共查询到20条相似文献，搜索用时 46 毫秒
1.
Enache DI Edwards JK Landon P Solsona-Espriu B Carley AF Herzing AA Watanabe M Kiely CJ Knight DW Hutchings GJ 《Science (New York, N.Y.)》2006,311(5759):362-365
The oxidation of alcohols to aldehydes with O2 in place of stoichiometric oxygen donors is a crucial process for the synthesis of fine chemicals. However, the catalysts that have been identified so far are relatively inactive with primary alkyl alcohols. We showed that Au/Pd-TiO2 catalysts give very high turnover frequencies (up to 270,000 turnovers per hour) for the oxidation of alcohols, including primary alkyl alcohols. The addition of Au to Pd nanocrystals improved the overall selectivity and, using scanning transmission electron microscopy combined with x-ray photoelectron spectroscopy, we showed that the Au-Pd nanocrystals were made up of a Au-rich core with a Pd-rich shell, indicating that the Au electronically influences the catalytic properties of Pd. 相似文献
2.
The prevailing view of CO oxidation on gold-titanium oxide (Au/TiO(2)) catalysts is that the reaction occurs on metal sites at the Au/TiO(2) interface. We observed dual catalytic sites at the perimeter of 3-nanometer Au particles supported on TiO(2) during CO oxidation. Infrared-kinetic measurements indicate that O-O bond scission is activated by the formation of a CO-O(2) complex at dual Ti-Au sites at the Au/TiO(2) interface. Density functional theory calculations, which provide the activation barriers for the formation and bond scission of the CO-O(2) complex, confirm this model as well as the measured apparent activation energy of 0.16 electron volt. The observation of sequential delivery and reaction of CO first from TiO(2) sites and then from Au sites indicates that catalytic activity occurs at the perimeter of Au nanoparticles. 相似文献
3.
Madix RJ 《Science (New York, N.Y.)》1986,233(4769):1159-1166
One of the primary objectives of modern surface chemistry of transition metals is the synthesis of surface compounds and complexes and the understanding of their reactivity, structure, and bonding. Such considerations are paramount for advancing understanding of catalysis, adhesion, organic thin-film growth, and electrocatalysis. On selected metals, particularly copper, silver, and gold, selective scission of X-H bonds (where X is oxygen, carbon, nitrogen, or sulfur) by surface-bound atomic oxygen occurs to form moderately stable species that can be isolated for further study. Selective oxidation reactions may occur heterogeneously by means of this novel oxygen- activated route. Furthermore, this selective chemistry offers a paradigm for synthesis of a wide variety of surface organometallic complexes, whose formation can be predicted from acid-base principles. These subjects are discussed in this article with emphasis on their role in catalytic oxidation cycles. 相似文献
4.
以Ni、Fe、Co等3种不同金属掺杂的TiO2介孔材料作催化剂对中药渣进行催化裂解,研究不同催化剂对生物油产率及油品的影响,采用热值分析和气质联用(GC-MS)分析裂解油的特性,利用N2吸附-脱附对催化剂进行表征。研究表明,Ni/TiO2的催化效果优于Fe/TiO2和Co/TiO2,Ni/TiO2作催化剂时,裂解油中脂肪烃和烷基苯的种数最多,且其中与汽油或柴油相近的组分占大多数,而芳香族化合物数量明显较少。在Ni/TiO2的催化作用下,大分子中的氧多以H2O分子的形式脱去,因而生物油中含水率较高,导致其热值降低。 相似文献
5.
以250W高压汞灯为光源，采用固定相TiO2,Pt/TiO2和Fe^3 /TiO2光化氧化降解聚乙烯醇（PVA），研究了不同表面处理方式对TiO2光催经活性的影响。结果表明，通过光化学沉积法在TiO2表面上担载1．0Pt制备的催化剂对PVA具有很好的光催化活性，此时光照60min后，PVA的光解率可达78．4％，但过量的Pt却降低了TiO2的光催化活性。研究还表明，高温灼烧法在TiO2表面上担载Fe^3 无助于提高TiO2降解PVA的光催化活性，随着Fe^3＋含量的升高，TiO2对PVA的光催化活性明显下降。结合SEM手段，认为TiO2活性的降低可能与其比表面积的降解有关。 相似文献
6.
为了获得具有网络结构和纳米级粒子的TiO2光催化材料,使之负载到活性炭纤维(ACF)上,并在紫外光的作用下,达到有效降低室内空气中污染物的目的,以钛酸丁酯(Ti(OC4H9)4为原料,乙酸和乙酰丙酮为水解催化剂,利用Sol-Gel方法制备凝胶,并利用超临界流体干燥手段制备TiO2气凝胶.溶胶-凝胶反应溶液的配比为Ti(OR)4∶ EtOH∶ H2O∶ AcOR∶ ACACH=20∶ 40∶ 5∶ 0.2∶ 2(体积比,mL),可在120min左右得到醇凝胶.将醇凝胶置于-21℃条件下陈化1～3d,然后在12h内自然升温至室温,24h内置于超临界流体中进行干燥,可以得到具有纳米结构的TiO2气凝胶.该气凝胶可用于制备ACF/TiO2复合材料. 相似文献
7.
Matthey D Wang JG Wendt S Matthiesen J Schaub R Laegsgaard E Hammer B Besenbacher F 《Science (New York, N.Y.)》2007,315(5819):1692-1696
We studied the nucleation of gold clusters on TiO2(110) surfaces in three different oxidation states by high-resolution scanning tunneling microscopy. The three TiO2(110) supports chosen were (i) reduced (having bridging oxygen vacancies), (ii) hydrated (having bridging hydroxyl groups), and (iii) oxidized (having oxygen adatoms). At room temperature, gold nanoclusters nucleate homogeneously on the terraces of the reduced and oxidized supports, whereas on the hydrated TiO2(110) surface, clusters form preferentially at the step edges. From interplay with density functional theory calculations, we identified two different gold-TiO2(110) adhesion mechanisms for the reduced and oxidized supports. The adhesion of gold clusters is strongest on the oxidized support, and the implications of this finding for catalytic applications are discussed. 相似文献
8.
Direct and selective replacement of carbon-hydrogen bonds with new bonds (such as C-C, C-O, and C-N) represents an important and long-standing goal in chemistry. These transformations have broad potential in synthesis because C-H bonds are ubiquitous in organic substances. At the same time, achieving selectivity among many different C-H bonds remains a challenge. Here, we focus on the functionalization of C-H bonds in complex organic substrates catalyzed by transition metal catalysts. We outline the key concepts and approaches aimed at achieving selectivity in complex settings and discuss the impact these reactions have on synthetic planning and strategy in organic synthesis. 相似文献
9.
以水热法制备8种MWCNTs-TiO2纳米复合材料,通过XRD、SEM、Raman、BET、FTIR等方法对复合材料进行表征。以罗丹明B为降解目标物,考察MWCNTs-TiO2纳米复合材料在不同光源辐照下的光催化活性以及MWCNTs的管径和管长对复合材料光催化活性的影响。结果表明:MWCNTs与TiO2结合紧密,TiO2微粒均匀分散在MWCNTs上,引入MWCNTs能提高TiO2的比表面积,且不会改变TiO2的锐钛矿晶相。光催化过程中,MWCNTs的引入抑制复合材料中光生载流子复合,进而提高复合材料的光催化效率。紫外光辐照下,MWCNTs的引入对TiO2光催化活性有显著提高;而在可见光辐照下,管长较短的MWCNTs与TiO2复合后表现出更好的光催化活性,且MWCNTs(SM4)-TiO2表现出最佳的可见光催化活性,主要由复合材料在紫外光与可见光辐照下不同的光催化反应机制所致。 相似文献
10.
The high performance of Au-CeO2 and Au-TiO2 catalysts in the water-gas shift (WGS) reaction (H2O + CO-->H2 + CO2) relies heavily on the direct participation of the oxide in the catalytic process. Although clean Au(111) is not catalytically active for the WGS, gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(111) or Cu(100). In TiO(2-x)/Au(111) and CeO(2-x)/Au(111), water dissociates on O vacancies of the oxide nanoparticles, CO adsorbs on Au sites located nearby, and subsequent reaction steps take place at the metal-oxide interface. In these inverse catalysts, the moderate chemical activity of bulk gold is coupled to that of a more reactive oxide. 相似文献
11.
Wahlström E Vestergaard EK Schaub R Rønnau A Vestergaard M Laegsgaard E Stensgaard I Besenbacher F 《Science (New York, N.Y.)》2004,303(5657):511-513
Diffusion of oxygen molecules on transition metal oxide surfaces plays a vital role for the understanding of catalysis and photocatalysis on these materials. By means of time-resolved scanning tunneling microscopy, we provide evidence for a charge transfer-induced diffusion mechanism for O2 molecules adsorbed on a rutile TiO2(110) surface. The O2 hopping rate depended on the number of surface donors (oxygen vacancies), which determines the density of conduction band electrons. These results may have implications for the understanding of oxidation processes on metal oxides in general. 相似文献
12.
RA Periana DJ Taube S Gamble H Taube T Satoh H Fujii 《Science (New York, N.Y.)》1998,280(5363):560-564
Platinum catalysts are reported for the direct, low-temperature, oxidative conversion of methane to a methanol derivative at greater than 70 percent one-pass yield based on methane. The catalysts are platinum complexes derived from the bidiazine ligand family that are stable, active, and selective for the oxidation of a carbon-hydrogen bond of methane to produce methyl esters. Mechanistic studies show that platinum(II) is the most active oxidation state of platinum for reaction with methane, and are consistent with reaction proceeding through carbon-hydrogen bond activation of methane to generate a platinum-methyl intermediate that is oxidized to generate the methyl ester product. 相似文献
13.
Schrock RR 《Science (New York, N.Y.)》1983,219(4580):13-18
Several well-characterized transition metal catalysts contain a metal-carbon double bond or a metal-carbon triple bond. In other homogeneous (or heterogeneous) catalyst systems in which the metal is likely to be in a relatively high oxidation state, such as molybdenum(VI) or tungsten(VI), metal-carbon multiple bonds may play an important role. Some recent results suggest that even supposedly well understood reactions such as ethylene polymerization may actually involve catalysts that behave as if they contained a metal-carbon double bond instead of a metal-carbon single bond. The chemistry of metal-carbon double and triple bonds should eventually complement and perhaps. overlap the known chemistry of complexes containing metal-oxygen double bonds or metal-nitrogen triple bonds, respectively; unique catalytic reactions involving carbon, nitrogen, and oxygen ligands multiply bonded to transition metals are therefore possible. 相似文献
14.
氧化钛/活性炭纳米光催化剂氧化苯酚的研究 总被引：1，自引：0，他引：1
以活性炭(AC)为载体,利用溶胶-凝胶工艺制备氧化钛(TiO2)溶胶,通过浸渍法制备负载型 TiO2／AC纳米光催化剂以及掺杂Fe3+和Cu2+的M-TiO2／AC纳米复合光催化剂。以紫外灯做光源,用制得的 TiO2／AC纳米光催化剂对苯酚溶液进行光催化氧化降解试验,并研究了掺杂Fe3+和Cu2+的M-TiO2／AC纳米复合光催化剂对苯酚的催化活性。结果表明,在紫外光条件下,TiO2／AC纳米光催化剂对苯酚的降解率达99％,较日光条件下高;掺杂Fe3+能提高M-TiO2／AC纳米复合光催化剂对苯酚的催化活性。 相似文献
15.
光催化氧化法降解有机磷农药的动力学研究 总被引：1，自引：0，他引：1
[目的]进一步对有机磷敌敌畏农药光催化降解的反应动力学进行研究。[方法]采用Sol-gel法在玻璃圆形反应器上镀制了TiO2膜,以紫外/二氧化钛膜(UV/TiO2)光催化氧化法来降解有机磷农药敌敌畏溶液,探讨了光催化反应时间、溶液的初始浓度对降解敌敌畏溶液的影响。[结果]由玻璃筒负载的TiO2膜对单一的敌敌畏溶液具有很好的光催化降解效果,TiO2膜具有很好的光催化活性。敌敌畏溶液的初始浓度越低,光催化降解效果越好,经90 min光催化氧化处理后,不同浓度敌敌畏的降解率都能达到90%以上。动力学研究表明,敌敌畏的降解速率对敌敌畏浓度为一级反应,反应速率方程为:Ct=C0e-0.0719t(mg/L)。[结论]光催化降解有机磷农药敌敌畏溶液具有很好的降解效果。 相似文献
16.
以钛酸四丁酯为钛源负载活性炭制备了TiO2/C复合催化剂,从催化剂的用量、循环使用次数以及与P25比较等几个方面分别考察了该复合催化剂的催化降解甲基橙的活性.实验结果表明,TiO2/C复合催化剂提高了催化活性. 相似文献
17.
Over H Kim YD Seitsonen AP Wendt S Lundgren E Schmid M Varga P Morgante A Ertl G 《Science (New York, N.Y.)》2000,287(5457):1474-1476
The structure of RuO(2)(110) and the mechanism for catalytic carbon monoxide oxidation on this surface were studied by low-energy electron diffraction, scanning tunneling microscopy, and density-functional calculations. The RuO(2)(110) surface exposes bridging oxygen atoms and ruthenium atoms not capped by oxygen. The latter act as coordinatively unsaturated sites-a hypothesis introduced long ago to account for the catalytic activity of oxide surfaces-onto which carbon monoxide can chemisorb and from where it can react with neighboring lattice-oxygen to carbon dioxide. Under steady-state conditions, the consumed lattice-oxygen is continuously restored by oxygen uptake from the gas phase. The results provide atomic-scale verification of a general mechanism originally proposed by Mars and van Krevelen in 1954 and are likely to be of general relevance for the mechanism of catalytic reactions at oxide surfaces. 相似文献
18.
[目的]研究竹活性炭比表面积及其孔径对TiO2/BAC光催化降解甲醛性能的影响。[方法]以竹子为原料,按照不同浸渍比,用磷酸活化法制备不同孔径和比表面积的系列竹活性炭（BAC）作为载体;通过溶胶凝胶法制备负载型光催化剂（TiO2/BAC）,以水溶液中的甲醛作为目标污染物,考察所得的一系列负载型光催化剂的光催化性能;采用氮气吸附、SEM进行表征,研究了竹活性炭的孔径和比表面积对负载型光催化剂性能的影响。[结果]竹活性炭吸附和TiO2光解的协同效应使TiO2/BAC光催化剂对水溶液中甲醛的处理效率显著提高;比表面积较大、微孔较多、平均孔径为2~3 nm的竹活性炭有利于TiO2的负载,制备得到的复合光催化活性较高。[结论]为TiO2光催化剂的固化负载研究提供了理论依据。 相似文献
19.
Carbon-fluorine bonds are among the most unreactive functionalities in chemistry. Interest in their activation arises in part from the high global warming potentials of anthropogenic polyfluoroorganic compounds. Conversion to carbon-hydrogen bonds (hydrodefluorination) is the simplest modification of carbon-fluorine bonds, but efficient catalytic hydrodefluorination of perfluoroalkyl groups has been an unmet challenge. We report a class of carborane-supported, highly electrophilic silylium compounds that act as long-lived catalysts for hydrodefluorination of trifluoromethyl and nonafluorobutyl groups by widely accessible silanes under mild conditions. The reactions are completely selective for aliphatic carbon-fluorine bonds in preference to aromatic carbon-fluorine bonds. 相似文献
20.
Although n-type titanium dioxide (TiO2) is a promising substrate for photogeneration of hydrogen from water, most attempts at doping this material so that it absorbs light in the visible region of the solar spectrum have met with limited success. We synthesized a chemically modified n-type TiO2 by controlled combustion of Ti metal in a natural gas flame. This material, in which carbon substitutes for some of the lattice oxygen atoms, absorbs light at wavelengths below 535 nanometers and has a lower band-gap energy than rutile (2.32 versus 3.00 electron volts). At an applied potential of 0.3 volt, chemically modified n-type TiO2 performs water splitting with a total conversion efficiency of 11% and a maximum photoconversion efficiency of 8.35% when illuminated at 40 milliwatts per square centimeter. The latter value compares favorably with a maximum photoconversion efficiency of 1% for n-type TiO2 biased at 0.6 volt. 相似文献