In situ observation of the dynamic behavior of Cu-Al-O _x catalysts for water gas shift reaction during daily start-up and shut-down (DSS)-like operation

To compare the catalytic performances against daily start-up and shut-down (DSS) operations between co-precipitated (CP) and impregnated (IMP) Cu-Al-O _x catalysts for the water gas shift (WGS) reaction, in situ X-ray adsorption fine structure (XAFS) measurements, temperature-programmed reduction (TPR) profiles, X-ray diffraction (XRD) patterns and high resolution transition electron microscopy with an energy dispersive X-ray spectroscopy (TEM-EDS) analysis were performed. In situ XAFS studies clearly indicated that the Cu species were frequently oxidized and reduced during DSS operations with steam treatment (DSS-like operation). Based on in situ XAFS and H ₂-TPR profiles, the highly active and stable CP-catalyst possessed more susceptible Cu particles to oxidation/reduction (described as redoxable) than the IMP-catalyst even after the DSS-like operations. Interestingly, the XRD and TEM-EDS analysis showed small Cu particles which were covered with a card-house structure of the in situ formed boehmite in the case of the CP-catalyst after the DSS-like operations. According to these results, we concluded that the superior durability of the CP-catalyst against frequent redox changes was attributed to the nanoscale coordination with the in situ formed boehmite structure which preserves the small-redoxable Cu particles.