New “Nanoconcentrators” Improves Catalytic Performance


2D Perovskite Berkeley Peidong-image-2A group of scientists at the University of Amsterdam (UvA) has developed a new approach in enhancing catalytic performance. In the current issue of Nature Chemistry (“Self-assembled nanospheres with multiple endohedral binding sites pre-organize catalysts and substrates for highly efficient reactions”) they present functionalised, self-assembled nanospheres that enable highly efficient catalytic conversion by acting as ‘nanocentrators’.

 

Schematic representation of the working principle of the nanoconcentrator
 

Schematic representation of the working principle of the nanoconcentrator. The gold(I) catalysts (drawn in red) are located in the sphere. Once the substrate (in black) is deprotonated the anionic substrate (in green) enters the sphere to pre-organize close to the catalyst via hydrogen bonding to the guanidine-binding site (displayed in blue). After rapid conversion of the substrate, the neutral cyclic product leaves the sphere. (Image: HIMS)

 

The new catalytic nanosphere concept was inspired by the working principles of natural enzymes. These bind molecules in well-defined pockets close to their active sites, thus introducing a pre-organization organisation that facilitates highly efficient transformations. The researchers mimic this enzymatic behaviour in synthetic nanocontainers that in addition , which can contain very high local catalyst concentrations , which and further enhances the catalytic performance.

 

Self-assembly
The new nanocontainers are formed by self-assembly: mixing 12 palladium metals and 24 so-called ditopic nitrogen ligands leads to formation of nano-sized spheres. The ligands are modified with guanidinium binding motifs so that the resulting nanocontainers are able to bind sulfonates and carboxylates in their interior. Sulfonate guests are thereby bound much more strongly than carboxylates because of so-called cooperative binding (employing multiple binding sites). The researchers use this to firmly fix the sulfonated gold-based catalyst, while the remaining binding sites are available for the pre-organisation of the carboxylate moieties that are to be converted (the substrates).

 

Enhanced reaction rates
The working principles of this ‘nanoconcentrator’ system were established using a gold-catalysed cyclization reaction (shown above). The local high concentration of the metal catalyst combined with the pre-organization of the substrate resulted in dramatically enhanced reaction rates in comparison to common systems where the catalyst and the reactants are not pre-organised but just both dissolved in a solvent. Reaction rates usually increase with catalyst and substrate concentration; however this is generally limited by solubility issues or unfavorable catalyst/reactant ratios. This issue has now been solved by taking advantage of local concentrations in the self-assembled nanoconcentrator.

 

Widely applicable strategy
Since many existing metal catalysts are utilized with sulfonate groups (generally to make them water soluble), the presented nanoconcentrator system potentially provides a widely applicable general strategy to many different reactions. Furthermore, the researchers established that the encapsulated sulfonate-containing gold catalysts did not (or only slowly) convert neutral (acid) substrates. This provides a starting point for the development of more complex catalyst systems with substrate-selective catalysis and base-triggered on/off switching.
Source: Universiteit van Amsterdam
 
      
 
Advertisements

U of Wisonsin-Madison: Researchers Invent a Metal-Free Fuel Cell: Molecular vs. ‘Solid’ Catalyst: Why that’s Important


UW Cata Fuel Cell 480547266The development of fuel cell technology has been hamstrung by the need for expensive and difficult-to-manufacture catalysts like platinum, rhodium or palladium. But a team of researchers from the University of Wisconsin-Madison believe they’ve found an ingenious alternative that employs a molecular, rather than solid, catalyst.

A fuel cell generates electricity from chemicals by reacting hydrogen and oxygen at its anode and cathode, respectively. Specifically, a catalyst at the anode oxidizes the hydrogen fuel to create free electrons and charged ions. The ions pass through the electrolyte while the electrons pass through a separate wire (to drive an electronic device) and the two recombine in the cathode with oxygen to create water or CO2.

The team, led by Professor Shannon Stahl and lab scientist James Gerken, noticed that the aerobic oxidation reactions they had studied in their previous work closely mimicked the oxygen reaction in fuel cells. To see if this aerobic reaction could work as a fuel cell, they built one using a catalyst composed of nitroxyl and nitrogen oxide molecules to react with its electrode and oxygen. “While this catalyst combination has been used previously in aerobic oxidations, we didn’t know if it would be a good fuel cell catalyst,” Stahl said in a statement. “It turns out that it is the most effective molecular catalyst system ever reported.”

The results are more than impressive. “This work shows for the first time that molecular catalysts can approach the efficiency of platinum,” Gerken continued. “And the advantage of molecules is that you can continue to modify their structure to climb further up the mountain to achieve even better efficiency.”