Authors:Hermínio Digo, Susana Pinto, and Joaquim Moura Ramos
The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC).
The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10C min-1. The melting peak showed an onset at Ton = 144C (417 K) and a maximum intensity at Tmax = 152C (425 K), while the onset of the glass transition signal was at Ton = 6C. The melting enthalpy was found to be ΔmH = 28.90.3 kJ mol-1, and the heat capacity jump at the glass transition was ΔCP = 108.10.1 J K-1mol-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed
the determination of the activation energy at the glass transition temperature (245 kJ mol-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as ΔfHmo(C14H10O5, cr) = - (837.63.3) kJ mol-1, by combustion calorimetry.
Authors:Susana Pinto-Castilla, Santiago Marrero, Yraida Díaz, Joaquín L. Brito, Pedro Silva, and Paulino Betancourt
A novel synthesis route was designed to obtain highly active vanadium based catalysts. Three different activated carbons were used as supports (one of them being treated with ozone). The supported catalysts were characterized by XRD, TEM, XPS and EPR. These systems were tested in hydrotreating reactions (HDS, HDN and hydrogenation). The characterization results showed well dispersed vanadium nanoparticles. However, it was evidenced that during the synthesis process, a vanadium carbide phase was produced within vanadium oxides. Reactivity studies showed that the vanadium catalysts were slightly better for HDS and hydrogenation reactions than a commercial NiMoS catalyst, but that was not the case for HDN reactions. The reduction method proposed is potentially an excellent route to synthesize more active supported vanadium carbide catalysts than the conventional TPS method. Under reaction conditions, carbide and sulfide vanadium species coexist in the catalyst; vanadium carbide sites probably remain intimately mixed with the active vanadium sulfide sites.