Copper Catalyst Precipitation Sequence for Activity and Stability
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Solution Overview
Problem
Existing methods for producing copper-containing catalysts for water-gas shift and methanol synthesis result in catalysts with relatively low activities and poor stability, particularly due to high alkali content and inadequate copper crystallite dispersion.
Innovation Solution
A method involving two separate precipitation steps with a basic and acidic solution, forming copper hydroxycarbonate and alumina phases, and incorporating silica, to create well-dispersed copper crystallites with controlled silica content, enhancing catalyst performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single precipitation step using aluminium nitrate is used, then the manufacturing process is simple, but the catalyst activity is low
Solution Approach 1:
The single precipitation step is divided into two sequential precipitation steps. The first step precipitates copper hydroxide/carbonate using a basic precipitant, and the second step precipitates alumina using alkali metal aluminate. This segmentation allows each metal to be precipitated under optimized conditions, improving copper dispersion and catalyst activity while maintaining reasonable process complexity.
2Ease of manufacture
If copper and zinc are co-precipitated against alkali metal aluminate, then the manufacturing process is simplified, but the catalyst activity is low
Solution Approach 1:
The precipitation process is segmented into two steps: first precipitating copper compounds with a basic precipitant, then precipitating alumina with alkali metal aluminate. This prevents copper from competing with alumina for precipitation, ensuring better copper dispersion and higher catalyst activity.
Solution Approach 2:
Instead of precipitating copper against aluminate (which causes low activity), the method inverts the sequence by first precipitating copper with a basic precipitant, then adding aluminate to precipitate alumina. This reversal of the precipitation order resolves the activity problem.
3Ease of manufacture
If acidic aluminium solutions are used for precipitation, then the manufacturing process is simplified, but the catalyst stability is poor
Solution Approach 1:
The method changes the pH parameter control strategy by using a basic precipitant in the first step to precipitate copper, then using alkali metal aluminate in the second step. This parameter change avoids the stability issues associated with acidic aluminium solutions while maintaining process simplicity.
4Ease of manufacture
If high levels of alkali are retained in the catalyst, then the manufacturing process is simplified, but the catalyst activity and stability are reduced
Solution Approach 1:
The method extracts and removes excess alkali through controlled precipitation sequences and washing steps. By precipitating copper first with a basic precipitant and then alumina with alkali metal aluminate, the process allows for more effective removal of retained alkali, improving both catalyst activity and stability.
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 method produces catalysts with high initial activity and excellent stability, achieving copper surface areas greater than 45 m²/g and BET surface areas greater than 95 m²/g, suitable for carbon oxide conversion processes.
Implementation Method 1
combining an acidic copper-containing solution with a basic precipitant solution in a first precipitation step to form a first precipitate
Implementation Method 2
combining an alkali metal aluminate solution with an acidic solution in a second precipitation step to form a second precipitate
Implementation Method 3
washing, drying and calcining the catalyst precursor to form the copper-containing catalyst
Data Source
AI summary
A method for preparing a copper-containing catalyst is described comprising the steps of: (a) combining an acidic copper-containing solution with a basic precipitant solution in a first precipitation step to form a first precipitate, (b) combining an alkali metal aluminate solution with an acidic solution in a second precipitation step to form a second precipitate, (c) contacting the first and second precipitates together in a further precipitate mixing step to form a catalyst precursor, and (d) washing, drying and calcining the catalyst precursor to form the copper-containing catalyst, wherein at least 70% by weight of the copper in the catalyst is present in the first precipitate and a silica precursor is included in the first precipitation step, the second precipitation step or the precipitate mixing step, to provide a catalyst with a silica content, expressed as SiO2, in the range of 0.1 to 5.0 wt %.