Migration of Cu species in Cu/SAPO-34 during hydrothermal aging

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

“…It is likely that calcination at 750 • C causes oxidic copper species to move into the structure. This interpretation is consistent with findings that Cu ions migrate from the catalyst surface into ion [28,42,49,50] (for example during solid-state ion-exchange) and with our observation that Cu/SAPO-34 1.49 and 1.60 wt % Cu are grey in colour after calcination at 550 • C and turn blue after the second calcination at 750 • C. UV-vis spectra were acquired for the two samples calcined at 550 and 750 • C and are shown in the top panel of Figure 12. The two spectra differ mainly in the region between 350 and 550 nm.…”

“…As discussed above, it is a possibility that for the highest copper nitrate concentration (0.8 M) some of these copper oxide particles remain, and that the copper therein is inactive for some of the reactions. into ion exchange positions in the SAPO-34 pores [28,42,49,50] (for example during solid-state ionexchange) and with our observation that Cu/SAPO-34 1.49 and 1.60 wt % Cu are grey in colour after calcination at 550 °C and turn blue after the second calcination at 750 °C. UV-vis spectra were acquired for the two samples calcined at 550 and 750 °C and are shown in the top panel of Figure 12.…”

“…Despite the formation of some oxidic copper species, the catalysts are all under-exchanged, which we defined as less than 2 Cu per Si for silicoaluminophosphates such as SAPO-34. The amount of oxidic copper on Cu/SAPO-34 with a loading of~1.60 wt % Cu decreased significantly after high temperature treatment at 750 • C, compared to a sample treated at only 550 • C. On the basis of conclusions drawn in other studies, we can attribute this to the migration of external CuO clusters to the ion exchange positions in the pores of the CHA structure [49][50][51]. Interestingly, at the lower copper loading of 1.20 wt %, we found the amount of CuO observable by UV-vis to be negligible, independently of the calcination temperature.…”

High hydrothermal stability of Cu–SAPO-34 catalysts for the NH3-SCR of NOx

“…5, Cu x -SAPO-34 maintained the CHA framework structure basically after high temperature calcination. However, two extra peaks at 35.29°and 38.49°related to CuO phases were observed in Cu 6.62 -SAPO-34 and Cu 8.84 -SAPO-34 [30,31]. In the Cu x -SAPO-34 with low Cu loading (<5.15 wt.%), no Cu-related phases were observed in the XRD patterns, suggesting that copper oxide was present in a highly dispersed amorphous state.…”

High-efficiency reduction of NO emission from diesel exhaust using a CeWO catalyst

“…Various catalysts have been reported to be effective for NH 3 /urea-SCR, including vanadium-based catalysts [5], Fe-, Cu-, Ce-exchanged zeolite materials [4,[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], and various vanadium-free oxide catalysts [22][23][24][25][26][27][28]. The toxicity of active vanadium species, together with the low stability at high temperatures, has restrained the wide application of vanadium-based catalysts, while the activities of vanadiumfree oxide catalysts are often insufficient and mainly tested using simulating gas in laboratory.…”