vanadates have shown promise for efficiently converting NOX to N-2 at elevated temperatures (NH3-SCR) (e.g., CeVO4, ErVO4, and TbVO4). However, these vanadates have limitations as cata-lytic sites because of three major issues such as weak hydro-thermal stability, low N-2 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 Ce1-XErXVO4 solid solutions were deposited onto WO3-promoted TiO2 supports (WO3-TiO2) to form ErX catalysts, whereas a control simulating a commercial catalyst (V) was also synthesized using WO3-TiO2 for comparison. Bimetallic Ce1-XErXVO4 (X = 0.25, 0.5, and 0.75) showed enhanced redox features, improved the quantities of Lewis/Bronsted 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 Ce1-XErXVO4 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 ErX 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 N-2 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 degrees 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.