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The effect of Mn addition on the promotion of oxygen reduction reaction performance for PtCo/C catalysts

The effect of Mn addition on the promotion of oxygen reduction reaction (ORR) performance for PtCo/C catalysts is investigated. The structures, surface compositions, chemical compositions, local structural parameters including coordination numbers and bond distances, morphologies and electrochemical properties of prepared catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-atomic emission spectrometer (ICP-AES), extended X-ray absorption fine structure (EXAFS), high resolution transmission electron microscopy (HRTEM) and rotating disk electrode (RDE) technique, respectively.For PtCo/C catalysts modified with 0.4 and 3.2wt% of Mn, the Pt/Co atomic ratio is 3.5 and the size is about 3.0nm with the same face centered cubic (fcc) structure. Moreover, Mn-modified PtCo/C catalysts have the same surface composition, which is about Pt/Co/Mn of 62/32/6, and their ORR activity are both higher than that of PtCo/C and commercial Pt/C catalysts. After accelerated durability test (ADT) of 1700 cycles, Mn-2 with 3.2wt% Mn addition still presents the best ORR mass activity, which is about 420% of commercial Pt/C. In the Mn-modified PtCo/C system, due to the existence of the neighboring Co and/or Mn oxide, there is OH repulsion between Pt–OH and these non-noble metal hydroxides or oxides, decreasing the OH coverage on Pt and increasing the number of free Pt active sites. Besides, based on the XAS analysis, the unfilled d-orbital values and extent of hybridization of Pt and Co/Mn of the PtCo and Mn-modified samples are very similar. Therefore, the promotional effect on ORR performance of Mn-2 is attributed to the most enhanced Pt-skin structure, highest Pt usage, and comparable electron transfer number during ORR instead of changes in d-orbital vacancy and alloying degree.

Microwave-assisted synthesis of PtRu/CNT and PtSn/CNT catalysts and their applications in the aerobic oxidation of benzyl alcohol in base-free aqueous solutions

Ru promoted the reaction by reacting with surface Pt-hydride species to liberate free Pt active sites while adding Sn enhances the electronic interactions. Moreover, acid functionalized CNT was identified as the superior support due to its hydrophilic surfaces, conical stacking structures, and tubular structure with mesoporous open-ended morphology.

Chemical kinetics parameters of nuclear graphite gasification

This paper provides chemical kinetics parameters for the gasification of nuclear graphite grades of IG-110, IG-430, NBG-18 and NBG-25 and presents empirical correlations for their surface areas of free active sites as a function of mass. The kinetics parameters for the four elementary chemical reactions of gasification of these grades of nuclear graphite include the values and Gaussian distributions of the specific activation energies and the values of the pre-exponential rate coefficients for the adsorption of oxygen and desorption of CO and CO2 gases. The values of these parameters and the surface area of free active sites for IG-110 and NB-25, with fine and medium petroleum coke filler particles, are nearly the same, but slightly different from those of NBG-18 and IG-430, with medium and fine coal tar pitch coke filler particles. Recommended parameters are applicable to future safety analysis of high and very high temperature gas cooled reactors in the unlikely event of a massive air ingress accident.

Fabrication of a novel PtPbBi/C catalyst for ethanol electro-oxidation in alkaline medium

This work presents a general strategy to fabricate a new type of ternary intermetallic PtPbBi/C nano-catalyst. X-ray diffraction, transmission electron microscope and X-ray photoelectron spectroscopy data demonstrate that some Pb atoms are imbedded into Pt lattice to form PtPb alloy particles in the microwave action. The PtPb/C catalyst surface is further modified by Bi via a spontaneous and irreversible chemisorption approach. Ethanol oxidation peak current on PtPbBi/C (217.9mAcm−2) is about 4.1 times higher than that on Pt/C (53.6mAcm−2) in cyclic voltammograms. Tafel plots show that both ethanol dehydrogenation and removal of CO-like species are greatly enhanced on the novel PtPbBi/C catalyst. Constant potential and linear current sweep tests indicate that the addition of Pb and Bi causes the formation of abundant oxygenated species on the catalyst surface at low potential. These oxygenated species can react with poisonous intermediates formed during ethanol oxidation, and help the release of free Pt active sites for further adsorption and electro-oxidation of ethanol molecules.

Low‐Temperature Gas‐Phase Oxidation of Benzyl Alcohol on Mesoporous K‐Cu‐TiO2 through Oxidative Dehydrogenation

AbstractA highly selective, gas‐phase benzyl alcohol‐to‐benzaldehyde transformation is achieved over mesoporous multi‐component metal oxide K‐Cu‐TiO2 (prepared by AcHE process) at a surprisingly low temperature: the b.p. of benzyl alcohol, 203 °C. We propose that highly efficient selective oxidation over K‐Cu‐TiO2 occurs through an oxidative dehydrogenation mechanism based on the catalytic performance with controlled oxygen addition and the observation of surface hydride species on the catalyst surface by electron paramagnetic resonance spectroscopy and spin‐trapping techniques. It was observed that the benzyl alcohol conversion increased sharply with the increase in p and reached a maximum of 80.4 % at p/pBA=0.4–0.6. A further increase in the p slightly decreased the benzyl alcohol conversion. The fact that the reaction rate was independent of the oxygen pressure after the stoichiometric p/pBA ratio (0.5) could indicate a fast reoxidation of CuIH by molecular oxygen, which is, therefore, not the rate‐controlling step. No hydride species have been detected on the catalyst that was collected from the alcohol oxidation reaction performed with added O2, suggesting that O2 acts as efficient hydrogen acceptor and accelerate the reaction by liberating free active CuI sites. Based on understanding of the reaction mechanism, in addition to the low‐temperature reaction condition, stoichiometrical addition of O2 proves effective in the stabilisation of the CuI oxidation state for highly selective benzyl alcohol oxidative dehydrogenation over a wide reaction temperature range (up to 310 °C).

Validation of gasification model for NBG-18 nuclear graphite

This paper introduces a chemical kinetics model and compares its calculations with reported measurements of weight loss and total gasification rate for different NBG-18 nuclear graphite specimens in experiments performed at 876–1226K. Results show that the gasification rate is chemical-kinetics limited at low and intermediate temperatures and diffusion-limited at high temperatures. At high temperatures, the model calculates the diffusion velocity of oxygen through the boundary layer using a developed correlation for Reynolds numbers of 0.006–1000. The agreement of the calculations with reported measurements of the total gasification rate and transient weight loss confirms the soundness of the chemical kinetics approach and validates the developed model and the multi-parameter optimization algorithm for determining the chemical kinetics parameters, based on reported measurements. These parameters are the values and Gaussian-like distributions of the specific activation energies for oxygen adsorption and desorption of CO, the specific activation energy for desorption of CO2, the initial surface area of free active sites and the rate constants for the four elementary chemical reactions in the model. The performed parametric analyses for NBG-18 nuclear graphite specimens investigated the effects of temperature and oxygen partial pressure on total gasification rate and production rates of CO and CO2 gases, for wide ranges of temperatures and oxygen partial pressures.

Comparison of oxidation model predictions with gasification data of IG-110, IG-430 and NBG-25 nuclear graphite

A phenomenological oxidation kinetics model of graphite is presented and its results are compared with the reported experimental gasification data for nuclear graphite of IG-110, IG-430 and NBG-25. The model uses four elementary chemical kinetics reactions, employs Gaussian-like distributions of the specific activation energies for adsorption of oxygen and desorption of CO gas, and accounts for the changes in the effective surface areas of free active sites and stable oxide complexes with weight loss. The distributions of the specific activation energies for adsorption and desorption, the values of the pre-exponential rate coefficients for the four elementary chemical reactions and the surface area of free active sites are obtained from the reported measurements using a multi-parameter optimization algorithm. At high temperatures, when gasification is diffusion limited, the model calculates the diffusion velocity of oxygen in the boundary layer using a semi-empirical correlation developed for air flows at Reynolds numbers ranging from 0.001 to 100. The model also accounts for the changes in the external surface area, the oxygen pressure in the bulk gas mixture and the effective diffusion coefficient in the boundary layer with weight loss. The model results of the total gasification rate and weight loss with time in the experiments agree well with the reported measurements for the three types of nuclear graphite investigated, at temperatures from 723 to 1226 K and weight loss fractions up to ∼0.86.

Influence of polyhydric solvents on the catalytic & adsorption properties of self-oriented mesoporous SBA-15 silica

Mesoporous materials (2–50 nm) have generated much interest due to its multi-faceted applications as catalysts, adsorbents and drug delivery systems. This study is the first of its kind to systematically investigate the effect of polyhydric solvents on the morphology, catalytic and adsorption properties of self-oriented mesoporous silica. Three different mesoporous SBA-15 silica materials were synthesized using Water (SW), Glycerol (SG) and Ethylene Glycol (SEG) as solvent. They were characterized using FE-SEM, HR-TEM, small angle XRD, FT-IR, BET and solid state NMR. Morphological studies such as pore characteristics, surface area and the functionalization were carried out by comparing their catalytic and adsorption properties. Each mesoporous sample was used to catalyze biodegradable aliphatic polyester synthesis namely poly (butylene succinate), poly (butylene pimelate) and poly (butylene sebacate) and compared with a conventional homogeneous catalyst SnCl2·2H2O. The results offered higher purity and yield of polyesters and they took the order as SW > SG > SEG. The adsorption efficiency of each mesoporous sample was compared using the fluorescent dye Rhodamine-B and it took a reverse order (SEG > SG > SW) to that of the catalytic efficiency. This difference may be attributed to the difference in free active sites, ordered morphology of pores and surface area. The synthesized polyesters were characterized using FT-IR, 1H NMR, XRD, GPC, DSC and the adsorption studies, using UV–Visible spectrophotometer.

A Highly Conserved Motif within the NH2-terminal Coiled-coil Domain of Angiopoietin-like Protein 4 Confers Its Inhibitory Effects on Lipoprotein Lipase by Disrupting the Enzyme Dimerization

Lipoprotein lipase (LPL) is a principal enzyme responsible for the clearance of chylomicrons and very low density lipoproteins from the bloodstream. Two members of the Angptl (angiopoietin-like protein) family, namely Angptl3 and Angptl4, have been shown to inhibit LPL activity in vitro and in vivo. Here, we further investigated the structural basis underlying the LPL inhibition by Angptl3 and Angptl4. By multiple sequence alignment analysis, we have identified a highly conserved 12-amino acid consensus motif that is present within the coiled-coil domain (CCD) of both Angptl3 and Angptl4, but not other members of the Angptl family. Substitution of the three polar amino acid residues (His(46), Gln(50), and Gln(53)) within this motif with alanine abolishes the inhibitory effect of Angptl4 on LPL in vitro and also abrogates the ability of Angptl4 to elevate plasma triglyceride levels in mice. The CCD of Angptl4 interacts with LPL and converts the catalytically active dimers of LPL to its inactive monomers, whereas the mutant protein with the three polar amino acids being replaced by alanine loses such a property. Furthermore, a synthetic peptide consisting of the 12-amino acid consensus motif is sufficient to inhibit LPL activity, although the potency is much lower than the recombinant CCD of Angptl4. In summary, our data suggest that the 12-amino acid consensus motif within the CCD of Angptl4, especially the three polar residues within this motif, is responsible for its interaction with and inhibition of LPL by blocking the enzyme dimerization.

Ultra-sensitive detection of mutated papillary thyroid carcinoma DNA using square wave stripping voltammetry method and amplified gold nanoparticle biomarkers

This study presents an ultra-sensitive technique for the electrochemical detection of the mutated BRAF gene associated with papillary thyroid carcinomas (PTC). In the proposed approach, a biotinylated 30-nucleotides probe DNA was immobilized in a streptavidin-modified 96-well microtiter plate and the free active sites of the streptavidin were blocked using biotinylated bovine serum albumin (BSA). The biotinylated target DNA was then added and allowed to hybridize with the immobilized probe DNA for 30min. Subsequently, streptavidin-labeled gold nanoparticles were added, and a nanoparticle enlargement process was performed using gold ion solution and formaldehyde reductant. The gold particles were then dissolved in bromide and DNA hybridization detection process was performed using a square wave stripping voltammetry (SWSV) technique. The results indicated a stable SWSV response in differential detection between blank solution and target DNA solution with a concentration of 130aM. Moreover, the coefficient of determination (R2) of the semi-log plot of the SWSV response current against the target DNA concentration (0.52–1300aM) was found to be 0.9982. The detection limit was estimated to be 0.35aM (based on a signal-to-noise ratio of 3:1). This value was approximately three orders of magnitude lower than that obtained using the same method but without gold amplification process. Finally, the proposed approach is successful in differentiating between the mutant and wildtype BRAF sequences that are present in genuine 224-nucleotides DNA.

Comparison of Dissolution Profiles for Sustained Release Resinates of BCS Class I Drugs Using USP Apparatus 2 and 4: A Technical Note

In vitro dissolution specifications are established to ensure batch-to-batch consistency while pointing out any potential problems with in vivo bioavailability among different drug products (1). At early stages of formulation development, in vitro dissolution testing provides guidance on optimizing drug release from formulations. While at later stages, it may be employed as an indicator of the in vivo performance of drug products to potentially reduce the number of bioavailability/bioequivalence studies. An established IVIVC can be further used to set meaningful dissolution specifications that take clinical consequences into account in the hope of facilitating regulatory approvals of post approval changes. Among the different in vitro systems available for testing, USP Dissolution apparatus 4 offers a viable option for carrying out dissolution of novel dosage forms (2,3). USP Dissolution apparatus 4 is helpful in: testing robustness of the formulation with respect to the variations in the intralumenal environment, maintaining sink conditions for the poorly soluble drugs (4,5) and non tedious method to change pH of the dissolution medium (6). USP Dissolution apparatus 4 has been extensively studied for the prediction of in vivo performance of orally administered dosage forms like amoxicillin capsules (7), paracetamol (8), carbamazepine (9), danazole capsules (10), spironolactone (11). It is the method of choice for extended release and poorly soluble drugs. Point to point correlation of in vitro release data using flow through cell apparatus is established for monolithic extended release formulations of highly permeable isosorbide-5-mononitrate (12). Similarly, good in vitro in vivo correlation was reported for vincamine extended release formulations (13). The development of flow through cell came about as an attempt to provide controlled hydrodynamic environment and renewable stream to the sample and has proven to be a useful tool in determining the in vitro release of the extended release formulations. Extended release formulation can be formulated using polymer (14), lipids/waxes (15), ion exchange resins (16) etc. Ion exchange resins have recently been gaining importance in pharmaceutical industries in the manufacturing of extended release formulations. IER are water insoluble, cross-linked polymers containing salt forming groups in repeating positions on the polymer chains. IER form a complex with the drug through weak ionic bonding. Drug release from resinate depends on pH and electrolyte concentration within the gastrointestinal tract. With basic drugs, strong cationic exchange resins (sulfonic acid) yield strong drug resin bonding resulting in slower elution of drug from resinates and this principle has exhibited the potential of resins as sustained release agents (17,18). The presence of released drug and ion exchange resin with free active sites has a significant effect on the further release of drug from resinate. This effect will be more pronounced while dealing with BCS class I drugs. Butler et al. (6) has mentioned the usage of USP Dissolution apparatus 4 particularly for drugs with low solubility as it can maintain the sink condition, independent of drug solubility. Hitherto there are no reports in the literature that cite the necessity of maintaining sink conditions while performing in vitro release of sustained release resinates of highly soluble drug. Release data based on a well thought out test is of tremendous value in selection of right formulation. Therefore, the present work was focused on studying the effect of USP Dissolution apparatus 2 and 4 on the in vitro release of drug from resinates of BCS class I drugs.

Mechanistic origin of the different activity of Rh-ZSM-5 and Fe-ZSM-5 in N 2O decomposition

A temporal analysis of products (TAP) reactor was used to study relationships between the mechanism of direct N 2O decomposition over metal-loaded zeolites and their resulting activity. Rh-ZSM-5 (prepared by incipient wetness) and Fe-ZSM-5 (prepared by liquid-ion exchange) were chosen as prototypic catalysts displaying low (<550 K) and high (>650 K) temperature activity, respectively. Transient studies at the same contact time revealed the higher activity of Rh-ZSM-5 below 623 K and significantly stronger N 2O adsorption over Rh species than over Fe species in the zeolites. Several microkinetic models were applied for simultaneous fitting the transient responses of N 2O, N 2, and O 2. Classical reaction schemes failed to describe the experimental data. The preferred models of N 2O decomposition over Rh-ZSM-5 and Fe-ZSM-5 differ in the reaction pathways of O 2 formation. For both catalysts, free active metal sites (*) and those occupied by monoatomic oxygen species (*-O) from N 2O participate in the decomposition of gas-phase N 2O. Gas-phase O 2 is formed directly on N 2O interaction with *-O over Rh-ZSM-5, whereas the latter reaction over Fe-ZSM-5 leads to a surface bi-atomic oxygen species (O-*-O), followed by its transformation to *-O 2. The latter species desorbs as molecular oxygen. Comparison of ion-exchanged and steam-activated Fe-ZSM-5 [J. Phys. Chem. B 110 (2006) 22586] revealed that the reaction mechanism is independent of the iron constitution induced by the preparation and activation routes, despite important differences in catalytic activity. Our quantitative microkinetic analysis demonstrated that both the stronger reversible N 2O adsorption and, most importantly, the faster desorption of O 2 are distinctive mechanistic features of Rh-ZSM-5, likely indicating its high de-N 2O activity.

The kinetics of the electrochemical reduction of perchlorate ions on rhodium

The reduction of ClO 4 − ions in acid media was studied at smooth polycrystalline rhodium electrodes by voltammetry, chronoamperometry and impedance spectroscopy. On the basis of the experimental results, a new mechanism for the electrocatalytic reduction of ClO 4 − ions has been proposed. According to this reaction scheme, the reduction process is starting with the adsorption of perchlorate ions at free active sites on the metal surface. It is also assumed that the whole process starting from perchlorate ion occurs on the surface and the role of desorption of intermediates can be neglected. On the basis of the kinetic model an expression has been derived for the impedance of the electrode, which fits the experimental data quite well.

Influence of fine lactose and magnesium stearate on low dose dry powder inhaler formulations

The behaviour of dry powder blends for inhalation, depending on the amount of fine lactose particles smaller than 10 μm and the presence of magnesium stearate (MgSt), was studied in this work. A laser light diffraction method was developed to determine accurately size and volume fraction of these fine lactose particles in coarse carrier lactose ( x 50 ∼ 220 μm). A linear relationship between measured volume fraction undersize at 10 μm Q 3(10 μm) and added fine lactose could be established. Aerodynamic particle size distribution analysis of lactose showed that the fine lactose was attached to the coarse particles. In the presence of MgSt this interaction was increased. Consequently, the number of free active sites on the carrier surface was reduced and the investigated drug (formoterol fumarate dihydrate) was more effectively delivered. Addition of fine lactose and MgSt improved the aerodynamic performance the drug, as determined by resulting fine particle fraction, by 3% (for each 1% of added fine lactose) and 10%, respectively. Stability tests indicated that added MgSt was the most relevant of the studied parameter to achieve a stable aerodynamic performance. Its ability to protect the moisture uptake into the system was considered as rational for this effect.

Mathematical modelling of oscillatory behaviour during methane oxidation over Ni catalysts

There are many experimental demonstrations of oscillatory behaviour during methane oxidation over Ni catalysts however the origin of the nonlinear behaviour in this system is not clearly understood yet. The new kinetic scheme for methane oxidation over Ni catalysts and mathematical model of the nonlinear reaction dynamics are developed. The model is derived in the mean field approximation and describes qualitatively the main properties of oscillatory behaviour observed experimentally during the reaction of methane oxidation over Ni catalysts. It was demonstrated that thermokinetic oscillations in this system originate due to periodic oxidation–reduction of the catalyst surface, the variation of the selectivity of the process and the competition of reactants for the free active sites.

Swift heavy ion induced structural and chemical changes in BOPP film

Swift heavy ions (SHIs), such as, 80MeV Si7+ and 120MeV Ag9+ ions were used to irradiate 15μm bi-axially oriented polypropylene (BOPP) films. The fluence (Φ) dependence of the structural and chemical changes in BOPP was investigated. The irradiated BOPP films were analyzed ex situ by means of FTIR, UV and DSC. Due to SHI irradiation, the isotactic helical structure of polypropylene (PP) gets reduced. PP undergoes distortion of its crystal lattice in magnitude proportional to the fluence. The scission of C–H bonds and production of unsaturated groups like dienes and trienes occurred after irradiation with Si ions for Φ⩾1012ions/cm2 and Ag ions for Φ⩾1011ions/cm2. It was found that Ag ions are better than Si ions for creation of free radical active sites on BOPP. The observed findings are very useful particularly in the selection of optimum experimental conditions for SHI induced graft copolymerization.

Destruction of o-Chloroaniline in UV/TiO2 Reaction with Photosensitizing Additives

The photodecay of o-chloroaniline (o-ClA) in TiO2 suspension with and without the use of additives was examined under an ultraviolet light at 300 nm. An analysis showed that the disappearance of o-ClA followed a pseudo first-order reaction and can be described by the Langmuir−Hinshewood (LH) model. The application of various dosages of TiO2 indicated a discontinuous linear increment at a break point of 0.1 g L-1 TiO2. The change in the system pH has a significant effect on the performance of the process. This is a mixed result of the surface charge of TiO2 and the chemical characteristic of o-ClA, which is discussed in detail in this paper. The further enhancement of the UV/TiO2 process by adding H2O2 is feasible if the dosage is carefully controlled. The addition of excess amounts of H2O2 should be avoided to minimize the scavenging of hydroxyl radicals in the solution and valence-band holes at the TiO2 surface. The use of the sensitizer Rose Bengal (RB) in the UV/TiO2 process, however, is not suggested. This is because RB is not sensitive at the optimal wavelength for the photocatalytic process involving TiO2; in addition, the RB may become an additional competitor (with the probe) for the free radicals and active sites on the TiO2 surface.

Kinetics of the partial oxidation of methanol over a Fe-Mo catalyst

The intrinsic steady-state kinetics of the partial oxidation of methanol to formaldehyde over a commercial Fe-Mo catalyst has been studied experimentally in a differentially operated reactor at temperatures of 230–260 °C, over a wide range of methanol and oxygen concentrations. The principal products found were formaldehyde, water, dimethyl ether (DME) and dimethoxymethane (DMM). The kinetics of the formaldehyde formation from methanol could be well described with Langmuir–Hinshelwood kinetics, assuming two different metal oxide sites, one containing adsorbed oxygenates and the other one containing lattice oxygen. The presence of water vapor lowered the formaldehyde formation rate significantly, especially at lower water partial pressures. These results could be well explained in terms of competitive adsorption of water with methanol on the free active catalyst sites. For the most important side reactions, i.e. dimethyl ether formation as well as dimethoxymethane formation the forward reaction rates were determined from the selectivity data. The conversion rate of dimethyl ether to formaldehyde was also measured with separate experiments in the differential reactor. Carbon monoxide was not formed during the differential kinetic measurements of formaldehyde formation from methanol. Therefore, the rate of formaldehyde oxidation to CO was studied separately in a dual bed catalyst, where formaldehyde was formed in the first integral reactor at low temperatures and subsequently converted to CO in a differential reactor. The rate of CO formation was first order in formaldehyde and the oxygen dependency was the same as that for the formaldehyde formation from methanol. Rate expressions for all reactions were formulated based on the above assumptions and a multivariate Levenberg–Marquardt method was used to fit all the model constants to all the experiments for all reaction rates simultaneously, while additionally accounting for axial concentration profiles in the reactor. The observed influences of composition and temperature on the reaction rates could be well described.

Structure and chemical composition of supported Pt–Sn electrocatalysts for ethanol oxidation

Carbon supported PtSn alloy and PtSnO x particles with nominal Pt:Sn ratios of 3:1 were prepared by a modified polyol method. High resolution transmission electron microscopy (HRTEM) and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of PtSn particles. The particles are predominantly single nanocrystals with diameters in the order of 2.0–3.0 nm. According to the XRD results, the lattice constant of Pt in the PtSn alloy is dilated due to Sn atoms penetrating into the Pt crystalline lattice. While for PtSnO x nanoparticles, the lattice constant of Pt only changed a little. HRTEM micrograph of PtSnO x clearly shows that the change of the spacing of Pt (1 1 1) plane is neglectable, meanwhile, SnO 2 nanoparticles, characterized with the nominal 0.264 nm spacing of SnO 2 (1 0 1) plane, were found in the vicinity of Pt particles. In contrast, the HRTEM micrograph of PtSn alloy shows that the spacing of Pt (1 1 1) plane extends to 0.234 nm from the original 0.226 nm. High resolution energy dispersive X-ray spectroscopy (HR-EDS) analyses show that all investigated particles in the two PtSn catalysts represent uniform Pt/Sn compositions very close to the nominal one. Cyclic voltammograms (CV) in sulfuric acid show that the hydrogen ad/desorption was inhibited on the surface of PtSn alloy compared to that on the surface of the PtSnO x catalyst. PtSnO x catalyst showed higher catalytic activity for ethanol electro-oxidation than PtSn alloy from the results of chronoamperometry (CA) analysis and the performance of direct ethanol fuel cells (DEFCs). It is deduced that the unchanged lattice parameter of Pt in the PtSnO x catalyst is favorable to ethanol adsorption and meanwhile, tin oxide in the vicinity of Pt nanoparticles could offer oxygen species conveniently to remove the CO-like species of ethanolic residues to free Pt active sites.

A simple discrimination of the promoter effect in alcohol oxidation and dehydrogenation over platinum and palladium

Several models have been suggested to interpret the positive effect of Bi, Pb, and other metal promoters in the oxidative dehydrogenation of alcohols over Pt-group metal catalysts, though the experimental proof to these models is mainly missing. Here we propose a new and simple approach for clarifying the promoter effect: the comparison of dehydrogenation in inert atmosphere and oxidative dehydrogenation in the presence of oxygen over promoted and unpromoted catalysts. As test reactions the transformations of 1-phenylethanol, 2-octanol, and cinnamyl alcohol to the corresponding carbonyl compounds in a slurry reactor are used. The observed promoter effects can be classified into three groups: (i) acceleration of the hydrogen abstraction (dehydrogenation) step, (ii) acceleration of a reaction involving the transfer of (chemisorbed) oxygen, e.g., oxidation of the coproduct hydrogen or a surface impurity, thus generating free active sites, and (iii) a combination of these two different processes. This discrimination revealed that the metal promoter may have a dual effect on the aerobic oxidation of alcohols, and this behavior may rationalize some former controversial interpretations. Besides, this study presents the first evidence for the promoting effect of Bi in alcohol dehydrogenation in the absence of oxygen.