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Catalytic combustion is considered as one of the most efficient routes for removing volatile organic compounds. In recent years, the catalytic activities of catalysts have usually been evaluated by the values of TOF and T98. It is difficult, however, to measure the values accurately because the influencing factors are numerous and easy to be overlooked. In this work, the influence of the catalytic test procedure on TOF and T98 values was investigated. Supported Pd or Pt catalysts were prepared via the incipient wetness impregnation method. The catalytic activities of the same catalyst were very different when evaluated in different catalytic test procedures. Indeed, the catalytic test procedures affected the TOF and T98 values remarkably. It was found that the different coking behavior in different catalytic test procedures is the major cause. The influences on coke formation in toluene combustion - such as reaction temperature, reaction time, and catalyst type - were investigated. [ABSTRACT FROM AUTHOR]

We synthesized SiCN nanowires by a combination of high-energy ball milling and post-heat treatment using high-purity silicon and carbon nanopowders (<100 nm), and evaluated the effects of process parameters on their structural, chemical, optical properties, photoelectrocatalytic and photocatalytic activities. Cubic SiCN crystal phase with a lattice constant of 4.35 Å was observed. The optical bandgap of 2.20 eV was observed with nanowire diameters ranging from 23 nm to 37 nm. The SiCN nanowires showed good photocatalytic activity with the highest degradation percentage of ∼99% in 40 min for the degradation of Rhodamine B dye under visible light, and a degradation rate of 0.0841 min −1 . The SiCN nanowires showed no significant reduction in photocatalytic activity for five consecutive cycles, indicating that they are extremely stable against organic dyes. The SiCN nanowires were used for photoelectrochemical water splitting and the effect of electrolytes was studied. The highest photocurrent density of 5 × 10 -2 mAcm -2 vs. Ag/AgCl in 0.1 M KOH solution was achieved owing to the improved visible light collection and electron hole separation. The exchange current density, Tafel slopes, and limiting diffusion current density were found to be 3.17 mAcm -2 , 68.13 mVdec −1 , and 1.54 mAcm -2 , respectively. Further, the specific capacitance of the SiCN nanowires was estimated, obtained of 188 mFcm -2 at a current density of 5 mAcm -2 . [ABSTRACT FROM AUTHOR]

Thermal treatment of a product formed in the interaction of activated aluminum with water yielded alumina having a specific surface area of 250 m2 g-1, uniform pore size distribution, and average pore size of 7.8 nm. A platinum catalyst on its basis exhibited high activity and stability in propane conversion at a selectivity of propylene formation higher than 90% and suppressed reaction of hydrogenolysis of C-C bonds. [ABSTRACT FROM AUTHOR]

This paper presents the results of comparative analysis of three run cycles of platinum catalyst for higher paraffins C9-C14 dehydrogenation process, performed using mathematical model. The results of model calculations were compared with the experimental data obtained at the industrial unit. It was established that deactivation of the platinum dehydrogenation catalyst is influenced by the technological modes of its operation, such as temperature, pressure, hydrogen/feedstock molar ratio and water supply. In the process of higher paraffins dehydrogenation, the phenomenon of platinum catalyst self-regeneration is observed. This occurs due to the action of feedstock components, in particular water and hydrogen involved in oxidation and hydrogenation of intermediate condensation products (coke structures). Model calculations showed that with a decrease in the hydrogen/feedstock molar ratio and simultaneous increase in water supply, depending on the temperature and composition of feedstock, it is possible to slow down deactivation process and increase the catalyst service life. This fact was experimentally confirmed at industrial unit. [ABSTRACT FROM AUTHOR]

Several commercial carbons were tested with respect to their thermal stability and electrochemical activity as Pt catalyst support for oxygen reduction reaction (ORR). TGA analysis revealed that carbons with low BET surface such as graphite nanoparticles (GNP 500 , 100 m² g −1 ) are less prone to degradation than ordered mesoporous carbon (OMC, 1000 m²g −1 ). Moreover, high Pt loading favored considerably carbon oxidation rate in air. Best results in terms of activity for ORR and stability during electrochemical accelerated degradation tests (ADT) were yielded by Pt/GNP 500 and Pt/OMC, respectively. High graphitization level and mesoporous surface structure of carbon were found to be determinant for sustainable Pt stability. Addition of certain amount of PTFE to Nafion as binder in gas diffusion electrode (GDE) catalyst layer clearly improved electrochemical surface area (ECSA) retention. Comparative identical location TEM images of electrochemically-aged Pt on Vulcan and OMC demonstrated positive influence of mesoporous carbon surface on immobilization of catalyst particles and consequently on ECSA retention. After 10,000 ADT cycles, ECSA retention was close to 30% for Pt/OMC compared to about 1% for Pt/Vulcan. This was due to dramatic increase of Pt particle size on Vulcan support up to 40 nm compared to about 15 nm for Pt on OMC. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles have been previously synthesized by a facile precipitation procedure by mixing aqueous solutions of Zn(II) acetate and dissolved Na 2 CO 3 at pH ca. 7.0 without the addition of a template. The as-prepared ZnO material was anealed at 400 °C in air for 2 h. The Pt-ZnO catalysts (0.5 or 1.0 Pt wt.%) were obtained by photochemical deposition method on the surface of the prepared ZnO sample, using hexachloroplatinic acid (H 2 PtCl 6 ). It has been shown that Zn 2+ is lost from the photocatalyst to the medium and a replacement of the cationic vacancies of Zn 2+ by Pt 4+ cations occurs during the platinization process of the ZnO samples, regardless of whether the platinum metal photodeposition process. The as-prepared catalysts were characterized by XRD, BET, FE-SEM, TEM, XPS and diffuse reflectance spectroscopy (DRS). Three different probe molecules were used to evaluate the photocatalytic properties under UV-illumination: Methyl Orange and Rhodamine B were chosen as dye substrates and Phenol as a transparent substrate. High conversion values (ca. 100%) and a total organic carbon (TOC) removal of 90–96%, were obtained over these photocatalysts after 160 min of UV illumination. In general, it was observed that the presence of Pt on ZnO affects the lattice parameters and the crystallite size. Although ZnO can completely degrade RhB, MO and Phenol totally in ca. 60 min, the process is more efficient for Pt–ZnO photocatalysts. [ABSTRACT FROM AUTHOR]

The development of new catalysts for low temperature fuel cells requires accurate characterization techniques to evaluate their performance. As initially only small amounts of catalyst are available, preliminary screening must rely on suitable test methods. In this work, using a carbon supported platinum benchmark catalyst, the rotating disc electrode (RDE) technique was revisited in order to develop a detailed testing protocol leading to comparable results between different laboratories. The RDE results were validated by comparison with data measured both in proton exchange membrane single cells and via the relatively new floating electrode technique. This method can be operated with small amounts of catalyst but does not suffer from low limiting currents and allows prediction of high current capability of newly developed catalysts. Different durability testing protocols were tested with all three methods. Such protocols need to be able to introduce changes in the reference catalyst, but must not be too harsh as otherwise they cannot be applied to alloy catalysts. In all protocols an upper potential limit of 0.925 V was used, as this produced degradation in the chosen benchmark catalyst, but still represents realistic conditions for alloy catalysts. [ABSTRACT FROM AUTHOR]

Abstract: In the field of renewable energy, the splitting of water into hydrogen and oxygen fuel gases using water electrolysis is a prominent topic. Traditionally, these catalytic processes have been performed by platinum‐group metal catalysts, which are effective at promoting water electrolysis but expensive and rare. The search for an inexpensive and Earth‐abundant catalyst has led to the development of 3d‐transition‐metal phosphides for the hydrogen evolution reaction. These catalysts have shown excellent activity and stability. In this review, we discuss the electronic and crystal structures of bulk and surface of selected Fe, Co, and Ni phosphides, and their relationships to the experimental catalytic activity. The various synthetic protocols towards the state‐of‐the‐art transition metal phosphide electrocatalysts are also discussed. [ABSTRACT FROM AUTHOR]

Development of Pt catalysts alloyed with transition metals has led to a new class of state-of-the-art electrocatalysts for oxygen reduction at the cathode of proton exchange membrane fuel cells; however, the durability of Pt-based alloy catalysts is challenged by poor structural and chemical stability. There is a need for better understanding of the morphological and compositional changes that occur to the catalyst under fuel cell operation. Here, we report in-depth characterization results of a Pt-Co electrocatalyst incorporated in the cathode of membrane electrode assemblies, which were evaluated before and after accelerated stress tests designed specifically to enhance catalyst degradation. Electron microscopy, spectroscopy, and 3D electron tomography analyses of the Pt-Co nanoparticle structures suggest that the small- and intermediate-sized Pt-Co particles, which are typically Pt-rich in the fresh condition, undergo minimal morphological changes, whereas intermediate- and larger-sized Pt-Co nanoparticles that exhibit a porous "spongy" morphology and initially have a higher Co content, transform into hollowed-out shells, which is driven by continuous leaching of Co from the Pt-Co catalysts. We further show how these primary Pt-Co nanoparticle morphologies group toward a lower Co, larger size portion of the size vs. composition distribution, and provide details of their nanoscale morphological features. [ABSTRACT FROM AUTHOR]

An electrochemical flow cell system with catalyst-ionomer ink deposited on glassy carbon is used to investigate the aqueous stability of commercial PtCo alloys under cyclic potentials. An on-line inductively coupled plasma-mass spectrometer, capable of real-time measurements, is used to resolve the anodic and cathodic dissolution of Pt and Co during square-wave and triangle-wave potential cycles. We observe Co dissolution at all potentials, distinct peaks in anodic and cathodic Pt dissolution rates above 0.9 V, and potential-dependent Pt and Co dissolution rates. The amount of Pt that dissolves cathodically is smaller than the amount that dissolves anodically if the upper potential limit (UPL) is lower than 0.9 V. At the highest UPL investigated, 1.0 V, the cathodic dissolution greatly exceeds the anodic dissolution. A non-ideal solid solution model indicates that the anodic dissolution can be associated with the electrochemical oxidation of Pt and PtOH to Pt2+, and the cathodic dissolution to electrochemical reduction of a higher Pt oxide, PtOx (x > 1), to Pt2+. Pt also dissolves oxidatively during the cathodic scans but in smaller amounts than due to the reductive dissolution of PtOx. The relative amounts Pt dissolving oxidatively as Pt and PtOH depend on the potential cycle and UPL. [ABSTRACT FROM AUTHOR]

Inspired by the recent surface experimental results that the monatomic Pt catalysts has more excellent hydrogen production that Cu(111) surface, the mechanism of decomposition of formic acid on Cu(111) and single atom Pt 1 /Cu(111) surface was studied by periodic density functional theory calculations in the present work. The results show that the formic acid tends to undergo dehydrogenation on both surfaces to obtain the hydrogen product of the target product, and the selectivity and catalytic activity of Pt 1 /Cu (111) surface for formic acid dehydrogenation are better. The reason is that the single atom Pt 1 /Cu(111) catalyst reduces the reaction energy barrier (i.e., HCOO → CO 2  + H) of the critical step of the dehydrogenation reaction due to the fact that the single atom Pt 1 /Cu(111) catalyst binds formate weakly compared to that of Cu (111) one. Moreover, it was found that the Pt 1 /Cu (111) binds CO more strongly than that of Cu (111) one and thus leading to the difficult for the formation of CO. These two factors would make the single Pt atom catalyst had the high selectivity for the H 2 production. It is hoped that the present work may help people to design the efficient H 2 production from HCOOH decomposition by reduce the surface binding strength of HCOO species, for example, using the low coordination number active site like single atom or other related catalytic system. [ABSTRACT FROM AUTHOR]

Abstract: Electrocatalysts with high performance, increased stability, and high surface area are essential for the widespread commercialization of fuel cells. Nanostructured materials emerge as potential candidates to meet these targets. We report on the synthesis and characterization of a nanostructured platinum electrocatalyst for methanol oxidation. Using a simple, one-step electroless method, an interconnected platinum nanotube network was prepared. The highly ordered, high-surface-area catalyst exhibited enhanced current density and durability for methanol oxidation. The catalyst shows a peak current density of 1.43 mA cm−2 at 50 mV s−1 and retained 25% of its initial activity after 1 h. The high catalytic activity is a result of increased Pt–OH formation on nanocrystal aggregates at lower potentials.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Abstract: Ultra-low Pt-loaded (3–54 µg cm− 2) gas diffusion electrodes were prepared by a direct current unbalanced magnetron sputtering process. Pt films were deposited directly onto the microporous layer of the gas diffusion electrode and tested in a half-cell and proton exchange membrane fuel cell. While the apparent activity towards oxygen reduction reaction under half-cell conditions is dependent on Pt loading, mass activity is Pt loading independent, indicating constant catalyst utilization. Assuming the validity of the porous electrode model, kinetic parameters are extracted from the experimental data. Unlike the results from the half-cell study, the U–I curves of the proton exchange membrane fuel cell at different loadings show a decrease of the catalyst utilization at higher Pt loadings. The Pt structure on the gas diffusion electrode was investigated by electron microscopy, atomic force microscopy and X-ray diffraction.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Citric acid (CA), as the chelating agent, was introduced to obtain the enhanced Pt dispersion and catalytic activities for the Pt-based catalysts supported on oxygen-storage material. The role and content of CA were investigated systematically. It was found that the citric acid-assisted catalysts showed better Pt dispersion and smaller nanoparticle size of Pt. Thus, the catalyst had lower reduction temperature, preferable thermostability and possessed more oxidation state of Pt species under the oxidation atmosphere. The citric acid-induced fresh catalysts were excellent to convert CO and the corresponding aged ones exhibited higher activities for the elimination of all the target pollutants. Among the aged catalysts, P2-a (the mole ratio of Pt/CA is 2:1) presented the best performance. Particularly, compared with the reference sample (Pc-a), the light-off temperatures (T 50 ) of NO, HC and CO for P2-a decreased by 39 °C, 42 °C and 72 °C, respectively, and the full-conversion temperatures (T 90 ) of NO, HC and CO for P2-a decreased by 44 °C, 44 °C and 48 °C, respectively. Therefore, this work provides a facile and valid method to manufacture advanced catalysts for purification of the vehicle exhaust in the future. [ABSTRACT FROM AUTHOR]

This article describes findings of the correlation between the atomic scale surface structure and the electrocatalytic performance of nanoengineered Pt-Pd/C catalysts for oxygen reduction reaction (ORR), aiming at providing a new fundamental insight into the role of the detailed atomic decorated structure of the catalysts in fuel cell reactions. Carbon-supported Pt decorated Pd nanoparticles (donated as Pt-Pd/C), with Pt coverage close to a monolayer, were prepared from a simple galvanic replacement reaction between Pd/C particles and PtCl 4 2− at room temperature. The decorated architecture was confirmed by extensive microstructural characterization techniques, including TEM, XRD, XPS, HAADF-STEM, ICP and HS-LEIS. The catalysts were also examined for their intrinsic kinetic activities towards oxygen reduction reaction. The results have shown that the Pt-Pd/C catalysts are highly active towards molecular oxygen electrocatalytic reduction. These findings have profound implications to the design and nanoengineering of decorated surfaces of catalysts for oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Homogeneous ionomer networks are primarily important for the enhancement of fuel cell performance. Here, we report a bottom-up design of platinum (Pt) electrocatalysts with homogeneous ionomer layers, in which Pt nanoparticles are deposited on carbon nanotubes (CNTs) after sequentially wrapping with polybenzimidazole (PBI) and end-capped hyperbranched sulfonated macromolecules (E-HBM) (CNT/PBI/E-HBM/Pt). E-HBM, which are proton conductive macromolecules, are homogeneously coated on CNTs owing to the base-acid interaction between PBI and E-HBM. The durability and oxygen reduction reaction (ORR) results indicate that CNT/PBI/E-HBM/Pt exhibits higher Pt stability and ORR activity compared with the electrocatalyst without E-BHM. The Nafion ionomer-free membrane electrode assembly (MEA) fabricated from CNT/PBI/E-HBM/Pt (704 mW cm−2) shows higher power density than the MEA from CNT/PBI/Pt with Nafion ionomer (30 wt %, 603 mW cm−2) owing to the unique bottom-up design resulting in high Pt utilization efficiency. [ABSTRACT FROM AUTHOR]

Hierarchical porous nitrogen-doped carbon (HPNC) derived from chitosan is synthesized through a novel metal ion-templated strategy. In this process, the absorbed Cu(II)-loaded chitosan was calcined at various temperatures which results in carbon/Cu composites. After removal of Cu particles with acid medium, hierarchical porous carbon forms which includes macropores, mesopores and micropores. The specific surface area of HPNC900 reaches 755 m 2 g −1 . The XPS results show that all the carbon materials contain nitrogen as the doped element due to the use of chitosan as a nitrogen-containing carbon source. Furthermore, highly dispersed Pt nanoparticles have been successfully deposited on the as-prepared HPNC through the in-situ reduction method. The average size of Pt nanoparticles anchored on HPNC900 is only 2.76 ± 0.33 nm. The synthesized products are characterized by TEM, SEM and XRD analysis techniques. Among the studied electrocatalysts, the as-prepared Pt/HPNC900 electrocatalyst (HPNC fabricated at 900 °C) shows superior electrocatalytic activity and stability towards methanol oxidation in comparison with Pt/Vulcan XC-72 catalyst. The current density of methanol oxidation on Pt/HPNC900 is ∼2.5 times higher than that of Pt/Vulcan XC-72 catalyst. The enhanced electrocatalytic activity is ascribed to hierarchical porous structures, nitrogen-doped surface characteristic and high BET specific surface area of HPNC. Therefore, the present method is very useful for fabrication of high-performance electrocatalyst for methanol oxidation. [ABSTRACT FROM AUTHOR]

High overpotentials and low efficiency are two main factors that restrict the practical application for MoS2, the most promising candidate for hydrogen evolution catalysis. Here, RhMoS2 nanocomposites, the addition of a small amount of Rh (5.2 wt%), exhibit the superior electrochemical hydrogen evolution performance with low overpotentials, small Tafel slope (24 mV dec−1), and long term of stability. Experimental results reveal that 5.2 wt% RhMoS2 nanocomposite, even exceeding the commercial 20 wt% Pt/C when the potential is less than −0.18 V, exhibits an excellent mass activity of 13.87 A mgmetal−1 at −0.25 V, four times as large as that of the commercial 20 wt% Pt/C catalyst. The hydrogen yield of 5.2 wt% RhMoS2 nanocomposite is 26.3% larger than that of the commercial 20 wt% Pt/C at the potential of −0.25 V. The dramatically improved electrocatalytic performance of RhMoS2 nanocomposites may be attributed to the hydrogen spillover from Rh to MoS2. [ABSTRACT FROM AUTHOR]

Photonic crystals can delay the propagation of light and increase its path length through a slow-light effect, which could have immense potential in improving photocatalytic conversion efficiencies. We employed a colloidal crystal template method to synthesize TiO2 photonic crystals (PC-TiO2), with platinum nanoparticles (Pt NPs) being deposited on the surface of the PC-TiO2 support at different loading amounts by the gas bubbling-assisted membrane reduction (GBMR) method. A series of Pt/PC-TiO2 photocatalysts with well-defined inverse-opal structure have uniform Pt NPs (about 2.5 nm) homogeneously dispersed on the pore walls of the support. The slow-light effect of photonic crystals effectively enhances the absorption efficiency of solar irradiation. Moreover, the Pt deposition significantly extends the spectral response and reduces the recombination rates of photoinduced electron-hole pairs. As a result, the Pt x/PC-TiO2 catalysts exhibit excellent photocatalytic activity for the reduction of CO2 in the presence of H2O. In addition, we propose a reaction mechanism for the photoreduction of CO2 under light irradiation. [ABSTRACT FROM AUTHOR]

Polymer electrolyte fuel cells (PEFCs), at the early stage of their commercialization, possess potential for different applications. Analogous to any other new technologies, PEFC technology is also facing several challenges and uncertainties during precommercialization phase. Platinum, used as the catalyst in PEFCs, is considered as one of the key obstacles towards the commercialization as it contributes significantly to the overall cost. In the present work, a life-cycle cost analysis is carried out based on the annual growth in the platinum price and the discount rate based on the local market for different economic zones. It is observed that the high investment in platinum could be beneficial instead of acting as the hurdle if the salvage value of platinum is considered. Based on the platinum cost per kW of the fuel cell, two different scenarios (32 and 3 US$ kW) are considered. It is observed that in spite of very high cost of platinum, the net present value of the fuel cell is comparable with the scenario with low investment cost in platinum when the salvage value of platinum is considered. In some situations, the high investment cost in the platinum offers high salvage value leading to a profitable case. Hence, the high cost of platinum might promote the commercialization of the fuel cells if appropriate business model is in place. [ABSTRACT FROM AUTHOR]

The catalytic isotope exchange water - hydrogen is the most used front-end process within detritiation technologies. The research in the field of hydrogen isotopes separation has been of interest in the institute for many years, the main aim being the development of detritiation facilities for CANDU and fusion reactors. There are numerous methods to assess the performance of the catalytic packing which equips the isotopic exchange columns, often making it impossible to compare the results. This paper presents an analysis performed on a mixed catalytic packing (catalyst and hydrophilic) using two theoretical methods of performance evaluation. The mixed catalytic packing is structured type and consists of a Pt/C/PTFE catalyst located in an ordered hydrophilic package made by stainless steel. For modeling the isotopic transfer which takes place in this mixed catalytic packing, there were considered two cases: 1 - the packing is ordered, the catalyst evenly distributed in volume unit without taking into account the distribution geometry and 2- the packing is ordered but the catalyst is uniformly distributed following a particular geometry. The analysis of theoretical and experimental data highlights how the considered theoretical model affects the values of catalytic packing performance. [ABSTRACT FROM AUTHOR]

Within the last decade, metal-free heteroatom doped carbon nanomaterials have gained attention as effective electrocatalysts for the oxygen reduction reaction (ORR) in many electrochemical systems. Since then, reports have stated that the ORR catalytic activity, onset potential, and H2O production selectivity of these materials is similar to that of platinum-based catalysts. These statements rely on cyclic voltammetry (CV) and rotating disc electrode (RDE) measurements in liquid alkaline electrolyte. However, fuel cell researchers aim to replace the costly platinum catalysts in the more prominent acidic solid electrolyte proton exchange fuel cell (PEFC). In this respect, there are only a few reports of unpromising activity, stability, and H2O production selectivity. In addition, only few reports have been presented on the implementation of such materials in cathode catalyst layers of actual PEFC devices. This mini-review aims to summarize and evaluate results of these reports. Material synthesis, cell power, open circuit voltage, stability properties, and proposed active sites are reviewed. To date, the highest reported PEFC power densities with guaranteed metal-free heteroatom doped carbon cathode catalysts have reached up to 321 mW cm−2; which although a promising value is substantially short of values obtained for platinum based catalysts. [ABSTRACT FROM AUTHOR]

Carbon xerogels represent nowadays an outstanding alternative to carbon blacks for the preparation of efficient fuel cell electrocatalysts, due to their easily tunable and well developed mesoporous structure. To further improve both activity and durability of Pt/C catalysts, the introduction of heteroatoms (such as O, N, S, P, B, etc.) in the structure of carbon materials has been proposed. In the present work, highly mesoporous carbon xerogels (CXGs) have been subjected to a sulfurization process with elemental sulfur. The insertion of S into the carbon matrix does not compromise their mesoporous structure. Pt catalysts supported on sulfurized carbon xerogels show enhanced catalytic activity towards both the methanol electro-oxidation and the oxygen electro-reduction reactions, exceeding not only the performance of the catalyst supported on the bare xerogel, but also of the catalyst supported on a commercial carbon black. The sulfurization treatment is also effective in improving the resistance of Pt/CXG catalysts towards corrosion phenomena occurring at the fuel cell cathode. [ABSTRACT FROM AUTHOR]

The impact of Nafion on the oxygen reduction reaction (ORR) activity is studied for Pt/C and Pt-alloy/C catalysts using thin-film rotating disk electrode (TF-RDE) methods in 0.1 M HClO 4 . Ultrathin uniform catalyst layers and standardized activity measurement protocols are employed to obtain accurate and reproducible ORR activity. Nafion lowers the ORR activity which plateaus with increasing loading on Pt catalysts. Pt particle size is found not to have significant influence on the extent of the SA decrease upon Nafion incorporation. Catalysts using high surface area carbon (HSC) support exhibit attenuated activity loss resulting from lower ionomer coverage on catalyst particles located within the deep pores. The impact of metallic composition on the activity loss due to Nafion incorporation is also discussed. [ABSTRACT FROM AUTHOR]

We report a systematic study on the correlation of the modified electronic structure of nanocrystal catalysts with the adsorption properties of the substrate and the resultant catalytic activity by using Baeyer-Villiger oxidation catalyzed by composition-controlled Pt-based nanocubes (NCs) as a model heterogeneous catalysis reaction. The incorporation of 3d transition metals into Pt to form PtM (M=Zn, Co, and Ni) alloy NCs allowed fine-tuning of the electronic structure of Pt. PtM NCs with a higher-lying d band center exhibited higher catalytic performance owing to the enhanced initial activation of the carbonyl group of the substrate. This work emphasizes the importance of fine-tuning the electronic structure of heterogeneous catalysts to advance their catalytic function. [ABSTRACT FROM AUTHOR]

The effects of phosphorus poisoning on the activity of PtPd and Pt diesel oxidation catalysts and on the activity of the support material were investigated using the gas phase laboratory-scale-aging procedure. The catalysts were treated using two different phosphorus concentrations (0.065 and 0.13 mol/L (NH)HPO). The deactivation was studied by inductively coupled plasma optical emission spectroscopy, electron microscopy, X-ray diffractometry, X-ray photoelectron spectrometry and Fourier-transform infrared reflectance, N-physisorption, and activity measurements with CO, CH and NO. The amount of accumulated phosphorus was higher on the Pt catalyst surface than on the PtPd catalyst and significantly higher on the surface of the bare support material. Phosphorus concentration was uniform throughout the support layer (down to the 10 μm), and phosphorus was found as phosphate, although it can also form compounds like AlPO with the support. The treatment with low phosphorus concentration was found to have a clear deactivation effect only for CH oxidation activity on PtPd catalysts above 200 °C. The treatment with high phosphorus concentration significantly decreased the activity of both the PtPd and Pt catalysts. In particular, the CH and NO oxidation activities of the fresh and P-treated Pt catalysts were higher than those of the PtPd catalysts for the entire temperature range. [ABSTRACT FROM AUTHOR]

Tip-generation/substrate-collection mode (TG-SC) of scanning electrochemical microscopy (SECM) was used to study oxygen reduction reaction (ORR) at nanoporous Pt films depending on their pore characteristics. Nanoporous Pt films were electrodeposited in solutions containing Pt precursor, Triton X -100, and lead acetate. The varied composition of electroplating solutions could control the porosities of the deposited Pt films with three different degrees (denoted as npPt-I, npPt-II, and npPt-III): npPt-I had only nanoscale pores but npPt-II and npPt-III had both nanoscale and microscale pores; and npPt-III possessed additional microscale pores. Recessed Pt tips deposited with three different npPts were used to observe their ORR activities in TG-SC mode of SECM, considering its advantage of ~100% collection efficiency for H2O2 (2-e transfer product of ORR). The SECM results indicate that npPt-1 is beneficial for the kinetic controlled potential region via the O2 molecule confinement within npPt-I, while npPt-III is more advantageous in the mass-transport controlled region due to the more promoted O2 influx through the microscale pores leading to the more efficient utilization of the electrode surface for ORR. [ABSTRACT FROM AUTHOR]

Commercial silica (Ultrasil – BET surface area 158 m 2 /g) was modified with platinum and/or silver. Before metal loading, the silica was functionalized with one of the following organosilanes, 3-aminopropyltrimethoxysilane (APTMS) and 2-mercaptopropyltrimethoxysilane (MPTMS) or both of them. It was proved that the nature of organosilane (MPTMS or APTMS) used for functionalization of silica before silver and platinum loading, played an important role in the anchoring of Pt and Ag species and affected the kinds of bimetallic particles formed. The creation of alloy-like bimetallic structure depends on a combination of two parameters, the nature of organosilane and the method of modification by platinum and silver. If the one-pot method of modification was used, the functionalization of silica by MPTMS favoured alloy formation (PtAg/Si-M and PtAg/Si-AM samples). APTMS functionalization promoted alloy formation if the step-by-step modification was applied, independently of the sequence of metals loading. Core–shell structure was formed only if MPTMS functionalization of silica was used and silver species were loaded first (1Ag2Pt/Si-M sample). Bimetallic particles were not formed in two samples, PtAg/Si-A and 1Pt2Ag/Si-M. The presented results have proved that selectivity of bimetallic catalysts in methanol oxidation depends on metals loading and dispersion, whereas their activity is influenced by the interaction between platinum and silver in bimetallic particles. The highest selectivity to methyl formate (84%) for 100% conversion of methanol was reached over PtAg/Si-M at 373 K. [ABSTRACT FROM AUTHOR]

The association of palladium and platinum supported on alumina was studied for diesel oxidation catalyst application. The effect of propene, water and their combination on NO oxidation activity was investigated in flow reactor over Pt/Al 2 O 3 , Pd/Al 2 O 3 and two Pt–Pd/Al 2 O 3 catalysts, prepared by co-impregnation and sequential impregnation of the metals. Contrary to Pd/Al 2 O 3 , activity improvement due to the repetition of activity test was observed on Pt/Al 2 O 3 and both Pt–Pd/Al 2 O 3 . Metal sintering during activity test was revealed by CO chemisorption. The bimetallic catalysts reached their final stability and activity before Pt/Al 2 O 3 . The presence of water decreased the NO oxidation activity of all catalysts and the propene completely inhibited NO oxidation at low temperature until propene combustion occurred. The addition of palladium to Pt/Al 2 O 3 was found very efficient to oxidize propene and therefore significantly limited the inhibition of NO oxidation by propene. A mechanism was proposed to explain the NO oxidation promotion lying behind the addition of Pd. DRIFT measurements and flow reactor experiments showed that propene was less stable and able to react with surface nitrates on Pd-containing catalyst at low temperature (175 °C). On Pt/Al 2 O 3 , however, the propene consumption proceeded initially through selective catalytic reduction of NO, which took place at higher temperature (240 °C). In this way, propene combustion and consequently NO oxidation occurred at lower temperature on bimetallic catalysts than on Pt/Al 2 O 3 . [ABSTRACT FROM AUTHOR]

The influence of the supports (AlO, TiO and SiO) on the activity and selectivity of Pt-Ir catalysts for the ring opening (RO) of decalin was studied. It was found that the properties of the supports strongly influence the distribution, size and Pt-Ir interaction of the metal particles. They therefore also influence the catalytic activity for reactions like dehydrogenation and hydrogenolysis, but also specifically the activity for RO reactions of naphthenes. Via their acid sites the supports influence RO reactions although the effect is not very marked on conversion because the acidity differences are not very significant among them. The results show that the highest decalin conversion for three different supports, alumina, silica and titania, is obtained with the catalysts of highest metal loading. The best selectivity to RO products is obtained with Pt-Ir(1.0)/AlO catalyst. Moreover this catalyst shows the highest performance for MCP RO. Graphical Abstract: [Figure not available: see fulltext.]. [ABSTRACT FROM AUTHOR]

This study aimed to determine the influence of Ir content on the behavior of Pt-Ir/C catalysts for hydrogen iodide decomposition in iodine–sulfur thermochemical water-splitting cycle. A series of bimetallic x Pt- y Ir/C catalysts ( x = 4, 3, 2.5, 2, 1 wt.%; y = 1, 2, 2.5, 3, 4 wt.%) were prepared by co-impregnation and reduction method. For comparison, monometallic 5%Pt/C and 5%Ir/C catalysts were also prepared. The catalysts were characterized by X-ray diffraction and transmission electron microscopy. Changing the Ir content in the bimetallic Pt-Ir/C catalysts can modify the particle size and dispersion state of the supported metal nanoparticles. The results of the characterizations of the fresh and used catalysts indicated that the size of the Pt nanoparticles has significantly increased after HI decomposition whereas that of the Pt-Ir nanoparticles is more resistant to particle growth. Among the Pt, Ir, and binary Pt-Ir catalysts, the bimetallic 2.5%Pt-2.5%Ir/C exhibited the highest catalytic activity toward HI decomposition. The 70 h durability test showed that the Pt-Ir bimetallic catalyst possessed good activity maintenance. [ABSTRACT FROM AUTHOR]

The surface structure and catalytic properties of Pt-Ru bimetallic catalysts with identical bulk composition can be continuously tuned by treatment at different temperatures. The activity of these catalysts in CO oxidation was positively related to the treatment temperature, but the opposite trend was observed for the solvent-free oxidation of benzyl alcohol. It was found that migration of Pt to the surface occurred when the treatment temperature was increased. During this process, the surface of the Pt-Ru nanoparticles changed from a Ru-rich surface to a Pt-rich surface. The electronic interactions between Pt and Ru became stronger with increased treatment temperature, and the amount of oxidized Pt species on the surface was higher for the samples treated at higher temperatures. Therefore, oxidized Pt species are more active in CO oxidation than other metallic species, but are less active in the selective oxidation of benzyl alcohol. [ABSTRACT FROM AUTHOR]

Electrocatalyst support affects not only catalytic activity of a catalyst, but also mass transportation and electron transfer in the catalyst layers of an electrode for proton exchange membrane fuel cells. Multi-dimensional and combined carbon materials such as Vulcan XC-72, carbon nanotubes (CNTs), and home-made coiled carbon nanotubes (CCNTs) are applied to enhance the catalyst activity and utilization. Three-dimensional CCNTs with large specific surface area and graphitic characteristic are synthesized by solid-state catalytic method. This obtained CCNTs and commercial CNTs are used as support to prepare platinum catalysts via modified ethylene glycol method, respectively. And the electrochemical surface areas (ECSAs) of the as-prepared Pt/CNTs, Pt/CCNTs and commercial Pt/C (JM) catalyst are evaluated by cyclic voltammetry. Then each two and three kinds of above catalysts mixed with different mass ratios are investigated. The ECSAs of Pt/C–Pt/CCNTs (95:5) and Pt/C–Pt/CNTs–Pt/CCNTs (80:10:10) are calculated to be 106 m 2 g Pt −1 and 111 m 2 g Pt −1 , with respect to 70 m 2 g Pt −1 of Pt/C (JM) catalyst. And these mixed catalysts also demonstrate improved oxygen reduction reaction activities. This is mainly attributed to the unique structure of CCNTs, which can construct a multi-dimensional network to facilitate the mass transportation and electrons/protons transfer. [ABSTRACT FROM AUTHOR]

For optimizing both the activity and stability of Pt-based catalysts for methanol oxidation reaction (MOR), several carbon nanotubes(CNTs)-supported catalysts such as Pt-on-Au/CNTs, Pd-on-Au/CNTs, Pt-on-Pd-on-Au/CNTs, Pt-on-Pd/CNTs, and Pd-on-Pt/CNTs catalysts are synthesized mainly through electrodeposition method. The activity and stability comparisons show that Pt-on-Au/CNTs has a higher MOR activity but a lower stability than Pd-on-Au/CNTs. To utilize the merits of the Pt and Pd components, Pt-on-Pd-on-Au/CNTs and Pt-on-Pd/CNTs catalysts are synthesized. The Pt-on-Pd-on-Au/CNTs and Pt-on-Pd/CNTs catalysts shows higher MOR activity than Pd-on-Au/CNTs and Pd/CNTs catalysts and higher stability than Pt-on-Au/CNTs, suggesting a synergistic interaction between Pt and Pd in catalyzing methanol oxidation reaction. Calculation shows that the total mass activity of Pt-on-Pd/CNTs with quite low Pt amount is on a similar level as that of Pt/CNTs for MOR oxidation, indicating the Pt-on-Pd catalyst could have promising potential as a low-Pt catalyst for MOR in alkaline media. [ABSTRACT FROM AUTHOR]

When pure mesoporous silica (MCF-17) was modified with aluminum (A1 modified MCF-17), Lewis acid sites were created, but this material was inactive for the catalytic conversion (reforming) of n-hexane to isomers. When colloidally synthesized platinum nanoparticles were loaded onto traditional MCF-17, the catalyst showed very low activity toward isomer production. However, when Pt nanoparticles were loaded onto Al modified MCF-17, isomerization became the dominant catalytic pathway, with extremely high activity and selectivity (>90%), even at high temperatures (240-360 °C). This highly efficient catalytic chemistry was credited to the tandem effect between the acidic Al modified MCF-17 and the Pt metal. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate that the activity of a hydrogen-bond-donating (HBD) catalyst embedded within a coordination frame-work can be allosterically regulated in situ by controlling oligomerization via simple changes in coordination chemistry at distal Pt(II) nodes. Using the halide-induced ligand rearrangement reaction (HILR), a heteroligated Pt(Il) triple-decker complex, which contains a catalytically active diphenylene squaramide moiety and two hydrogen-bond-accepting (HBA) ester moieties, was synthesized. The HBD and HBA moieties were functionalized with hemilabile ligands of differing chelating strengths, allowing one to assemble them around Pt(Il) nodes in a heteroligated fashion. Due to the hemilabile nature of the ligands, the resulting complex can be interconverted between a flexible, semiopen state and a rigid, fully closed state in situ and reversibly. FT-IR spectroscopy, ¹H DOSY, and ¹H NMR spectroscopy titration studies were used to demonstrate that, in the semiopen state, intermolecular hydrogen-bonding between the HBD and HBA moieties drives oligomerization of the complex and prevents substrate recognition by the catalyst, In the rigid, fully closed state, these interactions are prevented by steric and geometric constraints. Thus, the diphenylene squaramide moiety is able to catalyze a Friedel--Crafts reaction in the fully closed state, while the semiopen state shows no reactivity. This work demonstrates that controlling catalytic activity by regulating aggregation through supramolecular conformational changes, a common approach in Nature, can be applied to man-made catalytic frameworks that are relevant to materials synthesis, as well as the detection and amplification of small molecules. [ABSTRACT FROM AUTHOR]

By the combination of solvothermal alcoholysis and post-nitriding method, titanium nitride nanotubes (TiN NTs), with high surface area, hollow and interior porous structure are prepared successfully and used at a support for Pt nanoparticles. The TiN NTs supported Pt (Pt/TiN NTs) catalyst displays enhanced activity and durability towards methanol oxidation reaction (MOR) compared with the commercial Pt/C (E-TEK) catalyst. X ray diffraction (XRD), nitrogen adsorption/desorption, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) measurements are performed to investigate the physicochemical properties of the synthesized catalyst. SEM and TEM images reveal that the wall of the TiN NTs is porous and Pt nanoparticles supported on the dendritic TiN nanocrystals exhibit small size and good dispersion. Effects of inherent corrosion-resistant, tubular and porous nanostructures and electron transfer due to the strong metal–support interactions of TiN NTs contribute to the enhanced catalytic activity and stability of Pt/TiN NTs towards the MOR. [ABSTRACT FROM AUTHOR]

The electrolysis of water using renewable energy inputs is being actively pursued as a route to sustainable hydrogen production. Here we introduce a recyclable redox mediator (silicotungstic acid) that enables the coupling of low-pressure production of oxygen via water oxidation to a separate, catalytic hydrogen production step outside the electrolyzer that requires no post-electrolysis energy input. This approach sidesteps the production of high-pressure gases inside the electrolytic cell (a major cause of membrane degradation) and essentially eliminates the hazardous issue of product gas crossover at the low current densities that characterize renewables-driven water-splitting devices. We demonstrated that a platinum-catalyzed system can produce pure hydrogen over 30 times faster than state-of-the-art proton exchange membrane electrolyzers at equivalent platinum loading. [ABSTRACT FROM AUTHOR]

Highlights: [•] The activities of the Pt–Sn/SiO2 catalysts were strongly influenced by the reduction method. [•] The Pt–Sn/SiO2 (DR) showed the highest activity among the Pt–Sn/SiO2 catalysts tested. [•] Pt3Sn alloy acts as active site for dehydrogenation of propane, whereas PtSn alloy shows low or no activity. [ABSTRACT FROM AUTHOR]

Sulfur-doped graphene (SG) is prepared by a thermal shock/quench anneal process and investigated as a unique Pt nanoparticle support (Pt/SG) for the oxygen reduction reaction (ORR). Particularly, SG is found to induce highly favorable catalyst-support interactions, resulting in excellent half-cell based ORR activity of 139 mA mgPt −1 at 0.9 V vs RHE, significant improvements over commercial Pt/C (121 mA mgPt −1) and Pt-graphene (Pt/G, 101 mA mgPt −1). Pt/SG also demonstrates unprecedented stability, maintaining 87% of its electrochemically active surface area following accelerated degradation testing. Furthermore, a majority of ORR activity is maintained, providing 108 mA mgPt −1, a remarkable 171% improvement over Pt/C (39.8 mA mgPt −1) and an 89% improvement over Pt/G (57.0 mA mgPt −1). Computational simulations highlight that the interactions between Pt and graphene are enhanced significantly by sulfur doping, leading to a tethering effect that can explain the outstanding electrochemical stability. Furthermore, sulfur dopants result in a downshift of the platinum d-band center, explaining the excellent ORR activity and rendering SG as a new and highly promising class of catalyst supports for electrochemical energy technologies such as fuel cells. [ABSTRACT FROM AUTHOR]

A stable photoactive metal-organic framework UiO-66(Zr) sensitized by adsorbed or directly added rhodamine B dye exhibited photocatalytic activity for hydrogen evolution under visible-light illumination (λ ≥ 420 nm). Using Pt as a co-catalyst, the adsorbed and directly added dye extremely enhanced the photocatalytic activity to 30 and 26 times the value afforded by bare Pt@UiO-66(Zr), respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] Morphological changes of single nanoparticles occur during exposure to reactive gases. [•] The reconstructions are imaged operando by field emission techniques. [•] On rhodium, reconstructions have only a limited influence on the structure sensitivity of the O2–H2 reaction at T >500K. [•] On platinum, the NO2–H2 reaction occurs first on {011} facets, whereas (001) plane becomes active as the reconstruction proceeds. [Copyright &y& Elsevier]

Abstract: Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbon materials with very different structure, have been functionalized in a nitric–sulfuric acid mixture. Further on, the materials have been platinized by a microwave assisted polyol method. The relative degree of graphitization has been estimated by means of Raman spectroscopy and X-ray diffraction while the relative concentration of oxygen containing groups has been estimated by X-ray photoelectron spectroscopy, which resulted in a graphitic character trend: Pt/GNF > Pt/F-GNF ⋙ Pt/MWCNT > Pt/F-MWCNT. Transmission electron microscopy showed that the Pt particle size is around 3 nm for all samples, which was similar to the crystallite size obtained by X-ray diffraction. The activity towards electrochemical reduction of oxygen has been quantified using the thin-film rotating disk electrode, which has shown that all the samples have a better activity than the commercially available electrocatalysts. The trend obtained for the graphitic character maintained for the electrochemical activity, while the reverse trend has been obtained for the accelerated ageing test. Long-term potential cycling has demonstrated that the functionalization improves the stability for multi-walled carbon nanotubes, at the cost of decreased activity. [Copyright &y& Elsevier]

Highlights: [•] Activity of Pt/Al2O3 for hydrocarbon oxidation was promoted by addition of Pd. [•] Formation of PtPd alloy was confirmed, resulting in sintering suppression of Pt. [•] Creation of Pt-enriched surface is responsible for high oxidation activity. [•] Addition of W into PtPd/Al2O3 causes an enhancement of oxidation activity. [•] W additive can create strong Lewis acidic sites on Al2O3 surface. [ABSTRACT FROM AUTHOR]

SiC-supported Pt nanocatalyst was prepared by electrodeposition of Pt nanoparticles on the surface of high-surface-area SiC, which was fabricated by a versatile carbothermal reduction method. Characterization studies show that such synthesis protocol leads to well distribution of Pt nanoparticles, with a mean particle size of 2.9 nm on the support. This catalyst has been electrochemically characterized toward methanol oxidation, which exhibits higher catalytic activity, durability, and electrochemical active surface area than the electrodeposited Pt on multiwalled carbon nanotubes (MWCNTs). Further investigation reveals that the SiC-supported Pt also shows superior CO tolerance to Pt/MWCNTs. These results suggest that high-surface-area SiC could be a promising supporting material for constructing high-performance methanol oxidation electrocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: Several Pt-on-Au/SnO2-CNTs catalysts with different Pt loadings are synthesized through site-selective electrodeposition for catalytic methanol oxidation reaction (MOR) in alkaline media. The catalysts are tested to exhibit extremely high Pt mass activity towards MOR, and the catalytic mechanism is proposed based on the synergetic effect between Pt and Au, in which the Pt entities provide Pt-OH for oxidation of alkoxide (CH3O−) while the Au surfaces provide adsorption sites for alkoxide. It is expected that this mechanism could be extended to developing high performance non-Pt catalysts for MOR in alkaline media. [Copyright &y& Elsevier]

Highlights: [•] Properties of Pd-Pt catalysts were influenced by metal precursor and pretreatment. [•] Pd acetate and Pt(NH3)4(OH)2 gave the most active Pd-Pt catalysts. [•] Thiophene HDS activity correlated with content of β-Pd hydride phase in the catalysts. [Copyright &y& Elsevier]

The oxygen reduction reaction (ORR) activity as a function of thickness of the Pt shell on Pt-Ni alloy nanoparticles was established. We demonstrated that the effects of transition metals could only extend to a very thin Pt shell, which was 0.9-1.0 nm for Pt3Ni. [ABSTRACT FROM AUTHOR]

We report on the direct promotional effect of sodium on the water-gas shift activity of platinum supported on oxygen-free multiwalled carbon nanotubes. Whereas the Na-free Pt catalysts are shown to be completely inactive, the addition of sodium is found to improve the water-gas shift activity to levels comparable to those obtained with highly active Pt catalysts on metal oxide supports. The structure and morphology of the catalyst surface was followed using aberration-corrected HAADF-STEM, which showed that atomically dispersed platinum species are stabilized by the addition of sodium. In situ atmospheric-pressure X-ray photoelectron spectroscopy (AP-XPS) experiments demonstrated that oxidized platinum Pt-OHx contributions in the Pt 4f signal are higher in the presence of sodium, providing evidence for a previously reported active-site structure of the form Pt-Nax-Oy-(OH)z. Pt remained oxidized in all redox experiments, even when a H2-rich gas mixture was used, but the extent of its oxidation followed the oxidation potential of the gas. These findings offer new insights into the nature of the active platinum-based site for the water-gas shift reaction. A strong inhibitory effect of hydrogen was observed on the reaction kinetics, effectively raising the apparent activation energy from 70 ± 5 kJ/mol (in product-free gas) to 105 ± 7 kJ/mol (in full reformate gas). Increased hydrogen uptake was observed on these materials when both Pt and Na were present on the catalyst, suggesting that hydrogen desorption might limit the water-gas shift reaction rate under such conditions. [ABSTRACT FROM AUTHOR]