Improved NH3-SCR activity by the cooperation of FeVO4 and CeO2 nanosheet catalysts: structure and mechanism

Abstract

A series of FeVO₄/CeO₂ nanosheet catalysts featuring various mass percentages (x%) of FeVO₄ (denoted x%FeV/CeO₂-S) were synthesized and employed in selective catalytic reduction (SCR) of NO_x with NH₃. Among them, 10%FeV/CeO₂-S exhibited the optimal NH₃-SCR activity, achieving over 90% NO_x conversion and more than 98% N₂ selectivity at 216–365 °C, while 10%FeV/CeO₂-P catalyst prepared by loading FeVO₄ on CeO₂ nanoparticles showed over 90% NO_x conversion and above 96% N₂ selectivity at 272–345 °C. The combination of FeVO₄ with CeO₂ nanosheets was superior to that with CeO₂ nanoparticles, which significantly improved the NH₃-SCR activity of the catalyst at low and medium temperatures and broadened the operating temperature window. CeO₂ nanosheets interacted with FeVO₄ stronger than with CeO₂ nanoparticles, which was conducive to the dispersion of FeVO₄, inhibited the grain growth of CeO₂ nanosheets, and improved the ratios of lattice defects, Ce³⁺ and oxygen vacancies. Moreover, the morphology of the nanosheets was conducive to the electron transfer between Ce, Fe and V. These finally enhanced the surface acidity and redox ability of the FeVO₄/CeO₂ nanosheet catalysts. As the mass percentage of FeVO₄ increased, it tended to gather on the surface of CeO₂ nanosheets, which weakened the interaction between them. When the mass percentage of FeVO₄ increased to 20%, the specific surface area and the surface acidity decreased greatly, leading to a significant decline in NH₃-SCR activity. Furthermore, the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms was observed on the 10%FeV/CeO₂-S catalyst.