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

Abstract

In the present study we propose a more promising catalyst for the deNOx process to eliminate harmful nitrogen oxides from the environment. The study was performed with a computer calculation using density functional theory (DFT) based on an ab initio method. Two zeolite catalysts, FAU and MFI, were selected with additional Cu–O–Zn bimetallic dimer adsorbed inside the pores of both zeolites. Based on the analysis of preliminary studies, the most probable way of co-adsorption of nitric oxide and ammonia was selected, which became the initial configuration for the reaction mechanism. Two types of mechanisms were proposed: with hydroxyl groups on a bridged position of the dimer or a hydroxyl group on one of the metal atoms of the dimer. Based on the results, it was determined that the FAU zeolite with a bimetallic dimer and an OH group on the zinc atom was the most efficient configuration with a relatively low energy barrier. The real advantage of the Cu–Zn system over FAU and MFI in hydrothermal conditions has been demonstrated in comparison to a conventional Cu–Cu catalyst.

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.…”

“…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].…”

Odors Adsorption in Zeolites Including Natural Clinoptilolite: Theoretical and Experimental Studies

“…As part of the publication, calculations using the DFT method were also performed. For this purpose, a cluster model of zeolites was developed and computational processes for adsorption were performed [21][22][23].…”