Reduction and oxidation kinetics of NiWO4 as an oxygen carrier for hydrogen storage by a chemical looping process.

NiWO4 with a volumetric storage density (VSD) of 496 g L-1 was studied to evaluate its H2 storage potential as an oxygen carrier under a chemical looping (CL) process scheme. The material was synthesized by precipitation and calcined at 950 °C for 5 hours in air. Characterization consisted in XRD, BET surface area, SEM and EDS analysis. NiWO4 hydrogen storage reduction-oxidation evaluation was performed by TGA using 5% v H2/Ar and 2.2% v H2O/Ar at 800 °C. Global kinetics for the reduction step was studied from 730 to 870 °C using 2 to 5% v of H2/Ar. While oxidation kinetics was examined from 730 to 870 °C using 0.8 to 2.2% v H2O/Ar. A hydrogen storage multicycle stability test was performed by exposing NiWO4 to 17 consecutive redox cycles. XRD results of the synthesized material indicate NiWO4 as the only crystalline phase. Fully reduced material found only W and Ni species, while reoxidation led back to NiWO4. BET surface area of synthesized material was 4.25 m2 g-1. SEM results showed fresh NiWO4 composed of non-porous large particles (1-5 µm). After reduction, the material shown a porous coral-like morphology with particles between 50 to 100 nm. EDS analysis results confirmed the compositions of the reduced (Ni + W) and fully oxidized NiWO4 species, respectively. Oxygen carrier reaction conversions for both reduction and regeneration steps were 100%. Global kinetic studies indicate a first order reaction for the two reduction steps and during oxidation, with activation energies of 22.1, 48.4 and 53.4 kJ mol-1 for the two reduction and oxidation steps, respectively. NiWO4 multicycle stability test shown no loss of VSD and fast reduction and oxidation kinetics under the studied conditions after seventeen consecutive redox cycles, which confirms the potential of this material with respect to current oxygen carriers reported in the literature for hydrogen storage applications.

Ion exchange resins as catalyst for the isomerization of alpha-pinene to camphene.

Camphene is an industrial intermediate compound for commercial chemicals such as isoborneol, isobornyl acetate and camphor. Industrially, the conventional process for camphene production consists of the isomerization of alpha-pinene using acidic TiO2 as catalyst. The use of this catalyst presents problems such as considerable time for preparation, reproducibility and recovery of catalyst from products after the alpha-pinene isomerization. For the first time, a commercial exchange resin was used as catalyst for this reaction. Based on the concentration of product as a function of the reaction time, the path of the alpha-pinene transformation to camphene and byproducts is proposed. Temperature and alpha-pinene/catalyst ratio were studied in order to optimize the yield to camphene production. The obtained results were comparable with those reported for acidic TiO2.