Oxides, ternary molybdenum

Our work was initiated on the reduced ternary molybdenum oxides with the thought that the metal cluster electron count (MCE) should be variable for the Mo308 cluster units. Based on Cotton s previous molecular orbital treatment of such clusters (16) it appeared that MCE s from 6 to 8 could be accommodated, but it was not clear whether the seventh and eighth electrons would occupy bonding or antibonding orbitals with respect to the M-M interactions. We thus set about to determine this from structural data on suitable compounds. The attempted replacement of Zn2+ with Sc3+ to secure the compound ZntSc°Mo308 was conducted via the reaction shown in equation 1. 

Table II. Characteristics of metal-metal bonded ternary and quaternary molybdenum oxides.

R. E. McCarley No, we have done very little work along this line, although I think important results will be obtained from studies of mixed 0, S phases. So far we have found no direct structural analogies between the reduced ternary molybdenum oxide phases and the various ternary sulfide or selenide phases of the Chevrel type. 

Our relatively innocent venture into the chemistry of molybdenum oxide systems has led to the discovery of a whole new class of ternary oxide compounds dominated in their structural features by strong metal-metal interactions. Interest in the question of whether the trinuclear clusters in the well known compound Zn.Mo 0 (10, 11) could accept more than 6 electrons in the metal-... 

In the ternary systems Mo-Nb-V mixed oxide phases containing Mo-Nb and Mo-V have been detected in addition to molybdenum oxide, as reveled in Table 2 for the samples Mo/Nb/V=3/l/l and 3/0.5/1.5, respectively. 

Chevrel phases are frequently considered to be reduced molybdenum sulfides because of the low molybdenum oxidation state relative to M0S2. These compounds are also stable under HDS conditions. The low oxidation states are maintained and no decomposition or transformation to other sulfides has been detected for most compounds (61). Chevrel phases usually are obtained through solid-state syntheses at high temperatures (1000-1300°C) by direct combination of the elements or by direct insertion of ternary metal into the binary MogSg... 

In another example, the high temperature reaction of calcium and strontium sub-nitrides with molybdenum foil has also recently been claimed to produce novel molybdenum ternary nitride oxides which contain isolated [MoN4] tetrahedra in an ordered sub-lattice of and anions. High temperature-high pressure syntheses are also yielding novel metastable structures, such as the spinel analogues mentioned previously. There is therefore an ever-increasing base of nitrides and oxynitrides with diverse structures and potential catalytic interest. 

LoJacono et al. (108) also utilized X-ray diffraction methods to study the structural and phase transformations which occurred in the Bi-Fe-Mo oxide system. They detected two ternary compounds containing bismuth, molybdenum, and iron. One of the compounds formed when the atomic ratio Bi/Fe/Mo = 1 1 1 the other formed when the atomic ratio Bi/Fe/Mo = 3 1 2. The X-ray data indicated a close structural relationship of the bismuth iron molybdate compounds with the scheelite structure of a-phase bismuth molybdate. Moreover, their structures were similar to compound X. The structure of the Bi/Fe/Mo = 3 1 2 compound was identical to the compound reported by Sleight and Jeitschko (107). The authors proposed that the structures of both of the compounds could be viewed as resulting from the substitution of Fe3+ in the a-phase lattice. In the Bi/Fe/Mo = 1 1 1 compound, 1 Mo6+ ion is replaced by 2 Fe3+ ions one Fe3+ ion occupies a Mo6+ site the other Fe3+ ion occupies one of the vacant bismuth sites. In the Bi/Fe/Mo = 3 1 2 compound, the Fe3+ ion replaces one Mo6+ ion while the additional Bi3+ ion occupies one of the vacant bismuth sites. 

The thiomolybdites are a class of molybdenum-sulfur compounds which contain molybdenum in a low oxidation state, usually +3. Two main types of such materials exist. The first type has the formula MMoS2 where M is a monovalent cation, usually an alkali metal. The second type has the formula MMo2S4 where M is a divalent cation, usually a transition metal. There are other thiomolybdite species, of composition other than that described above, which have been identified in ternary phase studies involving the M-Mo-S system (M = a transition element), but these have not been well characterized. 

Among the most interesting systems are some ternary oxides of lower-valent molybdenum that contain infinite chains of octahedral clusters fused on opposite edges. This type of structure is similar to those found in the lower-halides of... 

The structure of a highly active cerium-molybdenum-tellurium acrylonitrile catalyst(l ) has previously been described in terms of binary (Ce,Mo)0 and ternary (Ce,Mo,Te)0 phases( ). It was concluded that none of the constituent oxides (CeO, ... 

The most studied systems for oxidative propane upgrading are vanadium [2], vanadium-antimony [3], vanadium-molybdenum [4], and vanadium-phosphorus [5] based catalysts. Another family of light paraffin oxidation catalysts are molybdenum based systems, e.g. nickel-molybdates [6], cobalt-molybdates [7] and various metal-molybdates [8-9]. Recently, we investigated binary molybdates of the formula AM0O4 where A = Ni, Co, Mg, Mn, and/or Zn and some ternary Ni-Co-molybdates promoted with P, Bi, Fe, Cr, V, Ce, K or Cs [10-11]. A good representative of these systems is the composition Nio.5Coo.5Mo04 which was recently selected for an in depth kinetic study [12] and whose mechanistic aspects are now further illuminated here. 

---