A new technique to deposit nanoparticles synthesized in reverse micellar microemulsions onto support material without agglomeration is named thermal destabilization of microemulsion. The multifaceted Pt crystals, mostly truncated octahedra, were produced inside reverse micelles with an average size of 2.5 nm and a narrow size distribution. After deposition, the Pt crystals were found to be well dispersed on the support with an average size of 2.5 nm. After testing with hydrogenation of a-methyl styrene, the produced Pt-catalyst showed higher activity (6 times higher) and stability than commercial ones. The advantages of this synthesis route of nanoparticles include simple operation, and the ease of controlling the size and shape of nanoparticles without using capping agents.
We recently introduced a new method to synthesize an active and stable Pt catalyst, namely thermo- Schomäcker, J. Mater. Chem., 2012, 22 (23), 11605-11614). We are able to produce Pt nanocrystals with a small size (2.5 nm) of an isotropic structure i.e. truncated octahedral and deposit them well on support materials. Although we have obtained good results, the performance of the catalyst still needed to be improved and optimized. We followed the strategy to retain the small size but change the shape to an anisotropic structure of Pt nanocrystals which produces more active sites by means of a weaker reducing agent. We found that our catalysts are more active than those we reported before and even show the potential to be applied in a challenging reaction such as hydrogenation of levulinic acid.
It is well known that the activities of supported metal catalysts are strongly dependent upon the size, shape and dispersion of the nanoparticles on the support material. There are several techniques which can be implemented in order to produce such catalysts, e.g. wet impregnation, however the deposition of nanoparticles (NPs) on the support material without agglomeration still proves a challenge. This is particularly significant when attempting to maintain the size and shape of the particles during the deposition process. We have introduced a new method to deposit metal NPs, namely thermo-destabilization of microemulsions (please see J. Mater. Chem., 2012, 22, 11605–11614 and Nanoscale, 2013, 5, 796–805), in which the NPs are formed prior the deposition process. This method is an ingenious approach to control the dispersion of NPs on the support material and depositing NPs evenly with a narrow size distribution. In this paper we expound the important role of the surface charges of NPs and the support material, as indicated by zeta potentials, on the metal dispersion, and how they affect the catalytic activity. We also investigate the influence of other parameters such as the pore size and the pre-calcination of the support on the catalytic activities of the resulting supported metal catalysts.DFG, EXC 314, Unifying Concepts in Catalysi
We synthesized Ag, Pd, Pt, and Ru nanoparticles by employing antioxidants in the natural reductants, i.e., green tea leaf, coffee, peppermint leaf, and grape seeds. The results from the characterization with transmission electron microscopy (TEM) show metal nanoparticles with different shapes. The catalytic testing in the hydrogenation of α-methylstyrene (AMS) shows very high activity of the produced Pt nanodendrites. This excellent activity is due to the anisotropic structure of Pt nanodendrites which provides many defects, kinks, steps, and edges, thus providing a high number of active sites. In a challenging reaction such as the hydrogenation of levulinic acid, which is normally carried out at high temperature (100−240 °C) and high pressure (50−100 bar), the produced Pt nanodendrites are already active at much lower reaction conditions (1.3 bar and 70 °C), with an overall performance of about 100% of γ-valerolactone (GVL) selectivity and 94% conversion in 5 h.
Platinum and palladium nanoparticles, supported and stabilized by polymeric core-shell architectures, proved to be active catalysts for hydrogenation reactions. Here, two different reactions were used as probes to investigate the influence of the polymeric support: the hydrogenation of α-methyl styrene (AMS) to cumene and the partial hydrogenation of 1,5-cyclooctadiene (COD). We found that the stability of the nanoparticles and the rate of reaction are higher in the presence of a hydrophobic octadecyl shell within a three-shell polymer system. The kinetic study of AMS hydrogenation showed much higher activities for palladium nanoparticles than for platinum nanoparticles, and the obtained results (e.g., 35 kJ/mol for the activation energy) are of the same order of magnitude as reported earlier for palladium supported on alumina. A methanol/n-heptane biphasic mixture was tested for catalyst recycling and allowed for highly efficient catalyst separation with very low metal leaching.
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