Stability and surface catalytic properties of fluorite-structured yttria-doped bismuth oxide under reducing environment

High temperature stability and catalytic properties of fluorite-type 25 mol% Y2O3 doped Bi2O3 (BY25) pellets under methane atmosphere were studied by XRD, transient TGA and fixed-bed reactor measurements. In methane the fluorite-type BY25 exhibits good catalytic properties for oxidative coupling of methane (OCM) with C-2 selectivity higher than 90% and C-2 formation rate in the range of 1-3 mu mol/g.s. BY25 maintains its fluorite-type phase structure and catalytic properties as long as only nonstoichiometric oxygen in BY25 is consumed (less than 20% of the total oxygen). Prolonged (>5-7 min) exposure of BY25 to methane results in consumption of stoichiometric oxygen, leading to reduction of metal ions and destruction of the fluorite structure of BY25. These results suggest that the stability and catalytic properties of the surface of the BY25 membrane exposed to methane stream in membrane reactor applications can be maintained if sufficient oxygen is provided from the other side of the membrane. (C) 1999 Academic Press.