Rice University team discovers highly efficient catalyst

Prof Michael Wong and his team reported this month that sub-nanometre clusters of tungsten oxide lying on top of zirconium oxide are a highly efficient catalyst. The catalyst turns straight-line molecules of n-pentane, one of many hydrocarbons in petrol, into better-burning branched n-pentane.

While the catalytic capabilities of tungsten oxide have long been known, it takes nanotechnology to maximise their potential, said Wong, a Rice professor of chemical and biomolecular engineering and of chemistry.

After the initial separation of crude oil into its basic components - including petrol, kerosene, heating oil, lubricants and other products - refineries crack (by heating) heavier by-products into molecules with fewer carbon atoms that can also be made into petrol. Catalysis further refines these hydrocarbons.

Refineries strive to make better catalysts, said Wong, although ‘compared with the academic world, industry hasn’t done much in terms of new synthesis techniques, new microscopy, new biology, even new physics. But these are things we understand in the context of nanotechnology.

‘We have a way to make a better catalyst that will improve the fuels they make right now. At the same time, a lot of existing chemical processes are wasteful in terms of solvents, precursors and energy. Improving a catalyst can also make the chemical process more environmentally friendly. Knock those things out and they gain efficiencies and save money.’

Wong and his team have worked for several years to find the proper mix of active tungsten oxide nanoparticles and inert zirconia. The key is to disperse nanoparticles on the zirconia support structure at the right surface coverage.

‘We want to maximise the amount of these nanoparticles on the support without letting them touch,’ added Wong. ‘If we hit that sweet spot, we can see an increase of about five times in the efficiency of the catalyst. But this was very difficult to do.’

The team had to find the right chemistry, at the right high temperature, to attach particles a billionth of a metre wide to grains of zirconium oxide powder. With the right mix, the particles react with straight n-pentane molecules, rearranging their five carbon and 12 hydrogen atoms in an isomerisation process.

According to Rice University, making the catalyst should be straightforward for industry now that the catalyst formula is known.

‘Because we’re not developing a whole new process – just a component of it – refineries should be able to plug this into their systems without much disruption,’ said Wong.

Maximising petrol is important as the world develops new sources of energy, added Wong. ‘There’s a lot of talk about biofuels as a significant contributor in the future, but we need a bridge to get there. Our discovery could help by stretching current fuel-production capabilities.’

A new paper detailing the process can be found in the Journal of the American Chemical Society. Wong and his team were assisted by labs at Lehigh University, the Centre for Research and Technology Hellas and the DCG Partnership of Texas.