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Silica-niobia oxides

The intrinsic (measured in cyclohexane, apolar and aprotic solvent) and effective (measured in water or other liquids) acidity of series of mixed silica-niobia oxides have been determined by this method with the principal aim of disclosing relationships between the surface acid properties and catalytic activity [9]. Dispersed niobia... [Pg.548]

Impregnation has been used to prepare a number of catalysts having different metal support combinations. Highly loaded nickel catalysts supported on alumina, titania, silica, niobia and vanadium pentoxide were prepared by adsorption of nickel nitrate from an ammoniacal solution onto the support material. The supported salts were dried at 120°C and calcined at 370°C before reduction to the supported metallic nickel. It was found that the ease of reduction depended on the crystallinity of the support. Amorphous or poorly crystalline supports made the reduction of the nickel oxide more difficult than on crystalline supports. As examples of its generality, this procedure was also used to prepare... [Pg.277]

Bofia, V., Castricum, H.L., Garcia, R Schmuhl, R., Petukhov, A.V., Blank, D.HA, and ten Elshof, J.E. (2009) Structure and growth of polymeric niobia-silica mixed-oxide sols for microporous molecular sieving membranes a SAXS study. Chem. [Pg.708]

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... [Pg.261]

Extend the model from Problem 5 to simulate the pH shifts for alumina and silica seen in Figure 13. Then model other oxides titania (PZC 6, 8 OH/nm2), niobia (PZC 2.5, 5 OH/nm2), magnesia (PZC 12, 10 OH/nm2). [Pg.192]

Halides (chloride, in particular) also react promptly with surface OH groups, as has been shown for [W(=CCMe3)Cl3(dme)] and several inorganic oxides (silica, alumina, silica-alumina, niobia) [5-7]. The same was observed for the reaction of [V(=0)Cl3] with silica in this case, using a large excess of the vanadium complex, one mole of HCl is released per mole of grafted vanadium [8]. [Pg.418]

A more widely used method of heterogenization has also been applied to MTO, by using a metal oxide support onto which the MTO is applied. MTO has been applied onto niobia (Nb2Os) both via impregnation and sublimation [39] and onto silica (Si02) via reaction of a bipyridine-containing siloxane [40]. In a similar manner, MTO has been immobilized on the mesoporous silica MCM-41 [41]. Zeolite NaY has been used as a support material by the in situ immobilization of the MTO catalyst [42]. [Pg.136]

Acrolein Zirconium and niobium mixed oxides have been shown to catalyze the dehydration of glycerol to acrolein, at 300°C in the presence of water with high selectivity (72%) at nearly total glycerol conversion [50]. Silica-supported niobia catalysts can also be used with similar catalytic performance [51]. Catalytic results for small-sized H-ZSM 5 zeolites showed that the high density of Bronsted acid sites favors acrolein production [52]. Acrolein production from glycerol has also been carried out in subcritical water at 360°C and 34 MPa with catalytic quantities of ZnS04 (791 ppm [g/g]) [52],... [Pg.101]

The group 5-7 supported transition metal oxides (of vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and rhenium) are characterized by terminal oxo bonds (M =0) and bridging oxygen atoms binding the supported oxide to the cation of the support (M -0-MSUpport). The TOF values for ODH of butane or ethane on supported vanadia were found to depend strongly on the specific oxide support, varying by a factor of ca. 50 (titania > ceria > zirconia > niobia > alumina > silica). [Pg.102]

Catalysts containing niobia supported on various oxides have been the subject of considerable recent interest [1-4]. The molecular structures and reactivity of niobium oxides supported on alumina, titania, zirconia and silica have been intensively investigated over the last few years. Niobia supported on silica has been shown to be active for the dehydrogenation and dehydration of alcohols, photo-oxidation of propene and oxidative decomposition of methyl tertiary butyl ether. Titania supported niobia is active for the selective catalytic reduction (SCR) of NO by NH3. [Pg.270]

Inorganic oxides may present several different types of reactive functional groups, among them several kinds hydroxyl groups, strained rings, oxo groups, and Lewis-acidic vacant sites. The occurrence and relative abundance of these different sites depend primarily on the identity of the oxide (silica, alumina, niobia, etc.), the synthesis and conditioning of the oxide, and the eventual calcination and other thermal treatment of the solid immediately before use. [Pg.665]

As an attempt in this direction, a hierarchy was recently developed for nickel catalysts (6). The basic idea is to monitor the chemical properties of a catalyst as probed by hydrogen chemisorption, ethane hydrogenolysis, and carbon monoxide hydrogenation. The hierarchy, originally developed for Ni/I O catalysts, was later extended to nickel supported on phosphate-containing materials and a niobia-silica surface phase oxide. In this paper the usefulness of the hierarchy will be illustrated by its ability to differentiate between support effects of niobia and phosphate, and to establish the intermediate degree of interaction of niboia-silica. [Pg.124]

Supports and Catalysts. The preparation of the supports used in this study was discussed in detail elsewhere. The two phosphate supports, A O AIPO and 4MgO lSA O 10A1P0 were co-precipi-tated using the necessary nitrate salts, phosphoric acid, and ammonium hydroxide at a fixed pH (.] ) Niobia was precipitated by adding ammonium hydroxide to a methanolic solution of niobium chloride (8). The niobia-silica support was prepared by impregnating SiO (Davison 952) to incipient wetness with a hexane solution of niobium ethoxide. The sample was then dried and calcined to obtain a homogeneous surface phase oxide (9). [Pg.124]

Even for an SMSI oxide, the extent of interaction is dependent on many parameters and a comparison among samples must be done systematically. Under high reduction temperatures encapsulation of the metal particle leads to a decline in CO hydrogenation in niobia-containing support. The niobia-silica surface phase oxide, which shows a similar mechanism of interaction to niobia but is less interacting, should prove useful as a model system in future studies. [Pg.134]

The surface vanadium oxide species on silica, water-treated silica, alumina, ceria, titania, zirconia, niobia and titania-silica have been characterized and studied for the selective oxidation of ethane. [Pg.303]

A multinuclear solid-state NMR approach is applied to four templated mesoporous oxides (silica, titania, niobia and tantala) to include and MAS NMR and double resonance Nb, REAPDOR. MAS NMR provides the clearest indication of the local wall structure. [Pg.277]


See other pages where Silica-niobia oxides is mentioned: [Pg.5676]    [Pg.150]    [Pg.5675]    [Pg.1834]    [Pg.343]    [Pg.119]    [Pg.121]    [Pg.124]    [Pg.113]    [Pg.420]    [Pg.37]    [Pg.375]    [Pg.153]    [Pg.672]    [Pg.123]    [Pg.134]    [Pg.867]    [Pg.71]    [Pg.286]    [Pg.302]    [Pg.52]    [Pg.726]    [Pg.249]    [Pg.669]    [Pg.54]    [Pg.53]    [Pg.287]    [Pg.272]    [Pg.527]    [Pg.690]    [Pg.330]    [Pg.336]    [Pg.549]   
See also in sourсe #XX -- [ Pg.548 ]




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