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1.
TiO 2–Al 2O 3 composite supports have been prepared by chemical vapor deposition (CVD) over γ-Al 2O 3 substrate, using TiCl 4 as the precursor. High dispersion of TiO 2 overlayer on the surface of Al 2O 3 has been obtained, and no cluster formation has been detected. The catalytic behavior of Mo supported on Al 2O 3, TiO 2 and TiO 2–Al 2O 3 composite has been investigated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the Mo catalysts supported on TiO 2–Al 2O 3 composite, in particular for the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) is much higher than that of conversion obtained over Mo catalyst supported on Al 2O 3. The ratio of the corresponding cyclohexylbenzenes/biphenyls is increased over Mo catalyst supported on TiO 2–Al 2O 3 composite support. This means that the reaction rate of prehydrogenation of an aromatic ring rather than the rate of hydrogenolysis of C–S bond cleavage is accelerated for the HDS of DBT derivatives. The Mo/TiO 2–Al 2O 3 catalyst leads to higher catalytic performance for deep HDS of gas oil. 相似文献
2.
The present paper gives a detailed review of the different studies under investigation in our laboratory concerning the use of TiO 2 and TiO 2–Al 2O 3 composites prepared by chemical vapor deposition (CVD) as support for sulfide catalysts in the HDS of dibenzothiophene (DBT) derivatives. The supports investigated here are: TiO 2 (from Degussa, 50 m 2/g), Al 2O 3 (Nikki, 186 m 2/g) and TiO 2–Al 2O 3 supports prepared by CVD of TiCl 4 on alumina. Using several characterization techniques, we have demonstrated that the support composite presents a high dispersion of TiO 2 over γ-Al 2O 3 without forming precipitates up to ca. 11 wt.% loading. Moreover, the textural properties of the support composite are comparable to those of alumina. XPS investigations of Mo and NiMo catalysts supported on the different carriers show that Mo-oxide species exhibit a higher degree of sulfidation on the surface of TiO 2 and TiO 2–Al 2O 3 than on alumina. The HDS tests of 4,6-DMDBT under mild operating conditions (573 K, 3 MPa) show that sulfide catalysts supported on the composite support (ca. 11 wt.%) are more active than those supported on to TiO 2 or Al 2O 3. This higher HDS catalytic activity is attributed to the promotion of the hydrodesulfurization pathway, whereby the pre-hydrogenation of one of the aromatic rings adjacent to the thiophenic one may reduce the steric hindrance caused by the two methyl groups adjacent to the sulfur atom during the C–S bond cleavage. 相似文献
3.
Catalytic activities of Al 2O 3–TiO 2 supporting CoMo and NiMo sulfides (CoMoS and NiMoS) catalysts were examined in the transalkylation of isopropylbenzene and hydrogenation of naphthalene as well as the hydrodesulfurization (HDS) of model sulfur compounds, conventional gas oil (GO), and light cycle oil (LCO). Al 2O 3–TiO 2 supporting catalysts exhibited higher activities for these reactions except for the HDS of the gas oil than a reference Al 2O 3 supporting catalyst, indicating the correlation of these activities. Generally, more content of TiO 2 promoted the activities. Inferior activity of the catalyst for HDS of the gas oil is ascribed to its inferior activity for HDS of dibenzothiophene (DBT) in gas oil as well as in model solvent decane, while the refractory 4,6-dimethyldibenzothiophene (4,6-DMDBT) in gas oil as well as in decane was more desulfurized on the catalyst. Characteristic features of Al 2O 3–TiO 2 catalyst are discussed based on the paper results. 相似文献
4.
Mo---Co or Mo---Ni catalysts supported on alumina (Al 2O 3) have been widely used for hydrodesulfurization (HDS) of heavy petroleum fractions. In order to enhance the catalytic activities for HDS, a composite type support (TiO 2-Al 2O 3) prepared by the chemical vapor deposition (CVD) method has been studied. We found that Mo catalyst supported on TiO 2-Al 2O 3 showed much higher catalytic activity for HDS of dibenzothiophene derivatives than the catalysts supported on Al 2O 3. 相似文献
5.
Alumina–titania supports containing 5–50 wt.% of TiO 2 were prepared by coprecipitation method using inorganic precursors (sodium aluminate and titanium chloride). DTA-TGA, XRD, SEM, TPD NH3, and IR spectroscopy were used to characterise these materials. The study shows that the promoting effect of nickel on the HDS activity of molybdenum catalysts supported on Al 2O 3TiO 2 is significantly lower than that for molybdenum catalyst supported on Al 2O 3, and depends on the TiO 2 content. The SEM results show that in the case of rich Al support (20 wt.% of TiO 2) molybdenum was aggregated on the external surface of the catalyst, whereas it was uniformly dispersed on the external surface of alumina. Results also show that molybdenum is preferably supported on aluminum oxide. Application of Al 2O 3TiO 2 oxides enhances the HDN activity of nickel–molybdenum catalysts. The highest HDN efficiency was obtained for the NiMo/Al 2O 3TiO 2 catalyst containing 50 wt.% of TiO 2. HDN activity was found to depend on protonic acidity and anatase content. 相似文献
6.
The effect of the TiO 2–Al 2O 3 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 TiO 2 into the support, and particularly over rich- and pure-TiO 2-based catalysts. It is suggested that the increase in activity be due to an improvement in reducing and sulfiding of molybdena over TiO 2. 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 TiO 2 content and large differences are observed between the catalysts supported on pure Al 2O 3 and pure TiO 2. In contrast, in the case of the thiophene test, the pure Al 2O 3-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 Al 2O 3-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 Al 2O 3- and pure TiO 2-based catalysts is relatively small and dependent on the H 2 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 H 2 partial pressure on the thiophene HDS, and on the effect of H 2S concentration on gasoil HDS demonstrate the importance of these parameters, in addition to the nature of the reactant, to perform an adequate catalyst ranking. 相似文献
7.
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al 2O 3 containing mixed oxide supports, TiO 2 containing mixed oxide supports, ZrO 2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO 2 containing mixed oxides received maximum attention, especially TiO 2–Al 2O 3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
8.
A novel TiO 2/Al 2O 3/cordierite honeycomb-supported V 2O 5–MoO 3–WO 3 monolithic catalyst was studied for the selective reduction of NO with NH 3. The effects of reaction temperature, space velocity, NH 3/NO ratio and oxygen content on SCR activity were evaluated. Two other V 2O 5–MoO 3–WO 3 monolithic catalysts supported on Al 2O 3/cordierite honeycomb or TiO 2/cordierite honeycomb support, two types of pellet catalysts supported on TiO 2/Al 2O 3 or Al 2O 3, as well as three types of pellet catalysts V 2O 5–MoO 3–WO 3–Al 2O 3 and V 2O 5–MoO 3–WO 3–TiO 2 were tested for comparison. The experiment results show that this catalyst has a higher catalytic activity for SCR with comparison to others. The results of characterization show, the preparation method of this catalyst can give rise to a higher BET surface area and pore volume, which is strongly related with the highly active performance of this catalyst. At the same time, the function of the combined carrier of TiO 2/Al 2O 3 cannot be excluded. 相似文献
9.
Hydrotreating of Maya heavy crude oil over high specific surface area CoMo/TiO 2–Al 2O 3 oxide supported catalysts was studied in an integral reactor close to industrial practice. Activity studies were carried out with Maya crude hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), and hydrodeasphaltenization (HDAs) reactions. The effect of support composition, the method of TiO 2 incorporation, and the catalyst deactivation are examined. Supported catalysts are characterized by BET specific surface area (SSA), pore volume (PV), pore size distribution (PSD), and atomic absorption. It has been found that sulfided catalysts showed a wide range of activity variation with TiO 2 incorporation into the alumina, which confirmed that molybdenum sulfided active phases strongly depend on the nature of support. The pore diameter and nature of the active site for HDS, HDM, HDN, and HDAs account for the influence of the large reactant molecules restricted diffusion into the pore, and/or the decrease in the number of active sites due to the MoS 2 phases buried with time-on-stream. The textural properties and hysteresis loop area of supported and spent catalysts indicated that catalysts were deactivated at the pore mouth due to the metal and carbon depositions. The atomic absorption results agreed well regarding the textural properties of spent catalysts. Thus, incorporation of TiO 2 with γ-Al 2O 3 alters the nature of active metal interaction with support, which may facilitate the dispersion of active phases on the support surface. Therefore, the TiO 2 counterpart plays a promoting role to HDS activity due to the favorable morphology of MoS 2 phases and metal support interaction. 相似文献
10.
Evaluation of Co---Mo catalysts prepared on various TiO 2-Al 2O 3 supports has been made for thiophene under atmospheric pressure, dibenzothiophene under high pressure and gasoil in a classical pilot plant. Comparison of activities indicates DBT as more representative of a real feedstock and the Co---Mo/TiO 2 (50%)-Al 2O 3 (50%) catalyst appears more active than the Co---Mo/Al 2O 3 sample toward HDS, HDN and hydrodearomatization. 相似文献
11.
Ag-based catalysts supported on various metal oxides, Al 2O 3, TiO 2, and TiO 2–Al 2O 3, were prepared by the sol–gel method. The effect of SO 2 on catalytic activity was investigated for NO reduction with propene under lean burn condition. The results showed the catalytic activities were greatly enhanced on Ag/TiO 2–Al 2O 3 in comparison to Ag/Al 2O 3 and Ag/TiO 2, especially in the low temperature region. Application of different characterization techniques revealed that the activity enhancement was correlated with the properties of the support material. Silver was highly dispersed over the amorphous system of TiO 2–Al 2O 3. NO 3− rather than NO 2− or NO x reacted with the carboxylate species to form CN or NCO. NO 2 was the predominant desorption species in the temperature programmed desorption (TPD) of NO on Ag/TiO 2–Al 2O 3. More amount of formate (HCOO −) and CN were generated on the Ag/TiO 2–Al 2O 3 catalyst than the Ag/Al 2O 3 catalyst, due to an increased number of Lewis acid sites. Sulfate species, resulted from SO 2 oxidation, played dual roles on catalytic activity. On aged samples, the slow decomposition of accumulated sulfate species on catalyst surface led to poor NO conversion due to the blockage of these species on active sites. On the other hand, catalytic activity was greatly enhanced in the low temperature region because of the enhanced intensity of Lewis acid site caused by the adsorbed sulfate species. The rate of sulfate accumulation on the Ag/TiO 2–Al 2O 3 system was relatively slow. As a consequence, the system showed superior capability for selective adsorption of NO and SO 2 toleration to the Ag/Al 2O 3 catalyst. 相似文献
12.
The typical physico-chemical properties and their hydrodesulfurization activities of NiMo/TiO 2-Al 2O 3 series catalysts with different TiO 2 loadings were studied. The catalysts were evaluated with a blend of two kinds of commercially available diesels in a micro-reactor unit. Many techniques including N 2-adsorption, UV–vis DRS, XRD, FT-Raman, TPR, pyridine FT-IR and DRIFT were used to characterize the surface and structural properties of TiO 2-Al 2O 3 binary oxide supports and the NiMo/TiO 2-Al 2O 3 catalysts. The samples prepared by sol–gel method possessed large specific surface areas, pore volumes and large average pore sizes that were suitable for the high dispersion of nickel and molybdenum active components. UV–vis DRS, XRD and FT-Raman results indicated that the presence of anatase TiO 2 species facilitated the formation of coordinatively unsaturated sites (CUS) or sulfur vacancies, and also promoted high dispersion of Mo active phase on the catalyst surfaces. DRIFT spectra of NO adsorbed on the pure MoS 2 and the catalysts with TiO 2 loadings of 15 and 30% showed that NiMo/TiO 2-Al 2O 3 catalysts possessed more CUS than that of pure MoS 2. HDS efficiencies and the above characterization results confirmed that the incorporation of TiO 2 into Al 2O 3 could adjust the interaction between support and active metals, enhanced the reducibility of molybdenum and thus resulted in the high activity of HDS reaction. 相似文献
13.
Mo/TiO 2 catalysts were modified with Nb by two different methods, sol–gel and surface deposition, in order to study the effect of Nb incorporation on the thiophene HDS activity. The results show that the formation of Nb–Ti mixed oxides leads to catalysts with poor HDS activity while the deposition of Nb oxide species on the surface of TiO 2 leads to catalysts with activities larger than those of Mo/Al 2O 3 and Mo/TiO 2. This increase in activity was attributed to the formation of a larger population of Mo sulfur anionic vacancies when Nb was surface deposited on the TiO 2. 相似文献
14.
Ni–Mo/Al 2O 3–MCM-41 supported catalysts have been investigated for modification of MCM-41 by using sol–gel alumina incorporation method. Different catalysts were synthesized with variation of Si/Al molar ratios of 10, 50, 100 and 200. High specific surface area ordered meso-porous solid (MCM-41) was synthesized by using organic template method. In order to modify the low acidity of silica solid, the surface of MCM-41 was modified by incorporation of alumina. The surface acidity of solids modified significantly with variation of alumina content in the supports. The sol–gel method of alumina incorporation was used, which does not modify extensively the pore characteristics of MCM-41 material during the preparation of Al 2O 3–MCM-41. The X-ray diffraction intensities indicated that alumina as well as MCM-41 were present in the synthesized supports. Additionally, the hydrothermal stability of the Al 2O 3–MCM-41 materials was maintained up to 873 K using sever conditions like 100% water vapor stream. The catalytic activity of the catalysts was tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). Selectivity was oriented mainly to the production of biphenyl (BP) and for high Si/Al ratios toward cyclohexylbenzene (CHB) and showed a higher conversion and better selectivity to hydrogenation (cyclohexylbenzene). 相似文献
15.
Ni/Al 2O 3 catalyst modified by small amounts of Mo show unusual properties in the steam reforming of hydrocarbons. There are no data about the effect of small amounts of molybdenum on reduction of the Ni-Mo supported catalysts. The properties of these very complex systems depend on the conditions of successive preparation stages (calcination, reduction) or the process conditions. A series of Ni/Al2O3 catalysts modified by Mo were prepared in order to investigate the influence of promoter amounts and preparation sequence on their properties. Temperature programmed reduction (TPR) has been employed to study the reducibility of Ni-Mo/Al2O3 catalysts. Catalysts were further characterized by BET area, H2 chemisorption and X-ray diffraction measurements. The TPR curves of Ni-Mo/Al2O3 catalysts are very complex. Mo addition leads to the decrease of catalysts reducibility. However, complete reduction of NiO and MoO3 can be achieved at 800 °C. The reduction course depends on the sequence of nickel and molybdenum addition into the support. Precise measurements of Ni peaks positions in the XRD pattern of Ni/Al2O3 and Ni-Mo/Al2O3 samples show the possibility of Ni-Mo solid solution formation. 相似文献
16.
MoNi/Al 2O 3 catalysts have been widely used for hydrodesulphurisation of oil fractions. In order to enhance the catalytic activities for HDS and HDN, catalysts supported on titania-modified alumina carriers have been studied. The MoNi/Al 2O 3–TiO 2catalysts were characterised by benzene sorption, ammonia sorption, temperature programmed reduction, X-ray diffraction and scanning electron microscopy. The supports effect was examined by comparing thiophene conversion and sulphur or nitrogen contents in diesel oil fraction. 相似文献
17.
Ni catalysts supported on γ-Al 2O 3, CeO 2 and CeO 2–Al 2O 3 systems were tested for catalytic CO 2 reforming of methane into synthesis gas. Ni/CeO 2–Al 2O 3 catalysts showed much better catalytic performance than either CeO 2- or γ-Al 2O 3-supported Ni catalysts. CeO 2 as a support for Ni catalysts produced a strong metal–support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO 2 had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/γ-Al 2O 3 catalysts for this reaction. A weight loading of 1–5 wt% CeO 2 was found to be the optimum. Ni catalysts with CeO 2 promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO 2-promoted catalysts are attributed to the oxidative properties of CeO 2. 相似文献
18.
A carbon-based sulfonated catalyst was prepared by direct sulfonation and carbonization (in moderate conditions:200 °C, 12 h) of red liquor solids, a by-product of paper-making process. The prepared sulfonated cata-lyst (SC) had aromatic structure, composed of carbon enriched inner core, and oxygen-containing (SO3H, COOH, OH) groups enriched surface. The SO3H, COOH, OH groups amounted to 0.74 mmol·g^-1, 0.78 mmol·g^-1, 2.18 mmol·g^-1, respectively. The fresh SC showed much higher catalytic activity than that of the traditional solid acid catalysts (strong-acid 732 cation exchange resin, hydrogen type zeolite socony mobile-five (HZSM-5), sulfated zir-conia) in esterification of oleic acid. SC was deactivated during the reactions, through the mechanisms of leaching of sulfonated species and formation of sulfonate esters. Two regeneration methods were developed, and the catalytic activity can be mostly regenerated by regeneration Method 1 and be fully regenerated by regeneration Method 2, respectively. 相似文献
19.
Co–Mo model sulfide catalysts, in which CoMoS phases are selectively formed, were prepared by means of a CVD technique using Co(CO) 3NO as a precursor of Co. It is shown by means of XPS, FTIR and NO adsorption that CoMoS phases form selectively when the Mo content exceeds monolayer loading. A single exposure of MoS 2/Al 2O 3 to a vapor of Co(CO) 3NO at room temperature fills the edge sites of the MoS 2 particles. It is suggested that the maximum potential HDS activity of MoS 2/Al 2O 3 and Co–Mo/Al 2O 3 catalysts can be predicted by means of Co(CO) 3NO as a “probe” molecule. An attempt was made to determine the fate of Co(CO) 3NO adsorbed on MoS 2/Al 2O 3. The effects of the support on Co–Mo sulfide catalysts in HDS and HYD were investigated by use of CVD-Co/MoS 2/support catalysts. XPS and NO adsorption showed that model catalysts can also be prepared for SiO 2-, TiO 2- and ZrO 2-supported catalysts by means of the CVD technique. The thiophene HDS activity of CVD-Co/MoS 2/Al 2O 3, CVD-Co/MoS 2/TiO 2 and CVD-Co/MoS 2/Al 2O 3 is proportional to the amount of Co species interacting with the edge sites of MoS 2 particles or CoMoS phases. It is concluded that the support does not influence the HDS reactivity of CoMoS phases supported on TiO 2, ZrO 2 and Al 2O 3. In contrast, CoMoS phases on SiO 2 show catalytic features characteristic of CoMoS Type II. With the hydrogenation of butadiene, on the other hand, the Co species on MoS 2/TiO 2, ZrO 2 and SiO 2 have the same activity, while the Co species on MoS 2/Al 2O 3 have a higher activity. 相似文献
20.
The activity and selectivity of rhenium promoted cobalt Fischer–Tropsch catalysts supported on Al 2O 3, TiO 2 and SiO 2 have been studied in a fixed-bed reactor at 483 K and 20 bar. Exposure of the catalysts to water added to the feed deactivates the Al 2O 3 supported catalyst, while the activity of the TiO 2 and SiO 2 supported catalysts increased. However, at high concentrations of water both the SiO 2 and TiO 2 supported catalyst deactivated. Common for all catalysts was an increase in C 5+ selectivity and a decrease in the CH 4 selectivity by increasing the water partial pressure. The catalysts have been characterized by scanning transmission electron microscope (STEM), BET, H 2 chemisorption and X-ray diffraction (XRD). 相似文献
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