Bulk V-Nb-O, Mo-Nb-O, Te-Nb-O, and V-Mo-Te-Nb-O mixed metal oxides were synthesized and characterized with Raman spectroscopy, XRD, and BET methods. The interaction of the V and Mo cations with the Nb2O5 lattice followed three stages: (1) cations were initially incorporated into the Nb2O5 lattice forming a solid solution or compound as well as on the Nb2O5 surface, (2) a two-dimensional surface cation overlayer was formed after saturation of the solid solution, and (3) microcrystalline metal oxide phases (e.g., V2O5 and MoO3) were formed after completion of the two-dimensional surface cation monolayer. The catalytic properties of these bulk mixed metal oxides were investigated for the oxidative dehydrogenation (ODH) of propane to propylene, and their activity follows the trend: V-Nb-O > Mo-Nb-O>>Nb2O5 > Te-Nb-O. The highest propane conversions and propylene yields were found when the two-dimensional surface metal oxide monolayers were formed, which suggests that the surface metal oxide species are the surface active sites in these bulk mixed metal oxide catalysts for propane ODH. Furthermore, the number of surface active sites present in the bulk mixed metal oxides was determined by comparative studies between the bulk mixed metal oxides and the corresponding model Nb2O5-supported metal oxides. These numbers can be used further for the calculation of the TOF (turn-over-frequency) values and quantitative comparison of the catalytic behavior of the different bulk mixed metal oxide catalysts for propane ODH. The catalytic results over the model Nb2O5-supported metal oxides demonstrate that the propane ODH reaction is structure insensitive because the TOF is independent of the number and the structure of surface active sites. The composition and calcination temperature of the bulk mixed metal oxide catalysts affects the surface density of the active sites, which controls their catalytic behavior for propane ODH.

Selective oxidation of ethane by oxygen was examined over silica catalysts supporting cesium and bismuth. Aldehydes of C1–C3 were obtained with total selectivity of about 40% at ethane conversion lower than 5%. The catalytic performance was strongly dependent upon the bismuth loading on the catalysts. The higher turn-over-rate and the higher selectivity to aldehydes were observed at the Bi loadings lower than 0.5%. Characterization of the catalysts showed that isolated or highly dispersed Bi on the catalyst surface was indispensable for the high aldehyde yield. Cesium also plays an important role for the high ethane reactivity and the high aldehyde selectivity. A reaction pathway was proposed in which ethane is oxidized into acetaldehyde, but not through ethylene, and acrolein is formed through a cross-condensation of acetaldehyde and formaldehyde.

The oxidation of ethane by oxygen was studied over silica catalysts supporting different amounts of vanadium with and without cesium. Three different catalytic properties of the product selectivity were observed, aldehyde formation, oxidative dehydrogenation (ODH), and combustion, depending upon the vanadium loading amount and the presence or the absence of cesium. A very low loading of vanadium (V:Si=0.02–0.1 at.%) and the addition of Cs (Cs:Si=1 at.%) on silica were found to be important for the formation of aldehyde. Not only acetaldehyde but also acrolein were observed in the aldehyde formation from ethane. On the other hand, catalysts with medium and high vanadium loadings (V:Si=0.5–20 at.%) gave a dehydrogenated product, ethene, when Cs was not added to the catalysts. The addition of cesium to the catalysts with medium and high vanadium loadings changed the catalytic property from ODH to combustion. The different types of vanadyl species were identified by UV–visible and IR measurements in samples with different vanadium loadings. It was estimated that isolated vanadyl species with tetrahedral coordination, which were found mainly on the catalysts with vanadium loading lower than 0.5 at.%, became the active site for the aldehyde formation through the interaction with Cs. As a plausible reaction path giving acrolein from ethane, cesium-catalyzed cross-condensation between acetaldehyde and formaldehyde, formed in the reaction, was proposed. Polymeric vanadyl species with octahedral coordination and vanadium–oxygen clusters with dioxo tetrahedral coordination were detected in the samples with medium (0.5–5.0 at.%) and high (10 and 20 at.%) vanadium loadings, respectively. Both species show the ODH catalytic property without cesium, but they bring about a deep oxidation of ethane if cesium is added to the catalysts.

A series of nanopowder Ce–Zr–Pr oxide catalysts were synthesized by a new method which was a low temperature synthesis approach combining rotating evaporation and auto-combustion techniques. The catalysts were characterized by means of XRD, Raman, and SEM. The results showed that the synthesized catalysts had a cubic fluorite structure, nanoparticle sizes and good catalytic activity for soot oxidation.

Al2O3 and SiO2 were used to load chromium oxides with incipient-wetness impregnation method. These supported chromia catalysts were evaluated for the dealkylation of C10+ heavy aromatics in hydrogen flow and were characterized with BET, XRD, FT-IR, UV–vis DRS and H2-TPR techniques. The results indicate that the catalytic activity of supported chromia catalysts on SiO2 is higher than that of on Al2O3. Structural characterization results show that surface reduced CrOx species are the active sites for hydrodealkylation of C10+ heavy aromatics. (C10+ heavy aromatics denote the aromatics whose carbon numbers are equal to or greater than 10.) The structural models of CrOx species on the Al2O3 or SiO2 support surface were also proposed.