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Specific Properties of Nanoparticles
Published in Ko Higashitani, Hisao Makino, Shuji Matsusaka, Powder Technology Handbook, 2019
Wolfgang Peukert, Johannes Walter
The data are consistent with the following model:90 the more weakly the surface metal atom is attached to the nanoparticle, the more strongly it binds small adsorbates. Its strength of attachment to the nanoparticle is dominated by the number of metal-metal bonds which bind it there, but also by the strength of metal/oxide interfacial bonding. This same combination of bond strengths controls sintering rates as well: the less stable a surface metal atom is in the nanoparticle, the greater is the thermodynamic driving force for it to sinter and the faster is its sintering rate. These correlations provide key insights into how and why specific structural properties of catalyst nanoparticles dictate their catalytic properties. For example, they explain why supported silver (and also gold) catalysts must contain nanoparticles smaller than about 6 nm to have high activity for combustion and selective oxidation reactions. Only below about 6 nm, metal atoms are so weakly attached to the catalyst that they bind oxygen sufficiently strongly to enable the activation of O2.90 For palladium nanocrystals it was shown that the performance for formic acid oxidation depends on the surface structure.91Figure 1.8.7 depicts the maximum current densities for structures with different proportions of {111} to {100} facets. It was found that nanocubes with slight truncation at the corners are the best choice for formic acid oxidation.
Fundamentals of Atomically Dispersed Metallic Materials
Published in Wei Yan, Xifei Li, Shuhui Sun, Xueliang Sun, Jiujun Zhang, Atomically Dispersed Metallic Materials for Electrochemical Energy Technologies, 2023
Rongbo Sun, Xiao Han, Xun Hong
A single-atom catalyst is a catalyst formed by dispersing metal atoms in the form of single isolated atoms on the support. There are no metal–metal bonds between atoms of the same metallic element. In 2011, Zhang and his team reported a carbon monoxide oxidation catalyst that uniformly supports monodisperse platinum atoms on iron oxide surfaces. This work was the first to propose the concept of “single-atom catalysis” (SACs) concept [25].
Recent advances in polyoxothiometalate chemistry
Published in Journal of Coordination Chemistry, 2022
[MoV2O2(µ-S)2]2+ consists of two MoV cations, bridged by two sulfide anions and possessing two terminal oxo anions, one attached to each MoV. Both oxo anions lie on the same side of the molecule, giving overall C2v symmetry, and the oxo anions are tilted approximately 18° away from each other, giving the overall cation a slight bend [21]. This gives a tendency to form closed atomically precise structures, rather than extended oligomers. Each MoV possesses three uncoordinated faces for an octahedral geometry, which are occupied by labile solvent ligands in solution, and present easy points of attachment to constructing POTMs. The equatorial positions (relative to the oxo ligand) are more available due to lower steric hindrance, the axial position is both more sterically crowded and less electronically favorable due to the trans oxo ligand. The MoV cations are separated by 2.8 Å, giving a formal single metal-metal bond occupied by the single electrons present on each molybdenum; this lends stability to the building block, despite the V oxidation state which is unusual for molybdenum otherwise. [WV2O2(µ-S)2]2+ possesses the same structure, with tungsten in place of molybdenum.