CHANGE of scene

The Robert Robinson Laboratories Liverpool University's chemistry department have the scruffy-but-homely atmosphere common to most university labs. Posters for student elections jostle with lab rosters on the walls, and the air is filled with the strangely comforting smell of a melange of organic solvents. Walking into the Leverhulme Centre for Innovative Catalysis (LCIC), on the first floor, is like entering a different world an enclave of quiet, buff-painted, modern art-adorned corridors. Something different is going on here.

Since the LCIC's present director, Eric Derouane, came aboard in 1995, the centre has expanded from three staff to a permanent staff of nine with 60-65 full-time researchers. According to Derouane, the centre sees itself floating between industry and academia. 'In a way,' he says, 'we're carrying out industry's blue skies research for them. Some 80-90 per cent of our work is long-term, but it's directed by the needs of industry.'

The centre doesn't operate like a university department. 'We are the only centre in the UK to bring together heterogeneous, homogeneous, and biological catalysis with surface science,' comments assistant director Rasmita Raval. 'We can put together an interdisciplinary team, like an R&D team in industry. But we have a council of internationally recognised scientists who make sure we're doing real science, not research that industry ought to be doing itself.'

A cluster of cherries

The centre has gained such a standing internationally, says Derouane, that it can now 'cherry-pick' scientists from around the world. One such is Ivan Kozhevnikov, who specialises in the use of polyoxymetallates metal-oxygen clusters to catalyse a wide range of reactions with very high selectivity.

'Polyoxymetallates are currently hot topics in catalysis,' he explains, 'because many of their properties can be varied easily.' Acidic polyoxymetallates, known as heteropolyacids, are attracting particular interest, he adds, as they can replace liquid acid catalysts, such as sulphuric acid and aluminium chloride. 'They are stronger solid acids than sulphuric acid, and are more efficient, with broader versatility.'

Heteropolyacids are the focus of much attention for the major petrochemical companies. BP, for example, is testing their potential on several large-scale processes. 'They can do this at low temperatures and pressures; also, they often display greater selectivity,' says Kozhevnikov

'The chemistry that occurs is multistep and extremely complex, but we can make multifunctional catalysts so the whole thing work in a single vessel.'

The inside of the reactor is also at the forefront of Jianliang Xiao's research. But Xiao is concerned with the catalyst's environment. 'Lots of organic solvents are being phased out because of environmental factors,' he explains, 'so we have to look at new ways to do the reactions.' Xiao's work focuses on two of these new media: supercritical fluids, particularly carbon dioxide, and ionic liquids.

In simple terms, ionic liquids are molten salts. Xiao uses organic ions, chiefly based around an imidozolium cation (an aromatic five-membered ring containing two nitrogen atoms, separated by a carbon, each bearing organic substituents). These are liquid from 200 C down to 100 C.

Ionic liquids have no vapour pressure, says Xiao, which means no volatile emissions. But for catalyst scientists, their chief advantage is that their solvent power can be 'tuned' easily and precisely, by changing the substituents on the nitrogen atoms. 'For example,' Xiao enthuses, 'you could make the catalyst soluble in the liquid, but the product insoluble. You'd get automatic product separation, and you wouldn't be faced with the problem of how to recover the homogeneous catalyst.'

The liquids can also affect how the catalysts work. Reaction mechanisms are determined by the transition state formed by catalyst and reactants, but this is influenced by the solvent structure. Changing this can make the catalyst more effective or selective, claims Xiao.

Xiao's work on supercritical (SC) fluids parallels that on ionic liquids, because these too have tuneable solvent power. 'Around the critical point of carbon dioxide 72.9atm pressure and 31 C the density of the fluid changes dramatically. Solvent power is a function of density.' Dropping the pressure slightly can make a catalyst or product crash out of solution, with no solvent residues.