The right support to tackle trans fats

A palladium-based catalyst on diatomite — a siliceous powder derived from the remains of fossilized algae — could help lower levels of unhealthy ‘trans fats’ in hydrogenated oils like those in margarine, a study reported in the journal Catalysis in Industry has found¹.

The hydrogenation of vegetable oils, which transforms unsaturated fats into their saturated equivalents, alters the physical properties and quality of edible fats, creating solid fats with extended shelf life. However, the process can also change the naturally occurring ‘cis’ double bonds into the corresponding ‘trans’ isomers, producing trans fatty acids that the World Health Organisation has linked to increased risk of coronary heart disease.

Industrial vegetable oil hydrogenation for the manufacture of products, such as margarine, is performed using nickel-based catalysts. Although effective, this process requires high temperatures that promote the formation of trans isomers as well as decomposition of the produced fats and formation of toxic oil-soluble salts.

Kainaubek Toshtay and A. B. Auezov Al-Farabi, at the Kazakh National University in Kazakhstan, conceived the idea of loading small amounts of palladium on activated diatomite, an abundant natural resource in Kazakhstan, as a potential hydrogenation catalyst.

“The task was to obtain active sorbents to purify vegetable oils first and then develop a catalyst support to hydrogenate these oils using modified diatomite with a high surface area and predominant mesopore content,” Auezov says.

By treating the diatomite with acid and then heating it, the researchers produced a highly porous support with nanometre-sized pores. Next, they added a catalyst precursor solution to the activated support to allow tiny, well-defined palladium particles to deposit in a uniform fashion over the support surface.

The palladium catalyst was more active and selective at a lower temperature than a commercial nickel catalyst, and the transformation process at this lower temperature produced half the amount of trans isomers in the hydrogenated fat. A lower palladium concentration reduced the catalytic activity but produced fewer trans isomers. Taken together, these findings suggest that activated diatomite is a promising catalyst support for hydrogenation of plant oils.

Furthermore, the catalytic activity varied depending on the “specific composition of some vegetable oils,” Toshtay notes, most notably the initial unsaturated fat content.

The activity was highest for sunflower and safflower oils, which mostly consist of unsaturated linoleic acids, while the lowest was for rapeseed oil which, unlike sunflower oil, contains sulfur-based carbohydrates that poison catalysts.

The researchers are also currently evaluating the performance of other metal catalysts for the hydrogenation of vegetable oils.