Low-Temperature Solid-State Ion-Exchange Method for Preparing Cu-SSZ-13 Selective Catalytic Reduction Catalyst

Abstract

Solid-state ion-exchange (SSIE) is an effictive method to prepare Cu-SSZ-13, but usually requires high temperatures or assistance of NH 3 for catalyst activation. Herein, an environmentally friendly low-temperature solid-state ionexchange (LT-SSIE) method was developed. Cu salts that can decompose at temperatures lower than 300 °C (e.g., CuAc 2 and Cu(NO 3 ) 2 ) were chosen as Cu precursors. An impregnation method was adopted to obtain high dispersion of the precursors inside the channels of SSZ-13, as confirmed by scanning transmission electron microscopy. A calcination in air at 300 °C for 30 min was found enough for catalyst activation. In situ X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, thermogravimetry, ultraviolet−visible spectroscopy and H 2 temperature-programmed reduction were performed to monitor the activation prcoess of CuAc 2 -impregnated SSZ-13. The ion-exchange sites of SSZ-13 are occupied by Cu 2+ ions originating from CuAc 2 at 250−300 °C, revealing the nature of the LT-SSIE process between CuAc 2 and SSZ-13.

Activity of Cu–Al–Oxo Extra-Framework Clusters for Selective Methane Oxidation on Cu-Exchanged Zeolites

“… 8 Among the variety of zeolite topologies, zeolite MOR, having straight 12-membered-ring (MR) channels and intersecting 8-MR side pockets, had the best utilization of copper. 3 , 6 , 9 Dimeric 10 − 15 and trimeric 16 − 19 Cu–oxo clusters have been proposed to be the main active sites. Al pairs in the 8-MR side pockets of MOR favor the formation and stabilization of such active Cu–oxo sites.…”

“…Copper-exchanged zeolites have shown activity in the selective oxidation in repeatable single turnovers using O 2 as oxidant. ,, Grootheart et al were the first to demonstrate this via a cyclic three-stage process, which is depicted schematically in Figure . Among the variety of zeolite topologies, zeolite MOR, having straight 12-membered-ring (MR) channels and intersecting 8-MR side pockets, had the best utilization of copper. ,, Dimeric − and trimeric − Cu–oxo clusters have been proposed to be the main active sites.…”

“…Copper-exchanged zeolites have shown activity in the selective oxidation in repeatable single turnovers using O 2 as oxidant. ,, Grootheart et al were the first to demonstrate this via a cyclic three-stage process, which is depicted schematically in Figure . Among the variety of zeolite topologies, zeolite MOR, having straight 12-membered-ring (MR) channels and intersecting 8-MR side pockets, had the best utilization of copper. ,, Dimeric − and trimeric − Cu–oxo clusters have been proposed to be the main active sites. Al pairs in the 8-MR side pockets of MOR favor the formation and stabilization of such active Cu–oxo sites. ,,, It has been established that each Cu–oxo cluster is able to oxidize one CH 4 at ambient pressure and up to two CH 4 at higher CH 4 chemical potentials …”

Controlling Dynamic Structural Transformation of Atomically Dispersed CuOx Species and Influence on Their Catalytic Performances

“…There are many reports on this subject concerning CuO x dispersions. For example, isolated Cu atoms in zeolite pores have been found to be the active sites for the NH 3 -SCR reaction. − For CuO x species supported on the oxide carriers such as γ-Al 2 O 3 , there are also studies on CuO x dispersions. The control of dispersion was mainly achieved by varying the loading amount of Cu .…”

Review of the application of Cu-containing SSZ-13 in NH3-SCR-DeNOx and NH3-SCO

“…, after 150–500 °C NH 3 -SCR-DeNO x due to movement of external CuO to Cu + / 2+ ions inside the zeolite channels under reaction conditions 113 ), or LT-SSIE ( e.g. , application of the copper salts that decompose below 300 °C), 122 as well as the use of NO and NH 3 for the generation of the [Cu(NH 3 ) x ] + (≥2), 112 were reported. Furthermore, Zhang et al 47 claimed that the application of the NH 4 + -form (rather than the H-form) led to the presence of more Cu 2+ ions and fewer CuO x species.…”