Surface ligand effect

Periodic DFT calculations provided the O2 binding energy and dissociation barrier on Pd-Co/C. ° Improvements to this system have been attempted by probing lattice-strain and surface-ligand effects on Pd alloys. ... 

Selective Reactions on Modified Metal Surfaces the Ligand Effect. 201... 

Recently, however, the development of nanotechnology may provide the changes on the research and development of practical catalysts. As mentioned in the previous section we can now design and synthesize a metal nanoparticle with not only various sizes and shapes, but also with various combinations of elements and their locations. Thus, we can now design the synergetic effect of two elements. In the case of core/shell structured bimetallic nanoparticles, the shell element can provide a catalytic site and the core element can give an electronic effect (a ligand effect) on the shell element. Since only the atoms on the surface can be attached by substrates, the thickness of the shell should be an important factor to control the catalytic performance. 

Pseudomorphic Pt monolayers on Ru(0001) interact very weakly with H pd, OHad, or Oad, because of electronic ligand (vertical ligand effects) and strain effects (tensile strain), in agreement with results obtained under UHV conditions and in DPT calculations. Therefore, base CVs on these surfaces do not show pronounced voltammettic features. 

Describe the differences between ensemble effects and ligand effects (in relation to bimetallic surfaces), and how these may play a role in the adsorption activity of a surface. 

It is difficult to predict the effect of surface functionalization on the optical properties of nanoparticles in general. Surface ligands have only minor influence on the spectroscopic properties of nanoparticles, the properties of which are primarily dominated by the crystal field of the host lattice (e.g., rare-earth doped nanocrystals) or by plasmon resonance (e.g., gold nanoparticles). In the case of QDs, the fluorescence quantum yield and decay behavior respond to surface functionalization and bioconjugation, whereas the spectral position and shape of the absorption and emission are barely affected. 

Munro AM, Plante IJL, Ng MS, Ginger DS (2007) Quantitative study of the effects of surface ligand concentration on CdSe nanocrystal photoluminescence. J Phys Chem C 111 6220-6227... 

Fig. 22. TPRS spectra for CO/HCOOH from Cu/Ni alloys of varying surface composition (100). (a) 37% Ni (b) 46% Ni (c) 54% Ni (d) 61% Ni (e) 68% Ni. The peak shifts indicate weak ligand effects (see text). Reprinted with permission from Journal of Inorganic Chemistry 17, 1978. Copyright 1978, American Chemical Society.

The organoactinide surface complexes exhibited catalytic activities comparable to Pt supported on sihca [at 100% propylene conversion at —63°C, >0.47s (U) and >0.40 s (Th)], despite there being only a few active sites (circa 4% for Th, as determined by CO poisoning experiments and NMR spectroscopy) [92]. Cationic organoactinide surface complexes [Cp An(CH3 ) ] were proposed as catalytic sites. This hypothesis could be corroborated by the use of alkoxo/hydrido instead of alkyl/hydrido surface ligands, which led to a marked decrease of the catalytic activity, owing to the oxophilic nature of the early actinides [203, 204]. Thermal activation of the immobihzed complexes, support effects, different metal/ligand environments and different olefins were also studied. The initial rate of propylene conversion was increased two-fold when the activation temperature of the surface complexes under H2 was raised from 0 to 150°C (for Th 0.58 0.92 s" ). 

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