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 Co 2+ 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 AlCl 3 and TEOS of Si/Al=30.3 showed the best de N 2 O performance. Analysis on Co (Ⅱ) ion exchange capacity demonstrated the content of Al pairs followed the sequence: AlCl 3 (0.84) > Al(NO 3 ) 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 N 2 O 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 (γ site), whereas those synthesized from silicic acid were concentrated in the channel intersections (6-MRs β site). The theoretical calculation revealed that the O 2 desorption at γ-site Co 2+ of ZSM-5 zeolite required to overcome less energy barrier (23.8 kcal/mol) than that at β-site one.