LT-NA and Mn/DOC Catalyst for Low-Temperature NOx Adsorption

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Solution Overview

Problem

Current catalysts employed in selective catalytic reduction (SCR) processes for reducing nitrogen oxides (NOx) in lean-burn engine exhausts face challenges at low temperatures, particularly during the 'cold start' period, and are sensitive to the NO2 to total NOx ratio in the feed gas.

Innovation Solution

The use of a low-temperature NOx adsorber (LT-NA) composition, such as Pd/zeolite, in combination with a diesel oxidation catalyst (DOC) containing a manganese-containing support material, to enhance NO2 formation and improve the NO2 to NOx ratio, thereby improving the efficiency of downstream SCR catalyst performance across a wide range of operating temperatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a conventional SCR catalyst is used, then NOx reduction is effective at high temperatures, but catalytic activity is insufficient at low temperatures (cold start period)

Engineering Contradiction:

Improveoperating temperature rangeVSAvoidcatalytic activity at low temperature

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The emission treatment system is segmented into three distinct functional zones: a low-temperature NOx adsorber (LT-NA) for cold start conditions, a diesel oxidation catalyst (DOC) for intermediate temperature oxidation, and a selective catalytic reduction (SCR) catalyst for high-temperature NOx reduction. This segmentation allows each component to operate optimally within its designated temperature range, resolving the contradiction between high-temperature effectiveness and low-temperature activity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The low-temperature NOx adsorber performs preliminary action by adsorbing NOx during the cold start period before the SCR catalyst becomes active. This preliminary adsorption stores NOx that can later be desorbed and reduced when temperatures rise, ensuring continuous NOx control across the full temperature range.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If the NO2 to total NOx ratio in feed gas varies, then SCR reaction efficiency changes, but the system must maintain consistent performance across varying ratios

Engineering Contradiction:

ImproveNOx reduction efficiencyVSAvoidsensitivity to NO2/NOx ratio variations

Core Design Contradiction:

ProductivityVSAdaptability or versatility

Solution Approach 1:

The diesel oxidation catalyst acts as an intermediary that converts NO to NO2, thereby controlling and stabilizing the NO2/NOx ratio in the feed gas to the SCR catalyst. This intermediary function decouples the SCR reaction efficiency from variations in upstream NOx composition, allowing consistent high-temperature NOx reduction performance regardless of feed gas composition changes.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If a single catalyst component is used, then device complexity is low, but it cannot effectively treat emissions across wide temperature ranges

Engineering Contradiction:

Improvetemperature range coverageVSAvoidnumber of catalyst components

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The emission treatment system achieves universality by integrating three catalyst components, each designed for specific temperature ranges and functions: the LT-NA for low-temperature NOx adsorption, the DOC for intermediate-temperature oxidation of CO and HC, and the SCR catalyst for high-temperature NOx reduction. This multi-functional arrangement allows the system to effectively treat emissions across the entire operating temperature range of the diesel engine.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 configuration effectively adsorbs NOx at low temperatures and enhances NO2 formation, leading to improved NOx reduction efficiency even at low temperatures and varying NOx ratios, thus addressing the limitations of current SCR catalysts.

Implementation Method 1

a low-temperature NOx adsorber (LT-NA) composition (e.g., Pd/zeolite) for adsorbing NOx from an exhaust gas at low temperature

Methodology Applied

Scientific EffectAdsorption: Adsorption

Implementation Method 2

emission treatment system for oxidation of hydrocarbons and carbon monoxide and for NOx abatement in an exhaust stream

Methodology Applied

Scientific EffectOxidation: Oxidation

Implementation Method 3

the DOC advantageously comprises a manganese-containing support material (e.g., Mn/Al2O3), which raises the NO2/NOx ratio of the treated exhaust gas

Methodology Applied

Scientific EffectCatalysis: Catalysis

Data Source

PatentUS12285745B2Coordinated emission control system including diesel oxidation catalyst and low temperature NO<sub>x </sub>adsorber

Publication Date: 2025.04.29 BASF MOBILE EMISSIONS CATALYSTS LLC

AI summary

The present disclosure is directed to an emission treatment system for oxidation of hydrocarbons and carbon monoxide and for NOx abatement in an exhaust stream of a lean burn engine, the emission treatment system including a low-temperature NOx adsorber (LT-NA) that includes a molecular sieve impregnated with at least one PGM component positioned in fluid communication with the exhaust stream; and an oxidation catalyst that includes a refractory metal oxide support containing manganese impregnated with platinum positioned in fluid communication with the exhaust stream, each of the LT-NA and the oxidation catalyst being disposed on a substrate. The invention provides a catalyst article combining an oxidation catalyst with a LT-NA and a related method of treatment of an exhaust gas.