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1.
Pt, Pt–Sn and Pt–W supported on γ‐Al2O3 were prepared and characterized by H2 chemisorption, TEM, TPR, test reactions of n‐C8 reforming (500°C), cyclohexane dehydrogenation (315°C) and n‐C5 isomerization (500°C), and TPO of the used catalysts. Pt is completely reduced to Pt0, but only a small fraction of Sn and of W oxides are reduced to metal. The second element decreases the metallic properties
of Pt (H2 chemisorption and dehydrogenation activity) but increases dehydrocyclization and stability. In spite of the large decrease
in dehydrogenation activity of Pt in the bimetallics, the metallic function is not the controlling function of the bifunctional
mechanisms of dehydrocyclization. Pt–Sn/Al2O3 is the best catalyst with the highest acid to metallic functions ratio (due to its lower metallic activity) presenting a
xylenes distribution different from the other catalysts. The acid function of Pt–Sn/Al2O3 is tuned in order to increase isomerization and cyclization and to decrease cracking, as compared to Pt and Pt–W.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Acetylene (C2H2) is a reactive molecule with a low C : H stoichiometry that can be used to evaluate aspects of the resistance of metal-based catalysts to the formation of carbonaceous residue (coking). Herein we summarize our results for C2H2 chemisorption and thermal reaction on four well-defined, ordered surface alloys of Pt–Sn prepared by Sn vapor deposition on Pt(100) and Pt(111) single crystals under UHV conditions. While chemisorption of C2H2 under UHV conditions on Pt is completely irreversible, i.e., thermal decomposition leads to complete conversion of the chemisorbed monolayer into surface carbon, alloying with Sn strongly reduces the amount of carbon thus formed. In addition, the temperature for complete dehydrogenation of the carbonaceous residue formed from acetylene decomposition (polymerization) is increased by up to 100 K, from 760 to 860 K. Both of these phenomena are consistent with observations of increased lifetimes and decreased coking for technical Pt–Sn bimetallic catalysts compared to Pt catalysts used for hydrocarbon conversion reactions. 相似文献
3.
随着对丙烯需求的日渐增加,由丙烷催化脱氢制丙烯来实现对丙烯的增产,已成为增产丙烯的重要手段之一。利用水热法制备一系列不同Sn掺杂量的Sn-MFI载体,采用等体积浸渍法制备相同Pt负载量的Pt/Sn-MFI催化剂,通过XRD、N2吸附-脱附、FT-IR和H2-TPR等表征考察不同Sn掺杂量的催化剂对丙烷催化脱氢性能的影响。结果表明,Pt/Sn1. 3%-MFI催化剂具有最高的催化丙烷脱氢活性和稳定性,丙烷初始转化率为43. 3%,丙烯选择性为98. 9%。反应360 min后,丙烷转化率为25. 1%,选择性保持不变。 相似文献
4.
G. Aguilar‐Ríos P. Salas M.A. Valenzuela H. Armendáriz J.A. Wang J. Salmones 《Catalysis Letters》1999,60(1-2):21-25
Propane dehydrogenation was carried out in hydrogen and steam as reaction media on Pt/MgAl2O4 and Pt–Sn/ MgAl2O4 catalysts. A wide range of Pt and Pt–Sn concentrations was explored. Monometallic Pt catalysts were completely poisoned by
steam. Concerning bimetallic Pt–Sn catalysts, tin played an important role related to the activation of platinum particles
when the reaction was carried out in steam. On the other hand, tin inhibited cracking reactions leading to an increase of
catalysts stability. Activation energy in hydrogen was the same for monometallic and bimetallic catalysts: 22 kcal/mol; while
for the reaction in steam, values ranging from 10 to 15 kcal/mol were obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
6.
采用铝箔盐酸回流-油柱成型法制备了不同Sn掺杂量的Sn(x)-θ-Al_2O_3载体,并采用真空浸渍法制备了Pt/Sn(x)-θ-Al_2O_3催化剂。对制备的催化剂进行XRD、N2物理吸附-脱附、NH3-TPD、H2-TPR和TG-DTA表征,研究了在载体中掺入助剂Sn对Pt/Sn(x)-θ-Al_2O_3催化剂结构及丙烷脱氢催化反应性能的影响。结果表明,在载体制备过程中掺入Sn,可以提高催化剂反应活性和产物选择性,当Sn掺杂质量分数为1.0%时,催化剂具有最优的丙烷脱氢反应性能,15 h的平均丙烷转化率为32.4%,平均丙烯选择性为95.5%。 相似文献
7.
在Pt—Sn/Al2O3催化剂上丙烷脱氢反应动力学 总被引:3,自引:0,他引:3
研究了丙烷在Pt-Sm/Al2O3催化剂上的脱氢反应动力学。在氮烃比1.0,反应温度460~500℃范围内,验证了该反应机理,获得反应速率表达式。 相似文献
8.
Pt催化丙烷脱氢过程中结焦反应的粒径效应与Sn的作用 总被引:1,自引:0,他引:1
用乙二醇还原法制备了Pt颗粒平均粒径分别为2.0、4.6、12.1 nm的Pt/Al2O3催化剂,同时用浸渍法制备了PtSn/Al2O3双金属催化剂,并考察了各催化剂在丙烷脱氢过程中的结焦行为。分别用H2化学吸附、透射电镜、热重分析、元素分析、红外光谱、拉曼光谱等手段对催化剂进行了表征。表征结果显示,催化剂金属上的结焦速率与Pt金属颗粒粒径密切相关。具有较小Pt颗粒的催化剂金属上的结焦速率明显大于具有较大Pt颗粒的催化剂。具有较小Pt颗粒的催化剂上生成的焦含有较少的氢,其石墨化程度也较高。本研究中PtSn/Al2O3催化剂金属上的结焦速率高于Pt/Al2O3催化剂,并且在双金属上生成的焦具有更高的石墨化程度。结合Pt/Al2O3催化剂上的结焦机理,对高性能丙烷脱氢催化剂提出了新的概念设计。 相似文献
9.
Direct methanol fuel cell (DMFC) electrode catalysts with improved electrochemical properties have been prepared by dispersing platinum–tin (Pt–Sn) nanoparticles onto graphene sheets. During the deposition, a majority of the oxygenated functional groups on the graphene oxide nanosheets were removed, resulting in the formation of graphene. Microstructural characterization shows that metallic Pt, Pt–Sn alloy and tin dioxide (SnO2) nanoparticles were distributed on the graphene sheets, representing different lattice planes during the synthetic process. In terms of the electrocatalytic properties, graphene-supported Pt–Sn and graphene-supported Pt catalysts exhibited much higher current densities compared with that of commercial carbon black-supported Pt catalysts. Graphene-supported Pt–Sn increased the electrocatalytic activity, which is strongly influenced by the addition of Sn in its alloyed and oxidized forms, boosting the reaction more readily because of the lower oxidation potential. 相似文献
10.
A. Kelaidopoulou E. Abelidou G. Kokkinidis 《Journal of Applied Electrochemistry》1999,29(11):1255-1261
Platinum particles dispersed in a poly(2-hydroxy-3-aminophenazine) film (pHAPh/Pt) provide a better catalyst than smooth Pt for the electrooxidation of methanol and formic acid in perchloric acid aqueous solutions. The catalytic activity of the Pt particles is further enhanced when Sn is codeposited in the polymer film. In the case of formic acid oxidation, the activity of Pt nanoparticles is influenced by adatoms of Tl, Pb and Bi deposited undepotential conditions. The upd-modified Pt particles are much more active than bare Pt particles. The morphology and identity of the metallic dispersion were examined by transmission electron microscopy. 相似文献
11.
A comparative study between carbon supported Platinum–Tin (Pt–Snsyn), synthesized via the carbonyl route, and the commercial (Pt3Sn) from E–TEK is reported. The electro-oxidation of methanol and adsorbed CO, in sulphuric acid medium, were used as probes to evaluate the performance of these electrocatalysts. In-line differential mass spectrometry (DEMS) was used for this purpose. Both nanoparticulate materials had a mean particle size of <d> = 1.68 ± 0.72 nm, and <d> = 3.58 ± 1.94 nm, respectively. It is demonstrated that, under the same experimental conditions, our homemade Pt–Snsyn is less sensitive to poisoning by CO. This observation was again verified during the oxidation of methanol. These results are discussed in terms of the local disorder of the particles surface atoms, favourably induced by size effect and the preparation route employed. 相似文献
12.
C.L. Li O. Novaro X. Bokhimi E. Muñoz J.L. Boldú J.A. Wang T. López R. Gómez N. Batina 《Catalysis Letters》2000,65(4):209-216
The characterization of the coke deposited on an industrial Pt–Sn/γ‐Al2O3 catalyst, used in a continuous reforming process, was performed with AFM, XRD, FTIR, EPR, NMR, TG‐DTG and DTA techniques.
Composition, structure and location of the coke on the catalyst were investigated. The coke was predominantly deposited on
the catalyst surface and in the interstices between the catalyst particles. Its content increased along the reactor from top
to bottom. Coke was deposited in the form of uniform films and clusters of three‐dimensional disks with diameters between
0.12 and 0.18 μm. It had a pseudo‐graphite structure produced by the dehydrogenation and polymerization of the aromatic precursor
compounds. The coked catalyst showed a good combustion behavior; it was regenerated below 550°C. These results are important
to elucidate the coke formation mechanism, to generate new continuous reforming catalysts, and to optimize the reactor operation
parameters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
《Catalysis communications》2001,2(11-12):369-374
Platinum and Platinum–tin bimetallic catalysts supported on alumina were prepared by co-impregnation of both metallic precursors on the support and used as catalysts for the oxidation of SO2. Platinum dispersion was determined by means of H2–O2 titration. Tin addition (1 and 2 wt%) only slightly decreased the exposed platinum atoms suggesting that tin is mainly over the support. At temperatures lower than 300 °C, SO2 did not react with oxygen. Nevertheless, when the temperature was increased, the SO2 oxidation began. The ignition temperatures for SO2 oxidation (taken at 50% conversion) were 345 °C for 1% Pt/Al2O3 and 520 °C for 1% Pt–2% Sn/Al2O3. The strong displacement on activity suggests that tin plays an important role as inhibitor of the SO2 oxidation reaction. 相似文献
14.
Infrared spectra of adsorbed CO have been used as a probe to monitor changes in Pt site character induced by the coking of
Pt/Al2O3 and Pt–Sn/Al2O3 catalysts by heat treatment in heptane/hydrogen. Four distinguishable types of Pt site for the linear adsorption of CO on
Pt/Al2O3 were poisoned to different extents showing the heterogeneity of the exposed Pt atoms. The lowest coordination Pt atoms (ν(CO)
< 2030 cm−1) were unpoisoned whereas the highest coordination sites in large ensembles of Pt atoms (2080 cm−1) were highly poisoned, as were sites of intermediate coordination (2030–2060 cm−1). Sites in smaller two‐dimensional ensembles of Pt atoms (2060–2065 cm−1) were partially poisoned, as were sites for the adsorption of CO in a bridging configuration. The addition of Sn blocked
the lowest coordination sites and destroyed large ensembles of Pt by a geometric dilution effect. The poisoning of other sites
by coke was impeded by Sn, this effect being magnified for Cl‐containing catalyst. Oxidation or oxychlorination of coked catalyst
at 823 K followed by reduction completely removed coke from the catalyst surfaces.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
《Fuel Processing Technology》1994,41(1):13-25
This work presents a detailed study of coke deposition on a PtSn catalyst under industrial conditions. The spent catalyst was submitted to Soxhlet extraction and the “soluble coke” was characterized by means of IR, UV and GC-MS. The catalyst before and after coke extraction was characterized by means of IR, carbon content and temperature-programmed oxidation (TPO). Coke formation on the catalyst involves several processes: (i) successive dehydrogenation/cyclization of alkyl chains (polyene route); (ii) n-alkane oligomerization; (iii) Diels-Alder-type reactions. The structure of insoluble coke is quite different from that of soluble coke: the elimination of the latter one causes disappearance of the low-temperature oxidation zone (TPO). Soluble coke contains dominant proportion of aliphatic groups whereas polyaromatic structures predominate in insoluble coke. 相似文献
16.
Pt–Sn/ALa10 and Pt–Pb/ALa10 catalysts (10 wt% La2O3) were studied in the selective hydrogenation of crotonaldehyde. Oxidized Pt2+ and reduced Pt0 species were identified by XPS on the bimetallic catalysts. High selectivity to crotylalcohol was obtained on the Pt–Pb/ALa10 catalyst where an electron transfer effect from Pb to Pt was proposed. For the Pt–Sn/ALa10 catalyst the formation of Pt–SnO x –La2O3 complexes showing low activity and low selectivity was inferred. 相似文献
17.
采用原子吸收光谱法标定Sn、中子活化法标定Ru、Ir、Pt、Pd,获得系列回归方程:W_(pd)=4.4816×10 ̄(-5)I_(pd)+0.0202(g/m ̄2)建立了一套简便的快速定量测定涂层组分的方法。 相似文献
18.
本文在阐明计算机模拟与专家系统基本概念的基础上,着重综述了国内外关于棉花的生育期、叶龄、不合与呼吸作用等6个方面的模拟模型,提出了现有模型存在的问题以及今后的发展方向与前景。 相似文献
19.
采用铝箔盐酸回流-油柱成型法制备了不同Sn掺杂量的Sn(x)-θ-Al2O3载体,并采用真空浸渍法制备了Pt/Sn(x)-θ-Al2O3催化剂。对制备的催化剂进行XRD、N2物理吸附-脱附、NH3-TPD、H2-TPR和TG-DTA表征,研究了在载体中掺入助剂Sn对Pt/Sn(x)-θ-Al2O3催化剂结构及丙烷脱氢催化反应性能的影响。结果表明,在载体制备过程中掺入Sn,可以提高催化剂反应活性和产物选择性,当Sn掺杂质量分数为1.0%时,催化剂具有最优的丙烷脱氢反应性能,15 h的平均丙烷转化率为32.4%,平均丙烯选择性为95.5%。 相似文献
20.