Researchers develop new, more-efficient selective oxidation catalyst

"Our new catalysts contain a transition metal, such as zirconium or hafnium, bound to several organic ligands and act as a bank for oxygen atoms and electrons," Manz said. "Oxidants, such as oxygen molecules, deposit oxygen atoms into the bank. Substrate molecules, such as organic compounds containing double bonds, can extract oxygen atoms from this bank to produce oxidized products.

"By stabilizing the energy of oxygen atoms and electrons, the catalyst lowers the energy cost of selective oxidation reactions just like a bank facilitates the sale of a car from one person to another. Our catalyst improves this process by passing through a chemical intermediate -- called an eta-3-ozone intermediate -- in which the two oxygen atoms from molecular oxygen can be easily separated from each other and passed on to two different molecules of substrate. This makes the reaction more efficient by eliminating the need to form a reaction co-product," continued Manz.

To develop the new catalysts, Manz and Yang spent more than one million computational hours on supercomputing clusters in the eXtended Science and Engineering Discovery Environment (XSEDE), a National Science Foundation funded program.

"Our goal is to develop less expensive, more environmentally friendly, and lower energy selective oxidation processes by using molecular oxygen as the oxidant," Manz said. "The key challenge is to develop catalysts and reaction processes that can sequentially transfer oxygen atoms from molecular oxygen to substrate molecules without producing co-products or by-products.

"For simple substrates, such as oxidizing ethylene to produce ethylene oxide, this is already possible using commercialized processes," he said. "However, for more challenging substrates this is not yet commercially feasible. Millions of tons of environmental waste by-products are produced each year due to inefficient selective oxidation processes. These inefficient selective oxidation processes also waste many gigawatts of energy.

"Our new catalyst family activates molecular oxygen and allows both of its oxygen atoms to be transferred to substrate molecules, thereby eliminating the need to produce a co-product. This should enable new selective oxidation processes to be commercially developed that lower waste generation and energy consumption."

Manz and Yang are working with Arrowhead Center, which has filed a patent for the catalyst. The duo hopes to collaborate with researchers to synthesize and experimentally test their catalysts.

"Our long-term goal is to work with industrial companies to commercialize this new technology," Manz said. "We are interested in developing commercial applications for fine chemical production, commodity chemical production, or both."

Last month, the pair's paper, "Computationally designed zirconium organometallic catalyst for direct epoxidation of alkenes without allylic H atoms: aromatic linkage eliminates formation of inert octahedral complexes," was published in Theoretical Chemistry Accounts.

Manz said he and Yang were happy with the paper's publication, which is their third in a series on a new catalytic route passing through eta-3-ozone intermediates for selective oxidations using molecular oxygen as the oxidant without requiring a co-reductant.

"Based on our most recent computations, we are currently writing a follow-up paper that will use our new catalyst in a two-step process that generates an intermediate oxidant to selectively oxidize even more challenging substrates such as propene to produce propylene oxide," Manz said.