Selective Catalytic Reduction Catalyst Layering for NOx Control
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Solution Overview
Problem
Existing NOx catalysts with a two-layer structure face inefficiencies in NOx reduction at low temperatures due to the upper catalyst layer oxidizing ammonia, reducing the overall NOx removal rate, and the high-temperature catalyst layer interfering with the delivery of the reducing agent to the low-temperature catalyst layer.
Innovation Solution
A selective catalytic reduction NOx catalyst with a low-temperature catalyst layer positioned under a high-temperature catalyst layer, where the reducing agent concentration is controlled based on temperature to ensure efficient delivery to the low-temperature catalyst layer, using a controller to adjust the supply valve's addition of ammonia to maintain optimal concentrations and prevent oxidation at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the upper catalyst layer is designed to reduce NOx at low temperatures, then low-temperature NOx reduction capability is improved, but ammonia is oxidized into NOx at high temperatures, decreasing overall NOx removal rate
Solution Approach 1:
The catalyst is divided into two distinct layers: an upper catalyst layer for low-temperature NOx reduction and a lower oxidation catalyst layer for high-temperature ammonia oxidation prevention. This segmentation allows each layer to perform its specific function without interfering with the other, resolving the contradiction between low-temperature reduction capability and high-temperature ammonia stability
Solution Approach 2:
Different catalyst compositions are assigned to different spatial locations (layers). The upper layer contains catalyst components optimized for low-temperature NOx reduction, while the lower layer contains oxidation catalyst components. This local differentiation enables each region to exhibit the desired properties for its specific temperature range and function
2Productivity
If the upper catalyst layer has high reducing capability, then NOx reduction efficiency is improved, but the reducing agent is adsorbed and not delivered to the lower catalyst layer, decreasing reduction efficiency
Solution Approach 1:
The catalyst system is segmented into two layers with distinct functions: the upper layer performs NOx reduction while the lower layer performs oxidation. This segmentation prevents the upper layer from excessively adsorbing the reducing agent, ensuring adequate delivery to the lower layer while maintaining high reduction efficiency
Solution Approach 2:
The lower oxidation catalyst layer acts as an intermediary that processes excess reducing agent and prevents it from escaping untreated. It also creates a chemical environment that facilitates proper reducing agent distribution, ensuring both high reduction efficiency and adequate reducing agent utilization
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 enables efficient NOx reduction at both low and high temperatures by ensuring the reducing agent is effectively delivered to the low-temperature catalyst layer, maintaining high NOx removal efficiency across varying engine conditions.
Implementation Method 1
a selective catalytic reduction NOx catalyst having a catalyst substrate and a plurality of catalyst layers made up of catalyst particles having the property of selectively reducing NOx with a reducing agent
Implementation Method 2
the reducing agent concentration in a reducing agent atmosphere during a period in which the reducing agent is added may be controlled in a manner depending on the temperature of the selective catalytic reduction NOx catalyst
Data Source
AI summary
An apparatus may have a selective catalytic reduction NOx catalyst including a high-temperature catalyst layer having high capability of reducing NOx at high temperatures and a low-temperature catalyst layer having higher capability of reducing NOx at low temperatures than that of the high-temperature catalyst layer. The low-temperature catalyst layer may be arranged closer to a catalyst substrate than the high-temperature catalyst layer. A supply valve may add an addition quantity of reducing agent for reducing NOx to exhaust gas flowing into the selective catalytic reduction NOx catalyst. A controller may comprise at least one processor configured to control addition of the reducing agent by the supply valve such that the reducing agent concentration in a reducing agent atmosphere formed in the exhaust gas flowing into the selective catalytic reduction NOx catalyst is higher when the temperature of the selective catalytic reduction NOx catalyst is in a specific low temperature range.