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1.
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
2.
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
3.
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
4.
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
5.
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
6.
Composite types of TiO 2–Al 2O 3 supports, which are γ-aluminas coated by titania, have been prepared by chemical vapor deposition (CVD), using TiCl 4 as a precursor. Then supported molybdenum catalysts have been prepared by an impregnation method. As supports, we employed γ-alumina, anatase types of titania, and composite types of TiO 2–Al 2O 3 with different loadings of TiO 2. We studied the conversion of Mo from oxidic to sulfidic state through sulfurization by X-ray photoelectron spectroscopy (XPS). The obtained spectra unambiguously revealed the higher reducibility from oxidic to sulfidic molybdenum species on the TiO 2 and TiO 2–Al 2O 3 supports compared to that on the Al 2O 3 support. Higher TiO 2 loadings of the TiO 2–Al 2O 3 composite support led to higher reducibility for molybdenum species. Furthermore, the catalytic behavior of supported molybdenum catalysts has been investigated for hydrodesulfurization (HDS) of dibenzothiophene (DBT) and methyl-substituted DBT derivatives. The conversion over the TiO 2–Al 2O 3 supported Mo catalysts, in particular for the 4,6-dimethyl-DBT, is much higher than that obtained over Al 2O 3 supported Mo catalyst. The ratio of the corresponding cyclohexylbenzene (CHB)/biphenyl (BP) derivatives is increased over the Mo/TiO 2–Al 2O 3. This indicates that the prehydrogenation of an aromatic ring plays an important role in the HDS of DBT derivatives over TiO 2–Al 2O 3 supported catalysts. 相似文献
7.
Effect of additives, In 2O 3, SnO 2, CoO, CuO and Ag, on the catalytic performance of Ga 2O 3–Al 2O 3 prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H 2O, CoO, CuO and Ag showed good additive effect. When H 2O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga 2O 3–Al 2O 3 was depressed considerably, while an intensifying effect of H 2O was observed for In 2O 3- and SnO 2-doped Ga 2O 3–Al 2O 3. Of several metal oxide additives, In 2O 3-doped Ga 2O 3–Al 2O 3 showed the highest activity for NO reduction by propene in the presence of H 2O. Kinetic studies on NO reduction over In 2O 3–Ga 2O 3–Al 2O 3 revealed that the rate-determining step in the absence of H 2O is the reaction of NO 2 formed on Ga 2O 3–Al 2O 3 with C 3H 6-derived species, whereas that in the presence of H 2O is the formation of C 3H 6-derived species. We presumed the reason for the promotional effect of H 2O as follows: the rate for the formation of C 3H 6-derived species in the presence of H 2O is sufficiently fast compared with that for the reaction of NO 2 with C 3H 6-derived species in the absence of H 2O. Although the retarding effect of SO 2 on the activity was observed for all of the catalysts, SnO 2–Ga 2O 3–Al 2O 3 showed still relatively high activity in the lower temperature region. 相似文献
8.
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
9.
Three different supports were prepared with distinct magnesia–alumina ratio x = MgO/(MgO + Al 2O 3) = 0.01, 0.1 and 0.5. Synthesized supports were impregnated with Co and Mo salts by the incipient wetness method along with 1,2-cyclohexanediamine- N, N, N′, N′-tetraacetic acid (CyDTA) as chelating agent. Catalysts were characterized by BET surface area, Raman spectroscopy, SEM-EDX and HRTEM (STEM) spectroscopy techniques. The catalysts were evaluated for the thiophene hydrodesulfurization reaction and its activity results are discussed in terms of using chelating agent during the preparation of catalyst. A comparison of the activity between uncalcined and calcined catalysts was made and a higher activity was obtained with calcined MgO–Al 2O 3 supported catalysts. Two different MgO containing calcined catalysts were tested at micro-plant with industrial feedstocks of heavy Maya crude oil. The effect of support composition was observed for hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs) and hydrodenitrogenation (HDN) reactions, which were reported at temperature of 380 °C, pressure of 7 MPa and space-velocity of 1.0 h −1 during 204 h of time-on-stream (TOS). 相似文献
10.
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
11.
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V 2O 5/Al 2O 3 catalysts was investigated. The Pd/V 2O 5/Al 2O 3 catalysts were more active than V 2O 5/Al 2O 3 and Pd/Al 2O 3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V 4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
12.
Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。 相似文献
13.
Both low loaded 15% Co/Al 2O 3 and more highly loaded 25% Co/Al 2O 3 catalysts are studied, in order to explore the impact of cluster size on the stability of the cobalt cluster to support-influenced reoxidation processes at high H 2O/CO ratios. XAFS and activity data suggest that there are two regions for the water effect: at lower H 2O/CO ratios water influences CO conversion by reversible kinetic effects while at higher H 2O/CO ratios cobalt re-oxidation processes occur. The latter regime where water was added at and above 25% are examined. Synthesis conditions were maintained constant while argon balancing gas was replaced by added water. Catalyst samples were withdrawn from the reactor during synthesis at different partial pressures of added water and cooled in the wax product under inert gas. The EXAFS results suggest that, unlike the smaller clusters on unpromoted and, especially noble-metal promoted, 15% Co/Al 2O 3 catalysts, the larger crystallites (>10 nm by chemisorption and XRD) on 25% Co/Al 2O 3 undergo oxidation by H 2O to CoO, most likely confined to the surface. The clusters are re-reduced when H 2O was switched off, and the activity displayed an important recovery. 相似文献
14.
Sulfidation of trimetallic CoNiMo/Al 2O 3 catalysts was studied by thermogravimetry at 400 °C under flow and pressure conditions. Results were compared with those obtained on prepared and industrial CoMo/Al 2O 3 and NiMo/Al 2O 3 catalysts. The amount of sorbed H 2S on the sulfided solids was measured at 300 °C in the H 2S pressure range 0–3.5 MPa at constant H 2 pressure (3.8 MPa). The adsorption isotherms were simulated using a model featuring dissociated adsorption of H 2S on supported metal sulfides and bare alumina. The amount of sulfur-vacancy sites could thus be determined under conditions close to industrial practice. A relationship with activity results for thiophene HDS and benzene hydrogenation was sought for. 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.
The Pd–Pt/Al 2O 3 bimetallic catalysts showed high activities toward the wet oxidation of the reactive dyes in the presence of 1% H 2 together with excess oxygen. Palladium was believed to act as a co-catalyst to spillover the adsorbed H 2 onto the surface of the oxidized Pt surface, and thereby the reducibility of the Pt increased greatly. The organic dye molecule adsorbed on the reduced Pt surface more easily than the oxidized Pt surface under the competition with excess oxygen, which is an essential step for the catalytic wet oxidation (CWO). The Pd–Pt/Al 2O 3 catalysts also produced H 2O 2 from H 2/O 2 mixture, and the hydroxyl radical was formed through the subsequent decomposition of H 2O 2. Additional oxidation of the reactive dyes was obtained with hydroxyl radical. The high activities of the Pd–Pt/Al 2O 3 catalysts were believed to be due to the combined effects of the faster redox cycle resulting from the increased reducibility of Pt surface and the additional oxidation of the reactive dyes with hydroxyl radical. 相似文献
17.
Ethanol steam reforming was studied over Ni/Al 2O 3 catalysts. The effect of support (- and γ-Al 2O 3), metal loading and a comparison between conventional H 2 reduction with an activation method employing a CH 4/O 2 mixture was investigated. The properties of catalysts were studied by N 2 physisorption, X-ray diffraction (XRD) and temperature programmed reduction (TPR). After activity tests, the catalysts were analyzed by scanning electron microscopy (SEM) and thermogravimetric analysis (TG/DTA). Ni supported on γ-Al 2O 3 was more active for H 2 production than the catalyst supported on -Al 2O 3. Metal loading did not affect the catalytic performance. The alternative activation method with CH 4/O 2 mixture affected differently the activity and stability of the Ni/γ-Al 2O 3 and the Ni/-Al 2O 3 catalyst. This activation method increased significantly the stability of Ni/-Al 2O 3 compared to H 2 reduction. SEM and TG/DTA analysis indicate the formation of filamentous carbon during the CH 4/O 2 activation step, which is associated with the increasing catalyst activity and stability. The effect of temperature on the type of carbon formed was investigated; indicating that filamentous coke increased activity while encapsulating coke promoted deactivation. A discussion about carbon formation and the influence on the activity is presented. 相似文献
18.
The effect of Al 2O 3 levels on the properties of NiO in coprecipitated NiO–Al 2O 3 samples were investigated, using samples with up to 60.7 wt.% Al 2O 3 that had been calcined in the range 300–700°C. Characterization techniques included BET surface area of fresh and reduced catalysts, X-ray diffraction analysis of structure and crystallite size, magnetic susceptibility measurements, oxidizing power, and reducibility in H 2. Only NiO was detected in samples with up to 4.1 wt.% Al 2O 3 for all sample calcination temperatures. Surface areas were similar for all fresh samples but decreased rapidly after calcination at high temperatures. The surface area loss was less for the higher Al 2O 3-containing samples. Nickel oxide crystallite sizes increased at higher calcination temperatures, but remained approximately the same for each Al 2O 3 level. The NiO was nonstoichiometric (NiO1+x), with x decreasing at higher calcination temperatures and increasing with small amounts of added Al2O3 through a maximum at about 3 wt.% Al2O3. However, this did not correlate well with microstrain in the NiO crystallites nor with reducibility, which decreased with Al2O3 addition. At higher levels of Al2O3 (13.6 wt.% and above), surface areas increased with higher Al2O3 loadings, but NiO crystallite sizes remained approximately the same, independent of both Al2O3 content and calcination temperature. X-ray diffraction patterns were very diffuse, and it was not possible to rule out the presence of pseudo-spinel combinations of NiO and Al2O3. Reducibility was more difficult than with low Al2O3 levels, and nonstoichiometry was low and independent of Al2O3 content. Reducibilities of all samples calcined at 300°C correlated well with the final BET surface area of the reduced samples, indicating that more dispersed NiO crystallites are more difficult to reduce, a conclusion that supports a model for reduction proposed previously. 相似文献
19.
以Al_2O_3为载体,RuCl_3·xH_2O和FeCl_3·6H_2O为活性组分前驱体,采用吸附-沉淀法制备了Ru-Fe/Al_2O_3和Ru/Al_2O_3催化剂,以马来酸二甲酯加氢合成丁二酸二甲酯为探针反应,结合H_2-TPR和XRD表征技术,考察Fe改性Ru基催化剂的氧化-还原性能及催化活性。经氧化-还原循环处理后,催化剂Ru-Fe/Al_2O_3上马来酸二甲酯加氢活性高于Ru/Al_2O_3。XRD结果显示,经处理的Ru-Fe/Al_2O_3上未见金属Ru的特征衍射峰,而Ru/Al_2O_3上出现了金属Ru的特征衍射峰。结合H_2-TPR结果推断,Ru与Fe之间发生了相互作用,这种协同作用可以改善Ru/Al_2O_3催化剂的热稳定性。 相似文献
20.
Al 2O 3–SiO 2 mixed oxide has been investigated as a support for hydrotreating catalyst with variation of its composition [Si/(Si + Al) = 0.06, 0.12, 0.31, 0.56, 0.78] and its interaction with the surface active metals (NiMo). The composition of support and surface species (NiMo) of catalysts were characterized by specific surface area, atomic absorption, SEM-EDX, XRD, temperature programmed reduction (TPR), Raman analysis, scanning electron microscopy (STEM) and transmission electron microscopy (TEM). Incorporation of SiO 2 in Al 2O 3 promotes a weak interaction between the active phases and particularly catalyst that predominated with SiO 2 content. The oxide and sulfided catalysts characterization indicated that the effect of support is responsible to form different catalytic sites. Crystallization of MoO 3 phases and a relatively longer crystal of MoS 2 in the sulfided catalyst were attributed to an increasing SiO 2 content in the support. The catalytic behavior of the NiMo supported catalysts is explained in terms of structural changes on the surface due to the support and active metal interactions. The activity of the different catalysts evaluated in the thiophene hydrodesulfurization reaction was higher for the catalyst having lower SiO 2 content in the support. 相似文献
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