Browsing by Subject "Catalyst supports"

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Open Access
Gold catalysts supported on ceria doped by rare earth metals for water gas shift reaction: influence of the preparation method
(2009) Andreeva, D.; Ivanov, I.; Ilieva, L.; Abrashev, M. V.; Zanella, R.; Sobczak, J. W.; Lisowski, W.; Kantcheva, M.; Avdeev, G.; Petrov, K.
Gold catalysts based on ceria, doped by various RE metals (La, Sm, Gd, Yb, Y) were studied. The influence of the preparation methods on structure, properties and catalytic activity in the WGS reaction was investigated. The catalysts' supports were prepared using two different methods: co-precipitation (CP) and mechanochemical activation (MA). The catalysts were tested in a wide temperature interval without and after reactivation. All samples were characterized using a combination of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) and TPR. It was found that the catalytic activity of MA catalysts is higher than CP ones. The gold catalysts based on ceria doped by Yb and Sm exhibited the highest activity. After reactivation in air the MA samples almost kept the WGS activity same, while the CP catalysts increased it. The catalysts of a single- and double-phase structure are formed as a result of CP and MA preparation, respectively. There are no big differences in the gold particles size (2-3 nm) depending on dopants and on the preparation techniques. The RS spectra analysis indicates that most probably the oxygen vacancies are adjacent to Me3+ dopant and the ceria structure seems to be better ordered than in the case of alumina as a dopant. There is no distinct correlation between reducibility and WGS activity. The XPS analysis disclose positively charged gold particles in addition to metallic gold within a surface region of fresh samples and only metallic gold on the samples after catalytic processing. There is no simple correlation between the concentration of Ce3+ in the samples and their WGS activity.
Open Access
Gold supported on ceria doped by Me3+ (Me = Al and Sm) for water gas shift reaction: Influence of dopant and preparation method
(2010) Andreeva, D.; Kantcheva, M.; Ivanov, I.; Ilieva, L.; Sobczak, J. W.; Lisowski, W.
Gold catalysts supported on ceria doped by Sm and Al were studied. The influence of the preparation method, as well as the nature of dopants on the structure, properties and WGS activity are investigated. The applied methods of preparation cause the modification of ceria in a different extent. In the sample prepared by co-precipitation (CP) and doped by Al, the vacancies are located within the bulk of ceria structure, whereas in the corresponding AuCeSmCP sample the vacancies are located most likely around Sm and the ceria structure seems to be better ordered than the Al doped ceria. There is no distinct correlation between the reducibility and WGS activity of the studied catalysts. The Au 4f XPS spectra of fresh samples reveal higher contribution of dispersed form of Au for Sm doped catalysts than for the corresponding Al doped samples. The Ce 3d XPS spectra disclose also a higher concentration of Ce3+ evaluated before the catalytic operation for Sm doped catalysts as compared with the Al doped fresh samples. The observations by "in situ" FT-IR spectroscopy agree well with the model of active sites and the, mechanism of the WGS reaction proposed recently by some of us. The amount of formate species observed on the AuCeSmCP is higher than that on the AuCeAlCP catalyst and parallels the catalytic activity. The higher concentration of active sites on the surface of the AuCeSmCP catalyst facilitates the dissociation of water.