Uranium antimony catalyst ammoxidation

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). 

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. 

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]. 

Another propylene ammoxidation catalyst that was used commercially was U-Sb-0. This catalyst system was discovered and patented by SOHIO in the mid-1960s (26,27). Optimum yield of acrylonitrile from propylene required sufficient antimony in the formulation in order to ensure the presence of the USbaOio phase rather than the alternative uranium antimonate compound USbOs (28-30). The need for high antimony content was understood to stem from the necessity to isolate the uranium cations on the surface, which were presumed to be the sites for partial oxidation of propylene. Isolation by the relatively inactive antimony cation prevented complete oxidation of propylene to CO2. Later publications and patents showed that the activity of the U-Sb-0 catalyst is increased by more than an order of magnitude by the substitution of a tetravalent cation, tin, titanium, and zirconium (31). Titanium was found to be especially effective. The promoting effect results in the formation of a solid solution by isomorphous substitution of the tetravalent cation for Sb + within the catalytically active USbaOio- phase. This substitution produces o gen vacancies in the lattice and thus increases the facility for diffusion of lattice o gen in the solid structure. As is discussed below, the enhanced diffusion of o gen is directly linked to increased activity of selective (amm)oxidation catalysts based on mixed metal oxides. 

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