The Effect of Copper Loading on the Selective Catalytic Reduction of Nitric Oxide by Ammonia Over Cu-SSZ-13

Abstract

The effect of Cu loading on the selective catalytic reduction of NO x by NH 3 was examined over a series of Cu ion-exchanged (20-80%) SSZ-13 zeolite catalysts. High NO reduction efficiencies (80-95%) were obtained over all catalyst samples between 250 and 500°C, and at the gas hourly space velocity of 200,000 h -1 . Both NO reduction and NH 3 oxidation activities under these conditions were found to increase slightly with increasing Cu loading at low temperatures. However, NO reduction activity was suppressed with increasing Cu loadings at high temperatures ([500°C) due to excess NH 3 oxidation. The optimum Cu ion exchange level appears to be *40-60% since higher than 80% NO reduction efficiency was obtained over 50% Cu ion-exchanged SSZ-13 up to 600°C. The NO oxidation activity of Cu-SSZ-13 was found to be low regardless of Cu loading, although it was somewhat improved with increasing Cu ion exchange level at high temperatures. During the ''fast'' SCR (i.e., NO/ NO 2 = 1), only a slight improvement in NO x reduction activity was obtained for Cu-SSZ-13. Regardless of Cu loading, near 100% selectivity to N 2 was observed; only a very small amount of N 2 O was produced even in the presence of NO 2 . The apparent activation energies for NO oxidation and NO SCR were estimated to be *58 and *41 kJ/mol, respectively.

Environmentally-benign catalysts for the selective catalytic reduction of NOxfrom diesel engines: structure–activity relationship and reaction mechanism aspects

“…Therefore, although the NH 3 -SCR performance of Cu-CHA catalysts has been well recognized, the understanding of the intrinsic active Cu sites is still in debate and ongoing. Besides, Kwak et al 150 noticed that regardless of the Cu ion-exchange degree, the NO oxidation ability of Cu-SSZ-13 catalysts was very low; even under ''fast SCR'' conditions, the NO x conversion was only slightly improved, with little formation of N 2 O. Compared with other Cu-based zeolite catalysts or even other NH 3 -SCR catalysts, the abovementioned ''abnormal'' results indicate that a totally different NH 3 -SCR reaction mechanism may exist over the Cu-SSZ-13 catalyst, which needs to be investigated in detail using various methods in future research.…”

Impact of Copper Loading on NH3-Selective Catalytic Reduction, Oxidation Reactions and N2O Formation over Cu/SAPO-34

“…Thus, optimum deNO x efficiency over a range of temperatures is usually obtained at an intermediate Cu content [13] due to its positive correlation with both the SCR reaction and the competitive NH 3 oxidation reaction. Moreover, Cu site distribution has been found to vary with Cu loading on a number of different zeolites [14][15][16][17].…”

Effect of the Nature and Location of Copper Species on the Catalytic Nitric Oxide Selective Catalytic Reduction Performance of the Copper/SSZ‐13 Zeolite

“…[7,[9][10][11] The ion-exchanged copper-containing SSZ-13 zeolite, based on the small-pore chabazite (CHA) zeolite topology, recently demonstrated higher activity and selectivity to N 2 over a wide temperature range and better hydrothermal stability than did Cu/ ZSM-5 and Cu/BEA zeolites. [12][13][14][15][16][17] Typically, the catalytic SCR performance of the copper-containing zeolite greatly depends on the location and nature of copper species. The existence of various types of copper species in the zeolite has been proposed: Cu 2 + and Cu + monomers, [CuÀOÀCu] 2 + dimers, and CuO x clusters.…”

“…[24,25] The NO reduction activity was suppressed at high temperatures if the ion-exchanged Cu/SSZ-13 zeolite with high copper content was used for the SCR of NO x . [14] The copper loading in the OP-0.37 and IE-0.36 samples are the same (Table 1). Although the isolated copper ions dominate in both samples as demonstrated by the EPR spectra, the distribution of copper ions and their nature after dehydration are different, as confirmed from TPR, CO IR, and Raman spectroscopy.…”