A study on the selective catalytic reduction of NO_x by ammonia on sulphated iron-based catalysts

Abstract

The roles of Fe3+ and SO42− are different at low and high temperatures due to their interaction. It is the appropriate contents of Fe3+ and SO42− that can result in high NH3-SCR activity at varying temperatures.

Reduction of Typical Diesel NOx Emissions by SCR-NH3 Using Metal-Exchanged Natural Zeolite and SBA-15 Catalysts

“…A very promising NO conversion efficiency at 350 • C for Fe-CLIN catalysts (above 85%) was observed (Figure 7a). This behavior was also reported by literature [29,54] for CATCO (approximately 91%) in the presence of water. However, in the presence of SO 2 both FeMORD and CATCO catalysts show a NO conversion efficiency above 91%.…”

“…SO 2 adsorption is competitive with NH 3 adsorption at Lewis acid sites and occurs rapidly and irreversibly at low temperatures. Sulfur dioxide reacts with surface ions producing sulfite and sulfate species at temperatures between 200 and 350 • C. Above 350 • C in the presence of oxygen, only sulfate species are formed on the surface, whereas sulfur trioxide (SO 3 ) is adsorbed at higher temperatures, which can lead to a reduction in the activity of catalysts in the presence of SO 2 [53][54][55].…”

Novel Preparation of Cu and Fe Zirconia Supported Catalysts for Selective Catalytic Reduction of NO with NH3

“…This indicates that more Fe species are present in higher valence state on Fe-Zr catalyst, corresponding to higher content of Zr 3+ species. Moreover, recently on functionalized iron hydroxyapatite catalysts it was clearly shown that the presence of Fe 3+ highly dispersed on the surface led to a high selectivity to N 2 , a satisfactory activity in a wide temperature window [41] and improved catalytic activity [34]. Figure 4A,B presents catalytic results of Cu-Zr catalyst.…”

“…The activities of sulphate Fe-based catalysts improved significantly compared to the Fe/Zr catalyst, when tested in the temperature range of 250-500 • C. The authors showed that sulphate supplied higher number of acid sites, which could adsorb more NH 3 species that can react with gaseous NO + O 2 . Recently, Liu et al [34] investigated the selective catalytic reduction of NOx with ammonia over sulphated iron-based catalysts in using different loadings of Fe 3+ and SO 4 2− on zirconia support. Their results indicated that the interaction between Fe 3+ and SO 4 2− can have an effect on the redox ability, acid sites, and adsorption of NOx and NH 3 .…”