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1.
The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported on Al 2O 3, TiO 2, ZrO 2 and MgO. The promotion of V 2O 5/Al 2O 3 catalyst with alkali metals (Li, Na, K) was also attempted. Evaluation of temperature programmed reduction patterns showed that the reducibility of V species is affected by the support acid–base character. The catalytic activity is favored by the V reducibility of the catalyst as it was confirmed from runs conducted at 450–550°C. V 2O 5/TiO 2 catalyst exhibits the highest activity in oxydehydrogenation of propane. The support’s nature also affects the selectivity to propene; V 2O 5 supported on Al 2O 3 catalyst exhibits the highest selectivity. Reaction studies showed that addition of alkali metals decreases the catalytic activity in the order non-doped>Li>Na>K. Propene selectivity significantly increases in the presence of doped catalysts. 相似文献
2.
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
3.
Vanadium oxide spread highly on TiO 2 (anatase, A) and SnO 2, and rather densely on TiO 2 (rutile, R) and ZrO 2 to make the monolayer in less than 4–5 V nm −2. Profile of acid site of the monolayer was measured by temperature programmed desorption of ammonia, and its relation with the surface oxidation state was studied. The acid site density was high on the V 2O 5/TiO 2 (A) independent of the degree of oxidation. On the other hand, that of V 2O 5/TiO 2 (R) and V 2O 5/ZrO 2 depended on the oxidation state, and the high value of the concentration was observed on the oxidized one. The strength of acid site generated on the V 2O 5 monolayer on TiO 2 was as high as on the HZSM-5 zeolite. Turnover frequency (TOF) of propane conversion, and product selectivity were measured in propane oxidation. Among tested oxides, the V 2O 5/TiO 2 (A) showed the high TOF and selectivity to form propylene, while those loaded on TiO 2 (R) and ZrO 2 the small TOF and poor selectivity. Therefore, the reaction profile of activity and selectivity could be related with the extent of spreading and solid acidity. An idea of limit of the acid site density ca. 1.5 nm −2 on the monolayer was elucidated. 相似文献
4.
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
5.
Surface-phase ZrO 2 on SiO 2 (SZrOs) and surface-phase La 2O 3 on Al 2O 3 (SLaOs) were prepared with various loadings of ZrO 2 and La 2O 3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH 4/CO 2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al 2O 3 and Pt/SiO 2 catalysts. CO 2 or CH 4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides. The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
6.
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
7.
Catalytic activities of various Pt/MO x/SiC systems for carbon oxidation under simulated diesel exhaust gas were investigated in temperature-programmed reactions. When Pt/MO x (MO x=TiO 2, ZrO 2, Al 2O 3) was loaded onto silicon carbide (SiC), the oxidation activities became higher than those of Pt/MO x alone or other Pt/MO x/SiC systems (MO x=Ta 2O 5, WO 3, Nb 2O 5, SnO 2, SiO 2, CeO 2, MoO 3, V 2O 5). Among them, Pt/TiO 2/SiC exhibited the highest activity. We discuss the activity of MO x=TiO 2, ZrO 2, and Al 2O 3 in connection with NO oxidation activity, adsorption of sulfate onto the support, Pt dispersion, and specific surface area of the catalyst. Furthermore, we investigated the catalytic performance of Pt/TiO 2/SiC in more detail under isothermal conditions and in a staged arrangement. 相似文献
8.
The effects of a large number of sintering aids for the densification of magnesia were examined. Al 2O 3, BaO, Fe 2O 3, P 2O 5, SiO 2, TiO 2, Y 2O 3 and ZrO 2 are effective for the sintering of CVD-MgO powders at low doping levels. The effects of TiO 2 and ZrO 2 are significant. Heavy doping is harmful for densification. The eight oxides above are also effective for the sintering of seawater MgO, but the degree of effectiveness is smaller than for CVD-MgO. In the doping of BaO, P 2O 5, SiO 2 and TiO 2, which form eutectic liquids with MgO below 1600°C, there is an optimum firing temperature for densification. Vickers hardness of doped MgO is proportional to the relative density and is unaffected by doping. Corrosion resistance of MgO ceramics for liquid PbO is also unaffected by dopants, except for P2O5. 相似文献
9.
A systematic reactivity study of N 2O, NO, and NO 2 on highly dispersed CuO phases over modified silica supports (SiO 2–Al 2O 3, SiO 2–TiO 2, and SiO 2–ZrO 2) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N 2O) to selective reductions by hydrocarbons (N 2O, NO, and NO 2) and oxidation (NO to NO 2). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO 2–Al 2O 3 and SiO 2–ZrO 2, led to a better activity and selectivity of CuO for the reactions of N 2O, NO, and NO 2 reductions and N 2O decomposition than SiO 2–TiO 2. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values. 相似文献
10.
NiO/Al_2O_3基催化剂用于替代贵金属催化剂,被广泛应用于石油和石化领域生产过程的加氢、脱硫和脱氮。采用TPR方法,研究不同Ni含量NiO/Al_2O_3及不同载体的催化剂还原特性。结果表明,NiO/Al_2O_3催化剂在10%H_2-Ar气氛下,还原温度范围较宽,为(300~800)℃,其中,(500~600)℃还原速率最大;随着NiO含量的增加,起始还原温度降低,还原耗氢量按比例增加;以MgO为载体的NiO催化剂还原呈现双峰特征,以SiO2和TiO2为载体的NiO催化剂的初始还原温度比NiO/Al_2O_3催化剂降低(100~200)℃。 相似文献
11.
To get the low temperature sulfur resistant V 2O 5/TiO 2 catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V 2O 5/TiO 2 catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V 2O 5/TiO 2 catalysts showed high catalytic activity for NH 3 selective catalytic reduction (NH 3-SCR) of NO x carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V 2O 5/TiO 2 > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V 2O 5/TiO 2 for maximum NO x conversion, which also showed high resistance to SO 2 in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V 2O 5/TiO 2 and compared with commercial W(10%)V 2O 5/TiO 2 catalyst. High electrical conductivity difference (Δ G) for Sb(2%)/V 2O 5/TiO 2 catalyst with temperature was observed. SO 2 deactivation experiments were carried out for Sb(2%)/V 2O 5/TiO 2 and W(10%)/V 2O 5/TiO 2 at a temperature of 230 °C for 90 h, resulted Sb(2%)/V 2O 5/TiO 2 was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V 2O 5/TiO 2 than Sb(2%)/V 2O 5/TiO 2 catalyst. 相似文献
12.
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
13.
Fresh and used EUROCAT Oxide-2 catalyst made up of V 2O 5, WO 3 and TiO 2 with SiO 2, Al 2O 3 and CaO as main additives have been studied by means of temperature programmed reduction (TPR). As in the EUROCAT Oxide-1 project (V 2O 5/TiO 2 catalysts) for similar conditions similar profiles were obtained in the different laboratories. In contrast to the V 2O 5/TiO 2 catalysts (EUROCAT Oxide-1 project), where the vanadia content could be determined by TPR with reasonable reliability, the exact determination of the vanadia and tungsta loading for the ternary catalysts is not possible because of the occurrence of several superimposed phenomena (reduction of vanadia, tungsta and titania and formation/reduction of CaWO 4, reactions are not completed at maximal temperature reached), which are not discernible by TPR. 相似文献
14.
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
15.
The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO 2, SiO 2–Al 2O 3, activated carbon, mordenite type zeolites, MgO, TiO 2 and Al 2O 3. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO 2 and Al 2O 3 containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrO x catalysts supported on TiO 2 and Al 2O 3 also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrO x/TiO 2 revealed stronger water tolerance than CrO x/Al 2O 3 due to the surface hydrophobicity. 相似文献
16.
The structural and catalytic properties of MoO 3 catalysts supported on ZrO 2, Al 2O 3, TiO 2 and SiO 2 with Mo surface densities, ns, in the range of 0.5–18.5 Mo/nm 2 were studied for the oxidative dehydrogenation (ODH) of ethane by in situ Raman spectroscopy and catalytic activity measurements at temperatures of 400–540 °C. The molecular structure of the dispersed surface species evolves from isolated monomolybdates (MoO 4 and MoO 5, depending on the support) at low loadings to associated MoO x units in polymolybdate chains at high loadings and ultimately to bulk crystalline phases for loadings exceeding the monolayer coverage of the supports used. The nature of the oxide support material and of the Mo–O–support bond has a significant influence on the catalytic behaviour of the molybdena catalysts with monolayer coverage. The dependence of reactivity on the support follows the order ZrO 2 > Al 2O 3 > TiO 2 > SiO 2. The oxygen site involved in the anchoring Mo–O–support is of relevance for the catalytic activity. 相似文献
17.
The reduction of nitrogen monoxide by propene on V 2O 5/ZrO 2 doped with or without calcium has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Considerable promoting effect of calcium doping on the reduction of nitrogen monoxide by propene was observed on the V 2O 5/ZrO 2 catalysts. For the reaction of a mixture of NO+C 3H 6, carbonyl and carboxylate species were observed above 373 K, although nitrate species formed at room temperature on V 2O 5/ZrO 2 doped with calcium. No bands due to a compound including both carbon and nitrogen atoms were observed. Thus, the redox mechanism, i.e. propene reduces the catalyst and nitrogen monoxide oxidizes the catalyst, is confirmed on V 2O 5/ZrO 2 catalysts doped with or without calcium. The analysis of the V=O band in the region of 1100–900 cm −1 indicates that this promotion is mainly due to new V=O species formed by the addition of calcium onto the catalyst. This species is easily reproduced in comparison with the other V=O species on the surface in the reoxidation process of the catalyst. 相似文献
18.
The physico-chemical characteristics and the reactivity of sub-monolayer V 2O 5-WO 3/TiO 2 deNO x catalysts is investigated in this work by EPR, FT-IR and reactivity tests under transient conditions. EPR indicates that tetravalent vanadium ions both in magnetically isolated form and in clustered, magnetically interacting form are present over the TiO 2 surface. The presence of tungsten oxide stabilizes the surface V IV and modifies the redox properties of V 2O 5/TiO 2 samples. Ammonia adsorbs on the catalysts surface in the form of molecularly coordinated species and of ammonium ions. Upon heating, activation of ammonia via an amide species is apparent. V 2O 5-WO 3/TiO 2 catalysts exhibits higher activity than the binary V 2O 5/TiO 2 and WO 3/TiO 2 reference sample. This is related to both higher redox properties and higher surface acidity of the ternary catalysts. Results suggest that the catalyst redox properties control the reactivity of the samples at low temperatures whereas the surface acidity plays an important role in the adsorption and activation of ammonia at high temperatures. 相似文献
19.
The hydrogenation of CO over an Rh vanadate (RhVO 4) catalyst supported on SiO 2 (RhVO 4/SiO 2) has been investigated after H 2 reduction at 500°C, and the results are compared with those of vanadia-promoted (V 2O 5–Rh/SiO 2) and unpromoted Rh/SiO 2 catalysts. The mean size of Rh particles, which were dispersed by the decomposition of RhVO 4 after the H 2 reduction, was smaller (41 Å) than those (91–101 Å) of V 2O 5–Rh/SiO 2 and Rh/SiO 2 catalysts. The RhVO 4/SiO 2 catalyst showed higher activity and selectivity to C 2 oxygenates than the unpromoted Rh/SiO 2 catalyst after the H 2 pretreatment. The CO conversion of the RhVO 4/SiO 2 catalyst was much higher than that of V 2O 5–Rh/SiO 2 catalyst, and the yield of C 2 oxygenates increased. We also found that the RhVO 4/SiO 2 catalyst can be regenerated by calcination or O 2 treatment at high temperature after the reaction. 相似文献
20.
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
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