Enhanced catalytic activity for simultaneous removal of PCDD/Fs and NO over carbon nanotubes modified MnOx-CeO2/TiO2 catalyst at low temperature

Abstract

Simultaneous catalytic removal of polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs) and nitrogen oxides (NO x ) emission at low temperature is of great significance to solve the multiple air pollution problem caused during waste incineration. A novel catalyst with excellent low-temperature activity towards PCDD/Fs catalytic decomposition, as well as selective catalytic reduction (SCR) of NO with NH 3 is urgently needed to simultaneously control PCDD/Fs and NO emissions. Manganese-cerium composite oxides supported on titanium dioxide (MnO x -CeO 2 /TiO 2 ) or TiO 2 and carbon nanotubes (CNTs) composite carrier (MnO x -CeO 2 /TiO 2 -CNTs) were prepared using sol–gel method, and their catalytic activity towards simultaneous abatement of ortho-dichlorobenzene (o-DCBz, model molecular to simulate PCDD/Fs) and NO was investigated. In comparison with their removal, the simultaneous removal efficiencies of o-DCBz and NO over MnO x -CeO 2 /TiO 2 catalyst are lowered to 27.9% and 51.3% at 150\xa0°C under the gas hourly space velocity (GHSV) of 15,000\xa0h −1 , due to the competition between the reactants for the limited surface acid sites and surface reactive oxygen species. CNTs addition improves the catalytic activity for their simultaneous removal. The optimum condition occurs on MnO x -CeO 2 /TiO 2 combined with 20 wt.% CNTs that above 70% of o-DCBz and NO are removed simultaneously. Characterization results reveal that MnO x -CeO 2 /TiO 2 -CNTs catalyst with proper CNTs content has larger Brunauer–Emmet–Teller surface area and greatly improved surface acidity property, which are beneficial to both o-DCBz and NO adsorption. Moreover, the\xa0relatively higher surface atomic concentration of Mn 4+ as well as the existence of abundant surface Ce 3+ atom accelerates the redox cycle of the catalyst and enriches the surface reactive oxygen species. All the above factors alleviate the competition effect between o-DCBz catalytic oxidation and NH 3 -SCR reaction and are conducive to the simultaneous abatement of o-DCBz and NO. However, excess CNTs make less contribution on enhancing the interaction between Mn atom and Ce atom, thereby resulting in less improvement in the catalytic activity.