Diesel Oxidation Catalyst for Low-Temperature NOx Storage
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Solution Overview
Problem
Existing diesel oxidation catalysts are ineffective at low temperatures, particularly in cold-start conditions, and struggle to provide sufficient NO2 content for efficient NOx removal by downstream SCR catalysts, especially in engines with reduced exhaust gas temperatures due to improved fuel efficiency.
Innovation Solution
A novel diesel oxidation catalyst composite comprising a first oxidation component with platinum and palladium on a refractory metal oxide support, a NOx storage component with alumina, silica, titania, or ceria, and a second oxidation component with a zeolite and platinum, designed to store and thermally release NOx at low temperatures, enhancing NO2 production for SCR catalyst activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional oxidation catalysts are used, then they can oxidize CO and HC at high temperatures, but they are ineffective at low temperatures and cannot provide sufficient NO2 for SCR catalyst activation
Solution Approach 1:
The catalyst is divided into three distinct functional components: a first oxidation component (Pt/Pd on refractory metal oxide) for CO and HC oxidation, a NOx storage component (alumina, silica, titania, or ceria) for NOx adsorption and release, and a second oxidation component (zeolite with Pt) for low-temperature oxidation and NO2 generation. This segmentation allows each component to perform its specific function effectively across the operating temperature range.
Solution Approach 2:
The catalyst composite performs multiple functions simultaneously: oxidizing CO and HC, storing and releasing NOx, generating NO2, and activating SCR catalysts. The combination of different catalyst components enables this multi-functionality, addressing the limitations of single-function catalysts at low temperatures.
2Use of energy by moving object
If exhaust gas temperature is reduced to improve fuel efficiency, then fuel economy improves, but NOx abatement efficiency deteriorates due to insufficient NO2 production
Solution Approach 1:
The NOx storage component adsorbs NOx during the exhaust pulse and stores it for later release. The second oxidation component then converts this stored NOx to NO2 in advance or during the exhaust pulse, ensuring sufficient NO2 is available for SCR catalyst activation even when exhaust temperatures are low, thus maintaining NOx abatement efficiency while allowing reduced exhaust temperatures for improved fuel economy.
Solution Approach 2:
The NOx storage component acts as an intermediary between the exhaust stream and the SCR catalyst. It temporarily holds NOx and works with the second oxidation component to generate NO2, which then activates the SCR catalyst. This intermediary mechanism ensures reliable NOx abatement even at low exhaust temperatures.
3Ease of manufacture
If palladium-based catalysts are used to reduce cost, then manufacturing cost decreases, but light-off temperature increases and sulfur tolerance deteriorates
Solution Approach 1:
Different regions of the catalyst have different compositions optimized for specific functions: the first oxidation component uses Pt/Pd ratio optimized for cost and activity, the NOx storage component uses alumina/silica/titania/ceria for NOx adsorption, and the second oxidation component uses zeolite with Pt for low-temperature NO2 generation. This local quality optimization allows Pd to be used cost-effectively while maintaining low light-off temperature through the zeolite component.
Solution Approach 2:
The catalyst is a composite material combining Pt/Pd on refractory metal oxide, NOx storage components (alumina, silica, titania, or ceria), and zeolite with Pt. This composite structure leverages the cost advantages of Pd while the zeolite and Pt components ensure low light-off temperature and improved sulfur tolerance through synergistic effects.
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 effectively stores and releases NOx at temperatures below 350°C, promoting SCR reactions at low temperatures and improving NOx abatement efficiency by generating sufficient NO2 for downstream SCR catalysts, even when exhaust temperatures are below 180°C.
Implementation Method 1
a NOx storage component comprising one or more of alumina, silica, titania, ceria, or manganese
Implementation Method 2
oxidation catalysts that include manganese and/or ceria
Implementation Method 3
selective catalytic reduction (SCR) of NOx, which involves the reaction of NOx in the presence of a reductant
Data Source
AI summary
An oxidation catalyst composite, methods, and systems for the treatment of exhaust gas emissions from a diesel engine are described. More particularly, described is an oxidation catalyst composite including a first oxidation component comprising a first refractory metal oxide support, palladium (Pd) and platinum (Pt); a NOx storage component comprising one or more of alumina, silica, titania, ceria, or manganese; and a second oxidation component comprising a second refractory metal oxide, a zeolite, and Pt. The oxidation catalyst composite is sulfur tolerant, adsorbs NOx and thermally releases the stored NOx at temperature less than 350° C.