Abstract
The performances in methane steam reforming of Ni catalysts supported on (Ce0.75Zr0.25)O2−y (CZ) and (Ce0.75/1.025Zr0.25/1.025Pr0.025/1.025)O2−y (CZP), which were fired at various temperatures before Ni deposition, were studied. The catalytic activities of the Ni/CZP catalysts were several per cent higher than those of the Ni/CZ catalysts in terms of both CH4 conversion and H2 yield. Distinct catalytic activities were observed, even after oxidation, for Ni/CZP with supports pre-fired at 1073 and 1273 K. These observations are discussed in terms of the structural characteristics of the catalysts. The X-ray diffraction profiles and Raman spectra indicated that CZP was a mixture of two phases, i.e., a Pr-rich λ phase and a Ce-rich cubic phase. The higher catalytic performances of the Ni/CZP catalysts than of the Ni/CZ catalysts and the retention of catalytic activity even after oxidation were attributed to a strained but coherent interface between the λ phase and the cubic phase, at which oxygen vacancies were easily formed. The Ni/CZ catalyst with the CZ support pre-fired at 1273 K also showed distinct catalytic activity even after oxidation. The activity of Ni/CZ after oxidation was also attributable to an active interface between a Zr-rich tetragonal phase and a Ce-rich cubic phase, similar to the case of the Ni/CZP catalyst.
