Rhodium Catalyst Dispersion Control via pH Adjustment
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Solution Overview
Problem
Conventional lean NOx trap catalysts experience performance deterioration due to noble metal aggregation, leading to a decrease in active surface area and catalyst activity over time, especially under high-temperature conditions.
Innovation Solution
A catalyst comprising rhodium supported on a zirconium-containing oxide with added elements like calcium, lanthanum, cerium, or yttrium, and a NOx absorbing material such as magnesium or barium, where the pH of the mixed solution is controlled to maintain a high degree of rhodium dispersion, preventing aggregation and maintaining catalyst performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lean NOx trap catalyst is used, then NOx purification function is achieved in lean range, but catalyst performance deteriorates due to noble metal aggregation after duration test
Solution Approach 1:
The patent applies preliminary action by controlling the pH of the aqueous solution during the catalyst preparation process to be 4 or higher before the noble metal is deposited. This preliminary pH control prevents noble metal aggregation from occurring in the first place, rather than attempting to reverse aggregation after it has occurred. The alkaline environment during preparation ensures that the noble metal particles remain dispersed on the carrier surface, maintaining high active surface area and catalyst performance stability over time
Solution Approach 2:
The patent utilizes parameter changes by specifically adjusting and controlling the pH parameter of the aqueous solution to be 4 or higher during the catalyst preparation process. This parameter change fundamentally alters the chemical environment to prevent noble metal aggregation. By changing the pH parameter from acidic/neutral to alkaline conditions, the patent achieves stable noble metal dispersion and maintains catalyst performance without the deterioration seen in conventional catalysts
2Quantity of substance
If noble metal amount is reduced to lower cost, then manufacturing cost decreases, but catalyst activity and purification efficiency decrease
Solution Approach 1:
The patent applies parameter changes by controlling the pH of the aqueous solution to be 4 or higher during preparation, which fundamentally changes how the noble metal distributes on the carrier surface. This parameter control enables the noble metal to form highly dispersed, fine particles with maximum surface area exposure, significantly enhancing catalytic activity per unit mass of noble metal. Consequently, the patent can reduce the overall noble metal content while maintaining or even improving NOx purification efficiency
Solution Approach 2:
The patent employs composite materials by combining the noble metal with a specifically designed carrier that has alkaline surface properties. This composite structure, where the carrier's alkaline characteristics interact with the noble metal during preparation and operation, enhances the noble metal's dispersion and catalytic efficiency. The synergistic effect of this composite material system allows for reduced noble metal loading while maintaining high purification performance
3Duration of action of stationary object
If high temperature load is applied to test catalyst durability, then catalyst lifetime is evaluated, but noble metal aggregates and active surface area decreases
Solution Approach 1:
The patent applies preliminary action by establishing a stable, alkaline environment during the catalyst preparation process that creates strong initial bonding between the noble metal particles and the carrier surface. This preliminary stabilization prevents noble metal aggregation from occurring during subsequent high-temperature operation. The alkaline pH condition during preparation creates a more thermally stable configuration that resists sintering and aggregation even when the catalyst is subjected to prolonged high-temperature load
Solution Approach 2:
The patent applies beforehand cushioning by using the alkaline aqueous solution environment during preparation to create a protective dispersion state of the noble metal on the carrier. This preliminary protective state acts as a cushion against the damaging effects of subsequent high-temperature operation. The alkaline environment during preparation establishes a stable configuration that cushions the noble metal particles against thermal aggregation, maintaining their dispersion even after duration tests at elevated temperatures
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 catalyst maintains high dispersion of rhodium and prevents aggregation, thereby sustaining catalyst activity and NOx purification efficiency even after being subjected to load and high temperatures, reducing the need for noble metal and improving NOx purification rates.
Implementation Method 1
a zirconium-containing oxide which supports rhodium
Implementation Method 2
a NOx absorbing material comprising at least one selected from the group consisting of magnesium, barium, sodium, potassium and cesium
Data Source
Figure 1
AI summary
An exhaust gas purifying catalyst includes: rhodium; a zirconium-containing oxide which supports rhodium, and comprises: at least one element selected from the group consisting of calcium, lanthanum, cerium, neodymium and yttrium; and zirconium; and a NOx absorbing material comprising at least one selected from the group consisting of magnesium, barium, sodium, potassium and cesium. A degree of dispersion of rhodium is 20% or more after baking at 900 °C in air for three hours. A method for manufacturing the exhaust gas purifying catalyst includes: mixing the zirconium-containing oxide with water, thereby preparing an aqueous liquid of the zirconium-containing oxide; and supporting rhodium on the zirconium-containing oxide by mixing the aqueous liquid of the zirconium-containing oxide with an aqueous solution of a rhodium salt. A pH of a mixed liquid of the aqueous solution of the rhodium salt and the aqueous liquid of the zirconium-containing oxide is adjusted to 7 or more.