Cordierite and citric acid regulate crystal structure of manganese oxide for effective selective catalytic reduction of nitrogen oxide

Abstract

Catalyst is the key to effective selective catalytic reduction of nitrogen oxide, and developing catalyst is always one of the hottest topics in both field of industry and academy. In order to realize an industrial application, one catalyst must grow on a specific support. However, seldom work compared the difference of catalyst growth with or without support. In this work, Mn2+ growth on cordierite (a typical commercial catalyst support) was investigated. The formed active species were detailedly characterized. As a result, orthorhombic cordierite guided Mn2+ to form orthorhombic oxide (γ-MnO2). In comparison, Mn2+ preferred to form tetragonal β-MnO2 without the guide of cordierite. During the synthesis, cordierite and citric acid promoted γ-MnO2 dispersion, increased growth of exposed (301) facet, and created lattice distortion between (301) and (101) planes. β-MnO2 mainly exposed (101) facet. The best catalyst was γ-MnO2, which was mostly dominated by (301) facet and had an obvious lattice distortion from 75° to 78° between (301) and (101) planes. In comparison, 0.1 g of the γ-MnO2 reached a catalytic conversion rate 1.6 times bigger than 1.0 g of β-MnO2 at 250 °C. This work helps to understand guiding effect of support on formed catalytic species, which is in favor of developing effective commercial catalysts for environmental pollutants.