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Abstract: Rechargeable lithium‐oxygen (Li‐O2) batteries are one of the most promising technologies for next‐generation energy storage, which is also a critical part of the future renewable energy portfolio; however, its commercialization is still hindered by several challenges. The high charge overpotential, in particular, not only causes problems by increasing the possibility of electrolyte decomposition but also induces a low round‐trip efficiency and coulombic efficiency. Here, by choosing the right component proportion in Pt‐Cu bimetallic electrocatalysts that optimize electrocatalytic activity of electrochemical reactions, especially of oxygen evolution reactions, a superior electrochemical behavior is demonstrated, with a low charge overpotential of 0.2 V and cycleability of 50 discharge/charge cycles before capacity fading. The optimized Pt‐Cu bimetallic electrocatalysts significantly reduce the charge overpotential and furthermore enhance the efficiency, stability, and cycleability of an aprotic Li‐O2 battery. [ABSTRACT FROM AUTHOR]

Highly dispersed and highly stable supported bimetallic catalysts were prepared using a two-step process. Pt nanoparticles (NPs) were first deposited on porous γ-AlO particles by atomic layer deposition (ALD). Au NPs were synthesized by using gold(III) chloride as the Au precursor, and then immobilized on ALD Pt/γ-AlO particles. The Au-Pt bimetallic catalysts were highly active and highly stable in a vigorously stirred liquid phase reaction of glucose oxidation. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The turnover rate (TOR, normalized to sites measured by CO chemisorption before reaction) and selectivity for the aqueous phase reforming of glycerol have been determined for Pt/C and PtMo/C catalysts. While the TOR of PtMo/C is higher than that of Pt/C by about 4 times at comparable conversion, the selectivity to C-O bond cleavage is higher, thus reducing the H yield at high conversion. Under reaction conditions on Pt/C, CO is observed as the most abundant Pt surface species with a fractional coverage of about 0.6 using operando X-ray absorption spectroscopy. Since there is little CO in the effluent (CO:CO ratios > 100:1, when CO is detected), it is thought that surface CO is converted to H and CO by the water gas shift reaction. DFT calculations suggest that the role of metallic Mo is to alter the electronic properties of Pt lowering the binding energy of CO and reducing the activation energies of dehydrogenation and C-O bond cleavage. Because the activation energy for C-O cleavage is lowered more than for dehydrogenation, the selectivity for C-O bond cleavage is increased, ultimately lowering the H yield compared to Pt/C. [ABSTRACT FROM AUTHOR]

A carbon supported PtMo aqueous phase reforming catalyst for producing hydrogen from glycerol was characterized by analysis of the reaction products and pathway, TEM, XPS and XAS spectroscopy. Operando X-ray absorption spectroscopy (XAS) indicates the catalyst consists of bimetallic nano-particles with a Pt rich core and a Mo rich surface. XAS of adsorbed CO indicates that approximately 25% of the surface atoms are Pt. X-ray photoelectron spectroscopy indicates that there is unreduced and partially reduced Mo oxide (MoO and MoO), and Pt-rich PtMo bimetallic nano-particles. The average size measured by transmission electron microscopy of the fresh PtMo nano-particles is about 2 nm, which increases in size to 5 nm after 30 days of glycerol reforming at 31 bar and 503 K. The catalyst structure differs from the most energetically stable structure predicted by density functional theory (DFT) calculations for metallic Pt and Mo atoms. However, DFT indicates that for nano-particles composed of metallic Pt and Mo oxide, the Mo oxide is at the particle surface. Subsequent reduction would lead to the experimentally observed structure. The aqueous phase reforming reaction products and intermediates are consistent with both C-C and C-OH bond cleavage to generate H/CO or the side product CH. While the H selectivity at low conversion is about 75%, cleavage of C-OH bonds leads to liquid products with saturated carbon atoms. At high conversions (to gas), these will produced additional CH reducing the H yield and selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of thermal treatment on the structure of Pd-on-Au catalysts was assessed using TCE HDC as a model reaction. • Based on the Pd and temperature, the NPs went from Au core/Pd shell to Au core/PdAu surface alloy or PdAu alloy structures. • Activity correlated with Pd ensemble size, with up to ten times enhanced activity compared to monometallic Pd. • These results show the importance of structure on activity as well as the potential use of the NPs at high temperatures. Palladium metal supported on gold in the form of surface ensembles have enhanced catalytic properties compared to monometallic Pd, as exemplified by Pd-decorated Au nanoparticles (Pd-on-Au NPs) for various room-temperature reactions. Whereas the catalytic properties and nanostructure of Pd-on-Au NPs are not known at higher temperatures, this work focuses on thermal annealing effects on the Pd-on-Au NP nanostructure, bimetal distribution, and room-temperature water-phase trichloroethene hydrodechlorination (TCE HDC) as the model reaction. Analysis of the average coordination environment of Pd and Au atoms through x-ray absorption spectroscopy showed that as-synthesized Pd-on-Au NPs transitioned from a Au core/Pd shell structure to Au-rich core/PdAu surface alloy or PdAu mixed alloy structures depending on the Pd surface coverage (30–150 sc%) and annealing temperature (100–400 °C). The HDC activity strongly correlated with Pd ensemble size, where the as-formed Pd islands exhibited one order of magnitude enhanced activity compared to monometallic Pd. Higher annealing temperatures led to a surface/mixed alloy structure with smaller Pd ensemble size, resulting in lower activity but still ∼3 times more active than monometallic Pd. These results illustrate the importance of catalyst structure on activity and the usefulness of metal-decorated metal catalysts for higher-temperature reactions. [ABSTRACT FROM AUTHOR]

Nitroarene reduction reactions are commercialized catalytic processes that play a key role in the synthesis of many products including medicines, rubbers, dyes, and herbicides. Whereas bimetallic compositions have been studied, a better understanding of the bimetallic structure effects may lead to improved industrial catalysts. In this work, the influence of surface palladium atoms supported on 3-nm Au nanoparticles (Pd-on-Au NPs) on catalytic activity for 4-nitrophenol reduction is explored. Batch reactor studies indicate Pd-on-Au NPs exhibit maximum catalytic activity at a Pd surface coverage of 150 sc%, with an initial turnover frequency of ∼3.7 mol-nitrophenol/mol-metal surface /s, which was ∼5.5× and ∼13× more active than pure Au NPs and Pd NPs, respectively. Pd NPs, Au NPs, and Pd-on-Au NPs below 175 sc% show compensation behavior. Three-dimensional Pd surface ensembles (with ∼4–5 atoms) previously identified through X-ray adsorption spectroscopy provide the active sites responsible for the catalytic maximum. These results demonstrate the ability to adjust systematically a structural feature ( i.e. , Pd surface coverage) to yield a more active material. [ABSTRACT FROM AUTHOR]

Abstract: Two groups of catalysts containing Ni and/or Co metals and MgAlO x as support material were made using coprecipitation and incipient wetness impregnation methods, respectively. The mechanism of metal particle growth during reduction of the monometallic Ni or Co and bimetallic Ni–Co catalysts was studied using X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS). The results show that the bimetallic Ni–Co catalysts made by coprecipitation method resulted in smaller metal nanoparticles upon reduction. TEM confirmed this observation and revealed that this catalyst has well-dispersed, more uniform metal particles. The metal reduction extent of Ni monometallic catalysts and the bimetallic catalysts made by impregnation was similar with respect to each metal. For the bimetallic Ni–Co catalysts made by coprecipitation, the interactions between two metals in reduction were observed such that Ni reduction was mitigated by Co, and Co reduction was promoted by Ni. And the first derivative of XANES of such made catalysts indicated stronger interaction between Ni and Co atoms and, perhaps, alloy formation. Time resolved analysis found that Ni reduction followed the second order kinetics at early stage and Co proceeded through the zero order all the way in catalyst reduction. The catalyst stability enhancement by Co atoms and the mechanism of Ni and Co interaction during reduction are explained. [Copyright &y& Elsevier]