Progress on Selective Catalytic Ammonia Oxidation (NH₃‐SCO) over Cu−Containing Zeolite‐Based Catalysts

Abstract

The selective catalytic oxidation of ammonia into nitrogen and water vapor (NH 3-SCO) has proven to be the most efficient technique for the removal of NH 3 from the oxygen-containing diesel exhausts. Until now, two reviews over investigated catalysts have been published in 2015-2016 (Jabłońska et al., RCS. Adv. 2015; Appl. Catal. B: Environ. 2016). Among various NH 3-SCO catalysts, Cu-and/or Fe-containing zeolites are considered as promising candidates due to their benign nature, NH 3 storage capacity, very high NH 3 conversion and N 2 selectivity. The present review focusses only on the Cucontaining zeolites (mainly on chabazite (CHA): SSZ-13, SAPO-34) catalysts) applied in NH 3-SCO starting from 2015. The synthesis/preparation methods and the state of Cu in catalysts on the activity and selectivity are highlighted. The advantages of the understanding of the reaction mechanism are reviewed. Finally, an outlook is given together with expected inspirations for future research directions in developing zeolite-based catalysts.

New insights into the NH3-selective catalytic reduction of NO over Cu-ZSM-5 as revealed by operando spectroscopy

“…S17a † ) might be due to the reaction between the Brønsted acid adsorbed NH 3 (B-NH 3 ) and L-NO 3 − followed by restoration of the proton from H-cleavage of NH 3 . 61 The NH 3 oxidation reaction was followed by the NH 3 -SCR reaction where NO participated and reacted with surface nitrates, resulting in the formation of NO 2 and NO 2 − (reaction 2, Scheme 1 ) that avoid the surface blockage by nitrates. 3 Unfortunately, we cannot confirm the formation of surface nitrites as the O–N–O stretching frequency was covered by the signal from symmetric stretching of N–H as well as the intense signal from the zeolite structure.…”

Modified Layered Silicas as Catalysts for Conversion of Nitrogen Pollutants in Flue Gases—A Review

“…Thus, effective catalysts for the selective oxidation ammonia to nitrogen, tailored to the parameters of real flue gases emitted by power stations and diesel engines, are still needed. Among the various catalytic systems, modified layered clay minerals and zeolites have been studied as catalysts of the NH 3 -SCO process [71,[82][83][84].…”

“…Zeolites modified with transition metals have been reported to be active and selective catalysts of NH 3 -SCO [8,82,83]. Wang et al [83] compared the catalytic activity of coppermodified zeolites with different framework structures.…”

An Application of Steady‐state Isotopic‐transient Kinetic Analysis (SSITKA) in DeNOx Process

“…The sites that lead to NO formation appear to be different (active in a rapid insertion of lattice oxygen once the NH 3 adsorbs on these sites; residence time of 0.1044 s) from the ones that lead to N 2 and/or N 2 O formation (residence time of 13.57–17.42 s). Furthermore, NO produced from NH 3 oxidation using the lattice oxygen could further react with NH 3 , according to nowadays widely accepted the internal ( in‐situ ) selective catalytic reduction (i‐SCR) mechanism for NH 3 oxidation [65,66] . Besides the application of SSITKA, also, the temporal analysis of products (TAP) has been applied in a limited number of studies concerning the ammonia oxidation.…”