Russell R. Chianelli

Hydrodesulfurization catalysis by transition metal sulfides

Abstract The primary effect in the hydrodesulfurization of dibenzothiophene by transition metal sulfides is “electronic,” i.e., it is related to the position the metal occupies in the periodic table. This effect, which determines the ability of the transition metal sulfides to catalyze the HDS reaction, varies over three orders of magnitude across the periodic table. The first-row transition metal sulfides are relatively inactive, but the second- and third-row transition metals show maximum activity with Ru and Os. HDS activity as a function of periodic position yields typical “volcano” plots.

Catalysis by transition metal sulfides: A theoretical and experimental study of the relation between the synergic systems and the binary transition metal sulfides

Both a systematic experimental study of the promoting effect of the first row transition metals on the hydrodesulfurization (HDS) activity of MoS2 and a systematic theoretical study of the electronic structure of simple clusters which model these catalyst systems have been carried out. A comparison of measured trends in activity with calculated trends in electronic structure makes it possible to establish an electronic basis for the promotion effects observed in the MoS2 systems. Both Co and Ni, which serve as promoters, have the ability to donate electrons to Mo, while Cu, which serves as a poison, withdraws electrons from Mo. The other first row transition metals, which have little effect on the HDS activity of MoS2, do not have the ability to donate to or accept electrons from Mo. Thus promotion is associated with an increase in electron density on Mo while poisoning is associated with a decrease in electron density. These results are consistent with previous results which related particular electronic factors to the HDS activity of binary sulfide catalysts.

Catalysis by transition metal sulfides: The relation between calculated electronic trends and HDS activity

Recent measurements of the catalytic activity of a series of transition metal sulfides showed that the ability of a particular sulfide to catalyze the HDS reaction is related to the position of the transition metal in the periodic table (Pecoraro, T. A., and Chianelli, R. R., J. Catal.67, 430 (1981)). In order to understand the specific origin of these periodic trends in activity, SCF-Xα calculations of the electronic structure of cluster models of the first and second row transition metal sulfides were carried out. The results of these calculations were used to identify several electronic factors which appear to be related to the catalytic activity of the transition metal sulfides. The computed quantities which measure these factors were combined to form an activity parameter for each sulfide. This parameter shows a direct correlation with the catalytic activity of the sulfides. A model for the binding of thiophenic molecules to the surface of the sulfide catalyst is suggested. This model is consistent both with the correlation between bulk electronic structure and catalytic activity of the sulfides and with the ligand properties of thiophene in transition metal complexes.

Structure and properties of molybdenum sulfide: Correlation of O2 chemisorption with hydrodesulfurization activity☆

The chemisorption of oxygen has been used in a dynamic mode for the characterization of a number of samples of molybdenum disulfide. Their hydrodesulfurization activities (for dibenzothiophene) had previously been determined. Surface areas of the activity-tested catalysts gave little or no correlation with catalytic activity. However, a clear, linear relationship emerged when activities were plotted against O2 chemisorption capacities of the activity-tested catalysts. These results are discussed in terms of the anisotropic nature of molybdenum disulfide.

Catalytic Properties of Single Layers of Transition Metal Sulfide Catalytic Materials

Single layer transition metal sulfides (SLTMS) such as MoS2, WS2, and ReS2, play an important role in catalytic processes such as the hydrofining of petroleum streams, and are involved in at least two of the slurry‐catalyst hydroconversion processes that have been proposed for upgrading heavy petroleum feed and other sources of hydrocarbon fuels such as coal and shale oils. Additional promising catalytic applications of the SLTMS are on the horizon. The physical, chemical, and catalytic properties of these materials are reviewed in this report. Also discussed are areas for future research that promise to lead to advanced applications of the SLTMS.

Periodic trends in hydrodesulfurization: in support of the Sabatier principle

Abstract Periodic effects form the basis for progress in understanding the role of structure/function relationships in hydrodesulfurization (HDS). Theoretical results of Toulhoat, and Raybaud et al. based on ab initio calculations using density functional theory calculations as well as experimental results of Berhault et al. have recently confirmed the initial proposal of Pecoraro and Chianelli about the Sabatier principle interpretation for HDS activity either for transition metal binary bulk sulfides or for cobalt promotion of MoS2-based catalysts. An optimum HDS activity corresponds to a moderate active site-organic sulfur-containing reactant interaction. An update is presented here with a special attention to the electronic foundations of the Sabatier principle as applied to HDS catalysis.

Structure of poorly crystalline MoS2 - A modeling study

Current interest in amorphous and poorly crystallized phases of the layered transition metal dichalcogenides arises primarily from their unique catalytic and electrochemical properties not present in the corresponding crystalline phases. Computer calcultions of the scattered X-ray intensity from model structures of poorly crystalline (px-) MoS2 are compared here with experimental patterns from materials prepared at different temperatures. The results are used to identify the salient features of the observed diffraction patterns of px-MoS2 in which the measured diffuse scattered intensity may be clearly attributed to the stacking and rotational disorder of the layers as well as the limited number of these layers. A procedure for the interpretation of the X-ray diffraction pattern of px-MoS2 has thereby been developed in which the entire scattering pattern may be calculated without separation into Bragg peaks (of varying breadth and shape) and diffuse background.

The adsorption and binding of thiophene, butene and H2S on the basal plane of MoS2 single crystals

Abstract The adsorption of thiophene, butene and H 2 S has been studied using the basal plane of MoS 2 single crystals in the temperature range of 77–300 K. Only at the lowest temperatures did thiophene adsorb and then desorb intact at 165 K using a partial pressure of 10 −6 Torr. H 2 S and butene behaved similarly and all of the molecules have binding energies in the range of 8–10 kcal/mole.

Fundamental studies of transition-metal sulfide catalytic materials

Publisher Summary This chapter reviews the current understanding of the relation between the properties of the transition-metal sulfide (TMS) and how they catalyze hydrotreating reactions. The TMS are unique class of catalysts that are able to perform numerous hydrogenation and hydrogenolysis reactions in the presence of sulfur. In fact, they require sulfur for activity maintenance. The catalytic activity and selectivity of the TMS arises from the electronic and structural properties of the sulfides themselves. Support effects are secondary, improving sulfide dispersion and reducing metal cost in commercial catalysts. Fundamental effects can only be elucidated by studying TMS catalysts in their fully sulfided and catalytically stabilized states. Studies are often simplified by studying the unsupported TMS, which in the past have been commercial catalysts with extraordinarily stable catalytic activity. The study of supported catalysts can also be useful if the experiments are carefully designed and the results are compared consistently with those from unsupported systems.

The reactivity of MoS2 single crystal edge planes

The reactivity of the edge planes of MoS2 have been studied on single crystals. MoS2 edge planes have been shown to be reactive toward oxygen by both optical and scanning Auger studies. In addition it has been shown that Co incorporated at low levels into single crystals tends to surface segregate at MoS2 edge planes.