Tungsten modified natural limonite catalyst for efficient low-temperature selective catalytic reduction of NO removal with NH3: preparation and characterization.

ABSTRACT

With natural limonite as the precursor and an ammonium tungstate hydrate as modification, the W/limonite composite catalysts were synthesized by the impregnation method. Their structures and properties were systematically characterized and analyzed; the denitrification activity and resistance to water and sulfur on catalysts were investigated. The results indicated that the W/limonite composite with W/Fe mass ratio of 9% and calcination temperature of 300 °C had highly catalytic activity, enhanced resistance to sulfur and water. The NO conversion efficiency was maintained over 85% with NO initial concentration of 500 ppm, the gas hourly space velocity (GHSV) of 36,000 h-1, and reaction temperature of 100 °C, while it was greater than 98% with addition of 200 ppm SO2 and 3 vol. % H2O at the reaction temperature of 250 °C. The superior performance was mainly ascribed to the formation of W-OH species and W = O species with wide dispersion on the surface of goethite or in Fe2O3 lattice defects, to generate more acidic hydroxyl groups and more oxygen defects and strong acidity Brønsted for the SCR reaction.