Hydrodesulfurization catalytic mechanism

Take hydrodesulfurization catalysis, for example. We used an active Ti02 as the catalytic support to load the active species for catalysis. Till now, there are many works devoted to research the hydrodesulfurization catalysis mechanism by DFT and experiment, and the reaction pathway of hydrodesulfurization has been figured out. DFT was almost focused on the simulation of the active site. For example, Raybaud et al investigated the interaction of the reactants and intermediate with the M0S2 or NiMoS catalyst by DFT (Dupont et al, 2011). Also, they studied the interaction between active species and support (Costa et al, 2007). However, there was litde work on the interaction of reactants or resultants with catalytic support. The ReaxFF method can be apphed to investigate the reaction on Ti02. It can combine the effect of surface and the effect of transport into reaction process so that the reaction time and the transport time can be separately studied to find out the key influence factor. 

Whitehurst, Isoda, and Mochida write about catalytic hydrodesulfurization of fossil fuels, one of the important applications of catalysis for environmental protection. They focus on the relatively unreactive substituted di-benzothiophenes, the most difficult to convert organosulfur compounds, which now must be removed if fuels are to meet the stringent emerging standards for sulfur content. On the basis of an in-depth examination of the reaction networks, kinetics, and mechanisms of hydrodesulfurization of these compounds, the authors draw conclusions that are important for catalyst and process design. 

Catalytic hydrodesulfurization (HDS) is a very important industrial process that involves removal of sulfur from crude oils by high-temperature ( 400°C) treatment with hydrogen over Co- or Ni-promoted Mo or W catalysts supported on alumina. In an attempt to determine the mechanism of this process, many transition metal complexes of thiophene, a sulfur-containing heterocycle that is particularly difficult to desulfurize, have been prepared and their reactivities studied in order to compare their behavior with those of the free thiophenes that give H2S and C4 hydrocarbons under HDS conditions (88ACR387). Thiophene can conceivably bind to the catalyst surface by either cr-donation via a sulfur electron pair or through a variety of -coordination modes involving the aromatic system... 

For most reaction systems, the intrinsic kinetic rate can be expressed either by a power-law expression or by the Langmuir-Hinshelwood model. The intrinsic kinetics should include both the detailed mechanism of the reaction and the kinetic expression and heat of reaction associated with each step of the mechanism. For catalytic reactions, a knowledge of catalyst deactivation is essential. Film and penetration models for describing the mechanism of gas-liquid and gas-liquid-solid reactions are discussed in Chap. 2. A few models for catalyst deactivation during the hydrodesulfurization process are briefly discussed in Chap. 4. 

Participation of spillover hydrogen in the hydrodesulfurization of thiophene over Pt/HZSM-5 catalyst was assumed and examined. It was found that catalytic activity of PWSi02(quartz) mixed mechanically with HZSM-5 was higher than that obtained by simple addition of the data for the pure components(Figure 5). This implies that spillover hydrogen on Pt/HZSM-5 catalyst participates in the hydrodesulfurization of thiophene. The mechanism proposed is shown in Scheme 1. 

Many operations in chemical engineering require the contact of two liquid phases between which mass and heat transfer with reaction occurs. Examples are hydrometallurgical solvent extraction, nitrations and halogenations of hydrocarbons, hydrodesulfurization of crude stocks, emulsion polymerizations, hydrocarbon fermentations for single-cell proteins, glycerolysis of fats, and phase-transfer catalytic reactions. A most common method of bringing about the contact of the two phases is to disperse droplets of one within the other by mechanical agitation. 

Furthermore, it was assumed the existence of spillover hydrogen in the hydrodesulfurization of thiophene over RhAJSY catalyst. Thus, we tried to confirm the existence of spillover hydrogen in the hydrodesulfurization of thiophene over RH/USY catalyst. The catalytic activity of Rh/Si02(quartz) mixed mechanically with USY in the hydrodesulfurization of thiophene was examined. It was found that the activity of mixed catalyst obtained experimentally was higher than that calculated theoretically as shown in Figure 5. 

In this chemistry, it is natural to focus on models for the catalytic reactions that are most important economically or which are most poorly understood because of difficulties of direct study. One which best fits these criteria is the catalytic hydrotreatment of petroleum feedstocks, which is used to remove sulfur and other heteroatoms, which interfere with subsequent catalytic reactions such as petroleum reforming, from the hydrocarbons. Molybdemun sulfide is the most common metal sulfide used in this catalysis, and hydrogen activation and C-S bond hydrogenolysis are known to be key reactions occurring at the catalyst surface but details are difficult to obtain. Study of model binuclear and cluster complexes has elucidated mechanisms of several of the key reactions and Section 2.6 describes important recent advances in this field, with the focus being on models for hydrodesulfurization catalysts. 

Carbon-sulfur bond cleavages are extensively studied not only for synthetic applications but also for interests in catalytic desulfurization mechanism of the industrial hydrodesulfurization (HDS) process of naphtha, petroleum and lubricants... 

A. Hydrodesulfurization and hydrodenitrogenation catalysis. The supported metal sulfides used as catalysts for hydroprocessing reactions have been characterized by many techniques, but the nature of the catalytically active sites is still a matter of controversy which makes it difficult to understand the mechanisms, and relevant organometallic models need to be developed. 

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