PdAg Catalyst Crust for Selective Hydrogenation
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Solution Overview
Problem
Existing catalysts for selective hydrogenation of unsaturated hydrocarbon compounds in hydrocarbon cuts, particularly C3 cuts derived from steam cracking and catalytic cracking, face challenges in achieving optimal selectivity and activity due to issues with palladium particle distribution and bimetallic interactions, leading to inefficiencies in converting polyunsaturated compounds into alkenes while avoiding complete saturation.
Innovation Solution
A bimetallic PdAg catalyst with a specific preparation process involving a colloidal method for palladium deposition followed by liquid phase reduction and silver impregnation, resulting in a thin crust with palladium and silver atoms in close proximity, enhances catalyst performance by optimizing the proximity ratio and maintaining homogeneous particle sizes, thereby improving selectivity and activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional impregnation methods are used for metal deposition, then the preparation process is simple, but the local composition of the active phase is non-uniform and bimetallic interactions are insufficient
Solution Approach 1:
The support is pre-treated with a silane coupling agent before metal deposition, creating a surface with enhanced affinity for metal precursors. This preliminary action ensures uniform metal distribution and strong metal-support interaction, resolving the contradiction between composition uniformity and process simplicity.
Solution Approach 2:
A silane coupling agent serves as an intermediary between the support surface and metal precursors. This intermediary layer facilitates uniform metal deposition and enhances bimetallic interactions, achieving precise local composition control without excessive process complexity.
2Productivity
If palladium particle size is reduced to optimize structural sensitivity, then catalytic activity increases, but particle distribution uniformity becomes more difficult to control
Solution Approach 1:
The pH of the impregnation solution is optimized to enhance metal precursor adsorption on the silane-treated support, enabling uniform distribution of sub-3 nm palladium particles. This parameter change allows achieving high catalytic activity while maintaining precise particle size distribution control.
Solution Approach 2:
The support's porous structure with specific surface area and pore volume characteristics is utilized to accommodate and uniformly distribute ultra-fine palladium particles. The porous architecture provides numerous anchoring sites, ensuring uniform particle distribution while maintaining small particle sizes for high activity.
3Productivity
If metal particles are deposited throughout the support volume, then the catalyst utilizes the entire support structure, but intragranular material transfer causes loss of activity and selectivity
Solution Approach 1:
Metal particles are concentrated in a peripheral crust layer rather than uniformly distributed throughout the support volume. This local quality approach ensures that active sites are positioned where reactants first contact the catalyst, preventing intragranular material transfer issues while maintaining high catalyst utilization and selectivity.
Solution Approach 2:
The metal distribution is transitioned from a three-dimensional volumetric distribution to a two-dimensional surface-concentrated distribution in a peripheral crust. This dimensional change eliminates internal mass transfer problems while maximizing catalyst effectiveness at the reaction interface.
4Quantity of substance
If the crust thickness is increased to enhance metal loading, then more active sites are available, but mass transfer resistance increases and selectivity decreases
Solution Approach 1:
The crust thickness is precisely controlled within an optimized range through adjustment of impregnation conditions and metal precursor concentration. This parameter optimization achieves sufficient metal loading while maintaining thin crust structure that minimizes mass transfer resistance and preserves selectivity.
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 improved selectivity and activity in selective hydrogenation reactions, effectively converting polyunsaturated compounds into alkenes while minimizing the formation of alkanes, with enhanced stability and performance characteristics.
Implementation Method 1
a first step, referred to as step 1, wherein the palladium is deposited by a colloidal method
Implementation Method 2
a second step, referred to as step 2, wherein the silver is deposited following liquid phase reduction of the catalyst containing palladium
Implementation Method 3
a second step, referred to as step 2, wherein the silver is deposited following liquid phase reduction of the catalyst containing palladium
Implementation Method 4
The process of selective hydrogenation allows the polyunsaturated compounds in oil cuts to be transformed by conversion of the most unsaturated compounds into the corresponding alkenes
Implementation Method 5
A bimetallic PdAg catalyst with a specific preparation process involving a colloidal method for palladium deposition followed by liquid phase reduction and silver impregnation, resulting in a thin crust with palladium and silver atoms in close proximity, enhances catalyst performance
Data Source
AI summary
Disclosed are a catalyst, its preparation and use in selective hydrogenation, which catalyst has a porous support grain on which are deposited palladium and silver, and at least one alkali and/or alkaline earth metal; the porous support contains a refractory silica, alumina and/or silica-alumina oxide, where at least 80 wt. % of the palladium is distributed in a crust at the periphery of the support, and at least 80 wt. % of the silver is distributed in a crust at the periphery of the support, the local content of palladium at each point along the diameter of the grain follows the same course as the local content of silver.