Potassium deactivation of Cu-SSZ-13 catalyst for NH3-SCR: Evolution of salts, zeolite and copper species

Insight into the Potassium Poisoning Effect for Selective Catalytic Reduction of NOx with NH3 over Fe/Beta

“…The bands noticed at 3347 and 3275 cm –1 are ascribed to the N–H vibration of NH 4 + adsorbed on Brönsted (B) acid sites, and the band noted at 3179 cm –1 is associated with the N–H vibration of ammonia species linked to Lewis (L) acid sites . In addition, the bands at 1628, 1293, and 1170 cm –1 are assigned to ammonia species adsorbed on L acid sites, and the band at 1464 is associated with the bending vibration of NH 4 + coordinated to B acid sites. , Note that the deposition of 0.25% K almost did not induce the remarkable change of the bands attributed to ammonia species adsorbed on B and L acid sites of Fe/Beta. In sharp contrast, upon a further increase of the loading of deposited K, a serious decline of all of the peak intensities was observed for K–Fe/Beta (≥0.50%) catalysts.…”

“…In the past few years, extensive investigations have been conducted on the deactivation of V 2 O 5 /TiO 2 -based catalysts caused by K, Na, Ca, and Mg. It makes sense that the decreased acidity and redox ability are the main reasons resulting in the deactivation of the catalyst. − Tremendous efforts have also been made on the study of deactivation mechanism of Cu-based zeolites, such as Cu-SAPO-18, Cu-SAPO-34, and Cu-SSZ-13 molecular sieves, ,, by these alkali and alkaline earth metals. It has been proposed that the transformation of the most active isolated Cu 2+ to less active copper oxide clusters originating from the alkali and alkaline earth metal poisoning is recognized to be the predominated reason resulting in the deactivation of copper-exchanged zeolites.…”

Inhibition Effect of Phosphorus Poisoning on the Dynamics and Redox of Cu Active Sites in a Cu-SSZ-13 NH3-SCR Catalyst for NOx Reduction

“…Nitrogen oxides (NO x ) emitted from both stationary sources (e.g., coal-fired power plants and industrial boilers) and mobile sources (e.g., gasoline- and diesel-powered vehicles) are harmful to human health as a class of respiratory irritants, , and they participate in the formation of secondary air pollutants such as fine particulate matter (PM 2.5 ), ground-level ozone (O 3 ), photochemical smog, etc . , For NO x in diesel exhausts, selective catalytic reduction with ammonia (NH 3 -SCR), using small-pore Cu-SSZ-13 zeolite with a chabazite (CHA) framework topology as the catalyst, has been widely utilized and proven to be a reliable technology to meet the stringent emission regulations. − Cu-SSZ-13 demonstrates excellent activity over a wide temperature range from 200 to 500 °C, good N 2 selectivity, and superior hydrothermal stability as compared to other Cu-zeolite catalysts (e.g., Cu-beta and Cu-ZSM-5). − In spite of the advantages, the practical use of Cu-SSZ-13 is still restricted by issues like chemical poisoning by sulfur (S), phosphorus (P), alkali and alkaline earth metals (e.g., Na, K, Ca, and Mg), zinc (Zn), etc . − …”

Theoretical Study on the NOx Selective Catalytic Reduction on Single-Cu Sites and Brønsted Acid Sites in Cu-SSZ-13

“…NO x exhaust gases, products of the oxidation of nitrogen during the combustion of fuels at high temperatures, are still one of the major contributors to local air pollution; hence, their emission is being strictly controlled. , One successful strategy of reducing NO x emissions is through their selective reduction by ammonia to N 2 over heterogeneous catalysts such as transition-metal-exchanged zeolites and transition-metal oxide. − Copper-exchanged zeolites, and in particular Cu-SSZ-13, have been commercialized as they are highly active and also stable in a broad range of temperatures. − ,,, For that reason, the selective catalytic reduction (SCR) of ammonia over Cu-SSZ-13 has been the subject of many experimental − ,,,,,− and theoretical studies. ,,,,,,− These studies led to the establishment of eqs – for the reduction of NO and NO 2 to N 2 . The so-called “Standard SCR” ,, is given by eq . Additionally, if NO 2 is present in the exhaust gases, nitrogen can also be formed via eq .…”