A Study of Hydrocarbon Oxidation on a Solid Electrolyte-Aided Catalyst Film.

An electrochemical reactor using yttria-stabillized zirconia (YSZ) as a solid electrolyte and gold and silver as anode and cathode metals, respectively, (i. e. hydrocarbon, Au�bYSZ�bAg, O₂) has been used for hydrocarbon oxidation. Despite the inertness of the goldanode in the dissociative activation of molecular oxygen,partial oxidation of hydrocarbon to the corresponding oxygenated compounds have been observed together with comlete oxidation over the gold anode under oxygen pumping. The production rate of the oxygenats increased withincreasing oxygen pumping through YSZ at 723-748K. This is the first evidence that can clarify the activity of oxygen species from oxidei, i. e. lattice oxygen species in YSZ. The MoO₃ -Bi₂O₃ catalyst was prepared from MoO₃, three phase of bismuth molybdate �kBi₂Mo₃O₁₂ (��), Bi₂Mo₂O₉ (��), Bi₂MoO₆(��)�l and Bi₂O₃ and each catalyst was successfully depoisted by vacuum evaporation as a compact thin film on the Au anode. For propene oxidation, MoO₃ showed the highest activity among the catalysts use on the Au anode and its activity was up to 600 times higher than that obtained with the same catalyst using a mixed-gas flow reaction. These results suggest that oxygen species bound to molybdenum metal possess a definite role for both ��-H abstraction from propene and oxygen insertion into the allylic intermediate under a sufficient oxygen supply. The thin MoO₃ film was deposited also on Au anode by means of sputtering method at room temperature or 573K. Sputtering at 573K gave porous films conposed of leaf-like crystals with preferenitial orientation of (010) plane parallel to the pore channel and perpendicular to the u surface, resulting in the highest activity for acrylaldehyde production. Two scheelite-type molybdate, Pb_1-xBi₂x��MoO₄ (��=cation vacancy, x=0 or 0.04), catalyst films were succesfully prepared on the Au anode by vacuum evaporation. Theoxidation over the scheelite-type molybdate revealed that oxygen species transported through the bulk of the catalyst insert into the allylic intermediate to from the oxygenated products, i. e. acrylaldehyde from propene and methylvinyl ketone from 1-butene, while oxygen species chemisorbed on the catalyst surface accelererates dehydrogenation of the allylic intermediate of 1-butene to 1,3-butadiene or complete oxidation of alkene to carbon oxides.