Catalysts, solid

Solid acid catalyst Solid bridges Solid carbon dioxide... 

If we know the contact angle we can work out r quite easily. We assume that the nucleus is a spherical cap of radius r and use standard mathematical formulae for the area of the solid-liquid interface, the area of the catalyst-solid interface and the volume of the nucleus. For 0 0 90° these are ... 

The experimental setup is depicted schematically in Figure 1.2. Upon varying the potential of the catalyst/working electrode the cell current, I, is also varied. The latter is related to the electrocatalytic (net-charge transfer) reaction rate re via re=I/nF, as well known from Faraday s law. The electrocatalytic reactions taking place at the catalyst/solid electrolyte/gas three-phase-boundaries (tpb), are ... 

As shown schematically in Figure 1.4, ions arriving under the influence of the applied current or potential at the three-phase boundaries catalyst/solid electrolyte/gas form there adsorbed species (0(a), Na(a)) which have only three possibilities ... 

Catalyst Solid Electrolyte PyPd T ft) Kinetics in D dr/dp D) Kinetics in A drfdpA 9 Global r vs

[Pg.161]

Catalyst Solid Electrolyte Pa Pd T f C) Kinetics inD dr/apu) Kinetics in drtdpA 9 Global rvs[Pg.161]

Solid electrolyte cells can be used to alter significantly the work function catalytically active, catalyst electrode surface by polarizing the catalyst-solid electrolyte interface. 

Figure 5.17. Schematic representation of a metal crystallite deposited on YSZ and of the changes induced in its electronic properties upon polarizing the catalyst-solid electrolyte interface and changing the Fermi level (or electrochemical potential of electrons) from an initial value p to a new value p -eri30 31 Reprinted with permission from Elsevier Science.

Figure 8.63, Scanning electron micrographs of the Rh/YSZ catalyst top view (up) and a cross section of the catalyst-solid electrolyte interface (down).67,68 Reprinted from ref. 67 with permission from the Institute for Ionics.

Figure 2. Hydrogen adsorption and desorption Isotherms for rhodium catalysts. Solid lines denote total adsorption and dashed lines denote reversible adsorption. The meaning of symbols Is as follows ...

Phase-transfer catalysis is a special type of catalysis. It is based on the addition of an ionic (sometimes non-ionic like PEG400) catalyst to a two-phase system consisting of a combination of aqueous and organic phases. The ionic species bind with the reactant in one phase, forcing transfer of this reactant to the second (reactive) phase in which the reactant is only sparingly soluble without the phase-transfer catalyst (PTC). Its concentration increases because of the transfer, which results in an increased reaction rate. Quaternary amines are effective PTCs. Specialists involved in process development should pay special attention to the problem of removal of phase-transfer catalysts from effluents and the recovery of the catalysts. Solid PTCs could diminish environmental problems. The problem of using solid supported PTCs seems not to have been successfully solved so far, due to relatively small activity and/or due to poor stability. 

Figure 47.2. (a) Effect of residence time 156 s, fresh catalyst (solid symbol) 80 s, catalyst used once (open symbol) and (b) effect of catalyst particle size in citral hydrogenation at 25°C, 6.1 bar total pressure, residence time 156 s, solvent ethanol, 0.1 g catalyst Ni/Si02, initial citral concentration 0.02 M. 

The hydrazone was subsequently treated with KOH under the action of MW to undergo Wolff-Kishner reduction (leading to PhCH2Ph) within 25-30 min in excellent yields (95 %). As an extension, the reaction of neat 5- or 8-oxobenzopyran-2(lH)-ones with a variety of aromatic and heteroaromatic hydrazines is substantially accelerated by irradiation in the absence of any catalyst, solid support, or solvent [66] (Eq. 14). 

It is anticipated that the equilibrium filter cake mass would depend strongly on the axial velocity through the cross-flow filter assembly. The shear rate at the filter surface will increase the entrainment of the catalyst solids for a given permeate flow rate. Therefore, for each differential pressure condition, the axial velocity will be varied in order to quantify the effect of the wall shear on the filter cake resistance term. 

M. Okumura, K. Tanaka, A. Ueda, and M. Haruta, The reactivities of dimethylgold(lll)beta-diketone on the surface of Ti02—A novel preparation method for Au catalysts. Solid State Ionics 95(1-2), 143-149 (1997). 

Fig. 9. A comparison of the results computed from Eq. (12) for transitional burning (indicated by O) with the observed burning rate behavior for silica-alumina catalyst (solid curve).

Catalyst. Solids, liquids, or gases, which in small percentages accelerate or enable the reaction of two or more other chemicals without itself being consumed in the reaction. Sometimes the catalysts react momentarily with the other chemicals, creating conditions that permit the desired reaction to take place. 

Turning now to titanium based catalysts, solid-state NM R data are quite... 

Figure 6.9 Comparison of the radial distribution functions of the Pt foil (dashed line) and the Pt/Si02 catalyst (solid line) in Ar. Arrows show the positions of the second, third and fourth coordination shells. The Pt foil Fourier amplitude was divided by 2 for scaling purposes. (Reproduced from Reference [30].)...

Here, our attention is focused on heterogeneous catalysts, solids that accelerate reactions in gas or liquid phase. In general, a solid catalyst (the whole formulation) consists of... 

Comparison of simulated pressure drop for different filters (A-D) due to catalyst (solid lines) to the experimental data (points) (Karadimitra et al., 2004). 

Fig. 16. Change of the absorbance signal as a function of time for (a) cyclohexene and (b) TBHP on an uncoated ZnSe IRE (thin line) and on a ZnSe IRE coated with a methyl-modified Ti-Si aerogel catalyst (solid line). At time t = 0, the concentration at the inlet of the ATR flow-through cell was switched from 0 to 3 mmol/L, and at t = 122 s, it was switched back again (50).

An ESR study by Yabrov et al. [355] revealed that, at least at low V205 content (0.05—5 wt. %), vanadium forms a solid solution of V4+ and V3+ in Ti02. The samples investigated were sealed in the reactor after steady state operation of the o-xylene oxidation at 350°C. The V4+ solid solution, which is considered the active phase, is not formed by the catalyst pretreatment at high temperature, but requires the interaction of the reaction mixture as was shown by the analysis of fresh catalysts. Solid state reactions between V2Os and Ti02 were also studied by Cole et al. [89]. 

Liquid acids such as HC1 or H2SO4 have been found to be efficient catalysts. However, the catalysts produce intermediate compounds having methylene-amino bonds, such as N-benzyl compound, C6H5N(COOCH3)(CH2C6H5NHCOOCH3) [1], These intermediates do not produce isocyanates and have a harmful influence on the next thermal decomposition step. Since these compounds must be catalytically transformed to desired MDU, the condensation reaction has to be carried out in two steps to use the best characteristics of each catalyst. Solid acid catalysts such as a perfluorinated ion-exchange resin (Nafion) have received limited attention as catalysts for the condensation reaction [2]. 

Keywords Asymmetric synthesis, Chiral catalysis, Diversity-based approaches, Supported chiral catalysts, Solid-phase chemistry... 

Fic. 21. Metal concentration versus contact time results for demetallation of (a) Ni-etioporphyrin at 27 pm Ni feed and (b) Ni-tetra(3-methylphenyl) porphyrin at 63 ppm Ni feed at 345°C and 6.99 MPa H2 (1000 psig) on oxide CoMo/A1203 catalyst. Solid lines represent model calculations (Ware and Wei, 1985a). 

The science of catalysis covers a large spectrum of phenomena. We observe—with some pride and joy—that this volume presents eight topics which, like the rainbow, form an almost systematic and complete sweep of the major classes of topics in catalysis. It spans from the most classical mechanistic study (P. W. Selwood), to a presentation of a hard practical application (M. Shelef et al). As we sweep across, we cover characterization studies of catalyst solids in terms of electronic (G. M. Schwab), surface chemical (H. A. Benesi and B. H. C. Winquist), as well as physicochemical and structural (F. E. Massoth) parameters, chemical reaction mechanisms and pathways (G. W. Keulks et al., and B. Gorewit and M. Tsutsui), and a topic on reactor behavior (V. Hlavacek and J, Votruba), which takes us from the single catalyst particle to the macroscopic total reactor operation. 

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