A research team led by IIT Guwahati professors, Dr Akshai Kumar Alape Seetharam and Dr Hemant Kumar Srivastava, has formulated “pincer” catalytic systems that transform industrial and biomass waste into valuable chemicals. Tiny amounts of these “pincer catalysts” repeatedly convert large amounts of industrial waste such as glycerol into lactic acid and hydrogen. Such catalysts also efficiently convert bioethanol, a low-energy density fuel, into high-energy density butanol.
The conversion of valuable intermediates such as glycerol and ethanol, produced during the processing of biomass, into industrially useful chemicals has elicited much interest worldwide.
For instance, Glycerol, which is a by-product in biodiesel production, can be transformed into lactic acid and hydrogen — the former is extensively used in food, pharmaceutical, cosmetic and polymer industries, and the latter in the energy sector.
Similarly, ethanol obtained from biomass can be converted into high quality fuel. Bioethanol, which has lower energy density than gasoline and corrodes engine parts when used directly, can be transformed into higher energy butanol that is non-corrosive in nature.
“Pincer catalysts are complex molecules in which an organic moiety holds on tightly to a metal core, much like the claws of a crab”, explains Dr Akshai Kumar, adding that such an arrangement not only provides stability to the catalyst, but also selectivity to bring about the intended transformations.
The research team designed and tested a large library of “pincer catalysts” to be used for these transformations. The experiments were carried out under environmentally benign conditions without the use of hazardous reagents and solvents. The most efficient “pincer catalyst” was found to be one that had least crowding around the metal centre, scientists said.
Such an arrangement enabled easy removal of hydrogen from the starting materials, glycerol and ethanol, and their selective conversion into lactic acid and butanol, respectively.
The results of the experiments have been validated by theoretical studies. “Our computational studies have attributed the unprecedented activity of the pincer catalysts to the minimal crowding present at the metal centre and have enabled good understanding of the electronic and steric (crowding) factors that control reactivity,” says Dr Srivastava.
