A kinetic study of the liquid-phase hydrogenation of citral on Au/TiO2 and Pt-Sn/TiO2 thin films in capillary microreactors

The kinetics of the liquid-phase hydrogenation of citral (3,7-dimethyl-2,6-octadienal) on Au/TiO2 and Pt-Sn/TiO2 thin films was studied in the temperature range 313-353 K and citral concentrations of 0.25-10.0 mol m(-3). The thin films were deposited onto the inner walls of silica capillaries with internal diameter of 250 mu m. First-order dependence on hydrogen pressure and near zero order dependence on citral concentration were observed for the initial rate of citral hydrogenation over the Pt-Sn/TiO2 and Au/TiO2 thin films. The Au/TiO2 catalyst prevents citronellal formation. The highest yield of unsaturated alcohols was obtained on the Pt-Sn/TiO2 film at a reaction temperature of 343 K, liquid residence time of 30 min and a citral conversion of 99%. (C) 2011 Elsevier B.V. All rights reserved.

Alloys and oxides on carbon-supported Pt-Sn electrocatalysts for ethanol oxidation

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Aplicação de métodos computacionais no estudo das fases intermetálicas ordenadas pt-sn

Fuel cells are a very promising solution to the problems of power generation and emission of pollutant to the environment, excellent to be used in stationary application and mobile application too. The high cost of production of these devices, mainly due to the use of noble metals as anode, is a major obstacle to massive production and deployment of this technology, however the use of intermetallic phases of platinum combined with other metals less noble has been evaluated as electrodes in order to minimize production costs and still being able to significantly improve the catalytic performance of the anode. The study of intermetallic phases, exclusively done by experimental techniques is not complete and demand that other methods need to be applied to a deeper understanding of the behavior geometric properties and the electronic structure of the material, to this end the use of computer simulation methods, which have proved appropriate for a broader understanding of the geometric and electronic properties of the materials involved, so far not so well understood.. The use of computational methods provides answers to explain the behavior of the materials and allows assessing whether the intermetallic may be a good electrode. In this research project was used the Quantum-ESPRESSO package, based on the DFT theory, which provides the self-consistent field calculations with great precision, calculations of the periodic systems interatomic force, and other post-processing calculations that points to a knowledge of the geometric and electronic properties of materials, which may be related to other properties of them, even the electrocatalytic. The electronic structure is determined from the optimized geometric structure of materials by analyzing the density of states (DOS) projected onto atomic orbital, which determines the influence of the electrocatalytic properties of the material... (Complete abstract click electronic access below)

The effect of alloying in Pt-Sn/C electrocatalysts in the performance of a direct ethanol fuel cell

Work on Pt-Sn-C catalysts for ethanol oxidation showed that a thermal treatment at moderate temperatures leads to a significant increase in activity. The best activity was observed for Pt3Sn1 thermally treated at 200 degrees C and ascribed to a Pt3Sn1 phase plus a cleaning effect. However, electronic effects may be very important and these were not evaluated in the Pt3Sn1 phase. Therefore, in this work we investigated the effect of the degree of alloy on the electronic structure of Pt3Sn1 electrocatalysts by performing electrochemical in situ X-ray absorption (XAS) experiments in the Pt L-III XANES region. Overall, the results show that although the occupancy of the Pt 5d band depends on the degree of alloy other factors, such as the presence of tin oxides/hydroxides in the materials, have to be considered to understand the performance of the DEFC.

Study of ethanol electro-oxidation in acid environment on Pt(3)Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt(3)Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions This material was characterized using X-ray diffraction (XRD). and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt(3)Sn phase. Transmission election microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3 6 nm +/- 1 nm) The polarization curves for a direct ethanol fuel cell using Pt(3)Sn/C as the anode demonstrated Improved performance compared to that of a PtSn/C E-TEK. especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt(3)Sn phase. The maximum power density for the Pt(3)Sn/C electrocatalyst (58 mW cm(-2)) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm(-2)) This behavior is attributed to the presence of a mixed Pt(9)Sn and Pt(3)Sn alloy phase in the commercial catalysts (C) 2009 Elsevier B V All rights reserved

Sn@Pt and Rh@Pt core–shell nanoparticles synthesis for glycerol oxidation

The development and optimization of electrocatalysts for application in fuel cell systems have been the focus of a variety of studies where core–shell structures have been considered as a promising alternative among the materials studied. We synthesized core–shell nanoparticles of Sn x @Pt y and Rh x @Pt y (Sn@Pt, Sn@Pt2, Sn@Pt3, Rh@Pt, Rh@Pt2, and Rh@Pt3) through a reduction methodology using sodium borohydride. These nanoparticles were electrochemically characterized by cyclic voltammetry and further analyzed by cyclic voltammetry studying their catalytic activity toward glycerol electro-oxidation; chronoamperometry and potentiostatic polarization experiments were also carried out. The physical characterization was carried out by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The onset potential for glycerol oxidation was shifted in 130 and 120 mV on the Sn@Pt3/C and Rh@Pt3/C catalysts, respectively, compared to commercial Pt/C, while the stationary pseudo-current density, taken at 600 mV, increased 2-fold and 5-fold for these catalysts related to Pt/C, respectively. Thus, the catalysts synthesized by the developed methodology have enhanced catalytic activity toward the electro-oxidation of glycerol, representing an interesting alternative for fuel cell systems.

稀土墩子和稀土氧化物对甲醇在Pt催化剂上电催化氧化性能的影响

直接甲醇燃料电池( DMFC )具有甲醇来源丰富，价格低廉，在常温常压下是液体，易于携带储存；体积小，重量轻，结构简单，容易操作；维修方便，价格低等优点，近年来得到普遍的关注。然而，要达到DMFC的商品化还存在一些问题。其中一个是阳极催化剂的电催化活性低和易被甲醇氧化的中间产物，如CO毒化。对于甲醇阳极电催化剂人们进行了大量的研究，比较有效的都是Pt－过渡金属或金属氧化物复合催化剂，如Pt－Ru、 Pt－Sn、Pt佩Rh、Pt－Pd、Pt佩Re、Pt－Ru－Sn－W、Pt－WO。和Pt－TIO。等。本文研究了电解液中的稀土离子和与Pt形成复合催化剂的稀土氧化物对甲醇电催化氧化反应的促进作用，得到了如下的结果：1．电解液中的稀土Ho, Eu, Gd或Dy离子对甲醇在光滑Pt电极或DMFC中使用的Pt/C电极上的电催化氧化反应有促进作用，主要表现在的起始氧化电位负移和氧化电流增加。而电解液中加入其它种类的稀土离子对甲醇在光滑Pt电极或Pt/C电极上的电催化氧化反应有阻碍作用，如起始氧化电位正移，峰电流降低。Fu、H食Dy或Gd离子对一甲醇在Pt上的电催化氧化反应有促进作用的主要原因可能与这些稀土离子与甲醇生成配合物能力有关。2．不同Pt一稀土氧化物／C催化剂对甲醇电催化氧化反应有不同的影响。当稀土氧化物是Eu, Ho, Dy或Gd的氧化物时，甲醇在Pt一稀土氧化物／C催化剂上甲醇电催化氧化反应的极化性能和稳定性要优于在Pt/C催化剂上，而在其它的Pt-稀土氧化物／C催化剂上，甲醇电催化氧化的极化性能和稳定性要差于Pt/C电极。用不同方法制备的Pt一稀土氧化物／C催化剂对甲醇电催化氧化反应的促进作用取决于催化剂的制备方法。如先在活性碳上还原沉积Pt，再沉积上稀土氧化物所得的Pt－稀土氧化物／C催化剂的促进作用要优于先在稀土氧化物上还原沉积Pt，再一起沉积到活性碳上或先再活性碳上沉积稀土氧化物，再还原沉积上Pt的方法。另外，Pt和稀上氧化物的原子比为2：1时，pt－稀土氧化物／c催化剂对甲醇电催化氧化反应的催化活性最佳。稀土氧化物对pt／C催化剂对甲醇氧化反应的电催化性质的影响与稀土离子相似。但用稀土离子的方法比较简便，因此，相比之下，用稀土离子来促进甲醇在Pt上的电催化氧化反应方法较好。3．用Eu, Gd, Dy, Ho的氧化物制得的Pt-稀土氧化物／C复合催化剂对co的电催化氧化反应的催化活性要高于Pt/C催化剂。相对于的情况，在co在Eu, Gd, Dy,Ho的氧化物的Pt／稀土氧化物／C复合催化剂电极上的循环伏安图中，CO的氧化峰峰电位比在Pt/C电极的有不同程度的负移。吸．初步确定了电极和单体电池制备的较好的工艺参数和工作条件。在发明一种薄电极制备方法，确定最佳的电极催化层配方等的基础上，制得的单体电池，在25℃工作时，输出功率密度峰值达到28 mW/cm~2。

Pt-based anode catalysts for direct ethanol fuel cells

In the present work, several carbon supported PtSn and PtSnRu catalysts were prepared with different atomic ratios and tested in direct ethanol fuel cells (DEFC) operated at lower temperature (T=90 degreesC). XRD and TEM results indicate that all of these catalysts consist of uniform nano-sized particles of narrow distribution and the average particle sizes are always less than 3.0 nm. As the content of Sn increases, the Pt lattice parameter becomes longer. Single direct ethanol fuel cell tests were used to evaluate the performance of carbon supported PtSn catalysts for ethanol electro-oxidation. It was found that the addition of Sn can enhance the activity towards ethanol electro-oxidation. It is also found that a single DEFC of Pt/Sn atomic ratioless than or equal to2, "Pt1Sn1/C, Pt3Sn2/C, and Pt2Sn1/C" shows better performance than those with Pt3Sn1/C and Pt4Sn1/C. But even adopting the least active PtSn catalyst, Pt4Sn1/C, the DEFC also exhibits higher performance than that with the commercial Pt1Ru1/C, which is dominatingly used in PEMFC at present as anode catalyst for both methanol electro-oxidation and CO-tolerance. At 90 degreesC, the DEFC exhibits the best performance when Pt2Sn1/C is adopted as anode catalysts. This distinct difference in DEFC performance between the catalysts examined here is attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. It is thought that -OHads, Surface Pt active sites and the ohmic effect of PtSn/C catalyst determines the electro-oxidation activity of PtSn catalysts with different Pt/Sn ratios. (C) 2004 Elsevier B.V. All rights reserved.

Pt based anode catalysts for direct ethanol fuel cells

In the present work several Pt-based anode catalysts supported on carbon XC-72R were prepared with a novel method and characterized by means of XRD, TEM and XPS analysis. It was found that all these catalysts are consisted of uniform nanosized particles with sharp distribution and Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. Cyclic voltammetry (CV) measurements and single direct ethanol fuel cell (DEFC) tests jointly showed that the presence of Sn, Ru and W enhances the activity of Pt towards ethanol electro-oxidation in the following order: Pt1Sn1/C > Pt1Ru1/C > Pt1W1/C > Pt1Pd1/C > Pt/C. Moreover, Pt1Ru1/C further modified by W and Mo showed improved ethanol electro-oxidation activity, but its DEFC performance was found to be inferior to that measured for Pt1Sn1/C. Under this respect, several PtSn/C catalysts with different Pt/Sn atomic ratio were also identically prepared and characterized and their direct ethanol fuel cell performances were evaluated. It was found that the single direct ethanol fuel cell having Pt1Sn1/C or Pt3Sn2/C or Pt2Sn1/C as anode catalyst showed better performances than those with Pt3Sn1/C or Pt4Sn1/C. It was also found that the latter two cells exhibited higher performances than the single cell using Pt1Ru1/C, which is exclusively used in PEMFC as anode catalyst for both methanol electro-oxidation and CO-tolerance. This distinct difference in DEFC performance between the catalysts examined here would be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and additives. It is thought that an amount of -OHads, an amount of surface Pt active sites and the conductivity effect of PtSn/C catalysts would determine the activity of PtSn/C with different Pt/Sn ratios. At lower temperature values or at low current density regions where the electro-oxidation of ethanol is considered not so fast and its chemisorption is not the rate-determining step, the Pt3Sn2/C seems to be more suitable for the direct ethanol fuel cell. At 75 degreesC, the single ethanol fuel cell with Pt3Sn2/C as anode catalyst showed a comparable performance to that with Pt2Sn1/C, but at higher temperature of 90 degreesC, the latter presented much better performance. It is thought from a practical point of view that Pt2Sn1/C, supplying sufficient -OHads and having adequate active Pt sites and acceptable ohmic effect, could be the appropriate anode catalyst for DEFC. (C) 2003 Elsevier B.V. All rights reserved.

吸附在Pt/C催化剂上Eu~(3+)对CO电氧化的促进作用

引言目前影响质子交换膜燃料电池(PEMFC)迅速发展并商业化的主要问题之一是阳极催化剂抗CO的毒化能力。Pt因其对氢的氧化具有高的催化活性而广泛地用作PEMFC的阳极催化剂,也有人研究将其它金属用于PEMFC阳极催化剂,但催化活性要比Pt低得多[1~4]。而Pt作PEMFC的阳极催化剂一个问题是痕量的CO,如10~100ppm就可以使Pt催化剂中毒[5,6]。现在的PEMFC一般用高压氢作为燃料,有很大的不安全性。人们提出用两种方法来解决这个问题,一是用甲醇、甲烷或汽油现场重整制氢作燃料的方法,但用这种制氢方法制得的氢气中含有大量的CO,即使经过纯化,也会含有ppm级的CO。另一个方法是直接用小分子醇类化合物,如甲醇作燃料,被称为直接醇燃料电池(DAFC)[7~11],但醇类化合物在阳极氧化时会有中间产物,如CO的产生,容易使阳极Pt催化剂中毒。因此,研究抗CO中毒的阳极催化剂已成为PEMFC和DAFC中一个很重要的研究课题。许多文章已报道Pt与其它贵金属或过渡金属的合金催化剂,或Pt与过渡金属氧化物的复合催化剂有一定的抗CO中毒能力。如Pt鄄Ru[12~16]、Pt鄄Bi[17]、Pt鄄Sn[17~19]...

碳载Pt-TiO_2阳极催化剂对甲醇氧化的电催化活性和稳定性

近年来,直接甲醇燃料电池（DMFC）由于使用液体燃料而越来越受到重视,但目前DMFC存在的一个普遍的问题是常用的Pt阳极催化剂易被甲醇氧化的中间产物所毒化.因此,一些研究者研究了能抗甲醇氧化的中间产物毒化的Pt二元合金或Pt和过渡金属氧化物复合催化剂,如Pt-Ru[1]、Pt-Sn[2]、Pt-WOx[3]等.考虑至TiO2在酸性溶液中的稳定性,Hamnett研究组[4]和我们研究组[5]发现pt-TiO2/Ti复合电极对甲醇氧化有很好的电催化活性和抗中毒的能力.本文报道了制备能在DMFC中实际使用的碳载Pt-TiO2催化剂（Pt-TiO2/C）的方法和比较了Pt-TiO2/C和Pt/C电极对甲醇氧化的电催化活性和稳定性.用固相法制备含Pt20％的Pt/C催化剂[6],将制得的pt/C催化剂和Ti（OBu）4按摩尔比1:1的比例悬浮在乙醇中,超声波震荡并加水,使Ti（OBu）4完全水解成TiO2,并均匀沉积到Pt/C催化剂上,洗涤,真空干燥,500℃热处理

Mononuclear Pt(II) and Pd(II) 1,4-dithiolato complexes. Crystal structures of [Pt((−) DIOS) (PPh3)2] and [Pd(S(CH2) 4S)(Ph2P(CH2) 3PPh2)]. Application in styrene hydroformylation

Addition of 1,4-dithiols to dichloromethane solutions of [PtCl2(P-P)] (P-P = (PPh3)2, Ph2P(CH2)3PPh2, Phd2P(CH2)4PPh2; 1,4-dithiols = HS(CH2)4SH, (−)DIOSH2 (2,3-O-isopropylidene-1,4-dithiol-l-threitol), BINASH2 (1,1′-dinaphthalene-2,2′-dithiol)) in the presence of NEt3 yielded the mononuclear complexes [Pt(1,4-dithiolato)(P-P)]. Related palladium(II) complexes [Pd(dithiolato)(P-P)] (P-P=Ph2P(CH2)3PPh2, Ph2P(CH2)4PPh2; dithiolato = −S(CH2)4S−, (−)-DIOS) were prepared by the same method. The structure of [Pt((−)DIOS)(PPh3)2] and [Pd(S(CH2)4S)(Ph2P(CH2)3PPh2)] complexes was determined by X-ray diffraction methods. Pt—dithiolato—SnC12 systems are active in the hydroformylation of styrene. At 100 atm and 125°C [Pt(dithiolate)(P-P)]/SnCl2 (Pt:Sn = 20) systems provided aldehyde conversion up to 80%.

Methanol and ethanol electro-oxidation on Pt-SnO(2) and Pt-Ta(2)O(5) sol-gel-modified boron-doped diamond surfaces

The search for more efficient anode catalyst than platinum to be used in direct alcohol fuel cell systems is an important challenge. In this study, boron-doped diamond film surfaces were modified with Pt, Pt-SnO(2) and Pt-Ta(2)O(5) nano-crystalline deposits by the sol-gel method to study the methanol and ethanol electro-oxidation reactions in acidic medium. Electrochemical experiments carried out in steady-state conditions demonstrate that the addition of SnO(2) to Pt produces a very reactive electrocatalyst that possibly adsorbs and/or dissociate ethanol more efficiently than pure Pt changing the onset potential of the reaction by 190 mV toward less positive potentials. Furthermore, the addition of Ta(2)O(5) to Pt enhances the catalytic activity toward the methanol oxidation resulting in a negative shift of the onset potential of 170 mV. These synergic effects indicate that the addition of these co-catalysts inhibits the poisoning effect caused by strongly adsorbed intermediary species. Since the SnO(2) catalyst was more efficient for ethanol oxidation, it could probably facilitate the cleavage of the C-C bond of the adsorbed intermediate fragments of the reaction. (C) 2009 Elsevier B.V. All rights reserved.