MATERIALS SCIENCE AND CHEMISTRY
Sulfur in Ethylene Epoxidation on Silver
Principal Investigator:
Travis Jones
Affiliation:
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin (Germany)
Local Project ID:
SEES2
HPC Platform used:
Hazel Hen of HLRS
Date published:
One of the most influential chemicals in our daily lives is something many of us will never see: ethylene oxide. This chemical is a critical ingredient in our modern world, used to make everything from the plastic fibers of our clothes to the lubricants in our cars. Virtually all of it is produced by the catalytic reaction of ethylene and oxygen over a silver surface but, while this process has been known since 1931, just how it happens has remained a mystery. Researchers have used high-performance computing to gain new insight into this mystery by identifying the structure of the active catalyst surface and showing how it mediates the reaction of ethylene and oxygen to form ethylene oxide.
Ethylene oxide is one of the most produced chemicals in the world, yet most of us will never encounter it in our daily lives because it is highly reactive. This reactive nature makes ethylene oxide a powerful disinfecting agent, but moreover, it makes ethylene oxide an important intermediate for the chemical industry. In fact, a vast majority of the nearly 20 million tons of ethylene oxide produced every year is used in the manufacture of consumer products ranging from antifreeze for car radiators to polyester fibers [1].
Nearly all of this ethylene oxide is produced by a method first discover in 1931; the direct catalytic oxidation of ethylene over silver. This reaction, however, competes with the thermodynamically favored combustion of ethylene to form CO2, as shown in Figure 1.
Industrially, the reaction can be run such that 80-90% of the incoming ethylene is used to produce ethylene oxide, meaning only 10-20% is burned. Silver is the only catalyst known to be capable of such high selectivity to ethylene oxide, and though this reaction is an important entry point into the industrial chemistry, the way in which silver catalyzes ethylene epoxidation has remained the subject of debate since shortly after its discovery in 1931.
In the Sulfur in Ethylene Epoxidation on Silver project, Travis Jones, a researcher at the Fritz-Haber-Institut der Max-Planck-Gesellschaft in Berlin, and coworkers from around Europe have worked to shed new light on how silver selectively produces ethylene oxide.
Figure 1: Simplified reaction network showing the partial oxidation of ethylene to ethylene oxide (path to upper right) and the competing combustion of ethylene (path to lower right).
A major challenge of the work was in identifying the nature of the surface of the active catalyst. This challenge was met by a combination of experiment and theory. To do so, the possible experimental outcomes were computed for a large series of hypothetical surface structures to determine which of these possible structures are present during different conditions. Computing such properties with the required fidelity, however, required determining how thousands of electrons are distributed over the atoms of each surface, a formidable task only made possible through the use of high-performance computing.
With the Hazel Hen supercomputer, the researchers were able to predict the surface structure of the active catalyst under varying experimental conditions [2-4]. Through this approach, the researchers showed that under conditions where a high selectivity to ethylene oxide is observed, the silver surface is covered in two different phases: i) a previously observed Ag/O phase and ii) a unique 2D dimensional phase of silver/SO4, where the ethylene gas likely represented the source of sulfur [2].
After the nature of the active surface was identified, high-performance computing played a key role in determining how the catalyst can produce ethylene oxide and CO2. By performing quantum mechanical calculations of the two competing reactions—shown schematically in Figure 1—, the researchers were able to demonstrate the Ag/O phase present during reaction is only involved in the undesired CO2 formation [5]. Surprisingly, the calculations predicted a novel sulfur-oxygen species in the 2D dimensional phase of silver/SO4 phase is involved in ethylene oxide production, a predication that was verified experimentally [2].
These novel results were only made possible because the Hazel Hen supercomputer provided the computing power necessary to predict the atomic structure of active surface and solve the quantum mechanical equations governing the reactivity of ethylene on that surface. The radically new picture of catalytic ethylene oxide production emerging from this work opens the door to new strategies to improve catalytic performance by including sulfur management strategies instead of oxygen management alone. Such strategies, when adopted by both scientific research and by industrial development, are expected to lead to selectivity increases and extended catalyst lifetimes.
References:
1. Ethylene Oxide. S. Rebsdat, D. Mayer, In: Ullmann's Encyclopedia of Industrial Chemistry (Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2012).
2. The Selective Species in Ethylene Epoxidation on Silver. Travis E. Jones, Regina Wyrwich, Sebastian Böcklein, Emilia A. Carbonio, Mark T. Greiner, Alexander Yu. Klyushin, Wolfgang Moritz, Andrea Locatelli, Tefvik O. Menteş, Miguel A. Niño, Axel Knop-Gericke, Robert Schlögl, Sebastian Günther, Joost Wintterlin, and Simone Piccinin, ACS Catalysis 2018 8 (5), 3844-3852 DOI: 10.1021/acscatal.8b00660 URL: pubs.acs.org/doi/abs/10.1021/acscatal.8b00660
3. Are multiple oxygen species selective in ethylene epoxidation on silver? Emilia A. Carbonio, Tulio C. R. Rocha, Alexander Yu. Klyushin, Igor Píš, Elena Magnano, Silvia Nappini, Simone Piccinin, Axel Knop-Gericke, Robert Schlögl, and Travis E. Jones, Chemical Science 2018 9, 990-998 DOI: 10.1039/C7SC04728B URL: dx.doi.org/10.1039/C7SC04728B
4. LEED-I(V) Structure Analysis of the (7 × √3)rect SO4 Phase on Ag(111): Precursor to the Active Species of the Ag-Catalyzed Ethylene Epoxidation. Regina Wyrwich, Travis E. Jones, Sebastian Günther, Wolfgang Moritz, Martin Ehrensperger, Sebastian Böcklein, Patrick Zeller, Arne Lünser, Andrea Locatelli, Tevfik Onur Menteş, Miguel Ángel Niño, Axel Knop-Gericke, Robert Schlögl, Simone Piccinin, and Joost Wintterlin,The Journal of Physical Chemistry C 2018 122 (47), 26998-27004 DOI: 10.1021/acs.jpcc.8b09309 URL: pubs.acs.org/doi/abs/10.1021/acs.jpcc.8b09309
5. Oxidation of Ethylene on Oxygen Reconstructed Silver Surfaces. Travis E. Jones, Regina Wyrwich, Sebastian Böcklein, Tulio C. R. Rocha, Emilia A. Carbonio, Axel Knop-Gericke, Robert Schlögl, Sebastian Günther, Joost Wintterlin, and Simone Piccinin, The Journal of Physical Chemistry C 2016 120 (50), 28630-28638 DOI: 10.1021/acs.jpcc.6b10074 URL: pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b10074
Scientific Contact:
Travis Jones
Fritz-Haber-Institut der Max-Planck-Gesellschaft
Department of Inorganic Chemistry
Faradayweg 4-6, D-14195 Berlin (Germany)
e-mail: trjones [@] fhi-berlin.mpg.de
January 2019
HLRS project ID: SEES2