Hydrodesulfurization of thiophene

Here we illustrate how to use kinetic data to establish a power rate law, and how to derive rate constants, equilibrium constants of adsorption and even heats of adsorption when a kinetic model is available. We use the catalytic hydrodesulfurization of thiophene over a sulfidic nickel-promoted M0S2 catalyst as an example ... 

Mechanistically, hydrotreating of ring-type molecules such as thiophene and related molecules involves the hydrogenation of the unsaturated ring followed by cleavage of the bonds between the heteroatom and its carbon neighbors. Figure 9.8 illustrates this for the hydrodesulfurization of thiophene. 

Figure 9.8. Global reaction mechanism for the hydrodesulfurization of thiophene, in which the first step involves hydrogenation of the unsaturated ring, followed by cleavage ofthe C-S bond in two steps. Butadiene is assumed to be the first sulfur-free product,...

In this paper we will discuss the results that we have obtained studying two important processes, the synthesis of ammonia over Fe and Re catalysts and the hydrodesulfurization of thiophene on Mo. These examples illustrate two problems in catalysis to which our methods are particularly sensitive. The first is the effect of the structure of the catalyst on reaction rates. The sensitivity of the... 

Kinetics over the Mo(lOO) Crystal Surface. We have studied the hydrodesulfurization of thiophene over the initially clean Mo(lOO) single crystal surface in the temperature range 520K - 690K and at reactant pressures of 100 Torr < P(H ) 800 Torr and 0.1 Torr P(Th) < 10 Torr. Under these conditions the reaction is catalyzed at a constant rate for a period of approximately one hour after which the rate begins to decrease with time. The rates reported here are all initial rates of reaction calculated from data collected in the period over which they remain constant. 

The studies of ammonia synthesis over Fe and Re and the hydrodesulfurization of thiophene over Mo, described above, illustrate the importance and success of our approach of studying catalysis over single crystal samples at high pressures. The use of surfaces having a variety of orientations allows the study of reactions that are surface structure sensitive 6Uid provides insight into the nature of the catalytic site. Here we have shown that the ammonia synthesis... 

Smectite-type materials containing transition metal divalent cations (Ni2+, Co2, and Zn2+) in octahedral sheets were synthesized. The synthetic smectites were thermally stable and had large surface areas and high pore volumes after evacuation at 873 K. Catalytic activities of synthetic smectites were investigated. The Ni2 -containing smectites were active for the isomerization of 1-butene and the oligomerization of ethylene. The Co2+-containing smectites were active for the hydrodesulfurization of thiophene. 

Several excellent reviews of the early work on thiophene reduction are available. The present discussion will not cover the important industrial topic of catalytic hydrodesulfurization of thiophenes in petroleum. ... 

Although of little synthetic interest at the present time, mention must be made of desulfurizations by transition metal carbonyls. Thus thiols and/or sulfides are desulfurized by complexes such as [MofCOIe], [Fe3(CO)i2], [Co2(CO)s] and [Os3(CO)i2]. Coupling desulfurizations of dithioketals have been performed with [W(CO)6] or [Mo(CO)6], and a recent review gives further information about the hydrodesulfurization of thiophenes. 

Hydrodesulfurization of thiophene Cr-M impr. with H2S/H2 The activity of the presulfided catalyst was very high and greater than the unsulfided catalyst, but decreased slowly with time. Activity was postulated to arise from chromium (oxy) sulfides. 59... 

Hydrodesulfurization of thiophene over noble metals supported onZSM-5 zeolites... 

Pt/HZSM-5 showed high and stable catalytic activity for the hydrodesulfurization of thiophene at 400 C and its catalytic activity was higher than that of commercial C0M0/AI2O3 catalyst. It is concluded that the Brdnsted acid site and spillover hydrogen formed on Pt particle in Pt/HZSM-5 catalyst play an important role for the hydrodesulfurization of thiophene. 

In the present work, the catalytic activity of noble metals (R, Rh, Pd, Ru) supported on NaZSM-5 and HZSM-5 zeolites were studied in the hydrodesulfurization of thiophene in order to develop more highly active... 

Hydrodesulfurization of thiophene was carried out at 400 C at 1 atm using conventional fixed-bed flow reactor. Thiophene was introduced into the reactor with flowing hydrogen saturated by thiophene at O C. The reaction products were analyzed by gaschromatograph. 

The catalytic activity of various noble metals supported on NaZSM-5 and HZSM-5 zeolites was examined in the hydrodesulfurization of thiophene at 400 C (Figure 1). The activity was markedly changed by the the kind of noble metal and the order of the catalytic activities of noble metal/NaZSM-5 catalysts was as follows ... 

Rgure 2 shows the hydrodesulfurization of thiophene over various noble metal/HZSM-5 catalysts. It was found that the order of the catalytic activities of noble metal/HZSM-5 corresponded to that found with NaZSM-5 preparations. Pt/HZSM-5 catalyst showed stable activity. This activity was the highest, even higher than the activity of the C0M0/AI2O3 catalyst. The reaction products in the hydrodesulfurization of thiophene over noble metalsM-5 catalysts were hydrogen sulfide and C1-C4 hydrocarbons. 

Noble metals supported on HZSM-5 zeolite show higher catalytic activity than on NaZSM-5, suggesting that the Brbnsted acid sites of HZSM-5 in noble metal/HZSM-5 catalysts play important role in the hydrodesulfurization of thiophene. 

Figure 1. Hydrodesulfurization of thiophene over noble metal/NaZSM-5 catalysts at 400°C.

Figure 3. Effect of introduction of hydrogen sulfide on the hydrodesulfurization of thiophene over nobie metal/HZSM-5 catalysts at 400 C.

Results suggest that interaction of the hydrogen sulfide and the platinum on the HZSM-5 is not very strong, therefore, the metallic nature of platinum is easily regenerated by the hydrogen during hydrodesulfurization. By this reason, Pt/HZSM-5 catalyst shows high and stable activity for the hydrodesulfurization of thiophene. 

As mentioned above, Pt/HZSM-5 showed higher activity than Pt/NaZSM-5 in the hydrodesulfurization of thiophene. This indicates that the BrSnsted acid site of HZSM-5 in Pt/HZSM-5 catalyst plays an important role for the hydrodesulfurization of thiophene.lt can be assumed that the Brdnsted acid site in the Pt/HZSM-5 catalyst is one site active for the activation of thiophene, whereas R is an active site for the activation of hydrogen. In other words, Pt/HZSM-5 catalyst is a bifunctional catalyst for the hydrodesulfurization of thiophene, in which both Brdnsted acid and platinum metal sites are active sites. 

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. 

Figure 5. Hydrodesulfurization of thiophene over Pt/quartz(A), HZSM-5(B) and mechanically mixed (R/quartz(A) + HZSM-5(B)) catalysts at 40(TC.

It was observed that Pt/HZSM-5 was of higher catalytic activity than commercial C0M0/AI2O3 in the hydrodesulfurization of thiophene. Therefore, there is a possibility for using Pt/HZSM-5 as highly active, second generation hydrodesulfurization catalyst for petroleum feedstocks. 

Olguin, E., Vrinat, M., Cedeno, L., Ramirez, I., Borque, M., and Lopez-Agudo, A. The use of Ti02-A1203 binary oxides as supports for Mo-based catalysts in hydrodesulfurization of thiophene and dibenzothiophene. Applied. Catalysis. A, General, 1997, 165, 1. 

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