Breakthrough in Computational Chemistry: Models of Catalytic Reactions at the Atomic Level

In a major breakthrough in computational chemistry, chemical engineers from the University of Wisconsin-Madison have created a model that shows how catalytic reactions work at the atomic level. This newfound understanding can enable engineers and chemists to design better catalysts and improve industrial procedures, potentially resulting in huge energy savings, since catalysis is involved in the production of 90% of the products we use every day.

Catalysts speed up chemical reactions without changing themselves. They play an important role in the processing of petroleum products and the production of a wide variety of goods, including pharmaceuticals, plastics, food additives, fertilizers, environmentally friendly fuels and various industrial chemicals.

Scientists and engineers have spent decades fine-tuning catalytic reactions—but because it’s currently impossible to directly observe them at the extreme temperatures and pressures often associated with catalysis on an industrial scale, they don’t know exactly what happens to the nanoscale and the atoms. scales. This new research helps unravel this mystery with potentially huge ramifications for the industry.

In fact, just three catalytic reactions—the reformation of steam and methane to produce hydrogen, the synthesis of ammonia to produce fertilizer, and the synthesis of methanol—use nearly 10% of the world’s energy.

said Manos Mavrikakis, a professor of chemical and biological engineering at Madison who led the research. “By reducing the energy you need to run all of these processes, you also reduce the impact on the environment.”

Mavrikakis and postdoctoral researchers Lang Xu and Konstantinos G. Papanicolaou along with graduate student Lisa G publish news of their progress in the April 7, 2023 issue of the journal Knowledge.

Manu Mavrikakis. Credit: University of Wisconsin-Madison

In their research, University of Washington Madison engineers developed and used powerful modeling techniques to simulate catalytic reactions at the atomic level. In this study, they observed reactions involving transition metal catalysts in the form of nanoparticles, which include elements such as platinum, palladium, rhodium, copper, nickel and others important for industry and green energy.

According to the current model of solid surface catalysis, the solid atoms of the transition metal catalyst provide a two-dimensional surface to which the reactant chemicals attach and participate in the reaction. When enough pressure, heat, or electricity is applied, the bonds between the atoms in the chemical reactants break, allowing the fragments to recombine into new chemical products.

“The prevailing assumption is that these metal atoms are highly bonded to each other and provide only ‘landing points’ for the reactants. What everyone assumed was that the metal-metal bond remained intact during the reaction it catalyzed,” said Mavrikakis. “So here, for the first time, we are asking a question. , “Could the energy breaking the bonds in the reactants be as great as the energy needed to break the bonds in the catalyst?”

According to the Mavrikakis model, the answer is yes. The energy provided for many catalytic processes is sufficient to break bonds and allow single metal atoms (known as adatoms) to separate and begin walking on the surface of the catalyst. These adatoms coalesce into groups, which act as sites on the catalyst where chemical reactions can occur much more easily than the original solid surface of the catalyst.

Using a combination of special calculations, the team looked at the important industrial interactions of eight transition metal catalysts and 18 reactants, determining the energy levels and temperatures that might form these tiny metal clusters, as well as the number of atoms in each group, which can also have a big effect on reaction rates.

Their experimental collaborators at the University of California, Berkeley, used an atomic scanning tunneling microscope to examine the adsorption of carbon monoxide on nickel (111), a stable crystalline form of nickel useful in catalysis. Their experiments confirmed that models showing defects in catalyst structures can also influence how single metal atoms dissociate, as well as how reaction sites form.

Mavrikakis says the new framework challenges the foundations of how researchers understand catalysis and how it occurs. This may also apply to other non-metallic catalysts, which he will investigate in the future. It is also relevant for understanding other important phenomena, including erosion and tribology, or the interaction of moving surfaces.

“We are revisiting some very well-established assumptions in understanding how catalysts work and, more generally, how molecules interact with solids,” said Mavrikakis.

Reference: “Active Site Formation in Transition Metals Through Reaction-Induced Migration of Surface Atoms” by Lang Shaw, Konstantinos G. Papanicolaou, Barbara AJ Lechner, Lisa G, Gabor A. Somorgay, Mikel Salmeron Manos Mavrikakis 6 Apr. 2023 Available here. Knowledge.
DOI: 10.1126/science.add0089

The authors acknowledge support from the US Department of Energy, Basic Energy Science, Department of Chemical Science, and Catalysis Science Program, Grant DE-FG02-05ER15731; Office of Basic Energy Sciences, Division of Materials Science and Engineering, US Department of Energy under Contract No. DE-AC02-05CH11231, with Structure and Dynamics of Material Interfaces Program (FWP KC31SM).

Mavrikakis acknowledges financial support from the Miller Institute at UC Berkeley through the Miller Visiting Professorship in the Department of Chemistry.

The team also uses the National Energy Research Scientific Computing Center, a DOE Science Office User Facility supported by the US Department of Energy’s Office of Science under Contract No. DE-AC02-05CH11231 uses NERSC award BES-ERCAP0022773.

Part of the computational work was performed using the supercomputing resources at the Center for Nanomaterials, the DOE office of the Science User Facility located at Argonne National Laboratory, with support from DOE contract DE-AC02-06CH11357.