Effect of CO₂ on the DeNO_x Activity of a Small Pore Zeolite Copper Catalyst for NH₃/SCR

Abstract

Exposure of CuSSZ13 to CO 2 at temperatures below 300 8C can deactivate its low-temperature deNOx activity during NH 3 /SCR, with the severity of deactivation being dependent on reaction temperature. The adsorption of NO on Cu 2 + ion is inhibited by CO 2 due to its competitive adsorption, while NH 3 adsorption on acidic sites of CuSSZ13 is largely unaffected by CO 2 , as evidenced by NO-and NH 3 -TPD in the presence of CO 2 . Under O 2 -rich conditions, CO 2 forms unidentate carbonates on Cu 2 + sites suppressing the formation of nitrates, a key reaction intermediate essential for NOx reduction during the NH 3 /SCR reaction, as revealed in an in situ FTIR study.Selective catalytic reduction (SCR) of NO x by urea (urea/SCR) is one of the most efficient and reliable technologies to remove NO x from diesel engine exhaust to meet ever-tightening emission regulations including EURO VI and SULEV without any direct fuel penalty.[1] ZSM5-based catalysts, including CuZSM5 and Mn-Fe/ZSM5, have been regarded as representative urea/ SCR catalysts, mainly owing to their high deNO x activity in the low-temperature region [2] suitable for diesel exhaust temperatures of the advanced engine, for example, the homogenous charge-compression ignition engine, for high fuel efficiency. [3] However, those catalysts still suffer from hydrothermal deactivation during the regeneration of the diesel particulate filter-(>750 8C), which hampers their commercial application to the diesel after-treatment system, [4] although the addition of Er has significantly improved the hydrothermal stability of the Mn-Fe/ ZSM5 catalyst. [2b] In recent years, small-pore zeolite catalysts such as CuSSZ13 and CuSAPO34 have been touted as commercial urea/SCR catalysts owing to their robust hydrothermal stability as well as their excellent low-temperature deNO x activity.[5] Moreover, the CuSSZ13 catalyst has shown high resistance toward hydrocarbon poisoning.[6] Although extensive studies have been conducted to understand the exceptional hydrothermal stability of the CuSSZ13 catalyst, there has been no systematic investigation on the effect of CO 2 on the catalytic activity of CuSSZ13 even though CO 2 is always abundantly present in the exhaust gas stream at approximately 10 %. Indeed, Hudson et al. recently reported that CO 2 molecules are readily adsorbed on the surface of SSZ13.[7] Thus, it is highly desirable and timely to study the effect of CO 2 on the deNO x performance of CuSSZ13 for the urea/SCR, a de facto NH 3 /SCR.We examined the CO 2 -induced deactivation of Cu-(3 wt %)SSZ13 by long-term durability tests in the presence of 10 % CO 2 . To understand the deactivation mechanism of CuSSZ13, the effect of CO 2 on the adsorption of NO x and NH 3 on CuSSZ13 was also investigated by NO x and NH 3 temperature-programmed desorption (TPD) and surface IR spectroscopy studies.The deNO x performance of CuSSZ13 prepared in the present study was examined in the NH 3 /SCR, as depicted in the inset of Figure 1. In the absence of CO 2 , CuSSZ13 revealed excell...

Temperature-Dependent Influencing Mechanism of Carbon Monoxide on the NH3–SCR Process over Ceria-Based Catalysts

“…The reasons might be due to the deposition of some nitrogenous species as the surface N content increased (see Table 1), where a similar phenomenon was also found in previous works. 34,37 All of the above results further confirmed the good stability of the catalysts during the SCR reaction in the presence of CO/CO 2 . The differences in SCR catalytic performance could not be attributed to the changes in physiochemical properties.…”

“…However, in addition to SO 2 , there still existed a certain amount of other interference components (acid gases, alkali, alkaline-earth, heavy metals, etc.) in the flue gas, − which would poison the SCR catalysts and decrease denitration efficiency. − Compared with the above-mentioned interference components, few studies regarding the influence of CO on the SCR reaction had been conducted . Normally, certain amounts of CO exist in the flue gases, especially those from industrial boilers and kilns.…”

Low Temperature Performance of Selective Catalytic Reduction of NO with NH3 under a Concentrated CO2 Atmosphere

“…Kim et al [24] reported that CO 2 -induced deactivation in SCR was due to the adsorption of NH 3 by CO 2 , and supression of the formation of nitrates, which are a key reaction intermediate for NO x reduction. Yang et al [43] also reported that CO 2 may compete for the adsorbed NH 3 , which should be desirable for NO conversion.…”

“…Therefore, more understanding of NH 3 -SCR in the presence of an abundance of CO 2 is essential for the future development of SCR technology combined with oxy-fuel combustion processes. However, it is found that there are a few works investigating the influence of CO 2 on SCR [24,25]. For example, Kim et al [24] studied the effect of CO 2 on SCR using a small pore zeolite copper catalyst; and reported that CuSSZ13 catalyst can be deactivated by 10% CO 2 at low temperatures (<300˝C).…”

“…However, it is found that there are a few works investigating the influence of CO 2 on SCR [24,25]. For example, Kim et al [24] studied the effect of CO 2 on SCR using a small pore zeolite copper catalyst; and reported that CuSSZ13 catalyst can be deactivated by 10% CO 2 at low temperatures (<300˝C). Magnusson et al [25] studied the influence of 6% CO 2 during SCR, and found no significant influences.…”