Guido Petrini

Deactivation Phenomena on Ti-Silicalite

Abstract The stability and deactivation behavior of Ti-silicalite employed as a catalyst in the ammoximation of cycloexanone to cycloexanonoxime have been investigated. The reaction was performed in liquid phase using H2O2 as an oxidizing agent. The solid was characterized by various techniques: chemical analysis, thermogravimetry, IR and UV-Vis spectroscopy, XRD, gas adsorption and a Standard Activity Test. Three main deactivation processes are identified: (i) slow dissolution of the framework with accumulation of Ti on the external surface of the remaining solid; (ii) direct removal of Ti from the framework and (iii) pore filling by by-products.

Determination of transport parameters of porous catalysts from permeation measurements

Abstract Pressure dependences of the permeability of various non-adsorbing gases were measured for several porous catalysts. A modified Ridgen-Blaine quasi-stationary method was applied for permeability measurements using a constant-volume electronic pressure transducer. To fit the experimental data properly, it was necessary to consider the flux equation for the transition region between Knudsen flow and viscous flow with slip. The flux equation derived for a capillary was transformed for a porous medium using the model of mean transport pore where the slip constant was considered to be an adjustable parameter. Values of this constant found experimentally for the catalysts studied (0.8–1.0) were only slightly higher than the values expected for capillaries (0.6–0.8). The flux equation was verified in the whole transition region between the Knudsen and the continuum region using various gases and catalysts with different pore sizes. The flux equation parameters characterize the transport properties of the individual porous media independently of measurement conditions (pressure, temperature, gas used).