Molybdenum disulphide in lubrication. A review

CoMo—Al2O3 catalysts are used for hydrotreating and desulphurisation in petroleum processing. The catalyst prepared in the oxide form is inactive and is presulphided before use. ESCA analysis has shown that, during this activation, a state similar to Mo4+ sulphide in MoS2 is formed on the surface. To gain more insight into the properties of the sulphide formed by presulphiding, we have examined the properties of MoS2 and report findings with two samples, one prepared with a high basal plane area and the other with a high edge plane area. We used four experimental tests: reaction with carbon disulphide and with thiophene and adsorption of hydrogen and thiophene below reaction temperatures. ESCA was used to follow changes in the surface composition of the sulphides and the results were compared with those found with an active commercial CoMo catalyst. The MoS2 sample having a higher edge plane area adsorbed hydrogen and thiophene more strongly, gave bigger yields of methane from carbon disulphide and gave a higher proportion of butane relative to butenes in the hydrogenolysis of thiophene. However, the sample having mainly basal plane MoS2 showed the higher conversion of thiophene. Our results suggest that the basal plane of MoS2 catalyses hydrogenolysis whereas the edge plane promotes a variety of other hydrogenation reactions. Comparison with the performance of a sulphided CoMo—Al2O3 catalyst indicates that the dominant reaction site resembles the basal plane of MoS2. However, the commercial catalyst shows distinctive patterns of reaction with carbon disulphide during presulphiding and may also show differences in hydrogen adsorption, particularly when the surface contains excess sulphur.

Catalytic activity of the basal and edge planes of molybdenum disulphide

Reactivity of molybdenum disulfide surfaces studied by XPS

The effect of carbon aspect ratio on the friction and wear of PTFE

X-ray photoelectron spectroscopy (XPS) is a powerful tool to study surface properties (< 10 nm) and is being widely used in almost all branches of science and engineering. This review provides a pedagogical description of the fundamental understanding of XPS based surface characterization with the necessary background and key concepts, details on primary factors influencing surface analysis, issues in XPS analysis and identification of chemical bonding/oxidation state of elements. The basic theory of XPS and the most frequently used “core level peaks” analysis in the conventional use of XPS are presented, along with the details of valence band analysis. The challenges encountered during surface analysis, especially for phase composition identification, are briefly discussed. Further, a few selected recent applications of the XPS technique in various scientific fields are also highlighted. The recent development in the area of surface phase identification by valence band analysis using XPS, along with its advantages and challenges in the determination of nanoscale thin film phase composition are also detailed. This review also provides an overview of the significance of XPS as a tool for surface characterization in the field of material science, nanoscience, mining and mineral extraction, metallurgy, semiconductors, coatings, inorganic materials, tribology, organic materials, corrosion science and electrochemistry. The review should be an ideal material for researchers and also serves as an excellent reference for freshers who plan to begin research on this topic. 

Review on surface-characterization applications of X-ray photoelectron spectroscopy (XPS): Recent developments and challenges

Adsorptive studies of the surfaces of graphite and MOS2have shown that these consist of two distinct types of site. The sites on the basal-plane surface differ from those on the edge surface with respect to their relative affinities for different organic compounds. These findings led to the development of grinding techniques to produce graphite and MoS2 powders possessing different ratios of basal-plane:edge-surface area.Grinding graphite and MoS2 in the presence of low-viscosity, volatile hydrocarbons produced very thin flake-like powders, consisting predominantly of basal-plane surface. These fine flakes showed a high affinity for long-chain n-paraffins and were therefore termed oleophilic solids. Grinding under reduced pressure also produced very fine powders, having, however, a more granular structure exhibiting a far lower ratio of basal-plane: edge-surface area. These were termed polar solids to distinguish them from the solids ground in liquid hydrocarbons.The cold-forming properties of the...

R. E. Witheridge

Papers

THE IMPORTANCE OF SURFACE PROPERTIES AND PARTICLE SHAPE IN THE COMPACTION OF GRAPHITE AND MoS2