Ammonia Generating Catalyst for NOx Reduction
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Solution Overview
Problem
Current gasoline engine exhaust after-treatment systems, particularly those operating under lean conditions, face challenges in reducing nitrogen oxides (NOx) emissions effectively, as traditional three-way conversion catalysts are not efficient in oxygen-rich environments, and alternative technologies like urea SCR systems are complex and inefficient in fuel-rich conditions.
Innovation Solution
An exhaust gas treatment system comprising an ammonia generating catalyst with a NOx storage component, refractory metal oxide support, platinum, and palladium, where the platinum to palladium ratio is greater than 1, and a downstream ammonia selective catalytic reduction (SCR) catalyst, which is substantially free of ceria, to efficiently convert NOx to ammonia for reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional three-way conversion catalysts are used, then NOx, CO, and HC pollutants can be abated under stoichiometric conditions, but they are not effective for reducing NOx emissions when the gasoline engine runs lean due to excessive oxygen in the exhaust gas
Solution Approach 1:
The exhaust after-treatment system is divided into two separate functional segments: a lean NOx trap (LNT) catalyst for NOx storage during lean operation, and a downstream SCR catalyst for NH3-based NOx reduction. This segmentation allows each catalyst to be optimized for its specific function rather than requiring a single catalyst to handle all conditions.
Solution Approach 2:
Ammonia (NH3) serves as an intermediary substance that is generated in situ by the LNT catalyst during rich-to-lean transitions and then consumed by the downstream SCR catalyst to reduce NOx emissions. This intermediary mechanism enables indirect NOx reduction without requiring direct contact between reductants and NOx in the exhaust stream.
2Reliability
If urea SCR systems are used to reduce NOx under oxygen-rich environment, then NOx reduction can be achieved, but the system complexity increases due to requiring a secondary fluid tank with injection system
Solution Approach 1:
The LNT catalyst performs self-service by automatically generating ammonia from engine-out NOx during rich-to-lean transitions. This in-situ ammonia generation eliminates the need for external urea storage tanks, injection systems, and associated control mechanisms, thereby simplifying the overall system while maintaining effective NOx reduction capability.
Solution Approach 2:
The system recovers and reuses engine-out NOx by converting it to ammonia through the LNT catalyst during rich operation, which is then utilized by the SCR catalyst during lean operation. This closed-loop approach transforms a waste product (NOx) into a useful intermediate (NH3) for continued NOx reduction, eliminating the need for external chemical additives.
3Use of energy by moving object
If lean-burn gasoline engines are used to improve fuel efficiency and reduce CO2 emissions, then fuel economy improves, but NOx emissions increase and present significant challenges for after-treatment
Solution Approach 1:
The exhaust after-treatment system utilizes periodic lean-rich-lean cycling of the engine operation to alternately charge and discharge the LNT catalyst. During lean periods, NOx is stored in the LNT; during rich periods, the stored NOx is converted to ammonia. This periodic action enables continuous NOx management while maintaining overall lean-burn operation for fuel efficiency.
Solution Approach 2:
The system converts the harmful effect of excessive oxygen in lean exhaust (which prevents traditional catalysts from working) into a beneficial mechanism by using that oxygen to drive the LNT storage reaction, which subsequently enables ammonia generation and SCR-based NOx reduction. The oxygen-rich environment that normally disables NOx control becomes the driving force for the storage mechanism.
4Reliability
If ammonia generating catalyst stores NOx in lean periods, then NOx can be utilized for NH3 formation, but the oxygen storage component consumes fuel during lean to rich transitions which reduces NH3 formation efficiency
Solution Approach 1:
The invention extracts and removes the oxygen storage component (OSC) from the LNT catalyst formulation, using instead a non-OSC-based NOx storage mechanism relying on barium oxide and other alkaline earth metal oxides. This extraction eliminates the fuel-consuming oxygen storage/re-release cycle while maintaining NOx storage capability, thereby improving NH3 formation efficiency without penalty to fuel economy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This system achieves high conversion efficiency of NOx to ammonia, storing NOx in lean operations and converting it to ammonia in rich conditions, thereby reducing NOx emissions effectively without the complexity of urea SCR systems.
Implementation Method 1
an ammonia generating catalyst comprising a NOx storage component, a refractory metal oxide support, a platinum component, and a palladium component
Implementation Method 2
an ammonia selective catalytic reduction (SCR) catalyst downstream of the ammonia generating catalyst
Data Source
AI summary
Described are exhaust gas treatment systems for treatment of a gasoline engine exhaust gas stream. The exhaust gas treatment systems comprise an ammonia generating catalyst and an ammonia selective catalytic reduction (SCR) catalyst downstream of the ammonia generating catalyst. The ammonia generating catalyst comprises a NOx storage component, a refractory metal oxide support, a platinum component, and a palladium component. The ammonia generating catalyst is substantially free of ceria. The platinum and palladium components are present in a platinum to palladium ratio of greater than about 1 to 1.