Silver-Modifier Catalyst for Lean NOx Reduction
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Solution Overview
Problem
Existing technologies fail to effectively reduce nitrogen oxides (NOx) in exhaust gases containing excess oxygen, as three-way catalysts are not effective in lean burn conditions, and ammonia-based SCR systems are complex, hazardous, and limited to large facilities, while silver/alumina catalysts produce toxic intermediates and require a gap between catalysts for optimal performance.
Innovation Solution
A catalyst system comprising a silver component supported on an inorganic oxide with a modifier oxide on a second inorganic oxide support, eliminating the need for a gap between catalysts and avoiding toxic intermediates, using hydrocarbons or alcohols as reducing agents to convert NOx to nitrogen without forming carbon monoxide or toxic nitrogen-containing intermediates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If three-way catalysts are used to reduce nitrogen oxides, then NOx removal is effective, but the catalyst is not effective in lean burn conditions with high oxygen concentrations
Solution Approach 1:
The invention changes the operating parameters by designing a catalyst specifically for lean burn conditions with high oxygen concentrations (up to 10% or more), rather than attempting to make three-way catalysts work in these conditions. The catalyst composition and structure are optimized for the specific parameter range of lean exhaust gases.
Solution Approach 2:
The invention extracts and addresses only the NOx reduction function for lean burn conditions, separating it from the three-way catalyst system that attempts to handle multiple functions (NOx reduction, CO oxidation, HC oxidation) simultaneously. This dedicated lean-NOx catalyst focuses on the specific problem of NOx removal in high-oxygen environments.
2Reliability
If ammonia-based SCR systems are used to reduce nitrogen oxides, then NOx reduction is effective, but the system becomes complex, hazardous, and limited to large facilities
Solution Approach 1:
The invention uses self-service by utilizing hydrocarbons or alcohols that are already present in the exhaust gas or can be simply injected, eliminating the need for separate ammonia storage, handling, and injection systems. The catalyst system itself performs the reduction function without requiring complex external ammonia delivery infrastructure.
Solution Approach 2:
The invention replaces the expensive and hazardous ammonia with cheaper, easier-to-handle hydrocarbons or alcohols that can be introduced into the exhaust stream without special permits or complex safety systems. These reducing agents are readily available and do not require the same level of regulatory compliance as ammonia.
3Reliability
If silver/alumina catalysts are used to reduce nitrogen oxides with hydrocarbons, then NOx reduction is achieved, but toxic nitrogen-containing intermediates are formed
Solution Approach 1:
The invention converts the harmful effect of toxic intermediate formation into a benefit by designing a catalyst that promotes complete reduction reactions. The modified catalyst system ensures that hydrocarbons fully reduce NOx to nitrogen gas without forming toxic intermediates, turning the potential harm of intermediate formation into a demonstration of superior catalyst design.
Solution Approach 2:
The invention uses composite materials by combining silver with specific modifiers (such as alkali metals, alkaline earth metals, or rare earth elements) on alumina support. This composite catalyst structure synergistically enhances NOx reduction while suppressing the formation of toxic intermediates that occur with pure silver catalysts.
4Reliability
If non-catalytic reduction with hydrocarbons is used, then NOx reduction is achieved, but larger amounts of reducing agent are required and the method is limited to low oxygen levels
Solution Approach 1:
The invention replaces the non-catalytic chemical reduction process with a catalytic system. The catalyst provides an alternative reaction pathway with lower activation energy, enabling NOx reduction to proceed efficiently at lower temperatures and with smaller amounts of reducing agent compared to non-catalytic thermal reduction.
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 system achieves high NOx conversion efficiency across a wide range of NOx concentrations, is compact, and non-hazardous, reducing emissions while minimizing secondary pollutant formation.
Implementation Method 1
a first catalyst comprising approximately 0.2 to approximately 15 weight percent of at least one silver component selected from the group consisting of silver and silver compounds and at least one first inorganic oxide support, where the silver component is supported on the first inorganic oxide support
Implementation Method 2
a second catalyst comprising approximately 1 to approximately 30 weight percent of a modifier oxide selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rehenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof and at least one second inorganic oxide support
Data Source
AI summary
A catalyst system and a method for reducing nitrogen oxides in an exhaust gas by reduction with a hydrocarbon or oxygen-containing organic compound reducing agent are provided. The catalyst system contains a silver catalyst and a modifier catalyst, where the modifier catalyst contains a modifier oxide, where the modifier oxide is selected from the group consisting of iron oxide, cerium oxide, copper oxide, manganese oxide, chromium oxide, a lanthanide oxide, an actinide oxide, molybdenum oxide, tin oxide, indium oxide, rhenium oxide, tantalum oxide, osmium oxide, barium oxide, calcium oxide, strontium oxide, potassium oxide, vanadium oxide, nickel oxide, tungsten oxide, and mixtures thereof. The modifier oxide is supported on an inorganic oxide support or supports, where at least one of the inorganic oxide supports is an acidic support. The catalyst system of the silver catalyst and the modifier catalyst provides higher NOx conversion than either the silver catalyst or the modifier catalyst alone.