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The alloying of metals with foreign elements is a common approach for manipulating catalytic properties of active sites. For palladium-based catalysts, incorporation of light elements receives far less attention than Pd-metal alloys even though incorporated light element are catalytically significant. Due to their small size, light elements (H, B, C, and O) can occupy octahedral sites in Pd to form an interstitial phase, while palladium adjusts its lattice to accommodate the incorporation of larger light elements (S and P) to form distinct phases. The incorporated light element modifies the electronic structure of palladium, influencing the binding energy of substrates and reactive intermediates. Pd hydride and oxide often form in situ during hydrogenation or oxidation reactions, respectively, representing the (more, less) active phase of the catalyst. The reactive interstitial hydrogen dissolved in Pd tends to hydrogenate reactants completely and unselectively. Pd oxide can be the active phase for oxidation reactions, and the incorporated oxygen or oxygen vacancies may participate in the reaction directly. Incorporated light elements change geometric aspects of Pd ensembles, serving the role of site blocking, ensemble isolation, or serve as an additional active site, endowing Pd with bifunctional character. We review the synthetic approaches for incorporating light elements into the palladium lattice. We summarize the catalytic influence of light element incorporation into the palladium lattice with respect to electronic and geometric modification, in situ incorporated hydrogen and oxygen, and discuss the influence of light element incorporation into Pd on specific reactions (i.e., selective hydrogenation, oxidation, electrocatalysis, and C C cross coupling).

In this feature article, we provide an account of the Langmuir Lecture delivered by Kristen Fichthorn at the Fall 2020 Virtual Meeting of the American Chemical Society. We discuss how multiscale theory and simulations based on first-principles DFT were useful in uncovering the intertwined influences of kinetics and thermodynamics on the shapes of Ag and Cu cubes and nanowires grown in solution. We discuss how Ag nanocubes can form through PVP-modified deposition kinetics and how the addition of chloride to the synthesis can promote thermodynamic cubic shapes for both Ag and Cu. We discuss kinetic factors contributing to nanowire growth: in the case of Ag, we show that high-aspect-ratio nanowires can form as a consequence of Ag atom surface diffusion on the strained surfaces of Marks-like decahedral seeds. On the other hand, solution-phase chloride enhances Cu nanowire growth due to a synergistic interaction between adsorbed chloride and hexadecylamine (HDA), which leaves the {111} nanowire ends virtually bare while the {100} sides are fully covered with HDA. For each of these topics, a synergy between theory and experiment led to significant progress.

H 2 adsorption on Au catalysts is weak and reversible, making it difficult to quantitatively study. We demonstrate H 2 adsorption on Au/TiO 2 catalysts results in electron transfer to the support, inducing shifts in the FTIR background. This broad background absorbance (BBA) signal is used to quantify H 2 adsorption; adsorption equilibrium constants are comparable to volumetric adsorption measurements. H 2 adsorption kinetics measured with the BBA show a lower E app value (23 kJ/mol) for H 2 adsorption than previously reported from proxy H/D exchange (33 kJ/mol). We also identify a previously unreported H-O-H bending vibration associated with proton adsorption on electronically distinct Ti-OH metal-support interface sites, providing new insight into the nature and dynamics of H 2 adsorption at the Au/TiO 2 interface.

The development of an in situ nonthermal plasma technology improved the oxidation and energy release of boron nanoparticles. We reduced the native oxide layer on the surface of boron nanoparticles (70 nm) by treatment in a nonthermal hydrogen plasma, followed by the formation of a passivation barrier by argon plasma-enhanced chemical vapor deposition (PECVD) using perfluorodecalin (C10F18). Both processes occur near room temperature, thus avoiding aggregation and sintering of the nanoparticles. High-resolution transmission electron microscopy (HRTEM), high-angular annular dark-field imaging (HAADF)-scanning TEM (STEM)-energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) demonstrated a significant reduction in surface oxide concentration due to hydrogen plasma treatment and the formation of a 2.5 nm thick passivation coating on the surface due to PECVD treatment. These results correlated with the thermal analysis results, which demonstrated a 19% increase in energy release and an increase in metallic boron content after 120 min of hydrogen plasma treatment and 15 min of PECVD of perfluorodecalin. The PECVD coating provided excellent passivation against air and humidity for 60 days. We conclude in situ nonthermal plasma reduction and passivation lead to the amelioration of energy release characteristics and the storage life of boron nanoparticles, benefits conducive for nanoenergetic applications.

Ag nanocubes (AgNCs) are predominantly synthesized by the polyol method, where the solvent (ethylene glycol) is considered the reducing agent and poly(N-vinylpyrrolidone) (PVP) the shape-directing agent. An experimental phase diagram for the formation of Ag nanocubes as a function of PVP monomer concentration (Cm) and molecular weight (Mw) demonstrated end groups of PVP impact the final Ag product. Measured rates of the initial Ag+ reduction at different PVP Cm and Mw confirmed the reducing effect originates from end-groups. PVP with well-defined aldehyde and hydroxyl end groups lead to the formation of Ag nanocubes and nanowires respectively, indicating the faster reducing agent formed kinetically preferred nanowires. We demonstrate PVP end-groups induce initial reduction of Ag+ to form seeds followed by autocatalytic reduction of Ag+ by ethylene glycol (and not solvent oxidation products) to form Ag nanostructures. The current study enabled a quantitative description of the role of PVP in nanoparticle shape-control and demonstrates a unique opportunity to design nanostructures by combining nanoparticle synthesis with polymer design to introduce specific physicochemical properties.

The redox properties of ceria make it suitable as a catalyst or support in oxidation reactions. Ceria-supported transition metal nanoparticles or isolated single atoms provide a metal-support interface that reduces the energy cost to remove interfacial oxygen atoms, providing active oxygen species that can participate in Mars van Krevelen oxidation processes. CO oxidation is a key probe reaction to test the reducibility of ceria-supported catalysts and is also practically important in the elimination of CO at relatively low temperatures in various applications. Preferential oxidation of CO (PROX) in excess H2 controls the CO concentration to ultra-low levels to prevent poisoning of hydrogen oxidation electrocatalysts. The reactivity of catalysts in CO oxidation and selectivity towards CO over H2 in PROX is dependent on the type and dispersion of metal species, the structural and chemical properties of CeO2, and the synthetic preparation methods of the catalysts. In this review, we summarize recently published works on catalytic CO oxidation and PROX reactions on ceria-supported metal nanoparticles and single atoms. We summarize the reactivity on different supported metals, and on different CeO2 surfaces with the same metal. We summarize the most likely reaction mechanisms as suggested by density functional theory calculations. The factors contributing to selectivity towards CO oxidation in PROX reactions on various supported metals are also discussed.

We demonstrate that atomically thin Pt shells deposited on transition metal carbide or nitride cores induce up to a 4-fold enhancement in C2H4 selectivity during the partial hydrogenation of acetyl...

Bimetallic NiAu catalysts have garnered broad interest for a variety of reactions including automotive emissions, selective hydrogenation, selective oxidation, hydrodechlorination, and biomass conversion. However, the bulk immiscibility of the two metals, complicating catalyst synthesis, has limited studies of this bimetallic system. We report a solution-phase synthesis for Ni and bimetallic NiAu heterogeneous catalysts. Using oleylamine as a capping agent, an optimized synthesis for Ni catalysts led to supported particles with a narrow size distribution (4.7 ± 0.4 nm). Gold was added to the Ni nanoparticles via galvanic displacement of Ni in organic solution, the particles were deposited onto commercial alumina, and oleylamine capping agent was removed. The catalytic activity of the bimetallic materials in 1-octyne partial hydrogenation was in between the activity of monometallic Ni and Au catalysts. At high space velocity, the bimetallic catalysts largely maintained the high alkene selectivity associate...

Cobalt(II) ions were adsorbed to the surface of rod-shape anatase TiO2 nanocrystals and subsequently heated to promote ion diffusion into the nanocrystal. After removal of any remaining surface bound cobalt, a sample consisting of strictly cobalt-doped TiO2 was obtained and characterized with powder X-ray diffraction, transmission electron microscopy, UV-visible spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy, SQUID magnetometry, and inductively-coupled plasma atomic emission spectroscopy. The nanocrystal morphology was unchanged in the process and no new crystal phases were detected. The concentration of cobalt in the doped samples linearly correlates with the initial loading of cobalt(II) ions on the nanocrystal surface. Thin films of the cobalt doped TiO2 nanocrystals were prepared on indium-tin oxide coated glass substrate, and the electrical conductivity increased with the concentration of doped cobalt. Magnetic measurements of the cobalt-doped TiO2 nanocrystals reveal paramagnetic behavior at room temperature, and antiferromagnetic interactions between Co ions at low temperatures. Antiferromagnetism is atypical for cobalt-doped TiO2 nanocrystals, and is proposed to arise from interstitial doping that may be favored by the diffusional doping mechanism.

We report a thermolytic reduction of silver precursors in the presence of anatase TiO2 nanorods to form Ag–TiO2 hybrid nanocrystals (HNCs). Upon changing the reaction conditions, the size and numbe...

We utilize a continuous injection approach (CIA) rather than the traditional incremental injection approach (IIA) to deliver ligand (or receptor) to the calorimeter cell to evaluate thermodynamic binding parameters for three common ligand-receptor binding models-single independent, competitive, and two independent binding sites-using isothermal titration calorimetry (ITC). A general mathematical expression for the binding isotherm for any binding stoichiometry under continuous delivery of ligand (or receptor) resulting in an analytical solution for the thermodynamic binding parameters is presented. The advantages of CIA include reduction in experimental time, estimation of thermodynamic binding parameter values, and automation of the experiment since thermodynamic parameters are estimated in situ. We demonstrate the inherent advantages of CIA over IIA for the three binding models. For the single independent site model, we utilized the binding of Ba2+ ions to ethylenediaminetetraacetic acid (EDTA), while competitive binding was captured by titration of Ca2+ ions into a buffered solution of Ba2+ and EDTA. We experimentally simulated a two independent binding site system by injecting Ca2+ into a solution of EDTA and 1,3-diaminopropane-N,N,N',N'-tetraacetic acid (DPTA). The results demonstrate estimation of thermodynamic parameters with greater confidence and simultaneous reduction in the experimental time of 83% and titrating reagent of 50%, as compared to IIA.

Amine-impregnated sorbents can be applied in CO₂ sequestration, but they suffer from low amine utility due to slow diffusion of CO₂, leading to reduced accessibility of buried amines. We examined silica-supported polyethylenimine (PEI) sorbents and blended them with polyethylene glycol (PEG) as an additive to study the role of PEG in modifying sorption performance. We report an increase in amine efficiency, a decrease in the heat of sorption and regeneration temperature, and a change CO₂ amine speciation with the addition of PEG. The increase in viscosity due to CO₂ sorption leads to greater diffusion resistance; increases in viscosity were lower during CO₂ sorption in blends with higher PEG composition. ¹³C NMR results on CO₂-saturated PEI–PEG blends revealed the formation of carbamic acid and carbamate and showed a larger fraction of carbamic acid in PEG-rich samples. We propose PEG increases the amine efficiency by enabling the diffusion of CO₂ due to viscosity reduction and changes in the CO₂-amine speciation (carbamate versus carbamic acid), which modifies the theoretical CO₂/amine stoichiometry.

The existing literature suggests it is particularly difficult to access the catalytically relevant, and relatively complex, intermetallic γ-brass crystal structure through traditional nanoparticle (NP) synthesis techniques. We introduce a simple and rational approach to access this phase in M-Zn (M = Pd, Cu, Ni) systems as silica-supported single-phase nanocrystals. This hybrid approach involves the initial synthesis of supported M/SiO2 through traditional approaches (dry impregnation and strong electrostatic adsorption) followed by heating to high temperatures in the presence of a stoichiometric amount of metallic Zn in an evacuated closed system for several hours. We demonstrate the generality of this method with three different catalytically important bimetallic systems: Pd-Zn, Ni-Zn and Cu-Zn. Of these three, Pd-Zn is by the far the most popular in terms of catalytic applications and yields the smallest particle size (∼8 nm). We tested the influence of various synthesis parameters on phase purity and particle size distribution in case of the synthesized γ-brass Pd-Zn/SiO2 supported catalysts and provide general guidelines towards optimization of synthesis. Upon transformation of Pd/SiO2 to γ-brass Pd-Zn/SiO2, a precipitous drop in CO adsorption and a 25 kJ/mol increase in the ethylene hydrogenation barrier is observed, indicating the catalytic active sites are significantly modified as a result of alloying. We anticipate these catalysts may find applications in various Pd-catalyzed chemistries.

Atomically thin platinum (Pt) shells on titanium tungsten carbide (TiWC) and titanium tungsten nitride (TiWN) core nanoparticles display substantially modified catalytic performance compared to com...

In this article, we highlight the growing application of intermetallic compounds in heterogeneous catalysis. We clearly discuss intermetallics as distinct from other multi-metallic systems (such as alloys, surface modifiers and dopants). Intermetallics possess a number of attributes over random alloys (i.e., solid solutions) and serve as model catalysts for a number of industrially relevant reactions. We review a variety of methods used for the synthesis of a large number of intermetallic compounds and discuss how standard material characterization techniques can be extended to intermetallics to gain important insight regarding active site morphology, a critical metric in heterogeneous catalyst design. We further summarize the use of intermetallics in understanding changes in reactivity and selectivity due to geometric and electronic effects, with emphasis on determining compositional and structural factors of the active site. We conclude with a brief summary of avenues for future advances in the field and its potential to contribute to environment and economy.

The use of polar aprotic solvents in acid-catalyzed biomass conversion reactions can lead to improved reaction rates and selectivities. We show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts, specifically chlorides. Reaction kinetics studies of the Brønsted acid-catalyzed dehydration of fructose to hydroxymethylfurfural (HMF) show that the use of catalytic concentrations of chloride salts leads to a 10-fold increase in reactivity. Furthermore, increased HMF yields can be achieved using polar aprotic solvents mixed with chlorides. Ab initio molecular dynamics simulations (AIMD) show that highly localized negative charge on Cl− allows the chloride anion to more readily approach and stabilize the oxocarbenium ion that forms and the deprotonation transition state. High concentrations of polar aprotic solvents form local hydrophilic environments near the reactive hydroxyl group which stabilize both the proton and chloride anions and promote the dehydration of fructose., Despite the potential advantages of using polar aprotic solvents for biomass upgrading reactions, fundamental understanding of these solvation effects is limited at present. Here, the authors show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts.

The major products from hydrothermal reactions of tryptophan at 350 and 400 °C in the absence of catalyst were indole and methyl indoles, indicating simultaneous deoxygenation and deamination. In the presence of carbon-supported Ni and NiM catalysts (M = Ru, Cu, Pd, Pt) primary aromatic amines also appeared, via cleavage of the heterocyclic ring of the indoles. Ni and NiCu catalysts have the lowest selectivity for the formation of this family of compounds, while NiRu had the highest selectivity. Catalysts containing noble metals also produced monosubstituted alkylaromatics, due to the deamination of the aromatic amines, with the NiPt catalyst providing the highest molar yield (∼7%). We propose catalytic and non-catalytic hydrothermal reaction pathways for tryptophan based on the observed product distributions. The bimetallic particles were smaller than the pure Ni particles and the surfaces of NiRu and NiPd particles were enriched in Ni, relative to the nominal bulk composition.

Selective hydrogenation of linear alkenes in the presence of aromatics is desired to prevent gum formation in pyrolysis gasoline (PYGAS) upgrading. To examine the competitive hydrogenation between linear alkenes and aromatics, we investigate ethylene and benzene competitive hydrogenation on different catalysts. Through density functional theory (DFT) calculations, we show the adsorption energies of benzene and ethylene correlate on monometallic close-packed surfaces, with benzene binding stronger for the same C to surface metal atom ratio. DFT calculations demonstrate Bronsted–Evans–Polanyi and scaling relationships hold, and these are fed into microkinetic modeling to predict the rate of ethylene and benzene hydrogenation with only ethylene and hydrogen binding energies as the surface descriptors. Due to stronger binding, benzene adsorption will dominate the surface. Higher barriers for benzene hydrogenation versus ethylene hydrogenation lead to benzene poisoning at temperatures at which ethylene hydroge...

Intermetallic compounds offer unique opportunities for atom-by-atom manipulation of catalytic ensembles through precise stoichiometric control. The [Pd, (M), Zn] γ-brass phase allows for controlled synthesis of Pd-M-Pd catalytic sites (M = Zn, Pd, Cu, Ag and Au) isolated in an inert Zn matrix. These multi-atom heteronuclear active sites are catalytically distinct from Pd single atoms and fully coordinated Pd. We quantify the unexpectedly large effect of active site composition (i.e., identity of M atom in Pd-M-Pd sites) on ethylene selectivity during acetylene semi-hydrogenation. Subtle stoichiometric control demonstrates Pd-Pd-Pd sites are active for ethylene hydrogenation, whereas Pd-Zn-Pd sites show no measurable ethylene to ethane conversion. Agreement between experimental and density functional theory predicted activities and selectivities demonstrates precise control of Pd-M-Pd active site composition. The diversity and well-defined structure of intermetallics can be utilized to design active sites assembled with atomic-level precision.

Intermetallic compounds offer unique opportunities for atom-by-atom manipulation of catalytic ensembles through precise stoichiometric control. The (Pd, M, Zn) γ-brass phase enables the controlled synthesis of Pd-M-Pd catalytic sites (M = Zn, Pd, Cu, Ag and Au) isolated in an inert Zn matrix. These multi-atom heteronuclear active sites are catalytically distinct from Pd single atoms and fully coordinated Pd. Here we quantify the unexpectedly large effect that active-site composition (that is, identity of the M atom in Pd-M-Pd sites) has on ethylene selectivity during acetylene semihydrogenation. Subtle stoichiometric control demonstrates that Pd-Pd-Pd sites are active for ethylene hydrogenation, whereas Pd-Zn-Pd sites show no measurable ethylene-to-ethane conversion. Agreement between experimental and density-functional-theory-predicted activities and selectivities demonstrates precise control of Pd-M-Pd active-site composition. This work demonstrates that the diversity and well-defined structure of intermetallics can be used to design active sites assembled with atomic-level precision.

Ag nanocubes (AgNCs) are predominantly synthesized by the polyol method, where the solvent (ethylene glycol) is considered the reducing agent and poly(

Cobalt(ii) ions were adsorbed to the surface of rod-shape anatase TiO

The synthesis of two-dimensional (2D) zeolites has garnered attention due to their superior properties for applications that span catalysis to selective separations. Prior studies of 2D zeolite catalysts demonstrated enhanced mass transport for improved catalyst lifetime and selectivity. Moreover, the significantly higher external surface area of 2D materials allows for reactions of bulky molecules too large to access interior pores. There are relatively few protocols for preparing 2D materials, owing to the difficultly of capping growth in one direction to only a few unit cells. To accomplish this, it is often necessary to employ complex, commercially unavailable organic structure-directing agents (OSDAs) prepared via multistep synthesis. However, a small subset of zeolite structures exist as naturally layered materials where postsynthesis steps can be used to exfoliate samples and produce ultrathin 2D nanosheets. In this study, we selected a common layered zeolite, the MWW framework, to explore methods of preparing 2D nanosheets via one-pot synthesis in the absence of complex organic templates. Using a combination of high-resolution microscopy and spectroscopy, we show that 2D MMW-type layers with an average thickness of 3.5 nm (ca. 1.5 unit cells) can be generated using the surfactant cetyltrimethylammonium (CTA), which operates as a dual OSDA and exfoliating agent to affect Al siting and to eliminate the need for postsynthesis exfoliation, respectively. We tested these 2D catalysts using a model reaction that assesses external (surface) Bronsted acid sites and observed a marked increase in the conversion relative to three-dimensional MWW (MCM-22) and 2D layers prepared from postsynthesis exfoliation (ITQ-2). Collectively, our findings identify a facile and effective route to directly synthesize 2D MWW-type materials, which may prove to be more broadly applicable to other layered zeolites.

Myosin II (MII) activity is required for elongating mammalian sensory axons to change speed and direction in response to Nerve Growth Factor (NGF) and laminin-1 (LN). NGF signaling induces faster outgrowth on LN through regulation of actomyosin restraint of microtubule advance into the growth cone periphery. It remains unclear whether growth cone turning on LN works through the same mechanism and, if it does, how the mechanism produces directed advance. Using a novel method for substrate patterning, we tested how directed advance occurs on LN by creating a gap immediately in front of a growth cone advancing on a narrow LN path. The growth cone stopped until an actin-rich protrusion extended over the gap, adhered to LN, and became stabilized. Stepwise advance over the gap was triggered by microtubule +tip entry up to the adhesion site of the protrusion and was independent of traction force pulling. We found that the probability of microtubule entry is regulated at the level of the individual protrusion and is sensitive to the rate of microtubule polymerization and the rate of rearward actin flow as controlled by adhesion-cytoskeletal coupling and MII. We conclude that growth cone navigation is an iterative process of variation and selection. Growth cones extend leading edge actin-rich protrusions that adhere transiently (variation). Microtubule entry up to an adhesion site stabilizes a protrusion (selection) leading to engorgement, consolidation, protrusive activity distal to the adhesion site, and stepwise growth cone advance. The orientation of the protrusion determines the direction of advance.

The local structures of rhodium complexes derived from the immobilization of Wilkinson’s complex, RhCl(PPh3)3, on SBA-15 silica functionalized with primary–amine, secondary–amine, or diphenylphosphine groups within the mesoporous channels were characterized by a series of techniques including XRD, HR-TEM, multinuclear (13C/29Si/31P) solid-state NMR, 2D 31P{1H} HETCOR NMR, XPS, and Rh K-edge EXAFS. Immobilization of RhCl(PPh3)3 through covalent bond formation with different functional groups grafted to the silica surface lead to variations in the local structure of the Rh center that has important implications for catalysis. The immobilized Rh complexes demonstrated high activity for the addition of alkynes with thiols (hydrothiolation) or sulfonic acids (hydrosulfonation) with excellent regio- and stereoselectivity under mild reaction conditions. This work demonstrates the elucidation of the local structure of the immobilized Rh complexes requires a complimentary multi-technique characterization approach that probes both the metal center itself and surrounding ligands.

Amine-based solid sorbents represent promising replacements for aqueous alkanolamines for CO2 capture because they reduce significantly the sorbent regeneration energy and avoid instrument corrosio...

We report the sequential, quantitative loading of transition-metal ions (Cr3+, Mn2+, Fe2+, Co2+, Ni2+, and Cu2+) onto the surface of rod-shaped anatase TiO2 nanocrystals in bimetallic combinations (6C2 = 15) to form M,M′-TiO2 nanocrystals. The materials were characterized with transmission electron microscopy (TEM), powder X-ray diffraction (XRD), elemental analysis, X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy. TEM and XRD data indicate that the sequential adsorption of metal ions occurs with the retention of the phase and morphology of the nanocrystal. Atomistic models of the M,M′-TiO2 nanocrystals were optimized with density functional theory calculations. Calculated UV–visible absorption spectra and partial charge density maps of the donor and acceptor states for the electronic transitions indicate the importance of metal-to-metal charge transfer (MMCT) processes.

Supported metal catalysts, which are composed of metal nanoparticles dispersed on metal oxides or other high-surface-area materials, are ubiquitous in industrially catalysed reactions. Identifying and characterizing the catalytic active sites on these materials still remains a substantial challenge, even though it is required to guide rational design of practical heterogeneous catalysts. Metal-support interactions have an enormous impact on the chemistry of the catalytic active site and can determine the optimum support for a reaction; however, few direct probes of these interactions are available. Here we show how benzyl alcohol oxidation Hammett studies can be used to characterize differences in the catalytic activity of Au nanoparticles hosted on various metal-oxide supports. We combine reactivity analysis with density functional theory calculations to demonstrate that the slope of experimental Hammett plots is affected by electron donation from the underlying oxide support to the Au particles.

We report the formation of high surface area hollow Mn3O4 nanoparticles that form as a result of the galvanic reaction of Cu2+ with MnO nanocrystals concomitant with a nanoscale Kirkendall effect. The MnO nanocrystals were prepared according to the ultralarge scale synthesis reported by Hyeon, which allowed the preparation of hollow Mn3O4 in multigram quantities. Ex-situ analyses with transmission electron microscopy and powder X-ray diffraction show the morphology and phase stability of the hollow particles correlate with DSC-TGA data and show collapse of the hollow particles at temperatures greater than 200 °C. Electrodes fabricated from hollow Mn3O4 exhibited excellent initial Li ion storage capability (initial discharge capacity = 1324 mAh/g) but poor cycling performance (97% loss of discharge capacity after 10th cycle), whereas Mn3O4-MWCNT electrodes exhibited good reversibility and discharge capacity of 760 mAh/g after 100 cycles.

Catalytic dehydration of lactic acid in the presence of water is a potentially green, synthetic approach for the production of acrylic acid, and development of a highly selective catalyst is a primary challenge, leading to a resurgence in catalyst exploration and discovery. However, because the complexity in the analytical assessment of the efficiency of catalysts stemming from the possible presence of dimers in lactic acid feedstocks has often been neglected in the literature, we demonstrate, without consideration of the dimer during catalyst evaluation, that they can have a substantial influence on the determination of conversion of lactic acid and selectivity to acrylic acid in aqueous solution. In one example of a modified zeolite catalyst, a true acrylic acid of selectivity of 64% was overestimated to be 80% if the dimers in the feed solution were neglected in the analytical analysis. A survey of the literature demonstrated very few researchers account for the possible presence of lactic acid dimers ...

In the liquid-phase catalytic processing of molecules using heterogeneous catalysts—an important strategy for obtaining renewable chemicals from biomass—many of the key reactions occur at solid–liquid interfaces. In particular, glucose isomerization occurs when glucose is adsorbed in the micropores of a zeolite catalyst. Since solvent molecules are coadsorbed, the catalytic activity depends strongly and often nonmonotonically on the solvent composition. For glucose isomerization catalyzed by NaX and NaY zeolites, there is an initial steep decline when water is mixed with a small amount of the organic cosolvent γ-valerolactone (GVL), followed by a recovery as the GVL content in the mixed solvent increases. Here we elucidate the origin of this complex solvent effect using operando solid-state NMR spectroscopy. The glucopyranose tautomers immobilized in the zeolite pores were observed and their transformations into fructose and mannose followed in real time. The microheterogeneity of the solvent system, mani...

Methodology for direct catalytic conversion of olefins into cyclic carbonates using peroxide and carbon dioxide under relatively mild conditions is demonstrated. The protocol utilizes packed bed flow reactors in series to couple rhenium catalyzed olefin epoxidation and aluminum catalyzed epoxide carboxylation in a single sequence.

X-ray absorption near-edge structure (XANES) is a common technique for elucidating oxidation state and first shell coordination geometry in transition metal complexes, among many other materials. However, the structural information obtained from XANES is often limited to the first coordination sphere. In this study, we show how XANES can be used to differentiate between C, Si, and Ge in the second coordination shell of Ti-O-(C, Si, Ge) molecular complexes based on differences in their Ti K-edge XANES spectra. Experimental spectra were compared with theoretical spectra calculated using density functional theory structural optimization and ab initio XANES calculations. The unique features for second shell C, Si, and Ge present in the Ti K pre-edge XANES are attributed to the interaction between the Ti center and the O-X (X = C, Si, or Ge) antibonding orbitals.

Previous attempts to characterize the γ-brass crystal structure of Ni–Zn (15.4–24% Ni) have failed to identify the location of the Ni and Zn atoms in the crystal lattice for more than 15.4% Ni content (Ni8Zn44) due to the similar X-ray diffraction cross sections of Ni and Zn. Ni8Zn44 is known to have a typical γ-brass crystal structure (space group 217, I43m, 52 atom unit cell with four distinct symmetry positions: inner tetrahedral, outer tetrahedral, octahedral, and cuboctahedral) where Ni atoms reside in outer tetrahedral sites completely isolated from each other and coordinated by 12 Zn atoms. We utilize neutron diffraction to identify the substitution positions of Zn by Ni when the Ni content is increased above 15.4% and up to 19.2% (Ni10Zn42). Upon increasing the Ni content above 15.4% (Ni9Zn43 and Ni10Zn42), Zn in the γ-brass octahedral positions are replaced by Ni leading to the formation of Ni–Ni–Ni trimers, which are absent in Ni8Zn44. Density functional theory (DFT) calculations confirm our ne...

Interest in liquid-phase reactions over heterogeneous catalysts is growing rapidly, partially because of the desire to find efficient methods for biomass conversion to renewable fuels and chemicals. The presence of a solvent can affect reactions at surfaces by competing with reactants and products for adsorption sites and solvating adsorbed species. Mass transport limitations can also have a pronounced effect on liquid-phase reaction rates. Because many heterogeneous catalysts were designed to be stable under gas-phase reaction conditions, their operation in liquid reaction media at moderately elevated temperatures can result in unexpected structural changes. In some cases, components derived from the evolving catalyst contribute significantly to the catalytic activity. Solvents, as well as byproducts from biomass feedstocks, can also act as homogeneous catalysts to alter the intrinsic reactivity of the heterogeneous catalyst. In this contribution, we discuss each of these phenomena and provide illustrati...

Chloride (Cl–) is often used together with polyvinylpyrrolidone (PVP) in the polyol synthesis of Ag nanocubes. In the literature, shape control is attributed predominantly to the preferential binding of PVP to Ag(100) facets compared to Ag(111) facets, whereas the role of Cl– has not been well studied. Several hypotheses have been proposed regarding the role of Cl–; however, there is still no consensus regarding the exact influence of Cl– in the shape-controlled synthesis of Ag nanocubes. To examine the influence of Cl–, we undertook a joint theoretical–experimental study. Experimentally, we examined the influence of Cl– concentration on the shape of Ag nanoparticles (NPs) at constant H+ concentration. In the presence of H+, in situ formed HNO3 etches the initially formed Ag seeds and slows down the overall reduction of Ag+, which promotes the formation of monodisperse Ag NPs. Ex situ experiments probed the evolution of Cl– during the growth of Ag nanocubes, which involves the initial formation of AgCl na...

Polyvinylpyrrolidone (PVP) is used in the synthesis of Ag nanoparticles (NPs) with controlled shape, most commonly producing cubes. The mechanism for shape control is unclear but believed by many to be caused by preferential binding of PVP to Ag(100) facets compared to Ag(111) facets and assumed by most to be the result of thermodynamic control, whereby facets with lower interfacial free energy predominate. To investigate this mechanism, we measured adsorption isotherms of PVP on different-shaped Ag NPs, to determine the thermodynamics of PVP adsorption to Ag(100) and Ag(111) facets. The equilibrium adsorption constant is independent of PVP molecular weight and depends only weakly on NP shape (and thus Ag facet). The equilibrium adsorption constant for PVP on Ag(111) (2.8 M–1) is about half that on Ag(100) (5 M–1). From a Wulff construction, this difference is not nearly enough to produce cubes via thermodynamic control. This result indicates the importance of kinetic control of the Ag nanoparticle shape ...

The activity and selectivity of activated-carbon-supported Ni, Pt, Ru, and Ni-Ru bimetallic catalysts was examined for hydrothermal denitrogenation of indole. The molar yield of pyrrole ring-opening compounds, without an added hydrogen source, are in the order: Ni

This paper focuses on the development of a rigorous model for isothermal CO2 adsorption columns which describes the spatiotemporal dynamics of CO2 concentrations in the bulk and solid bed by a set of partial and location-varying ordinary differential equations. By considering both dispersion and convection phenomena, the model provides the spatiotemporal behavior of the adsorption rate and circumvents the unphysical simplifying assumptions of linear driving force and uniform adsorption rates through the column length invoked in previous modeling efforts. The proposed model is then employed to compute physical quantities originating from material conservation laws such as the adsorption rate constant and CO2 adsorption capacity from a set of experimental data without using empirical parameter assumptions invoked in previous research. The spatiotemporal dynamics of CO2 adsorption in an aminosilica packed bed are successfully predicted by the proposed model. The adsorption rate constant and capacity of the b...

In catalytic applications of surface-modified mesoporous silica materials, distinguishing and quantifying different types of functional groups on the surface is crucial for enabling accurate evaluation of catalytic activity and possible cooperativity among mixed functional groups. We investigated sulfonic acid groups supported on SBA-15 mesoporous silica as a promising organic–inorganic hybrid solid acid catalyst and developed a robust technique for sulfur quantification and speciation after oxidation of grafted thiol groups to sulfonic acid. We combined SH-selective titration (Ellman's test), acid–base titration and ICP-OES analysis to quantitatively monitor S speciation at each step of the preparation of these catalysts. Ellman's test confirmed the successful grafting of SH groups on SBA-15, which is in good agreement with ICP-OES total S determination (∼0.8 mmol gcat−1). These SH groups were converted in a subsequent 30% H2O2 treatment to SO3H groups, while significant leaching of S during oxidation limited the yield of grafted SO3H (∼0.3 mmol gcat−1) in the final catalyst. The influence of grafting and oxidation conditions on S speciation was investigated, and the presence of partially oxidized S on the surface was quantified. Despite the loss of a fraction of grafted S, the prepared sulfonic acid-functionalized SBA-15 catalysts exhibited comparable catalytic activity per H+ with homogeneous sulfonic acid catalysts in esterification reactions. Re-grafting of SH groups after oxidation was shown to be effective in achieving the coexistence of SH and SO3H groups on the surface, and a catalytic study revealed no cooperativity between SH and SO3H for the esterification reaction.

Nerve growth factor (NGF) stimulation of embryonic mouse sensory axon outgrowth is MII dependent. NGF regulates two actomyosin processes: transverse actin bundling and peripheral retrograde (radial) network actin flow. These two processes oppose microtubule advance and differentially involve MIIA and MIIB, respectively., Nerve growth factor (NGF) promotes growth, differentiation, and survival of sensory neurons in the mammalian nervous system. Little is known about how NGF elicits faster axon outgrowth or how growth cones integrate and transform signal input to motor output. Using cultured mouse dorsal root ganglion neurons, we found that myosin II (MII) is required for NGF to stimulate faster axon outgrowth. From experiments inducing loss or gain of function of MII, specific MII isoforms, and vinculin-dependent adhesion-cytoskeletal coupling, we determined that NGF causes decreased vinculin-dependent actomyosin restraint of microtubule advance. Inhibition of MII blocked NGF stimulation, indicating the central role of restraint in directed outgrowth. The restraint consists of myosin IIB- and IIA-dependent processes: retrograde actin network flow and transverse actin bundling, respectively. The processes differentially contribute on laminin-1 and fibronectin due to selective actin tethering to adhesions. On laminin-1, NGF induced greater vinculin-dependent adhesion–cytoskeletal coupling, which slowed retrograde actin network flow (i.e., it regulated the molecular clutch). On fibronectin, NGF caused inactivation of myosin IIA, which negatively regulated actin bundling. On both substrates, the result was the same: NGF-induced weakening of MII-dependent restraint led to dynamic microtubules entering the actin-rich periphery more frequently, giving rise to faster elongation.

We report the sequential, quantitative loading of transition-metal ions (Cr

The structures of ZnO-supported Ni catalysts were explored with in situ X-ray absorption spectroscopy, temperature-programmed reduction, X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy, and electron energy loss spectroscopy. Calcination of nickel nitrate on a nanoparticulate ZnO support at 450 °C results in the formation of Zn-doped NiO (ca. Ni0.85Zn0.15O) nanoparticles with the rock salt crystal structure. Subsequent in situ reduction monitored by X-ray absorption near-edge structure (XANES) at the Ni K edge reveals a direct transformation of the Zn-doped NiO nanoparticles to a face-centered cubic alloy, Ni1–xZnx, at ∼400 °C with x increasing with increasing temperature. Both in situ XANES and ex situ HRTEM provide evidence for intermetallic β1-NiZn formation at ∼550 °C. In comparison to a Ni/SiO2 catalyst, Ni/ZnO necessitates a higher temperature for the reduction of NiII to Ni0, which highlights the strong interaction between Ni and...