Alessandra Frattini

Heteropolyacids as effective catalysts to obtain zero sulfur diesel

This paper deals with the catalytic properties of different supported heteropolyacids (HPAs), both molybdenum- and tungsten-based, in the oxidative desulfurization process of diesel. We are jointly developing a new oxidative desulfurization process, aimed at reducing the sulfur content in diesel to less than 10 ppm (parts per million) using in situ produced peroxides. In this new process, high-molecular-weight organosulfur compounds, such as 4,6-dimethyl-dibenzothiophene (DMDBT), difficult to be eliminated by conventional hydrodesulfurization, are oxidized to the corresponding sulfones and subsequently removed by adsorption. Molybdenum-based HPAs, with Keggin structure, proved to be the most active and selective catalysts for oxidizing DMDBT with on-stream lifetimes exceeding 1500 h time on stream (t.o.s.).

A new approach to the characterization of V species in doped-V/Ti/O catalysts by means of TPR and TPO measurements: a study of the effect of promoters in the oxidation of o-xylene

Abstact Titania-supported vanadium oxide systems, catalysts for the oxidation of o-xylene to phthalic anhydride, were characterized by means of Raman spectroscopy, Thermal-Programmed Reduction and Oxidation, and adsorption/TP Desorption of methanol, with the aim of defining a method for the quantification of the different V species. It was found that vanadium oxide, either as polyvanadate dispersed over titania, or in the form of bulk vanadia, spontaneously releases molecular oxygen at 600-650°C, whereas isolated V species, chemically interacting with the support, is not susceptible of self-reduction. The latter species is that predominant in samples having low vanadium oxide loading ( 2 surface area 22.5 m2/g), and possesses the highest intrinsic activity in o-xylene conversion. In samples having higher vanadia loading, instead, the activity is determined by the amount of dispersed polyvanadate and of bulk vanadia. The effect of Sb, promoter of activity for V/Ti/O catalysts, was explained in terms of an increase of the dispersion of the most active species, and of stabilization of the latter towards segregation. These promotional effects are more pronounced in the co-presence of Cs and Sb.