Effect of MoS2 morphology on the HDS activity of hydrotreating catalysts

We have applied near-edge X-ray absorption fine structure (NEXAFS) to characterize the surface and bulk properties of Li_xNi_1–xO catalysts. In our experimental set-up, NEXAFS spectra of powder materials could be obtained by measuring the intensity of either electron-yield or fluorescence-yield. While the electron-yield method is sensitive only to the top few atomic layers, the fluorescence-yield method can detect species up to a few thousands angstroms deep into the bulk structure. The ability to distinguish surface and bulk compositions is demonstrated in studies of a number of Li_0.5Ni_0.5O samples, of which the surface compositions vary as a function of preparation procedures. In addition, NEXAFS investigations following the reaction of Li_xNi_1–xO with CH₄ have also been carried out and the results indicate that the initial surface reaction intermediates are Li₂CO₃.     

Hydrodesulfurization of Diesel Feeds by Association of a Catalytic Process and a Separation Process Using Charge-Transfer Complexes

While deep hydrodesulfurization of gas oil is more and more important, elimination of sulfur compounds such as 4,6-dialkyldibenzothio-phenes still attracts considerable attention. A new process based on the association of a separation process by charge-transfer complex (CTC) formation and classical catalytic hydrotreating (HDT) was evaluated. The results indicated that a CTC pretreatment allows the rate of hydrodesulfurization (HDS) to increase and the final sulfur level to decrease. This process is even more efficient for feeds difficult to desulfurize.     

Ruthenium sulphide catalysts supported on alumina : physicochemical characterization and catalytic properties in hydrotreating reactions

Ruthenium sulphide catalysts supported on alumina were prepared using ruthenium III chloride trihydrate and they were sulphided under a N₂/H₂S(15%) flow at a number of temperatures. The properties of the catalysts in thiophene hydrodesulphurization, biphenyl hydrogenation and pyridine conversion have been investigated and interpreted in relation to their characterization by X-ray photoelectron spectroscopy, high resolution electron microscopic observations and temperature-programmed reduction data. The results show the importance of the sulphidation step in the genesis of different active RuS₂ particles. The relation between the activity and the nature of the exposed crystallographic planes is discussed.     

Preparation and properties of chromium‐containing hydrotreating catalysts (Ni–Mo)/ZrO2–Cr2O3

The properties of hydrotreating catalysts (Ni–Mo)/ZrO₂–Cr₂O₃ containing either 10 or 90 mol% of Cr₂O₃ have been studied in the model reactions of thiophene hydrodesulfurisation (HDS) and tetralin hydrogenation (HYD). Catalysts were characterized by X‐ray diffraction, UV‐visible spectroscopy and measurements of textural properties. It has been shown that the presence of chromium in the NiMo/ZrO₂ systems makes them more hydrogenating, because of the formation of chromium sulphide Cr₂S₃. Mixed hydrous or crystalline oxide Cr–Zr can be sulfided under mild conditions (400°C, H₂S/H₂) leading to highly dispersed Cr₂S₃ which is impossible for individual Cr₂O₃. Such systems are several times more active in HYD of tetralin than industrial NiMo/Al₂O₃ reference catalyst. At the same time in the presence of chromium, the synergy of catalytic activity between Ni and Mo in the reaction of HDS of thiophene was lowered, apparently because of hindering of formation of mixed sulfide Ni–Mo–S active sites due to the stronger interaction between Ni and Cr species than that of Ni and Mo. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic activities of Co(Ni)Mo/TiO2–Al2O3 catalysts in gasoil and thiophene HDS and pyridine HDN: effect of the TiO2–Al2O3 composition

The effect of the TiO₂–Al₂O₃ mixed oxide support composition on the hydrodesulfurization (HDS) of gasoil and the simultaneous HDS and hydrodenitrogenation (HDN) of gasoil+pyridine was studied over two series of CoMo and NiMo catalysts. The intrinsic activities for gasoil HDS and pyridine HDN were significantly increased by increasing the amount of TiO₂ into the support, and particularly over rich- and pure-TiO₂-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO₂. The inhibiting effect of pyridine on gasoil HDS was found to be similar for all the catalysts, i.e., was independent of the support composition. The ranking of the catalysts for the gasoil HDS test differed from that obtained for the thiophene test at different hydrogen pressures. In the case of gasoil HDS, the activity increases with TiO₂ content and large differences are observed between the catalysts supported on pure Al₂O₃ and pure TiO₂. In contrast, in the case of the thiophene test, the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also, in the thiophene test the difference in intrinsic activity between the pure Al₂O₃-based catalyst appeared relatively more active than the catalysts supported on mixed oxides. Also in the thiophene test, the difference in intrinsic activity between the pure Al₂O₃- and pure TiO₂-based catalysts is relatively small and dependent on the H₂ pressure used. Such differences in activity trend among the gasoil and the thiophene tests are due to a different sensitivity of the catalysts (by different support or promoter) to the experimental conditions used. The results of the effect of the H₂ partial pressure on the thiophene HDS, and on the effect of H₂S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking.     

Unexpected Support Effect in Hydrotreating: Evidence of a Metallic Character for ReS<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and ReS<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> Catalysts

Abstract  

Rhenium sulfide based catalysts were prepared by the incipient wetness impregnation method over alumina and silica supports and evaluated for 4,6-dimethyldibenzothiophene hydrodesulfurization in a high-pressure stirred-tank reactor. The catalyst prepared over silica was about six times more active for hydrodesulfurization than the corresponding catalyst prepared over alumina and a NiMo/Al₂O₃ industrial reference catalyst. This surprising and positive SiO₂ support effect was explained by a metallic character of the supported sulfide, which was demonstrated using a kinetic approach of competitive hydrogenations and by XPS characterization.     

噻吩加氢脱硫反应中NiMo催化剂的研究

采用连续流动微反装置,考察了催化剂载体、载体焙烧温度、催化剂制备方法及催化剂中Ni/Mo配比对NiMo催化剂催化噻吩加氢脱硫反应性能的影响,并用BET,XRD和TPR对催化剂进行了表征。结果表明,催化剂载体影响催化剂的性能,对于无Ni助剂的催化剂,负载在TiO2载体上的Mo催化剂活性高于负载在ZrO2上的催化剂,而助剂Ni的添加改变了活性顺序,使负载在TiO2载体上的NiMo催化剂活性低于负载在ZrO2上的催化剂;催化剂制备方法影响催化剂的性能,以共浸法制备的催化剂表现出高的催化活性;Ni/Mo配比影响催化剂的性能,当Ni/Mo摩尔比为0 6时,催化剂具有最高活性。     

Preparation and characterization of highly active ruthenium sulphide supported catalysts

Ruthenium sulphide catalysts supported on alumina were prepared using different precursor salts [ruthenium (III) chloride trihydrate, ruthenium (III) acetylacetonate and triruthenium dodecacarbonyl] and sulphided under various atmospheres. The properties of the catalysts in thiophene hydrodesulphurization are interpreted in relation to the XPS characterizations. These results show the importance of the sulphidation step in the absence of hydrogen in order to obtain a well sulphided, well dispersed and highly active catalyst.On leave from the Central Research Institute for Chemistry of the Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri ut 56–57, Hungary.     

Trapping of radiolytic hydrogen by amorphous cobalt oxysulfide

Hydrogen production from the radiolysis of liquid and gaseous hydrocarbons was studied in the presence of several transition metal sulfides. Cobalt oxysulfide obtained by aqueous precipitation was the most efficient admixture to decrease radiolytic production of hydrogen by pure hydrocarbons or mixtures of saturated and unsaturated hydrocarbons. Cobalt oxysulfide was characterized by XRD, scanning and transmission microscopy, and IR spectroscopy. It seems to be amorphous compound with the impurities of lamellar Co(OH)₂ phase. The organic phases were analysed before and after irradiation by γ-rays or protons in order to elucidate the origin of the effect. It has been shown that the solid does not change the composition neither the amount of the organic radiolysis products, neither in liquid nor in gas phase experiments. Therefore the presence of solid does not influence any radiolysis processes in the organics. Amorphous cobalt oxysulfide acts essentially as a trap of hydrogen, being able to absorb considerable amounts of H₂ (up to 0.5 mol H₂/at. Co). The study of the solid-gas interaction showed that slow reaction of cobalt oxysulfide with hydrogen occurs at ambient conditions independently of the irradiation of the system.