Effect of sintering on the catalytic functionalities of MOS2/Al2O3 catalysts

Effect of sintering on physico-chemical and catalytic properties of Mo, Co-Mo, Ni-Mosupported on -Al₂O₃ is reported. Such effects on hydrodesulfurization (HDS), hydrogenation (HYD) and hydrodeoxygenation (HDO) are investigated as a function of sintering temperature. The results indicated that HDS and HYD have different optimum calcination temperatures and these functionalities originate from different sites. The results are discussed in the light of molybdenum sulfide dispersion, promotional effects and phase transformations of active component, promoters and support.     

MoO_3/TiO_2-SiO_2催化剂的阈值效应

采用气相流动吸附法制备TiO2 /SiO2 复合载体 ,浸渍法担载一定量MoO3。用XRD、LRS和TPR等考察了MoO3在TiO2 /SiO2 表面的分散状态 ,中压固定床反应装置测定MoO3/TiO2 SiO2 、MoO3/SiO2 催化剂的噻吩加氢脱硫(HDS)、环己烯加氢 (HYD)和苯加氢 (BHD)活性。结果表明 ,(1 )TiO2 的加入有利于加强MoO3与载体之间的相互作用 ,促进MoO3在载体表面的分散 ,提高其分散阈值 ;(2 )当MoO3载量低于分散阈值时 ,其HDS、HYD和BHD活性随MoO3载量的增加而明显增大 ,但在高于分散阈值后 ,几乎保持不变 ,能明显体现负载型Mo催化剂在HDS、HYD和BHD反应中的阈值效应 ;(3 )MoO3 TiO2 /SiO2 催化剂的HDS、HYD和BHD活性都较MoO3/siO2 催化剂高 ,TiO2 能很大程度地改善MoO3/SiO2 催化剂的HDS、HYD活性。     

The functionalities of Pt/γ-Al2O3 catalysts in simultaneous HDS and HDA reactions

A Pt/γ-Al₂O₃ catalyst was tested in simultaneous hydrodesulfurization (HDS) of dibenzothiophene and hydrodearomatization (HDA) of naphthalene reactions. Samples of it were subjected to different pretreatments: reduction, reduction–sulfidation, sulfidation with pure H₂S and non-activation. The reduced catalyst presented the best performance, even comparable to that of Co(Ni)Mo catalysts. All catalyst samples were selective to the HDS reaction over HDA, and to the direct desulfurization pathway of dibenzothiophene HDS over the hydrogenation reaction pathway of HDS. The effect of H₂S partial pressure on the functionalities of the reduced Pt/γ-Al₂O₃ catalyst was studied. The results showed that an increase in H₂S partial pressure does not cause poisoning, but an inhibition effect, without changing the catalyst selectivity. Accordingly, the activity trends were ascribed to adsorption differences between the different reactive molecules over the same catalytic active site. TPR characterization along with a thermodynamics analysis showed that the active phase of reduced Pt/γ-Al₂O₃ is constituted by Pt⁰ particles. However, presulfidation of the catalyst leads to a mixture of PtS and Pt⁰ which has a negative effect on the catalytic performance without changing catalyst functionalities.     

TiO2–ZrO2 mixed oxide as a support for hydrotreating catalyst

Pure TiO₂, ZrO₂ and TiO₂–ZrO₂ mixed oxides are prepared by urea hydrolysis. Hydrotreating catalysts containing 12 wt% molybdenum are prepared using these oxides and characterized by BET surface area, pore volume, XRD and oxygen chemisorption. It is observed that oxides produced by the method of urea hydrolysis have higher surface area as compared to those available commercially. With increasing zirconia content in the mixed oxide, the surface area increases and a maximum value is obtained for a mixed oxide having Ti and Zr molar ratio of 65/35. XRD results indicate that mixed oxides are poorly crystalline in nature. Thiophene hydrodesulfurization, cyclohexene hydrogenation and tetrahydrofuran hydrodeoxygenation are taken as model reactions for evaluating catalytic activities. It is found that both O₂ uptake and catalytic activities increase with increasing zirconia content in mixed oxide and reach maximum values for the 12 wt% Mo/TiO₂–ZrO₂ (65/35) catalyst. With further increases in zirconia content, O₂ uptake and catalytic activities decrease and the lowest values are observed for the pure ZrO₂ supported catalyst.     

A DFT study on benzene adsorption over tungsten sulfides: surface model and adsorption geometries

Benzene adsorption on a WS₂(100) surface was studied by ab initio periodic DFT computations. Benzene adsorption is facile on the bridge site of the bare W edge via η² or η³ coordination. Taking into account the stable configuration at the W edge under typical hydrotreating reaction conditions (623 K, H₂S/H₂ = 0.01), benzene adsorption is found to be difficult, even when defective bridge sites are created.     

Triaxial behaviour of concrete under high stresses: Influence of the loading path on compaction and limit states

The aim of this study is to characterize the behaviour of concrete under high triaxial loading at levels of confinement and axial stress of the order of the GigaPascal. This study is carried out within a more general scope of understanding concrete behaviour under impact. The studied concrete has properties as close as possible to those used in current construction projects. A triaxial press of high capacity is used to characterize the triaxial behaviour of concrete according to various loading paths. Hydrostatic, triaxial, proportional and oedometric tests are performed and show the influence of the loading path on the compaction process. The triaxial and proportional tests show the existence of strain limit states, defining a limit states threshold independent from the loading path.