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A novel concept for sustainable catalyst preparation

The conventional way to prepare a supported metal catalyst is shown below:

 

In this process, a metal ore is converted into the metal which is then dissolved, often in nitric acid, to make a salt, such as nickel nitrate. This is then added to a solid catalyst support, such as aluminium oxide, dried and heated in air at high temperature (typically 500 C) to convert the nitrate into an oxide which is then reduced back to the metal using a chemical reductant such as hydrogen. During this process a large quantity of nitrogen oxides (NOx) is released that must be captured and disposed off to protect the environment. In addition the process requires a lot of energy.

it would be much better if a direct process coud be developed in which the metal starting material is deposited onto the support, ideally as a metal, or at least as an ionic compound, without going through these energy intensive and environmentally unfavourable dissolution and precipitation stages.

 

To prepare a gold on carbon catalyst, a  gold wire and a graphite rod are placed in the electrochemical cell in the presence of appropriate ions and a voltage applied.

 

 

By varying the preparation conditions it is possible to deposit small (< 10 nm) gold particles on carbon.

 

In preliminary catalyst tests for the hydrogenation of benzyl alcohol, some of these catalysts perform much better than the standard World Gold Council (WGC) catalyst.

Catalyst
Au loading (wt.%)

Conversion of

benzyl alcohol/%

Selectivity to

benzaldehyde/%

World Gold Council
0.8
1.6
23.7
Au/carbon black
2.1
9.3
14.8
Au/titania
0.5
7.2
27.6