The structure and catalytic properties of SrTiO3 perovskite-type oxide catalysts for oxidative coupling of methane (OCM) have been studied by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and microreactor tests. It has been shown that OCM catalytic properties of SrTiO3 catalysts are correlated to the Sr/Ti atomic ratio. Increasing Sr/Ti ratio in the perovskite?-type SrTiO3 catalysts results in the surface enrichment of Sr element, leading to the the higher content of adsorbed oxygen species on the surface of catalysts and thus higher C2 selectivity for OCM reaction.
MoO3/MCM-49 has been synthesized under the special condition and it shows a high activity and selectivity for nonoxidative aromatization of methane with a long lifetime and extreme capacity of anti-coking. MoO3/MCM-49 is considered as a very promising catalyst for the title reaction.
MCM 56, a novel layered zeolite, has been synthesized under a stirring condition by hydrothermal method and characterized by XRD, TEM, TG and DTA. TEM shows that most of the crystals exist in the form of single layer. Based on the experimental facts and framework type which MCM 56 belongs to, MCM 56 should consist of very thin MWW type layers which are just one unit cell along the c direction, and have a unique architecture with two dimensional 10 MR pore system inside the layer and 12 MR cups(half of the MWW cages described in the MCM 22 or MCM 49) on the crystal exterior without cages between layers.
The dispersion state and catalytic properties of anatase-supported vanadia species are studied by means of X-ray diffraction (XRD), laser Raman spectroscopy (LRS), H2 temperature-programmed reduction (TPR) and the selective oxidation of o-xylene to phthalic anhydride. The almost identical values of the experimental dispersion capacity of V2O5 on anatase and the surface vacant sites available on the preferentially exposed (001) plane of anatase suggest that the highly dispersed vanadium cations are bonded to the vacant sites on the surface of anatase as derived by the incorporation model. When the loading amount of V2O5 is far below its dispersion capacity, the dispersed vanadia species might mainly consist of isolated VOx species bridging to the surface through V-O-Ti bonds. With the increase of V2O5 loading the isolated vanadia species interact with their nearest neighbors (either isolated or polymerized vanadia) through bridging V-O-V at the expenses of V-O-Ti bonds, resulting in the increase of the ratio of polymerized to isolated vanadia species and the decrease of the reactivity of the associated surface oxygen anions and, consequently, although the activity increases with loading to reach a maximum value, the turn over number (TON) of the V2O5/TiO2 catalyst decreases linearly. When the loading amount of V2O5 is higher than its dispersion capacity, the turn over number decreases more rapidly with the increase of V2O5 loading due to the formation of V2O5 crystallites in which the oxygen anions associated with V-O-V bonds are less reactive and only partially exposed on the surface.
