Pd-Fe Zeolite NOx Trap for Low-Temperature Adsorption
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Solution Overview
Problem
Current NOx adsorption systems for internal combustion engines are inefficient at low temperatures during the cold start period, particularly under lean-burn conditions, with insufficient NOx adsorption capacity and storage efficiency.
Innovation Solution
A NOx trap composition comprising palladium and iron supported on a zeolite, produced by heating an iron-containing beta zeolite in the presence of an inert gas and an organic compound, followed by calcination with a palladium compound, enhancing NOx adsorption capacity at low temperatures and providing an additional storage window between 200-250°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional NOx adsorbent materials (alumina, silica, ceria, zirconia, titania) coated with platinum group metals are used, then the system achieves high NOx reduction efficiency at operating temperature (200°C and higher), but the NOx adsorption capacity is insufficient during cold start period (below 200°C)
Solution Approach 1:
The patent employs a composite material system combining zeolite support with multiple metal components (palladium, iron, and other transition metals). This composite structure integrates the low-temperature adsorption capability of zeolite with the catalytic activity of metal oxides, enabling effective NOx storage during cold start and subsequent release/reduction at higher temperatures.
Solution Approach 2:
The patent modifies the chemical and physical parameters of the adsorbent material by incorporating specific metal ratios, oxidation states, and surface properties. The use of palladium and iron in specific proportions, along with controlled calcination temperatures, creates a material with optimized electronic and geometric properties for enhanced low-temperature NOx adsorption while maintaining high-temperature performance.
2Reliability
If NOx storage and release catalysts are used for cold start control, then NOx can be adsorbed during warm-up period and thermally desorbed at higher temperatures, but the overall NOx adsorption capacity remains not high enough especially at high NOx storage efficiency
Solution Approach 1:
The patent merges the NOx storage function with the reduction function in a single integrated catalyst composition. The zeolite-metal composite simultaneously provides NOx adsorption sites and catalytic reduction centers, allowing the system to both store and process NOx within the same component, thereby increasing overall capacity without requiring separate large-volume systems.
Solution Approach 2:
The patent utilizes the porous structure of zeolite as the primary support material. The high surface area and controlled pore size distribution of zeolite provide numerous active sites for NOx adsorption while facilitating mass transport. The porous structure is further enhanced by the incorporation of metal particles that occupy and modify the pore architecture, creating additional active sites within the pore network.
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
The NOx trap composition demonstrates improved NOx adsorption capacity below 200°C and an additional storage window between 200-250°C, effectively addressing the inefficiencies of existing systems during cold start conditions.
Implementation Method 1
heating an iron-containing beta zeolite in the presence of an inert gas and an organic compound to produce a reductively calcined iron/zeolite
Implementation Method 2
the resulting Pd-Fe/zeolite is then calcined at 400 to 600°C in the presence of an oxygen-containing gas
Implementation Method 3
NOx from a lean exhaust gas is adsorbed at temperatures below 200°C
Implementation Method 4
subsequently thermally desorbed above 200°C
Data Source
AI summary
A method to produce a NOx trap composition, and its use in a NOx trap and in an exhaust system for internal combustion engines, is disclosed. The NOx trap composition is produced by heating an iron-containing zeolite in the presence of an inert gas and an organic compound to produce a reductively calcined iron/zeolite. A palladium compound is then added to the reductively calcined iron/zeolite, and the resulting Pd-Fe/zeolite is then calcined at 400 to 600°C in the presence of an oxygen-containing gas to produce the NOx trap composition. The NOx trap composition shows low temperature NO capacity below 200°C, as well as an additional NO storage temperature window in the 200 to 250°C range.