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A series of cerium-zirconium mixed oxides doped with alkaline earth metals was prepared by calcining a mixture of Ce 0.8 Zr 0.2 O 2 and the nitrate salt of alkaline earth metals at 1173 K. The results from X-ray diffraction, Raman spectroscopy and analytical electron microscopy indicated the alkaline earth compounds were dispersed on the surface of Ce 0.8 Zr 0.2 O 2 . The doped mixed oxides were evaluated in the catalytic reaction of solid coke under tight contact conditions with 10 vol.% O 2 in He at 693 K and with 100 vol.% H 2 O at 993 K using thermogravimetric analysis. For coke oxidation with O 2 , the weight loss was first order in coke, and the measured first order rate constant was proportional to the total surface area of catalyst at low catalyst loadings. For coke gasification with H 2 O, the weight loss was nearly zero order in coke, and the measured areal reaction rate was independent of the total surface area of catalyst at low catalyst loadings. The addition of alkaline earth metals inhibited coke oxidation with dioxygen but promoted coke gasification with steam. [ABSTRACT FROM AUTHOR]

• Both NiAl 2 O 4 and NiCr 2 O 4 were stable during ethylene steam reforming at 873 K. • Both Fe and Ni in the NiFe 2 O 4 spinel catalyst reduced during steam reforming. • The NiFe 2 O 4 spinel catalyst severely coked during ethylene steam reforming. • The reforming rate increased after oxidation of the spent NiAl 2 O 4 and NiCr 2 O 4. Spinel oxides containing Ni cations can be present in the barrier layers of ethane steam cracker tubes. As Ni is known to catalyze steam reforming side reactions as well as coke deposition, the catalytic performance of Ni spinel catalysts was investigated. A series of NiM 2 O 4 spinel catalysts (M = Al, Cr, Fe) was synthesized from a sol-gel method and thoroughly characterized. The NiAl 2 O 4 and NiCr 2 O 4 catalysts were active for ethylene steam reforming at 873 K without degradation of the spinel structure. The NiFe 2 O 4 catalyst was the least stable because of partial reduction of Fe3+ to form Fe 3 O 4 , which facilitated Ni-Fe alloy particle formation and severe coking. The reforming activity and the coke deposited on the NiAl 2 O 4 and NiCr 2 O 4 catalyst both increased after oxidative regeneration at 873 K, suggesting a slow reduction of Ni2+ to Ni metal particles during steam reforming that subsequently sinter into larger NiO particles during oxidative regeneration. [ABSTRACT FROM AUTHOR]