Boosting the low-temperature activity and sulfur tolerance of CeZr2Ox catalysts by antimony addition for the selective catalytic reduction of NO with ammonia

Abstract

In this paper, a series of Sb modified CeZr2Ox mixed oxides (SbyCZ) were synthesized by citrate method for the selective catalytic reduction of NO with ammonia (NH3-SCR). Experimental results exhibited that the Sb addition could bring a great improvement of SCR activity at 200–360 °C owing to the enhancement in surface area, redox ability and surface acidity. More importantly, the sulfur tolerance of the catalyst with proper Sb loading contents was dramatically improved. For instance, above 85% deNOx efficiency was retained over Sb0.5CZ catalyst after 24 h reaction in the presence of 100 ppm SO2 and 5 vol.% H2O. As for pure CeZr2Ox and the catalysts with low Sb loading contents, the serious accumulation of ammonium sulfates resulted in the deactivation after SO2 exposure. However, with excessive Sb addition, more labile oxygen readily reacted with SO2 and the redox cycle was then disrupted, leading to the decrease of SCR activity. With an appropriate Sb loading contents, the sulfate species preferentially formed around Sb cations could restrain the further consumption of oxygen species in Ce-O-Ce or Ce-O-Zr mode by SO2 via a space confinement effect. Thus, a certain amount of labile oxygen was preserved to drive the SCR reaction, thereby enhancing the sulfur tolerance of the catalyst.