Surface Composition Of Catalysts Research Articles

Spray Pyrolyzed High Surface Area Ni-Based Hydrogen Evolution Electrocatalysts for AEM Electrolyzer Applications

The most widely used hydrogen evolution electrocatalyst for alkaline electrolyzer applications is Ni. However, in order to achieve desired rates of hydrogen generation, large amounts of Ni are required. High surface area Ni electrocatalysts are typically obtained via the caustic leaching of Ni-Al mixtures to obtain Raney Ni. While this process is relatively inexpensive, thick electrodes are needed to ensure enough active surface areas. In this work, an alternative approach for the synthesis of unsupported high-surface-area Ni-based electrocatalysts via spray pyrolysis will be presented. This versatile technique allows the fine-tuning of particle morphology for controlled synthesis of materials with high purity and uniform composition. Furthermore, the promotion effect of rare-earth metal oxides (REO) on the electrochemical activity of Ni electrocatalysts will be studied for rare-earth atomic compositions of 0-10%. Increased surface area of Ni-REO electrocatalysts will be obtained by producing a solute concentration gradient using low melting point precursors, resulting in hollow catalyst particles during the evaporation process. Synthesized catalyst materials will be characterized using XRD for crystallography and phase composition, XPS for elemental catalyst surface composition, electron microscopy (SEM, TEM) for micro and nano-sized morphology, and pore size analysis (BET and PSD). Physical/chemical characterization will be correlated to the observed electrocatalytic activity for the hydrogen evolution reaction (HER) in alkaline electrolytes to better understand the co-catalyst effect of REO on the Ni HER activity.

Electrochemical promotion of carbon supported Pt, Rh and Pd catalysts for H2 oxidation in aqueous alkaline media

AbstractBACKGROUNDThe effect of electrochemical promotion of catalysis (EPOC) for the case of H2 oxidation reaction over commercial M (M=Pt, Rh, Pd)/Vulcan XC72 (ETEK) electrodes immersed in alkaline media was explored in this study. Various reactant mixtures (H2 and O2) fed simultaneously through a glass frit to the anodic electrode which was immersed in the electrolyte. Both positive and negative currents were applied between anode and cathode while all the reactants were followed by mass spectrometry.RESULTSIn the case of Pt electrode, it was found that application of small positive currents resulted in a reversible enhancement of both oxygen and hydrogen consumption rate, higher than the expected Faradaic one (I/2F). Pd and Rh electrodes exhibited lower catalytic activity at ambient temperature while positive current applications induced an acceleration of the catalytic reaction. Interestingly, modification of the catalytic activity of Pd and Rh electrodes was found to be irreversible even under negative current applications.CONCLUSIONCommercially available, carbon supported metal (Pt, Rh, Pd) catalysts, can be electrochemically promoted during hydrogen oxidation reaction in alkaline media. The rate enhancement could be explained by modification of the work function of the catalytic surface (thus the strength of the reactant's adsorption bond) during potential or current application as well as modification of the catalyst surface composition. © 2018 Society of Chemical Industry

Pt-Ru/C Catalyst Performance during Direct Methanol Fuel Cell Operation

A methodology for the electroless deposition (ED) of ruthenium (Ru) on a commercial, carbon-supported Platinum (Pt) catalyst has been developed for electrochemical and fuel cell applications [1, 2]. Several different bimetallic catalysts composed of Pt and Ru have been produced using this methodology with promise of having better catalytic activity. Figure 1 shows how the SEA/ED method produces a finer, more evenly dispersed bimetallic distribution with less monometallic clustering [1]. These bimetallic catalysts have shown higher activities compared to both commercially-available Pt-Ru/C catalysts and monometallic Pt or Ru catalysts [3, 4]. This method’s bimetallic catalyst is proven to show better resistance to CO poisoning as well [3, 5, 6]. In application, this Pt-Ru/C catalyst has promise to be an optimal catalyst for use in a Direct Methanol Fuel Cell (DMFC). The objective for this study is to test the performance of the new Pt-Ru/C catalyst within a DMFC and compare the results to the commercially-available catalyst. This includes synthesis of the SEA/ED, Pt-Ru/C catalyst, characterization of the commercially-available and newly-synthesized catalyst with analysis, and finally, testing of each catalyst within a DMFC testing station and analyzing performance results. The DMFC testing and comparison is important to help show the catalysts’ real-world performance as well as effects of possible CO-poisoning during operation. The newly-synthesized catalyst has an increased electrochemical area as well as a better bi-metallic dispersion, to allow ruthenium to better prevent any platinum from being poisoned, causing the catalyst to perform better and last longer. 1. Diao, W., et al., Preparation and Characterization of Pt–Ru Bimetallic Catalysts Synthesized by Electroless Deposition Methods. ACS Catalysis, 2015. 5(9): p. 5123-5134. 2. Cho, H.-R. and J.R. Regalbuto, The rational synthesis of Pt-Pd bimetallic catalysts by electrostatic adsorption. Catalysis Today, 2015. 246: p. 143-153. 3. Garrick, T.R., et al., The Effect of Bimetallic Surface Composition for Methanol Oxidation. Student Posters (General) - 223rd Ecs Meeting, 2013. 53(29): p. 79-84. 4. Garrick, T.R., et al., The Effect of the Surface Composition of Ru-Pt Bimetallic Catalysts for Methanol Oxidation. Electrochimica Acta, 2016. 195: p. 106-111. 5. Galhenage, R.P., et al., Platinum–ruthenium bimetallic clusters on graphite: a comparison of vapor deposition and electroless deposition methods. Physical Chemistry Chemical Physics, 2015. 17(42): p. 28354-28363. 6. Kabbabi, A., et al., In situ FTIRS study of the electrocatalytic oxidation of carbon monoxide and methanol at platinum–ruthenium bulk alloy electrodes. Journal of Electroanalytical Chemistry, 1998. 444(1): p. 41-53. Figure 1

Morphological and Compositional Effects of Electrochemically Fabricated Cobalt Phosphide on Water Electrolysis

Recently, development of alternative energy for future has been under investigation to prevent environmental pollution caused by the huge use of fossil fuels. Among them, hydrogen is known as a clean energy source which does not emit pollutants. Effective hydrogen production using water electrolysis is one of the promising methods due to the simple procedure and high purity of product. However, its high cost limits the practical application of water electrolysis owing to the highly loaded platinum which is known as the best active catalyst for hydrogen evolution reaction (HER) To solve this problem, transition metals based compounds have been investigated as catalysts for HER. In this study, the cobalt phosphide was fabricated on the carbon paper by using electrodeposition method. The morphology and composition of cobalt phosphide was controlled by bath composition and deposition potential/time. The morphology and composition of prepared CoPx catalyst was characterized by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Furthermore, transmission electron microscopy was utilized to examine the crystal structure and surface composition of CoPx catalyst at the surface. All electrochemical measurements to explore the HER activity were conducted by using conventional three electrodes cell system with N2-purged 0.5 M H2SO4 electrolyte. The HER catalytic activity and electrochemical surface area of CoPx was measured by using cyclic voltammetry. Especially, the electrochemical surface area was estimated by double layer capacitance measurement varying the scan rates. As a result, it was revealed that the intrinsic HER activity of prepared CoPx catalyst has significant relationship with their morphology and composition. Furthermore, the developed catalyst was adopted as hydrogen-evolving electrode for proton exchange membrane water electrolyzer (PEMWE).

Promoted Iron Nanocrystals Obtained via Ligand Exchange as Active and Selective Catalysts for Synthesis Gas Conversion.

Colloidal synthesis routes have been recently used to fabricate heterogeneous catalysts with more controllable and homogeneous properties. Herein a method was developed to modify the surface composition of colloidal nanocrystal catalysts and to purposely introduce specific atoms via ligands and change the catalyst reactivity. Organic ligands adsorbed on the surface of iron oxide catalysts were exchanged with inorganic species such as Na2S, not only to provide an active surface but also to introduce controlled amounts of Na and S acting as promoters for the catalytic process. The catalyst composition was optimized for the Fischer–Tropsch direct conversion of synthesis gas into lower olefins. At industrially relevant conditions, these nanocrystal-based catalysts with controlled composition were more active, selective, and stable than catalysts with similar composition but synthesized using conventional methods, possibly due to their homogeneity of properties and synergic interaction of iron and promoters.

Engineering phase and surface composition of Pt3Co nanocatalysts: A strategy for enhancing CO tolerance

Improving the CO tolerance of Pt-based catalysts is very meaningful for the application in proton exchange membrane fuel cells and direct alcohol fuel cells. The behavior of Pt-based bimetallic catalysts is depended on their phase and surface composition. In this work, we tuned the surface composition of Pt3Co nanocatalysts by heat treatment under different atmosphere. The results of atomic-resolution HAADF-STEM, XRD, XPS and electrochemical characterization demonstrated that the surface composition of Pt3Co catalysts with Co-increased, Intermetallic and Pt-increased were obtained by metal segregation approach. Due to the differences in the surface atomic distribution and alloying extent, the nanocatalysts show different CO poisoning tolerance in the order of Co-increased>Intermetallic>Pt-increased. CO stripping voltammetry and in-situ Fourier transform infrared spectroscopy (FTIRS) were used together to investigate the origin of varied CO poisoning tolerance on three Pt3Co catalysts. The results illustrated that electronic effect plays a major role in weakening CO adsorption on Pt3Co nanocatalysts and thus promoting CO oxidation to form COOHad intermediate consistent with Langmuir-Hinselwood mechanism. Oxophilic effect promotes the oxidation of COOHad intermediate into the final products CO2/CO32-. This work provides a new insight into tuning phase and surface composition of catalysts thus enhancing CO tolerance of Pt-based bimetallic catalysts.

Effect of surface composition of Fe catalyst on the activity for the production of high-calorie synthetic natural gas (SNG)

An Fe2O3 catalyst was applied to the production of high-calorie synthetic natural gas (SNG). With this catalyst, the product distribution changed as the surface composition of the Fe2O3 catalyst changed. The effect of these changes on the catalytic activity was investigated. The active phases of the Fe2O3 catalyst were a mixture of low-carbon FeCx and Fe3C, which was maintained for 10 h, accompanied by the regeneration of Fe3O4. The surface Fe concentration increased after 10 h reaction, and this increased the CO conversion. In addition, the amounts of adsorbed C2H4 and C3H6 increased, which resulted in an increase in carbon chain growth. The surface concentration of oxygen also increased due to the regeneration of Fe3O4, thus reducing the C3H6 adsorption strength; in contrast, C2H4 adsorption increased, resulting in an enhanced paraffin-to-olefin (p/o) ratio for C2 hydrocarbons and reduced p/o ratio for C3 hydrocarbons.

Applicability of MOS structures in monitoring catalytic properties, as exemplified for monolayer-iron-oxide-coated porous platinum films

Metal Oxide Semiconductor (MOS) capacitor devices comprised of monolayer iron oxide-coated as well as non-coated polycrystalline Pt deposited on oxidized silicon carbide substrates have been fabricated and their usefulness as realistic model systems in catalyst studies/development was evaluated. The CO oxidation characteristics of both iron oxide- and non-coated Pt catalysts were investigated using mass spectrometry, monitoring the carbon dioxide production rate for different combinations of carbon monoxide (CO) and oxygen concentrations at various temperatures. Additionally, the output capacitance of the MOS model catalysts was recorded for each individual CO oxidation activity. A low-temperature shift in CO oxidation characteristics for the monolayer-coated compared to the non-coated Pt catalysts was observed, similar to that previously reported for monolayer iron oxide grown on single-crystalline Pt substrates. A strong correlation between the output capacitance of the MOS structures and the CO oxidation characteristics was found for both monolayer- and non-coated model catalysts. Furthermore, the devices exhibit retained MOS electrical output and CO oxidation characteristics as well as an unaffected catalyst surface composition, as confirmed by photoelectron spectroscopy, even after 200h of continuous model catalyst operation. In addition to the implications on practical applicability of monolayer iron oxide coating on widely used polycrystalline Pt films in real-world catalysts and sensors, the findings also point to new possibilities regarding the use of MOS model systems for in situ characterization, high-throughput screening, and tailoring of e.g. catalyst- and fuel-cell-electrode materials for specific applications.

Surface Composition Control of the Binary Au–Ag Catalyst for Enhanced Oxidant-Free Dehydrogenation

Effective control of surface composition of bimetallic catalysts is challenging yet important, as synergistic effects between two metals play vital roles in heterogeneous catalysis. This study involves methods of loading control, thermal activation, and selective surface etching to modify the bimetallic surface on the Au–Ag/SBA-15 catalyst and gains insight into the nature of the promotional effect of Ag modification over Au catalysts. The binary Au–Ag/SBA-15 catalyst prepared following a stepwise metal-loading procedure is found for the first time to be active in benzyl alcohol dehydrogenation without oxidant or hydrogen acceptor. A direct correlation is established between the surface compositions of the Au–Ag nanoparticles and their intrinsic catalytic activities. Au–Ag element analytical techniques, including X-ray fluorescence, X-ray photoelectron spectroscopy, and high-sensitivity low-energy ion scattering spectroscopy, are applied to acquire compositional information in bulk and on the surface. As ...

Deactivation of Au/CeO2 catalysts during CO oxidation: Influence of pretreatment and reaction conditions

The influence of the pretreatment on the activity and deactivation behavior of a high surface area 4.5wt.% Au/CeO2 catalyst during low temperature CO oxidation reaction (Treact=80°C) was studied in a multi-technique approach. Furthermore, the influence of changing from a close-to-stoichiometric (1% CO, 1% O2 rest N2), to O2-rich (1% CO, 5% O2 rest N2) and CO-rich (5% CO, 1% O2 rest N2) gas mixtures was investigated. Findings from kinetic and deactivation measurements are correlated with experimental data on the Au particle size, Au and Ce oxidation state, and on the nature of adsorbed species after the different pretreatments and during/after subsequent reaction, which were obtained by operando and in situ methods such as operando X-ray absorption spectroscopy and IR spectroscopy, as well as ex situ X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. These data revealed that the pretreatment significantly affects catalyst structure, surface composition and activity in the initial stages of the reaction. During reaction, however, the catalyst surface composition approaches a dynamic equilibrium state, which is largely reached already after 10min time on stream and which is independent of the pretreatment. Consequently, under present reaction conditions, longer-term deactivation is not dominated by the buildup of site blocking adsorbed species such as surface carbonates, but by slow processes such as reduction/re-oxidation of the bulk support during the reaction in combination with a modest irreversible Au NP growth.

Electrochemical Study of Platinum-Ruthenium-Copper Trimetallic Nanostructures for Methanol Oxidation

Direct methanol fuel cells commonly utilize platinum based catalysts due to their efficiency for methanol oxidation (MOR). Platinum based electrocatalysts are limited by intermediates adsorbing onto the electrocatalyst’s surface.1 Methanol oxidation forms multiple intermediate species, which are integral in generating electrons that drive the fuel cell.2 The production of intermediate species can also slow down reaction kinetics, while specific intermediate species can strongly adsorb onto active sites along the platinum catalyst surface reducing the number of MOR reactive sites. In order to remove the adsorbed intermediates, the MOR onset potential will shift to a more oxidizing potential.1These limitations can be addressed by developing a durable electrocatalyst that resists CO poisoning, maintains efficiency for MOR, and reduces the onset potential of methanol oxidation. An electrocatalyst comprised of nanomaterials could address some of these limitations, due to their synthetically tunable properties. Nanomaterials can be tailored to possess the ideal composition, morphology, and surface roughness for the catalysis of specific reactions. Previous studies have shown that Pt-based nanomaterials are efficient electrocatalysts, and their activity can be attributed to energetically favorable surface facets, as well as synergistic properties of alloys, specifically electronic and geometric effects.3 Geometric effects allow for the contraction or expansion of the nanomaterial’s crystal lattice, altering its electrochemical activity for a specific fuel.4 Electronic effects occur when the center d-band shifts, weakening the bond to the adsorbed species. In the case of MOR, the oxidation of CO would become more energetically favorable.1 These effects improve the resistance of intermediate poisoning, as well as the activity of the electrocatalyst by freeing more reactive sites. These effects can also influence the activity of pair sites in platinum alloyed nanomaterials, through the bifunctional mechanism.1 , 3 , 5 Previous work by our group investigated the effect of anisotropic alloyed nanostructures electrochemical activity, which demonstrated that the platinum-copper nanodendrites can enhance the MOR activity, while maintaining the dendritic morphology of the nanostructures.1 Current research focuses on the development of multimetallic nanostructures with various morphologies, surface roughness, as well as investigating each nanomaterial’s electrocatalytic activity. Multimetallic nanostructures are formed by first synthesizing copper nanomaterials. Then platinum and ruthenium precursor salts can alloy and co-reduce onto the vertices and edges of the copper nanomaterials, through galvanic replacement and co-reduction mechanisms. The morphology, porosity, surface roughness, and composition of these ruthenium-platinum-copper nanomaterials can be synthetically tailored. Platinum and ruthenium were chosen as secondary alloying metals with copper due to their binding energy for species such as –CO, -OH.6 During the synthetic process pair sites between Pt, Cu, and Ru will form, which could improve resistance towards intermediate poisoning and activity for MOR. The activity of these supportless electrocatalysts will be evaluated by cyclic voltammetry and chronoamperometry. The electrochemical surface area, the charging double layer capacitance, surface diffusion, the efficiency for MOR, and the resistance for CO for each electrocatalyst will be evaluated. Additionally, the morphological and electrochemical durability of each multimetallic nanomaterial in electrolyte and analyte will also be studied in this work. As previously discussed the pair site can affect the electrocatalytic activity for MOR; this work will also study the influence of the nanomaterial's copper core on the electrocatalytic properties. 1. Chen, A.; Holt-Hindle, P., Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications. Chemical Reviews 2010, 110(6), 3767-3804. 2. Cohen, J. L.; Volpe, D. J.; Abruna, H. D., Electrochemical determination of activation energies for methanol oxidation on polycrystalline platinum in acidic and alkaline electrolytes. Physical Chemistry Chemical Physics 2007, 9(1), 49-77. 3. Lee, H.-Y.; Vogel, W.; Chu, P. P.-J., Nanostructure and Surface Composition of Pt and Ru Binary Catalysts on Polyaniline-Functionalized Carbon Nanotubes. Langmuir 2011, 27(23), 14654-14661. 4. Wang, J. X.; Ma, C.; Choi, Y.; Su, D.; Zhu, Y.; Liu, P.; Si, R.; Vukmirovic, M. B.; Zhang, Y.; Adzic, R. R., Kirkendall Effect and Lattice Contraction in Nanocatalysts: A New Strategy to Enhance Sustainable Activity. Journal of the American Chemical Society 2011, 133(34), 13551-13557. 5. Sun, X.; Li, D.; Ding, Y.; Zhu, W.; Guo, S.; Wang, Z. L.; Sun, S., Core/Shell Au/CuPt Nanoparticles and Their Dual Electrocatalysis for Both Reduction and Oxidation Reactions. Journal of the American Chemical Society 2014, 136(15), 5745-5749. 6. Rossmeisl, J.; Ferrin, P.; Tritsaris, G. A.; Nilekar, A. U.; Koh, S.; Bae, S. E.; Brankovic, S. R.; Strasser, P.; Mavrikakis, M., Bifunctional anode catalysts for direct methanol fuel cells. Energy & Environmental Science 2012, 5 (8), 8335-8342.

Tuning Pt-Skin or M-Rich Surface on Bimetallic Nanoparticles (Pt3Ni, PtBi, Pt3Co) for Enhanced Electrocatalytic Activities

Controlling surface composition of bimetallic catalysts is of significance in energy conversion and storage. We synthesized a series of bimetallic catalysts of different surface composition on porous graphitic carbon (PtBi/PC, Pt3Ni/PC, Pt3Co/PC: figures A, C, E, G) with average diameter < 4 nm by controlled thermal treatment method. Formic acid oxidation on Pt/C is performed via the poisoning path (figure B), whereas oxidation of formic acid to form CO2 is done via the non-poisoning path on the PtBi/PC (figure D). The value of the peak current density is 4.6 times of that of the Pt/C catalysts. Pt3Ni catalyst with Pt-skin surface showed over 300% increase in mass activity compared with Pt/C for the oxygen reduction reaction (figure F). When we tuned the surface composition to Ni-rich, it showed 300% increasein mass activity when compared with Pt/C towards oxidizing of HCOOH. Ethanol oxidation on Pt3Co/PC with Pt-skin surface showed 2.5 times on mass activity than that of Pt/C. In addition, we proposed a new method to characterize Pt-skin or M-rich structure by using formic acid oxidation as probe reaction with the characterization of cyclic voltammetry and electrochemical in situFTIRs. Our approach to control surface composition can be used to design nanocatalysts for different reaction and enhance their catalytic performances. and The method is simple and clean that is effective and promotional to be industrialized. Figure 1

(Invited) Fundamental Aspects of Electrocatalysis at Work in Water Electrolysis

Text: A general aspect of electrocatalysis described most recently in [1,2] , is the involvement of the electrode (over)potential in generation of catalytically active sites. It has been demonstrated that , in a wide variety of ORR processes taking place in low temperature fuel cells, the electrocatalytic process is "ignited" by a potential-driven change in steady state catalyst surface composition . The common involvement of such potential-driven, surface composition change in the mechanism of electrocatalytic processes , has led to the conclusion that fuel cell electrocatalytic processes , particularly the ORR, are, in general, "redox mediated" , including so at metal electrocatalysts such as Pt [1,2]. In this paper, the applicability of the same type mechanism to electrocatalytic processes in water electrolysis, particularly the OER, is elucidated. Much the same way as in the case of ORR at a variety of electrocatalyst surfaces, the OER also exhibits generally a dependence on overpotential of: 'low Tafel slope of 60 mV/decade ,or lower, at low currents, followed by higher Tafel slope of around 120mV/decade at higher currents '. This general pattern is fully expected for a mechanism involving potential activation of surface sites. Inclusion of the change of active site population with potential in the expression for the current potential dependence, results in potential-dependence of the pre-exponential factor, with the consequence of a low Tafel slope around the standard potential of the redox couple mediator [1,2]. Recently reported polarization curves for the OER ,to be discussed in this talk (3), exhibit the typical behavior described above. As commonly done, the interpretation was given in the form of change in RDS with overpotential. The insight proposed here, sugegsts that the RDS may very well remain the same throughout the relevant potential range and the observed change in Tafel slope is fully explained by change with overpoential in steady state, active surface site population. Much the same way as in the case of fuel cell electrocatalysis [1,2], the important consequence of such general mechanism is that the effectiveness of the electrocatalyst depends on the magnitude of the overpotential required to activate the surface-redox-mediating system. Proximity of E0,surf.redox to E0,cell process should enable, in principle, high voltage efficiency of the electrolyzer. (1) S. Gottesfeld, ECS Trans. 2014 61(31): 1-13 (2) S. Gottesfeld, ECS Trans. 2015 66(29): 13-30 (3) R.I. Doyle and E.G. Lyons. JECS, 160, H42, 2013

Use of Mesoporous Molecular Sieves in the Production of Fine Chemicals: Preparation of Dihydroquinolinones of Pharmaceutical Interest From 2′‐Aminochalcones

AbstractSolid catalysts can be an alternative to homogeneous mineral Brønsted and Lewis acids for the synthesis of pharmaceuticals provided that the diffusional and adsorption properties of the reactants and products can be controlled. Structured micro and especially monolayered zeolites and mesoporous materials can be active and selective for intramolecular cyclization reactions and, more specifically, for intramolecular aza‐Michael cyclizations of 2′‐aminochalcones to yield aryl‐2,3‐dihydro‐4(1 H)‐quinolinones of pharmaceutical interest. However, the catalyst deactivates by strong adsorption of the basic quinolinone product. Product desorption has been controlled by optimizing catalyst pore structure and surface composition, together with a proper selection of solvent and reaction temperature. Process intensification for the synthesis of aryl‐2,3‐4(1 H)‐quinolinones of pharmaceutical interest has been achieved by preparing catalysts that allow the one‐pot synthesis of the dihydroquinolinones starting from 2′‐nitrochalcones with excellent yields.

The Effect of the Surface Composition of Ru-Pt Bimetallic Catalysts for Methanol Oxidation

A series of Ru-Pt bimetallic catalysts prepared by the electroless deposition of controlled and variable amounts of Ru on the Pt surface of a commercially-available 20wt% Pt/C catalyst has been characterized and evaluated for the oxidation of methanol. The activity of each Ru-Pt catalyst was determined as a function of surface composition via cyclic voltammetry. For the Ru-Pt bimetallic catalysts, activity passed through a maximum at approximately 50% monodisperse Ru surface coverage. However, due to the monolayer coverage of Ru on Pt, the amount of metal in the catalyst is minimized compared to a bulk 1:1 atomic ratio of Ru:Pt seen in commercial bimetallic catalysts. Chemisorption and temperature programmed reduction experiments confirmed that the surface had characteristics of a true bimetallic catalyst. On a mass of Pt basis, the activity of this composition for methanol oxidation was 7 times higher than pure Pt and 3.5 times higher than a commercial catalyst with a 1:1 Pt:Ru bulk atomic ratio.

Tuning Pt-skin to Ni-rich surface of Pt3Ni catalysts supported on porous carbon for enhanced oxygen reduction reaction and formic electro-oxidation

Controlling surface composition of bimetallic catalysts is of significance in energy conversion and storage. Here, we controlled thermal treatment to synthesize different surface composition of bimetallic catalysts with average diameter <4nm. We report the synthesis of Pt3Ni catalyst with Pt-skin surface directly supported on porous graphitic carbon (PC), which showed over 300% increase in mass activity compared with Pt/C for the oxygen reduction reaction (ORR). The high activity and stability are attributed to the Pt-skin structure and the morphology of PC. When we tuned the surface composition to Ni-rich, it showed 300% increase in mass activity when compared with Pt/C towards oxidizing of HCOOH. Our approach to control surface composition can be used to design nanocatalysts for different reaction and are simple, effective and promotional to be industrialized.

CO induced surface segregation as a means of improving surface composition and enhancing performance of CuPd bimetallic catalysts

A series of copper rich CuPd/Al2O3 catalysts were prepared and characterised by FTIR spectroscopy using CO as a probe molecule. After reduction, the surface composition was largely composed of Cu with evidence of a small concentration of isolated Pd atoms. It was found that CO induced surface segregation could be used to increase the surface Pd concentration and depending on the Cu:Pd ratio, the formation of Pd–Pd dimers was possible. Changes in surface composition were quantified and correlated with catalyst activity and selectivity for selective acetylene hydrogenation. For the catalyst with optimum Cu:Pd ratio (50:1), it was possible to use CO induced segregation to increase activity considerably (20K temperature reduction to achieve 100% conversion) whilst only marginally affecting ethylene selectivity (≈5% decrease in ethylene selectivity). An estimate of the detection limit by FTIR of the minimum surface coverage of isolated Pd and Pd–Pd dimers is given.

Trimetallic Platinum-Ruthenium-Copper Nanotubes for Methanol Oxidation

Platinum materials are traditionally utilized as the standard electrocatalysts in direct methanol fuel cells; however, platinum is hindered by CO poisoning, which is an intermediate of methanol oxidation.1 CO adsorption to platinum active sites causes slow kinetics for methanol oxidation (MOR), and requires higher onset potential for the removal of adsorbed CO and commencement of methanol oxidation.1 Bimetallic Pt-based nanomaterials can function as efficient electrocatalysts due to the synergistic properties of alloys, specifically electronic and geometric effects.2 Electronic effects occur when the center d-band is shifted upwards, weakening the bond to the adsorbed CO, allowing for easier oxidation of CO.1 The geometric effects allow for the contraction or expansion of their crystal lattice, resulting in the alternation of the electrochemical activity for a specific fuel.3 When platinum is alloyed with either copper or ruthenium, the electrocatalysts can become more tolerant to CO adsorption.2 , 4 In addition, the bifunctional alloys can enhance electrocatalytic activity for MOR. An oxygenated species (-OH) favorably adsorb onto the additional metal, aids in the oxidation of CO adsorbed on platinum.1 Anisotropic nanostructures can increase the electrochemical activity while maintaining the stability of catalysts. Additionally, nanomaterials possess tunable surface area, morphologies, and surface facets that enable the formation of a catalyst with enhanced electrocatalytic activity.5 , 6 We have demonstrated that the platinum-copper nanodendrites can enhance the MOR activity and maintain the dendritic morphology of the nanostructures.7 In this work, we synthesize binary and ternary metallic nanotubes and study their activity for MOR. Bimetallic nanostructures are formed first by alloying platinum precursor salts with copper nanowires through the galvanic replacement and co-reduction mechanisms. This process forms hollow platinum-copper nanotubes with controllable surface roughness. To further improve the activity for MOR, we alloy ruthenium into platinum-copper nanostructures. The morphology, surface roughness, and composition of these ruthenium-platinum-copper nanotubes can be synthetically tuned by controlling the precursor ratio, reaction time, and reaction temperature. The electrochemical activity for MOR will be evaluated by cyclic voltammetry and chronoamperometry to characterize the electrochemical surface area, the efficiency for MOR, the tolerance for CO, and the stability of the electrocatalysts in acidic media. The enhanced activity of these multimetallic nanostructures as supportless electrocatalysts for MOR will be discussed. 1. Chen, A.; Holt-Hindle, P., Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications. Chemical Reviews 2010, 110 (6), 3767-3804.2. Lee, H.-Y.; Vogel, W.; Chu, P. P.-J., Nanostructure and Surface Composition of Pt and Ru Binary Catalysts on Polyaniline-Functionalized Carbon Nanotubes. Langmuir 2011, 27 (23), 14654-14661.3. Wang, J. X.; Ma, C.; Choi, Y.; Su, D.; Zhu, Y.; Liu, P.; Si, R.; Vukmirovic, M. B.; Zhang, Y.; Adzic, R. R., Kirkendall Effect and Lattice Contraction in Nanocatalysts: A New Strategy to Enhance Sustainable Activity. Journal of the American Chemical Society 2011, 133 (34), 13551-13557.4. Sun, X.; Li, D.; Ding, Y.; Zhu, W.; Guo, S.; Wang, Z. L.; Sun, S., Core/Shell Au/CuPt Nanoparticles and Their Dual Electrocatalysis for Both Reduction and Oxidation Reactions. Journal of the American Chemical Society 2014, 136 (15), 5745-5749.5. Koenigsmann, C.; Zhou, W.-p.; Adzic, R. R.; Sutter, E.; Wong, S. S., Size-Dependent Enhancement of Electrocatalytic Performance in Relatively Defect-Free, Processed Ultrathin Platinum Nanowires. Nano Letters 2010, 10 (8), 2806-2811.6. Li, M.; Liu, P.; Adzic, R. R., Platinum Monolayer Electrocatalysts for Anodic Oxidation of Alcohols. The Journal of Physical Chemistry Letters 2012, 3 (23), 3480-3485.7. Taylor, E.; Chen, S.; Tao, J.; Wu, L.; Zhu, Y.; Chen, J., Synthesis of Pt–Cu Nanodendrites through Controlled Reduction Kinetics for Enhanced Methanol Electro-Oxidation. ChemSusChem 2013, 6 (10), 1863-1867.

Water: the most effective solvent for liquid-phase hydrodechlorination of chlorophenols over Raney Ni catalyst

Catalytic hydrodechlorination (HDC) has proved to be an efficient approach to dispose chlorinated organic compounds (COCs). The influence of solvent on the HDC of chlorophenols with H2 over Raney Ni catalyst was investigated. We found that protic solvents, especially water, significantly accelerated liquid-phase HDC that was sluggish in aprotic solvents. Among the selected solvents, water was the most effective solvent for liquid-phase HDC over Raney Ni catalyst. To study the mechanism for the rate acceleration in the HDC that was promoted by protic solvents, catalysts were characterized by SEM, EDX, and XRD techniques. It was found that solvent could affect surface composition and surface micro-topography of Raney Ni catalyst. On the basis of these studies, an effective and practical reaction system was developed to dispose chlorophenols over Raney Ni catalyst; a broad range of chlorophenols were efficiently hydrodechlorinated in aqueous solutions under mild conditions, and the catalyst could be reused at least five times without any loss of catalytic activity.

Determining surface composition of mixed oxides with pH

In this study we have developed a 2-surface model with the EPHL (“Equilibrium pH at high oxide loading”) method for mixed and composite oxides. Oxide charging parameters, namely the protonation and deprotonation constants and the hydroxyl surface densities, can be established from measurements of the pure oxides and used in the 2-surface model to predict the point of zero charges (PZC) of mixed and composite oxides. The accuracy of these predictions has been demonstrated with diverse control samples of known surface composition (physical mixtures of silica and alumina of high and low surface area). The EPHL method has been extended to composite materials (bound catalysts) and can explain correlations of reactivity with catalyst surface composition. The “apparent surface coverage” (ASC) of a particular mixed or composite oxide sample may then be determined by comparing the PZC of the material to either the 2-surface model results, using parameters of the individual oxides, or a calibration curve of EPHL measurements of physical mixtures of the individual ingredients.