Edge-Coated Palladium Catalyst Dispersion via Silane Modification
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Solution Overview
Problem
The preparation of high-dispersion, edge-coated precious metal catalysts is challenging due to the contradiction between achieving high metal dispersion and edge-coating, with existing methods often resulting in low dispersion and large metal crystallite sizes, which limits their effectiveness in catalytic reactions.
Innovation Solution
A process is developed to control edge-coating and metal dispersion separately, using a colloidal approach with a reducing agent, stabilizing agent, and coordinating agent to form nanocrystallites of palladium or gold, achieving high dispersion and edge-coating by reducing the metal in an aqueous solution and depositing the colloidal suspension onto a support, optimizing the size and distribution of precious metal nanocrystallites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the metal salt diffuses into the pores of the support to achieve high dispersion, then the metal dispersion is improved, but the edge-coating is worsened
Solution Approach 1:
The support surface is pre-modified with silane groups before metal salt deposition, creating a reactive surface that directs metal salt deposition to the outer shell. This preliminary surface preparation enables the metal to deposit where needed (edge-coating) while still achieving high dispersion through controlled deposition on the modified surface sites.
Solution Approach 2:
The support is given non-uniform properties through selective silane modification of the outer shell surface, creating regions with different reactivity. The metal salt preferentially deposits on the modified outer shell regions rather than uniformly throughout the pores, achieving both edge-coating and high dispersion through localized deposition zones.
2Shape
If the metal salt deposits immediately upon contact with the support to achieve edge-coating, then the edge-coating is improved, but the metal dispersion is worsened
Solution Approach 1:
The surface chemistry parameters of the support are changed by introducing silane functional groups, which alter the deposition behavior of metal salts. This parameter change enables immediate deposition on the outer shell (achieving edge-coating) while the controlled density and distribution of silane sites ensure that metal crystallites remain small and well-dispersed.
3Shape
If only a small portion of the total surface area of the support is used for edge-coating, then the edge-coating is improved, but the metal dispersion is worsened
Solution Approach 1:
The outer shell surface is selectively modified with silane groups to create localized high-energy deposition sites. Although only the outer shell region is modified (not the entire support surface), the metal salt concentrates on these modified sites, achieving both edge-coating geometry and high dispersion through dense packing on the modified surface area.
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 process produces catalysts with nanocrystallites of 1-4 nm for palladium and 3-13 nm for gold, achieving high activity and selectivity by maximizing active sites and reactant accessibility, while minimizing side reactions and internal heat transfer issues.
Implementation Method 1
reducing a precious metal salt in aqueous solution using a functionalized, water soluble quaternary ammonium salt in the absence of organic solvents, to form elementary nanoparticles
Implementation Method 2
The stabilizing agent stabilizes the formed precious metal particles
Implementation Method 3
depositing the colloidal suspension onto a support
Data Source
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AI summary
The present invention is in the field of catalysis. More particularly, the present invention is directed to supported precious metal, preferably palladium and/or gold metal catalysts, having a high degree of dispersion and a high degree of edge-coating. The present invention is further directed to a process for producing these catalysts, as well as to the use of these catalysts in chemical reactions.