Oxidative methanol steam reforming on Cu/ZrO2 and Cu/CeO2/Al2O3 catalysts prepared by sol-gel method
Cammarano, Claudia (2009) Oxidative methanol steam reforming on Cu/ZrO2 and Cu/CeO2/Al2O3 catalysts prepared by sol-gel method. [Tesi di dottorato] (Inedito)
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Cu/ZrO2 and Cu/CeO2/Al2O3 systems were investigated as catalysts for oxidative steam reforming of methanol (OSRM). The materials were prepared by modified sol-gel methods and characterized for physical and chemical properties by chemical analysis, XRD, N2 adsorption, DTA, XPS, TPR and N2O dispersion measurements. The catalytic activity was investigated in two laboratory plants. The first one allowed a quantitative evaluation of the catalytic activity in oxidative steam reforming of methanol (OSRM) and steam reforming of methanol (SRM). The second apparatus allowed pre-treatments and in situ characterization of the catalysts before and after each SRM catalytic test and on-line semi-quantitative analysis of the products. Two different procedures, based on different Cu precursors were investigated for the preparation of Cu/ZrO2 systems: it was found that the preparation method strongly influences all the properties studied. Very high surface areas were observed and a highly dispersed Cu metallic phase was obtained after a reductive treatment with H2. The presence of ZrO2 favoured the Cu+ oxidation state, that has a likely role in the OSRM reaction. The catalysts showed high activity for the oxidative steam reforming of methanol. A noticeable activity was observed also with the not pre-reduced catalysts, indicating that the formation of a metallic phase, although with lower activity, can occur directly under reaction conditions. Cu/CeO2/Al2O3 systems were prepared by a totally new one pot sol-gel method. The catalysts showed a huge surface area and resulted to contain very dispersed CeO2 and CuO phases on a poorly crystalline alumina matrix. A highly dispersed Cu metallic phase was obtained after a reductive treatment with H2. The presence of CeO2 favoured the Cu+ oxidation state. The activity of the pre-reduced catalysts resulted high, in terms of hydrogen production rate, if compared with data on similar Cu/Ce/Al systems, notwithstanding the absence of the well known promoter ZnO. Also for these systems the unreduced materials showed a noticeable activity for the OSRM process, indicating that the metallic phase, although with lower activity, can be formed directly under reaction conditions. On the other hand, the reduction conditions (under H2 or methanol with different concentration) strongly influenced the properties of the active phase, since copper obtained under strong reducing conditions (under H2 or high methanol concentration) was more active than that obtained under milder conditions (low methanol concentration). The different catalytic performances observed in OSRM and SRM tests indicate a strong influence of the presence of O2 in the reaction system. The activity for SRM, in the absence of oxygen was, in fact very low. This behaviour was explained either considering the occurrence of H spillover or the CeO2 assisted oxidation of Cu to Cu+.
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