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Converting CO

In this work, we discuss the role of manganese oxide as a promoter in Cu catalysts supported on graphitic carbon during hydrogenation of CO

Solid electrolytes based on LiBH4 receive much attention because of their high ionic conductivity, electrochemical robustness, and low interfacial resistance against Li metal. The highly conductive hexagonal modification of LiBH4 can be stabilized via the incorporation of LiI. If the resulting LiBH4-LiI is confined to the nanopores of an oxide, such as Al2O3, interface-engineered LiBH4-LiI/Al2O3 is obtained that revealed promising properties as a solid electrolyte. The underlying principles of Li+ conduction in such a nanocomposite are, however, far from being understood completely. Here, we used broadband conductivity spectroscopy and 1H, 6Li, 7Li, 11B, and 27Al nuclear magnetic resonance (NMR) to study structural and dynamic features of nanoconfined LiBH4-LiI/Al2O3. In particular, diffusion-induced 1H, 7Li, and 11B NMR spin-lattice relaxation measurements and 7Li-pulsed field gradient (PFG) NMR experiments were used to extract activation energies and diffusion coefficients. 27Al magic angle spinning NMR revealed surface interactions of LiBH4-LiI with pentacoordinated Al sites, and two-component 1H NMR line shapes clearly revealed heterogeneous dynamic processes. These results show that interfacial regions have a determining influence on overall ionic transport (0.1 mS cm-1 at 293 K). Importantly, electrical relaxation in the LiBH4-LiI regions turned out to be fully homogenous. This view is supported by 7Li NMR results, which can be interpreted with an overall (averaged) spin ensemble subjected to uniform dipolar magnetic and quadrupolar electric interactions. Finally, broadband conductivity spectroscopy gives strong evidence for 2D ionic transport in the LiBH4-LiI bulk regions which we observed over a dynamic range of 8 orders of magnitude. Macroscopic diffusion coefficients from PFG NMR agree with those estimated from measurements of ionic conductivity and nuclear spin relaxation. The resulting 3D ionic transport in nanoconfined LiBH4-LiI/Al2O3 is characterized by an activation energy of 0.43 eV.

Efficient storage of hydrogen is one of the biggest challenges towards a potential hydrogen economy. Hydrogen storage in liquid carriers is an attractive alternative to compression or liquefaction at low temperatures. Liquid carriers can be stored cost-effectively and transportation and distribution can be integrated into existing infrastructures. The development of efficient liquid carriers is part of the work of the International Energy Agency Task 40: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia and closed CO2-cycle methanol-based storage options as well for liquid organic hydrogen carriers.

Despite the great commercial relevance of zinc-promoted copper catalysts for methanol synthesis, the nature of the Cu-ZnO

ChemCatChem celebrates the achievements of female-led research groups in the field of catalysis. With this initiative, we seek to highlight the breadth and depth of the best research developed by women, and to increase its visibility in the wider catalysis community. Women of Catalysis offers a resource to aid in improving the representation of female scientific talent on invited speaker lists, conference and editorial boards, and as leaders in research consortia.

Supported metal catalysts are widely used in the chemical industry, commonly with added metal oxide promoters to enhance the catalytic performance. Here, we discuss manganese oxide as an efficient promoter for the Cu-based hydrogenation of ethyl acetate; a model hydrogenation reaction. A series of carbon-supported MnOx-Cu catalysts was prepared with 6 nm MnOx-Cu particles, while varying the Mn loading between 0 and 33 mol% Mn/(Cu+Mn), without changing the Cu loading or support structure. At temperatures of 180 to 210 °C and a pressure of 30 bar, the addition of 11 mol% Mn to Cu gave a 7-fold enhancement in activity, and better catalyst stability. Furthermore, the apparent activation energy decreased from ∼100 to 50 kJ mol-1. State-of-the-art characterization allowed to establish a correlation between catalyst structure and performance.

Supported copper nanoparticles are a promising alternative to supported noble metal catalysts, in particular for the selective gas phase hydrogenation of polyunsaturated molecules. In this article, the catalytic performance of copper nanoparticles (3 and 7 nm) supported on either silica gel or graphitic carbon is discussed in the selective hydrogenation of 1,3-butadiene in the presence of a 100-fold excess of propene. We demonstrate that the routinely used temperature ramp-up method is not suitable in this case to reliably measure catalyst activity, and we present an alternative measurement method. The catalysts exhibited selectivity to butenes as high as 99% at nearly complete 1,3-butadiene conversion (95%). Kinetic analysis showed that the high selectivity can be explained by considering H2 activation as the rate-limiting step and the occurrence of a strong adsorption of 1,3-butadiene with respect to mono-olefins on the Cu surface. The 7 nm Cu nanoparticles on SiO2 were found to be a very stable catalyst, with almost full retention of its initial activity over 60 h of time on stream at 140 °C. This remarkable long-term stability and high selectivity toward alkenes indicate that Cu nanoparticles are a promising alternative to replace precious-metal-based catalysts in selective hydrogenation.

Electrochemical conversion of CO2 is an attractive alternative to releasing it to the atmosphere. Catalysts derived from electroreduction of metal oxides are often more active than when starting with metallic phase catalyst. The origin of this effect is not yet clear. Using ZnO nanorods, we show that the initial structure of the oxide as well as the electrolyte medium have a profound impact on the structure of the catalytic active Zn phase, and thereby the selectivity of the catalysts. ZnO nanorods with various aspect ratios were electrochemically reduced in different electrolytes leading to metallic Zn with different structures; a sponge‐like structure, nanorods and nanoplates. The sponge‐like Zn produced syngas with H2 : CO=2, and some formate, the nanorods produced only syngas with H2 : CO=1, while Zn nanoplates exhibited 85 % selectivity towards CO. These results open a pathway to design new electrocatalysts with optimized properties by modifying the structure of the starting material and the electroreduction medium., The structure to evolve: Electron micrographs illustrates the evolution of Zn structure from the electroreduction of ZnO nanorods, and the effects on the product selectivity in the CO2 electroreduction. This work shows that the structure/morphology, and hence product selectivity of oxide‐derived Zn catalysts in CO2 electroreduction, can be tuned by changing the structure/aspect ratio of the staring ZnO nanorods and the reduction condition.

Extending the toolbox from mono- to bimetallic catalysts is key in realizing efficient chemical processes. Traditionally, the performance of bimetallic catalysts featuring one active and one selective metal is optimized by varying the metal composition, often resulting in a compromise between the catalytic properties of the two metals. Here we show that by designing the atomic distribution of bimetallic Au-Pd nanocatalysts, we obtain a synergistic catalytic performance in the industrially relevant selective hydrogenation of butadiene. Our single crystalline Au-core Pd-shell nanorods were up to 50 times more active than their alloyed and monometallic counterparts, while retaining high selectivity. We find a shell thickness dependent catalytic activity, indicating that not only the nature of the surface but also several sub-surface layers play a crucial role in the catalytic performance, and rationalize this finding using density-functional-theory calculations. Our results open up a novel avenue for the structural design of bimetallic catalysts.

Solid electrolytes based on LiBH4 receive much attention because of their high ionic conductivity, electrochemical robustness, and low interfacial resistance against Li metal. The highly conductive hexagonal modification of LiBH4 can be stabilized via the incorporation of LiI. If the resulting LiBH4-LiI is confined to the nanopores of an oxide, such as Al2O3, interface-engineered LiBH4-LiI/Al2O3 is obtained that revealed promising properties as a solid electrolyte. The underlying principles of Li+ conduction in such a nanocomposite are, however, far from being understood completely. Here, we used broadband conductivity spectroscopy and 1H, 6Li, 7Li, 11B, and 27Al nuclear magnetic resonance (NMR) to study structural and dynamic features of nanoconfined LiBH4-LiI/Al2O3. In particular, diffusion-induced 1H, 7Li, and 11B NMR spin–lattice relaxation measurements and 7Li-pulsed field gradient (PFG) NMR experiments were used to extract activation energies and diffusion coefficients. 27Al magic angle spinning NMR revealed surface interactions of LiBH4-LiI with pentacoordinated Al sites, and two-component 1H NMR line shapes clearly revealed heterogeneous dynamic processes. These results show that interfacial regions have a determining influence on overall ionic transport (0.1 mS cm–1 at 293 K). Importantly, electrical relaxation in the LiBH4-LiI regions turned out to be fully homogenous. This view is supported by 7Li NMR results, which can be interpreted with an overall (averaged) spin ensemble subjected to uniform dipolar magnetic and quadrupolar electric interactions. Finally, broadband conductivity spectroscopy gives strong evidence for 2D ionic transport in the LiBH4-LiI bulk regions which we observed over a dynamic range of 8 orders of magnitude. Macroscopic diffusion coefficients from PFG NMR agree with those estimated from measurements of ionic conductivity and nuclear spin relaxation. The resulting 3D ionic transport in nanoconfined LiBH4-LiI/Al2O3 is characterized by an activation energy of 0.43 eV.

Efficient and more sustainable production of transportation fuels is key to fulfill the ever-increasing global demand. In order to achieve this, progress in the development of highly active and selective catalysts is fundamental. The combination of bimetallic nanoparticles and reactive support materials offers unique and complex interactions that can be exploited for improved catalyst performance. Here, we report on cobalt–nickel nanoparticles on reducible metal oxides as support material for enhanced performance in the Fischer–Tropsch synthesis. For this, different cobalt to nickel ratios (Ni/(Ni + Co): 0.0, 0.25, 0.50, 0.75, or 1.0 atom/atom) supported on reducible (TiO2 and Nb2O5) or nonreducible (α-Al2O3) oxides were studied. At 1 bar, Co–Ni nanoparticles supported on TiO2 and Nb2O5 showed stable catalytic performance, high activities and remarkably high selectivities for long-chain hydrocarbons (C5+, ∼80 wt %). In contrast, catalysts supported on α-Al2O3 independently of the metal composition showed lower activities, high methane production, and considerable deactivation throughout the experiment. At 20 bar, the combination of cobalt and nickel supported on reducible oxides allowed for 25–50% cobalt substitution by nickel with increased Fischer–Tropsch activity and without sacrificing much C5+ selectivity. STEM-EDX and IR of adsorbed CO pointed to a cobalt enrichment of the nanoparticle’s surface and a weaker adsorption of CO in Co–Ni supported on TiO2 and Nb2O5 and not on α-Al2O3, modifying the rate-determining step and the catalytic performance. Overall, we show the strong effect and potential of reducible metal oxides as support materials for bimetallic nanoparticles for enhanced catalytic performance.

Extending the toolbox from mono- to bimetallic catalysts is key in realizing efficient chemical processes

Lithium borohydride is a promising lithium ion conductor for all-solid-state batteries. However, the compound only exhibits high ionic conductivity at elevated temperatures, typically above 110 °C. It was shown that the addition of oxides such as silica or alumina increases the room temperature ionic conductivity by 3 orders of magnitude. The origin of this remarkable effect is not yet well understood. Here, we investigate the influence of oxide surface groups on the ionic conductivity of LiBH

The development of efficient catalysts for hydrogen generation via ammonia decomposition is crucial for the use of ammonia as an energy carrier. Here, we report the effect of pore confinement of NaNH2 and KNH2 on ammonia decomposition catalysis. For the first time, Ni- or Ru-doped NaNH2 and KNH2 were confined in carbon nanopores using a combination method of solution impregnation and melt infiltration. Structure characterization indicates the nanoscale intimacy between transition metals and alkali metal amides inside the pores of the carbon support. As a result, 8 wt % Ni-doped NaNH2 and KNH2 nanocomposites give NH3 conversions of 79 and 60%, respectively at 425 °C, close to the performance of a 5 wt % Ru/C reference catalyst. 0.8 wt % Ru-doped nanocomposites exhibit even better catalytic performance, with about 95% NH3 conversion at a moderate temperature of 375 °C. The hydrogen production rates of these Ni- and Ru-doped nanocomposites in a pure NH3 flow are about 3–4 times higher than for the recently reported novel catalysts such as Ni–Li2NH and Ru–Li2NH/MgO. Interestingly, the apparent activation energies of the Ru- or Ni-based catalysts decrease 20–30 kJ mol–1 by co-confinement with alkali metal amides. The strategy of nanoconfinement of alkali metal amides in porous hosts may open a new avenue for effectively generating H2 from NH3 at low temperatures.

Solid-state electrolytes are crucial for the realization of safe and high capacity all-solid-state batteries. Lithium-containing complex hydrides represent a promising class of solid-state electrolytes, but they exhibit low ionic conductivities at room temperature. Ion substitution and nanoconfinement are the main strategies to overcome this challenge. Here, we report on the synthesis of nanoconfined anion-substituted complex hydrides in which the two strategies are effectively combined to achieve a profound increase in the ionic conductivities at ambient temperature. We show that the nanoconfinement of anion substituted LiBH4 (LiBH4–LiI and LiBH4–LiNH2) leads to an enhancement of the room temperature conductivity by a factor of 4 to 10 compared to nanoconfined LiBH4 and nonconfined LiBH4–LiI and LiBH4-LiNH2, concomitant with a lowered activation energy of 0.44 eV for Li-ion transport. Our work demonstrates that a combination of partial ion substitution and nanoconfinement is an effective strategy to boost the ionic conductivity of complex hydrides. The strategy could be applicable to other classes of solid-state electrolytes.

The electrocatalytic reduction of CO2 (CO2RR) and H+ (or H2O) into chemicals and fuels is attracting attention as a way to address current energy and environmental issues. One of the main focus in this field is the development and understanding of electrocatalysts that can promote the electrochemical CO2 reduction efficiently, and with high selectivity for the desired product. Copper electrodes are extensively studied and stand out because of their unique ability to produce a range of different products including hydrocarbons and oxygenates, which is ascribed to their intermediate binding strength for the CO intermediate. The use of oxide-derived Cu electrodes has arisen, because it promotes CO and COOH formation at low overpotentials, even though the electrodes are operating at potentials where the CuO should be reduced to metallic copper. Inspired by this, some recent studies have also shown that the use of sulfur-containing Cu or sulfide-derived Cu increases the selectivity towards formates, ethanol, propanol, or ethylene at intermediate overpotentials. The origin of these effects is still under debate, but it is often attributed to a change in the binding energy of the intermediates such as *OCHO, *COOH, and CO due to the formation of specific Cu surface structures or the presence of sub-surface sulfur or oxygen in the Cu or mixed phases. In this work, we investigated the phase stability and catalytic performance of carbon-supported sulfide (CuS and Cu2S) derived Cu nanoparticles in the electrochemical reduction of CO2 in aqueous media. The CuS@C and Cu2S@C nanoparticles were prepared via a novel, liquid phase sulfidation method, in which carbon-supported CuO (CuO@C) nanoparticles were converted to either CuS@C (25±13 nm) or Cu2S@C (17±1 nm) as shown in Figure 1a. The stability of the supported nanoparticles was investigated using cyclic voltammetry, where reduction peaks were observed in the first cathodic scans of both CuS@C and Cu2S@C (figure 1c). The reduction was monitored operando under CO2 reduction conditions using in-situ X-ray absorption spectroscopy (XAS). The in-situ XAS spectra showed that at a potential of -0.9V vs. the reversible hydrogen electrode (RHE), both CuS@C and Cu2S@C are reduced to metallic Cu@C. Finally, the products formed by the CuS@C and Cu2S@C-derived catalysts were compared to those of CuO@C-derived catalyst. At current densities of -1.5mA/cm2, the CuS@C- and Cu2S@C-derived catalysts show increased production of formate (figure 1d), while CO production is suppressed, in comparison to the CuO@C catalyst. Cu-sulfide derived catalyst showed differences in formate production, indicating the initial Cu-sulfide phase influences the product selectivity. Figure 1

In Table 2 of this Full Paper, the units for the turnover frequencies (TOF) are given as 10-13 s-1. The correct units for the TOF are 10-3 s-1. The authors and editorial office apologize for the oversight.

Supported gold nanoparticles are highly selective catalysts for a range of both liquid-phase and gas-phase hydrogenation reactions. However, little is known about their stability during gas-phase catalysis and the influence of the support thereon. We report on the activity, selectivity, and stability of 2–4 nm Au nanoparticulate catalysts, supported on either TiO2 or SiO2, for the hydrogenation of 0.3% butadiene in the presence of 30% propene. Direct comparison of the stability of the Au catalysts was possible as they were prepared via the same method but on different supports. At full conversion of butadiene, only 0.1% of the propene was converted for both supported catalysts, demonstrating their high selectivity. The TiO2-supported catalysts showed a steady loss of activity, which was recovered by heating in air. We demonstrated that the deactivation was not caused by significant metal particle growth or strong metal–support interaction, but rather, it is related to the deposition of carbonaceous species under reaction conditions. In contrast, all the SiO2-supported catalysts were highly stable, with very limited formation of carbonaceous deposits. It shows that SiO2-supported catalysts, despite their 2–3 times lower initial activities, clearly outperform TiO2-supported catalysts within a day of run time.

Energy Frontier Research Centers have been developed by the Department of Energy to accelerate research synergism among experimental and theoretical scientists in catalysis. The overall goal is to advance tools of synthesis, characterization, and computation of solid catalysts to design and predict catalytic properties at the atomic level. The Center for Atomic-Level Catalyst Design (CALC-D) has the goal of significantly advancing: (a) the tools of materials synthesis, allowing catalysts identified by computation to be prepared with atomic-level precision, (b) characterization methods such as advanced spectroscopy to understand surface structures of the working catalyst unambiguously, and (c) the ability of computational catalysis to accurately model reactions at working conditions.

The increasing demand for high capacity yet safe storage of renewable energy calls for the development of all-solid-state batteries. A major hurdle in this development is the identification of new suitable types of solid-state electrolytes. Nanoconfined lithium borohydride is a solid-state electrolyte candidate due to its high lithium-ion mobility at ambient temperatures. The origin of the high lithium-ion mobility is not fully understood, however. We studied nanocomposites of lithium borohydride and nanoporous silica Santa Barbara Amorphous-15 (SBA-15) with different pore sizes, using 1H, 6,7Li, and 11B solid-state NMR at various temperatures, to get in-depth insights into the phase behavior and ion dynamics of lithium borohydride in the silica pores. The results allow us to formulate a detailed dynamic model for lithium borohydride confined in SBA-15; bulklike LiBH4 is separated from the pore walls by an amorphous, highly dynamic LiBH4 fraction displaying both Li+ and BH4 - diffusion even at ambient temperatures. As shown by 11B temperature-jump exchange NMR, this dynamic fraction increases as a function of temperature. Li+ exchange between the bulklike and "dynamic" LiBH4 fraction is slow at ambient temperatures, but at elevated temperatures (≥90 °C), above the phase transition of the bulklike fraction, lithium ions rapidly diffuse through both LiBH4 fractions and exchange between these confined fractions at rates approaching the megahertz time scale.

The rapidly expanding toolbox for design and preparation is a major driving force for the advances in nanomaterials science and technology. Melt infiltration originates from the field of ceramic nanomaterials and is based on the infiltration of porous matrices with the melt of an active phase or precursor. In recent years, it has become a technique for the preparation of advanced materials: nanocomposites, pore-confined nanoparticles, ordered mesoporous and nanostructured materials. Although certain restrictions apply, mostly related to the melting behavior of the infiltrate and its interaction with the matrix, this review illustrates that it is applicable to a wide range of materials, including metals, polymers, ceramics, and metal hydrides and oxides. Melt infiltration provides an alternative to classical gas-phase and solution-based preparation methods, facilitating in several cases extended control over the nanostructure of the materials. This review starts with a concise discussion on the physical and chemical principles for melt infiltration, and the practical aspects. In the second part of this contribution, specific examples are discussed of nanostructured functional materials with applications in energy storage and conversion, catalysis, and as optical and structural materials and emerging materials with interesting new physical and chemical properties. Melt infiltration is a useful preparation route for material scientists from different fields, and we hope this review may inspire the search and discovery of novel nanostructured materials.

Nano-sizing and scaffolding have emerged in the past decade as important strategies to control the kinetics, reversibility, and equilibrium pressure for hydrogen storage in light metal hydride systems. Reducing the size of metal hydrides to the nanometer range allows fast kinetics for both hydrogen release and subsequent uptake. Reversibility of the hydrogen release is impressively facilitated by nanoconfining the materials in a carbon or metal–organic framework scaffold, in particular for reactions involving multiple solid phases, such as the decomposition of LiBH4, NaBH4, and NaAlH4. More complex is the impact of nanoconfinement on phase equilibria. It is clear that equilibrium pressures, and even decomposition pathways, are changed. However, further experimental and computational studies are essential to understand the exact origins of these effects and to unravel the role of particle size, physical confinement, and interfaces. Nevertheless, it has become clear that nanoconfinement is a strong tool to change physicochemical properties of metal hydrides, which might not only be of relevance for hydrogen storage, but also for other applications such as rechargeable batteries.

Nature materials 12(1), 34 - 39 (2013). doi:10.1038/nmat3471, Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage/conversion1 and as catalysts for the sustainable production of fuels and chemicals2, 3, 4. However, the tendency of nanoparticles to grow into larger crystallites is an impediment for stable performance5, 6. Exemplarily, loss of active surface area by metal particle growth is a major cause of deactivation for supported catalysts7. In specific cases particle growth might be mitigated by tuning the properties of individual nanoparticles, such as size8, composition9 and interaction with the support10. Here we present an alternative strategy based on control over collective properties, revealing the pronounced impact of the three-dimensional nanospatial distribution of metal particles on catalyst stability. We employ silica-supported copper nanoparticles as catalysts for methanol synthesis as a showcase. Achieving near-maximum interparticle spacings, as accessed quantitatively by electron tomography, slows down deactivation up to an order of magnitude compared with a catalyst with a non-uniform nanoparticle distribution, or a reference Cu/ZnO/Al2O3 catalyst. Our approach paves the way towards the rational design of practically relevant catalysts and other nanomaterials with enhanced stability and functionality, for applications such as sensors, gas storage, batteries and solar fuel production., Published by Nature Publishing Group, Basingstoke

The research on complex hydrides for hydrogen storage was initiated by the discovery of Ti as a hydrogen sorption catalyst in NaAlH4 by Boris Bogdanovic in 1996. A large number of new complex hydride materials in various forms and combinations have been synthesized and characterized, and the knowledge regarding the properties of complex hydrides and the synthesis methods has grown enormously since then. A significant portion of the research groups active in the field of complex hydrides is collaborators in the International Energy Agreement Task 32. This paper reports about the important issues in the field of complex hydride research, i.e. the synthesis of borohydrides, the thermodynamics of complex hydrides, the effects of size and confinement, the hydrogen sorption mechanism and the complex hydride composites as well as the properties of liquid complex hydrides. This paper is the result of the collaboration of several groups and is an excellent summary of the recent achievements.

Alkaline treatment (desilication) is an effective treatment to increase mesoporosity. However, the concomitant decrease in Si/Al ratio affects the strengths of the acidic sites and hence catalytic activity and selectivity. Therefore instead we subjected template containing zeolites to 1 M NaOH to induce additional porosity. All zeolites tested (ZSM-5, ZSM-12 and Beta) consisted of small crystallites (30–200 nm) that were agglomerated into larger particles between 1 and 5 μm. Mesopore formation occurred by slowly removing outer layers of individual crystallites, thereby preserving the Si/Al ratio as well as the crystallinity. Inter-crystalline mesopores were formed for all zeolites, but the treatment was most effective for zeolites with small crystallites. The external surface area of ZSM-5 was increased from 90 to 149 m2 g−1 and for zeolite Beta from 70 to 158 m2 g−1. The catalytic performance was tested at 413 K for 3 h for etherification of 1,2-propylene glycol with 1-octene to form octyl-ether. For ZSM-5, conversion increased from 1.2% to 5.6% upon alkaline treatment in the presence of a template, while only to 5% for the template-free treated sample with a significantly higher external surface area (205 m2 g−1). The parent zeolite Beta was significantly more active (30% conversion, 88% selectivity), which can be ascribed to its larger pore size. Nevertheless also in this case alkaline treatment in the presence of the template significantly increased the activity to 40% conversion with similar selectivity. As only the mesoporosity was changed upon alkaline treatment it suggests that the etherification of 1,2-propylene glycol with 1-octene is affected by intra-crystalline diffusion. Our work illustrates the possibilities to use alkaline treatment of templated zeolites to decouple accessibility changes from acidity, and to gain further insight in zeolite catalysis.

Control over the size and size distribution of supported nanoparticles is key to their efficient use in catalysis. In the preparation of nanoparticles by impregnation using nitrate precursors, the support pore diameter can be used to influence the average crystallite size. However, the particle size distributions obtained via this method are generally broad and the dispersions relatively low. Higher dispersions and narrow particle size distributions are obtained via thermal decomposition of the metal nitrate precursor in 1% (v/v) NO in Ar instead of air. Here we will show that by combining the confinement effect of ordered mesoporous silica with a decomposition step of metal nitrates in NO, silica supported nickel and cobalt oxides with a tunable particle size (2–4 nm) can be obtained at high loadings (10–20 wt%).

The catalytic performance and optical properties of bimetallic nanoparticles critically depend on the atomic distribution of the two metals in the nanoparticles. However, at elevated temperatures, during light-induced heating, or during catalysis, atomic redistribution can occur. Measuring such metal redistribution in situ is challenging, and a single experimental technique does not suffice. Furthermore, the availability of a well-defined nanoparticle system has been an obstacle for a systematic investigation of the key factors governing the atomic redistribution. In this study, we follow metal redistribution in precisely tunable, single-crystalline Au-core, Ag-shell nanorods in situ, both at a single particle and an ensemble-averaged level, by combining in situ transmission electron spectroscopy with in situ extended X-ray absorption fine structure validated by ex situ measurements. We show that the kinetics of atomic redistribution in Au-Ag nanoparticles depend on the metal composition and particle volume, such that a higher Ag content or a larger particle size led to significantly slower metal redistribution. We developed a simple theoretical model based on Fick's first law that can correctly predict the composition- and size-dependent alloying behavior in Au-Ag nanoparticles, as observed experimentally.

Large mordenite crystals hold interest for fundamental research on separation and catalysis as well as emerging applications such as functional devices. A number of methods are now available to obtain large mordenite crystals. However, it still remains a challenge to synthesize large and uniform crystals with a desired aspect ratio. Moreover, a detailed description of a reproducible synthesis method is still lacking. We report here large and uniform mordenite crystals (27 × 36 × 30 μm3) with an accessible micropore volume of 0.17 cm3/g that can be reproducibly synthesized. The synthesis procedure is described in detail. The effects of synthesis parameters on mordenite morphology (size and aspect ratio of the crystals), such as silicon precursors, H2O content, Na2O/SiO2/Al2O3 ratios, alcohol additives, have been systematically studied. Large mordenite crystals (up to 85 μm) with prismatic shape were formed from a dense synthesis gel with high SiO2/Al2O3 and Na2O/SiO2 ratios, or by adding alcohol additives. Moreover, the aspect ratio of the large crystals was controlled by finely altering the above synthesis parameters. In the presence of an excess amount of alcohol, hollow and core–shell mordenite crystals were formed.

Aqueous impregnation of mesoporous silica as a first step in catalyst preparation was studied to investigate the distribution of the metal-precursor solution over the support. The degree of pore-filling after impregnation was determined using the freezing point depression of confined liquids. A separate bulk melting transition observed with differential scanning calorimetry in combination with TGA and N2-physisorption allowed rigorous quantification of the extent of pore-filling of the support. The micro- and mesoporous volumes of different mesoporous silica were filled up to 90−100% with water. With KCl solution, at maximum 75−85% of the pores were filled. However, the total pore-filling reached 85−90% when the estimated volume of physisorbed water was included. As a case study for catalyst preparation, silica supports were also impregnated with an aqueous Ni(NO3)2 solution. Generally, the solution occupied up to 80−90% of the pore volume, similar to the pore-filling with KCl. This study shows that order...

Electron tomography and image analysis are combined to characterize ordered mesoporous silica SBA-15. The morphology of the mesopores with average diameter 6 nm is analyzed in terms of cylinders having variable radii and centers that are statistically centered on the points of a distorted hexagonal lattice. The variations in the mesopore centers and radii add up and result in pore wall corrugation with amplitude of 1.6 nm. The correlation length of the corrugation along the pore axis was found to be 4-5 nm. The amplitude of the corrugation compared well with the 1.9 nm thick microporous corona obtained from X-ray diffraction (XRD). In general, the present approach provides a detailed microscopic 3D model of nanostructured materials that complements macroscopic measurements such as physisorption and XRD.

An explanation is put forward for the beneficial effect of thermal decomposition of supported Ni3(NO3)2(OH)4 in NO/He flow (0.1–1 vol%) that enables preparation of well-dispersed (3–5 nm particles) 24 wt% Ni-catalysts via impregnation and drying using aqueous [Ni(OH2)6](NO3)2 precursor solution. Moreover, combining electron tomography, XRD and N2-physisorption with SBA-15 support yielded a clear picture of the impact of air, He and NO/He gas atmospheres on NiO shape and distribution. TGA/MS indicated that NO2, N2O, H2O products evolved more gradually in NO/He. In situ XRD and DSC revealed that NO lowers the nitrate decomposition rate and appears less endothermic than in air supposedly due to exothermic scavenging of oxygen by NO, which is supported by MS results. The Ni/SiO2 catalyst prepared via the NO-method displayed a higher activity in the hydrogenation of soybean oil as the required hydrogenation time decreased by 30% compared to the traditionally air calcined catalyst.

In this contribution, we investigated the preparation of Ni/SiO2 catalysts with aqueous [Ni(OH2)6](NO3)2 solutions via the impregnation and drying method using ordered mesoporous silica SBA-15 (mesopore diameter of 9 nm) as model support to study each step in the preparation: impregnation, drying, calcination, and reduction. After impregnation, not all the mesopores of SBA-15 appeared filled with precursor solution. Consecutive drying led to formation of 9 nm Ni3(NO3)2(OH)4 crystallites exclusively within the mesopores. During air calcination, severe sintering and redistribution took place, resulting in a low NiO dispersion, including large NiO crystals outside of the mesopores and rodlike NiO particles inside the mesopores. The degree of sintering depended on the concentration of Ni3(NO3)2(OH)4 decomposition products (NO2, N2O, O2 and H2O), and in particular NO2 and O2 were found to promote sintering and redistribution. Therefore, maintaining low concentrations of the latter components during the thermal...

The nine-site benzene model of Zhao et al. (J. Phys. Chem. B 2005, 109, 5368−5374) has been used to systematically study the adsorption of benzene, propene, and benzene−propene mixtures in zeolites mordenite, Y, β, silicalite, and MCM22. Interaction parameters for the benzene−zeolite interactions have been fitted to available adsorption experiments from literature. As an independent check of our force field, we have performed additional adsorption experiments using the TEOM technique and excellent agreement between simulations and TEOM experiments was found. High adsorption selectivities for benzene in benzene−propene mixtures were found in all zeolites, except for silicalite.

The properties of many functional materials depend critically on the spatial distribution of an active phase within a support. In the case of solid catalysts, controlling the spatial distribution of metal (oxide) nanoparticles at the mesoscopic scale offers new strategies to tune their performance and enhance their lifetimes. However, such advanced control requires suitable characterization methods, which are currently scarce. Here, we show how the background in small-angle Xray scattering patterns can be analyzed to quantitatively access the mesoscale distribution of nanoparticles within supports displaying hierarchical porosity. This is illustrated for copper catalysts supported on meso-and microporous silica displaying distinctly different metal distributions. Results derived from X-ray scattering are in excellent agreement with electron tomography. Our strategy opens unprecedented prospects for understanding the properties and to guide the synthesis of a wide array of functional nanomaterials.

Nano-sizing and scaffolding have emerged in the past decade as important strategies to control the kinetics, reversibility, and equilibrium pressure for hydrogen storage in light metal hydride systems. Reducing the size of metal hydrides to the nanometer range allows fast kinetics for both hydrogen release and subsequent uptake. Reversibility of the hydrogen release is impressively facilitated by nanoconfining the materials in a carbon or metal–organic framework scaffold, in particular for reactions involving multiple solid phases, such as the decomposition of LiBH4, NaBH4, and NaAlH4. More complex is the impact of nanoconfinement on phase equilibria. It is clear that equilibrium pressures, and even decomposition pathways, are changed. However, further experimental and computational studies are essential to understand the exact origins of these effects and to unravel the role of particle size, physical confinement, and interfaces. Nevertheless, it has become clear that nanoconfinement is a strong tool to change physicochemical properties of metal hydrides, which might not only be of relevance for hydrogen storage, but also for other applications such as rechargeable batteries.

The rapidly expanding toolbox for design and preparation is a major driving force for the advances in nanomaterials science and technology. Melt infiltration originates from the field of ceramic nanomaterials and is based on the infiltration of porous matrices with the melt of an active phase or precursor. In recent years, it has become a technique for the preparation of advanced materials: nanocomposites, pore-confined nanoparticles, ordered mesoporous and nanostructured materials. Although certain restrictions apply, mostly related to the melting behavior of the infiltrate and its interaction with the matrix, this review illustrates that it is applicable to a wide range of materials, including metals, polymers, ceramics, and metal hydrides and oxides. Melt infiltration provides an alternative to classical gas-phase and solution-based preparation methods, facilitating in several cases extended control over the nanostructure of the materials. This review starts with a concise discussion on the physical and chemical principles for melt infiltration, and the practical aspects. In the second part of this contribution, specific examples are discussed of nanostructured functional materials with applications in energy storage and conversion, catalysis, and as optical and structural materials and emerging materials with interesting new physical and chemical properties. Melt infiltration is a useful preparation route for material scientists from different fields, and we hope this review may inspire the search and discovery of novel nanostructured materials.