Harding Bliss

Monte carlo simulation of a catalytic surface: Activity and selectivity of γ-alumina for dehydration

Abstract The acidic properties and catalytic activity of oxide surfaces have been shown in a number of cases to be directly influenced by their degree of hydration. In the present work the rates and selectivities of ethanol dehydration on a well characterized gamma alumina have been measured experimentally over the temperature range of 180 to 400 °C with feeds containing 0, 10, 20, and 40 mole % water. The effects of surface hydration and feed composition are compared with the predictions of a Monte Carlo simulation based on a model of the alumina surface and the mechanism of the dehydration reaction. The simulation is in good agreement with experiment, and points clearly to the distinctions which can be made between the separate effects of reaction energetics and surface configurations on rate and selectivity in the reaction.

Diffusional mass transport of nonadsorbed gases within porous structures: I. Experimentation and correlation

Abstract Counterdiffusion flux and flux ratio have been measured for the argon-helium system in four different, well-characterized porous structures. Pressures from 1 to 14.6 atm and temperatures from 0 ° to 69 °C were employed in the investigation. Care was taken to avoid the effects of extraneous factors in experimental work, and to ensure the absence of transport by surface diffusion. Variation of flux with pressure, temperature, and porosity is discussed with regard to the equations defining diffusion in transition range capillaries.

An experimental study of electronic factors in the dehydrogenation of ethanol on thin film ZnO

Electron transfer mechanisms involved in the adsorption and catalytic dehydrogenation of ethanol on thin-film zinc oxide were investigated. A primary objective was to measure changes in the electrical conductivity of the catalyst resulting from adsorption and surface reaction processes, and to study the effects of electrical fields in activity, selectivity and adsorptive capacity of the zinc oxide. At low temperatures ( 225 °C) the composite adsorbate layer, ethanol plus reaction products, also behaved as a donor. Individual components hydrogen, water, and ethylene adsorb as weak donors at 150 °C, while acetaldeyde adsorbs as a strong acceptor under such conditions. These results indicate that under reaction conditions the adsorbed layer consists primarily of ethanol and hydrogen product, the reaction step involving immediate desorption of acetaldehyde product. Field-effect experiments were conducted for temperatures from 100 to 250 °C. The activity and selectivity of the catalyst were not changed by external dc fields up to 104 V/cm, however strong effects of the field on the adsorptive capacity of the catalyst were observed for T ≥ 200 °C. These results indicate that the rate-limiting step is not affected by the surface concentration of free electrons and also suggests that the overall reaction rate is not limited by adsorption-desorption steps.

Diffusional mass transport of nonadsorbed gases within porous structures: II. Structural significance of the convergent-divergent pore model

Abstract Experimental results of counterdiffusion studies are correlated with the convergent-divergent pore structure model proposed previously. Relationship of the parameters of the model to porous structure properties is discussed; it is shown that these quantities may be determined from the volume-area distribution of a material and that the model may thus be employed for prediction of porous structure effects on diffusional mass transport.