This paper gives a survey of the catalytic properties of solid oxides which display oxygen ion or mixed (i.e. ionic + electronic) conductivity. Particular consideration is given to the oxidation-reduction reactions of gas phase components, but attention is also devoted to oxygen exchange between gas and oxide. An attempt has been made to relate and explain the observed phenomena such as catalytic activity and selectivity in terms of the electrical conducting properties of the oxides, which depend on their crystal and defect structures.In a number of cases possible applications of these materials in (electro)catalytic reactors, sensors, fuel cells, oxygen pumps, etc. are indicated.

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P-25, 55 i3 m2gsy; 2-1 Vanadium oxid has been deposited gn TiO (washed anatase, 10 m g ; Degussa Eurotitania, 46 m g-l) gy aqueous impregnation of (NH) [VO(C 0) ] and by reaction with VOCl org&Pc sol3eEttP. VO(OR) (R=lBu) and VO(acac) in Single applications of tl?;! last taree reagents form no z more than a mon!layer of vanadium oxide VO,, a monolayer being defined as 0.10 wt.% V,O$ per m of surface. When less than about four monolayers of VD are pre ent, there is in most cases only a single TPR peak: T,,, valueg, which increase with V 0 content, are almost independent of the method used but varv slightly with t&e5support (P-25 < Eurotitania < washed anatase). The 995 cm-l hand, characteristic of V=O in V205, VOX is present. only appears when more than a monolayer of In the sub-monolayer region, VD is best formulated as an oxohydroxy species bonded to two surface oxygens. AsXthe V 0 content is increased, layers of disordered V 0 are formed on limited ar a of the surface, but crystalline $2 V 0 only oc&F?s, probably on top of the disordered V 0 ezcseds about four monolayers, $ 7' when the V O5 content and takes the form of c cular crysta s exposing P only planes perpendicular to the a and b axes. INTRODUCTION A number of recent papers from our two laboratories have concerned the preparation, characterisation and catalytic properties of monolayers of vanadium oxide (VOX) on Ti02, principally as anatase [l-5]. These have been made chiefly by specific reactions between the vanadium precursor and the OH groups on the Ti02 surface: precursors used include VO(acac)2 in solution [2,3] and VOC13 both as vapour 141 and in solution [5]. These methods can be applied to give not more than a monolayer of VOX, this designation beinq used to denote that the species formed are not well-defined, but are certainly not equivalent to crystalline V205. However by repetition of the procedure [Z],

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The temperature-programmed reduction (t.p.r.) of bulk V,O, has been examined as part of a study of the reducibility of V,O,-containing catalysts. T.p.r. profiles have been studied as a function of flow rate, heating rate and sample weight. From experiments at different flow rates it is concluded that the order of the reduction rate in hydrogen is low or even zero. A rule of thumb has been derived to provide an easy check on possible exhaustion of hydrogen in the feed. The influence of sample weight and heating rate is explained in terms of the formation of water in the sample during reduction. The reduction of bulk V,O, to V,O, proceeds in several steps; intermediate species include V,O,, and VO,. The apparent activation energy of ca. 200 kJ mol-l indicates that solid-state diffusion influences the reduction process of V,O,.