Instability of zeolite Y supported cobalt sulfide hydrotreating catalysts in the absence of H2S

Ion exchanged CoNaY was sulfided at 473 and 673 K and subsequently heated in He at 673 and 773 K. The resulting samples were characterized by means of overall sulfur analysis, temperature programmed Ar treatment and Fourier transform infrared spectroscopy. It was shown that during He flushing at sufficiently high temperature a protolysis reaction occurs resulting in the decomposition of Co sulfide into Co²⁺ ions and H₂S.     

CO methanation over supported Mo catalysts in the presence of H2S

The effect of various Mo catalyst supports, i.e., γ-Al₂O₃, SiO₂, SiO₂–Al₂O₃, ZrO₂, yttria-stabilized zirconia (YSZ), CeO₂, and TiO₂, on CO hydrogenation in the presence of H₂S was examined. At 5 wt.% Mo loading, Mo/ZrO₂ was determined to be the most active catalyst for this reaction; its activity was dependent on the number of active sites, as determined via NO chemisorption. Raman spectroscopy revealed that MoO₃ transforms into MoS₂ during the reaction.     

Effect of H2S on the hydrogenation of carbon dioxide over supported Rh catalysts

The hydrogenation of CO₂ was studied on supported noble metal catalysts in the presence of H₂S. In the reaction gas mixture containing 22 ppm H₂S the reaction rate increased on TiO₂ and on CeO₂ supported metals (Ru, Rh, Pd), but on all other supported catalysts or when the H₂S content was higher (116 ppm) the reaction was poisoned. FTIR measurements revealed that in the surface interaction of H₂ + CO₂ on Rh/TiO₂ Rh carbonyl hydride, surface formate, carbonates and surface formyl were formed. On the H₂S pretreated catalyst surface formyl species were missing. TPD measurements showed that adsorbed H₂S desorbed as SO₂, both from TiO₂-supported metals and from the support. IR, XP spectroscopy and TPD measurements demonstrated that the metal became apparently more positive when the catalysts were treated with H₂S and when the sulfur was built into the support. The promotion effect of H₂S was explained by the formation of new centers at the metal/support interface.     

Reduction of supported cobalt catalysts by hydrogen

The reduction of cobalt catalysts supported on Al₂O₃, SiO₂, and TiO₂ was investigated using a closed system filled with hydrogen gas. Effects of support and metal loading on the rate of reduction were also discussed. The activation energy of reduction increased in the following order: Co/TiO₂2O₃2. For different metal loadings, it was found that the catalyst with the higher loading was more readily reducible than that with the lower metal loading. This was confirmed using the results from measurements of particle size, amount of CO adsorbed and activity.     

Ethylene polymerization with Cp2ZrCl2 supported on dealuminated Y zeolite

Y zeolites with different aluminium contents obtained by dealumination with ammonium hexafluorosilicate were evaluated as supports for bis(cyclopentadienyl)zirconium dichloride catalysts. The activities of the supported and homogeneous systems were compared for ethylene polymerization. The most active heterogeneous catalyst was the one supported on the zeolite with the higher Si/Al ratio and external area. Received: 5 June 1997/Revised: 2 September 1997/Accepted: 9 September 1997     

Synthesis,characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H₂ and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH₃-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO₂, ?-Al₂O₃ supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/?-Al₂O₃ catalyst. The WP/?-Al₂O₃ catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO₂ catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/?-Al₂O₃ catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/?-Al₂O₃ catalyst. In general, a support or promoter in the WP/?-Al₂O₃ catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.     

Synthesis, characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H₂ and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH₃-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO₂, γ-Al₂O₃ supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/γ-Al₂O₃ catalyst. The WP/γ-Al₂O₃ catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO₂ catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/γ-Al₂O₃ catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/γ-Al₂O₃ catalyst. In general, a support or promoter in the WP/γ-Al₂O₃ catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.     

负载型ZSM-5分子筛催化剂再生方法研究

吡啶合成中所用的催化剂为负载铅ZSM-5分子筛（Pb-ZSM-5）,活性很好,但反应过程中催化剂很易发生积炭失活。通过对O₂烧炭再生、水蒸汽再生和甲醇再生处理的催化剂进行评价以及进行BET、XRD和TPD 表征,结果表明,甲醇再生方法效果明显,提高了催化剂的寿命。催化剂再生过程要抑制“飞温”现象发生。     

Oxidic precursors of molybdena supported on nickel and magnesium aluminate hydrotreating catalysts

The oxidic precursors of molybdena-based hydrotreating catalysts have been prepared using nickel and magnesium aluminates and characterized by laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). Three series of supports (80, 120 and 140 m².g⁻¹) have been investigated. Their aluminate spinel structure was confirmed both by X-ray diffraction (XRD) and LRS. Nickel oxide and magnesia have also been detected on the low surface area systems. In both series, a surface deficit of the foreign cation has been observed relative to the Al³⁺ of the aluminate phase. This deficit was more pronounced for Ni²⁺. Deposition of molybdate species does not modify the surface composition of these supports and a monolayer-like coverage up to 4.5 to 5 Mo at.nm⁻² was obtained. Nickel added by impregnation was shown to interact with the supported oxomolybdate species, whereas the nickel of the support does not. These investigated supports closely resemble γ --- Al₂O₃ in the preparation of hydrotreating catalysts.     

Structural properties and HDS activity of NiMo catalysts supported on lanthana modified zeolite type X and Y

In the search for the active catalysts of hydrodesulfurization reaction, an attempt was made to use zeolites as supports. A series of NaLaX, Mo/NaLaX and NiMo/NaLaX as well as NaLaY, Mo/NaLaY and NiMo/NaLaY catalysts was prepared and their performance in this reaction was studied. It was shown that crystalline structure of the lanthana forms of the above zeolites only little collapsed after ion-exchange and impregnation with active Mo and NiMo components. The NiMo catalysts supported on the zeolites studied were found active in thiophene hydrodesulfurization. The catalysts with lanthana after the first step of ion exchange were the most active.     

Preparation and characterization of ceramic foam supported nanocrystalline zeolite catalysts

The influence of the viscosity of the ceramic slip on the manufacture of ceramic foams by the polymer sponge method was studied. The foams were coated with silicalite (100 nm) and HZSM-5 (650 nm) crystals by dipping them in a zeolite suspension without binder additives. The amount of zeolite loaded can be controlled through the zeolite content of the dipping suspension. Uniform coatings are achieved starting with about 1 g zeolite/m² foam.     

Characterization and catalytic activity of zeolite NaY supported iridium catalysts

Two catalysts were prepared (ca. 1 wt% Ir), one with metal particles located on the external surface of zeolite NaY and the other with metal particles located inside the zeolite supercages. The two catalysts exhibited very different activities and selectivities for the hydrogenolysis of n- butane, with the Ir in NaY catalyst much less active and less selective (53% ethane) than the Ir on NaY catalyst (83% ethane). The differences in catalytic activity and selectivity between Ir on NaY and Ir in NaY are attributed to differences in the size of the active metal particle, an ensemble effect, and not to the location (encagement) of the particle. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of cobalt precursors on NO oxidation over supported cobalt oxide catalysts

The effect of cobalt precursors such as cobalt acetate and cobalt nitrate on NO oxidation was examined over cobalt oxides supported on various supports such as SiO₂, ZrO₂, and CeO₂. The N₂ physisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction with H₂ (H₂-TPR), NO chemisorptions, and temperature-programmed oxidation (TPO) with mass spectroscopy were conducted to characterize catalysts. The NO uptake as well as the catalytic activity for NO oxidation was dependent on the kinds of cobalt precursors and supports for supported cobalt oxides catalysts. Among tested catalysts, Co₃O₄/CeO₂ prepared from cobalt acetate showed the highest catalytic activity. The catalytic activity generally increased with the amount of chemisorbed NO. Reversible deactivation was observed over Co₃O₄/CeO₂ in the presence of H₂O. On the other hand, irreversible deactivation occurred over the same catalyst even in the presence of 5 ppm SO₂ in a feed. The strongly adsorbed SO₂ can prohibit NO from adsorbing on the active sites and also can prevent formed NO₂ from desorbing off the catalyst surface. The formation of SO₃ cannot be observed from the chemisorbed SO₂ on Co₃O₄/CeO₂ during TPO.     

Preparation and properties of supported cobalt catalysts for Fischer-Tropsch synthesis

Alumina-supported cobalt catalysts have been prepared from different cobalt precursors to study the influence of the precursor on the ultimate metal particle size. Furthermore, the effect of the particle size on the catalytic performance (activity and selectivity) during Fischer-Tropsch synthesis has been investigated. The preparation of low-loaded cobalt catalysts (2.5 wt%) by incipient wetness impregnation using cobalt EDTA and ammonium cobalt citrate precursors resulted initially in very small cobalt oxide particles, as determined by XPS. The small oxide particles reacted during the thermal treatment in a reducing gas flow with the alumina support to cobalt aluminate, which was neither active nor selective during Fischer-Tropsch synthesis. The catalysts prepared with cobalt nitrate had larger particles that could be easily reduced to metallic cobalt. These catalysts were active under reaction conditions. High-loaded cobalt catalysts (5.0 wt%) prepared using ammonium cobalt citrate showed a larger particle size than the low-loaded catalyst prepared from the citrate precursor. The extent of reduction to metallic cobalt that could be achieved with the high-loaded catalyst was significantly higher than that with the low-loaded catalyst, as shown by magnetic measurements. Accordingly, the high-loaded catalyst exhibited a reasonable activity and, in addition, an interesting and remarkably high selectivity toward higher hydrocarbons, and also a very high Schultz-Flory parameter.     

Role of zeolite structure on NO reduction with diesel fuel over Pt supported zeolite catalysts

A highly desirable selective catalytic reduction (SCR) of NO with real life diesel fuel over Pt supported zeolites with different topologies (Pt-ZSM-5, Pt-FER, Pt-MOR and Pt-BEA) is studied under simulated exhaust conditions. The catalysts are characterized by CO chemisorption, NH₃-TPD and TGA. The NO conversion ability of these catalysts has been correlated with zeolite structure and acidity. Pt-MOR is found to be the most active catalyst, 90% NO conversion at 300 °C, however Pt-FER showed highly desirable low temperature window, 77% NO conversion below 260 °C. Over ZSM-5, BEA and Y with three dimensional pore structures extensive carbonaceous deposits are observed by TGA which are detrimental to NO conversion. On the other hand, FER zeolite having one dimensional pore structure did not allow extensive coke formation resulting in a highly desired low temperature NO conversion. The results suggest that, NO reduction mainly take place near the zeolite pore opening, which is in reasonable agreement considering the long and bulky molecules in diesel fuel.     

Combined catalytic partial oxidation and CO2 reforming of methane over supported cobalt catalysts

The combined partial oxidation and CO₂ reforming of methane to synthesis gas was investigated over the reduced Co/MgO, Co/CaO, and Co/SiO₂ catalysts. Only Co/MgO has proved to be a highly efficient and stable catalyst. It provided about 94–95% yields to H₂ and CO at the high space velocity of 105000 mlg^–1h^–1 and for feed ratios CH₄/CO₂/O₂=4/2/1, without any deactivation for a period of study of 110 h. In contrast, the reduced Co/CaO and Co/SiO₂ provided no activity for the formation of H₂ and CO. The structure and reducibility of the calcined catalysts were examined using X-ray diffraction and temperature-programmed reduction, respectively. A solid solution of CoO and MgO, which was difficult to reduce, was identified in the 800°C calcined MgO-supported catalyst. The strong interactions induced by the formation of the solid solution are responsible for its superior activity in the combined reaction. The effects of reaction temperature, space velocity, and O₂/CO₂ ratio in the feed gases (while keeping the C/O ratio constant at 1/1) were investigated over the Co/MgO catalyst. The H₂/CO ratio in the product of the combined reaction increased with increasing O₂/CO₂ ratio in the feed.     

Heterogeneous chlorination of formaldehyde with HCl in the presence of zeolite Y

Zinc substituted zeolite Y is a potential catalyst in the CH₂Cl₂ formation in a one step gas phase reaction of CH₂O with CHl. Methanol and dimetoxymethane are suggested as possible intermediates in the formation of CH₃Cl and CH₂Cl₂. The decomposition pathway of CH₂O on zeolites seems to play an important role in the chlorination reaction mechanism. A certain combination of such factors as temperature, catalyst acidity and cation action must occur in order to activate CH₂O molecules for the reaction with HCl. The chlorination reaction is accompanied by side reactions resulting in the formation of nonchlorinated compounds such as methyl formate, ethers, aldehyde.     

The influence of preparation method on the properties of NiMo sulfide catalysts supported on ZrO2

Highly loaded supported (Ni)Mo sulfide catalysts prepared using different methods have been studied. Two zirconia supports of high specific surface area were used, including amorphous or tetragonal ZrO₂ solids. The order of active components introduction as well as thermal treatment conditions were varied. The best performance in the reactions of hydrodesulfurisation of thiophene and hydrogenation of tetralin was shown by the coimpregnated systems sulfidized without calcination of the oxide precursor. Crystallized ZrO₂ support always provides higher activities in both reactions, than amorphous zirconia, despite very high specific surface area of the last. The differences between variously treated systems were explained using the results of characterizations including laser Raman spectroscopy, XPS spectroscopy and temperature programmed reduction.     

Effect of the electronic properties of Mo sulfide phase on the hydrotreating activity of catalysts supported on Al2O3, Nb2O5 and Nb2O5/Al2O3

Activity in thiophene hydrodesulfurization (HDS) and in the three routes of 2,6-dimethylaniline (DMA) decomposition was examined on Mo sulfide catalysts supported on Al₂O₃, Nb₂O₅ and Nb₂O₅–Al₂O₃. Catalysts activity is enhanced when Mo phase is deposited on niobium-containing support. For HDS and for the hydrogenation route of DMA decomposition, the niobium-containing support strongly contributes to the catalyst activity whereas the activity of the Mo phase per Mo atom decreases with the increase of niobium amount in the support. By contrast, as for the DMA route, which leads to xylene formation (XYL), the activity of the Mo sulfide phase per Mo atom is strongly enhanced. The electronic properties of the MoS₂ phase were studied by means of IR spectroscopy of CO adsorption. Comparison of ν(CO/Mo) wavenumbers reveals an upward shift when Mo sulfide phase is deposited on Nb-containing support. The modification of the electronic properties of the sulfide phase is related to an interaction Mo–Nb either through the formation of a mixed Mo–Nb sulfide phase, or through the interaction MoS₂ slabs – support whose strength depends on the support acidity. Hence, the beneficial effect for xylene formation route is attributed to a decrease of the electron density of the Mo sulfide phase that should strengthen the DMA adsorption on the sulfide phase.