Molybdenum carbides preparation

Peters, J. C., Odom, A. L., Cummins, C. C., A terminal molybdenum carbide prepared by methylidyne deprotonation. Chem. Commun. 1997, 1995-1996. 

Except for the fullerenes (see later), carbon atoms seldom coordinate a metal atom a well-characterized example of a naked carbon atom is a molybdenum carbide prepared, in a multistep procedure, by removing a terminal proton from a corresponding methylidyne species ... 

Choi J-S, Krafft J-M, Krzton A, Djega-Mariadassou G (2002) Study of residual oxygen species over molybdenum carbide prepared during in situ DRIFTS experiments. Catal Lett 81 (3) 175-180. doi 10.1023/a 1016568804706... 

Using MoC15 as molybdenum source it was possible to prepare molybdenum nitride in a new Mo2N modification which was isotypic with a-Mo2C molybdenum carbide 26... 

The molybdenum carbide samples were prepared by caburizing pure metal foils (12 X 8 X 1.5 mm) with a 20% CH4/H2 gas mixture in a quartz... 

There are two well-characterized examples of a naked carbon atom bound by a triple bond to a metal center (Fig 14.3.8). The molybdenum carbide anion [CMo N(R)Ar 3]- (R = C(CD3)2(CH3), Ar = C6H3Me2-3,5), an isoelectronic analog of NMo N(R)Ar 3, can be prepared in a multistep procedure via deprotonation of the d° methylidyne complex HCMo N(R)Ar 3. The Mo=C distance of 171.3(9) pm is at the low end of the known range for molybdenum-carbon multiple bonds. In the diamagnetic, air-stable terminal ruthenium carbide complex Ru(=C )C12(LL/)(L = L = PCy3, or L = PCy3 and L = l,3-dimesityl-4,5-dihydroimidazol-2-ylidene), the measured Ru-C distance of 165.0(2) pm is consistent with the existence of a very short Ru=C triple bond. 

Strategies for preparation are numerous and invoh widely differing starting metallic compounds, as we as different carbon and nitrogen sources. It is then fore instructive to consider the thermodynamics [2. of various kinds of transformations. The heats an free energies of formation from the elements at 2981 and 1000K are presented in Table 1 for carbides an Table 2 for nitrides. For illustration, different transfo mations to molybdenum carbide are presented at 2981 in Table 3 and at lOOOK in Table 4. 

Although Heppert s discovery and the subsequent work by Grubbs and others has received special attention, it must be emphasized that prior to the studies on ruthenium carbido complexes Christopher Cummins from MIT had reported the preparation of the anionic molybdenum carbide [CMo N(R)Ar 3] (R =... 

More publications were found related to carbides. First, Suslick s early report [64] that certain carbonyls sonicated in a decalin solvent under argon. For Fe and Co, nanostructured metals are formed for Mo and W, metal carbides (e.g., M02C) are produced. Molybdenum carbide was used later as a catalyst. The selectivity and catalytic activity of the Mo and W carbides was examined in the dehydrogenation of alkanes [140]. Another carbide that has already been mentioned is that of Pd [65], which was prepared by Maeda s group. Iron carbide was a byproduct that served as protective layer in Nikitenko s work on air-stable iron nanoparticles [70]. 

The tungsten and molybdenum carbides supported on alumina were prepared by UGICARB M0RG0N (Grenoble, France). The alumina support (grain size < 80 pm,... 

Using HRTM we found two principally differing forms of pores in the porous structure of Mo-ZSM-5 zeolites. Their origin may be connected to the conditions of the catalyst preparation and operation. Firstly, these are elongated mesopores 3-10 nm in diameter with an exposure to the zeolite surface. These pores are formed due to a partial zeolite dealumination in the process of the hydrothermal synthesis, and they contain a fraction of molybdenum carbide 2-5 nm in diameter (Fig. 3a). 

After that it was important to extract the metal from the molybdic earth. To do that Scheele planned to calcinate the earth with coal. But for some reason he could not perform the reaction himself and asked his friend P. Hjelm to do it. In 1790 Hjelm complied with the request. However, molybdenum obtained by him was contaminated with carbon and molybdenum carbide. The credit for preparing pure molybdenum (by reduction of the oxide with hydrogen) went to J. Berzelius (1817). 

In MAFBS experiments to produce molybdenum carbide, molybdenum and carbon black powders were mixed in a 2 1 molar ratio. Five grams of this mixture were added to the quartz tube and fluidized with argon. Visible heating effects in these experiments were similar to those in experiments to prepare chromium carbide. 

Other Preparative Methods for Molybdenum Carbides. Volatile inorganic compounds such as Mo(CO)e, W(CO)6, and WCle have been used as precursors for various experimental techniques to prepare metal carbides. Vaporization and decomposition of Mo(CO)e in the presence of a CH4/H2 mixture produced molybdenum oxycarbide with a surface area of 40 m /g (49). 

Janes, A., Thombeig, T., Kurig, H., and Lust, E. Nanoscale fine-tuning of porosity of carbide-derived carbon prepared from molybdenum carbide. Carbon Al, 23-29, 2009. 

Another method of forming double molybdenum carbides consists in the carbonization of Mo and Ni alloys prepared in a carbonization gas (mixture of pure methane and hydrogen) flow at a temperature of 1273-1473 K for 100-150 hours [8], As a result of carbonization, Ni(Mo,C) solid solutions with active carbon (graphite) on a plate surface form. 

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