In situ X-ray absorption spectroscopy study of CuO–NiO/CeO 2 –ZrO 2 oxides: redox characterization and its effect in catalytic performance for partial oxidation of methane

TOSCANI, LUCÍA M.; ZIMICZ, M. GENOVEVA; MARTINS, TEREZA S.; LAMAS, DIEGO G.; LARRONDO, SUSANA A.

RSC Advances

The Royal Society of Chemistry

Año: 2018 vol. 8 p. 12190 - 12203

In this work we analyze the effect of adding CuO to a NiO/Ce0.9Zr0.1O2 oxide by in situ X-ray absorptionnear-edge structure XANES technique in Ce L3, Ni K and Cu K absorption edges in terms of samplereducibility and catalytic activity. The oxidation states of Ce, Ni and Cu cations are followed up duringtemperature programmed reduction (TPR) experiments in diluted hydrogen and during catalytic tests forpartial oxidation of methane (POM) reaction. Redox behavior was correlated to conventional fixed bedreactor results. The effect of firing temperature, crystallite size, CeO2?ZrO2 support and the presence ofCu and/or Ni as an active phase is also analyzed. Results showed a beneficial effect of CuO addition interms of Ce and Ni reduction. A stronger interaction of NiO species with the support was revealed uponanalysis of XANES reduction profiles in sample NiO/ZDC in contrast to bimetallic CuO?NiO/ZDC sample.Reduction onset temperature was found to depend on Ni crystallite size, being markedly promotedwhen samples exhibited low values of crystallite size both in supported and non-supported CuO?NiOspecies. In situ catalytic experiments for partial oxidation of methane showed a clear interplay betweenthe redox behavior from the Ce in the CeO2?ZrO2 support and the Ni from the active phase. SampleNiO/ZDC exhibited a continuous reduction of Ce cations in CH4 : O2 feed flow, carbon formation wasdetected in X-ray Powder Diffraction (XPD) patterns and Ni re-oxidation was found to take place, clearindications of catalyst deactivation. In contrast, sample CuO?NiO/Ce0.9Zr0.1O2 displayed a slight reoxidationof Ce and no re-oxidation of Ni altogether with the suppression of carbon formation.