Hydrogenation is a process that has been used by the food industry to extend the shelf life of oils. Unfortunately the hydrogenation process also results in trans fats, which have been linked to high ‘bad’ cholesterol levels and heart disease.
Removal of trans fats has been a major challenge for the food industry, and considerable efforts have been made to develop formulations that do not use hydrogenated fats. In the past, hydrogenated fats have been a fixture in shortenings, some margarines, and baked goods like crackers, cookies and snacks.
The new study, funded with a grant from the National Science Foundation, was conducted by researchers at the University of California, Riverside. It was published in the early online issue of Nature Materials this week.
Led by professor of chemistry Francisco Zaera, they used platinum as a catalyst, but controlled the shape of the particles so that the catalyst was more selective about the chemical reaction that took place – that is, production of semi-hydrogenated fats without the accompanying trans fats.
The best shape for the particles was tetrahedral, with the atoms arranged in a hexagonal honeycomb lattice. This, the researchers report, mean that the harmless cis formation of the hydrogenated fats was preserved.
When atoms were arranged in other lattices, trans fats tended to form.
The researcher have not commented on the practical implications for the method and whether it could be used at an industrial level; it is also unknown whether industry has expressed an interest in the technology.
Zaera and colleagues are hailing their discovery a breakthrough as it is the first time that selectivity has been achieved for a heterogeneous catalyst by controlling the structure of the surface.
Heterogeneous catalysts are those that are in a different phase than the reactant materials – that is, they are solid, while the reactants are gas or liquid. They usually have ill-defined structures at their surfaces, because they usually have to be dispersed in a high surface area support, for their use to be optimized.
"The more control we can exert on how we prepare catalysts, the more we can control the catalytic selectivity of a particular chemical process," Zaera said. "Our work shows that it is possible to make heterogeneous catalysts that afford us more control on selectivity. This opens the door, we hope, for chemists to think about achieving selectivity for other reactions via the design of specific heterogeneous catalysts with specific shapes."
Homogenerous catalysts, in the same phase as the reactors, have traditionally been used in high selectivity reactions such as medicines and other fine chemicals. However heterogenerous catalysts tend to be preferable as they are easy to prepare, handle and separate from the mixture, can be reused, have high stability, and are lower cost.
Fore the next phase of the research, Zaera and his tem plan to find other reactors where selectivity is required; they will also look to improve synthetic techniques for making selective catalysts.
Nature Materials 8, 132 - 138 (01 Feb 2009)Doi: 10.1038/nmat2371
Tuning selectivity in catalysis by controlling particle shape
Authors: Ilkeun Lee, Françoise Delbecq, Ricardo Morales, Manuel A. Albiter, Francisco Zaera