Dry reforming of methane (DRM) is currently being studied as one of the potential routes for the production of syngas, which can further be converted to fuels. Nickel based catalysts are well studied for DRM, but are prone to deactivation by coking and sintering at high temperatures. Thus, a thermally stable catalyst which can resist coking and sintering is needed. Pyrochlores, which are thermally stable oxides, are promising catalysts. In the present work, Lanthanum Zirconate (La2Zr2O7) pyrochlores doped with Ni on B (Zr) site, were tested for their activity and stability towards DRM. Two catalysts, LNZ3 and LeNZ3, both with 3% Ni loadings were prepared using the modified Pechini method. But, the catalysts differ in the amount of La in the catalyst. One catalyst has La to Zr molar ratio as 1 (LNZ3) while the other has excess La, i.e., La to (Zr+Ni) molar ratio as 1 (LeNZ3). Ni is the active metal which is doped at the Zr site. Catalysts were studied using some thermal and spectroscopic characterization techniques. Activity tests were carried out by passing a reactant stream comprising 1:1 ratio of 10%CH4/He and 10%CO2/He(at 750°C temperature and a GHSV of 24,000 cm3 gcat-1 hr-1) over the catalysts for 48hrs. XRD of fresh LeNZ3 showed the presence of LaO3 phase as well as a perovskite phase containing La, Ni and Zr apart from pyrochlore structure. Also, XRD showed the presence of NiO phase in both the catalysts. In both the catalysts, an increase in lattice constant of pyrochlore structure suggests that atleast a portion of Ni is substituted into the pyrochlore lattice. XPS and SEM-EDS analysis were done to compare the surface and bulk compositions of the catalysts. On both catalysts, TPR showed reduction peaks at different temperatures, indicating different interaction strengths of Ni in the structure. TPSR showed that both the catalysts start activity towards DRM around 700°C. During long runs at DRM conditions, slightly higher CH4 and CO2 conversions were observed with LNZ3. Also, the LeNZ3 catalyst deactivated more rapidly LNZ3. TPO on spent catalysts confirmed the deposition of coke on the catalysts which is believed to be the cause of deactivation. Also, TPO suggest that most of the carbon is present in amorphous phase while some quantity of polymeric carbon is also seen.

Dry reforming of methane on Ni based pyrochlore catalysts: Effect of lanthanum amount

2019 Fall National Meeting

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