Temperature dependence of co-adsorption of carbon monoxide and water on highly dispersed Pt/C and PtRu/C electrodes studied by in-situ ATR-FTIRAS

ATR-FTIRAS measurements were conducted to investigate nature of water molecules co-adsorbed with CO on highly dispersed PtRu alloy and Pt catalysts supported on carbon black in the temperature range between 23 °C and 60 °C. Each catalyst was uniformly dispersed and fixed by Nafion^® film of 0.0125 μm thickness on a chemically deposited gold film. Adsorption of CO was conducted and monitored by ATR-FTIRAS for 30 min in 1% CO saturated 0.1 M HClO₄ after stepping the potential from 1.2 V and 1.0 V to 0.05 V on Pt/C and PtRu/C, respectively. Similar atop and bridge bonded CO bands were observed on both PtRu/C and Pt/C, but a smaller relative band intensity, bridge bonded vs. atop CO, was observed on PtRu/C compared to Pt/C. A distinct O-H stretching band was found around 3643 cm⁻¹ and 3630 cm⁻¹ on PtRu/C and Pt/C, respectively, upon CO adsorption. They are assigned to non-hydrogen bonded water molecules co-adsorbed with CO on these catalysts. We found that the number of non-hydrogen bonded water molecules co-adsorbed with a given number of CO molecules decreases with increasing temperature and is higher on PtRu/C than Pt/C at each temperature. We interpret the higher ability of water co-adsorption at PtRu/C over Pt/C is due to stronger H₂O-metal interactions on the alloy surface. We present a model of the CO-H₂O co-adsorbed layer based on the bilayer model of water on metal surfaces.     

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.     

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.     

CO tolerance and CO oxidation at Pt and Pt-Ru anode catalysts in fuel cell with polybenzimidazole-H3PO4 membrane

CO tolerance of H₂-air single cell with phosphoric acid doped polybenzidazole (PA-PBI) membrane was studied in the temperature range 140-180 °C using either dry or humidified fuel. Fuel composition was varied from neat hydrogen to 67% (vol.) H₂-33% CO mixtures. It was found that poisoning by CO of Pt/C and Pt-Ru/C hydrogen oxidation catalysts is mitigated by fuel humidification. Electrochemical hydrogen oxidation at Pt/C and Pt-Ru/C catalysts in the presence of up to 50% CO in dry or humidified H₂-CO mixtures was studied in a cell driven mode at 180 °C. High CO tolerance of Pt/C and Pt-Ru/C catalysts in FC with PA-PBI membrane at 180 °C can be ascribed to combined action of two factors—reduced energy of CO adsorption at high temperature and removal of adsorbed CO from the catalyst surface by oxidation. Rate of electrochemical CO oxidation at Pt/C and Pt-Ru/C catalysts was measured in a cell driven mode in the temperature range 120-180 °C. Electrochemical CO oxidation might proceed via one of the reaction paths—direct electrochemical CO oxidation and water-gas shift reaction at the catalyst surface followed by electrochemical hydrogen oxidation stage. Steady state CO oxidation at Pt-Ru/C catalyst was demonstrated using CO-air single cell with Pt-Ru/C anode. At 180 °C maximum CO-air single cell power density was 17 mW cm⁻² at cell voltage U = 0.18 V.     

Effect of chemisorbed carbon monoxide on Pt/C electrode on the mechanism of the hydrogen oxidation reaction

The influence of poisoning of Pt catalyst by CO on the kinetics and mechanism of H₂ oxidation reaction (HOR) at Pt/C electrode in 0.5 mol dm⁻³ HClO₄, saturated with H₂ containing 100 ppm CO, was examined with rotating disc electrode (RDE) at 22 °C. Commercial carbon black, Vulcan XC-72 was used as support, while Pt/C catalyst was prepared by modified polyol synthesis method in an ethylene glycol (EG) solution. The kinetically controlled current (I_k) for the HOR at Pt/C decreases significantly at CO coverage (Θ_CO) > 0.6. For Θ_CO < 0.6 the HOR takes place through Tafel-Volmer mechanism with Tafel reaction as rate-determining step at the low CO coverage, while Volmer step controls the overall reaction rate at the medium CO coverage. When CO coverage is higher then 0.6, Heyrovsky-Volmer mechanism is operative for the HOR with Heyrovsky as the rate-determining step (rds).     

Role of terrace/step edge sites in CO adsorption/oxidation on a polycrystalline Pt electrode studied by in situ ATR-FTIR method

ATR-FTIRAS measurements combined with linear potential sweep voltammetry were conducted to perform detailed analysis of CO adsorption/oxidation processes on a chemically deposited Pt film on Si ATR prism. Roles of terrace and step edge sites were clearly demonstrated based on the band analyses of the atop, CO(L), and bridge bonded CO, CO(B), spectra during the adsorption/oxidation processes. In the main current peak region above 0.45 V, a direct spectroscopic evidence was obtained to show oxidation of CO(L) and its diffusion to the step edge sites, where local coverage of CO(L) and CO(B) increases between 0.5 V and 0.64 V. This triggers further oxidation of the overall CO adlayer.     

In situ ATR-FTIR study of bulk CO oxidation on a polycrystalline Pt electrode

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) measurements were conducted to analyze the electrochemical oxidation of CO dissolved in bulk electrolyte solution on a polycrystalline Pt electrode during linear sweep (cyclic) voltammetry (CV) in 1% and 100% CO-saturated 0.1 M HClO₄. A CO adlayer was first formed on Pt at 0.05 V vs. the reversible hydrogen electrode (RHE) during CO bubbling in each electrolyte, followed by the CV measurement. In 1% CO-saturated 0.1 M HClO₄, a well-developed prepeak was found, showing an onset and a peak at around 0.25–0.3 V and 0.42 V, respectively. A major contribution of bridge-bonded CO, CO(B), to the prepeak is concluded based on a decrease in the corresponding band intensity. In 100% CO-saturated 0.1 M HClO₄, the onset of bulk CO oxidation takes place around 0.25–0.3 V, which is closely associated with a band intensity decrease of CO(B), whereas atop (linear) CO, CO(L), did not exhibit intensity change in this potential region. This suggests that vacant sites made available upon oxidation of CO(B) serve as active sites for bulk CO oxidation. The oxidation of CO(B) at such low potentials is interpreted in terms of an adsorption energy on Pt that is lower than that for CO(L) and also of the specific structure of an adlayer that consists of intermixed CO(L) and CO(B). The bulk CO oxidation becomes diffusion-limited by dissolved CO above ca. 0.72 V, where we observed hardly any infrared spectral features ascribed to reaction intermediates. During a negative-going scan back to 0.05 V from 1.2 V, a steep decrease of the bulk CO oxidation current takes place around 0.66 V, at which preferential adsorption of CO(L) is observed. A rigid CO(L) island formation is strongly suggested from its high CO stretching frequency vs. its very small initial coverage and from its subsequent dependence on potential, with a linear Stark shift characterized by a slope of −29 cm⁻¹/V. Such an island formation is in marked contrast to the adlayer structure with intermixed CO(L) and CO(B) initially formed at 0.05 V during CO bubbling. It is concluded that the Pt surface saturated with the CO adlayer formed initially at 0.05 V exhibits a low overpotential for bulk CO oxidation owing to its adlayer structure with intermixed atop and bridge-bonded CO.     

Surface-enhanced IR spectroscopy investigation on the electro-oxidation of CO adlayer at a polycrystalline Pt film electrode in Cl-containing HClO4

The electro-oxidation of CO adlayer on Pt electrode in Cl⁻-containing 0.1 M HClO₄ has been investigated with in situ attenuated-total-reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Two potentials were selected for predosing CO on the Pt electrode: one is in the H-UPD region, i.e., 0.1 V (vs. RHE) and the other is in the double-layer region, i.e., 0.45 V (vs. RHE). The broadening of the prewave and the main peak for the CO oxidation is observed, in addition to the positively shifted oxidation potentials. The spectroelectrochemical data suggest the specific adsorption of Cl⁻ starts at a potential as negative as 0.1 V which may compete with the adsorption of OH at CO-unoccupied sites (including but not limited to defect sites) and/or hinder the diffusion of CO to OH adsorption sites on Pt electrode, slowing down the CO oxidation. This competitive Cl⁻ adsorption at lower potentials disrupts the interfacial free H₂O structure on the top of CO adlayer, signaled by a reduced OH stretching band intensity.     

Electrocatalytic reduction of nitric oxide on Pt nanocrystals of different shape in sulfuric acid solutions

Pt tetrahexahedral (Pt-THH) nanocrystals enclosed with 24 {h k 0} facets, Pt nanothorns (Pt-Thorn) with a high surface density of atomic steps, and congeries of Pt nanoparticles (Pt-NP) were prepared and served as catalysts to study the electrocatalytic reduction of both adsorbed and solution nitric oxide. The structure sensitivity for the reduction of a saturated NO adlayer on the Pt nanocrystals (NCs) of different shape was studied by cyclic voltammetry (CV) and in situ FTIR spectroscopy in sulphuric acid solutions. The results revealed that two types of NO adsorbates can be reduced independently at separated potentials, i.e. the reduction of linear bonded NO (NO_L) on the Pt-NP electrode gives rise to a current peak at −0.01 V (vs. SCE), while the bridge adsorbed NO (NO_B) yields a current peak at −0.08 V. The in situ SNIFTIRS results confirmed the assignment of NO adsorbates, i.e. the NO_B species yielding a IR absorption bipolar band with its negative-going peak at 1636 cm⁻¹ and positive-going peak around 1610 cm⁻¹, and the NO_L species giving rise to a bipolar band with its negative-going peak at 1809 cm⁻¹ and positive-going peak around 1720 cm⁻¹. It has determined that the NO_L species can be preferentially formed on the Pt NCs with open surface structure, i.e. the more open the surface structure of the Pt NCs, the larger the relative quantity of NO_L versus NO_B. It has also revealed that the Pt NCs with a high surface density of atomic steps exhibit superior electrocatalytic activity for the reduction of solution NO species. The steady-state current density of NO reduction on Pt-THH NCs is 7.5-12 times as large as that on Pt-NP, and that on Pt-Thorn is 2.5-4 times of that on Pt-NP in the reduction potential region of electrochemical dynamic control.     

Activated carbon nanotubes-supported catalyst in fuel cells

The electrochemical property of platinum loaded on activated carbon nanotubes (Pt/ACNTs) was investigated by cyclic voltammograms (CVs) recorded in H₂SO₄ and H₂SO₄/CH₃OH aqueous solutions, respectively. Compared to 0.0046 A/cm² of Pt-loaded on pristine carbon nanotubes (Pt/CNTs) with a S_BET of 164 m²/g and 0.0042 A/cm² of conventional carbon black (Pt/C, Vulcan XC-72) with a S_BET of ∼250 m²/g, a better electrochemical activity (a high current density of 0.0070 A/cm² for weak-H₂ adsorption/desorption) of the Pt/ACNTs with high specific surface area (S_BET) of 830-960 m²/g was obtained. Furthermore, the highest current density of 0.079 A/cm² at 0.65 V in anodic sweep was observed during the methanol oxidation. On the basis of Pt size, utility ratio, and electro-active specific surface area (EAS), the Pt/ACNTs with a high Pt-loading of 50 wt.% exhibited the best electrochemical activity. The present ACNTs may be an excellent support material for electrochemical catalyst in proton exchange membrane and direct methanol fuel cells.     

Electro-catalytic oxidation of CO on Pt catalyst supported on carbon nanotubes pretreated with oxidative acids

Characteristics of nanosized Pt electro-catalyst deposited on carbon nanotubes (CNTs) were studied with CO-stripping voltammogram and chronoamperometry measurements. The CNTs were pretreated by oxidation in HNO₃, mixed HNO₃ + H₂SO₄ and H₂SO₄ + K₂Cr₂O₇ solution, respectively, to enable surface modification. Well-homogenized Pt particles (average size: ≈3 nm) were loaded onto the pretreated CNT samples by a modified colloidal method. TEM, BET, FTIR and XRD techniques were used to characterize the physicochemical properties of the pretreated CNT samples. In the electro-oxidation of CO, all the Pt/CNT samples showed lower on-set as well as peak potentials than the conventional Pt/XC-72 electro-catalyst, indicating that the Pt/CNT samples were more resistant to CO poisoning and could be superior anode electro-catalyst for the proton exchange membrane fuel cells (PEMFCs). Moreover, we found that the pretreatment of CNTs in mixed HNO₃ + H₂SO₄ solution was very beneficial for the performance enhancement of Pt/CNT electro-catalyst; the catalyst obtained as such gave the lowest peak potential and the highest catalytic activity for the electro-oxidation of CO. Larger amount of oxygen-containing functional groups, higher percentage of mesopores, and higher graphitic crystallinity of the pretreated CNTs were considered crucial for the performance enhancement, e.g., by strengthening the interaction between Pt nanoparticles and the CNT support and enhancing the mass diffusion in the electro-chemical reaction.     

In situ FTIR spectroscopic studies of (bi)sulfate adsorption on electrodes of Pt nanoparticles supported on different substrates

Nanostructured Pt electrodes were prepared by electrodeposition of Pt nanoparticles on different substrates (GC, Pt and Au) under cyclic voltammetric conditions and with various number (n) of potential cycling, and were denoted as nm-Pt/S(n) (S = GC, Pt and Au). Adsorption of (bi)sulfate on the nm-Pt/S(n) was studied by in situ FTIR reflection spectroscopy. It has been revealed that the nanostructured Pt electrodes exhibit anomalous IR properties for (bi)sulfate adsorption regardless of the different reflectivity of substrate, i.e. the IR absorption of (bi)sulfate species adsorbed on all the nm-Pt/S(n) electrodes is significantly enhanced and the IR band direction is completely inverted in comparison with the same species adsorbed on a bulk Pt electrode. The two IR bands around 1200 and 1110 cm⁻¹ attributed to adsorbed (bi)sulfate species are shifted linearly with increasing electrode potential, yielding Stark tuning rates () of 152.1 and 21.1 cm⁻¹ V⁻¹ on nm-Pt/GC(20), respectively. Along with increasing n, the Stark tuning rate of the IR band around 1200 cm⁻¹ decreases quickly and declined to 7.6 cm⁻¹ V⁻¹ on nm-Pt/GC(80), while the Stark tuning rate of the IR band near 1100 cm⁻¹ is fluctuated between 23.0 and 16.2 cm⁻¹ V⁻¹. It has determined that the enhancement of IR absorption of (bi)sulfate adsorbed on nanostructured Pt electrode is varied with substrate material and n, and a maximal 16-fold enhancement of the IR band near 1200 cm⁻¹ has been measured on the nm-Pt/GC(30) electrode. The in situ FTIR studies illustrated that the adsorption of (bi)sulfate occurs mainly in the double layer potential region, and reaches a maximum around 0.80 V. The results demonstrated also that the competitive adsorption of CO and oxygen species can inhibit completely (bi)sulfate adsorption, which has evidenced a weak interaction of (bi)sulfate with nm-Pt/S(n) electrode surface.     

CO adsorption and correlation between CO surface coverage and activity/selectivity of preferential CO oxidation over supported Ag catalyst: an in situ FTIR study

In situ IR measurements for CO adsorption and preferential CO oxidation in H₂-rich gases over Ag/SiO₂ catalysts are presented in this paper. CO adsorbed on the Ag/SiO₂ pretreated with oxygen shows a band centered around 2169 cm^–1, which is assigned to CO linearly bonded to Ag⁺ sites. The amount of adsorbed CO on the silver particles (manifested by an IR band at 2169 cm^–1) depends strongly on the CO partial pressure and the temperature. The steady-state coverage on the Ag surface is shown to be significantly below saturation, and the oxidation of CO with surface oxygen species is probably via a non-competitive Langmuir–Hinshelwood mechanism on the silver catalyst which occurs in the high-rate branch on a surface covered with CO below saturation. A low reactant concentration on the Ag surface indicates that the reaction order with respect to Pco is positive, and the selectivity towards CO₂ decreases with the decrease of Pco. On the other hand, the decrease of the selectivity with the reaction temperature also reflects the higher apparent activation energy for H₂ oxidation than that for CO oxidation.     

Infrared spectroscopic and voltammetric study of adsorbed CO on stepped surfaces of copper monocrystalline electrodes

Voltammetric and infrared (IR) spectroscopic measurements were carried out to study adsorbed CO on two series of copper single crystal electrodes n(1 1 1)-(1 1 1) and n(1 1 1)-(1 0 0) in 0.1 M KH₂PO₄ + 0.1 M K₂HPO₄ at 0 °C. Reversible voltammetric waves were observed below −0.55 V versus SHE for adsorption of CO which displaces preadsorbed phosphate anions. The electric charge of the redox waves is proportional to the step atom density for both single crystal series. This fact indicates that phosphate anions are specifically adsorbed on the step sites below −0.55 V versus SHE. Voltammetric measurements indicated that (1 1 1) terrace of Cu is covered with adsorbed CO below −0.5 V versus SHE. Nevertheless, no IR absorption band of adsorbed CO is detected from (1 1 1) terrace. Presence of adsorbed CO on (1 1 1) terrace is presumed which is not visible by the potential difference spectroscopy used in the present work. IR spectroscopic measurements showed that CO is reversibly adsorbed with an on-top manner on copper single crystal electrodes of n(1 1 1)-(1 1 1) and n(1 1 1)-(1 0 0) with approximately same wavenumber of CO stretching vibration of 2070 cm⁻¹. The IR band intensity is proportional to the step atom density. Thus CO is adsorbed on (1 1 1) or (1 0 0) steps on the single crystal surfaces. An analysis of the IR band intensity suggested that one CO molecule is adsorbed on every two or more Cu step atom of the monocrystalline surface. The spectroscopic data were compared with those reported for uhv system. The CO stretching wavenumber of adsorbed CO in the electrode-electrolyte system is 30-40 cm⁻¹ lower than those in uhv system.     

Interactions between interfacial water and CO adsorbed on Pt and Pt-Ru alloy surfaces under electrochemical conditions: Density-functional theory study

The structural and electronic properties of interfacial water and adsorbed CO on platinum and platinum/ruthenium alloy have been studied via density-functional theory calculations to gain insight into the water-adsorbate interaction under electrochemical conditions. The computational simulations reveal a new interpretation for the interaction of adsorbed CO and water at the electrochemical interfaces. The new interaction model rationalizes the observed quantitative relationship between infrared intensities for adsorbed bridging CO and water molecules that impart a high-frequency O-H stretch, ca. 3630-3660 cm⁻¹ on pure Pt and 3600-3620 cm⁻¹ on PtRu alloy. The theoretical modeling indicates that the observed feature common to both pure Pt and PtRu alloy surfaces is due to interfacial water molecules firmly hydrogen-bonded to bridging CO.     

CO tolerance effects of tungsten-based PEMFC anodes

The performance of proton exchange membrane fuel cells (PEMFC) fed with CO-contaminated hydrogen was investigated for anodes with PtWO_x/C and phosphotungstic acid (PTA) impregnated Pt/C electrocatalysts. A quite high performance was achieved for the PEMFC fed with H₂ + 100 ppm CO with anodes containing 0.4 mg PtWO_x cm⁻² and also for those with 0.4 mg Pt cm⁻² impregnated with ca. 1 mg PTA cm⁻². A decay of the single cell performance with time is observed, and this was attributed to an increase of the membrane resistance due to the polymer degradation promoted by the crossover of the tungsten species throughout the membrane.     

SFG study on potential-dependent structure of water at Pt electrode/electrolyte solution interface

Structure of water at Pt/electrolyte solution interface was investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at ca. 3200 cm⁻¹ and ca. 3400 cm⁻¹, which are known to be due to the symmetric OH stretching (υ₁) of tetrahedrally coordinated, i.e., strongly hydrogen bonded “ice-like” water, and the asymmetric OH stretching (υ₃) of water molecules in a more random arrangement, i.e., weakly hydrogen bonded “liquid-like” water, respectively. The SFG intensity strongly depended on electrode potential. Several possibilities are suggested for the potential dependence of the SFG intensity.     

Finely dispersed Pt nanoparticles in conducting poly(o-anisidine) nanofibrillar matrix as electrocatalytic material

A new approach based on stepwise oxidation of o-anisidine is explored for generating nanoporous films of poly(o-anisidine), POA and loading of Pt nanoparticles that are subsequently used for electrocatalysis of methanol oxidation are presented and compared with bulk Pt. POA film can easily be prepared by stepwise electro-oxidation procedure with very high porosity consisting of nanofibrillar structure using without templates. Controlled sizes of Pt nanoparticles were entrapped into POA matrix by a two-step process in which first PtCl₆²⁻ ions are sorbed into the pores of polymer matrix followed by electroreduction at −0.55 V in a 0.5 M H₂SO₄ solution. Loading of Pt nanoparticles (10-200 μg/cm²) onto POA matrix were accomplished by varying the concentration (2-10 mM) of the sorbate, i.e., H₂PtCl₆. The sizes of the Pt nanoparticles were determined from TEM analysis and Pt particles were found to be in the range of 10-20 nm. The crystallite phase of Pt particles in POA was examined from XRD pattern. AFM image further supports Pt particles embedded in POA matrix.     

Infrared Study of Benzene Hydrogenation on Pt/SiO2 Catalyst by Co-adsorption of CO and Benzene

FT-IR spectra of the co-adsorption of benzene and CO have been performed to identify the preferred adsorption sites of hydrogen and benzene on a Pt/SiO₂ catalyst for hydrogenation of benzene. Results of CO adsorbed on atop sites on Pt/SiO₂ includes: an α peak at 2091 cm⁻¹, a β peak at 2080 cm⁻¹ and a γ peak at 2067 cm⁻¹ indicating three kinds of adsorption sites for dissociative hydrogen on Pt/SiO₂. The site of lowest CO stretching frequency offers stronger adsorbates–metal interaction for benzene and hydrogen. Hydrogen binding on the site of lowest CO stretching frequency before benzene adsorption significantly enhances the reaction rate of benzene hydrogenation.     

CO oxidation and CO2 reduction on carbon supported PtWO3 catalyst

The activity of a carbon supported PtWO₃ (PtWO₃/C) catalyst in the CO oxidation and CO₂ reduction reactions was evaluated in sulfuric acid solution at room temperature.Cyclic voltammetry combined with on-line mass spectrometry shows that the oxidation of both saturated CO adlayer and dissolved CO on PtWO₃/C material commences at rather low potentials, ca. 0.18 and 0.12 V vs. RHE, respectively. However, the low-potential process seems to involve only a minor fraction of the CO adlayer, the major part of the adsorbed CO layer being oxidised at the potentials as high as those for pure Pt catalysts—ca. 0.7 V vs. RHE. PtWO₃/C material was found to reversibly de-activate upon a prolonged exposure to the CO-saturated solution due to the inhibition of the hydrogen tungsten bronze formation.The reduction of CO₂ on PtWO₃/C leads to the formation of an adsorbate - presumably CO - on the Pt sites of the catalyst. Although the rate of the adsorbate build-up on PtWO₃/C at 0.1 V is lower than that on pure Pt/C, our results indicate that upon a prolonged exposure of the PtWO₃/C electrode to a CO₂-saturated solution a complete poisoning of the Pt sites with the adsorbate is likely to occur at room temperature.