Pd–Ag/SiO2 xerogel catalyst forming by impregnation on alumina foams (original) (raw)
Related papers
Image analysis of X-ray microtomograms of Pd–Ag/SiO2 xerogel catalysts supported on Al2O3 foams
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004
In order to preshape and mechanically strengthen, Pd-Ag/SiO 2 xerogel catalysts were carried out in A1 2 0 3 foams (pore-sizes ~40 µm). The final material consists of a Pd-Ag/SiO 2 xerogel immobilized in the open cells of the alumina foam. The localization of the xerogel catalyst in alumina foams of various pore structure was studied by X-ray microtomography. The three-dimensional (3D) porous structure was reconstructed from the consecutive cross-sections obtained by this technique. Total porosity, porous density distribution, and pore-size distribution were determined by image analysis on the free and impregnated supports. Our results show that the success of the used impregnation technique depends on the pore structure of the support.
Journal of Catalysis, 2004
Pd/SiO 2 , Ag/SiO 2 , and Cu/SiO 2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag, and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). It appears that the metal complex acts as a nucleation agent in the formation of silica particles. The resulting catalysts are then composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica particles exhibiting a monodisperse microporous distribution. The metal dispersion has been determined from CO and O 2 chemisorption, TEM, and X-ray diffraction. Although metallic particles are located inside silica particles, their complete accessibility, via the micropore network, has been shown. 1,2-Dichloroethane hydrodechlorination over Pd/SiO 2 catalysts mainly produces ethane and the specific hydrodechlorination rate per gram of Pd decreases when metal loading increases. Hydrodechlorination over Pd/SiO 2 catalysts is a structure-insensitive reaction with regard to the ensemble size concept. Benzene oxidation over Ag/SiO 2 and Cu/SiO 2 catalysts produces H 2 O and CO 2 only and specific oxidation rate per gram of metal decreases when silver and copper loadings increase. Furthermore, it is concluded that benzene oxidation is a structure-insensitive reaction.
2006
The aim of this work is to simplify and generalize the synthesis procedure of bimetallic supported catalysts by sol-gel process. For Pd-Ag/SiO 2 co-gelled xerogels catalysts a number of synthesis procedures were compared: use of one or two specific alkoxides able to form a chelate with palladium and/or silver cations, reagent mixing in one or two steps, use of industrial grade chemicals instead of laboratory grade chemicals. The catalysts obtained are quite similar: same metal dispersion, same tailored morphology, same localization and accessibility of Pd-Ag alloy nanoparticles inside microporous silica, same activity and selectivity for hydrodechlorination of 1,2-dichloroethane into ethylene. For catalyst production at large scale the synthesis can be achieved in one step with 3-(2-aminoethyl)aminopropyltrimethoxysilane of industrial grade as chelating alkoxide, tetraethylorthosilicate (TEOS) of industrial grade and ethanol denatured with diethyl phthalate.
Fractal Characterization of Wide Pore Range Catalysts: Application to Pd–Ag/SiO2 Xerogels
Journal of Colloid and Interface Science, 2000
Fractal analysis has been applied to characterize the structure of Pd-Ag/SiO 2 catalysts dried under vacuum (150 • C and 12 hPa) with different concentrations of Pd-Ag. Nitrogen adsorptiondesorption, mercury porosimetry, and small-angle X-ray scattering measurements have been used. The different approaches to fractal analysis and their conditions of applicability are briefly described. Results are discussed in relation to those derived previously from classical interpretations. This analysis shows that Pd-Ag/SiO 2 xerogels exhibit a very open self-similar pore structure analogous to the structure of supercritically dried aerogels and that the micropore texture can be tailored by varying the silver content.
Journal of Non-crystalline Solids, 2005
Pd-Ag/SiO 2 and Pd-Cu/SiO 2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of either Pd and Ag or Pd and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). After an extensive study of the influences of synthesis operating variables over structural characteristics of gels, highly dispersed bimetallic Pd-Ag/SiO 2 and Pd-Cu/SiO 2 xerogel catalysts were obtained. These samples are then composed of completely accessible Pd-Ag and Pd-Cu alloy crystallites with sizes of 2-3.5 nm located inside silica particles exhibiting a monodisperse microporous distribution. It appears also that the metal complex acts as a nucleation agent in the formation of silica particles.
Nucleation Phenomenon in Silica Xerogels and Pd/SiO 2 , Ag/SiO 2 , Cu/SiO 2 Cogelled Catalysts
Journal of Sol-gel Science and Technology - J SOL-GEL SCI TECHNOL, 2003
Pd/SiO2, Ag/SiO2 and Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). It appears that, in cogelled samples, the metal complex acts as a nucleation agent in the formation of silica particles. The resulting catalysts are then composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica porous particles with a monodisperse microporous distribution. Xerogels without metal synthesized with EDAS and TEOS (C. Alié, R. Pirard, A.J. Lecloux, and J.-P. Pirard, J. Non-Cryst. Solids 289, 88 (2001)) verify this hypothesis of nucleation by EDAS.
Chemical Engineering Journal, 2009
Selective production of middle distillate (C 10 -C 20 ) from synthesis gas (CO + H 2 ) through wax hydrocracking was carried out in a dual-bed reactor. Co/TiO 2 catalyst was used in the first-bed reactor to produce wax (C 21+ ) from synthesis gas, and Pd-loaded mesoporous alumina xerogel (denoted as Pd/XA) catalysts were used in the second-bed reactor to produce middle distillate through wax hydrocracking. The effect of calcination temperature of mesoporous alumina xerogel supports on the wax hydrocracking performance of Pd/XA catalysts was investigated. The increment of middle distillate selectivity increased with increasing medium acidity of Pd/XA catalyst. Among the Pd/XA catalysts, the Pd catalyst loaded on mesoporous alumina xerogel support calcined at 800 • C retained the highest medium acidity, and at the same time, showed the best catalytic performance in the hydrocracking of wax.
Applied Catalysis A: General, 2004
The combination of results from carbon monoxide chemisorption, X-ray diffraction, and transmission electron microscopy allowed calculating the surface composition of the palladium-copper nanoparticles in Pd-Cu/SiO 2 cogelled xerogel catalysts. Values obtained indicate a very pronounced surface enrichment with copper. Surface compositions obtained with this method, which combines three different experimental techniques, are in agreement with the literature data previously obtained for surface segregation in Pd-Cu/SiO 2 catalysts by other techniques as low energy ion scattering and X-ray photoelectron spectroscopy. While 1,2-dichloroethane hydrodechlorination over pure palladium mainly produces ethane, increasing copper content in bimetallic catalysts results in an increase in ethylene selectivity, to reach 100% in ethylene selectivity for the sample containing 1.4 wt.% of palladium and 3.0 wt.% of copper.
Microporous and Mesoporous Materials, 2015
Ni-Cu/SiO 2 xerogel catalysts have been synthesized by cogelation of industrial tetraethoxysilane (Dynasil) and chelates of Ni and Cu with industrial 3-(2aminoethylamino)propyltrimethoxysilane (Dynasilan DAMO) in industrial ethanol denaturated with diethyl phtalate. Despite the use of industrial grade reagents, highly dispersed bimetallic Ni-Cu/SiO 2 xerogel catalysts were obtained. These samples are composed of completely accessible Ni-Cu alloy crystallites with sizes of 1.6-3.4 nm located inside silica particles exhibiting a monodisperse microporous distribution. It appears that the bimetallic complex acts as a nucleation agent in the formation of silica particles. The combination of results obtained from the calculation of the metal ratio in catalysts, H 2 chemisorption and transmission electron microscopy allowed calculating the surface composition of the nickel-copper particles in Ni-Cu/SiO 2 cogelled xerogel catalysts. Values obtained indicate a very pronounced surface enrichment with copper. While 1,2dichloroethane hydrodechlorination over pure nickel mainly produces ethane, increasing copper content in bimetallic catalysts results in an increase in ethylene selectivity. The specific consumption rate of 1,2-dichloroethane decreases when copper loading increases. The turnover frequency, that is, the number of catalytic cycle per active site (nickel atom and its surrounding copper atoms) and per second, seems to be independent of surface composition of alloy particles.
A TEM study on the localization of metal particles in cogelled xerogel catalysts
Journal of Catalysis, 2006
The localization of metal and alloy particles in monometallic Pd/SiO 2 and bimetallic Pd-Ag/SiO 2 sol-gel catalysts prepared by cogelation was examined by rotating transmission electron microscopy. The analysis of the resulting micrograph series provides a direct proof that the 2-to 3-nm active metal nanoparticles in those catalysts are located inside microporous silica particles or aggregates. Such localization has long been suspected but with, up to now, no direct evidence.