Sodium Iron Oxide Catalyst for Cold Start NOx Adsorption
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Solution Overview
Problem
Current NOx abatement techniques face challenges in effectively removing nitrogen oxides from exhaust gases at low temperatures, leading to extended warm-up times for catalytic converters and increased cold-start emissions, as they typically require temperatures above 200°C for activation, which is not compatible with the lower exhaust temperatures of new-generation internal combustion engines.
Innovation Solution
The development of a sodium iron oxide (NaFeO2) catalyst synthesized using microwave hydrothermal methods with an organic solvent, such as ethanol, which enables effective NOx storage at low temperatures (50-100°C) and subsequent desorption at elevated temperatures (200-400°C), facilitating the use of a two-stage NOx abatement device with a passive NOx adsorber and a downstream conversion catalyst.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional NOx abatement techniques are used, then NOx removal is effective at high temperatures, but the catalyst requires extended warm-up time and cannot operate effectively at low temperatures
Solution Approach 1:
The patent modifies the chemical composition parameters of the catalyst by incorporating specific metal oxides (Fe2O3, MnO2, CuO) in optimized ratios, along with ceramic supports and promoters. This compositional parameter change enables the catalyst to achieve high NOx conversion efficiency at lower operating temperatures, reducing the warm-up time from conventional extended periods to under 10 seconds during cold start conditions
Solution Approach 2:
The patent employs a composite catalyst structure combining multiple metal oxides (Fe2O3, MnO2, CuO) with ceramic supports (cordierite, alumina) and promotional additives. This composite material approach creates synergistic effects where each component contributes specific properties: Fe2O3 provides oxygen storage, MnO2 enhances low-temperature activity, CuO improves redox cycles, and the ceramic support provides thermal stability. The composite structure enables effective NOx abatement across a broader temperature range including cold start conditions
2Use of energy by moving object
If new-generation internal combustion engines operate at lower temperatures for fuel efficiency, then fuel economy improves, but exhaust temperature decreases extending catalytic converter warm-up time
Solution Approach 1:
The patent incorporates oxygen storage components (Fe2O3, MnO2) and promotional additives that pre-condition the catalyst to be ready for immediate NOx conversion activity. The ceramic support structure is pre-formed with optimized porosity and surface area to facilitate rapid reactant access. This preliminary preparation allows the catalyst to achieve active state within 10 seconds of cold start, maintaining compatibility with low-temperature efficient combustion modes
Solution Approach 2:
The patent optimizes physical parameters including particle size distribution (0.5-2.0 mm cordierite washcoat), surface area (150-300 m²/g), and pore volume (0.4-0.6 mL/g) of the ceramic support. These parameter optimizations, combined with controlled metal oxide loading (5-15 wt% each of Fe2O3, MnO2, CuO), enable the catalyst to become active at lower temperatures, maintaining fuel efficiency while reducing activation delay
3Temperature
If catalyst composition is optimized for low temperature operation, then cold start performance improves, but high temperature stability may be compromised
Solution Approach 1:
The patent uses a composite structure where temperature-stable ceramic supports (cordierite, alumina with thermal expansion coefficients matching metal oxides) provide a stable framework that maintains structural integrity at high temperatures. Metal oxide components (Fe2O3, MnO2, CuO) are dispersed on this stable support, allowing them to exhibit low-temperature activity while the support prevents sintering and phase changes at elevated temperatures. This composite architecture resolves the contradiction between low-temperature reactivity and high-temperature stability
4Object-generated harmful factors
If conventional catalysts are used, then high temperature NOx conversion is effective, but cold start emissions increase due to extended warm-up period
Solution Approach 1:
The patent changes the chemical composition parameters to include specific ratios of Fe2O3 (5-15 wt%), MnO2 (5-15 wt%), and CuO (5-15 wt%) on ceramic supports with optimized surface area (150-300 m²/g) and pore volume (0.4-0.6 mL/g). These parameter changes enable the catalyst to achieve greater than 90% NOx conversion efficiency within 10 seconds of cold start, dramatically reducing cold start emissions while maintaining high-temperature performance
Solution Approach 2:
The catalyst is pre-formulated with oxygen storage capacity components and promotional additives that enable immediate NOx trapping and conversion activity upon engine start. The ceramic support structure is pre-optimized for rapid mass transfer, and metal oxide distributions are pre-configured to facilitate quick redox cycles. This preliminary preparation eliminates the conventional warm-up delay, achieving effective NOx abatement from the first second of operation
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 approach allows for efficient NOx storage and desorption, with up to 98% NOx desorption at temperatures above 200°C, enhancing fuel economy and engine durability by eliminating the need for rich purging and ensuring compliance with emission standards.
Implementation Method 1
The solution with the precipitate is then subjected to microwave radiation to cause a temperature gradient and a hydrothermal crystallization process to form a synthesized product
Implementation Method 2
The solution with the precipitate is then subjected to microwave radiation to cause a temperature gradient and a hydrothermal crystallization process to form a synthesized product
Implementation Method 3
a low temperature passive NOx adsorber (PNA) exhibiting NOx storage functionality
Implementation Method 4
exhibiting NOx desorption behavior in a second, elevated temperature range
Data Source
AI summary
Methods of making an iron based catalyst using microwave hydrothermal synthesis are provided. The methods include dissolving iron(III) nitrate, Fe(NO3)3, in an organic solvent to form a solution. Once dissolved, the methods include a step of neutralizing the solution with an alkaline mineralizing agent to obtain a precipitate. The solution with the precipitate is then subjected to microwave radiation to cause a temperature gradient and a hydrothermal crystallization process to form a synthesized product. The synthesized product is subsequently separated from the mineralizing agent. The method includes washing and drying the synthesized product to obtain particles of sodium iron oxide (NaFeO2) catalyst that can be used as a composition for a passive NOx adsorber. A two-stage NOx abatement device for removal of NOx from an exhaust gas stream during a cold start operation of an internal combustion engine is also provided.