Multi-modal Pt Catalyst for Diesel NOx Oxidation Stability
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Solution Overview
Problem
Conventional platinum group metal-based diesel oxidation catalysts suffer from significant loss of NOx oxidation activity due to particle sintering, leading to decreased catalytic efficiency over time, especially at high temperatures, and are susceptible to sulfur poisoning when palladium is added in high concentrations.
Innovation Solution
The use of a catalyst composition with a multi-modal distribution of platinum group metal particles, specifically having two distinct size ranges (0.5-3 nm and 4-15 nm) and a fully reduced platinum group metal content, dispersed on refractory metal oxide supports, which enhances aging stability and maintains high catalytic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional platinum group metal-based diesel oxidation catalysts are used, then initial catalytic activity is achieved, but significant loss of NOx oxidation activity occurs due to particle sintering over time at high temperatures
Solution Approach 1:
The catalyst composition is segmented into multiple populations of platinum group metal particles with different size ranges (e.g., 0.5-3 nm and 4-15 nm). This segmentation allows small particles to provide high surface area and activity while large particles provide thermal stability and resistance to sintering, thereby maintaining reliable NOx oxidation activity over extended duration at high temperatures.
2Stability of the object's composition
If palladium is added in high concentrations to inhibit sintering, then particle stability is improved, but sulfur poisoning susceptibility increases
Solution Approach 1:
The invention changes the critical parameter from palladium concentration to platinum group metal particle size distribution. By controlling the size distribution (multiple populations with specific ranges) and maintaining fully reduced metal content, the invention achieves particle stability without requiring high concentrations of palladium, thereby avoiding increased sulfur poisoning susceptibility.
3Productivity
If platinum group metal particles are used for NOx oxidation, then catalytic activity is achieved, but particle sintering occurs at elevated temperatures leading to deactivation
Solution Approach 1:
The catalyst employs a composite structure consisting of multiple populations of platinum group metal particles with different size ranges dispersed on a refractory metal oxide support. This composite approach combines the high activity of small particles with the thermal stability of large particles and the support material, achieving both high NOx oxidation rate and reliable activity retention 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 composition exhibits reduced loss of NOx oxidation performance after aging and remains effective in converting hydrocarbons, CO, and NOx over extended periods, even at high temperatures, while minimizing sulfur poisoning risks.
Implementation Method 1
Platinum (Pt) remains the most effective platinum group metal for oxidizing NO to NO2
Implementation Method 2
oxidizing NO to NO2
Implementation Method 3
particle growth at elevated temperature (i.e., sintering), leading to a decrease in surface area
Implementation Method 4
convert both hydrocarbon and CO gaseous pollutants by catalyzing the oxidation of these pollutants to carbon dioxide (CO2) and water
Implementation Method 5
soot combustion by O2 according to the equation (C+O2→CO/CO2). This reaction typically temperatures in excess of 600° C
Implementation Method 6
Passive soot regeneration utilizes NO2 rather than O2 to oxidize soot according to the equation C+NO2CO/CO2+NO). This reaction is efficient at temperatures greater than 300° C
Data Source
AI summary
An oxidation catalyst composition is provided, the composition including a plurality of platinum group metal particles having a multi-modal distribution of particle sizes. The plurality of platinum group metal particles includes a first population of platinum group metal particles having a range of particle sizes of from about 0.5 nm to about 3 nm, and a second population of platinum group metal particles having a range of particle sizes of from about 4 nm to about 15 nm. Methods for the preparation and use of the catalyst composition are also provided, as well as catalyst articles and emission gas treatment systems employing such catalyst articles. The catalyst exhibits enhanced stability with respect to oxidation performance after degreening and/or aging, as compared to conventional oxidation catalysts, in particular less loss of NOx oxidation performance.