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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.
用廉价的丙烷脱氢制丙烯是解决丙烯供应紧张问题的途径之一,研究优异性能的丙烷脱氢催化剂具有重要意义。采用分步浸渍法制备不同类型的丙烷脱氢催化剂Pt/Al 2O 3,在固定床反应器中考察助催化剂Sn、Ga、In和K对催化剂性能的影响。结果表明,Pt-Sn/Al 2O 3催化剂性能略优于Pt-Ga/Al 2O 3和Pt-In/Al 2O 3,并且比较稳定。在Pt-Sn/Al2O3催化剂中加入适量K,可有效改善催化剂性能,但高温条件下积炭严重,有待深入研究和改进。 相似文献
3.
由丙烷直接催化脱氢制取丙烯已经成为增产丙烯的重要手段之一。以水热法制备Al_2O_3载体,采用等体积浸渍法制备不同PtSn负载量的PtSn/Al_2O_3催化剂。通过XRD、N2-吸附、拉曼光谱和H2-TPR等对其进行表征,并考察不同PtSn负载量对催化剂催化丙烷脱氢性能的影响。结果表明,在制备的催化剂中,Pt1.5Sn3/Al_2O_3具有最高的催化丙烷脱氢活性和稳定性,丙烷初始转化率高达55.6%,丙烯选择性98.1%。反应330 min后,丙烷转化率仅降约10%,选择性保持不变。 相似文献
4.
Oxidation of propene and propane to CO 2 and H 2O has been studied over Au/Al 2O 3 and two different Au/CuO/Al 2O 3 (4 wt.% Au and 7.4 wt.% Au) catalysts and compared with the catalytic behaviour of Au/Co 3O 4/Al 2O 3 (4.1 wt.% Au) and Pt/Al 2O 3 (4.8 wt.% Pt) catalysts. The various characterization techniques employed (XRD, HRTEM, TPR and DR-UV–vis) revealed the presence of metallic gold, along with a highly dispersed CuO (6 wt.% CuO), or more crystalline CuO phase (12 wt.% CuO). A higher CuO loading does not significantly influence the catalytic performance of the catalyst in propene oxidation, the gold loading appears to be more important. Moreover, it was found that 7.4Au/CuO/Al2O3 is almost as active as Pt/Al2O3, whereas Au/Co3O4/Al2O3 performs less than any of the CuO-containing gold-based catalysts. The light-off temperature for C3H8 oxidation is significantly higher than for C3H6. For this reaction the particle size effect appears to prevail over the effect of gold loading. The most active catalysts are 4Au/CuO/Al2O3 (gold particles less than 3 nm) and 4Au/Co3O4/Al2O3 (gold particles less than 5 nm). 相似文献
5.
采用水热处理对γ-Al2O3载体改性,并进行XRD、N2物理吸附-脱附、热重、NH3-TPD及H2-TPR表征。结果表明,γ-Al2O3经过"再水合-焙烧"过程,晶型变好,表面总酸量降低,Pt-Al2O3相互作用增加,提高了Pt Sn K/Al2O3催化剂的丙烷脱氢转化率、选择性及稳定性。其中,140℃处理4 h时,氧化铝负载的Pt Sn K催化剂表现出最优的丙烷脱氢性能,100 h内平均转化率为33.6%,平均选择性97.3%,失活参数为15.9%。 相似文献
6.
The ability of using niobium oxide (Nb 2O 5) as a support for preparing surface metal oxide species and testing the catalyst for the ODH of propane was done in the present study. Chromium oxide was used as the representative surface metal oxide species. To test the objective several loadings of Cr 2O 3/Nb 2O 5 were prepared by the incipient wetness impregnation technique. Surface area analysis, Raman, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy and TPR studies were used to characterize the sample. It was observed that surface chromium oxide species are formed similar to those on other oxide supports and similar monolayer coverages were achieved. However, the reduction characteristic ( Tmax temperature) was different due to the change in the Cr–O–support bond. The ODH of propane over the Cr 2O 3/Nb 2O 5 catalysts revealed that the activity increased up to monolayer coverage and then decreased due to the presence of Cr 2O 3 crystals. Similar observations were seen for the V 2O 5/Nb 2O 5 and MoO 3/Nb 2O 5 catalysts. The turnover frequency (TOF) was independent of coverage for the surface chromium, vanadium and molybdenum oxide species on Nb 2O 5. The constant TOF suggests the structure insensitivity of this type of reaction. The propene selectivities were high and relatively constant for the Cr 2O 3/Nb 2O 5 catalysts revealing the higher yields that can be obtained on this series of catalysts compared to the Cr 2O 3/Al 2O 3 and Cr 2O 3/TiO 2 catalysts. Additional studies involving tungsten and molybdenum oxide additives on 1% Cr 2O 3/Nb 2O 5 reveal the effect of exposed support surface on the propene selectivities. 相似文献
7.
Reticular oxygen of Al 2O 3 or CeO x supported on Al 2O 3 was used for the epoxidation of propene without any double bond cleavage. In batch reaction, Al 2O 3 alone was able to convert propene into propene oxide (PO) with 100% selectivity and 2% conversion of propene with a close to 3:1 ratio with respect to the number of Al(III) reduced to elemental Al. When Ce 2O 3/Al 2O 3 or CeO 2/Al 2O 3 was used, Al remained in its +3 oxidation state, while the Ce oxide was the oxidant as demonstrated by XPS analyses. CeO x/Al 2O 3 was more active (propene conversion yield of 4–5%) but the selectivity was lower (70%) as PO was isomerized into acetone and propionaldehyde. Interestingly the use of reticular oxygen very much improves the selectivity with respect to the use of pure O2. In fact, while propene was more efficiently oxidized (10%) with O2 in presence of Al2O3 or CeOx/Al2O3, the selectivity was as low as 40% because C1 and C2 products were formed. However, the use of reticular oxygen represents a selective two-step technique for the use of molecular oxygen as oxidant of propene. The used oxides can be re-oxidized and the whole process can be further improved towards higher yields. PO is quantitatively converted into propene carbonate by reaction with CO2 in presence of Nb2O5. 相似文献
8.
Catalytic reduction of NO by propene in the presence of oxygen was studied over SnO 2-doped Ga 2O 3–Al 2O 3 prepared by sol–gel method. Although SnO 2-doped Ga 2O 3–Al 2O 3 gave lower NO conversion than Ga 2O 3–Al 2O 3 in the absence of H 2O, the activity was enhanced considerably by the presence of H 2O and much higher than that of Ga 2O 3–Al 2O 3. The presence of SnO 2 and Ga 2O 3–Al 2O 3 species having intimate Ga–O–Al bondings was found to be essential for the promotional effect of H 2O. The promotional effect of H 2O was interpreted by the following two reasons. The first one is the removal of carbonaceous materials deposited on the catalyst surface by H 2O. The other is the selective inhibition by H 2O of the reaction steps resulting in propene oxidation to CO x without reducing NO. 相似文献
9.
Oxidized diamond demonstrated excellent support for the dehydrogenation of light alkanes to alkenes in the presence of CO 2. Oxidized diamond-supported Cr 2O 3 and V 2O 5 catalysts exhibited comparatively higher catalytic activities in the dehydrogenation of lower alkanes in the presence of CO 2. In the dehydrogenation of propane, the oxidized diamond-supported Cr 2O 3 and V 2O 5 catalysts in the presence of CO 2 afforded nearly twofold higher activities than that in the absence of CO 2. The activity of the oxidized diamond-supported V 2O 5 catalyst in the dehydrogenation of propane increased with increasing reaction temperatures. Furthermore, in the dehydrogenation of n-butane and iso-butane, a promoting effect of CO 2 on butane conversion and butenes yields was observed over the oxidized diamond-supported Cr 2O 3 and V 2O 5 catalysts, though the promotion effect was small. UV-Vis analyses of the fresh and the reacted catalysts in the presence and absence of CO2 revealed that CO2 kept the surface V2O5 and Cr2O3 in a state of oxidation slightly higher than that in the absence of CO2. 相似文献
10.
The behavior of fresh and aged EUROCAT V 2O 5–WO 3/TiO 2 SCR catalysts in the (I) oxidative dehydrogenation of light alkanes, and conversion of (ii) propan-2-ol, (iii) NO in the presence of propene and oxygen, (iv) propane and propene and (v) chloropropane is reported to analyse possible modifications of the catalyst properties during use and give a more comprehensive general picture of its surface and reactivity properties. 相似文献
11.
Hydrogen production from ethanol reforming over nickel catalysts supported on lanthanum loaded Al 2O 3 substrates was studied. Activity results revealed the enhancement in the reforming stability of the Ni catalysts with the increase in the lanthanum loading on Al 2O 3 substrates. Catalytic behavior of Ni/La–Al 2O 3 catalysts in the ethanol steam reforming was found to be the contribution of the activity of the La–Al 2O 3 supports for the ethanol dehydration reaction and the activity of the nickel metallic phase that catalyzes both dehydrogenation and CC bond rupture. Physicochemical characterization of catalysts revealed that acidity, nickel dispersion and nickel-support interaction depend on the La-loading on Al 2O 3. The better reforming stability of catalysts with the increase in La content was explained in terms of the ability of nickel surface and/or La–Ni interactions to prevent the formation of carbon filaments. 相似文献
12.
以浸渍法制备VMo/γ-Al 2O 3和VMoMg/γ-Al 2O 3催化剂,考察其催化丙烷氧化脱氢制丙烯的反应活性,采用XRD、UV-Vis DRS和In suit IR对催化剂进行表征。结果表明,V负载质量分数为3%、Mo负载质量分数为7%时的3V7Mo/γ-Al 2O 3催化剂表现出较好的催化性能;添加Mg后催化剂的催化性能有所改善,反应温度500 ℃时,丙烷转化率为18.19%,丙烯选择性74.76%。丙烷和丙烯在3V7Mo/γ-Al 2O 3和3V 7Mo 4Mg/γ-Al 2O 3催化剂上吸附后,C—H键的H与催化剂活性中心的晶格氧发生作用形成H—O键,且3V 7Mo 4Mg/γ-Al 2O 3催化剂上出现C—O键的温度比3V 7Mo/γ-Al 2O 3催化剂高,表明加入Mg有利于提高丙烯选择性。 相似文献
13.
The surface properties of a series of V 2O 5 catalysts supported on different oxides (Al 2O 3, H–Na/Y zeolite, MgO, SiO 2, TiO 2 and ZrO 2) were investigated by transmission electron microscopy and FTIR spectroscopy augmented by CO and NH 3 adsorption. In the case of the V 2O 5/SiO 2 system TEM images evidenced the presence of V 2O 5 crystallites, whereas such segregated phase was not observed for the other samples. VO x species resulted widely spread on the surface of Al 2O 3, H–Na/Y zeolite, MgO and SiO 2, whereas on TiO 2 and ZrO 2 they are assembled in a layer covering almost completely the support. Furthermore, evidences for the presence in this layer of V–OH Brønsted acid sites close to the active centres were found. It is proposed that propene molecules primarily produced by oxydehydrogenation of propane can be adsorbed on this acid centres and then undergo an overoxidation by reaction with redox centres in the neighbourhood. This features could account for the low selectivity of V 2O 5/TiO 2 and V 2O 5/ZrO 2 catalysts. 相似文献
14.
Noble metal (Rh, Pt, Pd, Ir, Ru, and Ag) and Ni catalysts supported on CeO 2–Al 2O 3 were investigated for water gas shift reaction at ultrahigh temperatures. Pt/CeO 2–Al 2O 3 and Ru/CeO 2–Al 2O 3 demonstrated as the best catalysts in terms of activity, hydrogen yield and hydrogen selectivity. At 700 °C and steam to CO ratio of 5.2:1, Pt/CeO 2–Al 2O 3 converted 76.3% of CO with 94.7% of hydrogen selectivity. At the same conditions, the activity and hydrogen selectivity for Ru/CeO 2–Al 2O 3 were 63.9% and 85.6%, respectively. Both catalysts showed a good stability over 9 h of continuous operation. However, both catalysts showed slight deactivation during the test period. The study revealed that Pt/CeO 2–Al 2O 3 and Ru/CeO 2–Al 2O 3 were excellent ultrahigh temperature water gas shift catalysts, which can be coupled with biomass gasification in a downstream reactor. 相似文献
15.
Chromium oxide catalysts supported on TiO 2 and Al 2O 3 were examined in a fixed-bed flow reactor system for the removal of PCE (perchloroethylene), a simulant of 2,3,7,8-TCDD (2,3,7,8-tetrachlorodibenzo- p-dioxin), and in a pilot plant employing actual flue gas from a sintering plant for the removal of PCDDs/PCDFs (poly-chlorinated dibenzo-dioxin/poly-chlorinated dibenzo-furan). The 12.5 wt.% chromium oxides supported on TiO 2 and Al 2O 3 revealed excellent stability and performance of PCE removal in the feed gas stream containing water vapor. In a pilot plant study, the catalysts washcoated on the honeycomb reactor revealed 93–95% of PCDDs/PCDFs removal activity over CrO x/Al 2O 3-HC20 (CrO x/Al 2O 3 catalyst washcoated on 20 cell-honeycomb), and more than 99% of the decomposition activity over CrO x/TiO 2-HC20 (CrO x/TiO 2 catalyst washcoated on 20 cell-honeycomb) at 325 °C and 5000 h −1 of reactor space velocity without the de novo synthesis of PCDDs/PCDFs. In particular, CrO x/TiO 2-HC20 showed 94% of PCDDs/PCDFs decomposition activity even at 280 °C reaction temperature. The catalyst also exhibited significant NO removal activity. The chromium oxide seems to be a promising catalyst for the removal of PCDDs/PCDFs and NO x contained in the flue gas. 相似文献
16.
Atomic layer epitaxy (ALE), a technique relying on saturating gas–solid reactions, was applied in the preparation of CrO x/Al 2O 3 catalysts using Cr(acac) 3 vapor and air as source materials for CrO x. Vaporized Cr(acac) 3 was reacted with preheated Al 2O 3, and the surface complex formed was treated with air to remove the ligand residues. The Cr loading increased from 1.3 to 12.5 wt.% as the number of saturating Cr(acac) 3 and air reactions was increased from one to 10. CrO x/Al 2O 3 catalysts were also prepared from solution by incipient wetness impregnation (0.3–21 wt.%). XPS and UV–VIS measurements of the catalysts revealed the presence of both Cr 6+ and Cr 3+. Although the oxidation state distribution was similar, H 2-temperature programmed reduction (TPR) and solubility measurements indicated that Cr 6+ surface sites were in stronger interaction with Al 2O 3 and more uniformly distributed in the catalysts prepared by ALE than by impregnation. On the basis of the activity of the catalysts in the dehydrogenation of i-butane, we propose that the dehydrogenation reaction uses both reduced Cr 6+, i.e. redox Cr 3+, and exposed non-redox Cr 3+ sites. Furthermore, the dehydrogenation reaction must be insensitive to the size of the CrO x ensembles since activities were similar for the catalysts prepared by ALE and impregnation. The decay of the dehydrogenation activity in successive prereduction–reaction–regeneration cycles was attributed to a decrease in the number of redox Cr 3+ sites. 相似文献
17.
The total oxidation of propane and its oxy-dehydrogenation to propene have been studied on spinel-type catalysts Mn 3O 4, Co 3O 4 and MgCr 2O 4 in a flow reactor and in an IR cell. Analogous studies have been performed on the oxy-dehydrogenation of n-butenes to 1,3-butadiene over MgFe 2O 4. Information on the reaction mechanism have been reached. The activation of the hydrocarbons is thought to occur by abstraction of a hydrogen from the weakest C–H bond, with a simultaneous reduction of a surface site and with the formation of a surface alkoxy-group. 相似文献
18.
Catalysts prepared as bulk VSb 0.1O x and supported V 2O 5/Al 2O 3, V 2O 5-Sb 2O 3/Al 2O 3 and Sb 2O 3/Al 2O 3 (containing 0.5, 1 or 2 theoretical monolayers of V 2O 5 or Sb 2O 3) were tested in the oxidative dehydrogenation of iso-butane at 550°C in i-C 4H 10:O 2:He=20:10:70 gas mixture. Fresh and used catalysts were characterised by BET, XRD and XPS. Reactivity and thermochemistry of active oxygen taking part in the redox cycle with ethane and hydrogene were studied using in situ differential scanning calorimetry. Temperature-programmed desorption of O 2 in He flow was also investigated and in situ DRIFT was applied to investigate surface species of the catalysts in flows of i-C 4H 10, O 2 and i-C 4H 10/O 2 mixture. Supported VSb yO x catalysts are more active and selective than bulk one. V-only supported catalysts display a high efficiency due to the high reactivity of VOX-species. In bulk catalyst, the surface is enriched with antimony. In supported samples, the surfaces V/Sb are close to the calculated ones. In the presence of antimony, the amount of active oxygen species and their reactivity in redox transformation is improved. The rates of vanadium reduction and reoxidation are also higher. Compared to V-only catalysts, supported V-Sb-catalysts display a lower coking activity and higher on-stream stability. 相似文献
19.
考察了氯的脱除对丙烷脱氢铂锡催化剂结构和反应性能的影响,并采用XRD、N 2吸脱附、TPR、NH 3-TPD、TEM和Raman等方法进行表征。结果表明,氯的脱除温度显著影响催化剂的酸性、孔体积、比表面积、孔径和Pt颗粒尺寸。随着处理温度的提高,催化剂酸性、比表面积、孔体积都呈现下降的趋势,平均孔径增加,Pt颗粒的烧结程度加剧。随着处理温度的增加,催化剂初活性逐渐降低,丙烯选择性增加,稳定性出现先增加后降低趋势。研究表明,氯的较佳的脱除温度为540℃,催化剂具有很好的脱氢性能和稳定性,收率最高。 相似文献
20.
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
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