Highly Efficient NO Abatement over Cu-ZSM-5 with Special Nanosheet Features

Abstract

Conventional Cu-ZSM-5 and special Cu-ZSM-5 catalysts with diverse morphologies (nanoparticles, nanosheets, hollow spheres) were synthesized and comparatively investigated for their performances in the selective catalytic reduction (SCR) of NO to N2 with ammonia. Significant differences in SCR behavior were observed, and nanosheet-like Cu-ZSM-5 showed the best SCR performance with the lowest T 50 of 130 °C and nearly complete conversion in the temperature range of 200–400 °C. It was found that Cu-ZSM-5 nanosheets [mainly exposed (0 1 0) crystal plane] with abundant mesopores and framework Al species were favorable for the formation of high external surface areas and Al pairs, which influenced the local environment of Cu. This motivated the preferential formation of active copper species and the rapid switch between Cu2+ and Cu+ species during NH3-SCR, thus exhibiting the highest NO conversion. In situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicated that the Cu-ZSM-5 nanosheets were dominated by the Eley–Rideal (E–R) mechanism and the labile nitrite species (NH4NO2) were the crucial intermediates during the NH3-SCR process, while the inert nitrates were more prone to generate on Cu-ZSM-5 nanoparticles and conventional one. The combined density functional theory (DFT) calculations revealed that the decomposition energy barrier of nitrosamide species (NH2NO) on the (0 1 0) crystal plane of Cu-ZSM-5 was lower than those on (0 0 1) and (1 0 0) crystal planes. This study provides a strategy for the design of NH3-SCR zeolite catalysts.

Cu/ZSM5-Geopolymer 3D-Printed Monoliths for the NH3-SCR of NOx

“…The NH 3 adsorption capacity of the catalysts was measured on grinded Cu-exchanged monoliths as well as on mechanical mixtures of pure materials, in order to investigate the effect of the interaction between ZSM5 and GP on the surface acidity of the catalysts. In line with literature data [44,45], the TPD profile of pure Cu/Z (Figure 5) showed a main composite peak with a maximum at about 190 • C, accompanied by poorly resolved shoulders at 260 and 340 • C, which can be assigned to the weak, moderate and strong acid sites, respectively. A further signal between 450 and 600 • C, typical of the pristine H-ZSM5, was largely reduced due to the high copper exchange ratio achieved in our Cu/Z sample [44].…”

Selective catalytic reduction of NO over hierarchical Cu ZSM-5 coated on an alumina foam support

“…48 NH 3 adsorbed on the Cu sites forming copper ammonia complexes is an active site for SCR reactions whereas the acid sites can stabilize the adsorbed ammonia at high temperatures and effectively inhibit NH 3 oxidation. 26,48,50…”

“…24 The desorption peak at a lower temperature of around 220 °C is attributed to NH 3 desorbed from the extra-framework Al and copper ions. 25,26 The hightemperature desorption peak centered at 350 °C is assigned to NH 3 desorbed from Brønsted acid sites (Si-(OH)-Al). 27 The high-temperature desorption peak is attributed to the presence of strongly acidic hydroxyl groups as sorption sites.…”

“…48 NH 3 adsorbed on the Cu sites forming copper ammonia complexes is an active site for SCR reactions whereas the acid sites can stabilize the adsorbed ammonia at high temperatures and effectively inhibit NH 3 oxidation. 26,48,50 Sjövall et al reported that 1 g of Cu ZSM-5 wash coated on a monolith with a surface area of 304 m 2 g −1 and a Cu loading of 2 wt% gives a NO conversion of 98% at 250 °C at a space velocity of 18 400 h −1 . 51 Metkar et al reported that 25 g of Cu ZSM-5 catalyst coated on a monolith with a surface area of 350 m 2 g −1 and a Cu loading of 2.5 wt% gives a NO conversion of 95% at 350 °C at a space velocity of 57 000 h −1 .…”

Hybrid Cu-Fe/ZSM-5 Catalyst Prepared by Liquid Ion-Exchange for NOx Removal by NH3-SCR Process

“…e H 2 -TPR profiles of Fe/ZSM-5, Cu/ZSM-5, and Cu-Fe/ZSM-5 catalysts are shown in Figure 6 to understand the redox proprieties of the catalysts better. ere can be three H 2 consumption zones observed in the TPR pattern of the Cu/ZSM-5 catalyst: the first peak at 180°C is corresponding to the reduction of external surface nanosized CuO to Cu + [34], the second sharp peak at about 250°C is related to the reduction of isolated Cu 2+ ions to Cu + in ion-exchange positions of zeolites, and another one located at 370°C as a trace, can be assigned to the reduction of CuO particles to Cu 0 and Cu + to Cu 0 [35]. According to the high copper content, the excess amount of copper is detected as CuO when the exchange sites have been involved.…”