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1.
S.H. Overbury Lorna Ortiz-Soto Haoguo Zhu Byungwhan Lee Michael D. Amiridis Sheng Dai 《Catalysis Letters》2004,95(3-4):99-106
Au catalysts supported on mesoporous silica and titania supports were synthesized and tested for the oxidation of CO. Two approaches were used to prepare the silica-supported catalysts utilizing complexing triamine ligands which resulted in mesoporous silica with wormhole and hexagonal structures. The use of triamine ligands is the key for the formation of uniformly sized 2–3 nm Au nanoparticles in the silica pores. On mesoporous titania, high gold dispersions were obtained without the need of a functional ligand. Au supported on titania exhibited a much higher activity for CO oxidation, even though the Au particle sizes were essentially identical on the titania and the wormhole silica supports. The results suggest that the presence of 2–3 nm particle size alone is not sufficient to achieve high activity in CO oxidation. Instead, the support may influence the activity through other possible ways including stabilization of active sub-nanometer particles, formation of active oxygen-containing reactant intermediates (such as hydroxyls or O2 ?), or stabilization of optimal Au structures. 相似文献
2.
Nikolaos Dimitratos Jose Antonio Lopez-Sanchez David Morgan Albert Carley Laura Prati Graham J. Hutchings 《Catalysis Today》2007,122(3-4):317-324
Solvent free oxidation of benzyl alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for benzyl alcohol oxidation. 相似文献
3.
采用共沉淀(CP)和沉积-沉淀法(DP)分别制备了0.5%(质量分数)金掺杂的Au-LSM和Au/LSM钙钛矿催化剂,以甲苯催化燃烧为模型反应测试催化剂活性,并用XRD、BET、H2-TPR对其进行表征。结果表明,Au掺杂并不改变La0.8Sr0.2MnO3催化剂的织构性质,但明显增强了催化剂表面氧的活动性,提高了其低温催化氧化活性。与DP法制备的Au/LSM相比,Au-LSM表现出更好的催化性能,其催化活性与商业贵金属Pd/Al2O3相当。通过对焙烧温度考察以及50 h的变温活性测试,Au-LSM催化性能并没有发生较大变化,催化剂具有良好的稳定性。 相似文献
4.
《Catalysis Reviews》2013,55(2):257-296
This is the first review of titanium dioxide‐zirconium dioxide (TiO2‐ZrO2) mixed oxides, which are frequently employed as catalysts and catalyst supports. In this review many details pertaining to the synthesis of these mixed oxides by various conventional and nonconventional methods and their characterization by several techniques, as reported in the literature, are assessed. These mixed oxides have been synthesized by different preparative analogies and were extensively characterized by employing various spectroscopic and nonspectroscopic techniques. The TiO2‐ZrO2 mixed oxides are also extensively used as supports with metals, nonmetals, and metal oxides for various catalytic applications. These supported catalysts have also been thoroughly investigated by different techniques. The influence of TiO2‐ZrO2 on the dispersion and surface structure of the supported active components as examined by various techniques in the literature has been contemplated. A variety of reactions catalyzed by TiO2‐ZrO2 and supported titania‐zirconia mixed oxides, namely; dehydrogenation, decomposition of chlorofluoro carbons (CFCs), alcohols from epoxides, synthesis of ?‐caprolactam, partial oxidation, deep oxidation, hydrogenation, hydroprocessing, organic transformations, NOx abatement, and photo catalytic VOC oxidations that have been pursued in the literature are presented with relevant references. 相似文献
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6.
Amorphous silica was modified by doping with titania through a surface sol–gel process and applied as the support for depositing
gold. These doped silica-supported gold catalysts were tested in the selective cyclohexane oxidation to cyclohexanone and
cyclohexanol using oxygen. Under the oxidation conditions of 150 °C, 1.5 MPa and 3 h, a selectivity of 91.7% for cyclohexanone
and cyclohexanol could be reached over the gold catalyst, affording a cyclohexane conversion of 8.4% and a turnover frequency
up to 40,133 per hour. Moreover, the catalytic activity and selectivity could be well retained in 4 recycling oxidation reactions,
showing a high stability of the gold catalyst supported on titania-doped silica. 相似文献
7.
《Catalysis communications》2007,8(1):57-64
Au, Ag and Au–Ag catalysts on different supports of alumina, titania and ceria were studied for their catalytic activity of ethylene oxidation reactions. An addition of an appropriate amount of Au on Ag/Al2O3 catalyst was found to enhance the catalytic activity of the ethylene epoxidation reaction because Au acts as a diluting agent on the Ag surface creating new single silver sites which favor molecular oxygen adsorption. The Ag catalysts on both titania and ceria supports exhibited very poor catalytic activity toward the epoxidation reaction of ethylene, so pure Au catalysts on these two supports were investigated. The Au/TiO2 catalysts provided the highest selectivity of ethylene oxide with relatively low ethylene conversion whereas, the Au/CeO2 catalysts was shown to favor the total oxidation reaction over the epoxidation reaction at very low temperatures. In comparisons among the studied catalysts, the bimetallic Au–Ag/Al2O3 catalyst is the best candidate for the ethylene epoxidation. The catalytic activity of the gold catalysts was found to depend on the support material and catalyst preparation method which govern the Au particle size and the interaction between the Au particles and the support. 相似文献
8.
Carbon supported Au-PtRu (Au-PtRu/C) catalysts were prepared as the anodic catalysts for the direct methanol fuel cell (DMFC). The procedure involved simple deposition of Au particles on a commercial Pt-Ru/C catalyst, followed by heat treatment of the resultant composite catalyst at 125, 175 and 200 °C in a N2 atmosphere. High-resolution transmission electron microscopy (HR-TEM) measurements indicated that the Au nanoparticles were attached to the surface of the Pt-Ru nanoparticles. We found that the electrocatalytic activity and stability of the Au-PtRu/C catalysts for methanol oxidation is better than that of the PtRu/C catalyst. An enhanced stability of the electrocatalyst is observed and attributable to the promotion of CO oxidation by the Au nanoparticles adsorbed onto the Pt-Ru particles, by weakening the adsorption of CO, which can strongly adsorb to and poison Pt catalyst. XPS results show that Au-PtRu/C catalysts with heat treatment lead to surface segregation of Pt metal and an increase in the oxidation state of Ru, which militates against the dissolution of Ru. We additionally find that Au-PtRu/C catalysts heat-treated at 175 °C exhibit the highest electrocatalytic stability among the catalysts prepared by heat treatment: this observation is explained as due to the attainment of the highest relative concentration of gold and the highest oxidation state of Ru oxides for the catalyst pretreated at this temperature. 相似文献
9.
Vasko Idakiev Tatyana Tabakova Krassimir Tenchev Zhong-Yong Yuan Tie-Zhen Ren Bao-Lian Su 《Catalysis Today》2007,128(3-4):223-229
New gold catalytic system prepared on ceria-modified mesoporous titania (CeMTi) used as water-gas shift (WGS) reaction catalyst is reported. Mesoporous titania (MTi) was synthesized using surfactant templating method through a neutral [C13(EO)6–Ti(OC3H7)4] assembly pathway. Ceria modifying additive was deposited on MTi by deposition precipitation (DP) method. Gold-based catalysts with different gold content (1–5 wt.%) were synthesized by DP of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N2 adsorption analysis and temperature-programmed reduction (TPR). The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H2O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new gold/ceria-modified mesoporous titania catalysts was compared with that of gold catalysts supported on simple oxides CeO2 and mesoporous TiO2, as well as gold/ceria-modified titania and reference catalyst Au/TiO2 type A (World Gold Council). A high degree of synergistic interaction between ceria and mesoporous titania and a positive modification of structural and catalytic properties by ceria has been achieved. It is clearly revealed that the ceria-modified mesoporous titania is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous titania catalytic system is found to be efficient catalyst for WGSR. 相似文献
10.
Procedures leading to the preservation of activity of supported gold catalysts for CO oxidation are reviewed. The inclusion
of iron as Fe(OH)3 in preparing catalysts using tin oxide, ceria and zirconia as supports gives better activity and much improved stability
with time-on-stream. In the case of Au/Fe-SnO2 (0.5–0.9% Au), the effect is maximal with ~4% Fe. The stability of catalysts based on ceria as support is also much better
when small amounts of either iron or lanthanum during preparation of the support by thermal decomposition of nitrates. Au/SnO2 catalysts often suffer initial deactivation followed by an increase in activity with time-on-stream; a period of refrigeration
(7d) induces an excellent stability at high conversion. 相似文献
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12.
采用MOF材料作模板,通过在Cu-BTC材料表面预先负载贵金属Au再热解的方法,成功制备了具有正八面体结构的新型多孔Au/CuxO负载型催化剂。通过降低热解环境中的O2浓度,调节氧化时间,实现了Au/Cu-BTC氧化产物组分的调节,分别制得了Au/Cu2O、Au/Cu2O-CuO、Au/CuO复合催化材料。将其用于CO催化氧化,发现所有Au/CuxO催化剂都表现出比Cu-BTC和Au/Cu-BTC更优异的催化性能,其中由于拥有较高的比表面积、Cu2O含量以及更好的Au的分散性,Au/Cu2O的CO氧化活性最佳,180℃即能实现CO的完全转化。 相似文献
13.
Graham J. Hutchings Silvio Carrettin Philip Landon Jennifer K. Edwards Dan Enache David W. Knight Yi-Jin Xu Albert F. Carley 《Topics in Catalysis》2006,38(4):223-230
Selective oxidation is of key importance in the synthesis of chemical intermediates. For many years a number of oxides and
supported metal catalysts have been used. The key questions involved in the design of selective oxidation catalysts are discussed
in the initial part of this paper. One of the most exciting recent developments in the field of selective oxidation has been
the discovery that supported gold catalysts are active. The second part of the paper discusses Au/C catalysts, which are shown
to be particularly versatile for oxidation reactions. Four examples of selective oxidation are described using molecular oxygen
as oxidant: (a) selective oxidation of glycerol to glycerate in the presence of base; (b) the oxidation of cyclohexane to
cyclohexanol and cyclohexanane in the presence of a radical initiator; (c) the oxidation of hydrogen to hydrogen peroxide,
and (d) the oxidation of benzyl alcohol to benzaldehyde under solvent free conditions. In contrast, the Au/C catalysts are
not active for oxidation of carbon monoxide at ambient temperature. These examples demonstrate that there exists a rich potential
for Au/C as a selective oxidation catalyst and that research efforts should now be focussed on selective oxidation using supported
gold catalysts. 相似文献
14.
15.
Gold particles supported on carbon and titania were explored as catalysts for oxidation of CO or glycerol by O2 at room temperature in liquid-phase water. Although Au/carbon catalysts were not active for vapor phase CO oxidation at room
temperature, a turnover frequency of 5 s−1 could be achieved with comparable CO concentration in aqueous solution containing 1 M NaOH. The turnover frequency on Au/carbon
was a strong function of pH, decreasing by about a factor of 50 when the pH decreased from 14 to 0.3. Evidently, a catalytic
oxidation route that was not available in the vapor phase is enabled by operation in the liquid water at high pH. Since Au/titania
is active for vapor phase CO oxidation, the role of water, and therefore hydroxyl concentration, is not as significant as
that for Au/carbon. Hydrogen peroxide is also produced during CO oxidation over Au in liquid water and increasing the hydroxyl
concentration enhances its formation rate. For glycerol oxidation to glyceric acid (C3) and glycolic acid (C2) with O2 (1–10 atm) at 308–333 K over supported Au particles, high pH is required for catalysis to occur. Similar to CO oxidation
in liquid water, H2O2 is also produced during glycerol oxidation at high pH. The formation of the C-C cleavage product glycolic acid is attributed
to peroxide in the reaction. 相似文献
16.
Ceria materials were modified by doping with gadolinia or yttria and by a hold period at 260 °C for 2 h during temperature-programmed calcinations to 650 °C. These doped ceria-supported copper oxide catalysts and the doped ceria material were characterized by temperature-programmed reduction, electron paramagnetic resonance, and CO oxidation activity test. It was observed that, as the doping concentration of gadolinia increases, the reduction temperature of the copper oxide species increases and the CO oxidation activity decreases. This is due to increased formation of the surface spinel species of copper oxide with gadolinia. As the yttria content increases to greater than 10 mol%, surface segregation occurs, which causes the amount of surface oxygen vacancies to decrease. It was also found that maintaining the temperature at 260 °C during calcination may decrease the amount of oxygen vacancies. The surface oxygen vacancies may be the active sites for CO oxidation over the oxygen ion conducting materials in the absence of any metal present. Gd doping leads to the formation of extrinsic oxygen vacancies, which increases the oxygen ionic conductivity of the doped ceria and thus increases the CO oxidation activities of the supported catalysts as well as of the doped ceria. 相似文献
17.
The investigations focused on the influence of doping an alumina support with different base metal oxides on the catalytic performance of gold catalysts to oxidize glucose to gluconic acid. Sodium oxide and calcium oxide strongly enhanced the reaction rate for catalysts prepared by both the deposition–precipitation and incipient wetness method. Urea was used as the precipitation agent in the former. The total selectivity of the catalysts was not influenced by the dopants. TEM analysis revealed very small gold particles of less than 2 nm for sodium doped catalysts prepared by the two methods. 相似文献
18.
Hydrogenation of 1,3-butadiene and of crotonaldehyde over highly dispersed Au catalysts 总被引:4,自引:0,他引:4
When Au is deposited as nano-particles on select metal oxides, it exhibits surprisingly high catalytic activity for many oxidation reactions. Therefore, there is also the possibility to improve the activities of Au catalysts for hydrogenation using the appropriate preparation methods like the gas-phase grafting method (GG) and the deposition precipitation method (DP). In this work, we investigated the hydrogenation of 1,3-butadiene and of crotonaldehyde over Au catalysts prepared by GG and DP and discussed the structure sensitivity of these reactions. From these experiments, it was found that the catalytic activities for the hydrogenation of 1,3-butadiene over Au catalysts was almost structure insensitive in terms of the size effect of Au particles and the influence of metal oxides supports and the crotonaldehyde hydrogenation over Au catalysts was slightly sensitive to the selection of the support in the view point of the product selectivity. 相似文献
19.
镍掺杂对二氧化钛光催化性能影响的研究 总被引:5,自引:0,他引:5
采用溶胶-凝胶法制备了纳米二氧化钛以及不同掺镍量的TiO2纳米粒子(原料中Ni∶TiO2的摩尔分数为1%、3%、5%、7%、9%)。用紫外光照射甲基橙溶液的光催化降解实验研究了掺镍对二氧化钛光催化剂催化效率的影响,试验结果表明,当用n(Ni)∶n(TiO2)=5%的Ni(NO3)2溶液进行镍掺杂时,制得的TiO2催化剂光催化效率最高,但与纯TiO2相比,镍掺杂会减弱TiO2的光催化效率。X射线衍射分析表明,未掺杂的TiO2以锐钛矿和金红石两种晶型混合存在,镍掺杂后TiO2的晶型几乎全为锐钛矿。镍掺杂后会减小TiO2粒子的尺寸,增大其比表面积。 相似文献
20.
Bethany J. Auten Huifang Lang Bert D. Chandler 《Applied catalysis. B, Environmental》2008,81(3-4):225-235
Polyamidoamine (PAMAM) dendrimers were used to template Pt, Au, and bimetallic Pt–Au dendrimer encapsulated nanoparticles (DENs) in solution. Adjusting the solution pH allowed for slow, spontaneous adsorption of the nanoparticles onto silica, alumina, and titania. After dendrimer removal, the catalysts were characterized with infrared spectroscopy of adsorbed CO and tested with CO oxidation catalysis. Infrared spectroscopy of the monometallic Pt catalysts showed a slight shift in the CO stretching frequency for the different supports. For the bimetallic catalysts, infrared spectra showed CO adsorbed on both Pt and on Au sites. Spectra collected during CO desorption showed substantial interactions between the two bands, confirming the presence of bimetallic particles on all the supports. The bimetallic catalysts were found to be more active than the monometallic catalysts and had lower apparent activation energies. The titania supported Pt–Au catalyst was resistant to deactivation during an extended treatment at 300 °C. Correlations between IR spectra and catalytic activity showed differences between the mono- and bimetallic materials and implicated a bimetallic Pt–Au ensemble at the catalytic active site. This is the first study to show that DENs are appropriate precursors for studying support effects on catalysis by metal nanoparticles, although the magnitude of the effects were small. 相似文献