Oxidative steam reforming of ethanol over M x La2-x Ce1.8Ru0.2O7-δ (M = Mg, Ca) catalysts: effect of alkaline earth metal substitution and support on stability and activity.

Alkaline earth metal substitutions on the A-site of pyrochlore oxide M x La2-x Ce1.8Ru0.2O7-δ (M = Mg, Ca) were studied as catalyst materials for oxidative/autothermal steam reforming of ethanol (OSRE/ATR). The as-prepared oxides were synthesized by a combustion method and characterized using powder X-ray diffraction (PXRD), and X-ray photoelectron and absorption spectroscopy (XPS and XAS). PXRD Rietveld analysis and elemental analysis (ICP-AES) support the formation of a pyrochlore-type structure (space group Fd3̄m) with a distorted coordination environment. The substitution of Mg2+ and Ca2+ ions affects the oxidation states of Ce4+/3+ and Ru n+ ions and creates oxygen vacancies, which leads to enhanced catalytic activity and reduced ethylene selectivity. A long-term stability test showed optimized catalysts Mg0.3La1.7Ce1.8Ru0.2O7-δ and Ca0.2La1.8Ce1.8Ru0.2O7-δ with S H2 = 101(1)% and S H2 = 91(2)% under OSRE conditions. The initial operation temperatures were lower than that of the unsubstituted catalyst La2Ce1.8Ru0.2O7-δ . Catalysts supported on La2Zr2O7 showed stable OSRE/ATR performance and low carbon deposition compared to catalysts supported on Al2O3. We ascribe the enhanced activity to well-dispersed alkaline earth metal and Ru ions in a solid solution structure, synergistic effects of (Mg, Ca)2+/Ce3+/4+/Ru n+ ions, and a strong catalyst-support interaction that optimized the ethanol conversion and hydrogen production.