Gas diffusion in the funnel-shaped porous network of cogelled supported metal catalysts

Poster (2003)

Mass transfer in low-density xerogel catalysts

in AIChE Journal (2001), 47(8), 1866-1873

Texture and morphology of a Pd-Ag/SiO2 hydrodechlorination low-density xerogel catalyst prepared by a cogelation sot-gel process were characterized in detail to examine mass transfer in such catalysts ... [more ▼]

Texture and morphology of a Pd-Ag/SiO2 hydrodechlorination low-density xerogel catalyst prepared by a cogelation sot-gel process were characterized in detail to examine mass transfer in such catalysts. The catalyst consists of active Pd-Ag nanocrystallites trapped inside elementary 20 nm microporous silica particles arranged in larger aggregates, which constitute the macroscopic pellet. To reach active sites, reactants must first diffuse through large pores located between aggregates of SiO2 Particles and then through smaller pores located between those elementary particles inside the aggregates. Finally, they, diffuse through micropores located inside silica particles. Diffusion in such a "funnel" structure cannot be described assimilating the pellet to a pseudo-continuum. Diffusion should be examined carefully at three levels of decreasing size: the macroscopic pellet, the aggregate of silica particles, and the elementary silica particle. This approach shows that cogelled xerogel catalysts have remarkable mass-transfer properties. [less ▲]

Method for the determination of the surface composition of alloy nanocrystallites in bimetallic catalysts

Poster (2001)

Process for the preparation of a catalyst and its use for the conversion of chloroalkanes into alkenes containing less chlorine

Patent (2000)

Process for the preparation of a catalyst including a metal of group VIII and a metal of group Ib, according to which the mixture including the alkoxide precursor of an inorganic oxide and complexes ... [more ▼]

Process for the preparation of a catalyst including a metal of group VIII and a metal of group Ib, according to which the mixture including the alkoxide precursor of an inorganic oxide and complexes including the metals of group VIII and Ib and difunctional complexing compounds including an electron-donor group and a hydrolysable group is hydrolysed in order to form a gel. Process for the conversion of chloroalkanes into alkenes containing less chlorine by means of hydrogen, using such a catalyst. [less ▲]

Dispersed Pd-Ag alloys for selective production of olefins from chlorinated alkanes

in Studies in Surface Science and Catalysis (2000), 130

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 ▲]

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

in Studies in Surface Science and Catalysis (1998), 118

Hydrodéchloration sélective du 1,2-dichloroéthane en éthylène sur un catalyseur xérogel Pd-Ag/SiO2

in Récents Progrès en Génie des procédés (1997, September 24)

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 ▲]