The role of reaction pathways and support interactions in the development of high activity hydrotreating catalysts

Abstract

Scanning tunneling microscopy (STM) investigations have recently provided the first atom-resolved images of reaction intermediates in the key steps of the hydrogenation (HYD) and direct desulfurization (DDS) pathways in hydrodesulfurization over MoS 2 nanoclusters. Surprisingly, special brim sites exhibiting a metallic character are observed to be involved in adsorption, hydrogenation and C-S bond cleavage. The insight is seen to provide a new framework for understanding the DDS and HYD pathways and the role of steric hindrance and poisons. Density functional theory (DFT) calculations have illustrated how support interactions may influence the activity of sulfided catalysts. The brim sites and the tendency to form vacancies are seen to differ in types I and II Co-Mo-S. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) studies show that the high activity Type II structures may be present as single sulfide sheets. Thus, stacking is not an essential feature of Type II catalysts. The article illustrates how the new scientific insight has aided the introduction of the new high activity BRIM TM type catalysts for FCC pre-treatment and production of ultra low sulfur diesel (ULSD). #

Adsorption of nitrogen‐ and sulfur‐containing compounds on NiMoS for hydrotreating reactions: A DFT and vdW‐corrected study

“…1,2 Hydrotreating in general, and hydrodesulfurization (HDS) in specific, is industrially carried out on promoted (nickel or cobalt) molybdenum sulfide (MoS 2 ) catalysts (nickel promoted molybdenum sulfide [NiMoS] or cobalt promoted molybdenum sulfide [CoMoS]). Experimental, specifically spectroscopy and microscopy, [3][4][5][6][7] and theoretical studies [8][9][10] have together shown that: (a) the active sites are located at or near the two types of edges-"metal" and "sulfur" edges-of the layered molybdenum disulfide particles, [11][12][13][14][15] (b) these edges can be decorated by sulfur atoms, sulfur dimers, and sulfohydryl (ASH) groups, under reaction conditions, [16][17][18][19][20][21][22][23][24][25] (c) sites with sulfur unsaturation, referred to as coordinatively unsaturated sites, are active for HDS, 13,15,26,27 (d) "brim" sites near the edges and above the MoS 2 layer can be potential alternative sites for HDS, 23,25,28 (e) cobalt and nickel promoter atoms replace the edge molybdenum atoms partially or completely, with cobalt preferring the sulfur edge while nickel substitutes molybdenum at the metal edge, [29][30][31][32] and (f) support interactions with the catalyst can affect the morphological characteristics such as shape, size, and orientation, the electron density, and the activity of the catalyst. …”

Adsorption Thermodynamics of Sulfur- and Nitrogen-containing Molecules on NiMoS: A DFT Study

“…Theoretical studies based on density-functional theory (DFT) have made significant contributions towards developing a fundamental understanding of hydrotreating catalysis and furthering the development of new highly active and selective hydrotreating catalysts [1]. For example, DFT calculations have provided new insights into the detailed surface structures of MoS 2 -based hydrotreating catalysts [2][3][4][5][6].…”

Major Successes of Theory-and-Experiment-Combined Studies in Surface Chemistry and Heterogeneous Catalysis

“…His contributions to the theories of surface chemical bonding and catalytic reaction over the past 30 years lead to a giant leap forward in our molecular level understanding of surface chemistry and heterogeneous catalysis [12][13][14][15][16][17][18][19][20][21]. Of course, his achievement is a result of his exceptional expertise in theoretical chemistry, but, from the point of view of an experimentalist, the more important factors perhaps are his willingness to work closely with experimentalists and his ability to grasp the essence of experimental development [22][23][24][25][26][27][28].…”