Cu50ox Synthesis Essay
Conditions: 2600 ppm N2O, balance He, 0.3 Mpa, GHSV-19,000 h-1. Fig.9. The T50 and T100 of different Cs-doped Cu50Ce50Ox catalysts
The activities of the catalysts with different Cs content for N2O decomposition are shown in Fig.8, and the T50 and T100 (the temperature at which 50% and 100% conversion of N2O decomposition is achieved) are shown in Fig.9. It’s found that the activity of the Cu50Ce50Ox catalyst is relative low, and T100 of N2O conversion is about 440 oC. The addition of small amount of Cs drastically enhances the activity of the Cu50Ce50Ox catalyst for N2O decomposition. The Cs1Cu50Ce50Ox shows the …show more content…
For Cs1Cu50Ce50Ox, after reaction with N2O, the amount of Ce3+ decreased a lot and the signal of CO-Ce4+ appeared, indicating the Ce3+ species were oxidized. I noticed that the CeO2 didn’t show any activities at 300 oC and the Ce-N2O peak was not detected in situ N2O-DRIFTs (Fig.12)[16, 36], thus the oxygen should come from the N2O decomposition taking place on Cu+, demonstrating the existence of oxygen migration step. The amount of Cu+ didn’t change, indicating the oxygen migration was faster than the regeneration of Cu2+-O. The Cu50Ce50Ox showed the similar tendency except the decrease of Cu+, which means its oxygen migration rate was much slower, and the oxygen migration step should be the rate limiting step.
3.4 The possible catalytic mechanism
Based on previous research and the DRIFT results, the N2O decomposition over Cs-doped Cu50Ce50Ox should undergo the following mechanism: N2O reversibly deposits on the active Cu+ sites (Eq. 1), then the activated N-O bond breaks, releasing N2 and oxidizing the Cu+ to Cu2+(Eq.2). After that, the Cu2+ was reduced by Ce3+, the Cu+ was regenerated and forming Ce-O(Eq.3), at last Ce-O bonds broke to form O2(Eq.4) as shown in Fig.13, just like the mechanism suggested over Cu/CeO2 and Ru/CeO2 catalyst[16, 36]:
Cu+ + N2O ↔ Cu+ - ONN (Eq. …show more content…
The peak at around 2200 cm-1 attributes to N2O absorbed on Cu[13, 27]. It could be found that there is a competitive adsorption between O2 and N2O. But the competitive adsorption seems too slight to account for the obvious decrease of activity. As discussed above, I proposed that the regeneration of Cu+ is the rate-determining step, and O2 may affect the reaction by inhibiting the regeneration step. CO-DIRFTs through different reactions are shown in Fig.15, and the Cu+-CO peak areas are listed in Table 2. It’s obvious that the amount of active Cu+ sites decreased a lot (about 40%) after reaction for 1h with the presence of oxygen for Cu50Ce50Ox, indicating the oxygen migration was certainly inhibited by O2, which is consistent with the expected. Meanwhile, the barely change of Cu+ for Cs1Cu50Ce50Ox indicates an excellent regeneration capacity, accounting for its good performance of oxygen inhibition resistance. The better regeneration capacity of Cs1Cu50Ce50Ox rooted from more Ce3+ sites with the Cs modification. Thus another way to improve the resisting inhibition of Ce-based catalyst for N2O decomposition could be pointed out through this mechanism, that’s trying to increase the oxygen migration capacity of CeO2. Fig.15 CO-DRIFTs of Cu50Ce50Ox and Cs1Cu50Ce50Ox in 1% CO-He at 50 oC for 30 min after reaction at 400 oC for 1h in different gas: He (black); 2600 ppm N2O + He (red); 2600