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Steering conversion of carbon dioxide and ethane to the desired product

2 ) And ethane (C 2 H 6 ) Shows two possible reaction pathways. Here, carbon is black and oxygen. Is red and hydrogen is white. By studying catalysts that combine different metals and palladium, scientists have identified two configurations or phases that determine the reaction pathway. Above: When a metal forms an alloy, the catalyst breaks the carbon-carbon bond to produce carbon monoxide and hydrogen gas (syngas). Bottom: When the metal separates to form an oxide interface, the catalyst promotes the breaking of carbon-hydrogen bonds and ethylene (C). 2 H Four ), Carbon monoxide, and water. Credits: Brookhaven National Laboratory “width =” 800 “height =” 308 “/>

This schematic shows two possible reaction pathways for carbon dioxide (CO).2) Ethane (C2H6), Where carbon is black, oxygen is red, and hydrogen is white. By studying catalysts that combine different metals and palladium, scientists have identified two configurations or phases that determine the reaction pathway. Above: When a metal forms an alloy, the catalyst breaks the carbon-carbon bond to produce carbon monoxide and hydrogen gas (syngas). Bottom: When the metal separates to form an oxide interface, the catalyst promotes the breaking of carbon-hydrogen bonds and ethylene (C).2HFour), Carbon monoxide, and water.Credits: Brookhaven National Laboratory

Carbon dioxide conversion (CO2And putting ethane (an underutilized component of natural gas) in what we need is a great way to make a strong greenhouse gas and unused hydrocarbon reservoir work. .. However, it can be difficult to drive such a reaction towards a particular product or another product. Discovering the fundamental principles that determine the behavior of a catalyst, the chemical “dealmaker” that holds the reactants together, may provide the key to a more selective reaction.


In a study just published in Journal of the American Chemical SocietyChemists at Brookhaven National Laboratory, Columbia University, and Binghamton University at the US Department of Energy describe the ability to determine the catalytic selectivity of a set of reactions.2 And ethane (C2H6) Convert to syngas (useful for power generation or the production of liquid fuels) or ethylene (building blocks for the production of paints, plastics, and other polymers).

“Both routes are valuable, but we need to selectively drive the reaction to one or the other so that the desired product can be extracted more easily and economically,” in Brookhaven and Colombia. Co-appointed chemist Jingguang Chen said. Who led the research? “We were trying to identify the main catalytic principles for choosing one or another pathway, with the idea that these principles could guide the design of catalysts for a wider range of reactions. did.”

To discover the key principles, the team conducted a detailed study of a series of bimetal catalysts using a variety of metals combined with palladium. For each combination, they investigated how the metals bound and measured how the mixture of reactants and products changed during the reaction.

They also use powerful X-rays at the National Synchrotron Light Source II (NSLS-II) and advanced photon sources (two DOE Science Department user facilities at Brookhaven and Argonne National Laboratory, respectively) to catalyze the atomic structure of the catalyst. And studied electronic properties.

He also conducted computational modeling research using a computing cluster at the Functional Nanomaterials Center in Brookhaven and a supercomputer at the National Energy Research and Science Computing Center at Lawrence Berkeley National Laboratory at DOE.

Modeling studies use the Density Functional Theory (DFT) to construct catalysts as the reaction progresses, based on the binding energies between different atomic sets and the energies required for fracture and reconstruction. Predicted how the placement of the will change. Chemical bond.

“In both theory and experiment, we examined not only the catalyst samples that were initially prepared, but also the catalyst samples that undergo phase transformations during the reaction,” said Ping Liu, a DFT calculation expert in the catalytic reactivity and structure group. Mr. says. Brookhaven’s Chemistry Department.

“When you combine two metals, they stay in one structure and are called bulk alloys. But under reaction conditions, when the catalyst is exposed to CO2 And ethane, those metals start to move. This is why synchrotrons like the NSLS-II are so important. High-intensity photon sources allow us to measure the electronic and physical structure of the active site under reaction conditions, “he says.

Strong interaction It was essential to this study in techniques such as controlled catalytic synthesis, synchrotron-based characterization studies, kinetic measurements, and theoretical modeling, “says Liu.

Chen agreed. “Without any of these technologies, we would not have been able to reach a conclusion, and we could only do this in the setting of a national laboratory with facilities and expertise in all these areas. You can, “he said.

So what were those conclusions? The discovery of two main principles that determine whether metal atoms move, how they move, and how their shifts promote reaction selectivity: descriptors.

The main principles are: 1) Bimetal catalyst “formation energy” — how tightly the two metals are bonded, 2) the binding energy between the catalyst and the oxygen released from the CO2 In reaction.

As shown in the upper half of the figure, if the two metals are strongly bonded (for example, palladium is paired with cobalt), the catalyst will not bond with free oxygen and will remain an alloy.This catalytic arrangement facilitates carbon-carbon bond cleavage and selectively converts CO.2 It then converts ethane into carbon monoxide and hydrogen gas — a component of syngas.

However, if the catalyst’s affinity for free oxygen is strong enough to overcome the alloy’s formation energy (as in the case of palladium paired with indium), the paired metal catalyst Form an oxide shell. Its composition favors the breaking of carbon-hydrogen bonds and drives the pathways that produce ethylene.

Other metals that scientists have combined with palladium have fallen somewhere in between these two extremes. Scientists have used the complete dataset to extract two key principles.

“By using the descriptors we have identified, we are now able to guide the design of catalysts for either path to produce either syngas or ethylene,” Chen said. increase.

In addition, as Liu pointed out, “These are generalized descriptors and are not only applicable to one or two specific catalysts. Our experiments and theories indicate that this approach is a palladium-based catalyst. For other bimetal catalysts, this is something we will consider in the future. ”


The void confinement effect of the nanoreactor promotes heterogeneous catalysis


For more information:
Zhenhua Xie et al, general descriptor of CO2-supported selective C–H / C–C bond cleavage in ethane, Journal of the American Chemical Society (2022). DOI: 10.1021 / jacs.1c13415

Quote: Steering conversion of carbon dioxide and ethane to the desired product (February 9, 2022) from https: //phys.org/news/2022-02-conversion-carbon-dioxide-ethane-desired.html to 2022 Obtained on February 9, 2014.

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Steering conversion of carbon dioxide and ethane to the desired product

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