Metal sulfide catalysts

Molybdenum disulfide catalysts, promoted by cobalt or nickel, are used to remove organosulfur compoimds from crude petroleum by hydrogenolysis— hydrodesulfurisation or HDS [124,125,126], These compounds are imdesirable because they poison motor vehicle autoexhaust catalysts and bum to sulfur dioxide, an environmental pollutant. The most difficult compounds to desulfurise are sulfur heterocyclics thiophene, benzothiophene, dibenzothiophene and their methyl substituted derivatives. A typical reaction is the removal of sulfiir from thiophene  

Dihydrogen molecules adsorb and dissociate on the catalyst the reactive siuTace species is the hydrogen atom [127]. In the technical catalysts used in the hydrotreatment of crude petroleum M0S2 is supported on alumina and promoted by cobalt. 

Inelastic neutron scattering has been applied since the early 1980s to characterise hydrogen and adsorbed species in the M0S2 catalysts [128]. Related catalysts, tungsten disulfide [129] and mthenium disulfide [130], 

For hydrogen-treated M0S2, possible hydrogen species are shown in Fig. 7.31 with their calculated vibration frequencies according to the atom superposition and electron delocalization molecular orbital method [134]. Typical spectra of hydrogen-treated RuS2 and M0S2 [130,131] are shown in Fig. 7.32. 

A recent spectrum of M0S2 [135], which includes the lattice modes, is shown in Fig.7.33. Early spectra of M0S2 [126,128] and WS2 [127,129] are similar to our M0S2 spectrum but of poorer quality. Peaks are listed and assigned in Table 7.21 [128,129,130,135,136,137]. 

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The performance of a supported metal or metal sulfide catalyst depends on the details of its preparation and pretreatraent. For petroleum refining applications, these catalysts are activated by reduction and/or sulfidation of an oxide precursor. The amount of the catalytic component converted to the active ase cind the dispersion of the active component are important factors in determining the catalytic performance of these materials. This investigation examines the process of reduction and sulfidation on unsupported 00 04 and silica-supported CO3O4 catalysts with different C03O4 dispersions. The C03O4 particle sizes were determined with electron microscopy. X-ray diffraction (XRD), emd... 

The catalysts applied in hydroprocessing operations are typically sulfided CoO—Mo03—A1203 or NiO—M0O3—A1203. The results of relevant studies281 and the application in refinery processes of these and other transition-metal sulfide catalysts were reviewed.282 Selection of catalysts and reactors for particular feeds and products is also an important issue.257,280,283,284... 

Eijsbouts, S., Mayo, S.W. and Fujita, K. (2007) Unsupported transition metal sulfide catalysts from fundamentals to industrial application. Appl. Catal. A Gen., 322, 58. 

In conclusion, EXAFS has provided important structural information on several supported catalyst systems. Two more applications - on the structure of the metal support interface and on the structure of metal sulfide catalysts - are discussed in Chapter 9. An important requirement for meaningful EXAFS data on catalysts is that the particles are monodisperse, such that the average environment, which determines the EXAFS signal, is the same throughout the entire cat-... 

Hydrotreating catalysts originated in the 1920s when German researchers developed unsupported metal sulfide catalysts to liquefy coal. However, it was not until the 1970s that the structures of these catalysts and the mechanisms of their catalytic action began to be understood. It was established that under catalytic reaction conditions, most of the molybdenum in industrial... 

In 1926, the First International Conference on Bituminous Coal (ICBC) was held in Pittsburgh, PA, at the midpoint of a three-decade-long period when coal represented a commodity of immense industrial importance and an object of intense scientific interest. At that time coal was the primary fuel of industry and the source of coke for steel manufacture and of many of the chemicals upon which a great new chemical industry rested. Gasification of coal still provided most of the town gas used for many domestic and commercial purposes. Efforts to convert coal to liquid fuels used the latest advances in high-pressure technology and led to the development of metal sulfide catalysts that are still mainstays in modem petroleum refining. 

Figure 1 Plot of the rates of dibenzothiophene HDS as a function of the transition metal sulfide catalyst. (Reprinted from Ref 19. 1981, with permission from Elsevier)...

Many minerals or their synthetic equivalents are of industrial importance, and the possibilities of greater understanding of their behavior and properties through application of the methods described in this book is a major stimulus to research. Two examples are chosen for discussion here The first is the zeolites, a group of framework alumino-silicates (with interstitial Na+, Ca +, and HjO), characterized by very open frameworks with large interconnecting spaces or channels the second is the transition-metal sulfide catalysts, materials already generally discussed in Chapter 6, but considered here specifically in relation to their catalytic properties. 

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