Sulphided Forms Research Articles

Simultaneous 1-pentene hydroisomerisation and thiophene hydrodesulphurisation over sulphided Ni/FAU and Ni/ZSM-5 catalysts

Bifunctional catalysts of nickel sulphide supported on zeolites NaY, USY and ZSM-5 have been tested in simultaneous thiophene hydrodesulphurisation (HDS) and 1-pentene hydroisomerisation (HYD/ISO). The catalysts were prepared by ion-exchange and studied in their oxidic and sulphided forms using several physico-chemical techniques such as chemical analysis, X-ray diffraction (XRD), IR of the framework vibration, N 2 adsorption–desorption isotherms, ammonia temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) of adsorbed NO. The best balance of the HDS and HYD functions was achieved over the Ni(6.6)USY sample, which showed an HDS/HYD ratio about three-fold larger than a commercial CoMo/Al 2O 3 catalyst as well as some skeletal isomerisation of 1-pentene (selectivity 2.7%). On the basis of the catalyst structure–activity relationship, it can be inferred that the catalytic response of Ni(6.6)USY catalyst is linked to a homogeneous distribution of nickel species within the zeolite pores and also to the greater acidity of the USY zeolite. NaY-supported and Ni(2.7)USY catalysts showed almost exclusively double bond isomerisation whereas both double bond and skeletal isomerisation were observed for the ZSM-5 and its nickel-loaded counterparts. Factors minimizing 1-pentene hydrogenation during the simultaneous HDS of thiophene and 1-pentene hydroisomerisation over sulphided Ni/NaY, Ni/USY and Ni/ZSM-5 catalysts are discussed.

Characterisation of thermal properties of oxide, reduced and sulphided forms of alumina supported Co(Ni)–Mo(W) catalysts prepared by co-precipitation

This study deals with alumina supported Co(Ni)–Mo(W) catalysts prepared in one step by the co-precipitation method. Results of temperature-programmed reduction (TPR) of oxide forms of the catalysts, and differential thermal analysis (DTA) and thermal gravimetry (TG) of the oxide, reduced and simultaneously reduced and sulphided forms of the catalysts are presented. Reduction of the catalysts has been found to begin already at about 150°C. It has been established that at 400°C the CoMo catalyst practically does not reveal any mass loss after 30 min reduction with hydrogen, while the NiMo catalyst shows a large mass loss after 60 min reduction, continuing with time. The catalyst NiW also shows a significant mass loss already after 10 min reduction with hydrogen, and this mass loss continues to occur as the time of reduction increases.

Effect of hydrogen pressure on detoxification of 1,2,3-trichlorobenzene by catalytic hydrodechlorination with both unsulphided and sulphided [formula omitted] catalyst

A process which has large potential as a disposal method of organic toxic wastes is hydrotreating. The present work has investigated the effects of hydrogen pressure on the catalytic hydrodechlorination of 1,2,3-trichlorobenzene using the unsulphided and sulphided forms of NiMo γ- Al 2 O 3 catalyst. All the experiments were carried out in a stirred autoclave at a constant temperature of 330°C and at the hydrogen pressures (kept constant during each experiment) in the range 35 ⩽ p H 2 ⩽ 100 bar. Hexadecane was used as reaction medium The experimental results allowed us to identify the reaction networks: (i) for the unsulphided form of the catalyst, there were parallel reactions to 1,2 and 1,3 dichlorobenzene. Both these species then reacting with hydrogen to form chlorobenzene, which in turn formed benzene; (ii) the sulphided form of the catalyst holds the same network but with one extra reaction from benzene to hydrocracking products. With the help of the Langmuir-Hinshelwood theory it was possible to gain an insight into the mechanism of the single reactions which form the networks: hydrogen is adsorbed according to a Langmuir-type dissociative adsorption and the rate determining step is the surface reaction. Finally it was demonstrated that the major dechlorination path of the reaction network is pressure independent with sulphided catalyst.

Effect of metal-organic compounds on thiophene hydrodesulphurization over sulphided forms of fluoride-containing CoMo/Al 2O 3 catalysts

The effect of adding fluoride at various stages of preparation of CoMo/γ-Al 2O 3 catalysts was investigated with X-ray photoelectron spectroscopy (XPS) and with a pulse reactor method for activity in hydrodesulphurization (HDS) of thiophene and deactivation by nickel and vanadium naphthenate (NiN and VN). Activity is lowered by increasing fluoride content, except for initial activity at a fluoride-to-aluminium (F/Al) ratio of 0.1. It may be correlated with a decreased surface area and dispersion of the molybdenum sulphide phase. Deactivation in HDS of thiophene strongly increases with the fluoride concentration, probably due to an increased acidity induced by the fluoride anions. XPS data suggest that fluoride is highly dispersed except at the highest concentration, i.e. F/Al=0.2. Fluorination of the catalysts has an inhibiting effect on deactivation by NiN and VN and the highest initial and final activity is observed at F/Al=0.1. XPS intensity data suggest that the dispersion of deposited metals decreases with increasing fluoride concentration and that the deposition occurs to a higher extent at the exterior of the particles than the interior under the conditions applied. Both sulphidic and oxidic forms are detected. The order of adding fluoride and the salts of cobalt and molybdenum results in minor differences in activity, except when metal naphthenates are deposited.

The effects of activation conditions on the porous structure of NiMo-Al 2O 3 catalyst

The results of investigating the porous structure of oxide, reduced and sulphided forms of alumina-supported nickel molybdena catalysts are presented. Microdistribution of the pores was determined by low-temperature nitrogen adsorption, and macrodistribution was determined by mercury porosimetry. The changes in pore-size distribution of different forms of NiMo-Al 2O 3 catalyst are discussed in relation to the conditions of its activation.

Kinetics of the isomerization of butenes over an industrial Co-Mo/Al2O3) Catalyst.: I: Determination of the relative rate constants by the method of wei and prater

The kinetics of the isomerization of butenes over an industrial CoO MoO 3/Al 2O 3 catalyst for hydrodesulphurization of Diesel fractions has been studied by the flow circulation method. The study was carried out under steady-state conditions at atmospheric pressure and in the temperature range 325–425°C. The selectivity of the catalyst for cis-2-butene is practically the same for both the reduced and the sulphided form, but the activity of the reduced form is greater. The selectivity decreases with increasing temperature, with contact time and with 1-butene concentration in the feed, for both the sulphided and the reduced form. Evidence was obtained that suggests that surface reactions are the rate-determining steps under these reaction conditions. The values of the relative rate constants for the three experimental temperatures of 325, 375 and 425°C were calculated by the Wei-Prater method. These values and those obtained for the activation energies show that cis-2-butene is a kinetic control product, as it is formed faster than trans-2-butene which is a thermodynamic control product.

E.s.r. study of zeolites containing transition metals and their hydrodesulphurizing activity

The hydrodesulphurizing activity of type Y zeolites modified with cobalt, nickel, molybdenum, zinc and copper is studied towards the reaction hydrogenolysis of diethylsulphide. The state of the metal components in the oxidized, reduced and sulphided forms of molybdenum-, cobalt- and nickel-containing zeolites is studied by means of e.s.r. spectroscopy. Sulphidation of the samples leads to a decrease in the Mo(V) content, to reduction of Co(II) and to an increase in dispersity of the metallic nickel phase. It is shown that efficient catalysts for hydrodesulphurization are obtained not only by the simultaneous use of cobalt and molybdenum as active components, but also by the separate use of cobalt or nickel.

Porous structure and surface area of oxide, reduced and sulphided forms of alumina-supported cobalt molybdena catalyst

The porous structure and surface area of alumina-supported cobalt molybdena catalysts were examined as functions of their activation conditions. It was revealed that the process of reduction by hydrogen as well as simultaneous reduction — sulphiding by a hydrogen and hydrogen sulphide mixture — results in the disappearance of pores of larger diameters. This is caused by the formation of monomeric, dimeric and/or polymeric species on pore surfaces as a result of thermal activation in hydrogen and H 2-H 2S atmospheres. On the basis of the shapes of the hysteresis loops of nitrogen adsorption-desorption isotherms and on t plots of the samples investigated it was found that the dominant pores are those with diameters in the mesopore range. The shapes of the mesopores resemble tubular capillaries with diameters o of various size and/or tubular capillaries with short necks and wide sloping bodies. Some of the mesopores can be closed at one end. The uniformity of pore sizes appearing after the H 2-H 2S treatment provides good conditions for the diffusion of reactant molecules of large diameter. This is especially important for such catalytic reactions as depolymerization of asphaltenes, hydrodemetallization of metal porphyrins and other hydrotreatment processes.

Molybdenum area and hydrogenation and hydrogenolytic activities of hydrorefining catalysts

A series of nickel or cobalt promoted molybdenum catalysts and one nickel-tungsten catalyst have been studied by oxygen chemisorption on reduced oxidic samples, by activities of oxidic and sulphided samples for 1-hexene hydrogenation and by activities of sulphided samples for benzothiophen and pyridine hydrogenolyses. A good correlation was obtained between oxygen chemisorption and hydrogenation activity on oxidic, partially reduced, forms of the catalysts, and a limited correlation for activities of sulphided forms. Parallel activities for hydrogenation and hydrogenolyses were observed.

The effect of sulphidation on the nature of active sites on nickel-molybdenum-alumina hydrorefining catalysts

A strong influence of sulphidation on the hydrogenation and hydrogenolytic activity of Mo-Al2O3 and Ni-Mo-Al2O3 hydrotreating catalysts has been found. Two kinds of active sites are distinguished, the first consisting of surface molybdenum atoms and serving mostly for hydrogenation, the second type formed by interaction of Mo with Ni atoms and being active in sulphided form for direct hydrogenolysis of the C-S bonds.

Importance de la sulfuration dans l'apparition de l'effet promoteur du cobalt des catalyseurs d'hydrodésulfuration Mo-Co-Al 2O 3

The effect of cobalt on the hydrodesulphurization (HDS) activities of alumina-supported Co-Mo catalysts in reduced and reduced-sulphided forms was investigated using various [Co]/([Co] + [Mo]) ratios. In the reduced form, cobalt has an inhibitory influence on the HDS activity and the synergetic effect of cobalt appears only in the sulphided form. Experiments with Mo-A1 2O 3 samples mechanically mixed with Co-Al 3O 3 show similar effects of cobalt on the activity as a result of the sulphuration. However, the HDS yields are much lower. The results appear to support simultaneously the synergy by contact model and the intercalation model that contribute together to the HDS activity. Their relative importance must depend on experimental conditions and mainly on catalyst preparation mode.

Comparative study of unsupported and supported Co-Mo hydrodesulphurisation catalysts

Catalytic activities of unsupported and alumina- or silica-supported cobalt-molybdenum catalysts in the oxidic and sulphided form are compared. Silica-supported catalysts behave essentially as unsupported catalysts. The behaviour of alumina-supported catalysts is quite different. The synergistic effect is much stronger, especially in the sulphided form, and the domain in which the synergism is exhibited is much broader. In addition, alumina brings about a strong hydrogenating activity. ESCA measurements have helped to investigate further the interaction between the cobalt-molybdenum system and alumina. In the oxide form, interaction is strong for both molybdenum (as indicated by a shift of the Mo(3d) line) and cobalt (which forms a pseudo-aluminate). In the sulphided form, no interaction between molybdenum and alumina can be detected. Two forms of cobalt can be distinguished, one corresponding to the pseudo aluminate, which does not play any role in catalysis, and the other corresponding to sulphided cobalt, which correlates with the synergistic behaviour.