Gold and Palladium Clean Up Chemical-Making Process

Environmental Health News, Audrey Moores and Wendy Hessler

A team of researchers have cleaned up the process to produce a versatile compound—called benzylbenzoate—that kills disease-causing mites, stabilizes fragrances and is a building block for pharmaceuticals. Benzylbenzoate is made from toluene—a cheap and readily available chemical in crude oil. The new process applies oxygen gas and toluene to a material made of carbon and tiny particles of metals gold and palladium. No solvents are used, and no waste byproducts are generated. The finding is also important because it is a stepping stone to a method to convert natural gas into a useful fuel like methanol.

The research team from the UK and U.S. exposed toluene to oxygen at 160 degrees Celcius and 10 bars of oxygen for two days. Under these conditions, a very small fraction—2.9%—of toluene was converted into a mixture of benzaldehyde, benzoic acid and a small quantity of the desired benzylbenzoate.

Then, they tested several materials for their ability to improve the reaction. One was gold nanoparticles deposited onto titania, because it actively promotes oxidation of alcohols and carbon monoxide.

In another approach, they deposited tiny particles of gold and palladium inside the carbon pores. In this setting, gold and palladium form an alloy that has unique properties, different from both pure gold and pure palladium.

They also varied the proportion of gold and palladium in the system and measured how it was impacting the chemical process.

Each system was analyzed using two criteria: 1) conversion—the number of toluene molecules transformed—and 2) selectivity—Did one toluene transform into one or several kinds of molecules?

The gold and palladium nanoparticles on the porous carbon offered the best materials to spur the difficult reaction that transforms toluene to benzylbenzoate. This process required 6,500 times less metal than toluene.