Sustained Low Temperature NOx Reduction

Effect of deposition of carbon deposits on charge flow in EGR valve in CI engine

“…Exhaust gas recirculation (EGR) is an emission control technology decreasing NO x emission in various CI engines: from light-duty engines through medium and heavy-duty engine to low-speed, two-stroke marine engines [6]. EGR technology is also utilized for enhancing the performance of selective catalytic reduction (SCR) catalysts [7].…”

Mitigated ammonium nitrate inhibition in SCR over Cu-SSZ-13 + Ce/Mn-oxide composite catalysts: insights from temperature-programmed desorption analysis

“…For metal-exchanged zeolite catalysts, zeolite physicochemical properties identified as key factors in resistance against NH 4 -NO 3 deactivation include (i) zeolite acidity, (ii) zeolite structure/porosity 9,17,[20][21][22][23][24][25][26] and (iii) chemistry of Lewis acid sites. 2,8,27,28 Zeolite acidity, regardless of strength (i.e., Lewis or Brønsted), has been demonstrated as a key factor in dictating formation and decomposition of NH 4 NO 3 during the SCR reaction. 25,[29][30][31] Zeolite structure and pore size are also important factors.…”

“…Specifically, Cu-zeolites tend to be less active than Fe-zeolites for the low-temperature fast SCR reaction. 2,8,27,28 This is likely due to a lower affinity of NH 3 toward Fe ions versus Cu which potentially underlies their relative tendencies towards NH 4 NO 3 inhibition. We recently demonstrated that combining a metal oxide (e.g., ceria-manganese oxide, Ce 1−x Mn x O y ), termed the selective catalytic oxidation (SCO) phase, with Cu-SSZ-13, referred to as the SCR phase, yielded an SCO-SCR composite catalyst with improved SCR performance and reduced NH 4 -NO 3 inhibition.…”

“…2,3 Improved low-temperature efficiency is achievable through the fast SCR reaction (NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O), particularly over metal-exchanged medium-/large-pore zeolites as well as V-based catalysts. 4–12 However, carrying out the fast SCR reaction at low temperatures is challenged by temporary deactivation by solid NH 4 NO 3 deposits formed via a reaction between NO 2 and NH 3 : 12–14 2NO 2 + 2NH 3 → NH 4 NO 3 + N 2 + H 2 OThe adverse impact of NH 4 NO 3 deactivation does not subside until the exhaust temperature surpasses the NH 4 NO 3 melting point (170–180 °C). Above this temperature, solid NH 4 NO 3 undergoes: (1) sublimation to gas-phase NH 4 NO 3 (eqn (2)), 15 (2) dissociation to NH 3 and HNO 3 (eqn (3)), 13,15,16 (3) thermal decomposition to NO x (eqn (4)–(6)), 16–18 and/or catalytic reduction by NO (eqn (7)).…”

“…Thus, deactivation from NH 4 NO 3 deposits becomes more persistent and sustained NO x abatement at low temperatures is unachievable.NH 4 NO 3 (s) ⇌ NH 4 NO 3 (g)NH 4 NO 3 ⇌ NH 3 + HNO 3 NH 4 NO 3 → N 2 O + 2H 2 O4NH 4 NO 3 → 2NO 2 + 3N 2 + 8H 2 O2NH 4 NO 3 → 2NO + N 2 + 4H 2 ONO + NH 4 NO 3 → NO 2 + N 2 + 2H 2 OFor metal-exchanged zeolite catalysts, zeolite physicochemical properties identified as key factors in resistance against NH 4 NO 3 deactivation include (i) zeolite acidity, (ii) zeolite structure/porosity 9,17,20–26 and (iii) chemistry of Lewis acid sites. 2,8,27,28 Zeolite acidity, regardless of strength ( i.e. , Lewis or Brønsted), has been demonstrated as a key factor in dictating formation and decomposition of NH 4 NO 3 during the SCR reaction.…”