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Sulphated zirconia by sol–gel route. The effects of the preparative variables
No full textA single step sol–gel reaction starting from Zr alkoxides, in water–propanol mixtures, was employed to obtain ZrO2–SO4
powders; sulphuric acid was used both as the sulphating agent and as the catalyst of the polycondensation reaction in the gel
formation. The water/alkoxide ratio and the acid catalyst amounts were varied in the starting mixtures. Samples prepared by using
nitric acid as the reaction catalyst and subsequently impregnated with sulphuric acid were also obtained for the sake of comparison.
All the samples were calcined at three temperatures (470, 550, and 630 C) for the same time length (5 h). The different characterizations
evidence the role played by the sol–gel reaction conditions in affecting the physico-chemical bulk and surface properties
of the powders. Particularly, the water/alkoxide ratio, while not influencing the final structure of the catalyst, is important in the
development of a high surface area and in the retention of sulphur after the calcination step. The sulphur content, instead, is critical
for the crystal phase development. Surface segregation of sulphate groups is associated with the development of well-defined
crystallites as calcination temperature grows
Physico-chemical features and catalytic activity of sulfated zirconia prepared by sol-gel method.The role of the solvent evaporation step.
No full textZrO2-SO4 powders have been prepared by following a single-step sol-gel preparative route using zirconium propoxide as the starting compound. Sulfuric acid was employed both as the sulfating agent and as the catalyst of the polycondensation reaction in the gel formation. Two different series of dried precursors were obtained by either evaporating the solvent in an oven at 100°C (xerogels) or in supercritical conditions (aerogels). All the samples were calcined at three temperatures (470, 550, and 630°C) for the same time length (5 h). The powders were characterized for phase composition-crystallinity, surface area-porosity, sulfur content and surface state (XPS). The catalytic activity of the calcined samples was tested in the isomerization of n-butane in a continuous system at 150°C in absence of H2 and 250°C in presence of H2. The role played by the conditions of the solvent elimination, at the end of the sol-gel reaction, in affecting the physicochemical and catalytic properties of the powders is discussed
Direct synthesis of hydrogen peroxide on zirconia-supported catalysts under mild conditions
No full textPalladium catalysts supported on SO4
=-, Cl−-, F−-, and Br−-doped zirconia were tested for the direct synthesis of hydrogen peroxide under
very mild (1 bar and 20 ◦C) and nonexplosive conditions. The catalysts were characterized by thermogravimetric/differential scanning calorimetry
analysis, N2 physisorption, and temperature-programmed reduction before and after catalytic tests to investigate the oxidation state of the metal.
The catalytic tests were carried out in different solvents, and the effect of the Pd oxidation state was ascertained. The best catalytic results
were observed in methanol, using H2/O2 mixtures containing a large excess of oxygen and using the sulfate-doped zirconia catalyst. Surfaceoxidized
Pd0 catalysts showed high catalytic activity and the highest selectivity.
2006 Elsevier Inc. All rights reserved
Direct synthesis of H2O2 on monometallic and bimetallic catalytic membranes using methanol as reaction medium
No full textTubular catalytic membranes (TMCs) active in the direct synthesis of hydrogen peroxide were prepared, characterized, and tested using
methanol as the reaction medium. Low hydrogen peroxide selectivity was found when only palladium was used as a catalyst, whereas palladium/
platinum bimetallic samples gave higher productivity and selectivity, with an optimum molar ratio of 18. The H2O2 decomposition rate is
influenced by the feed gases. O2 improves H2O2 stability, whereas H2 causes hydrogen peroxide to decompose at a higher rate. The most likely
decomposition pathway should be the reduction of H2O2 to water by H2. Bromide ion was used as a promoter and when used in excess (60 ppm)
causes a decrease in overall catalytic activity.
2005 Elsevier Inc. All rights reserved
Active and recyclable sulphated zirconia catalysts for the acylation of aromatic compounds
No full textDirect synthesis of H2O2. The use of Pd loaded carbon coated asymmetric a-Al2O3 membranes
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Performances of Pd-Me (Me = Ag, Pt) catalysts in the direct synthesis of H2O2 on catalytic membranes
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