Surface lattice oxygen activation via Zr4+ cations substituting on A2+ sites of MnCr2O4 forming ZrxMn1−xCr2O4 catalysts for enhanced NH3-SCR performance

Abstract

Zr4+ cations were incorporated into the lattice of MnCr2O4 spinels, forming a series of novel ternary ZrxMn1−xCr2O4 (x = 0, 0.05, 0.1 and 0.2) catalysts. The as-prepared Zr-doped catalysts all exhibited enhanced performance selective catalytic reduction of NOx by NH3 than undoped MnCr2O4 catalyst. Among all the prepared catalysts, the Zr0.05Mn0.95Cr2O4 exhibited the best catalytic performance, with good stability in the presence of H2O, the lowest T50 and T90 (149 °C and 201 °C, respectively) and the broadest T80 operation window (183–354 °C) under a gas hourly space velocity (GHSV) of 112,000 h−1. The characterization results revealed that Zr4+ cations were successfully incorporated, and the resultant lattice deformation changed the physical and chemical properties of the catalysts remarkably. The introduction of zirconium produced higher levels of beneficial Mn3+, Mn4+ and Cr5+ species and increased the acidity and redox ability, and electrons transfer effects might be established between Mn, Cr and Zr cations. Moreover, surface lattice oxygen species are activated by Zr doping, and play an important role in NH3-selective catalytic reduction (NH3-SCR). The promoted electrons transfer effects and surface lattice oxygen activation are further substantiated by density functional theory (DFT) results.