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1.
Gianmario Martra Franco Arena Salvatore Coluccia Franco Frusteri Adolfo Parmaliana 《Catalysis Today》2000,63(2-4):197-207
The surface properties of a series of V2O5 catalysts supported on different oxides (Al2O3, H–Na/Y zeolite, MgO, SiO2, TiO2 and ZrO2) were investigated by transmission electron microscopy and FTIR spectroscopy augmented by CO and NH3 adsorption. In the case of the V2O5/SiO2 system TEM images evidenced the presence of V2O5 crystallites, whereas such segregated phase was not observed for the other samples. VOx species resulted widely spread on the surface of Al2O3, H–Na/Y zeolite, MgO and SiO2, whereas on TiO2 and ZrO2 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 V2O5/TiO2 and V2O5/ZrO2 catalysts. 相似文献
2.
针对甲基吡啶氧化脱甲基反应,以TiO_2为载体经浸渍法制备Ag-Fe_2O_3-V_2O_5/TiO_2催化剂,结合结构表征和催化剂性能评价,考察制备条件对其催化甲基吡啶氧化脱甲基性能的影响。结果表明,通过Fe_2O_3改性可以提高Ag-V_2O_5/TiO_2催化剂对3-甲基吡啶氧化脱甲基化反应的催化性能,其作用主要是抑制V_2O_5团聚,促进V物种的分散。同时,锐钛矿相TiO_2载体表面B酸中心有利于催化3-甲基吡啶脱甲基,提高产物吡啶选择性。经实验优化,Ag-Fe_2O_3-V_2O_5/TiO_2催化剂适宜制备条件为:焙烧温度450℃、焙烧时间4 h、V_2O_5和Ag的负载质量分数分别为15%和1.5%、Fe与V物质的量比1∶2。在优化条件下,吡啶收率与选择性最高可达到62.97%和78.75%。 相似文献
3.
Two series of catalysts, V2O5/TiO2 and modified V2O5/TiO2, were prepared with a conventional impregnation method. They were tested in the selective oxidation of toluene to benzoic acid under microwave irradiation. The reaction conditions were optimized over V2O5/TiO2. It was found that in the microwave catalytic process the optimum reactor bed temperature of the titled reaction decreases to 500 K (600 K in the conventional process). The modification of V2O5/TiO2 with MoO3, WO3, Nb2O5 or Ta2O5, which has no negative influence on the reaction in the conventional catalytic process, can greatly promote the catalytic activities in the microwave process, leading to a high yield of benzoic acid (41%). The effects of microwave electromagnetic field on the catalysts are discussed. 相似文献
4.
Ha Heon Phil Maddigapu Pratap Reddy Pullur Anil Kumar Lee Kyung Ju Jung Soon Hyo 《Applied catalysis. B, Environmental》2008,78(3-4):301-308
To get the low temperature sulfur resistant V2O5/TiO2 catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V2O5/TiO2 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 V2O5/TiO2 catalysts showed high catalytic activity for NH3 selective catalytic reduction (NH3-SCR) of NOx carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V2O5/TiO2 > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V2O5/TiO2 for maximum NOx conversion, which also showed high resistance to SO2 in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V2O5/TiO2 and compared with commercial W(10%)V2O5/TiO2 catalyst. High electrical conductivity difference (ΔG) for Sb(2%)/V2O5/TiO2 catalyst with temperature was observed. SO2 deactivation experiments were carried out for Sb(2%)/V2O5/TiO2 and W(10%)/V2O5/TiO2 at a temperature of 230 °C for 90 h, resulted Sb(2%)/V2O5/TiO2 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%)/V2O5/TiO2 than Sb(2%)/V2O5/TiO2 catalyst. 相似文献
5.
Stefania Albonetti Sonia Blasioli Rosa Bonelli Joseph Epoupa Mengou Salvatore Scir Ferruccio Trifir 《Applied Catalysis A: General》2008,341(1-2):18-25
The influence of Lewis and Brønsted acid sites on the performance of V2O5/TiO2 and V2O5–WO3/TiO2 catalysts in the total oxidation of o-dichlorobenzene was investigated. Catalytic activity of these materials resulted strongly affected by their acidic properties. The presence of Brønsted acid sites significantly increases the o-DCB conversion but also leads to the uncompleted degradation of chlorinated compounds, promoting the formation of partial oxidation products, as dichloromaleic anhydride. On the contrary, Lewis acid sites, acting as absorbing sites, promote the further oxidation of intermediates to CO and CO2, without any by-products desorption.
Furthermore, the presence of water in the feed-stream was proven to decrease o-DCB conversion but also to play a positive role on process selectivity, increasing COx production. Plausible reasons for this effect are the reduction of Brønsted acid sites and the hydrolysis of anhydride during wet tests. 相似文献
6.
The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported on Al2O3, TiO2, ZrO2 and MgO. The promotion of V2O5/Al2O3 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. V2O5/TiO2 catalyst exhibits the highest activity in oxydehydrogenation of propane. The support’s nature also affects the selectivity to propene; V2O5 supported on Al2O3 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
7.
We investigated the suppression of SO2 oxidation activity by vanadium oxide in Pt-based diesel oxidation catalyst using reaction experiments, temperature programmed desorption (TPD), infrared (IR) and X-ray photoelectron spectroscopy (XPS). There was no interaction between Pt and S indicated by the XPS results. SO2 was not adsorbed on Pt at room temperature indicated by the absence of peak arising from SO2 in SO2 TPD spectra. SO2 molecules were adsorbed on the hydroxyl groups of TiO2 and migrated to Pt particles to react with oxygen adsorbed on it. V2O5 decreased the adsorption of SO2 on TiO2 by the blockage of V2O5 on TiO2. 相似文献
8.
Junko Oi-Uchisawa Akira Obuchi Ryuji Enomoto Jiayu Xu Tetsuya Nanba Shetian Liu Satoshi Kushiyama 《Applied catalysis. B, Environmental》2001,32(4):257-268
Catalytic activities of various Pt/MOx/SiC systems for carbon oxidation under simulated diesel exhaust gas were investigated in temperature-programmed reactions. When Pt/MOx (MOx=TiO2, ZrO2, Al2O3) was loaded onto silicon carbide (SiC), the oxidation activities became higher than those of Pt/MOx alone or other Pt/MOx/SiC systems (MOx=Ta2O5, WO3, Nb2O5, SnO2, SiO2, CeO2, MoO3, V2O5). Among them, Pt/TiO2/SiC exhibited the highest activity. We discuss the activity of MOx=TiO2, ZrO2, and Al2O3 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/TiO2/SiC in more detail under isothermal conditions and in a staged arrangement. 相似文献
9.
Effect of promoters including tungsten and barium on the thermal stability of V2O5/sulfated TiO2 catalyst for NO reduction by NH3 总被引:2,自引:0,他引:2
The effect of tungsten and barium on the thermal stability of V2O5/TiO2 catalyst for NO reduction by NH3 was examined over a fixed bed flow reactor system. The activity of V2O5/sulfated TiO2 catalyst gradually decreased with respect to the thermal aging time at 600 °C. The addition of tungsten to the catalyst surface significantly enhanced the thermal stability of V2O5 catalyst supported on sulfated TiO2. On the basis of Raman and XRD measurements, the tungsten on the catalyst surface was identified as suppressing the progressive transformation of monomeric vanadyl species into crystalline V2O5 and of anatase into rutile phase of TiO2. However, the NO removal activity of V2O5/sulfated TiO2 catalyst including barium markedly decreased after a short aging time, 6 h at 600 °C. This may be due to the transformation of vanadium species to inactive V–O–Ba compound by the interaction with BaO which was formed by the decomposition of BaSO4 on the catalyst surface at high reaction temperature of 600 °C. The addition of SO2 to the feed gas stream could partly restore the NO removal activity of thermally aged V2O5/sulfated TiO2 catalyst containing barium. 相似文献
10.
Reactivity of V2O5-WO3/TiO2 catalysts in the selective catalytic reduction of nitric oxide by ammonia 总被引:1,自引:0,他引:1
L. Lietti J. L. Alemany P. Forzatti G. Busca G. Ramis E. Giamello F. Bregani 《Catalysis Today》1996,29(1-4):143-148
The physico-chemical characteristics and the reactivity of sub-monolayer V2O5-WO3/TiO2 deNOx 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 TiO2 surface. The presence of tungsten oxide stabilizes the surface VIV and modifies the redox properties of V2O5/TiO2 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. V2O5-WO3/TiO2 catalysts exhibits higher activity than the binary V2O5/TiO2 and WO3/TiO2 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
11.
Motonobu Kobayashi Ryoji Kuma Sinyuki Masaki Noboru Sugishima 《Applied catalysis. B, Environmental》2005,60(3-4):173-179
TiO2-SiO2 with various compositions prepared by the coprecipitation method and vanadia loaded on TiO2-SiO2 were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH3 and in the undesired oxidation of SO2 to SO3, using BET, XRD, XPS, NH3-TPD, acidity measurement by the titration method and activity test. TiO2-SiO2, compared with pure TiO2, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V2O5. The SCR activity and N2 selectivity are found to be more excellent over vanadia loaded on TiO2-SiO2 with 10–20 mol% of SiO2 than over that on pure TiO2, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH3 adsorbed on the catalysts. With increasing SiO2 content, the remarkable activity decrease in the oxidation of SO2 to SO3, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V4+ on TiO2-SiO2, while V5+ exists on TiO2, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO2-SiO2 with low SiO2 content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NOx activity but also the low SO2 oxidation performance. 相似文献
12.
Kentaro Teramura Tsunehiro Tanaka Tomohiro Hosokawa Tai Ohuchi Masaya Kani Takuzo Funabiki 《Catalysis Today》2004,96(4):205-209
More than 0.22 mmol of isolated VO4 species of V2O5/Al2O3 exhibited the highest evolution of the partial oxidation products (alcohol and ketone) in the oxidation of cyclohexane and cyclopentane. The conversion of cyclohexane and the selectivity of the partial oxidation products were achieved to be 0.49% and 85% over 0.8 g of 3.5 wt.% V2O5/Al2O3, respectively, where the K/A ratio was 6.2. In addition, V2O5/Al2O3 can selectively oxidize various hydrocarbons in the liquid phase by the one-step oxygen atom insertion to CH bond. The order of priority was tertiary carbon > secondary carbon > primary carbon > benzene ring. 相似文献
13.
采用比表面积分别为101.86 m2·g-1(A)、86.37 m2·g-1(B)和7.78(C)m2·g-1(C)的TiO_2载体,通过分步浸渍法制备V2O5-Mo O3/TiO_2(A,B,C)选择性催化还原脱硝催化剂。在空速为10 000 h-1和氨氮体积比1.0条件下,以TiO_2(A)与TiO_2(B)为载体制备的催化剂脱硝活性在反应温度窗口(350~450)℃超过90%,且具有良好的高温抗硫中毒性能和相对较小的氨气氧化率。而以TiO_2(C)为载体制备的脱硝催化剂活性温度窗口窄,在350℃时获得的最高脱硝活性仅为73%,且对NH3的氧化作用较强。利用X射线衍射、低温N2吸附-脱附、紫外-可见漫反射光谱、H2程序升温还原和NH3程序升温脱附等对载体和催化剂进行表征。结果表明,活性组分V2O5在载体TiO_2(A)上分散性良好,主要以孤立态钒氧物种形式存在,因此,以TiO_2(A)为载体制备的催化剂比表面积、氧化还原性和表面酸性等性能更优。 相似文献
14.
The effect of sulphate on the catalytic properties of V2O5/TiO2 and WO3/TiO2 in the selective reduction of NO with NH3 has been investigated. For both catalytic systems, the presence of sulphate results in the enhancement of catalytic activity without reduction of selectivity to nitrogen. The rate of NO reduction depends on the sulphate content, which is affected by the original composition of titania, the method of catalyst preparation and the metal oxide loading. 相似文献
15.
Takashi Ohno Youhei Bunno Fumikazu Hatayama Yoshio Toda Hisashi Miyata 《Applied catalysis. B, Environmental》2001,30(3-4):421-428
The reduction of nitrogen monoxide by propene on V2O5/ZrO2 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 V2O5/ZrO2 catalysts. For the reaction of a mixture of NO+C3H6, carbonyl and carboxylate species were observed above 373 K, although nitrate species formed at room temperature on V2O5/ZrO2 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 V2O5/ZrO2 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
16.
烟酸作为重要的化工和医药中间体广泛应用于不同领域.相较于传统工艺,3-甲基吡啶气相一步催化氧化合成烟酸的方法具有成本低、污染低、产品质量高等优点,展现出良好的应用前景.目前V2O5/TiO2系列催化剂在3-甲基吡啶的氧化反应中表现出了良好的氧化活性.本文主要分析了催化剂表面的VOx结构,并概述了载体、制备方法、负载量、焙烧过程和助剂掺杂对结构的影响,探讨催化剂中各组分之间的相互作用,根据相关文献推测3-甲基吡啶氧化的反应机理.但该类催化剂仍然存在反应速率和选择性较低、温度窗口窄、反应过程中放出的热量对催化剂的影响等一些技术问题.文章从催化剂的开发和反应器的设计两方面进行了展望. 相似文献
17.
Hideji Aoki Yasuo Azuma Takashi Asaka Masayoshi Higuchi Kiyoshi Asaga Keiichi Katayama 《Ceramics International》2008,34(4):819-822
Porous TiO2 ceramics were prepared by adding various amounts of Li2O and V2O5 and the humidity sensitivity of the resulting ceramics was investigated by means of electrical measurements, scanning electron microscopy and mercury intrusion porosimetry. Simultaneous addition of Li2O and V2O5 to TiO2 enabled sintering at temperatures as low as 700 °C and also decreased the impedance of the ceramics. Furthermore, in the ceramics including these additives simultaneously, excellent humidity sensitivity as well as good response characteristics were observed. The microstructures of these ceramics depended on the firing temperature and the amount and ratio of Li2O/V2O5, and optimum humidity sensitivity was observed for the sample including both 0.25 mol% Li2O and 0.75 mol% V2O5 fired at 700 °C. These results indicated that the humidity sensitivity and its response characteristics were closely related to the microstructure, and that improving the uniformity of microstructure is important for improving humidity sensitivity and its response characteristics. 相似文献
18.
Pd/Nb2O5/Al2O3 catalysts were investigated on propane oxidation. Diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) analysis suggested that monolayer coverage was attained between 10 and 20 wt.% of Nb2O5. Temperature programmed reduction (TPR) evidenced the partial reduction of niobium oxide. The maximum propane conversion observed on the Pd/10% Nb2O5/Al2O3 corresponded to the maximum Nb/Al surface ratio. The presence of NbOx polymeric structures near to the monolayer could favor the ideal Pd0/Pd2+ surface ratio to the propane oxidation which could explain the promoting effect of niobium oxide. 相似文献
19.
The adsorption and transformation of ammonia over V2O5, V2O5/TiO2, V2O5-WO3/TiO2 and CuO/TiO2 systems has been investigated by FT-IR spectroscopy. In all cases ammonia is first coordinated over Lewis acid sites and later undergoes hydrogen abstraction giving rise either to NH2 amide species or to its dimeric form N2H4, hydrazine. Other species, tentatively identified as imide NH, nitroxyl HNO, nitrogen anions N2− and azide anions N3− are further observed over CuO/TiO2. The comparison of the infrared spectra of the species arising from both NH3 and N2H4 adsorbed over CuO/TiO2 strongly suggest that N2H4 is an intermediate in NH3 oxidation over this active selective catalytic reduction (SCR) and selective catalytic oxidation (SCO) catalysts. This implies that ammonia is activated in the form of NH2 species for both SCR and SCO, and it can later dimerize. Ammonia protonation to ammonium ion is detected over V2O5-based systems, but not over CuO/TiO2, in spite of the high SCR and SCO activity of this catalyst. Consequently Brönsted acidity is not necessary for the SCR activity. 相似文献
20.
Alumina–silica mixed oxide, synthesized by the sol–gel technique, was used as a support for dispersing and stabilizing the active vanadia phase. The catalysts were characterized employing 51V and 1H solid-state MAS NMR, diffuse reflectance FT-IR, BET surface area measurements. The partial oxidation activities of the catalysts were tested using methanol oxidation as a model reaction. 51V solid-state NMR studies on the calcined catalysts showed the peaks corresponding to the presence of both tetrahedral and distorted octahedral vanadia species at low vanadia loadings and with an increase in V2O5 content, the 51V chemical shifts corresponding to amorphous V2O5 like phases were observed. DRIFTS studies of the catalysts indicated the vibrations corresponding tetrahedral vanadia species at low and medium loadings and at high V2O5 contents the vibrations corresponding V=O bonds of V2O5 agglomerates were observed. The V/Al–Si catalysts exhibited high selectivity for the dehydration product dimethyl ether in the methanol partial oxidation studies showing the predominance of the acidic nature of the alumina–silica support over the redox properties of the active vanadia phase. 相似文献