Emissions to liquid fuels: development of advanced heterogeneous catalysts for CO2 valorisation

• Autores: Estelle C. Le Saché
• Directores de la Tesis: Tomás Ramirez Reina (dir. tes.), David Watson (codir. tes.)
• Lectura: En la University of Surrey ( Reino Unido ) en 2019
• Idioma: español
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• Resumen

  • CO2 utilisation is becoming an appealing topic in catalysis science due to the urgent need to deal with greenhouse gases (GHG) emissions. Herein, the dry reforming of methane (DRM) represents a viable route to convert CO2 and CH4 (two of the major GHG) into syngas, a highly valuable intermediate in chemical synthesis. Nickel-based catalysts are economically viable materials for this reaction, however they show inevitable signs of deactivation mainly caused by the agglomeration of the active phase and carbon deposition on the surface of the catalyst. In this work, stabilisation of Ni in a pyrochlore-perovskite structure is reported as a viable method to prevent fast deactivation. Substitution of Zirconium by Ni at various loadings in the lanthanum zirconate pyrochlore La2Zr2O7 is investigated in terms of reactant conversions under various reaction conditions. Crystallographic analysis of the catalysts showed the formation of phases corresponding to the pyrochlore structure La2Zr2-xNixO7-δ and an additional La2NiZrO6 perovskite phase at high Ni loadings. The pyrochlore mixed oxide shows high basicity and surface oxygen availability, leading to a material with high CO2 activation potential. In particular, the formation of lanthanum oxycarbonate is occurring upon CO2 activation. The best formulated catalyst shows excellent activity for various reforming reactions at temperatures as low as 600 °C and displays great stability over 350 hours of continuous dry operation. Versatility in feed ratio and syngas production was demonstrated. Carbon formation although inevitable, is limited using this formulation strategy. The presence of nanosized Ni particles contributes to the excellent performance of the catalyst. Exsolution of Ni from the host lattice is believed to occur upon activation pre-treatment of the catalyst and leads to small, well dispersed and highly active Ni clusters. Overall, this work showcases an appealing strategy to design economically viable advanced catalysts for chemical CO2 recycling via reforming reactions.