Tag Archives: catalysts

A switch to nature-based catalyst raises efficiency, reduces waste.

Largeron, M, and M-B Fleury. 2012. A biologically inspired Cu(I)/topaquinone-like co-catalytic system for the highly atom-economical aerobic oxidation of primary amines to imines. Angewandte Chemie http://dx.doi.org/10.1002/anie.201200587.

Synopsis by Jean-Philip Lumb, Aug 23, 2012

A multistep process to produce intermediary chemicals for manufacturing can be done in one step with only three ingredients and little to no waste, report French chemists. Their method combines a starter catalyst with a small amount of copper and oxygen from the air to transform base compounds – called amines – into other chemical middlemen – known as imines. Manufacturers use imines extensively to produce products and drugs.

In comparison to current methods, the novel process is more efficient. It uses fewer chemicals, relies on safer chemicals, creates less waste and works under normal temperature and pressure. Additional studies will need to repeat and optimize the methods before they can be used on an industrial scale.

A major direction in the field of green chemistry is to develop ways to turn one chemical into another with no leftover atoms – and therefore little to no waste. This increases chemical efficiency. Calculating the number of atoms that go into the process and comparing them to what comes out in the end product is a way to measure chemical efficiency. These reactions – dubbed atom economy – strive to have the two equal each other.

Atom economy is a big shift away from the traditional processes that rely on additives known as activating reagents, which are added multiple times during a chemical synthesis to propel the reactions forward. Efficiency is reduced, since in each step, the activating reagent is not incorporated into the product and is lost as waste.

This is particularly troubling when producing pharmaceuticals where multiple steps are required to transform starting materials into commercial products. In these cases, activating groups increase chemical waste, since activation often requires an additional step in the overall sequence and frequently creates equal amounts of a byproduct.

Activating reagents are usually needed for oxidation reactions, which are particularly important in chemical production. During oxidation, hydrogen is removed from its parent molecule and is added to another. The process is chemically inefficient because it creates an equal amount of chemical waste for each molecule that is oxidized.

Researchers are looking to plants and animals for natural ways to improve efficiency during oxidation reactions. One way is to replace activating reagents with catalysts. Biological systems are extremely efficient and routinely use catalysts in reactions where the chemical industry uses activating reagents. Unlike activating reagents, catalysts can be used in very small quantities. This would dramatically reduce chemical waste, since small quantities of catalysts affect a reaction and they can be frequently recovered after a reaction.

In this study, researchers in France have accomplished this by replicating the activity of an important class of enzymes known as copper-containing amine oxidases (CuAOs). These enzymes control the concentration of nitrogen-containing molecules in numerous biological settings, including in people. The enzymes drive the oxidation of an amine to an imine. By carefully modulating the reaction conditions, the authors were able to produce a variety of imines from readily available starting materials under very mild conditions. Water was the only byproduct.

The authors note the reactions will need more tweaking before they can be used industrially. Nevertheless, the reaction conditions go a long way toward alleviating the typical waste associated with amine oxidation and provide a promising direction for future research.

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Silver speeds chemical reactions with oxygen.

Huang, Z,  X Gu, Q Cao, P Hu, J Hao, J Li and X Tang. 2012. Catalytically active single-atom sites fabricated from silver particles. Angewandte Chemie http://dx.doi.org/10.1002/anie.201109065.

Synopsis by Marty Mulvihill

In a new study, researchers report using silver in a safer, cheaper, cleaner method to run chemical reactions – specifically the widely-used and universally-important oxidation reactions. The new system works at low temperatures and is 10 times more efficient than previous attempts.

In the quest to save money and prevent waste when making chemicals for industrial and consumer applications, laboratory chemists are looking to a new generation of catalysts to speed up reactions with less mess. Catalysts are added to chemical reactions to help efficiently transform raw materials into products.

In a recent advance, researchers report how silver – placed in a specific pattern on a stable molecular nanostructure – can act as a catalyst and promote reactions at low temperatures using safe and abundant materials like oxygen in the reaction.

The new system is 10 times more efficient than previous attempts. It not only conserves resources, but it will help researchers better understand how to use oxygen in industrial applications.

The silver-based catalyst converts oxygen from the air into a chemically reactive form that allows common industrial chemicals to be made more efficiently. The products of these reactions are the starting materials for a majority of chemical products.

Unlike previous catalysts that promote chemical reactions with oxygen, this silver-based model performs very well at low temperatures. Temperature is a key consideration. Lower temperatures reduce the amount of energy and potentially the cost of running these important reactions.

The new catalyst created by researchers in China represents a 10-fold improvement over previous methods for making these chemical products.

Catalysts increase the speed of chemical reactions. Yet they are not affected in the process. This allows catalysts to be reused and has helped expand their use in a wide range of manufacturing applications.

In addition to working at low temperatures, the catalyst uses oxygen as the only additional reactant. Traditionally oxidation reactions have used harsh chemicals and generated large quantities of hazardous waste. In this reaction the oxygen is incorporated into the product without producing any additional waste.

The results will help chemists understand how to better activate oxygen. Oxygen is often slow to react with other molecules because the molecule is very stable. It is usually found as two atoms paired together, hence its chemical nickname O2. These pairs must be broken apart before the individual oxygen atoms can react with other chemicals.

The new catalyst breaks the oxygen atoms apart. It uses individual silver atoms located near a surface that does not have oxygen as part of its molecular structure.

Using advanced chemical analysis tools, the scientists precisely characterized and explained the reactivity of the silver atoms that are attached to the surface of manganese oxide particle support. They verified the structure of their active catalyst with advanced microscopy and X-ray scattering techniques.

The catalyst is only in the development stages. Before it is ready for use in the chemical industry, chemists will need to show that it can perform oxidation reactions cheaply on a wide range of organic molecules. Read more science at Environmental Health News.

Chemists build a better biodiesel process.

Thitsartarn, W, and S Kawi. 2011. An active and stable CaO-CeO2 catalyst for transesterification of oil to biodieselGreen Chemistry http://dx.doi.org/10.1039/c1gc15596b.

Synopsis by Wim Thielemans, Dec 20, 2011

Scientists in Singapore develop a new chemical catalyst with fewer drawbacks than current versions to help make biodiesel production more attractive and sustainable.

A modified version of a well-known but inefficient chemical catalyst can propel faster, cleaner reactions that turn plants into diesel fuel better than existing methods.The new calcium-based catalyst is more reactive, stable and easier to recover from the final product, the Singapore researchers report in the journal Green Chemistry. While the catalyst may solve a major stumbling block in the effort to produce biodiesel, the process will need more testing in industrial settings.

Biodiesel production is gaining in importance as petroleum supplies become more limited and concern about climate change grows. Biodiesel can be used in unmodified diesel engines. Its use results in near-zero carbon dioxide emissions, if estimates consider plant growth, which extracts carbon dioxide from the atmosphere.

Biodiesel is generally produced from plant oils. Plant oils are star-like molecules with three arms. To turn the plant oil into biodiesel, the three arms need to be removed from the center. The separated arms then form the biodiesel.

Unfortunately, this transformation does not happen readily without chemical help. Chemists must use other molecules, called catalysts, to speed up this reaction.

Current catalysts make the reaction go faster, but they have various drawbacks that hamper their use on the large scale of a commercial biodiesel process. These drawbacks include: large amounts of catalyst may be needed; high temperatures are necessary to propel the reactions; the catalyst may be less stable if it is used for a longer time; it can be difficult to remove the catalyst from the final product; and the solid catalysts may be slow to dissolve into the biodiesel product.

Calcium-based catalysts – which are cheap and abundant – can break up the star-like plant oils. Unfortunately, they dissolve into the biodiesel and removing them generates large amounts of wastewater.

To solve this problem, researchers from Singapore made a new and very reactive calcium-based catalyst with high stability. The catalyst was formed from a solution containing calcium and cerium – a metal found in a number of minerals. By making the solution less acidic, the catalyst precipitates out and is recovered by filtering and drying.

The ratio of calcium and cerium was varied to see which combination would give the best catalyst performance. Cerium alone does not work very well.

The best catalyst found could be reused up to 18 times with more than 90 percent of plant oils separated into their arms. Very low amounts of the catalyst dissolved into the biodiesel.

This work is certainly promising as it may make biodiesel production more sustainable and cheaper. Of course, the catalyst will need to be tested in an industrial process. Read more science at Environmental Health News.

 

Pie Chart

Analysis of Green Chemistry publications over the past four years.

This figure is taken from Green chemistry: state of the art through an analysis of the literature by V. Dichiarante, D. Ravelli and A. Albini. Green Chemistry Letter and Reviews Vol. 3, No. 2, June 2010, 105-113.

 

As the label indicates, the pie chart shows a distribution of green chemistry topics as analyzed by articles produced in the year 2008. The majority of the pie chart (about 50%) is attributed to catalysis – or starting a reaction, under more favorable conditions that require less resources, whether those resources are heat, energy, reagents etc. Specifically, metal catalysts were the most cited catalysts used in many different reactions, specifically in those involving enzymes. Acids are also seen in this category, and according to the article, are used mainly in condensation reactions. The next largest section of the pie (about 40%) is attributed to media, or where/in what the reaction takes place. Many reactions require some liquid for a reaction to take place. Many of these liquids, especially in organic chemistry, are volatile or toxic compounds. As a result, most of the research done with green chemistry and the media of reactions use either no solvent, which allows for most reduction of waste. Water has also gained a prominent role in green chemistry literature as it is our universal solvent and usually can be recycled in a reaction. Ionic liquids are the third major media hit; they are liquids that have charged compounds in the solution to help guide a reaction. Ionic liquids are usually not volatile and are stored more easily compared to their organic counterparts. Finally, the last 10% of the pie chart goes to ‘new methods,’ or novel ways to do old reactions. Using microwaves to start and maintain a reaction is the most prominent method, followed by some research advances in photochemistry and ultrasounds, using light or sound respectively in reactions.

Bacteria clean up metal waste, then serve as catalysts.

Synopsis by Evan Beach, Dec 09, 2010

Gauthier, D, LS Sobjerg, KM Jensen, AT Lindhart, M Bunge, K Finster, RL Meyer and T Skrydstrup. 2010. Environmentally benign recovery and reactivation of palladium from industrial waste by using gram-negative bacteria. ChemSusChem 3:1036-1039.

A group of Danish scientists has developed a method to recycle valuable metals that would ordinarily have to be mined and refined before ending up in chemists’ hands. Their discovery means that the metals could be sourced instead from electronic waste or polluted water and soil.

The researchers used two species of bacteria and added hydrogen gas to recover the waste metals – palladium, platinum and rhodium – in a cheaper and more efficient way than conventional processes. Interest in using microbes to remove metals from waste is growing among scientists who are searching for the best methods.

This is the first time that researchers report that they can remove these platinum group metals from industrially contaminated water without altering the bacteria or diluting the liquid. Remarkably, the bacteria could remove up to 100 percent of the palladium from the polluted water.

Mining, industrial activities and manufacturing release these specific metals into the environment, where they can contaminate soil and water. All three of the metals examined are widely used in automotive, chemical, glass, electrical, medical and jewelry applications.

The microbes used in the study are naturally tolerant of metals. One species can be found in typical soils, and the other is more commonly found in industrial areas, near mines and metal factories.

The bacteria bind and absorb metal ions dissolved in water. Hydrogen gas can also remove metal from the water. Metal uptake and recovery are enhanced when the two are combined.

The contaminated water used in the study contained a mixture of eight different metals and was deep orange colored. Hydrogen gas and bacteria with and without added palladium were added to test tube samples.

The liquid cleared after 24 hours, indicating the metals had been removed. The bacteria were most selective for palladium – the recovery rates were 96-100 percent, compared to 70-74 percent for platinum and 55-57 percent for rhodium.

After recovering the bacteria, researchers asked what could be done with the metal-rich material. They went a step further and found a productive use. They showed that the microbes could drive a common chemical reaction that uses palladium to connect two hydrocarbon building blocks, a method often used in synthesizing pharmaceuticals. The conversion rates were 50-100 percent. The effectiveness was higher when the bacteria were pretreated with a small amount of pure palladium before exposure to the wastewater.

Further experiments will be aimed at understanding how the metals compete for the absorption sites on the bacterial surface, and thus, produce treatment methods that select for specific metals. In turn, the selective, one-metal binding could result in more active catalysts to be used in conventional processes.

IBM, Stanford Unveil Green Chemistry Breakthrough

Scientists from IBM and Stanford University have unveiled discoveries that could lead to the development of new types of biodegradable, biocompatible plastics. The result of a multi-year research effort, the breakthrough also could lead to a new recycling process that has the potential to significantly increase the ability to recycle and reuse common PET and plant-based plastics in the future. Todays announcement may have sustainability implications across a wide range of industries including biodegradable plastics, plastics recycling, healthcare and microelectronics. IBM and Stanford scientists are pioneering the application of organocatalysis to green polymer chemistry, which represents a fundamental shift in the field. This discovery and new approach using organic catalysts could lead to well-defined, biodegradable molecules made from renewable resources in an environmentally responsible way.

See the YouTube video: Stanford & IBM on Green Chemistry and plastics.

New book: “Recoverable and Recyclable Catalysts” by Maurizio Benaglia

recoverable solvents

Recoverable and Recyclable Catalysts Wiley | 2009 | ISBN: 0470681950 | 500 pages | PDF |

There is continued pressure on chemical and pharmaceutical industries to reduce chemical waste and improve the selectivity and efficiency of synthetic processes. The need to implement green chemistry principles is a driving force towards the development of recoverable and recyclable catalysts.

The design and synthesis of recoverable catalysts is a highly challenging interdisciplinary field combining chemistry, materials science engineering with economic and environmental objectives. Drawing on international research and highlighting recent developments, this book serves as a practical guide for both experts and newcomers to the field.

Topics covered include:

* An introduction to the principles of catalyst recovery and recycling
* Catalysts on insoluble and soluble support materials
* Thermomorphic catalysts, self-supported catalysts and perfluorous catalytic systems
* The development of reusable organic catalysts
* Continuous flow and membrane reactors

Each chapter combines principles with practical information on the synthesis of catalysts and strategies for catalyst recovery. The book concludes with a comparison of different catalytic systems, using case studies to illustrate the key features of each approach.

Recoverable and Recyclable Catalysts is a valuable reference source for academic researchers and professionals from a range of pharmaceutical and chemical industries, particularly those working in catalysis, organic synthesis and sustainable chemistry.