Deactivation mechanisms and regeneration of a bimetallic hydrodechlorination catalyst

in Studies in Surface Science and Catalysis (1999), 126

The temporal evolution of the activity and selectivity of a 1.9%Pd-3.7%Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene is examined. A comparison between the ... [more ▼]

The temporal evolution of the activity and selectivity of a 1.9%Pd-3.7%Ag/SiO2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene is examined. A comparison between the physico-chemical properties of the fresh catalyst and of the deactivated one suggests a deactivation mechanism by poisoning or coking of Ag sites at the surface of the active Pd-Ag particles. A regeneration treatment is proposed which allows to restore the initial properties of the fresh catalyst. [less ▲]

Preparation of low-density xerogels through additives to TEOS-based alcogels

in Journal of Non-Crystalline Solids (1999), 246(3), 216-228

A new process for preparing silica xerogels with similar textural properties to silica aerogels by drying under vacuum has been studied. The xerogels are produced by adding, before gelation, 3-(2 ... [more ▼]

A new process for preparing silica xerogels with similar textural properties to silica aerogels by drying under vacuum has been studied. The xerogels are produced by adding, before gelation, 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) to tetraethylorthosilicate (TEOS)-based alcogels, synthesised in a single base-catalysed (NH3) step. It is hypothesized that EDAS acts as a nucleation agent leading to silica particles with a hydrolysed EDAS core and a shell principally made of hydrolysed TEOS. The EDAS concentration and the basicity of the aqueous NH3 solution are important parameters influencing the resistance of the gel to drying stress. A decreasing EDAS/TEOS ratio or an increasing concentration of NH3 at constant EDAS content leads to less shrinkage during drying and so the final pore volume is larger. Gels prepared with a low EDAS/TEOS ratio (about 0.03) contain large particles (similar to 20 nm) due to the nucleation process by EDAS, thus the pores between those particles are also large and the drying stress is reduced. (C) 1999 Published by Elsevier Science B.V. All rights reserved. [less ▲]

Biodegradable and biocompatible inorganic-organic hybrid materials. 3. A valuable route to the control of the silica porosity

in Langmuir (1998), 14(7), 1905-1910

Porous silica has been successfully prepared from poly(epsilon-caprolactone)-silica hybrid materials on the basis of the template approach. The final texture of the porous silica has been analyzed by the ... [more ▼]

Porous silica has been successfully prepared from poly(epsilon-caprolactone)-silica hybrid materials on the basis of the template approach. The final texture of the porous silica has been analyzed by the nitrogen adsorption-desorption technique and by small-angle X-ray scattering (SAXS). The porosity of silica can be tailored by the poly(epsilon-caprolactone) (PCL) template, particularly molecular weight, molecular weight distribution, content, and type and number of reactive groups per chain. Increasing the molecular weight, content, and chain polydispersity of the PCL template and decreasing the reactivity and number of reactive groups per PCL chain result in a more heterogeneous microporosity and, as a rule, in larger pores, a broader pore size distribution, a larger specific surface area, and a larger total and microporous volume. [less ▲]

High temperature catalysts through sol-gel synthesis

in Journal of Non-Crystalline Solids (1998), 225

Porous silica obtained from biodegradable and biocompatible inorganic-organic hybrid materials

in Journal of Sol-Gel Science and Technology (1998), 13(1-3), 415-419

Porous silicas have been successfully prepared from poly(ε -caprolactone) (PCL)-silica hybrid materials based on the template approach. The final texture of the porous silica can be tailored by the PCL ... [more ▼]

Porous silicas have been successfully prepared from poly(ε -caprolactone) (PCL)-silica hybrid materials based on the template approach. The final texture of the porous silica can be tailored by the PCL template, i.e., molecular weight and molecular weight distribution, content, type and number of reactive end-groups per chain. Porosity has been investigated by nitrogen adsorption-desorption technique and small angle X-ray scattering (SAXS). [less ▲]

Pd-Ag/SiO2 sol-gel catalysts designed for selective conversion of chlorinated alkanes into alkenes

Conference (1998)

Kinetic study of 1,2-dichloroethane hydrodechlorination with a Pd-Ag/SiO2 sol-gel catalyst

in 1st European Congress on Chemical Engineering, ECCE1 (Vol. 4, pp. 2919-2922) (1997, May 04)

Palladium-silver sol-gel catalysts for selective hydrodechlorination of 1,2-dichloroethane into ethylene - I. Synthesis and characterization

in Journal of Catalysis (1997), 172(2), 322-335

Low-density xerogel Pd-Ag/SiO2 catalysts were prepared by a cogelation of tetraethoxysilane with organically substituted alkoxides capable of forming chelates with palladium and silver ions, followed by a ... [more ▼]

Low-density xerogel Pd-Ag/SiO2 catalysts were prepared by a cogelation of tetraethoxysilane with organically substituted alkoxides capable of forming chelates with palladium and silver ions, followed by a drying under vacuum, a calcination, and a reduction. The resulting Pd-Ag alloy particles have diameters of about 2-3 nm and are dispersed inside the silica particles which exhibit a monodisperse micropore size distribution centered at 0.8 nm. At low silver loading, the composition of the bimetallic particles is almost identical to the overall composition, but when this loading is increased, the percentage of silver in the alloy particles is appreciably lower than the overall percentage, In all bimetallic samples, a few large pure silver particles are observed. When dried under vacuum, the xerogels exhibit a texture similar to that of aerogels dried under supercritical conditions with pore volumes in the range 2-6 cm(3)/g and pores ranging from micro- to macropores of several hundred nanometers. When the silver loading is increased, xerogels containing palladium show aggregates of increasingly interpenetrated silica particles. This is explained bq an aggregation, during the gelation reaction, of colliding SiO2 particles which is limited by an increasingly slow sticking reaction due to the growing basicity in the precursor solution when the concentrations of Ag and associated compounds are increased. During thermal treatments, the Pd-Ag alloy seems to form by the migration, through the porous network, of silver which finally alloys with Pd crystallites trapped inside SiO2 particles. Whereas ethane is the main product when hydrodechlorination of 1,2-dichloroethane is performed over pure palladium, the dilution of this active metal by silver leads to a strong increase in ethylene selectivity. (C) 1997 Academic Press. [less ▲]

Rheological characterization on the BaTiO3 sol-gel transition

in Faraday Discussions (1997), 101

Textural properties and thermal stability of silica-zirconia aerogels

in Journal of Sol-Gel Science and Technology (1997), 8