Selective catalytic reduction of NO by NH3 over Mn–Cu oxide catalysts supported by highly porous silica gel powder: Comparative investigation of six different preparation methods

Abstract

In this study, Mn-based catalysts supported by highly porous silica gel powder (SSA up to 470 m2·g−1 and total pore volume up to 0.8 cm3·g−1) were prepared by six different methods in liquid solutions (electroless metal deposition, stepwise addition of a reducing agent, wet impregnation, incipient wetness impregnation, urea hydrolysis, and ammonia evaporation) and tested for selective catalytic reduction of NOx with ammonia (NH3-SCR de-NOx). Prior to the activity test all the catalysts prepared were characterized by ICP-OES, SEM, EDX mapping, XPS, XRD and N2 adsorption techniques to provide the comprehensive information about their composition and morphology, investigate the dispersion of active components on the carrier surface, identify the chemical forms and structural properties of the catalytically active species of the catalysts prepared. The results revealed that all the methods applied for preparation of SCR de-NOx catalysts can ensure the uniform distribution of Mn species on the carrier surface, however as it is typical for preparation techniques in a liquid phase the significant reduction in SSA and pore volume along with increasing the loading was observed. Considering both the physicochemical properties and the catalytic performance of the catalysts the least effective preparation method was shown to be ammonia evaporation, while the most attractive techniques are incipient wetness impregnation and electroless metal deposition.