Antimony tin oxide

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

Invented and developed independently in the late 1950s by D.G. Stewart in the Distillers Company, and R. Grasselli in Standard Oil of Ohio. The former used a tin/antimony oxide catalyst the latter bismuth phosphomolybdate on silica. Today, a proprietary catalyst containing depleted uranium is used. See also Erdolchemie, OSW, Sohio. 

The first mode of the high resolution C-NMR of adsorbed molecules was recently reviewed Q-3) and the NMR parameters were thoroughly discussed. In this work we emphasize the study of the state of adsorbed molecules, their mobility on the surface, the identification of the surface active sites in presence of adsorbed molecules and finally the study of catalytic transformations. As an illustration we report the study of 1- and 2-butene molecules adsorbed on zeolites and on mixed tin-antimony oxides (4>3). Another application of this technique consists in the in-situ identification of products when a complex reaction such as the conversion of methanol, of ethanol (6 7) or of ethylene (8) is run on a highly acidic and shape-selective zeolite. When the conversion of methanol-ethylene mixtures (9) is considered, isotopic labeling proves to be a powerful technique to discriminate between the possible reaction pathways of ethylene. 

Materials NaGeX zeolite was kindly supplied by Dr. G. Poncelet (Universite Catholique de Louvain) and the mixed tin-antimony oxide catalysts (SnSbO) by I.C.I. Ltd. The H-Z is the acidified form of commercially available Norton mordenite. The ZSM-5 and ZSM-11 zeolites were synthesized following the patent literature (15,16). 1-Butene (Prochem) was a natural abundance compound, while methanol (95 % l C, British Oxygen Corporation (B.O.C.)), ethanol (95 % C, B.O.C.) and ethylene ( 90 % C, Prochem) were JC-enriched compounds. For the latter a 30 % v/v dilution was realized prior to adsorption. 

All the catalysts (ca.0.6 g) were progressively dehydrated and activated at temperatures 573-673 K and at a final pressure of 2.10 Torr. The adsorption for all the reactants was made at room temperature. The mixed tin-antimony oxide samples were rapidly cooled down to 77 K in order to avoid isomerization of 1-butene following adsorption. 

As an illustration, the isomerization of 1-butene adsorbed on NaGeX or mixed tin-antimony oxides has been carried out. In the methanol to hydrocarbon conversion on the shape selective H-ZSM-5 zeolite, the surface methylation could be observed, the role of... 

Acidity, 27 284, 285 catalytic performance, 30 121 crystalline titanium silicates, 41 319-320 estimating, 37 166 heteropoly compounds, 41 139-150 ion exchange and, zeolites, 31 5-6 sulfate-supported metal oxides, 37 186-187 surface, monolayer dispersion, 37 34-35 tin-antimony oxide, 30 114-115, 125-1256 Acids, see also specific compounds adsorption of, on oxide surfaces, 25 243-245... 

Conductivity electrical, 27 20, 21 active site, 27 216, 217 temperature dependence, 27 20, 21 tin-antimony oxide, 30 100, 109 tin(IV) oxide, 30 108-109 Configurational-bias Monte Carlo method (CB-MC)... 

Acrolein is immediately passed through a second oxidation reactor to form acrylic acid. The reaction talces place at 475-575 E, over a tin-antimony oxide catalyst. A few by-products form, namely, formic acid (HCOOH), acetic acid (CH3COOH), low molecular weight polymers, carbon monoxide, and dioxide. But overall yields of propylene to acrylic acid are high—85 to 90%. 

Oxo-D process (Petro-Tex),180 and a technology developed by BP applying a tin-antimony oxide catalyst.181,182 The Phillips technology produces 1,3-butadiene with 88-92% selectivity at 75-80% conversion.179 A new catalyst used in the Nippon Zeon process offers improved process characteristics.183... 

Sb Mossbauer spectroscopy has been used to investigate the tin-antimony oxide catalysts used for selective oxidation of hydrocarbons (171). Recent investigations have been conducted to characterize FeSbO catalysts for ammoxidation of propene (172) and VSbO (173) and MoVSbNbO (174) catalysts for ammoxidation of propane. 

This article therefore seeks to examine in depth just one mixed oxide catalyst, tin-antimony oxide, which has been commercially developed (2-5) for the oxidation of propylene to acrolein as well as for the ammoxidation of propylene to acrylonitrile and the oxidative dehydrogenation of butenes to 1,3-butadiene. A recent book (6) and a subsequent review (7) have shown how little unanimity has been established about the fundamental properties of the material. In particular there seems to be much confusion as to the phase composition, the nature of the cationic oxidation states, the chemical environment of the cations, the charge compensation mechanism, the nature of the active sites, the distortion of the host tin(IV) oxide lattice by the dopant antimony atoms and whether any changes in the catalyst result from the adsorption and catalytic processes. 

In this article the tin-antimony oxide catalyst is considered in terms of... 

Since the early studies of tin-antimony oxides have already been excellently reviewed (6, 7) only those reports that have a major bearing on more recent investigations and are directly related to the objectives of this article will be cited in this work. It should also be noted that the sections and subsections in this article represent an attempt to assess the available data on specific aspects of the material according to the objectives. However, some deviation from rigorous adhesion to individual themes has been inevitable when considering the interdependence of certain properties. 

It would seem reasonable to presume that the preparation of tin-antimony oxides by coprecipitation would lead to a more intimate mixture of tin and antimony than would be achieved by solid state reactions between the respective oxides, and it would also seem reasonable that the close proximity... 

It is interesting that this mechanism, which was suggested during one of the early studies of tin-antimony oxides, has received so little subsequent attention, since it is a process that could be applied to some of the mechanisms of catalytic oxidation proposed in later studies. 

It is relevant that attention should now be drawn to the recent work, by Patterson, Pyke, Reid, Tilley, McAteer, et al. (12-16), who have examined several aspects of the structural and catalytic character of coprecipitated tin-antimony oxides. The structure characterization by Pyke, Reid, and Tilley (12) by X-ray diffraction techniques clearly showed that bulk equilibrium is difficult to establish in this system. This observation alone places some earlier data in a different perspective and implicitly demands a high degree of caution in the interpretation of physical and spectroscopic data recorded from these materials. The phase diagram (Fig. 1) defines the... 

It is interesting that the lattice parameters of the rutile type phase in tin antimony oxides containing a low antimony content and calcined at 600"C showed no significant difference from those of pure tin(IV) oxide. Much credit must be given to Pyke et al. 12 for their prophetic suggestion that crystallite formation by the aggregation of SnO2 octahedra was accompanied by a counter diffusion of antimony ions away from the tin rich nuclei to the surface, a model that has been subsequently verified by X-ray photoelectron spectroscopy (XPS) studies (75,27) and appears to be directly related to the catalytic nature of the material. 

Although twinning is a form of stress relief in crystals, it is also a means of changing the anion to cation stoichiometry and, more importantly in this system, may be the means by which sites with different coordination to the normal crystal matrix are achieved. Such an alteration would change the chemical properties of this localized region and thereby be of potential influence in the catalytic properties of the material. In particular, it could relate to the accommodation of cationic species in unusual or lower oxidation states and be relevant to the formation of specific active sites. Attention must therefore be given to a detailed consideration of the cationic oxidation states in the tin-antimony oxide catalyst, particularly in the solid solution phase. 

The Sb Mossbauer parameters (79) of tin-antimony oxides calcined at 600°C were related to the preparative procedure. The white precipitates, formed in alkaline media that contain hydrated tin(IV) and antimony(V) species, were considered to dehydrate after 16-hr calcination at 600°C to give blue, poorly crystalline, highly defective rutile type solids. The Mossbauer spectra revealed the presence of tin(IV), antimony(V), and anti-mony(III) species in oxygen environments and were consistent with the dehydration process inducing the reduction of antimony(V) as is observed in the pyrolysis of antimonic acid (26) and the transformation of the tin(IV) hydroxide gel to tin(IV) oxide (30). The coexistence of random arrays of such units in a noncrystalline monophasic solid is consistent with the X-ray diffraction study (72) that described these materials as single-phase amorphous solids. 

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