New technology can speed up chemical reactions 10,000 times faster than the current reaction rate limit

A new discovery by University of Minnesota and University of Massachusetts Amherst researchers could increase the speed and lower the cost of thousands of chemical processes used in developing fertilizers, foods, fuels, plastics, and more.

A team of researchers from the University of Minnesota and University of Massachusetts Amherst has discovered new technology that can speed up chemical reactions 10,000 times faster than the current reaction rate limit.

These findings could increase the speed and lower the cost of thousands of chemical processes used in developing fertilizers, foods, fuels, plastics, and more.

The research is published online in ACS Catalysis, a leading journal of the American Chemical Society.

In chemical reactions, scientists use what are called catalysts to speed reactions. A reaction occurring on a catalyst surface, such as a metal, will speed up, but it can only go as fast as permitted by what is called the Sabatier’s principle. Often called the “Goldilocks principle” of catalysis, the best possible catalyst aims to perfectly balance two parts of a chemical reaction. Reacting molecules should stick to a metal surface to react neither too strong nor too weakly, but “just right.” Since this principle was established quantitatively in 1960, the Sabatier maximum has remained the catalytic speed limit.

Researchers of the Catalysis Center for Energy Innovation, funded by the U.S. Department of Energy, found that they could break the speed limit by applying waves to the catalyst to create an oscillating catalyst. The wave has a top and bottom, and when applied, it permits both parts of a chemical reaction to occur independently at different speeds. When the wave applied to the catalyst surface matched the natural frequency of a chemical reaction, the rate went up dramatically via a mechanism called “resonance.”

“We realized early on that catalysts need to change with time, and it turns out that kilohertz to megahertz frequencies dramatically accelerate catalyst rates,” said Paul Dauenhauer, a professor of chemical engineering and materials science at the University of Minnesota and one of the authors of the study.

The catalytic speed limit, or Sabatier maximum, is only accessible for a few metal catalysts. Other metals that have weaker or stronger binding exhibit slower reaction rate. For this reason, plots of catalyst reaction rate versus metal type have been called “volcano-shaped plots” with the best static catalyst existing right in the middle at the volcano peak.

“The best catalysts need to rapidly flip between strong and weak binding conditions on both sides of the volcano diagram,” said Alex Ardagh, post-doctoral scholar in the Catalysis Center for Energy Innovation. “If we flip binding strength quickly enough, catalysts that jump between strong and weak binding actually perform above the catalytic speed limit.”

The ability to accelerate chemical reactions directly affects thousands of chemical and materials technologies used to develop fertilizers, foods, fuels, plastics, and more. In the past century, these products have been optimized using static catalysts such as supported metals. Enhanced reaction rates could significantly reduce the amount of equipment required to manufacture these materials and lower the overall costs of many everyday materials.

Dramatic enhancement in catalyst performance also has the potential to scale down systems for distributed and rural chemical processes. Due to cost savings in large-scale conventional catalyst systems, most materials are only manufactured in enormous centralized locations such as refineries. Faster dynamic systems can be smaller processes, which can be located in rural locations such as farms, ethanol plants, or military installations.

“This has the potential to completely change the way we manufacture almost all of our most basic chemicals, materials, and fuels,” said Professor Dionisios Vlachos, director of the Catalysis Center for Energy Innovation. “The transition from conventional to dynamic catalysts will be as big as the change from direct to alternating current electricity.”

To read the full research paper, entitled “Principles of Dynamic Heterogeneous Catalysis: Surface Resonance and Turnover Frequency Response,” visit the ACS Catalysis website.

The discovery of dynamic resonance in catalysis is part of a larger mission of the Catalysis Center for Energy Innovation, a U.S. Department of Energy-Energy Frontier Research Center, led by the University of Delaware. Initiated in 2009, the Catalysis Center for Energy Innovation has focused on transformational catalytic technology to produce renewable chemicals and biofuels via advanced nanomaterials. Learn more on the Catalysis Center for Energy Innovation website.

Learn more: Research Brief: Energy researchers break the catalytic speed limit

 

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Nanoparticles convert carbon dioxide into methane using ultraviolet light for energy

Duke University researchers have engineered rhodium nanoparticles (blue) that can harness the energy in ultraviolet light and use it to catalyze the conversion of carbon dioxide to methane, a key building block for many types of fuels. Credit: Chad Scales

Illuminated rhodium nanoparticles catalyze key chemical reaction

Duke University researchers have developed tiny nanoparticles that help convert carbon dioxide into methane using only ultraviolet light as an energy source.

Having found a catalyst that can do this important chemistry using ultraviolet light, the team now hopes to develop a version that would run on natural sunlight, a potential boon to alternative energy.

Chemists have long sought an efficient, light-driven catalyst to power this reaction, which could help reduce the growing levels of carbon dioxide in our atmosphere by converting it into methane, a key building block for many types of fuels.

Not only are the rhodium nanoparticles made more efficient when illuminated by light, they have the advantage of strongly favoring the formation of methane rather than an equal mix of methane and undesirable side-products like carbon monoxide. This strong “selectivity” of the light-driven catalysis may also extend to other important chemical reactions, the researchers say.

“The fact that you can use light to influence a specific reaction pathway is very exciting,” said Jie Liu, the George B. Geller professor of chemistry at Duke University. “This discovery will really advance the understanding of catalysis.”

The paper appears online Feb. 23 in Nature Communications.

Despite being one of the rarest elements on Earth, rhodium plays a surprisingly important role in our everyday lives. Small amounts of the silvery grey metal are used to speed up or “catalyze” a number of key industrial processes, including those that make drugs, detergents and nitrogen fertilizer, and they even play a major role breaking down toxic pollutants in the catalytic converters of our cars.

Rhodium accelerates these reactions with an added boost of energy, which usually comes in the form of heat because it is easily produced and absorbed. However, high temperatures also cause problems, like shortened catalyst lifetimes and the unwanted synthesis of undesired products.

In the past two decades, scientists have explored new and useful ways that light can be used to add energy to bits of metal shrunk down to the nanoscale, a field called plasmonics.

“Effectively, plasmonic metal nanoparticles act like little antennas that absorb visible or ultraviolet light very efficiently and can do a number of things like generate strong electric fields,” said Henry Everitt, an adjunct professor of physics at Duke and senior research scientist at the Army’s Aviation and Missile RD&E Center at Redstone Arsenal, AL. “For the last few years there has been a recognition that this property might be applied to catalysis.”

Rhodium nanocubes observed under a transmission electron microscope. Credit: Xiao Zhang

Xiao Zhang, a graduate student in Jie Liu’s lab, synthesized rhodium nanocubes that were the optimal size for absorbing near-ultraviolet light. He then placed small amounts of the charcoal-colored nanoparticles into a reaction chamber and passed mixtures of carbon dioxide and hydrogen through the powdery material.

When Zhang heated the nanoparticles to 300 degrees Celsius, the reaction generated an equal mix of methane and carbon monoxide, a poisonous gas. When he turned off the heat and instead illuminated them with a high-powered ultraviolet LED lamp, Zhang was not only surprised to find that carbon dioxide and hydrogen reacted at room temperature, but that the reaction almost exclusively produced methane.

“We discovered that when we shine light on rhodium nanostructures, we can force the chemical reaction to go in one direction more than another,” Everitt said. “So we get to choose how the reaction goes with light in a way that we can’t do with heat.”

This selectivity — the ability to control the chemical reaction so that it generates the desired product with little or no side-products — is an important factor in determining the cost and feasibility of industrial-scale reactions, Zhang says.

“If the reaction has only 50 percent selectivity, then the cost will be double what it would be if the selectively is nearly 100 percent,” Zhang said. “And if the selectivity is very high, you can also save time and energy by not having to purify the product.”

Now the team plans to test whether their light-powered technique might drive other reactions that are currently catalyzed with heated rhodium metal. By tweaking the size of the rhodium nanoparticles, they also hope to develop a version of the catalyst that is powered by sunlight, creating a solar-powered reaction that could be integrated into renewable energy systems.

“Our discovery of the unique way light can efficiently, selectively influence catalysis came as a result of an on-going collaboration between experimentalists and theorists,” Liu said. “Professor Weitao Yang’s group in the Duke chemistry department provided critical theoretical insights that helped us understand what was happening. This sort of analysis can be applied to many important chemical reactions, and we have only just begun to explore this exciting new approach to catalysis.”

Learn more: LIGHT-DRIVEN REACTION CONVERTS CARBON DIOXIDE INTO FUEL

 

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Scientists collaborate to maximize energy gains from tiny nanoparticles

nanoscale-catalyst-particles-720px

This high-resolution transmission electron micrograph taken at the CFN reveals the arrangement of cerium oxide nanoparticles (bright angular “slashes” at the bottom of the image) supported on a titania substrate (background)‹a combination being explored as a catalyst for splitting water molecules to release hydrogen as fuel and for other energy-transformation reactions.

Small Particles, Big Findings

Sometimes big change comes from small beginnings. That’s especially true in the research of Anatoly Frenkel, a professor of physics at Yeshiva University, who is working to reinvent the way we use and produce energy by unlocking the potential of some of the world’s tiniest structures: nanoparticles.

“The nanoparticle is the smallest unit in most novel materials, and all of its properties are linked in one way or another to its structure,” said Frenkel. “If we can understand that connection, we can derive much more information about how it can be used for catalysis, energy, and other purposes.”

“This work could lead to big gains in energy efficiency and cost savings for industrial processes.”

— Eric Stach, CFN

Frenkel is collaborating with materials scientist Eric Stach and others at the U.S. Department of Energy’s Brookhaven National Laboratory to develop new ways to study how nanoparticles behave in catalysts—the “kick-starters” of chemical reactions that convert fuels to useable forms of energy and transform raw materials to industrial products.

“We are developing a new ‘micro-reactor’ that enables us to explore many aspects of catalytic function using multiple approaches at Brookhaven’s National Synchrotron Light Source (NSLS), the soon-to-be-completed NSLS-II, and the Center for Functional Nanomaterials (CFN),” said Stach, who works at the CFN.  “This approach lets us understand multiple aspects of how catalysts work so that we can tweak their design to improve their function. This work could lead to big gains in energy efficiency and cost savings for industrial processes.”

High-tech tools for science

Until now, the methods for understanding catalytic properties could only be used one at a time, with the catalyst ending up in a different state for each of the experiments. This made it difficult to compare information obtained using the different instruments. The new micro-reactor will employ multiple techniques—microscopy, spectroscopy, and diffraction—to examine different properties of catalysts simultaneously under operating conditions. By keeping particles in the same structural and dynamic state under the same reaction conditions, the micro-reactor will give scientists a much better sense of how they function.

“These developments have resulted from the combination of unique facilities available at Brookhaven,” said Frenkel. “By working closely with Eric, we realized that there was a way to make both x-ray and electron-based methods work in a truly complementary fashion.

Each technique has strengths, Stach explained. “At the NSLS, using powerful beams of x-rays, we can tell how the entire group of nanoparticles behaves, while electron microscopy at the CFN lets us see the atomic structure of each nanoparticle.  By having both of these views of the catalysts we can more clearly understand the relationship between catalyst structure and function.”

Said Frenkel, “It was very satisfying for us to conduct the first tests with the reactor at each facility and receive positive results. I am particularly grateful to Ryan Tappero, the scientist who runs NSLS beamline X27A, for his expert help with x-ray data acquisition.”

Frenkel has had an ongoing collaboration with scientists at Brookhaven. Last year, with post-doctoral research associate Qi Wang, Frenkel and Stach measured properties of nanoparticles using the x-rays produced by the NSLS as well as atomic-scale imaging with electrons at the CFN. As reported in a paper published in the Journal of the American Chemical Society earlier this year, they discovered that rather than changing completely from one state to another at a certain temperature and size, as had been previously believed, there is a transition zone between states when particles are changing forms.

“This is of significance fundamentally because until now, the structures were known to merely change from one form to another—they were never envisioned to coexist in different forms,” Frenkel said. “With our information we can explain why catalysts often don’t work as expected and how to improve them.”

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