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Albonetti S.,Dip. Chimica Industriale Toso Montanari | Albonetti S.,Consortium for Science and Technology of Materials | Lolli A.,Dip. Chimica Industriale Toso Montanari | Lolli A.,Consortium for Science and Technology of Materials | And 4 more authors.
Applied Catalysis B: Environmental | Year: 2015

In the present work, a series of Au- and Au-Cu-containing catalysts based on different carriers such as TiO2 and CeO2 were studied with a view to increasing the activity and selectivity in 5-hydroxymethylfurfural oxidation by optimizing the interaction both between the metals and with the support. The results obtained demonstrated the high activity in HMF oxidation of gold supported on ceria and titania. Nevertheless, although the particle size of gold on both supports was comparable, Au/CeO2 showed significantly higher activity than Au/TiO2, thus corroborating the theory that not only the gold particle size, but the support also, plays a key role in HMF oxidation in the aqueous phase. Indeed, pre-made uniform nanoparticles, used for catalyst preparation, were surface-bound by poly(N-vinyl-2-pyrrolidone) - the stabilizer used during nanoparticle synthesis - whose presence proved to prevent the interaction of active phases with CeO2, while worsening the catalytic activity of both monometallic and bimetallic systems. The pre-treatment of the prepared catalysts was necessary to activate the materials, by maximizing the contact between the metal and the support and thus suggesting an important role of the ceria defects on 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid. © 2014 Elsevier B.V.

Benito P.,Dip. Chimica Industriale Toso Montanari | Gregori M.,Dip. Chimica Industriale Toso Montanari | Gregori M.,Consortium for Science and Technology of Materials | Andreoli S.,Dip. Chimica Industriale Toso Montanari | And 4 more authors.
Catalysis Today | Year: 2014

The effect of the preparation method on properties of Pd/Cu MCM-41 catalysts tested in the hydrodechlorination of CF3OCFClCF 2Cl to CF3OCFCF2 was studied. MCM-41 samples were synthesized using sodium silicate as silica source and cetyltrimethylammonium bromide as template. The incorporation of Pd and Cu active species has been performed by impregnation, inclusion in the MCM-41 synthesis procedure and using pre-formed Pd/Cu nanoparticles. The effect of the removal of the template was also studied using calcination and ionic exchange procedures. The hexagonal structure of MCM-41, large specific surface area and pore volume were preserved after inclusion of active species both as cations during the synthesis of MCM-41 or as Pd/Cu preformed nanoparticles. PXRD and HRTEM evidenced the formation of bimetallic particles in all the prepared catalysts; however their particle size and composition varied with the synthesis procedure. The template removal by ionic exchange avoided the sintering of copper species observed in calcined sample. The use of preformed nanoparticles led to small and well dispersed bimetallic species in the MCM-41 structure; however, also in this case, the template removal by calcination provoked both the increase of the particle size and the oxidation of metals. Catalytic performances in the hydrodechlorination of CF3OCFClCF2Cl, namely the dehalogenating activity and product selectivities, were dependent on catalysts properties. © 2014 Elsevier B.V.

Gregori M.,Dip. Chimica Industriale toso Montanari | Gregori M.,Consortium for Science and Technology of Materials | Benito P.,Dip. Chimica Industriale toso Montanari | Fornasari G.,Dip. Chimica Industriale toso Montanari | And 4 more authors.
Microporous and Mesoporous Materials | Year: 2014

A series of bimetallic mesostructured Pd/Cu MCM-41 catalysts were obtained by incipient wetness impregnation and direct hydrothermal synthesis using two different silica sources (silicates and Teos) and replacing the conventional hydrothermal treatment by the microwave hydrothermal one. Catalysts were tested in the hydrogen assisted dechlorination of CF3OCFClCF2Cl to CF3OCFCF2. The influence of the synthesis procedure on the supports and catalysts chemico-physical properties was investigated by XRD, N2 adsorption/desorption, HRTEM/EDS, and TPR. The incorporation of Pd and Cu in the course of MCM-41 synthesis, regardless of the hydrothermal treatment, did not destroy the typical hexagonal channel array and ordered pore system of MCM-41. However, the calcination for the removal of the template provoked the segregation of oxides, and thus large PdCu bimetallic particles are obtained after reduction. The impregnation leads to pore-occlusion, more remarkable for the sample obtained from silicates as silica source, and after reduction, both isolated monometallic Cu particles and large bimetallic PdCu particles coexist on the external surface of the support. The larger the metallic particles, the lower the conversion of CF3OCFClCF 2Cl; while the presence of monometallic particles may decrease the selectivity in CF3OCFCF2, fostering the formation of CF3OCHCF2 by dehalogenation. © 2014 Elsevier Inc. All rights reserved.

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