Colloidal Nanoparticle Deposition for Diesel Oxidation Catalysts
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Solution Overview
Problem
Conventional methods for preparing precious metal catalysts face challenges such as limited control over the structure and composition of metal nanoparticles, high temperature requirements, and low productivity, which affect the purification performance of exhaust gases from internal combustion engines.
Innovation Solution
A process involving the steps of adding a protecting agent to an aqueous metal precursor solution, followed by the addition of an alkali metal borohydride reducing agent and a support material, with pH adjustment and subsequent separation of solid and liquid phases, to produce highly dispersed metal particles on the support material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional impregnation methods are used to prepare supported catalysts, then the process is simple, but the control over the structure of the resulting materials (average particle size, particle composition and location of the active components) is limited
Solution Approach 1:
The patent applies preliminary action by pre-forming metal colloidal nanoparticles with controlled size and composition before deposition onto the support. The colloidal synthesis step (adding metal salt, protective agent, and reducing agent to form stabilized nanoparticles) prepares the metal phase in advance with precise structural control, which is then deposited onto the oxide support. This preliminary formation of controlled nanoparticles resolves the contradiction by achieving manufacturing precision through pre-controlled colloidal synthesis rather than relying on post-deposition structure control.
2Manufacturing precision
If metal carbonyl clusters are used as precious metal source, then high metal dispersions and homogeneity in particle size are achieved, but the stability of clusters on support surfaces and difficulties in synthesis and handling make large-scale applications problematic
Solution Approach 1:
The patent replaces unstable metal carbonyl clusters with more stable metal colloidal nanoparticles that can be synthesized from common metal salts (e.g., H2PtCl6, K2PdCl4) using protective agents (PVP, PVA) and reducing agents (NaBH4, KBH4). These colloidal nanoparticles are easier to synthesize, handle, and store on a large scale while maintaining controlled particle sizes and high metal dispersions. The use of aqueous-based colloidal synthesis makes the process more accessible and scalable compared to handling sensitive organometallic clusters.
3Manufacturing precision
If conventional impregnation with precious metal compound solution is used, then the precious metal is dispersed on the oxide support surface, but the atoms move and invite grain growth in the baking process making it difficult to maintain desired cluster size
Solution Approach 1:
The patent performs preliminary formation of the metal colloidal nanoparticles with controlled size before deposition onto the support. The protective agents (PVP, PVA) that stabilize the colloidal particles during synthesis continue to provide steric stabilization after deposition, preventing atom migration and grain growth during subsequent drying and calcination steps. This preliminary formation with protective coating resolves the stability issue by pre-establishing the desired cluster size and protecting it during thermal processing.
Solution Approach 2:
The protective agents (PVP, PVA) act as intermediaries between the metal nanoparticles and the oxide support surface. These polymers adsorb onto the nanoparticle surfaces, providing a protective barrier that prevents direct interaction between metal atoms and the support that would otherwise facilitate atom migration and grain growth. The protective agents mediate the interaction, allowing controlled deposition while maintaining nanoparticle integrity and size during subsequent thermal processing.
4Manufacturing precision
If polymer-stabilized precious metal colloids are used as precursors, then improved metal dispersions are achieved, but additional purification steps and inert atmospheres are required increasing process complexity
Solution Approach 1:
The patent extracts and eliminates the requirement for inert atmospheres and additional purification steps by using a simplified colloidal synthesis approach. The metal colloidal nanoparticles are synthesized in aqueous solution with protective agents that provide sufficient stability without requiring inert gas protection during deposition. The process directly deposits the colloidal suspension onto the support followed by simple drying and calcination, removing unnecessary process steps while maintaining high metal dispersions through the colloidal nature of the precursor.
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 process reduces the number of steps, eliminates the need for inert atmospheres, and achieves improved catalytic activity and thermal resistance, resulting in catalysts with controlled particle sizes and compositions suitable for diesel oxidation applications.
Implementation Method 1
adding a reducing agent to mixture (M1) to give a mixture (M2), wherein the reducing agent is an alkali metal borohydride
Implementation Method 2
adding a protecting agent to an aqueous solution of a metal precursor to give a mixture (M1)
Implementation Method 3
adding a support material to mixture (M2) to give a mixture (M3)
Data Source
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AI summary
The present invention relates to a process for preparing a catalyst, at least comprising the steps of adding a protecting agent to an aqueous solution of a metal precursor to give a mixture (M1), adding a reducing agent to mixture (M1) to give a mixture (M2), adding a support material to mixture (M2) to give a mixture (M3), adjusting the pH of mixture (M3), and separating the solid and liquid phase of mixture (M3). Furthermore, the present invention relates to the catalyst as such and its use as diese! oxidation catalyst.