Metal-based chemical catalysts have excellent green chemistry credentials—in principle at least. In theory, catalysts are reusable because they drive chemical reactions without being consumed.
Figure 1: A graphical representation of the retrievable and reusable polymer–metal catalyst, showing the palladium (blue) that links two imidazole polymer units (red) through their nitrogen atoms. Copyright : 2011 Yoichi Yamada
In reality, however, recovering all of a catalyst at the end of a reaction is difficult, so it is gradually lost. Now, chemists can retain, retrieve and reuse metal catalysts by trapping them with a polymer matrix, thanks to recent work by Yoichi Yamada at the RIKEN Advanced Science Institute, Wako, Yasuhiro Uozumi at RIKEN and Japan’s Institute for Molecular Science and Shaheen Sarkar, also at RIKEN1.
Attaching metal catalysts to an insoluble polymer support, which is recoverable at the end of a reaction by simple filtration, is far from a new idea. Traditionally, chemists attached their metal catalyst to an insoluble polymer resin. However, the metal invariably leached out of the polymer over time so the catalysts were still slowly lost.
Yamada and his colleagues’ approach, in contrast, integrated the metal into the polymer matrix, which trapped it much more effectively. The researchers achieved this level of integration by starting with a soluble polymer precursor instead of an insoluble resin. This material contains imidazole units, a chemical structure known to bind strongly to metals such as palladium (Fig. 1). An insoluble composite material formed only after the researchers added palladium to the mixture because it causes the imidazole units to self-assemble around atoms of the metal—a process that they call ’molecular convolution’.
Scanning electron microscopy revealed that the resulting polymer–palladium globules ranged from 100 to 1,000 nanometers in diameter, which aggregated into a highly porous structure reminiscent of a tiny bathroom sponge. “This sponge-like insoluble material can easily capture substrates and reactants from the solution, which readily react with metal species embedded in the sponge,” says Yamada.
The researchers showed that the catalyst is highly active as well as reusable; it is the most active catalyst yet reported for a carbon–carbon bond-forming reaction known as an allylic arylation. They also reused the catalyst multiple times with no apparent loss of activity, and detected no leaching of palladium from the polymer into the reaction mixture.
Yamada and colleagues are now developing a range of composite catalysts incorporating different metals that can catalyze many other kinds of reactions. “These extremely highly active and reusable catalysts will provide a safe and highly efficient chemical process, which we hope will be adopted for industrial chemical process,” Yamada says.
The corresponding author for this highlight is based at the Green Nanocatalysis Research Team, RIKEN Advanced Science Institute
Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University
How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung
Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.
Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....
Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.
The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....
An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.
We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
24.05.2017 | Event News
23.05.2017 | Event News
22.05.2017 | Event News
26.05.2017 | Life Sciences
26.05.2017 | Life Sciences
26.05.2017 | Physics and Astronomy