Influence of Ru-substitution on the performance of pyrochlore catalysts in oxidative steam reforming of ethanol

Abstract

This study introduces a series of Ru-substituted pyrochlore catalysts, achieved by using La₂Zr_2−xRu_xO_7−δ (LZRO-00–04, x = 0.0–0.4) during the oxidative steam reforming of ethanol reaction (OSRE). The samples were characterized using X-ray diffraction (XRD), temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS). The reduction behavior and catalytic performance correlate directly with the Ru content. The 5 wt% LZRO02 catalytic system outperforms the supported Ru-based catalyst (5 wt% RuO₂/LZO), boasting lower Ru concentrations (2.66 wt%). The enhancement is attributed to the uniform dispersion of Ru ≥ 4+ ions embedded within the pyrochlore structure, as convincingly supported by the XPS result. This underscores notable distinctions between the internal and external structures of the two systems. On the other hand, our extensive long-term testing of LZRO02 across γ-Al₂O₃ and lab-made LZO carriers, coupled with meticulous mapping and Raman analysis, revealed a significant observation: the catalyst exhibits notably reduced aggregation tendencies and enhanced activity when utilized on the LZO carrier. The La₂Zr_1.8Ru_0.2O_7−δ catalyst supported on LZO demonstrated selectivity of hydrogen S_H2 = 86.4(1)%; Y_H2 = 2.55(3) (mol/mol EtOH) for long-term stability tests at T = 400 °C, C/O = 0.6, and O₂/C₂H₅OH = 1.5. This discovery underscores the catalyst's remarkable stability and activity, making it a promising candidate for catalytic applications.