Pr-functionalized Cu/SAPO-34 with superior hydrothermal stability for NH3-SCR: The copper species and framework stabilization effect

The effects of adjustable Pr-additive modification on stabilizing the isolated Cu2+ species and zeolite framework of Cu/SAPO-34 had been systematically investigated for NH3-SCR. Apposite amendment of Pr-additive indeed boost catalytic performance and hydrothermal stability of Cu/SAPO-34. The T90 of fresh and aged Cu/Pr(1)-SAPO-34 with low loading of Pr were obviously lower than that of fresh Cu/SAPO-34, while the maximum NOx conversion of aged Cu/SAPO-34 was only 52.6% at 450 °C. Characteristic results disclosed that Cu/Pr(1)-SAPO-34 retained the large surface area, relatively ordered CHA structure, and abundant surface acid sites even after hydrothermal aging at 800 °C for 10 h with 10% H2O, which result from the more stable Cu2+ ions in the six-membered rings (Cu2+-2Z, 6MR) of fresh Cu/Pr(1)-SAPO-34. However, more unstable Cu2+ ions in the eight-membered rings ([Cu(OH)]+-Z, 8MR) existed in fresh Cu/SAPO-34 were transformed into bulk CuO, leading to the deterioration of structure and catalytic performance. In addition, although fresh Cu/Pr(3)-SAPO-34 with high loading of Pr possessed more Cu2+-2Z rather than [Cu(OH)]+-Z, it also suffered from the attack of hydrothermal aging owing to the presence of PrOx and PrPO4. Kinetic study and in situ DRIFTS results illustrated that SCR reaction over Cu/SAPO-34 and Cu/Pr(1)-SAPO-34 followed the L-H and E-R mechanism synchronously. Notably, the NOx reaction rates of Pr-introduced samples were faster than those of Pr-free catalysts.