New Insights into Reaction Mechanism of Selective Catalytic Ammonia Oxidation Technology for Diesel Aftertreatment Applications

Abstract

Mitigation of ammonia slip from SCR system is critical to meeting the evolving NH 3 emission standards, while achieving maximum NOx conversion efficiency. Ammonia slip catalysts (ASC) are expected to balance high activity, required to oxidize ammonia across a broad range of operating conditions, with high selectivity of converting NH 3 to N 2 , thus avoiding such undesirable byproducts as NOx or N 2 O. In this work, new insights into the behavior of an advanced ammonia slip catalyst have been developed by using accelerated progressive catalyst aging as a tool for catalyst property interrogation. The overall behavior was deconstructed to several underlying functions, and referenced to an active but non-selective NH 3 oxidation function of a diesel oxidation catalyst (DOC) and to the highly selective but minimally active NH 3 oxidation function of an SCR catalyst. In particular, it was shown that different functions of the ASC degrade independently, resulting in minimal changes to NH 3 conversion with substantial changes to product selectivity.

Insight into the Nature of Active Species of Pt/Al2O3 Catalysts for low Temperature NH3 Oxidation

“…[14] The catalyst for selective ammonia oxidation is an essential component of NH 3 -SCR diesel engine systems for NO x removal. [16] The state-of-the-art ASC systems include a combination of an ammonia oxidation (AMOX) catalyst (usually, Pt/Al 2 O 3 ) and a SCR catalyst in a duallayer architecture, [15,17,18] where a part of ammonia is oxidized over the Pt catalyst to N 2 and NO x , which is further transformed to N 2 over the SCR catalyst layer. [15] For higher NO x removal efficiency excess of ammonia is dosed resulting in its slip in the exhaust.…”

“…For higher NO x removal efficiency excess of ammonia is dosed resulting in its slip in the exhaust. To remove NH 3 before it reaches the environment the Ammonia Slip Catalyst (ASC) is additionally installed . The state‐of‐the‐art ASC systems include a combination of an ammonia oxidation (AMOX) catalyst (usually, Pt/Al 2 O 3 ) and a SCR catalyst in a dual‐layer architecture, where a part of ammonia is oxidized over the Pt catalyst to N 2 and NO x , which is further transformed to N 2 over the SCR catalyst layer.…”

An Overview of Lean Exhaust deNOx Aftertreatment Technologies and NOx Emission Regulations in the European Union

“…Dual-layer ASC catalysts have an inherently more complex behaviour due to the coupled reaction mechanisms and, moreover, they are also affected in a significantly different way by hydrothermal ageing, as discussed in Kamasamudram et al [51]. The possibility of combining NOx reduction and NH 3 oxidation functionalities in a single layer has also been investigated in the simulations published by Colombo et al [52].…”

Copper based catalysts for the selective ammonia oxidation into nitrogen and water vapour—Recent trends and open challenges

“…[33][34][35][36][37][38]. The desired products of NH3-SCO are nitrogen and water vapour, while nitrogen oxides (N2O, NO) are side-products [39]. Different NH3 oxidation paths can occur dependent on operation conditions and the type of catalyst used (Fig.…”