Temperature-programmed sulfidation catalysts

Figure 4.21. Temperature programmed sulfidation (TPS) of M0O3/AI2O3 catalysts in a mixture of H2S and H2, showing the consumption of these gases and the production of H2O as a function of temperature. Note that H2S evolves from the catalyst around 500 K, which is attributed to the hydrogenation of elementary sulfur. [Adapted from P. Arnoldy, J.A.M. van den Heijkant, G.D. de Bok and J.A. Moulijn, J.Coto/. 92 (1985) 35.]...

Figure 9.17 Quick EXAFS measurements show the effect of temperature-programmed sulfidation on the Mo K edge in NiMo/SiOj catalysts (adapted from Cattaneo et al. [60]).

Fig. 19. Combined QEXAFS and temperature-programmed sulfiding results of a Mo/ A1203 catalyst during sulfiding in a H2S/Ar gas mixture (a) Fourier transforms of the in situ EXAFS spectra above the Mo X-edge (b) variation in the H2S concentration in the gas outlet from the in situ EXAFS cell as simultaneously recorded by a mass spectrometer (61).

The sulfidation mechanism was investigated by temperature-programmed sulfidation, as the oxidic catalyst was heated in a flow of H2S and ff2, and the consumption of IH S and ff2 and the evolution of H20 were measured continuously (13). ft was found that IH S is taken up and H20 given off, even at room temperature, indicating a sulfur-oxygen exchange reaction. This conclusion was confirmed by quick extended X-ray absorption fine structure (QEXAFS) studies (Fig. f, phase 2), which also demonstrated... 

Since hydrotreating catalysts arc usually used in the presence of H2 and H2S, it is important to understand the influence of phosphorus on the reduction and sulfidation of the supported metal-oxo-specics. It is also important to know whether the phosphates arc sensitive to such treatments. In this section, activation of the catalysts is discussed on the basis of XPS, TPR, and temperature-programmed sulfidation results. Note that the bulk of the alumina support is not chemically modified by the reduction-sulfidation treatments. However, some hydrogen-reactive species and surface SH groups have already been detected on it (31, 70). 

Zeuthen, P. Blom, P. Muegge, B. Massoth, F.E. Temperature-programmed sulfidation and oxidation of Ni-Mo/alumina catalysts and reaction with ammonia. Appl. Catal. 1991, 68 (1),... 

A series of CoSx-MoSx/NaY catalysts was synthesized by intoducing Co(CO)3NO into MoSx/NaY evacuated at 673 K for 1 h, followed by second programmed sulfidation procedures. MoSx-CoSx/NaY catalysts were prepared in the reversed order of the metal sulfide accommodations into the zeolite cavities. When Co2(CO)g was used as the Co precursor, MoSx/NaY was impregnated with COj(CO)g dispersed in n-hexane, followed by evacuation at room temperature to remove the solvent. Co2(CO)g/MoSx/NaY was subsequently sulfided at 673 K to give CoSx/MoSx/NaY. The catalyst composition was determined by AAS and ICP. 

The title Spectroscopy in Catalysis is attractively compact but not quite precise. The book also introduces microscopy, diffraction and temperature programmed reaction methods, as these are important tools in the characterization of catalysts. As to applications, I have limited myself to supported metals, oxides, sulfides and metal single crystals. Zeolites, as well as techniques such as nuclear magnetic resonance and electron spin resonance have been left out, mainly because the author has little personal experience with these subjects. Catalysis in the year 2000 would not be what it is without surface science. Hence, techniques that are applicable to study the surfaces of single crystals or metal foils used to model catalytic surfaces, have been included. 

Other temperature-programmed techniques include Temperature Programmed Oxidation and Sulfidation (TPO and TPS) for investigating oxidation and sulfidation behaviour, and Temperature Programmed Desorption (TPD) (also called Thermal Desorption Spectroscopy [TDS]), which analyses gases desorbed from the surface of a solid or a catalyst on heating. 

MoS2 is observed after sulfidation at temperatures above 300 °C. These results are easily reconciled with those from XPS and RBS described before, be it that the temperatures at which the changes occur are higher in the QEXAFS study, which is in fact expected for a temperature-programmed measurement. In addition, the QEXAFS were made on high-surface area catalysts, where diffusion limitations are likely, whereas the XPS studies concern planar, thin films, in which virtually all material is in contact with the gas phase. 

On the other hand, morphological changes can occur on the minute scale [8], or transformations during activation of a catalyst (temperature-programmed reaction/ reduction/sulfidation), ignition of a reaction, or oscillations can even occur on the subsecond timescale [11, 14, 15],... 

The objective of the present study is to examine the reduction and sulfidation properties of the Fe-treated Y-zeolite by using temperature-programmed reduction (TPR) and sulfiding (TPS), in order to quantitatively determine the active species and support the production control of the commercial Fe-treated Y-zeolite catalysts. An interpretation of the reduction and sulfidation mechanisms of several types of Fe-treated Y-zeolites is presented. 

Sulfided samples were characterized with XRD, BET surface area, NO sorption capacity, ESR and FTIR spectroscopy. The details concerning the characterization procedures as well as certain properties of USY based samples can be found elsewhere (ref. 9, 10). The ammonia adsorption capacity of sulfided and non-sulfided catalysts and supports was measured from the desorption peak obtained during 3the temperature programmed desorption (heating rate 30 K min ). Each sample (0.1 g) after activation or sulfidation was saturated with ammonia (a series of 1 cm NH3 injections) at 375 K until full saturation was achieved. This was monitored as a sharp GC peak detected by thermal conductivity detector. Next, sample was purged 1 hour in purified helium at 375 K to remove the excess of weakly held ammonia and TPD started. 

Hexacarbonyl molybdenum Mo(CO)6 was successfully used to prepare intrazeolite molybdenum sulfide clusters in the cavities of NaY (CVD technique) [4,5,7,8]. The decomposition and sulfidation of Mo(CO)e encaged in NaY were extensively studied by Okamoto et al. [7-11] by means of temperature programmed decomposition (TPDE), XPS, and XAFS techniques. It has been claimed that the structure of molybdenum sulfides is described as molybdenum dinuclear sulfide clusters M02S4. de Bont et al. [12] supported the formation of molybdenum sulfide dimer species. The extremely high dispersion of molybdenum sulfide clusters prepared fi"om Mo(CO)6 was also suggested by an NO adsorption capacity much hi er than those of other conventional catalyst systems such as M0S2/AI2O3 [9]. 

Shu and Oyama have recently proposed a new type of hydrotreating catalytst transition metal phosphides supported on carbon [97], and compared their behavior in the deep HDS of 4,6-DMDBT with that of the silica-supported counterparts and a commercial alumina-supported Ni-Mo sulfide hydrotreating catalyst. The carbon-supported catalysts were prepared by temperature-programmed reduction of the corresponding phosphates, and the activity was studied under simulated industrial conditions of 613 K and 3.1 MPa with a model liquid feed coutaiu-ing 500-ppm sulfur as 4,6-DMDBT, 3000-ppm sulfur as dimethyl disulfide, aud 200-ppm nitrogen as quinoline. The Ni2P/C catalyst showed an excellent performance in HDS and HDN, and it was also the best for sulfur removal from... 

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