Catalyst materials accelerate chemical processes without undergoing modifications. They are essential in producing pharmaceuticals, polymers, food additives, fertilizers, green fuels, industrial chemicals, and many other items.
Chemical engineers at the University of Wisconsin Madison have created an atomic-scale model of catalytic processes. 90% of the items we see in our daily lives are made, at least partially, by catalysis. This understanding could allow engineers and chemists to develop more effective catalysts and adjust industrial processes, potentially saving significant energy.
Scientists and engineers have spent decades fine-tuning catalytic reactions. However, because it is currently impossible to directly observe those reactions at the extreme temperatures and pressures frequently involved in industrial-scale catalysis, they have yet to learn exactly what is happening on the nano and atomic scales. This new study contributes to uncovering that riddle, with potentially significant implications for the industry.
However, three catalytic reactions require nearly 10% of the world’s energy: steam-methane reforming to make hydrogen, ammonia synthesis to produce fertilizer, and methanol synthesis.
Manos Mavrikakis, a professor of chemical and biological engineering at UW–Madison who led the research, said, “If you decrease the temperatures at which you have to run these reactions by only a few degrees, there will be an enormous decrease in the energy demand that we face as humanity today. By decreasing the energy needed to run all these processes, you are also decreasing their environmental footprint.”
In order to mimic catalytic reactions involving transition metal catalysts in nanoparticle form, which include metals like platinum, palladium, rhodium, copper, nickel, and other crucial elements in industry and renewable energy, the UW-Madison engineers created and employed potent modeling tools.
According to the current rigid-surface model of catalysis, The closely packed atoms of transition metal catalysts form a 2D surface that chemical reactants adhere to and engage in reactions.
The bonds between the particles in the chemical reactants are broken when enough pressure, heat, or electricity is applied, allowing the fragments to recombine into new chemical products.
He said, “The prevailing assumption is that these metal atoms are strongly bonded to each other and simply provide ‘landing spots’ for reactants. Everybody has assumed that metal-metal bonds remain intact during the reactions they catalyze. So here, for the first time, we asked the question, ‘Could the energy to break bonds in reactants be of similar amounts to the energy needed to disrupt bonds within the catalyst?”
The most important detail in this article is that the energy required for many catalytic processes to occur is sufficient to break bonds, allowing single metal atoms to break free and begin moving on the catalyst surface. These adatoms join together to form clusters, which act as catalyst sites where chemical reactions can occur far more quickly than on the catalyst’s original stiff surface.
The researchers studied eight transition metal catalysts and 18 reactants in industrially significant interactions, discovering the energy levels and temperatures that were likely to result in the formation of such small metal clusters and the number of atoms in each group, which can have a significant impact on reaction speeds.
Additionally, they examined carbon monoxide adsorption on nickel (111), a stable, crystalline form of nickel used in catalysis, using atomically-resolved scanning tunneling microscopy. Their research supported models that suggested different catalyst structural flaws could also affect how reaction sites occur and how individual metal atoms pop loose.
According to Mavrikakis, the new approach calls into question the fundamental assumptions behind how researchers see catalysis and how it operates. He will look into other non-metal catalysts in his upcoming study because it might also apply to them. It is pertinent to comprehend other significant processes, such as corrosion and tribology or the interaction of moving surfaces.
He said, “We’re revisiting some well-established assumptions in understanding how catalysts work and, more generally, how molecules interact with solids.”
- Xu, L., Papanikolaou, Mavrikakis,etal. Formation of active sites on transition metals through reaction-driven migration of surface atoms. Science. DOI:10.1126/science.add0089