A study of copper/silica catalysts: reduction, adsorption and reaction

Metal Particle Size in Silica-Supported Copper Catalysts. Influence of the Conditions of Preparation and of Thermal Pretreatments

“…(1) The classical incipient wetness impregnation method may lead to metal particles (∼30 Å) as small as in samples prepared by cationic exchange, and not to a bimodal distribution of sizes with a population of large particles as reported in refs and , at least provided that the drying step is performed at room temperature. It is shown that the drying step, so often neglected in the literature, has a drastic influence on the size of the metal particles even though calcination and reduction are performed at much higher temperature.…”

“…It can be noted that the influence of the drying step (temperature and duration) on the size of metal particles has been completely neglected in the previous studies on impregnated Cu/SiO 2 samples. , More generally speaking, this step is usually neglected in the preparation of supported catalysts, and samples are usually dried in air at ∼100 °C without special care. In contrast to the published results (see Introduction), our results show that it is possible to obtain small metal particles in impregnated Cu/SiO 2 samples and that the key step to generate small metal particles is to dry the samples at room temperature.…”

“…They are usually prepared by impregnation with Cu(NO 3 ) 2 ·3H 2 O, , Cu(acetate) 2 ·H 2 O, − or CuCl 2 , by cationic exchange with [Cu(NH 3 ) 4 (H 2 O) 2 ] 2+ 15-19 or [Cu(en) 2 (H 2 O) 2 ] 2+ , by adsorption of Cu(acac) 2 , , and by deposition−precipitation of Cu(NO 3 ) 2 ·3H 2 O. ,− Among these studies, only a few on the metal particle sizes have been reported. For samples prepared by impregnation with copper nitrate, Jackson et al reported either a bimodal distribution of particle sizes, 60−100 and ∼4000 Å, or a single distribution of large particles, ∼4000 Å, depending on the silica support. Kuipjers et al reported a bimodal distribution in a 25 wt % Cu/SiO 2 catalyst: numerous particles smaller than 200 Å and a small number of very large ones, up to 3000 Å.…”

“…As such or promoted, the Cu/SiO 2 materials are efficient catalysts for many reactions: hydrogenation of alkynes to alkenes − and of ethene to ethane, selective hydrogenation of α,β-unsaturated carbonyl compounds to their corresponding unsaturated alcohols, methanol synthesis from H 2 and CO or CO 2 , dehydrogenation of alcohols, − hydrogenolysis of esters to their corresponding alcohols. ,,, They are also active for the water gas shift reaction . Often, their catalytic properties including deactivation depend on the size of the metal particles and the metal−support interaction, i.e., on the preparation route of these materials. ,,,,, It is therefore important to be able to control the size of the metal particles through the various steps of preparation leading to the activated catalyst.…”

“…This work deals with the preparation of silica-supported copper catalysts. They are usually prepared by impregnation with Cu(NO 3 ) 2 ‚3H 2 O, 9,10 Cu(acetate) 2 ‚H 2 O, [11][12][13] or CuCl 2 , 14 by cationic exchange with [Cu(NH 3 ) 4 (H 2 O) 2 ] 2+ [15][16][17][18][19] or [Cu-(en) 2 (H 2 O) 2 ] 2+ , 20 by adsorption of Cu(acac) 2 , 21,22 and by deposition-precipitation of Cu(NO 3 ) 2 ‚3H 2 O. 10,[23][24][25] Among these studies, only a few on the metal particle sizes have been reported.…”