Zeolite Core SCR Catalyst with Oxide Shell for Hydrocarbon Resistance
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Solution Overview
Problem
Conventional SCR catalysts face a significant drop in nitrogen oxide conversion performance and hydrothermal aging stability due to elevated hydrocarbon concentrations in diesel exhaust gases, which leads to adverse effects on the catalyst's long-term stability and activity.
Innovation Solution
A catalytically active material comprising a zeolite or zeolite-like core exchanged with transition metals, surrounded by a shell of oxides such as silicon dioxide, aluminum oxide, or cerium oxide, which prevents hydrocarbons from reaching the active sites, ensuring high tolerance to hydrocarbons and maintaining nitrogen oxide conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SCR catalysts are used in diesel exhaust gases with elevated hydrocarbon concentrations, then nitrogen oxide conversion performance decreases and hydrothermal aging stability deteriorates
Solution Approach 1:
A hydrophobic coating layer is introduced as an intermediary between the exhaust gas and the SCR catalyst. This coating selectively repels hydrocarbons while allowing ammonia and nitrogen oxides to reach the active sites, thereby protecting the catalyst from hydrocarbon poisoning and maintaining high NOx conversion performance even in high HC exhaust conditions
Solution Approach 2:
The catalyst surface properties are modified by changing the chemical composition and hydrophobicity parameters of the coating layer. By adjusting the composition to include hydrophobic materials and controlling the coating thickness and porosity, the catalyst achieves selective permeability that excludes hydrocarbons while permitting reactant access to active sites
2Duration of action of stationary object
If the SCR catalyst is exposed to high hydrocarbon concentrations during diesel exhaust treatment, then long-term stability and activity are adversely affected
Solution Approach 1:
The hydrophobic coating acts as a protective intermediary layer that prevents direct contact between hydrocarbons and the catalyst active sites. This barrier function maintains catalyst activity over extended periods by preventing hydrocarbon accumulation and degradation reactions that would otherwise occur during normal operation
Solution Approach 2:
A thin hydrophobic film coating is applied to the catalyst surface to create a protective barrier. This film is sufficiently thin to allow diffusion of ammonia and nitrogen oxides to the active sites while being thick enough to block hydrocarbons, thereby maintaining catalyst performance over the catalyst's service life
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 catalytically active material exhibits improved resistance to hydrocarbons, maintaining high nitrogen oxide conversion performance both before and after hydrothermal aging, with minimal exothermicity during hydrocarbon burnoff, thus enhancing the long-term stability and efficiency of the SCR catalyst.
Implementation Method 1
a shell (2) surrounding this core which is formed from one or more oxides selected from the group consisting of silicon dioxide, germanium dioxide, aluminum oxide, titanium oxide, tin oxide, cerium oxide, zirconium dioxide and mixed oxides thereof
Implementation Method 2
the selective catalytic reduction of the nitrogen oxides with the reducing agent ammonia over a catalyst suitable therefore, the SCR catalyst
Implementation Method 3
the oxidizable CO and HC pollutant gases can be converted to harmless carbon dioxide (CO2) by passage over a suitable oxidation catalyst
Implementation Method 4
the filter has to be heated to a temperature above the soot ignition temperature. This heat-up is effected by postinjection of fuel into the output piston stroke of the cylinder or into the exhaust gas line
Implementation Method 5
by catalytic conversion of the uncombusted hydrocarbons on an oxidizing catalyst (called 'heat-up catalyst')
Data Source
AI summary
The invention relates to a catalytically active material for reacting nitrogen oxides with ammonia in the presence of hydrocarbons. The material consists of an inner core (1) made of a zeolite exchanged with one or more transition metals or a zeolite-like compound exchanged with one or more transition metals. The core of the catalytically active material is encased by a shell (2), which is made of one or more oxides selected from silicon dioxide, germanium dioxide, aluminum oxide, titanium oxide, tin oxide, cerium oxide, zirconium dioxide, and mixed oxides thereof.