Subsurface discrimination

Based on the experimental data and some speculations on detailed elementary steps taking place over the catalyst, one can propose the dynamic model. The model discriminates between adsorption of carbon monoxide on catalyst inert sites as well as on oxidized and reduced catalyst active sites. Apart from that, the diffusion of the subsurface species in the catalyst and the reoxidation of reduced catalyst sites by subsurface lattice oxygen species is considered in the model. The model allows us to calculate activation energies of all elementary steps considered, as well as the bulk... 

Gennard et al. have calculated the surface energies of the (011) and (111) faces of both ceria and zirconia. They hnd that interatomic potential-based methods provide a correct estimate of the surface relaxations and the correct order of stability of the two faces examined, with the energy difference between the (Oil) and the (111) surfaces being approximately I J/m, as found in the QM study. However, interatomic potential-based methods do not discriminate adequately between the properties of the two materials. It was also found that geometric and electronic relaxations in the (111) surface are confined to the outermost oxygen ions, while in ihe (Oil) slabs they are more important and extend to the subsurface layers in a columnar way. The unsaturation of the surface ions in the (011) face may have important implications for catalytic activity. 

Figure 12.2 Principle of the spatial SORS concept for the discrimination of subsurface signals.

Fig. 2. Correlation of static surface elasticity (e0) at a film pressure of 6.5 mN m"1 with discriminant function Dl score for 28 films formed from microlayer and subsurface seawater FI surfactant extracts...

Tables 29 and 30 show activity and selectivity data as well as dispersion of copper on both Mn- and Ti-based perovskites. The dispersion of Cu was calculated from CO adsorption at 77 K assuming a CO Cu= 1 1 stoichiometry. A close look at the data reported in these tables indicate that neither the nature of the B cation nor the prereduction in H2 affect the catalytic behavior of the perovskites. Thus, the main conclusion from this work is that the active site is directly associated with the presence of surface copper species. To ascertain the oxidation state of Cu, Rodriguez-Ramos et al. (1991) resorted to the use of X-ray photoelectron spectroscopy. Figure 31 clearly shows that both the prereduced and used catalyst contain either Cu+ or Cu° or both types of reduced species. This technique does not allow us to discriminate between Cu° and Cu+ but a closer look at the Auger parameter corresponding to the L3M4 5M4 5 transition undoubtedly confirms that only Cu° is present in used catalysts. Furthermore, quantitative XPS measurements indicate that some migration of copper from the subsurface to the topmost layer seems to occur on prereduced catalysts and/or used catalysts.

The key value of ion scattering in all these examples is that it has the unique ability to discriminate between the surface atomic layer composition and that of subsurface layers. 

Horizons are usually seen as interfaces between subsurface layers of rocks of different properties. Thus reservoirs are discriminated in the depth extent from seismic cubes by their top and bottom horizons corresponding to their upper and lower limits, respectively. Horizons are usually manually or semi-automatically interpreted by analysing seismic data. However, new tools have recently emerged that allow an automated extraction of horizons from seismic. These new techniques are based on classification of a set of seismic waveform attributes along extrema (minima or maxima) in a seismic post stack cube. For further details on this, we refer to [4, 5]. 

On quiescent planets or satellites without substantial atmospheres, the surface temperature is determined by a balance between incident solar flux, thermally emitted radiation, and conductive heat transport into or out of the opaque surface. By measuring the surface temperature and the bolometric albedo the absorbed and emitted radiation can be found and the conductive flux into the solid body derived. After sunset or dining a solar eclipse the cooling rate of the surface depends on the thermal inertia of the subsurface layers. A study of such cooling rates provides a sensitive means of discriminating between powdery, sandy, or solid rock surfaces. We now review the theory behind such an analysis, and discuss examples of thermal inertia measurements. 

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