A new catalyst for converting methane, the main component of natural gas, into a liquid fuel–methanol–has been developed by researchers in Germany. The catalyst could make direct conversion of methane to methanol cheaper than it is with existing catalysts, but it will likely fall short of a holy grail of hydrocarbon chemistry–a catalyst that allows natural gas to replace petroleum fuels on a large scale.
The new catalyst is based on one of the few catalysts that convert methane directly to methanol, at low temperatures, without producing much carbon dioxide or other unwanted byproducts. That catalyst, developed by Roy Periana, now a professor of chemistry at the Scripps Research Institute, proved too expensive to commercialize.
The new catalyst, described in the early online version of the journal Angewandte Chemie, has “solved one of the main problems with Periana’s catalyst,” says Ferdi Schüth, director of the Max Planck Institute for Coal Research, who led the work. Because Periana’s catalyst is a liquid dissolved in sulfuric acid, it’s difficult to recycle, a serious problem because the catalyst requires the expensive metal platinum. The new catalyst is a solid, says Schüth, and so is much easier to recycle because it can be removed from the sulfuric acid simply with filters.
Schüth says the discovery of the solid catalyst was “serendipitous.” His colleagues had developed a polymer with a molecular structure that he recognized was similar to Periana’s catalyst. He was able to incorporate platinum into that structure and showed that the resulting solid catalyst performed as well as the liquid version.
Methane-based fuels could be significantly cleaner than petroleum ones. What’s more, the supply of natural gas is vast, with large supplies now being accessed with new drilling techniques and orders of magnitude more potentially available in the form of methane hydrates at the bottom of the ocean. But because it is a gas, methane is more expensive to transport and less convenient for use in vehicles than liquid fuels, and so far chemical methods of converting it to a liquid have been costly.
While the new catalyst does solve one of the problems with the Periana catalyst, “it is by no means the biggest problem,” says Jay Labinger, faculty associate in chemistry at Caltech. Indeed, Periana says that the development of a solid version of his catalyst will not be enough to commercialize it. He is working on new catalysts that use the similar mechanisms but cheaper and more effective materials.
The two key issues are typical problems for experimental catalysts–they don’t work fast enough, which increases the size and cost of equipment needed, and they don’t produce high enough concentrations of the desired product, making it expensive to separate the product from other chemicals. Labinger estimates that the rates of the new German catalyst need to increase by an order of magnitude, and Periana says the concentrations need to increase three- to fivefold.
Periana suggests, however, that the German catalyst may offer new directions for research, especially if the mechanisms involved in producing the methanol are different from his liquid catalyst. Indeed, Schüth says that one key component of Periana’s catalyst, chlorine, isn’t necessary with the new form, suggesting it could work by different means. Meanwhile, he’s also developing catalysts that use different materials. One is promising, he says, producing methanol at rates two times faster than Periana’s liquid catalyst.