Dilute solutions of hydrogen peroxide sit on shelves in medicine cabinets across the world.
Yet synthesizing the chemical at the large scale requires a surprisingly complicated process that is economically unfeasible for all but a few industrial facilities.
Chemists and engineers have long been working to develop simpler approaches, and a significant challenge can be stabilizing hydrogen peroxide once it forms because the molecule’s propensity to break down over the same materials utilized for its synthesis limits yields.
Now, chemical and biological engineers at the University of Wisconsin-Madison have uncovered new insight into how the compound decomposes. This advance, published March 21, 2016, in the Proceedings of the National Academies of Sciences, could inform efficient and cost-effective single-step strategies for producing hydrogen peroxide.
Consumers reach for highly watered-down hydrogen peroxide to clean out minor cuts and scrapes, but hydrogen peroxide also could be useful for numerous industrial processes, such as making precursor chemicals for flame retardants or flexible foam seat cushions.
Even though most applications would only require dilute solutions of hydrogen peroxide, current production methods rely on the few large facilities capable of synthesizing large volumes of highly concentrated chemicals; this necessitates transporting concentrated hydrogen peroxide solutions long distances to the end user, which comes with significant expense.
“A single-pot reaction would permit on-site production and make hydrogen peroxide an economically feasible oxidant for a number of chemical processes, in particular to replace more environmentally harmful oxidants such as chlorine,” says Tony Plauck, a chemical and biological engineering PhD student at UW-Madison and first author on the paper.
Scientists first proposed a single-step procedure to synthesize hydrogen peroxide in 1914 by combining pure hydrogen and oxygen gases over a material called a catalyst, which accelerates the chemical reaction by lowering the energy barriers preventing the components from combining, but doesn’t itself become transformed. Unfortunately, as more and more of the final hydrogen peroxide product accumulates in the vessel containing the mixture, the catalyst can also facilitate a subsequent undesirable chemical reaction wherein hydrogen peroxide breaks down into oxygen gas and water in a process called decomposition.
“One of the biggest catalytic challenges is finding a material that can actively produce hydrogen peroxide, but also something inactive towards decomposing hydrogen peroxide, which is a very thermodynamically favorable reaction,” says Plauck.
Some of the most widely studied materials for direct hydrogen peroxide synthesis are palladium-based catalysts. Many researchers investigate how hydrogen and oxygen come together and chemically react on regions of the catalyst’s surface called active sites. Yet, palladium can also catalyze the decomposition reaction, so the hydrogen peroxide produced under these conditions tends to rapidly break down, limiting the usefulness of palladium catalysts.
“Typical palladium catalysts exist as tiny highly dispersed palladium nanoparticles, which contain a variety of surface features that may vary in their ability to decompose hydrogen peroxide. If we understand where and how does hydrogen peroxide primarily decompose, we can propose some design criteria for future iterations of palladium catalysts,” says Plauck.
Plauck’s advisors on the project, Vilas Distinguished Achievement Professor and Paul A. Elfers Professor of Chemical and Biological Engineering Manos Mavrikakis and Vilas Research Professor and Michel Boudart Professor of Chemical and Biological Engineering James Dumesic, are experts in both theoretical and experimental approaches in catalysis. Their expertise in the computational techniques such as microkinetic modeling and density functional theory enabled the researchers to describe the experimentally observed decomposition reaction with unprecedented accuracy and detail.
“Hydrogen peroxide is currently prepared by a highly polluting process,” says Mavrikakis. “These insights open new avenues for the direct synthesis of a chemical that, among others, is needed in large volumes for the laundry and paper bleaching industry.”
The researchers first used computational modeling to investigate different surface features of palladium nanoparticles that may be responsible for hydrogen peroxide decomposition. Based on the theoretical models, they predicted experimentally observable parameters of the reaction, such as the rate of hydrogen peroxide decomposition. Then the researchers made those experimental measurements and revised various aspects of their models until the theoretical predictions agreed with the experiments.
Ultimately, their results suggested that multiple surface features of palladium nanoparticles can significantly contribute to the overall hydrogen peroxide decomposition activity of these catalysts. Furthermore, the theoretical models provided detailed insight into how the decomposition reaction might be suppressed on palladium.
The work was supported as part of a Dow Chemical Company University Partner Initiative with the University of Wisconsin-Madison. Eric E. Stangland of The Dow Chemical Company also contributed to the research.
Author: Sam Million-Weaver