First major discovery in hydroformylation in 50 years

Catalysts can be viewed as a parallel of the infamous philosopher's stone. They cannot change one element to another, but they can aid in transforming one chemical substance into another, while remaining unchanged themselves. Cobalt, a common mineral, does well in accepting atoms from other molecules and forming complex molecules.

Fellow researchers working on the study alongside Stanley include assistant professor of biological sciences David Vinyard and chemistry graduate students Drew Hood and Ryan Johnson. Researchers from ExxonMobil Chemical Company also contributed to the project.

Majority of industries -- about 75 percent -- choose to use rhodium-based catalysts because of the low-pressure technologies and cheaper-to-build facilities, but Stanley said not only can cobalt-based catalysts make more -- and better versions -- of certain aldehyde products, but the price of rhodium is excessive in comparison.

"A cationic cobalt bisphosphine catalyst is only about 20 times slower than the best rhodium catalysts," he said, "despite being 10,000 times less expensive." Today, the price of rhodium has reached closed to $9,800 an ounce, while cobalt has been steady around only 90 cents per ounce.

Louisiana, alone, has three large hydroformylation chemical plants: the ExxonMobil facility in Baton Rouge that uses the high-pressure cobalt catalyst technology; the Shell plant in Geismar that uses the medium-pressure phosphine-modified cobalt catalyst system; and the Dow chemical plant in Taft that uses low-pressure phosphine-modified rhodium catalysts.

"About 25 percent of products produced by hydroformylation require high-pressure cobalt or rhodium technologies," he explained. "This new cationic cobalt bisphosphine technology offers a far more energy efficient catalyst that can operate at medium pressures for these reactions."

Hydroformylation, or oxo, is the catalytic reaction that converts alkenes, carbon monoxide, and hydrogen into more complex organic products, like plasticizers -- a substance added to produce flexibility and to reduce brittleness -- and cleaning detergents.

Although the group's new cobalt catalyst has low selectivity to the generally desired linear aldehyde product for simple alkenes, Stanley said it has excellent activity and selectivity for internal branched alkenes that are difficult to hydroformylate.

For example, researchers are finding that washing detergents are less likely to dissolve in cold water because of their linearity -- a trait found in rhodium catalysts. Cobalt catalysts can make detergent molecules with more "branches" that can react to grease and water in a more efficient way.

Stanley said this is the first major discovery in hydroformylation in at least 50 years.

"What excites me the most is to have a discovery that could have real-life practical applications," he said. "Coming up with a catalyst that is very energy efficient, very green, that can actually be used on the large-scale, industrial side of things is the dream of every chemist."

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Journal Reference:

1. Drew M. Hood, Ryan A. Johnson, Alex E. Carpenter, Jarod M. Younker, David J. Vinyard, George G. Stanley. Highly active cationic cobalt(II) hydroformylation catalysts. Science, 2020; 367 (6477): 542 DOI: 10.1126/science.aaw7742