Investigation on the redox/acidic features of bimetallic MOF-derived CeMOx catalysts for low-temperature NH3-SCR of NOx

Abstract

Low-temperature selective catalytic reduction with NH3 (LT-SCR) is a promising approach for NOx remediation. This work utilized bimetallic metal-organic frameworks (MOFs) to prepare CeMOx (M=Ti, Cu) catalysts allowing the homogeneous distribution of promoters to investigate LT-SCR explicitly. The strong interfacial interaction between nanoscale-mixed components was characterized on CeTiOx by HRTEM, micro-Raman, and XPS, resulting in high acidity and good redox properties with abundant Ce3+ and Ti4+. It obtained over 80% conversion from 180 °C to 300 °C with 100% N2 selectivity, and maintained stable performance in SO2/H2O at a high GHSV of 150,000 h−1. In situ DRIFTS reveals that NH3 adsorption was promoted on CeTiOx, which accelerated reaction between NOx and adsorbed NH3 via Eley-Rideal mechanism. Meanwhile, the aliovalent substitution of ceria by Cu2+ was observed on CeCuOx, forming oxygen vacancies. Its high redox properties enhanced NOx conversion by Langmuir-Hinshelwood mechanism, but triggered NH3 peroxidation, leading to poor N2 selectivity.