Kinetic energy catalysts

Erosion. The abrasive is likely to be gas borne (as in catalytic cracking units), liquid borne (as in abrasive slurries), or gravity pulled (as in catalyst transfer lines). Because of the association of velocity and kinetic energy, the severity of erosion may increase as some power (usually up to the 3d) of the velocity. The angle of impingement also influences severity. At supersonic speeds, even water droplets can be seriously erosive. There is some evidence that the response of resisting metals is influenced by whether they are ductile or brittle. Probably most abrasion involved with hydrocarbon processing is of the erosive type. 

Figure 4.19. The LEIS spectrum of a CU/AI2O3 catalyst illustrates that Ions lose more energy in collisions with light elements than with heavy elements. Note the step In the background at the low kinetic energy side of...

X-ray absorption spectroscopy combining x-ray absorption near edge fine structure (XANES) and extended x-ray absorption fine structure (EXAFS) was used to extensively characterize Pt on Cabosll catalysts. XANES Is the result of electron transitions to bound states of the absorbing atom and thereby maps the symmetry - selected empty manifold of electron states. It Is sensitive to the electronic configuration of the absorbing atom. When the photoelectron has sufficient kinetic energy to be ejected from the atom It can be backscattered by neighboring atoms. The quantum Interference of the Initial... 

Modeling of Jet-Induced Attrition. Werther and Xi (1993) compared the jet attrition of catalysts particles under steady state conditions with a comminution process. They suggested a model which considers the efficiency of such a process by relating the surface energy created by comminution to the kinetic energy that has been spent to produce this surface area. The attrition rate, RaJ, defined as the mass of attrited and elutriated fines per unit time produced by a single jet, is described by... 

Routinely used X-ray sources are Mg Ka (1253.6 eV) and A1 Ka (1486.3 eV). In XPS one measures the intensity of photoelectrons N(E) as a function of their kinetic energy. The XPS spectrum, however, is usually a plot of N(E) versus Ek, or, more often, versus the binding energy Eb. Figure 3.3 shows the XPS spectrum of an alumina-supported rhodium catalyst, prepared by impregnating the support with... 

Figure 4.19 The LEIS spectrum of a Cu/Al203 catalyst illustrates that ions lose more energy in collisions with light elements than with heavy elements. Note the step in the background at the low kinetic energy side of the peaks. The high peak at low energy is due to sputtered ions. The low energy cut-off of about 40 eV is indicative of a positively charged sample (courtesy of J.P. Jacobs and H.H. Bron-gersma, Eindhoven).

Karstedt s catalyst, nickel analog, 8, 138-139 Kedarcidin, via ring-closing diene metathesis, 11, 208-209 Kendomycin, via ring-closing metathesis, 11, 239 KERD, see Kinetic energy release distribution Ketenes, niobium complexes, 5, 84 Ketenimines... 

It is thus now considered that the catalyst can initiate a reaction. According to this view, the reacting molecules (in the absence of catalyst) do not posses minimum kinetic energy for successful collisions. The molecules rebound from collisions without reacting at all. 

B Catalysts provide an alternate mechanism in both directions, but do not alter equilibrium (I is false, II is true). The kinetic energy of molecules increases with temperature, so the energy of their collisions increases also (III is true). Catalytic converters contain a heterogeneous catalyst (IV is false). 

Without a doubt, a complete picture of the dynamics of dissociative chemisorption and the relevant parameters which govern these mechanisms would be incredibly useful in studying and improving industrially relevant catalysis and surface reaction processes. For example, the dissociation of methane on a supported metal catalyst surface is the rate limiting step in the steam reforming of natural gas, an initial step in the production of many different industrial chemicals [1]. Precursor-mediated dissociation has been shown to play a dominant role in epitaxial silicon growth from disilane, a process employed to produce transistors and various microelectronic devices [2]. An examination of the Boltzmann distribution of kinetic energies for a gas at typical industrial catalytic reactor conditions (T 1000 K)... 

Because a set of binding energies is characteristic for an element, XPS can be used to analyze the composition of samples. Almost all photoelectrons used in laboratory XPS have kinetic energies in the range of 0.2 to 1.5 keV, and probe the outer layers of the catalyst. The mean free path of electrons in elemental solids depends on the kinetic energy. Optimum surface sensitivity is achieved with electrons at kinetic energies of 50-250 eV, where about 50% of the electrons come from the outermost layer. 

XANES studies of ruthenium-polystyrene hydrogenation catalysts (32) show strong multiple-scattering resonance due to carbon atoms in the first coordination shell which exhibit high backscattering at low kinetic energy of the photoelectron, in accordance with EXAFS results. 

For the purpose of the present chapter, a comment on the interpretation of oxygen Is binding energies in oxides seems appropriate. The contribution of the surface terminating layer and of a possible adsorbate to the total O Is spectrum of an oxide catalyst is low (an estimated 15% for laboratory XPS) as in oxides the depth of information [33] is commonly larger than estimated from the universal relation between kinetic energy and escape depth, which is vahd for metals only. 

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