Sulphide Catalysts

O. Weisser and S. Landa, Sulphide Catalysts, Their Properties and Applications, Pergamon Press, Oxford, UK, 1973. 

Active catalyst sites can consist of a wide variety of species. Major examples are coordination complexes of transition metals, proton acceptors or donors in a solution, and defects at the surface of a metallic, oxidic, or sulphidic catalyst. Chemisorption is one of the most important techniques in catalyst characterization (Overbury et al., 1975 Bartley et al, 1988 Scholten et at, 1985 Van Delft et al, 1985 Weast, 1973 and Bastein et al., 1987), and, as a consequence, it plays an essential role in catalyst design, production and process development. 

Huber and Wachtershauser (1997) were able to demonstrate the incorporation of CO at an Fe/Ni sulphide catalyst. Orgel, however, doubts that it is justified to draw further conclusions from this result, since this enzyme mechanism may have developed after protein synthesis began or evolved. Orgel considers the use of the mechanism referred to above of CO incorporation in biomolecules to be a result of chemical determinism. 

Partially Crystalline Transition Metal Sulphide Catalysts. Chiannelli and coworkers (6, 7, 8) have shown how, by precipitation of metal thio-molybdates from solution and subsequent mild heat-treatment many selective and active hydrodesulphurization catalysts may be produced. We have shown (18) recently that molybdenum sulphide formed in this way is both structurally and compositionally heterogeneous. XRES, which yields directly the variation in Mo/S ratio shows up the compositional nonuniformity of typical preparations and HREM images coupled to SAED (see Figure 2) exhibit considerable spatial variation, there being amorphous regions at one extreme and highly crystalline (18, 19) MoS at the other. 

The catalytic properties of unsupported transition metal sulphides have been examined for the reaction of dehydrogenation of tetrahydrothiophene. This study has shown that a selectivity higher than 90% for thiophene formation can be obtained for the most active catalysts, essentially the second row sulphide catalysts. The comparison between the catalytic activities in both dehydrogenation of tetrahydrothiophene and... 

Moreover, this study points out the ability of sulphides to catalyze either reactions involving the conversion of sulphur containing molecules without desulphurization (DHN of THT) or desulphurization of these molecules (HDS of thiophene) as well as classical hydrogenation reactions (HN of BP). These properties make the sulphide catalysts interesting to be applied to organic chemistry, particularly in thiochemistry. 

Weisser, 0 Landa, S. "Sulphide Catalysts their Properties and Applications Pergammon Press Oxford, N.Y. 1973. 

Interestingly sulphidic compounds, having a cation coordination which is similar to that of the oxides, show large differences in their sensitivity with respect to basic molecules like NH3. Whereas the desulphurization activity of cobalt sulphide catalysts is readily poisoned by ammonia, nickel sulphide maintains its activity to a significant extent. This agrees with the observed weak interaction of the adsorbent with the doubly occupied dangling bond orbital of the Ni2+ ion. 

Weisser, O. Lancia, S. Sulphide Catalysts, their Properties and Applications ... 

Wcisser. O., and l nda, S., Sulphide Catalysts, I heir Properties and Applications. Pergaraon, Oxford, 1973. 

Molybdenum Sulphide Catalysts. Pure molybdenum sulphide is active for metathesis reactions. Preferential degenerate but-2-ene conversions of cis-io-cis and trans-Xo-trans indicate some stereoselectivity. Okuhara and Tanaka found that, over molybdenum sulphide, olefins having vinyl groups exchange vinyl hydrogens selectively and rapidly, but hydrogen scrambling in but-2-ene is extremely slow. 

Sulphide Catalysts Characterization and Reactions Including Hydrodesulphurization... 

These reactions often occur together over sulphide catalysts. Fundamental studies of mechanisms and active sites have involved mainly M0S2 first this work is described and then reactions over other catalysts. 

---