Preparation, performances and reaction mechanism for the synthesis of H2O2 from H2 and O2 based on palladium membranes

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Physico-chemical features and catalytic activity of sulfated zirconia prepared by sol-gel method.The role of the solvent evaporation step.

ZrO2-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\ub0C (xerogels) or in supercritical conditions (aerogels). All the samples were calcined at three temperatures (470, 550, and 630\ub0C) 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\ub0C in absence of H2 and 250\ub0C 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

Sulphated zirconia by sol\u2013gel route. The effects of the preparative variables

A single step sol\u2013gel reaction starting from Zr alkoxides, in water\u2013propanol mixtures, was employed to obtain ZrO2\u2013SO4 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\u2013gel 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