Uranium antimony catalyst

More commonly, uranium has been used as a catalyst component for mixed-metal oxide catalysts for selective oxidation. Probably the most well known of these mixed oxide catalysts are those based on uranium and antimony. The uranium-antimony catalysts are exceptionally active and selective and they have been applied industrially. An interpretation of the catalyst structure and reaction mechanism has been reported by GrasselU and coworkers [42, 43] who discovered the catalyst The USb30io mixed oxide has been extensively used for the oxidation/ammoxida-tion reaction of propylene to acrolein and acrylonitrile. The selective ammoxida-tion of propylene was investigated by GrasseUi and coworkers [44], and it has been demonstrated that at 460 °G a 62.0% selectivity to acrolein with a conversion of 65.2% can be achieved. Furthermore, Delobel and coworkers [45] studied the selective oxidation of propylene over USb30io, which at 340 °C gave a selectivity to acrolein of 96.7%. 

Although acrylonitrile manufacture from propylene and ammonia was first patented in 1949 (30), it was not until 1959, when Sohio developed a catalyst capable of producing acrylonitrile with high selectivity, that commercial manufacture from propylene became economically viable (1). Production improvements over the past 30 years have stemmed largely from development of several generations of increasingly more efficient catalysts. These catalysts are multicomponent mixed metal oxides mostly based on bismuth—molybdenum oxide. Other types of catalysts that have been used commercially are based on iron—antimony oxide, uranium—antimony oxide, and tellurium-molybdenum oxide. 

In the 1960s, a number of binary oxides, including molybdenum, tellurium, and antimony, were found to be active for the reactions and some of them were actually used in commercial reactors. Typical commercial catalysts are Fe-Sb-O by Nitto Chemical Ind. Co. (62 -64) and U-Sb-O by SOHIO (65-67), and the former is still industrially used for the ammoxidation of propylene after repeated improvements. Several investigations were reported for the iron-antimony (68-72) and antimony-uranium oxide catalysts (73-75), but more investigations were directed at the bismuth molybdate catalysts. The accumulated investigations for these simple binary oxide catalysts are summarized in the preceding reviews (5-8). 

In comparison to the bismuth molybdate and cuprous oxide catalyst systems, data on other catalyst systems are much more sparse. However, by the use of similar labeling techniques, the allylic species has been identified as an intermediate in the selective oxidation of propylene over uranium antimonate catalysts (20), tin oxide-antimony oxide catalysts (21), and supported rhodium, ruthenium (22), and gold (23) catalysts. A direct observation of the allylic species has been made on zinc oxide by means of infrared spectroscopy (24-26). In this system, however, only adsorbed acrolein is detected because the temperature cannot be raised sufficiently to cause desorption of acrolein without initiating reactions which yield primarily oxides of carbon and water. 

The early catalyst for AN production was a multicomponent metal oxide, mainly consisting of bismuth and molybdenum oxides. Its composition has evolved over the past 40 years, constantly improved by continuous development work for increasingly better performances. Other catalytic materials that have been used in commercial processes include in their compositions, iron-antimony oxides, uranium-antimony oxides and tellurium-molybdenum oxides. 

The uranium-antimony oxide system remains as a basis of interest for catalysts. The preparation of a new uranyl antimonate has been described and it was prepared by hydrothermal synthesis from UO3, SbsOs and KCl [46]. A detailed structural analysis was reported, but more importantly the U0sSb204 was selective for the oxidation of propylene to acrolein. 

Structure and Activity of Promoted Uranium-Antimony Oxide Catalysts... 

At one time the preferred catalyst for propylene ammoxidation was a uranium-antimony oxide composition whose active phase was USb3O2 Q. We have found that the partial substitution of certain tetravalent metals for the pentavalent antimony in this phase greatly increases catalytic activity. 

Unless otherwise noted, catalysts were prepared by coprecipitating the hydrous oxides of uranium, antimony, and a tetravalent metal from a hydrocholoric acid solution of their salts by the addition of ammonium hydroxide. The precipitates were washed, oven dried, then calcined at 910 C overnight or at 930 C for two hours to form crystalline phases. Attrition resistant catalysts, containing 50% by weight silica binder, were prepared by slurrying the washed precipitate with silica-sol prior to drying. In some cases, small amounts of molybdenum or vanadium were added by impregnating the oven dried material with ammonium paramolybdate or ammonium metavanadate solution. The details of these preparations may be found elsewhere (5-8). 

A series of catalysts was prepared to study the effect of substituting titanium, zirconium, or tin for antimony in the USb3O2 Q lattice. The crystalline phases present in these materials were determined by X-ray powder diffraction. To provide a basis for comparison with the prior art, catalyst 1 listed in Table I was prepared following the published recipe ( ). This catalyst represents the old uranium-antimony oxide catalyst without any silica binder. The crystalline phases detected in catalyst 1 were USb3O2 Q and Sb20 as expected (3,4). 

Substituting titanium for antimony in the USb Oj g phase dramatically Increased catalytic activity. The relative activity for the USbj. Ti Oy series peaked at x=1.5. The best acrylonitrile selectivity was obtained at x=0.6 and x=1.0. Reduced activity and selectivity at higher titanium levels corresponded to USbO and UTiO formation. The USb2TiOy catalyst seemed to offer the best combination of activity and selectivity. Under optimum conditions (Table IV) it yielded 83-84 mol% acrylonitrile per pass compared to 78% for the old uranium-antimony oxide catalyst (1,2,4) which required six times the contact time to obtain comparable conversions. 

Replacing antimony with zirconium increased catalytic activity 11-fold. Figures 3 and 4 show that activity peaked at x-1.0. The USb2ZrOy catalyst was less selective than the corresponding titanium-substituted catalyst but compared favorably to the old uranium-antimony oxide catalyst. 

Table V shows the effect of Ti, Zr, and Sn addition when excess antimony was present. Although each Increased catalyst activity, the effect was much smaller than for the USb. M Oy compositions. Titanium addition about doubled the relative activity compared to the standard uranium-antimony oxide catalyst, while Zr and Sn addition had a smaller effect. The poor selectivity of the Distillers-type catalyst. No. 9, is attributed to the presence of USbO. ...

The effective molar paramagnetic moment of USb2TiOy was less than that of the standard uranium-antimony oxide composition (Figure 8) but still significant. As temperature was increased from 4 to 105 K, the effective magnetic moment of the old uranium-antimony oxide catalyst increased to a value corresponding to one unpaired electron which is consistent with At low temperatures the... 

Like the original uranium-antimony oxide catalyst, the titanium substituted catalysts were able to operate only a short time without regeneration. Otherewise, the catalyst became overreduced, the USb3O2 Q type phase decomposed, and selectivity suffered. The addition of small amounts of molybdenum or vanadium prevented over-reduction enabling the catalyst to operate without regeneration. 

The catalytic activity of the uranium-antimony oxide catalyst for propylene ammoxidation has been increased an order of magnitude by modifying the catalytically active phase rather than by adding various promoters to the optimum uranium-antimony oxide composition. This modification was accomplished by substituting titanium, zirconium, or tin for antimony in compositions with the empirical formula USb3 M Oy. Titanium and zirconium replaced... 

In other examples, extensively studied by Delmon et al., SbaOa was used with M0O3 for isobutene oxidation to methacrolein [29, 30], and for the dehydration of N-ethyl formamide [46,47]. Antimony is one of the elements frequently found in selective oxidation catalysts, as in the pionneering work on uranium antimony oxides for ammoxidation of propene [48], and more recently in ammoxidation of propane on V-Sb-Al system [49]. 

Hydroxybenzonitrile can be synthesized directly from p-cresol over the bismuth-molybdenum oxide, iron-antimony oxide or uranium-antimony oxide catalysts [81] normally used for the ammoxidation of propylene, although the catalysts are rapidly deactivated by coke-like deposits [81]. 

GrasseUi, R.K. and Suresh, D.D. Aspects of structure and activity in uranium-antimony oxide acrylonitrile catalysts.,/ Catal 1972, 25, 273-291. 

Catalysts used for preparing amines from alcohols iaclude cobalt promoted with tirconium, lanthanum, cerium, or uranium (52) the metals and oxides of nickel, cobalt, and/or copper (53,54,56,60,61) metal oxides of antimony, tin, and manganese on alumina support (55) copper, nickel, and a metal belonging to the platinum group 8—10 (57) copper formate (58) nickel promoted with chromium and/or iron on alumina support (53,59) and cobalt, copper, and either iron, 2iac, or zirconium (62). 

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 Sohio technology is based on a catalyst of bismuth an4 molybdenum oxides. Subsequent catalyst improvements came from the use of bismuth phosphomolybdate on a silica gel, and more recently, antimony-uranium oxides. Each change in catalyst was motivated Jby a higher conversion rate per pass to acrylonitrile. 

Shortly after the introduction of the bismuth molybdate catalysts, SOHIO developed and commercialized an even more selective catalyst, the uranium antimonate system (4). At about the same time, Distillers Company, Ltd. developed an oxidation catalyst which was a combination of tin and antimony oxides (5). These earlier catalyst systems have essentially been replaced on a commercial scale by multicomponent catalysts which were introduced in 1970 by SOHIO. As their name implies, these catalysts contain a number of elements, the most commonly reported being nickel, cobalt, iron, bismuth, molybdenum, potassium, manganese, and silica (6-8). 

Christie et al. (45) and Pendleton and Taylor (46) have recently reported the results of propylene oxidation over bismuth molybdate and mixed oxides of tin and antimony and of uranium and antimony in the presence of gas-phase oxygen-18. Their work indicated that for each catalyst, the lattice was the only direct source of the oxygen in acrolein and that lattice and/or gas-phase oxygen is used in carbon dioxide formation. The oxygen anion mobility appeared to be greater in the bismuth molybdate catalyst than in the other two. 

Under the reaction conditions used, a U3O8 catalyst demonstrated appreciable selective oxidation activity. The best results, in terms of both activity and selectivity to benzaldehyde, were obtained with the mixed oxides with U Mo atomic ratios in the range 8 2 to 9 1. The maximum yield of benzaldehyde was 40 mol%. On the other hand, antimony-based uranium oxides were not found to be effective as catalyst for this reaction. U—Mo and Bi—Mo mixtures also exhibited promising activity and selectivity to benzaldehyde. Bi—Mo and Bi—Mo—P—Si catalysts were also tested. Qualitahvely there was little difference between the product distributions from the two catalysts. The major products formed were benzaldehyde, benzene and carbon oxides, as well as traces of anthraquinone and benzoic acid. 

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