The pH and temperature evolution of the molecular configuration of oxo-tungsten(VI) species deposited on TiO2 by equilibrium deposition filtration and the temperature evolution of the samples texture are studied using in situ Raman spectroscopy, DR spectroscopy, N2 adsorption–desorption measurements, and TGA. Prior to drying, WO4 2– monomers retained above a bridging surface hydroxyl of TiO2 through H bonding (with a Ti2OH···O–WO3 umbrella configuration) prevail at pH = 9. A pH decrease results in a gradual transformation to an inner sphere monosubstituted species located above terminal surface oxygen (Ti–O–WO3). At pH = 7 both species coexist, whereas at pH = 5 the latter prevails with electrostatically retained polyoxotungstes also present. Heating to 100 °C causes the same effect resulted by the pH decrease at room temperature, that is, transformation of Ti2OH···O–WO3 into Ti–O–WO3, attributed to the removal of H2O molecules upon heating, thereby liberating surface Ti atoms. Progressive heating to higher temperatures causes further removal of surface hydroxyls (confirmed also by TGA) liberating more neighbor surface Ti atoms and favoring further anchoring. This leads to formation of bisubstituted dioxo (Ti–O)2–W(O)2 sites in the range 120–250 °C and to the prevalence of trisubstituted mono-oxo (Ti–O)3-WO sites at 430 °C. Polyoxotungstates are also detected in the sample with the highest W loading. The DRS spectra indicate a charge transfer effect between the surface O and Ti atoms proceeding via Ti–O–W surface bridges. Calcination of the support causes a decrease of the pore volume and pore area in the range of pores with small width and an increase in the range of pores with large width. This effect is not affected by the presence of the well dispersed “bi-dimensional” W species inferred by the Raman study.

Nickel catalysts are the most popular for steam reforming, however, they have a number of drawbacks, such as high propensity toward coke formation and intolerance to sulfur. In an effort to improve their behavior, a series of Ni-catalysts supported on pure and La-, Ba-, (La+Ba)-and Ce-doped γ-alumina has been prepared. The doped supports and the catalysts have been extensively characterized. The catalysts performance was evaluated for steam reforming of n-hexadecane pure or doped with dibenzothiophene as surrogate for sulphur-free or commercial diesel, respectively. The undoped catalyst lost its activity after 1.5 h on stream. Doping of the support with La improved the initial catalyst activity. However, this catalyst was completely deactivated after 2 h on stream. Doping with Ba or La+Ba improved the stability of the catalysts. This improvement is attributed to the increase of the dispersion of the nickel phase, the decrease of the support acidity and the increase of Ni-phase reducibility. The best catalyst of the series doped with La+Ba proved to be sulphur tolerant and stable for more than 160 h on stream. Doping of the support with Ce also improved the catalytic performance of the corresponding catalyst, but more work is needed to explain this behavior.

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The molecular structure and catalytic performance of (MoO x ) n /TiO 2 , (WO x ) n /TiO 2 and (VO x ) n /TiO 2 catalysts (synthesized by the equilibriumedepositionefiltration/EDF method) for oxidative dehydrogenation (ODH) of ethane were studied by in situ Raman spectroscopy at 430 C and catalytic measurements in the temperature range of 420e480 C. The extent of association within the deposited oxometallic phase followed the sequence (VO x ) n /TiO 2 >> (MoO x ) n /TiO 2 > (WO x ) n /TiO 2 ; a concurrent trend in reduction susceptibility was evidenced by exploiting the relative normalized Raman band intensities while monitoring the response of the vibrational properties of the catalytic samples under reactive (C 2 H 6 /O 2 /He) and reducing (C 2 H 6 /He) conditions by in situ Raman spectroscopy. The catalyst reactivity tracks the corresponding trend in reduction susceptibility as evidenced by the in situ Raman spectra. Selective reaction pathways are favored at high coverage whilst combustion routes are activated at low coverages due to the involvement of carrier lattice oxygen sites. The observed apparent reaction rates and activation energies are discussed in relation to various structural and reactivity aspects.