Defect-rich

Figure 6.7 Stripping voltammetry of saturated CO adlayers on Pt(l 11) cooled in a hydrogen-argon atmosphere (dashed line), leading to a well-defined smooth surface, and on Pt(lll) cooled in air (full line), leading to a less well-defined defect-rich surface sweep rate 50 mV/s.

It was proposed that a further nucleation process occurs at the interface between the central and outward components, making the boundary between them defect-rich. These discontinuities in the crystalline structure and in the porous network are not sufficiently large to be directly noticeable by optical microscopy or SEM [18], nevertheless it allows us to visualize the internal intergrowth structure. 

One more possibility to explain the T3 dependence of the ZPL width has been proposed in Ref. [16]. It was found here that in defect-rich crystals the modulation of the ZPL frequency by the fluctuating entire field produced by defects leads to the given dependence. 

Precipitation and coprecipitation Synthesis of defect-rich materials, easy to perform Homogeneity difficult to achieve... 

Thus the behavior of lattice defects bears some analogy to phase separation in fluids, or to the treatment of adsorption on localized sites. At low relative temperatures, the defects adopt a random distribution if they are sufficiently dilute if their concentration exceeds a certain value they segregate into defect-poor and defect-rich regions which can coexist. The concentration at which this occurs, and the relative temperature scale, depend on what can be represented as a nearest-neighbor attraction in the interaction potentials. The magnitude of the attractive interaction energy defines a critical temperature above which no segregation of defects occurs. 

Fig. 18. SFG spectra of CO adsorption on defect-rich Pd(l 1 1) at 190K at pressures in the range from 10 to 200mbar. A peak at 1990cm appeared that was not evident for CO on the perfect (1 1 1) surface adapted from (120) with permission from Elsevier.

In summary, a Pd(l 1 1) single-crystal surface is not sufficient to model the complex adsorption behavior of palladium nanoparticles, even for nanoparticles which mostly exhibit (111) facets. High Miller index stepped or kinked single-crystal surfaces may provide better models of nanoparticles. However, one should remember that CO adsorbed on defects of defect-rich Pd(l 11) became invisible at high coverages Furthermore, it will be demonstrated in a following section that the... 

Fig. 27. (a) SFG and (b) XPS Cls core-level spectra measured during CO adsorption at 300 K p and d refer to well-annealed (perfect) and defect-rich (ion-bombarded) Pd(l 1 1) surfaces, respectively. In (c) difference spectra are shown indicating adsorption on defect (2-1) and on-top (4-2) sites. XP spectra were normalized to the Pd3ds/2 integral intensity at 334.9 eV. (d) Coverage vs. pressure dependence determined from XPS (full symbols, full lines) and from SFG (open symbols, dashed lines) adapted from (274,324) with permission from Elsevier. 

Fig. 32. High-pressure SFG spectra of a 1 10 (molar) CO H2 mixture on Pd(l 11) (a) and on Pd/Al203 (b, c) (dS). Pressures and temperatures are indicated, (d) FEED patterns recorded before (lower) and after (upper) high-pressure gas exposure to Pd(l 11) (273). The post-reaction AE spectrum indicates that the surface remained clean during 6 h of gas exposure, (e) Schematic illustration of the reaction of on-top CO with hollow-bonded H to adsorbed formyl. (1) Cls XP spectra of smooth (perfect p ) and defect-rich ( d ) Pd(l 11), acquired with the sample in 0.05 mbar of CO + H2 the d spectrum shows an additional peak at 283.8 eV, attributed to carbonaceous deposits (324).

In Fig. 21 DCH crystals are shown before polymerization and at an intermediate conversion. It is typical for the thermal reaction that more perfect monomer crystals require longer reaction times than defect-rich crystals. There is evidence that in the radiation polymerization of DCH the polymer crystal perfection increases with decreasing temperature, i.e., the nucleation process requires a rather high thermal activation energy. 

While the single crystal (100) surface is completely unreactive, a defect-rich polycrystalline MgO surface exhibits a rich and complex chemistry when interacting with CO. 

Fig. 7 (A) MIE spectra of an MgO thin film at 95 K as a function of NO exposure. The Upper-most spectrum corresponds to that of the clean MgO(lOO) surface while the bottommost spectrum is that after a 307 L exposure of NO (B) MIE spectra of defect-rich MgO thin film at 95 K as a function of NO exposure. The uppermost spectrum corresponds to the defect-rich MgO film and the top-most spectrum to the 307 L-thick NO coverage (C) UP spectra of NO adsorbed on a defect-rich MgO film at 95 K. The dotted lines denote changes in the work function.

Fig. 8 Evolution of MgO 0(2p) and N O 7ct as a function of NO coverage. The open and filled symbols denote defect-rich and as-prepared TiOj, respectively.

Transition metal catalysts, specifically those composed of iron nanoparticles, are widely employed in industrial chemical production and pollution abatement applications [67], Iron also plays a cracial role in many important biological processes. Iron oxides are economical alternatives to more costly catalysts and show activity for the oxidation of methane [68], conversion of carbon monoxide to carbon dioxide [58], and the transformation of various hydrocarbons [69,70]. In addition, iron oxides have good catalytic lifetimes and are resistant to high concentrations of moisture and CO which often poison other catalysts [71]. Li et al. have observed that nanosized iron oxides are highly active for CO oxidation at low tanperatures [58]. Iron is unique and more active than other catalyst and support materials because it is easily reduced and provides a large number of potential active sites because of its highly disordered and defect rich structure [72, 73]. Previous gas-phase smdies of cationic iron clusters have included determination of the thermochemistry and bond energies of iron cluster oxides and iron carbonyl complexes by Armentrout and co-workers [74, 75], and a classification of the dissociation patterns of small iron oxide cluster cations by Schwarz et al. [76]. 

The reaction is conceived to occur with the adsorption of CO on the cluster and the adsorption of oxygen on the particle periphery as shown in Fig. 16.5 [6]. The production of CO was greatly enhanced for Au clusters supported on defect-rich films as compared to clusters supported on defect-poor films. Density functional theory (DFT) calculations indicated the reaction barrier was lowered from 0.8 to... 

The interaction of methanol vith the defect-poor and defect-rich films was studied using thermal desorption spectroscopy (TDS) (Figure 17.1c). For both films the desorption of physisorbed methanol at around 180 K is most dominant. 

CH30 -H+). (c) Thermal desorption spectra of CHjOH and H2 on defect-poor and defect-rich MgO(lOO) films. Note the desorption of H2 at 580 l< for defect-rich films. The insets show FTIR spectra recorded at 90 l< for adsorbed CH3OH on both defect-poor and defect-rich films. 

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