Role of Al pairs on effective N2O decomposition over the ZSM-5 zeolite catalyst

Series of ZSM-5 zeolites with diverse contents and locations of Al pairs were synthesized, and Co2+ ions were subsequently anchored at the Al pairs of ZSM-5 zeolites by wet ion-exchange with H protons. The Co-ZSM-5 sample derived from the mixtures of AlCl3 and TEOS of Si/Al=30.3 showed the best deN2O performance. Analysis on Co (II) ion exchange capacity demonstrated the content of Al pairs followed the sequence: AlCl3 (0.84) > Al(NO3)3 (0.73) > aluminum isopropoxide (0.65) and TEOS (0.84) > silicic acid (0.57). More Al pairs coordinated with protons or cobalt ions were essentially associated with better performances for N2O catalytic dissociation. Moreover, Si source had a significant effect on the location of Al pairs determined by UV-vis-DRS of bare Co (II), Al pairs of ZSM-5 zeolite synthesized from TEOS were enriched in the sinusoidal channel (gamma site), whereas those synthesized from silicic acid were concentrated in the channel intersections (6-MRs beta site). The theoretical calculation revealed that the O2 desorption at gamma-site Co2+ of ZSM-5 zeolite required to overcome less energy barrier (23.8 kcal/mol) than that at beta-site one.

Automated summary

Anchoring Co2+ ions at Al pairs of ZSM-5 zeolites can enhance the N2O catalytic dissociation performance. Co-ZSM-5 sample derived from the mixture of AlCl3 and TEOS exhibits the best performance. The coordination of Al pairs and the source of Si can affect the catalytic performance and the location of Al pairs.