Interactive size control of catalyst nanoparticles
5, 10, or maybe 15? How many nanometers should nanoparticles of a catalyst measure to optimise the course of reaction? Researchers usually perform laborious tests to find the answer. Scientists at the Institute of Physical Chemistry PAS a new technique to improve the process of such optimisation in microfluidic systems. The size of catalyst nanoparticles can now be changed as needed during a continuous flow through the catalyst bed.
The performance of metal-carrier catalysts often depends on the size of metal nanoparticles. Their size is usually determined over the course of many consecutive tests. The method is not very flexible: once the reactions have started, nothing can be done to the catalyst, the Institute of Physical Chemistry PAS informs in a press release.
The group led by Dr. Jacinto Sa from the institute presented a new technique that allows for optimisation of chemical reactions during the continuous microfluidic flow through the catalyst bed, literally "on the fly". This effect was achieved through interactive control of the size of the catalyst nanoparticles. Due to its simplicity and efficiency, this innovative technique should soon be find applications in the tests of the new catalysts for the pharmaceutical and perfumery industries.
"Flow catalysis is becoming more popular because it leads to the intensification of processes important for the industry. Our technique is the next step in this direction: we reduce the time needed to determine the sizes of catalyst nanoparticles. That means we can faster optimise the chemical reactions and even interactively change their course. An important argument here is also that the entire process is carried out within a small device, so we reduce costs of additional equipment" - says Dr. Sa, quoted in the press release.
The nickel catalyst NiTSNH2 used in the experiment, in the form of a fine black powder, was previously developed at the Institute of Physical Chemistry PAS. It consists of grains of polymeric resin covered with nickel nanoparticles. The grain size is approx. 130 micrometers and the nanoparticles of the catalyst are initially 3-4 nanometers.
"The essence of our achievement is showing how to modify the morphology of catalyst nanoparticles in a sequence with a chemical reaction. After each change in the size of the nanoparticles, we immediately get information about the effect of this modification on the catalyst activity. Therefore, it is easy to assess which nanoparticles are optimal for a given chemical reaction" - explains PhD student Damian Gizinski from the Institute of Physical Chemistry PAS.
In the microreactor described in the journal ChemCatChem, the researchers increased the sizes of the catalyst nanoparticles to 5, 9 and 12 nm in a controlled manner. The growth effect was achieved by flushing the catalyst bed with an alcohol solution containing nickel ions. Within the bed, they were deposited on the existing nanoparticles and reduced under the influence of hydrogen. The final size of the nanoparticles depends on the exposure time to the solution with Ni2+ ions, the Institute of Physical Chemistry PAS reports.
Experts from the institute explain that in the reaction with citral, the best catalytic performance was achieved with 9 nm nanoparticles. The researchers also observed that up to 9 nm the growth of nanoparticles favoured the redirection of the reaction towards citronellal production, while above this value the pathway to the citronellol was preferred. These two compounds have slightly different properties: citronellal is used to repel insects, especially mosquitoes, and as an antifungal agent; citronellol not only repels insects, but also attracts mites, it is also used to produce perfumes.
For potential applications of the new catalyst modification technique, it is important that the introduced changes seem to be relatively stable. In the test system, the catalysts remained stable for at least five hours after the modification in a continuous flow of the reaction solution.
Research on the interactive modification of catalysts was financed from the OPUS grant of the National Science Centre.
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