Gas-solid exchange

This assumes that the gas-solid exchange kinetics at the interface is rapid. When this process affects the exchange kinetics significantly dieii analysis of concentrations layer by layer in die diffused sample is necessaty. This can be done by the use of SIMS (secondary ion mass spectrometry) and the equation used by Kihier, Steele and co-workers for this diffusion study employs a surface exchange component. 

FIGURE 14 A Buhler HTK 1 camera mounted on a STOE diffractometer. The large cooling plate, the substantial surface of heated metal (the central strip serves as a sample holder, length 5 cm) and the large dead volume preclude an effective gas-solid exchange, lead to poor catalytic performance and thus render difficult the task of detection of products during XRD analysis. 

Boreskovl l and Winter, the gas-solid exchange reaction obeys first-order kinetics... 

Interdiffusion gradients produced by annealing at 1100 and 1200C yielded the self-diffusion coefficients that were comparable to those obtained from gas-solid exchange, indicating that the surface exchange reaction was fast enough. The results were interpreted in terms of a defect model in which O diffusion occurred by an... 

Diffusion of oxygen in monoclinic zirconia was studied using the oxygen-18 gas-solid exchange technique. The zirconia was in the form of spheres. Diffusion was measured as a function of equivalent oxygen pressure, using oxygen and CO-CO2... 

Thus for a fast fluidization, internals are used to redistribute the axial and radial gas-solid flow structure, that is, to improve the uniformity of gas-solid flow structure in space and to change the core-annulus flow structure, so as to promote radial gas-solid exchange. 

The Pd-ZSM-5 catalysts are prepared by impregnation and by solid exchange methods on the carrier of HZSM-5 and NaZSM-5 (Si/Al = 26) with variable palladium loading and different pre-treatment gas (He and O2). N2-physisorption, DRX and CH4-TPR are the main techniques used to characterise these catalysts. Furthermore, total methane oxidation is used to test their catalytic activity. Among the preparative variables, the solid exchange method, the NaZSM-5 support and the increase of the palladium loading improve considerably the activity of the Pd-ZSM-5 catalysts in methane oxidation. 

Furthermore, no significant differences are observed on the methane conversion or on the ignition temperatures of the Pd2HZSHe and the Pd2HZS02 catalysts. This result presumes that the catalyst pre-treatment with oxidant or with inert gas has the same effect on the activity of the Pd-HZSM-5 catalysts prepared by the solid-exchange method. Moreover, a noticeable methane conversion increase is observed when the NaZSM-5 support is used instead of the HZSM-5 zeolite. The ignition temperatures... 

Returning to the momentum equations, the third term on the right-hand side of Eqs. (145) and (146) contains the gas-solid momentum-exchange models Likewise, the fourth term on the right-hand side of Eqs. (146) contains the solid-solid momentum-exchange model fsm . Note that because solid-solid interactions conserve momentum, the latter must be defined such that... 

SCO SCPC SD SEC SMR SNG SOFC SPE SRES SULEV SUV Synthetic crude oil Super-critical pulverised coal System dynamics US Securities and Exchange Commission Steam methane reformer Synthetic natural gas Solid-oxide fuel cell Society of Petroleum Engineers IPCC Special Report on Emissions Scenarios Super-ultra-low-emission vehicle Sport utility vehicle... 

Agitated tank reactors Batch agitated reactor This is a batch stirred tank reactor. For liquid-solid systems, the liquid is agitated by a mechanical apparatus (impeller) and the reactor is of tank shape. For gas-solid systems, the gas is agitated and rapidly circulated through a fixed-bed of solids. This reactor is basically an experimental one used for adsorption, ion exchange, and catalysis studies. 

That products of intermediate oxidation level can be detected in the photocatalytic reactions of hydrocarbons and fossil fuels is also consistent with a surface bound radical intermediate . Photocatalytic isotope exchange between cyclopentane and deuterium on bifunctional platinum/titanium dioxide catalysts indicates the importance of weakly adsorbed pentane at oxide sites. The platinum serves to attract free electrons, decreasing the efficiency of electron-hole recombination, and to regenerate the surface oxide after exchange. Much better control of the exchange is afforded with photoelectrochemical than thermal catalysis > ) As before, hydrocarbon oxidations can also be conducted at the gas-solid interface... 

In adsorption chromatography the mobile phase is usually a liquid and the stationary phase is a finely-divided solid adsorbent (liquid-solid chromatography). Separation here depends on the selective adsorption of the components of a mixture on the surface of the solid. Separations based on gas-solid chromatographic processes are of limited application to organic mixtures. The use of ion-exchange resins as the solid phase constitutes a special example of liquid-solid chromatography in which electrostatic forces augment the relatively weak adsorption forces. 

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