Catalisadores de cobre suportados sobre óxido misto CeOr Ti02 preparados pelo método sol-gel: camcterizações fisico-quimicas e teste catalítico -conversão do metanol. São Cartos, 2001. 133 p. ;;;~;-~~~~~~~-~~~;/~~;:;;;:(~~~~~r)
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Prafa. Dra. ELISABETE MOREIRA ASSAF -IQSC/USP -------~~-------~---~--~--------------------------------------------------------------Prof. Dr. DILSON CARDOSO -UFSCar
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)f6stractThe N2 adsorption, X-ray diffraction, transmission electron microscopy, X-ray absorption and X-ray photoelectron spectroscopy techniques were employed in this work in order to study the structural and textural properties of the copper catalysts supported on ceria-modified Ti02, which were prepared by sol-gel method. The catalytic performance of the system was tested for methanol conversion.Samples with low content of ceria presented the highest surface area. The stability of Ti02 towards sintering showed higher with addition of ceria. The distribution of TiOz and Ce02 crystallographic phase was dependent of cerium content. The addition of ceria to the support modified the mechanisms of titania formation and caused the inhibition of anatase-rutilo transformation, provoked the formation of titania crystallite with smaller size and prevented the sintering of the sample. The images obtained by TEM confirmed that titania crystallite size became smaller with the addition of cerium. The pré-and pós-edges features of Ti K-edge XANES spectra for catalysts presented same variations with different ceria contents, which are also related to decreasing of the size of Ti02-anatase crystalline. The XANES analysis for Ce-Lm edge and the Ce 3d XPS spectra confirmed that the cerium atoms present in the catalysts are tetravalent. Furthermore, the Ce-Lm edge EXAFS analysis indicated that the local structure around Ce atoms was highly distorted for sample with low cerium contento The catalysts presented quite different Cu K-edge XANES spectra compared to the spectra of the CuO reference sample and the XPS spectrum reveled the presence of only Cu2+. The XPS results showed that a second Ti4+ species appear as the cerium content increases.Based on these results, we propose that a cerium surface layer is formed on the titania particles in a Ce-O-Ti structure, in which the cerium had its local structure distorted and a second Ti4+species was originated on the surface. In this situation, copper species are well dispersed on the mixed support and the catalyst presented a good methanol conversion indicating a synergistic effect between Cu and the Ce02-Ti02 support.xi. A conversão do metanol a formiato de metila ou formaldeído é uma reação industrialmente importante uma vez que estes produtos são utilizados como matéria prima na preparação de muitos produtos químicos. Para estas reações de transformação, a oxidação catalítica é a forma mais aplicada, pela qual é possível obte...