Heterogenized Homogeneous nanocatalysts – to get specific products with very high selectivity

· TGI - Cancer, TGI - Catalysis
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Catalysts: are substances that speed up the rates of chemical reactions without themselves being chemically changed.

Heterogeneous: in which catalyst is in a different phase from the reactants. Heterogeneous catalysts are valued for their sustainability because they can be recycled.

Homogeneous: in which catalyst and the reactants are in the same phase. Homogeneous catalysts are valued for their product selectivity as their properties can be easily tuned through relatively simple chemistry.

Catalysts are used to initiate virtually every industrial manufacturing process that involves chemistry. Metal catalysts have been the traditional workhorses, but in recent years nano-sized catalysts have surged in importance.

Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have combined the best properties of both types of industrial catalysts by encapsulating nanoclusters of a metallic heterogeneous catalyst within the branched arms of the molecules known as dendrimers.

Heterogenized homogeneous nanocatalysts are sustainable as shown by these TEM images in which there is almost no difference in the cluster size of dendrimer-encapsulated gold nanoclusters (white spots) before (left) and after cyclopropanation reactions.

The key to the success of this latest research was the encapsulation of metal nanoparticles inside dendrimers says Somorjai  who is a senior scientist with Berkeley Lab’s Materials Sciences Division, where he directs the Surface Science and Catalysis Program, and a professor of chemistry with the Chemistry Department at the University of California Berkeley.

The results are heterogenized homogeneous nanocatalysts that are sustainable and feature high reactivity and selectivity. Furthermore, these heterogenized homogeneous nanocrystals hold promise for bridging the gap between industrial catalysts, which carry out simple reactions, and a third type of catalyst, the proteins known as enzymes, that nature uses to carry out the complex reactions of biochemistry.

“Using cyclopropanation reactions catalyzed by dendrimer-encapsulated gold and other metal nanoclusters, including platinum, palladium and rhodium, we have demonstrated that changing the dendrimer properties allows catalytic reactivity in a heterogeneous catalyst to be tuned in a similar fashion to ligand modification in a homogeneous catalyst,” says world renowned catalysis chemist Gabor Somorjai. “Furthermore, they have shown that these heterogeneous catalysts employed in a fixed-bed flow reactor allow fine control over the residence time of the reactants and thus enable control over product distribution in a way that is not easily available for homogeneous catalysts.”

Given the flow systems are widely used in industrial chemistry, the concept of replacing homogeneous catalysts with dendrimer-encapsulated heterogeneous catalysts whose product selectivity can be controlled should be a popular alternative. For example, the catalysis of cyclopropane could be tuned to favor the formation of cyclopropanes that are critical components of cancer and cholesterol medicines.

The recyclability of these dendrimer-encapsulated heterogeneous catalysts is another major advantage.

“Highly selective catalysts, especially those that can be recycled readily, are vital for the development of sustainable chemical processes,” Gross says. “In the future, with our technique it should be possible to combine heterogeneous and homogeneous catalysts to get specific products with very high selectivity.”

 “From our work, it has become increasingly clear that at the molecular level, all catalysts—heterogeneous, homogeneous, and enzymes—function the same,” Somorjai says. “We have now proven that working with metal nanoclusters, the same chemistry can be done with heterogeneous or homogeneous catalysts.”

The paper is titled “Control of selectivity in heterogeneous catalysis by tuning nanoparticle properties and reactor residence time” and was published in Nature Chemistry.

Source:

rdmag

Lawrence Berkeley National Laboratory

1 Comment

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  1. TGI

    I was personally involved in such work (heterogenization of homogeneous catalysis) once in 2001 in France. We have developed Tin based catalysts on solid supports and also experimented with ionic liquids as one of the medium in the catalysts developed.

    This is a good piece of work.

    Like

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