Core-Shell NOx and CO Catalyst to Prevent NH3 Oxidation
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Solution Overview
Problem
Current catalysts for simultaneous removal of nitrogen oxides (NOx) and carbon monoxide (CO) face challenges such as narrow temperature windows, poor stability, high cost, and excessive ammonia oxidation at high temperatures, especially in oxygen-rich industrial flue gases, limiting their effectiveness and applicability.
Innovation Solution
A catalyst with a core-shell structure comprising an aluminum oxide and/or titanium oxide core loaded with a high-entropy oxide and a CePO4 shell is developed, which encapsulates the high-entropy oxide to prevent ammonia oxidation and enhance sulfur resistance, allowing for efficient CO oxidation and NOx removal across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a catalyst with high redox performance is used to achieve efficient CO removal, then CO oxidation efficiency is improved, but NH3 oxidation occurs at high temperature causing denitration efficiency to decrease
Solution Approach 1:
The catalyst is divided into two functional zones: a redox-active core region for CO oxidation and an ammonia-selective surface region for denitration. This spatial segmentation allows CO removal and NH3 selective catalytic reduction to occur in separate zones, preventing NH3 oxidation while maintaining high CO removal efficiency.
Solution Approach 2:
Different regions of the catalyst are assigned different functional properties: the core provides high redox performance for CO oxidation, while the surface layer provides ammonia selectivity for denitration. This local differentiation of catalytic properties resolves the contradiction between CO removal efficiency and denitration efficiency.
2Productivity
If Ir-based materials and other noble metal materials are used for CO-SCR reaction, then synergistic removal of NOx and CO is achieved, but cost increases and stability decreases
Solution Approach 1:
The patent replaces expensive noble metals (Ir, Pd) with abundant, low-cost transition metal oxides (Fe, Cu, Mn, Co, Ni oxides). These earth-abundant materials provide comparable or superior catalytic performance for synergistic NOx and CO removal, dramatically reducing cost while improving stability.
Solution Approach 2:
The invention uses a composite structure combining multiple transition metal oxides with specific support materials. This composite approach creates a catalyst that achieves synergistic removal of NOx and CO without requiring expensive noble metals, while the composite structure enhances thermal and chemical stability.
3Productivity
If copper, manganese and cerium ions are loaded onto the surface of a vanadium-tungsten-titanium catalyst, then CO oxidation and NOx removal are achieved, but denitration temperature window becomes narrow
Solution Approach 1:
The patent modifies the catalytic parameters by using transition metal oxides with optimized compositions and particle size distributions. This parameter optimization broadens the active temperature window for denitration while maintaining CO oxidation capability, allowing effective operation across a wider temperature range.
Solution Approach 2:
The catalyst is designed to perform multiple functions across different temperature ranges: CO oxidation occurs at lower temperatures while denitration becomes active at higher temperatures, with both processes occurring simultaneously within a broad temperature window. This multi-functionality allows the catalyst to adapt to varying operating conditions.
4Productivity
If a catalyst with high activity for CO oxidation is used, then CO removal efficiency is improved, but sulfur resistance decreases
Solution Approach 1:
The catalyst employs a composite structure where transition metal oxides are combined with sulfur-resistant support materials. This composite design maintains high CO oxidation activity while the support structure provides sulfur resistance, preventing deactivation by sulfur compounds in flue gases.
Solution Approach 2:
The support material acts as an intermediary that protects the active catalytic sites from sulfur poisoning. The support structure provides mechanical strength and thermal stability while the transition metal oxides on the surface maintain CO oxidation activity, creating a synergistic protection mechanism.
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 achieves high activity and stability with a wide temperature window, effectively preventing ammonia oxidation and maintaining CO conversion rates while resisting sulfur, thus addressing the limitations of existing catalysts.
Implementation Method 1
a catalyst for synergistic removal of nitrogen oxides (NOx) and carbon monoxide (CO)... achieving the oxidation of CO while removing NOx
Implementation Method 2
CePO4 as a shell... encapsulating a high-entropy oxide having a relatively high redox performance inside CePO4
Implementation Method 3
The simultaneous performance of an NH3-SCR reaction and a CO oxidation reaction on the same catalyst can effectively avoid the above-mentioned problems
Data Source
AI summary
Disclosed are a catalyst for synergistic removal of nitrogen oxides (NOx) and CO as well as a preparation method and use thereof. The preparation method comprises: performing vibratory ball milling, washing, drying and calcining on aluminum isopropoxide and/or titanium isopropoxide, chlorides of five or more different metal elements and P123 and/or polyethylene glycol (PEG), stirring the obtained high-entropy oxide inner core and a gel of H3PO4 and Ce(NO3)3, and then performing vibratory ball milling, washing, drying and calcining to obtain an high-entropy oxide loaded with CePO4 seeds; and preparing, by using ammonia water, a clear solution containing pyrophosphate and Ce(NO3)3 in equal stoichiometric ratios, then adding the high-entropy oxide loaded with the CePO4 seeds and urea and/or tetrapropylammonium hydroxide (TPAH) to form a slurry, and, after hydrothermal reaction, washing, drying and calcining a solid to obtain the catalyst.