Unique responses of Cu-SSZ-13 toward phosphorus: Al atoms on zeolite framework versus varied Cu species

Abstract

Phosphorus (P) poisoning of NH3-SCR catalysts is inevitable in application of NOx abatement of diesel exhaust. The distinct effects on Cu-SSZ-13 of P from different precursors (H3PO4 and (NH4)2HPO4) were figured out and the mechanism was further investigated. P-poisoned Cu-SSZ-13 (Si/Al = 6) catalysts were prepared and characterized using N2 adsorption, X-ray powder diffraction (XRD), scanning electron microscope with energy-dispersive X-ray spectroscopy mapping (SEM-EDX), ammonia temperature-programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature programmed reduction (H2-TPR), electron paramagnetic resonance (EPR) and 27Al solid-state magic angle spinning nuclear magnetic resonance spectroscopies (27Al NMR). Significant enhancement of high-temperature activities (400–600 °C) were observed for the catalysts with P loading of 0.3–0.9 wt%, since the appropriate incorporation enabled to bind P atoms to CuOx in remained framework. However, the high P content of 1.5 wt% resulted in a detrimental effect on framework to induce the accumulation of Cu species. Interestingly, the dominant P from H3PO4 was inclined to directly attack the framework Al leading to more severe dealumination, while the P from (NH4)2HPO4 interacted with Cu2+ to form copper phosphate with more Cu2+ migrating to the surface of the catalyst which promoted the NOx conversation at each active site resulting in the low-temperature catalytic activity unchanged. So, control of the P/Cu and form of P is capable of preventing P poisoning and unlocks the potential of Cu-SSZ-13 in exhaust treatment.