Experimental and Theoretical Studies of Sonically Prepared Cu–Y, Cu–USY and Cu–ZSM-5 Catalysts for SCR deNOx

Abstract

The objective of our study was to prepare Y-, USY- and ZSM-5-based catalysts by hydrothermal synthesis, followed by copper active-phase deposition by either conventional ion-exchange or ultrasonic irradiation. The resulting materials were characterized by XRD, BET, SEM, TEM, Raman, UV-Vis, monitoring ammonia and nitrogen oxide sorption by FT-IR and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). XRD data confirmed the purity and structure of the Y/USY or ZSM-5 zeolites. The nitrogen and ammonia sorption results indicated that the materials were highly porous and acidic. The metallic active phase was found in the form of cations in ion-exchanged zeolites and in the form of nanoparticle metal oxides in sonochemically prepared catalysts. The latter showed full activity and high stability in the SCR deNOx reaction. The faujasite-based catalysts were fully active at 200–400 °C, whereas the ZSM-5-based catalysts reached 100% activity at 400–500 °C. Our in situ DRIFTS experiments revealed that Cu–O(NO) and Cu–NH3 were intermediates, also indicating the role of Brønsted sites in the formation of NH4NO3. Furthermore, the results from our experimental in situ spectroscopic studies were compared with DFT models. Overall, our findings suggest two possible mechanisms for the deNOx reaction, depending on the method of catalyst preparation (i.e., conventional ion-exchange vs. ultrasonic irradiation).

Mechanisms for deNOx and deN2O Processes on FAU Zeolite with a Bimetallic Cu-Fe Dimer in the Presence of a Hydroxyl Group—DFT Theoretical Calculations

“…There is no reaction between NO 2 and hydrogen; instead, there is simultaneous coadsorption of nitric oxide and ammonia. The choice of this type of step is also motivated by the proposal of Bendrich et al [16] and our own research [35,36]. As with the previous structure here, the first two stages, B2-B3, of the process on bimetallic dimer with an OH group on iron are also exothermic.…”

“…An analysis of the mechanisms of the deNOx and deN 2 O process was carried out on the three types of systems deposited on the FAU zeolite mentioned in the Section 3. In all cases, the previously developed paths of the various stages of the reaction were used [16,35].…”

“…These attempts showed great promise, as the catalysts demonstrated very high NO conversion, selectivity to N 2 , and good thermal stability across a wide temperature range (about 230-500 • C) and resistance to the harmful effects of sulphur oxides. On this basis, this solution was proposed using FAU zeolite, which showed interesting properties in previous studies [35,36].…”

Theoretical Studies on the Mechanism of deNOx Process in Cu–Zn Bimetallic System—Comparison of FAU and MFI Zeolites

“…The next step was to carry out preliminary adsorption and coadsorption to initiate the deNOx mechanism, which was based on previous studies performed on the FAU and MFI zeolite with a deposited Cu–O-Cu dimer [ 43 ].…”

New Insights into the Effect of Ce Doping on the Catalytic Performance and Hydrothermal Stability of Cu-USY Zeolite Catalysts for the Selective Catalytic Reduction of NO with NH3

“…Additionally, the content of highly dispersed CuO x species was also increased due to the CuO x -CeO 2 strong interaction. These CuO x species could promote further oxidative decomposition of nitrate/nitrite intermediates and improve the catalytic performance [43][44][45]. But, at the same time, they also caused more serious byproduct formation.…”