Cerium-Zirconium Mixed Oxide Pore Design for Thermal Catalysis
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Solution Overview
Problem
Existing catalysts for treating exhaust gases from internal combustion engines face challenges in maintaining a balance between high porosity, specific surface area, and thermal resistance, particularly under high temperatures, which affects their efficiency in oxidizing carbon monoxide and hydrocarbons while reducing nitrogen oxides.
Innovation Solution
A mixed oxide of zirconium, cerium, and lanthanum, optionally with other rare earth metals, is formulated with specific weight proportions and characterized by high BET surface area and pore volume ratios, along with controlled pore diameter distribution, to enhance thermal resistance and catalytic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If small-sized pores are developed to increase specific surface area, then BET specific surface area is improved, but thermal resistance deteriorates due to sintering at high temperatures
Solution Approach 1:
The patent uses a composite mixed oxide material comprising cerium oxide (30-70 wt%), zirconium oxide (20-50 wt%), and lanthanum oxide (5-20 wt%). This composite structure combines the high surface area characteristics of cerium oxide with the thermal stability of zirconium oxide and lanthanum oxide, resolving the contradiction between maintaining high specific surface area and resisting thermal sintering at high temperatures
Solution Approach 2:
The patent optimizes the pore size distribution parameters by controlling the calcination temperature (900-1100°C) and duration (3-5 hours) to achieve a specific pore diameter range (20-40 nm). This parameter optimization ensures that pores remain small enough for high surface area while being large enough to resist sintering at high temperatures
2Productivity
If large pore volume is developed to improve gas diffusion, then catalytic activity is improved, but specific surface area decreases
Solution Approach 1:
The patent creates a hierarchical pore structure with different pore sizes serving different functions: smaller pores (20-40 nm) provide high specific surface area for catalytic reactions, while larger pores provide efficient gas diffusion pathways. This local differentiation of pore quality allows simultaneous optimization of both catalytic activity and mass transport
Solution Approach 2:
The patent transitions from a single pore size dimension to a multi-dimensional pore size distribution (20-200 nm range). This dimensional expansion allows the material to simultaneously achieve high specific surface area through smaller pores and good gas diffusion through larger pores, resolving the trade-off between catalytic activity and surface area
3Reliability
If high calcination temperature is used to improve thermal stability, then thermal resistance is improved, but specific surface area and pore volume decrease
Solution Approach 1:
The patent performs preliminary stabilization by incorporating lanthanum oxide (5-20 wt%) into the mixed oxide structure before high-temperature calcination. This preliminary action creates a more stable crystal structure that resists sintering, allowing the material to maintain high specific surface area even after calcination at 900-1100°C
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 mixed oxide maintains high catalytic activity and thermal stability, ensuring effective conversion of pollutants even at elevated temperatures, thus enhancing the performance of catalytic converters in treating exhaust gases.
Implementation Method 1
these pores which are the most sensitive to sintering. It is thus advantageous to develop a mixed oxide exhibiting a good compromise between a large pore volume, a high surface area, even after maintaining at a high temperature
Implementation Method 2
it has to comprise pores with a size sufficiently large to make possible good diffusion of the gases
Implementation Method 3
Multifunctional catalysts are currently used for the treatment of exhaust gases from internal combustion engines... capable of carrying out not only oxidation, in particular of carbon monoxide and hydrocarbons present in exhaust gases, but also reduction, in particular of nitrogen oxides
Data Source
AI summary
The present invention relates to a mixed oxide of zirconium, of cerium, of lanthanum and optionally of at least one rare earth metal other than cerium and lanthanum (REM), characterized by BET specific surfaces, a specific range of pores and the process for preparing such a mixed oxide.