Novel BN supported bi-metal catalyst for oxydehydrogenation of propane

A novel boron nitride (BN) supported Pt-Sn catalyst was used for the oxydehydrogenation of propane. BN is a graphite-like inert support which provides negligible interaction with metals. The Pt-Sn/BN catalysts were prepared by co-incipient wetness impregnation with various Sn loadings. A commercial support γ-Al₂O₃ was chosen to compare with BN. PtSn alloys were formed due to the partially reduced Sn in Pt-Sn/BN catalyst in H₂ at 400 °C. Furthermore, the crystalline phases of PtSn and SnPt₃ alloys were also observed from the XRD patterns of Pt-Sn/BN catalysts. However, PtSn alloys were not detected in Pt-Sn/γ-Al₂O₃ by XRD. The Sn addition clearly improved the activity and propylene selectivity of Pt-Sn/BN at 600 °C. The more the Sn loading, the higher the selectivity and yield of propylene were. A maximum yield of propylene (38.3%) was achieved on Pt-Sn (0.75 wt%)/BN catalyst at the start of reaction. The catalysts, Pt-Sn/γ-Al₂O₃, deactivated more rapidly than Pt-Sn/BN. The activity and selectivity enhancement are attributed to the formation of PtSn and/or SnPt₃ alloy particles on the BN support. Compared with the hydrophilic γ-Al₂O₃, the hydrophobic BN surface can expel H₂O during the oxidation of hydrogen resulting in the activity increase.     

Structural effects in electrocatalysis: electrooxidation of carbon monoxide on Pt3Sn single-crystal alloy surfaces

The kinetics of the electrochemical oxidation of carbon monoxide (CO) and CO/hydrogen mixtures (0.1 and 2% CO) in sulfuric acid electrolyte at 25–62°C was studied on different surfaces of the ordered single crystal Pt₃Sn alloy. Characterization of the surface composition and structure was determined in UHV using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and low energy ion scattering (LEIS) prior to determining the electrode kinetics using the classical rotating disk method (RDE) with CO dissolved in the electrolyte. Clean annealed and sputtered-cleaned but not-annealed surfaces of (110) and (111) orientation were studied. A remarkable difference in activity was observed between the annealed (111) surface and the sputtered but not-annealed (110) surface, with both surfaces having the same nominal surface composition, 20–25 at% Sn, but different local structures. The onset potential for CO oxidation on the (111) surface was shifted cathodically by 0.13 V relative to that for the sputtered (110) surface, and the onset comes remarkably close to 0 V on the reversible hydrogen potential scale. Relative to pure Pt surfaces (of any crystal structure), the potential shift is more than 0.5 V, corresponding to a catalytic activity that is higher by more than four orders of magnitude. Comparable shifts were observed for the oxidation of CO/H₂ mixtures. Both the structure sensitivity and the high catalytic activity of the Pt₃Sn surface are attributed to an adsorbed state of CO unique to this alloy and occurs at relatively high coverage on the (111) surface.     

Controlled Synthesis of Pt3Sn/C Electrocatalysts with Exclusive Sn–Pt Interaction Designed for Use in Direct Methanol Fuel Cells

Alloy-type Sn–Pt/C electrocatalysts with Pt/Sn = 1.8–3.0 ratios and exclusive Sn–Pt interaction have been prepared by means of controlled surface reactions (CSRs). As demonstrated by XRD, the incorporation of Sn onto Pt/C was achieved satisfactorily yielding a near-stoichiometric fcc Pt₃Sn alloy phase along with a certain amount of the Pt_(1 ? x)Sn_x solid solution. The content and dispersion of the fcc Pt₃Sn phase within the electrocatalysts can be controlled by tuning the reaction conditions of CSRs. No evidence of the presence of SnO₂ phases in the Sn-modified Pt/C samples was found by means of the XRD and EDS analysis. According to in situ XPS studies, the pre-treatment in hydrogen at 350 °C resulted in complete reduction of tin to Sn⁰. These results demonstrate that the method of CSRs is a powerful tool to create of Pt–Sn bimetallic nanoparticles exclusively, without tin introduction onto the carbon support. The performance of the intermetallic SnPt/C catalysts in the CO and methanol electrooxidation reactions depends on the actual composition of the exposed surface and the size of bimetallic particles. In the consecutive tin introduction the decrease of the amount of SnEt₄ precursor added per period, accompanied with an increase of the number of anchoring periods, resulted in an increase of the activity in both electrooxidation reactions as a consequence of an optimal balance of Pt/C ratio, the content of fcc Pt₃Sn phase and metal particle size. It was demonstrated that the increasing tin content above a certain (optimal) amount gives rise to a negative effect on the catalyst performance in the CO and methanol electrooxidation.     

N掺杂石墨烯负载Pt-Sn催化剂的制备及电催化性能研究

氮掺杂石墨烯负载Pt在直接乙醇燃料电池（DEFCs）中表现出较好的性能。Pt的高成本极大地限制了DEFCs的商业化应用。因此,采用一系列不同浓度水合肼还原氧化石墨烯的简单方法,合成了氮掺杂石墨烯负载Pt-Sn （Pt-Sn/G-N）。研究了Pt-Sn/G-N催化剂纳米粒子的均匀分散对乙醇氧化的电催化活性影响。通过控制不同的氮含量,进一步研究了Pt和Sn金属颗粒最适宜协同效应的比例。结果表明：当氧化石墨烯与水合肼的质量比为1∶7时,催化剂的Pt和Sn负载均最大,Pt与Sn的比值为1.41,Pt/Sn合金的平均粒径最小（1.8 nm）。此外,与其他催化剂相比,Pt-Sn/G-N （1∶7）具有最高的电催化活性,稳定性好,抗CO中毒能力强。即Pt-Sn/G-N （1∶7）的Pt与Sn实现了催化协同作用,为Pt-Sn催化剂在直接乙醇燃料电池（DEFCs）中的应用提供了更多的途径。     

A new synthesis of a highly dispersed and CO tolerant PtSn/C electrocatalyst for low-temperature fuel cell; its electrocatalytic activity and long-term durability

An effective method is developed for preparing highly dispersed and nano-sized PtSn/C electrocatalysts synthesized by borohydride reduction and subsequent hydrothermal treatment. From the XRD patterns, the Pt(2 2 0) peak of the PtSn/C catalysts shift slightly to lower 2θ values with increasing Sn content, compared with that of the Pt/C catalyst, suggesting the alloy formation. Based on the HR-TEM, the PtSn nanoparticles show average particle sizes of approximately 2.3 nm on the carbon surface, which is consistent with XRD data. The XPS result shows that the slight shift in the bulk metallic Pt(0) to higher binding energies is attributed to a significant contribution from the metal-support interaction and the nano-size effect. The methanol and CO oxidations on the PtSn/C catalysts occur at lower potentials as compared to the commercial Pt/C catalyst. This result suggests that Sn has the ability to promote the oxidation of adsorbed CO at lower potentials. In the single-cell and accelerated durability tests, the 3Pt1Sn/C catalyst shows higher performance under a pure H₂ and CO-containing H₂ gases and better durability under a 0.5 M H₂SO₄ solution than the commercial Pt/C catalyst, due to the coexistence of PtSn alloys and Sn oxides.     

Electrochemically assisted organosol method for Pt-Sn nanoparticle synthesis and in situ deposition on graphite felt support: Extended reaction zone anodes for direct ethanol fuel cells

Two electrochemically assisted variants of the Bönneman organosol method were developed for Pt-Sn nanoparticle synthesis and in situ deposition on graphite felt electrodes (e.g. thickness up to 2 mm). Tetraoctylammonium triethylhydroborate N(C₈H₁₇)₄BH(C₂H₅)₃ was employed as colloid stabilizer and reductant dissolved in tetrahydrofuran (THF). The role of the electric field at a low deposition current density of 1.25 mA cm⁻² was mainly electrophoretic causing the migration and adsorption of N(C₈H₁₇)₄BH(C₂H₅)₃ on the graphite felt surface where it reduced the PtCl₂-SnCl₂ mixture. Faradaic electrodeposition was detected mostly for Sn. Typical Pt-Sn loadings were between 0.4 and 0.9 mg cm⁻² depending on the type of pre-deposition exposure of the graphite felt: surfactant-adsorption and metal-adsorption variant, respectively. The catalyst surface area and Pt:Sn surface area ratio was determined by anodic striping of an underpotential deposited Cu monolayer. The two deposition variants gave different catalyst surfaces: total area 233 and 76 cm² mg⁻¹, with Pt:Sn surface area ratio of 3.5:1 and 7.7:1 for surfactant and metal adsorption, respectively. Regarding electrocatalysis of ethanol oxidation, voltammetry and chronopotentiometry studies corroborated by direct ethanol fuel cell experiments using 0.5 M H₂SO₄ as electrolyte, showed that due to a combination of higher catalyst load and Pt:Sn surface ratio, the graphite felt anodes prepared by the metal-adsorption variant gave better performance. The catalyzed graphite felt provided an extended reaction zone for ethanol electrooxidation and it gave higher catalyst mass specific peak power outputs compared to literature data obtained using gas diffusion anodes with carbon black supported Pt-Sn nanoparticles.     

CO/FTIR Spectroscopic Characterization of Pd/ZnO/Al2O3 Catalysts for Methanol Steam Reforming

An as-synthesized 8.8wt% Pd/ZnO/Al₂O₃ catalyst was either pretreated under O₂ at 773 K followed by H₂ at 293 K or under H₂ at 773 K to obtain, respectively, a supported metallic Pd° catalyst (Pd°/ZnO/Al₂O₃) or a supported PdZn alloy catalyst (PdZn/ZnO/Al₂O₃). Both catalysts were studied by CO adsorption using FTIR spectroscopy. For the supported PdZn alloy catalyst (PdZn/ZnO/Al₂O₃), exposure to a mixture of methanol and steam, simulating methanol steam reforming reaction conditions, does not change the catalyst surface composition. This implies that the active sites are PdZn alloy like structures. The exposure of the catalyst to an oxidizing environment (O₂ at 623 K) results in the break up of PdZn alloy, forming a readily reducible PdO with its metallic form being known as much less active and selective for methanol steam reforming. However, for the metallic Pd°/ZnO/Al₂O₃ catalyst, FTIR results indicate that metallic Pd° can transform to PdZn alloy under methanol steam reforming conditions. These results suggest that PdZn alloy, even after an accidental exposure to oxygen, can self repair to form the active PdZn alloy phase under methanol steam reforming conditions. Catalytic behavior of the PdZn/ZnO/Al₂O₃ catalyst also correlates well with the surface composition characterizations by FTIR/CO spectroscopy.     

The adsorption of Sn on Pt(1 1 1) and its influence on CO adsorption as studied by XPS and FTIR

The coverage of Sn on Pt(1 1 1) which is obtained by electrochemical deposition from 5×10⁻⁵ M Sn²⁺ in 0.5 M H₂SO₄ has been determined by XPS for different deposition times. Complete suppression of hydrogen adsorption corresponds to a coverage of ?_max=0.35 (Sn to surface Pt atoms).Co-adsorption of CO with Sn on Pt(1 1 1) has been studied by FTIR spectroscopy. The IR spectra of the stretching vibration of CO can be interpreted in terms of the vibrational signature of the Pt(1 1 1)/CO system and no vibrational bands associated with CO on Sn are detected. At high Sn coverages, the 1840 cm⁻¹ band associated with bridge-bonded CO and the 2070 cm⁻¹ band assigned to on-top CO are present, however, no hollow site adsorption which is characterized by the 1780 cm⁻¹ band is revealed within the resolution of the experiment. This vibrational signature corresponds to a less compressed adlayer compared to the (2×2)-3CO saturation structure on Pt(1 1 1). At lower Sn coverages, signatures from both the compressed and the less compressed CO adlayer structures are seen in the spectra. From earlier structural and electrochemical studies it is known that Sn is adsorbed in 2D islands and influences CO molecules in its neighbourhood electronically. This leads to a disappearance of the IR band from CO adsorbed in the hollow site at high Sn coverages and to higher population of the weakly adsorbed state of CO for all Sn-modified surfaces, i.e. a relative increase of the amount of CO oxidised at low potentials. In addition to this electronic effect, Sn also exerts a co-catalytic effect at low Sn coverages on that part of CO which is adsorbed at a larger distance from Sn due to a bi-functional mechanism. The IR spectra shows for the Sn-modified Pt(1 1 1) surface that the transition from the compressed CO adlayer which is characterized by the hollow site adsorption of CO to the less compressed one which exhibits a characteristic band associated with bridge-bonded CO occurs already at 250 mV instead of 400 mV.     

The electro-oxidation of carbon monoxide, hydrogen/carbon monoxide and methanol in acid medium on Pt-Sn catalysts for low-temperature fuel cells: A comparative review of the effect of Pt-Sn structural characteristics

The electrocatalytic activity for CO, H₂/CO and CH₃OH oxidation of Pt-Sn catalysts has been extensively investigated for a possible use as anode materials for low-temperature fuel cells. This paper presents an overview of the relationship between the structural characteristics of the catalysts (catalyst composition, degree of alloying, presence of oxides) and their electrocatalytic activity for the oxidation of the different fuels.     

Platinum-tin and platinum-copper catalysts for autothermal oxidative dehydrogenation of ethane to ethylene

The addition of various metals to Pt-coated ceramic foam monoliths was examined for the autothermal oxidative dehydrogenation of ethane to ethylene at 900°C at contact times of 5 ms. The addition of Sn or Cu to Pt-monoliths enhanced both C₂H₆ conversions and C₂H₄ selectivities significantly, giving higher C₂H₄ yields. No deactivation or volatilization of the catalysts was observed. For Pt-Sn, an increase in the Sn/Pt ratio from 1/1 to 7/1 increased both the conversion and the selectivity. For Pt-Sn (Sn/Pt = 7/1) versus Pt alone the conversion increased by up to 6% and the selectivity up to 5% for an increase in optimal yield from 54.5% with Pt to 58.5% with Pt-Sn. XRD and XPS measurements showed that Pt existed in the form of PtSn and Pt₃Sn alloys. The 1/1 Pt-Cu catalyst showed comparable performance, with conversion increasing by 5% and selectivity by 3%. The addition of several other metals to Pt-monoliths decreased both C₂H₆ conversion and C₂H₄ selectivity in the order, Sn>Cu>Pt alone>Ag>Mg>Ce>Ni>La> Co. For oxidative dehydrogenation ofn-butane and isobutane, Pt-Sn and Pt-Cu also showed higher conversion than Pt.This research was partially supported by NSF under Grant CTS-9311295.     

Tuning millisecond chemical reactors for the catalytic partial oxidation of cyclohexane

It is demonstrated that millisecond partial oxidation of cyclohexane can be tuned by varying the catalyst and operating conditions to generate product distributions that favor (1) oxygenates, (2) olefins, or (3) syngas (H₂ and CO). High selectivities to parent oxygenates require low conversions using low-temperature catalysts, such as Ag or Co. Olefins are favored by Pt or Pt-Sn and H₂ addition eliminates the production of CO and CO₂, thereby increasing olefin selectivities. For syngas, Rh is the catalyst of choice. Finally, a Pt-10% Rh single gauze gives high selectivities to both oxygenates and olefins.Conventional methods for the partial oxidation of cyclohexane are liquid-phase processes that are plagued by poor conversions, high recycle costs, long residence times (minutes to hours), and expensive catalysts. In contrast, with a cyclohexane–oxygen feed at C₆H₁₂/O₂=2, a Pt-10% Rh single gauze catalyst can give total selectivities exceeding 80% to oxygenates and olefins at 25% cyclohexane conversion and complete oxygen conversion. The products consist of nearly 60% selectivity to the C₆ products, cyclohexene and 5-hexenal. The temperature profile attained in the single-gauze reactor allows the preservation of these highly non-equilibrium products.Alternative catalysts for cyclohexane oxidation to oxygenates and olefins include α-alumina monoliths coated with Pt, Rh, Pt-Rh, Pt-Sn, Co, Mo or Ag. The Co, Mo and Ag catalysts give very high selectivities to C₆ oxygenates but are hindered by poor conversions (<5%) of both cyclohexane and oxygen at these millisecond contact times. H₂ addition to cyclohexane oxidation feed mixtures over Pt and Pt-Sn is shown to significantly increase the selectivities to C₆ olefins while reducing the formation of CO and CO₂.Cyclohexane oxidation in air over Rh monoliths enables the production of high yields (>95%) of syngas. This process could find applications in the automotive industry as the production of hydrogen from liquid fuels becomes important.     

Characterization and activity of Pt-Sn/Al2O3 catalysts of different preparation: coimpregnation and new Pt-Sn precursor

A new bimetallic Pt-Sn compound [Pt(NH₃)₄][SnCl₆] has been used as precursor for the preparation of supported Pt-Sn/Al₂O₃ catalysts. A comparison of a dried sample with that prepared by coimpregnation displays different behaviour in TPR, chemisorption. The initial catalytic activity properties were checked in the reactions of cyclohexane dehydrogenation and cyclopentane ring opening, whilen-hexane skeletal reactions were used to probe the quasisteady-state activity. The catalyst prepared via the Pt-Sn complex precursors exhibited some-what lower specific activity. This fact, together with enhanced olefin formation fromn-hexane was taken as an indication of lower amount of contiguous Pt atoms and some electronic interaction between Pt and Sn in that catalyst.On leave from Fachhochschule Ostfriesland, D-26723 Emden, Germany.     

Controlled modification of Pt/Al2O3 for the preferential oxidation of CO in hydrogen: A comparative study of modifying element

The catalytic performance of a series of Pt/Al₂O₃ catalysts, modified with Cr, Mn, Fe, Co, Ni, Cu and Sn, has been tested for the preferential oxidation of CO in hydrogen. The promoters were deposited onto the surface of a 5 wt.% monometallic Pt/Al₂O₃ catalyst using a controlled surface approach, to give a nominal promoter:Pt surface atomic ratio of 1:2 (corresponding to typically 0.15–0.25 wt.% of the promoting metal). The aim of this approach was to selectively create the Pt-promoter oxide interfacial sites considered to be important for the non-competitive dual-site mechanism proposed for such promoted catalysts. In this mechanism the promoting oxide is believed to act as an active oxygen provider, providing oxygen for the oxidation of the CO on the Pt. The catalysts were characterised using TEM, EDX, ICP-AES and CO chemisorption and results suggest that the promoter was successfully deposited on to the Pt surface. Even at the low loadings of promoter used, significant enhancement was observed in the catalytic performance of the PROX reaction in a simulated reformate mixture, for the Fe- and Co-promoted catalysts in particular (and to a lesser extent the Mn, Sn, Cu- and Ni-promoted catalysts), highlighting the successful preparation of the Pt-promoting metal oxide interfacial sites. The Mn-promoted catalyst, however showed no enhancement in the absence of water suggesting that the form of the promoting metal oxide may be particularly important for promotion of Pt for the PROX reaction.     

Adsorption behavior of NO and CO and their reaction over cobalt on zeolite beta

Adsorption behavior of NO and CO as well as their reaction was investigated on cobalt supported zeolite beta (Co/BEA) prepared by solid-state ion exchange (SSIE) and by impregnation (IMP). By temperature programmed desorption (TPD), two NO desorption peaks at 100 and 260‡C were observed over both SSIE and IMP catalysts with complete desorption after 450‡C. CO desorbed from SSIE catalyst between 50 and 200‡C. In the same temperature interval negligible CO₂ desorption was observed, most likely due to reaction of CO with trace of cobalt oxides. Over IMP catalysts, desorption of CO₂ was found mainly at 500‡C. By comparing CO TPD profiles from physical mixtures of cobalt oxides and HBEA, SSIE catalysts most likely contained cobalt cations in zeolite exchange position while IMP catalysts had cobalt in oxidic forms. The SSIE catalysts were active for NO reduction at 400 and 500‡C with a maximum conversion at 500‡C. However, the activity in the presence of water and oxygen was low. Water might inhibit the reaction by blocking active sites for NO and CO, while oxygen reacted with CO to form carbon dioxide. The activity of SSIE was better than IMP catalyst.     

Reduction of nitric oxide by carbon monoxide over silica-supported platinum-rhodium alloys,comparison with the CO + O2 reaction

The reduction of NO by CO was investigated over various silica-supported Pt-Rh alloy catalysts. Steady state catalytic activity as a function of temperature was measured over a range of gas phase compositions. The results were compared with those obtained earlier for the CO + O₂ reaction over the same catalysts. The results can be interpreted on the basis of our earlier Pt-Rh single crystal work. Important factors influencing the performance of the Pt-Rh alloy catalysts are the specific differences in intrinsic properties of Pt and Rh, the experimental conditions of the reaction and the composition of the alloy catalyst. We conclude that at the relatively high temperatures required for the CO + NO reaction the composition of the gas phase may induce large variations of the surface composition.     

CO oxidation on a Cu(100) catalyst

The oxidation of carbon monoxide by molecular oxygen on a single crystal Cu(100) catalyst was studied at 458 K using reactant gas mixtures with CO/O₂ ratios of 2/1, 10/1 and 25/1 at a total pressure of 10 Torr. The catalytic activities were found to be strongly dependent upon the CO/O₂ ratio. Under stoichiometric reaction conditions (CO/O₂ = 2), the initial CO oxidation activity decreased sharply; with a highly reducing reaction mixture (CO/O₂ = 25), the initial activity gradually increased. These changes in catalytic activities with reactant gas mixture composition correlate with changes in surface composition, namely an increase in the surface oxygen coverage. Post-reaction TPD revealed the presence of a carbonate-like species which decomposed at ca. 630 K.     

Probing the Influence of Alloyed Sn on Pt(100) Surface Chemistry by CO Chemisorption

The chemisorption properties of the c(2×2) and (3√2×√2)R45° Sn/Pt(100) alloy surfaces, along with the clean Pt(100) surface, were investigated using CO as a probe molecule. Temperature-programmed desorption (TPD) studies revealed a reduction in CO desorption peak temperature, and thus the chemisorption bond energy, by alloying Sn into the Pt(100) surface. A large decrease was observed in the saturation coverage of CO on these alloyed surfaces at 150 K compared to the Pt(100) surface. The initial sticking coefficient of CO was found, however, to be nearly independent of the surface Sn concentration. High-resolution electron energy loss spectroscopy (HREELS) studies showed that CO was only chemisorbed on atop sites on both alloys. Sn incorporation results in isolated Pt atoms at the surface of these two Sn/Pt(100) alloys and eliminates the possibility of CO bonding to multiple Pt centers, i.e., to pure-Pt 2- and 3-fold bridging sites.     

Enhanced boron removal from metallurgical grade silicon by the slag refining method with the addition of tin

An effective boron removal method was developed through a process of combining Si–Sn alloy with slag treatment. Boron content in refined silicon and boron removal fraction by slag containing 5 wt% CaO, 25 wt% SiO₂ and 70 wt% Na₂SiO₃ and was investigated under varied Si–Sn alloy composition, slag/Si–Sn alloy mass ratio and refining time. Boron was effectively removed by adding tin to metallurgical grade silicon. In particular, the boron content in metallurgical grade silicon decreased from 12.92 ppmw to 0.79 ppmw by adding 50 at% tin under a mass ratio of 2:1 (slag:alloy) at 1723 K. The amount of boron removed increased with increasing amount of tin added, mass ratio and refining time.     

Electro-oxidation of methanol on Pt-Rh alloys

Methanol adsorption and electro-oxidation on Pt-Rh alloys have been studied in aqueous 0.5 M H₂SO₄ for a broad range of alloy surface composition including the pure Pt and Rh metals. Adsorption results have been compared with equivalent data obtained for CO and CO₂ adsorption on these alloys. Current densities of continuous methanol oxidation on Pt, Rh and a Pt-Rh alloy with optimum surface molar fraction of Rh have been measured.Although on the pure Pt and Rh metals the methanol adsorption products exhibit similar energetic stability, as judged from the peak potential of electro-desorption, on the Pt-Rh alloys, there is a lowering of the stability. Similar behavior is observed for the CO and CO₂ adsorption products, however, the lowering for methanol is much less than for CO and CO₂. In the case of methanol, the maximum lowering is obtained for a surface molar fraction of Rh equal to ca. 0.65 and it is the same alloy surface composition that results in maximum lowering of the stability of the CO₂ adsorption products, but not of the CO adsorption products (optimal fraction of Rh equal ca. 0.10). Structural similarity of the methanol and the CO₂ adsorption products finds support in similar values of the electrons-per-site parameter obtained.Pt-Rh alloys show insufficient electrode potential improvement over Pt in continuous methanol electro-oxidation due to the susceptibility of Rh to strong poisoning by the methanol adsorption products, which switches off the bi-functional mechanism of methanol electro-oxidation on this alloy. The presence of Rh in the alloy with Pt additionally strongly lowers the methanol electro-oxidation turnover rate of the Pt component.     

CO tolerance and catalytic activity of Pt/Sn/SnO2 nanowires loaded on a carbon paper

Electrochemical activities and structural features of Pt/Sn catalysts supported by hydrogen-reduced SnO₂ nanowires (SnO₂NW) are studied, using cyclic voltammetry, CO stripping voltammetry, scanning electron microscopy, and X-ray diffraction analysis. The SnO₂NW supports have been grown on a carbon paper which is commercially available for gas diffusion purposes. Partial reduction of SnO₂NW raises the CO tolerance of the Pt/Sn catalyst considerably. The zero-valence tin plays a significant role in lowering the oxidation potential of CO_ads. For a carbon paper electrode loaded with 0.1 mg cm⁻² Pt and 0.4 mg cm⁻² SnO₂NW, a conversion of 54% SnO₂NW into Sn metal (0.17 mg cm⁻²) initiates the CO_ads oxidation reaction at 0.08 V (vs. Ag/AgCl), shifts the peak position by 0.21 V, and maximizes the CO tolerance. Further reduction damages the support structure, reduces the surface area, and deteriorates the catalytic activity. The presence of Sn metal enhances the activities of both methanol and ethanol oxidation, with a more pronounced effect on the oxidation current of ethanol whose optimal value is analogous to those of PtSn/C catalysts reported in literature. In comparison with a commercial PtRu/C catalyst, the optimal Pt/Sn/SnO₂NW/CP exhibits a somewhat inferior activity toward methanol, and a superior activity toward ethanol oxidation.