Catalysis Today | 2021
Er composition (X)-mediated catalytic properties of Ce1-XErXVO4 surfaces for selective catalytic NOX reduction with NH3 at elevated temperatures
Abstract
Abstract Catalytic rare earth metal vanadates have shown promise for efficiently converting NOX 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 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\u2009=\u20090.25, 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\u2009=\u20090 and 1). The optimal Er composition of Ce1-XErXVO4 studied was found to be X\u2009=\u20090.5. This was because Er0.5 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 Er0.5 in the selective NH3 oxidation and the NH3-SCR reactions, both of which should achieve high N2 productivities at elevated temperatures. In addition, Er0.5 subjected to hydro-thermal aging also extended its best NH3-SCR performance among all aged catalysts studied even to low temperature regime of