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1.
Carbon nanomaterials with graphene structure (single- and multiwall nanotubes and nanofibers) after oxidizing by a mixture of sulfuric and nitric acids and presumable introducing of carboxyl groups can be used as carrying agents of hydrogenation catalysts. Platinum in a concentration which should not exceed 10 wt % can be fixed using H2PtCl6 as a precursor in presence of an organic base. Catalysts based on these nanomaterials with the average size of platinum particles 6–8 nm exceed in activity the Pt/C catalyst with the size of platinum particles 65–70 nm, but are inferior to catalysts based on fullerene black with the average size of platinum particles 3–4 nm. 相似文献
2.
The effect of the reduction procedure of graphite oxide (GO) on activity of platinum supported catalysts in liquid-phase hydrogenation of nitrobenzene and dec-1-ene was studied. The following methods were applied to prepare the catalysts: simultaneous reduction of graphite oxide and H2PtCl6; deposition of platinum on graphite oxide which was preliminary subjected to reduction with sodium tetrahydroborate or hydrazine hydrate, or to thermal reduction at 1000 and 1050 °С. It was shown that at equal Pt particles size of ca. 2 nm the catalyst supported on thermally reduced graphite oxide is more active in the model reactions than the catalysts supported on chemically reduced graphite oxide. The catalyst prepared by simultaneous reduction was the least active. 相似文献
3.
Platinum clusters protected by polymerized micelles were prepared by radical polymerization of unsaturated surfactants which were involved in micelle-protected platinum clusters. The micelle-protected platinum clusters were successfully prepared by photoreduction of hexachloroplatinic acid in water in the presence of unsaturated surfactants. The platinum clusters thus obtained were characterized by electron microscopy and IR and 1H-NMR spectroscopies. The average diameter of the platinum particles was about 1 nm by electron microscopy, and the polymerization was confirmed by IR and 1H-NMR spectra. The platinum clusters thus obtained proved to be highly active catalysts for visible light-induced hydrogen generation in the system of EDTA/Ru(bpy)3 2+/MV2+. The polymerized micelle-protected platinum clusters showed higher catalytic activity than the linear polymer-protected one. The catalytic activity was affected by the electric charge of the surfactants in the polymerized micelle-protected platinum clusters. Nonionic polymers were superior to those having anionic and cationic hydrophilic groups from the viewpoint of catalytic activity. The nonionic polymerized micelle forms rigid hydrophobic cores which help charge separation and the formation of a sequential potential field. 相似文献
4.
Fixation of platinum from H2PtCl6 on fullerene black through non-conjugate double bonds or hydroxyl groups created on their base in the presence of an organic base with postreduction by formate ions allows platinum particles of size 3–4 nm to be obtained. These compositions catalyze 1-decene and nitrobenzene hydrogenation and exceed in activity the traditional catalyst Pt/C with platinum particle size of 70–80 nm. The average size of the fixed platinum particles affects the catalytic activity stronger than the specific surface area and the electron conduction of the carrying agent. 相似文献
5.
Kurzina I. A. Cadete Santos Aires F. J. Bertolini J. C. 《Theoretical and Experimental Chemistry》2004,40(4):241-245
We have studied platinum catalysts supported on silicon nitride Si3N4 in the process of deep oxidation of methane. We have used transmission electron microscopy and X-ray photoelectron spectroscopy to study the surface properties of the Pt/Si3N4 samples before and after the catalytic reaction. We have established that the metallic platinum particles in freshly prepared systems are characterized by average sizes of 1.7-5.3 nm, while after the catalytic reaction we observe formation of Pt crystallites up to 30-70 nm in size. We hypothesize that the observed deactivation of platinum catalysts in deep oxidation of methane is connected with crystallization of the metallic particles and their entrainment with the reaction products during catalysis. 相似文献
6.
Mario Castiglioni Stefano Deabate Edoardo Garrone Roberto Giordano Barbara Onida Giovanni Predieri Enrico Sappa 《Journal of Cluster Science》1997,8(3):381-405
The tetrahedral hydridic clusters H2Ru4(CO)13 (1), H2FeRu3(CO)13 (2), and HRuCo3(CO)12 (3) were supported on Chromosorb P and activated under dihydrogen flow. The resulting metal particles are active in the hydrogenation of pentenes, cyclic monoenenes and dienes, benzene, and toluene; these catalysts are effective under mild conditions and with a low metal loading. Experiments under dinitrogen showed that complex hydrogenation-dehydrogenation processes occur, as already observed for the same clusters during the homogeneous hydrogenation of cyclohexadienes. After the gas-chromatographic catalytic runs with cluster 1 as precursor, TEM microscopy showed the presence of very small supported metal particles (mean size 7.5 nm). The decomposition of cluster 1 to metal particles upon thermal treatment on Aerosil under vacuum or under dihydrogen was followed by means of IR spectroscopy; this catalyst hydrogenates benzene at room temperature with 100% conversion in a very short time (calculated activity was about 3200 TOFs). 相似文献
7.
Wenbao Zhang Chunhua Luo Caihua Wang Yumin Cui Kaibin Tang 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2016,90(13):2616-2618
Platinum clusters were supported on/in HLaNb2O7 nanosheets by topochemical reaction strategy for the first time. The as-prepared samples were analyzed using ICP OES and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms and X-ray photoelectron spectroscopy. The results showed that HLaNb2O7 nanosheets were modified with platinum clusters with good monodispersity. The product was a mesoporous solid with broad pore size distribution and large surface area. The oxidation state of platinum was zero and the size of Pt clusters was only about 1–2 nm. This study provides a novel approach to support metal clusters on layered compounds. 相似文献
8.
Vasile I Parvulescu Viorica Parvulescu Uwe Endruschat Pascal Granger Ryan Richards 《Chemphyschem》2007,8(5):666-678
Sol‐gel synthesis of silica and silica–tantalum oxide embedded platinum nanoparticles is carried out using Pt colloids as templates. These colloids are prepared by reduction with Na[AlEt3H] and stabilized with different ligands (ammonium halide derivatives, non‐ionic surfactants with polyether chains, and 2‐hydroxy‐propionic acid). The aim of the present study is to prepare mesoporous silica embedded Pt colloids combining the “precursor concept” with the model of catalyst preparation using preformed spheres. Nanoparticles of Pt incorporated in high surface area mesoporous materials are formed after calcination. Further, it is observed that calcination of these catalysts causes partial aggregation and oxidation of the parent colloids, a process that is largely dependent on the nature of the stabilizing ligands. Several methods have been used for characterization of these materials: adsorption‐desorption isotherms at 77 K, H2 chemisorption, X‐ray diffraction(XRD), 29Si and 13C magic angle spinning (MAS) NMR, ammonia diffuse reflectance Fourier transform infrared spectroscopy (NH3‐DRIFT), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS). It is found that both metal oxide systems exhibit Brønsted acidity (weaker for silica and quite strong for silica–tantalum oxide). In addition, NH3‐DRIFT experiments demonstrate the oxidative properties of the surface. Part of the adsorbed NH4+ species is oxidized to N2O. Testing these catalysts in the reduction of NO and NO2 with isopentane under lean conditions indicate that the activity of these catalysts is indeed dependent on the size of the platinum particles, with those of size 8–10 nm demonstrating the best results. The support likely contributes to this effect, particularly after Ta incorporation into silica. 相似文献
9.
N. B. Shitova V. A. Drozdov P. E. Kolosov M. D. Smolikov 《Reaction Kinetics and Catalysis Letters》2000,41(5):720-728
The formation of Pt/γ-Al2O3 and Pt/C catalysts from platinum carbonyl clusters H2[Pt3(CO)6]n (n = 2, 5) is studied. The strength of interaction between clusters (strong Lewis bases) and the support and the state of platinum
in catalysts are governed by the acceptor strength of the support. The formation of a stable platinum compound with a surface
of γ-Al2O3 (strong Lewis acid) is shown for a Pt/γ-Al2O3 catalyst by the method of radial distribution functions. In a Pt/C catalyst containing the same amount of Pt supported on
a carbon material known to be a weaker acceptor, metallic platinum is formed along with surface-bonded platinum. Proceeding
from the existence of the active phase of catalysts in the form of a surface platinum complex and platinum crystallites, the
properties of catalysts are discussed in the complete oxidation of methane and the dehydrogenation of cyclohexane, as well
as the high dispersity of platinum and its thermal stability 相似文献
10.
N. V. Smirnova A. B. Kuriganova D. V. Leont’eva I. N. Leont’ev A. S. Mikheikin 《Kinetics and Catalysis》2013,54(2):255-262
The structural and electrocatalytic properties of Pt/C and Pt-Ni/C catalysts prepared by the electrochemical dispersion of metals under the action of pulse alternating current in a solution of NaOH were studied. Using X-ray diffraction analysis and scanning and transmission electron microscopy, it was found that the synthesized Pt/C catalysts contained active constituent particles with the average size D 111 = 10.6 nm with a predominantly cubic shape. Upon the dispersion of a Pt3Ni alloy, the Pt-Ni/C catalyst containing the particles of a stoichiometric metal phase of Pt3Ni (D 111 = 9.6 nm) and also Pt x Ni particles (x > 3) enriched in platinum (D 111 = 8.1 nm). The synthesized catalysts possessed high electrocatalytic activity and stability in the reaction of methanol oxidation. The characteristics of these catalysts as anodes in the membrane-electronic unit of a hydrogen-air solid-polymer fuel cell were studied. 相似文献
11.
高度分散的Pt/TiO2的制备及光催化活性 总被引:1,自引:0,他引:1
用柠檬酸作为空穴捕获剂和分散剂, 在温和条件下用光催化还原法将3 nm金属铂沉积在7 nm的锐钛矿相及介孔二氧化钛纳米晶表面. TEM观察显示铂的负载量为w=1.0%时, 多数二氧化钛纳米晶表面沉积了岛状的铂团簇, XPS和电子衍射结果表明铂以游离态存在. 负载w=1.0%~2.0%铂的TiO2在苯酚光氧化反应中活性显著提高. Pt/TiO2在氨气中经550 ℃氮化, 可制得氮掺杂的Pt/TiO2可见光光催化剂, 氮化过程中铂团簇没有烧结和显著长大. 相似文献
12.
Metallic platinum was photodeposited on TiO2 particles, and morphological characteristics of the Pt/TiO2 catalyst were determined. The dispersion of metallic platinum was uniform and did not alter the morphology of the TiO2 particles. However, absorbance of the Pt/TiO2 catalyst for light with wavelength more than 400 nm was significantly improved by the addition of metallic platinum. Gaseous acetone was decomposed in an annular photoreactor coated with TiO2 or Pt/TiO2 catalysts using a UV or a fluorescent lamp as light source. The decomposition of acetone with the application of a UV lamp was obviously enhanced for experiments conducted with Pt/TiO2 catalyst. Decomposition of acetone was promoted considerably with increasing oxygen concentration for experiments conducted with oxygen less than 50,000 ppmv, yet the decomposition of acetone was kept relatively constant for experiments conducted with oxygen above 50,000 ppmv. On the basis of the mass balance for carbon species, the amount of organic intermediates formed for experiments conducted under various conditions was found to be minimal. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 209–216, 2008 相似文献
13.
Catalytically Active Rh Sub‐Nanoclusters on TiO2 for CO Oxidation at Cryogenic Temperatures 下载免费PDF全文
Hongling Guan Dr. Jian Lin Dr. Botao Qiao Dr. Xiaofeng Yang Dr. Lin Li Dr. Shu Miao Prof. Jingyue Liu Prof. Aiqin Wang Prof. Xiaodong Wang Prof. Tao Zhang 《Angewandte Chemie (International ed. in English)》2016,55(8):2820-2824
The discovery that gold catalysts could be active for CO oxidation at cryogenic temperatures has ignited much excitement in nanocatalysis. Whether the alternative Pt group metal (PGM) catalysts can exhibit such high performance is an interesting research issue. So far, no PGM catalyst shows activity for CO oxidation at cryogenic temperatures. In this work, we report a sub‐nano Rh/TiO2 catalyst that can completely convert CO at 223 K. This catalyst exhibits at least three orders of magnitude higher turnover frequency (TOF) than the best Rh‐based catalysts and comparable to the well‐known Au/TiO2 for CO oxidation. The specific size range of 0.4–0.8 nm Rh clusters is critical to the facile activation of O2 over the Rh–TiO2 interface in a form of Rh?O?O?Ti (superoxide). This superoxide is ready to react with the CO adsorbed on TiO2 sites at cryogenic temperatures. 相似文献
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16.
随着稀薄燃烧(lean-burn)发动机的推广使用和环保法规的日趋严格,消除稀燃尾气中的氮氧化物(N O x)已刻不容缓。N O x储存还原技术被认为是最具应用前景的方法之一[1,2]。目前,对Pt/BaA l2O4-A l2O3体系中N O x储存与还原机制的研究较多[1 ̄4],但对该体系中微量铂物种微观结构及其与性能的关系研究较少,这主要是由于Pt含量(0.1w t% ̄0.5wt%)太低,分散度较高,使表征方法受到很大限制。本文采用共沉淀-浸渍法制得具有较高比表面积和热稳定性的N O x储存还原催化剂Pt/BaA l2O4-A l2O3,应用荧光X-射线吸收精细结构方法(Fluores-cence-… 相似文献
17.
A. A. Shutilov G. A. Zenkovets S. V. Tsybulya V. Yu. Gavrilov G. N. Kryukova 《Kinetics and Catalysis》2012,53(3):409-418
The effect of the microstructure of titanium dioxide on the structure, thermal stability, and catalytic properties of supported CuO/TiO2 and CuO/(CeO2-TiO2) catalysts in CO oxidation was studied. The formation of a nanocrystalline structure was found in the CuO/TiO2 catalysts calcined at 500°C. This nanocrystalline structure consisted of aggregated fine anatase particles about 10 nm in size and interblock boundaries between them, in which Cu2+ ions were stabilized. Heat treatment of this catalyst at 700°C led to a change in its microstructure with the formation of fine CuO particles 2.5–3 nm in size, which were strongly bound to the surface of TiO2 (anatase) with a regular well-ordered crystal structure. In the CuO/(CeO2-TiO2) catalysts, the nanocrystalline structure of anatase was thermally more stable than in the CuO/TiO2 catalyst, and it persisted up to 700°C. The study of the catalytic properties of the resulting catalysts showed that the CuO/(CeO2-TiO2) catalysts with the nanocrystalline structure of anatase were characterized by the high-est activity in CO oxidation to CO2. 相似文献
18.
Synthesis of Supported Ultrafine Non‐noble Subnanometer‐Scale Metal Particles Derived from Metal–Organic Frameworks as Highly Efficient Heterogeneous Catalysts 下载免费PDF全文
Xinchen Kang Prof. Huizhen Liu Dr. Minqiang Hou Xiaofu Sun Hongling Han Prof. Tao Jiang Dr. Zhaofu Zhang Prof. Buxing Han 《Angewandte Chemie (International ed. in English)》2016,55(3):1080-1084
The properties of supported non‐noble metal particles with a size of less than 1 nm are unknown because their synthesis is a challenge. A strategy has now been created to immobilize ultrafine non‐noble metal particles on supports using metal–organic frameworks (MOFs) as metal precursors. Ni/SiO2 and Co/SiO2 catalysts were synthesized with an average metal particle size of 0.9 nm. The metal nanoparticles were immobilized uniformly on the support with a metal loading of about 20 wt %. Interestingly, the ultrafine non‐noble metal particles exhibited very high activity for liquid‐phase hydrogenation of benzene to cyclohexane even at 80 °C, while Ni/SiO2 with larger Ni particles fabricated by a conventional method was not active under the same conditions. 相似文献
19.
A. M. Gololobov I. E. Bekk G. O. Bragina V. I. Zaikovskii A. B. Ayupov N. S. Telegina V. I. Bukhtiyarov A. Yu. Stakheev 《Kinetics and Catalysis》2009,50(6):830-836
The specific activity of 0.8% Pt/Al2O3 catalysts in the deep oxidation of C1–C6
n-alkanes increases with an increase in the Pt particle size from 1 to 3–4 nm. Further coarsening of the particles insignificantly
changes the specific activity. The size effect was studied for a series of catalysts containing platinum nanoparticles 1 to
11 nm in diameter. The specific catalytic activity variation range depends on the size of the reacting hydrocarbon molecules.
As the platinum particle size increases, the specific catalytic activity increases 3–4 times for the oxidation of CH4 and C2H6 and by a factor of 20–30 for the oxidation of n-C4H10 and n-C6H14. 相似文献
20.
Lucie Smoláková árka Botková Libor apek Peter Priecel Agnieszka Soltysek Martin Kout Lenka Matějová 《催化学报》2013,34(10):1905-1913
Ni/Al2O3 catalysts for oxidative dehydrogenation(ODH) of ethane were prepared by impregnation of Al2O3 with nickel acetate or nickel nitrate,and by mechanical mixing of NiO and Al2O3.The Ni-based catalysts were characterized by N2 adsorption-desorption,X-ray diffraction,diffuse reflectance UV-visible diffuse reflectance spectroscopy,and temperature-programmed reduction of hydrogen.The results showed that formation of crystalline NiO particles with a size of < 8 nm and/or non-stoichiometric NiO species in the Ni/Al2O3 catalysts led to more active species in ODH of ethane under the investigated reaction conditions.In contrast,tetrahedral Ni species present in the catalysts led to higher selectivity for ethene.Formation of large crystalline NiO particles(22-32 nm) over Ni/Al2O3 catalysts decreased the selectivity for ethene. 相似文献