Impact of sulfation and desulfation on NO reduction using Cu-chabazite SCR catalysts

Abstract

a b s t r a c tThis bench reactor study investigates the impact of gaseous sulfur on the NO x reduction activity of Cuchabazite SCR (Cu-CHA) catalysts at SO 2 concentrations representative of marine diesel engine exhaust. After 2 h of 500 ppm SO 2 exposure at 250 and 400 • C in the simulated diesel exhaust gases, the NO x reduction activity of the sulfated Cu-CHA SCR catalysts is severely degraded at evaluation temperatures below 250 • C; however, above 250 • C the impact of sulfur exposure is minimal. EPMA shows that sulfur is located throughout the washcoat and along the entire length of the sulfated samples. Interestingly, BET measurements reveal that the sulfated samples have a 20% decrease in surface area. Furthermore, the sulfated samples show a decrease in NO x /nitrate absorption during NO exposure in a DRIFTS reactor which suggests that Cu sites in the catalyst are blocked by the presence of sulfur. SO 2 exposure also results in an increase in NH 3 storage capacity, possibly due to the formation of ammonium sulfate species in the sulfated samples. In all cases, lean thermal treatments as low as 500 • C reverse the effects of sulfur exposure and restore the NO x reduction activity of the Cu-CHA catalyst to that of the fresh condition.

Impact of Lubricant Additives on thePhysicochemical Properties and Activity of Three‐Way Catalysts

“…The formation of CePO 4 in aged TWCs has been reported in previous studies and has been clearly observed in this study when aging with ZDDP. Elsewhere, Larese et al [18] investigated the contaminants present in a TWC aged under real working conditions of ca. 30,000 km, and demonstrated the formation of CePO 4 in the aged catalyst with the aid of XRD.…”

Lean and rich aging of a Cu/SSZ-13 catalyst for combined lean NOx trap (LNT) and selective catalytic reduction (SCR) concept

“…Regeneration of the upstream particulate filter can also lead to a high temperature exhaust and oxygen depletion. 9 The effects of hydrothermal aging, [10][11][12][13][14][15][16] sulfur exposition and regeneration [17][18][19] have been studied to better understand the aging mechanism under practical operating conditions. Collapse of the zeolite structure, active metal agglomeration and dealumination are the most common identified aging mechanisms that occur during thermal aging.…”

Deactivation of Cu/SSZ-13 NH3-SCR Catalyst by Exposure to CO, H2, and C3H6

“…Nitrates and adsorbed NO 2 were formed on the surface of the catalyst as attested by the absorption bands in the region 1500-1700 cm −1 on all catalysts (not shown). A broad and intense feature, composed of three peaks at 2213, 2183, and 2158 cm −1 , was found on degreened and aged catalysts at 800 • C. These peaks were assigned to NO + in cationic sites (2158 cm −1 ) and NO + NO 2 adducts (2213, 2183 cm −1 ) [34,35]. A less intense band, attributed to NO adsorbed on isolated Cu 2+ [20,36,37], was found in the 1850-1950 cm −1 region.…”