Oxidative steam reforming of ethanol over M(x)La(2−x)Ce(1.8)Ru(0.2)O(7−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)La(2−x)Ce(1.8)Ru(0.2)O(7−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 Mg(2+) and Ca(2+) ions affects the oxidation states of Ce(4+/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 Mg(0.3)La(1.7)Ce(1.8)Ru(0.2)O(7−δ) and Ca(0.2)La(1.8)Ce(1.8)Ru(0.2)O(7−δ) with S(H(2)) = 101(1)% and S(H(2)) = 91(2)% under OSRE conditions. The initial operation temperatures were lower than that of the unsubstituted catalyst La(2)Ce(1.8)Ru(0.2)O(7−δ). Catalysts supported on La(2)Zr(2)O(7) showed stable OSRE/ATR performance and low carbon deposition compared to catalysts supported on Al(2)O(3). 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+)/Ce(3+/4+)/Ru(n+) ions, and a strong catalyst–support interaction that optimized the ethanol conversion and hydrogen production.