Acid-treated catalyst converts hydrogen and oxygen directly into hydrogen peroxide

A team of UK and US scientists have shown how hydrogen peroxide - an industrially important disinfectant and environmentally-friendly oxidising agent - can be made directly from oxygen and hydrogen. The new catalytic route could offer an efficient alternative to the existing indirect industrial process, the scientists say. 

While several catalysts are known to directly combine hydrogen and oxygen into hydrogen peroxide, they also promote a subsequent decomposition step, turning the desired product into water. Now, researchers at Cardiff University, UK, and Lehigh University, US, have developed a gold-palladium alloy catalyst that only promotes the desired reaction. 

’We can get very high selectivities [greater than 95 per cent], which are now comparable to the indirect process, and that makes a direct process a lot more feasible and viable,’ says Graham Hutchings, co-author of the research based at the Cardiff Catalyst Institute, Cardiff University. Key to the selectivity is an acid pre-treatment of the carbon support before the gold-palladium alloy nanoparticles are placed on it. This creates a much finer dispersion of metal particles, making them smaller which, the researchers believe, then block the active sites required for the subsequent decomposition reaction.

Important for industry

Direct approaches to make H2O could offer significant advantages over the current indirect process, in which oxygen is reacted with anthracene to give H2O2 and anthraquinone, before the latter is recycled back to anthracene by reaction with hydrogen.

’Most of the applications for using hydrogen peroxide tend to be at concentration levels of 3 to 8 volume per cent,’ says Hutchings. However, the indirect process produces it at concentrations above 50 per cent volume, and is only economical when run on large scale. ’With the direct process, you can imagine make small quantities of diluted H2O2 at a location where you want to use it,’ Hutchings adds. 

’The question of preparing H2O2 has really been a big challenge for industrialists for a very long time,’ says Sir John Meurig Thomas, honorary professor at the Department of Materials Science, University of Cambridge, UK. ’What they’ve done is demonstrate that it should be feasible to make a safe and direct method of preparing H2O2 and that’s a big step forward.’

’Local synthesis on a small scale obviously has advantages for medical applications like antiseptics,’ adds Pratibha Gai, professor of chemistry and physics at the University of York, UK. But Gai remarks that it remains to be seen whether this process can be scaled-up.

While the reaction has only been demonstrated for short reaction periods in small-scale lab experiments, the researchers suggest their discovery is of immense industrial importance - and are now collaborating with industrial partners.

Hutchings says the team are already working on a number of things to make scaling-up possible, such as demonstrating that the reaction can be sustained over longer periods, using a flow reactor as opposed to a batch reactor. ’It’s quite adventitious as to whether a particular breakthrough of this kind will make it to the marketplace, but potentially, I think it should,’ Thomas adds. 

James Urquhart