Hydrogen is expected to play an important role as an energy carrier in a future, more sustainable society. However, its compact, efficient, and safe storage is an unresolved issue. One of the main ...options is solid‐state storage in hydrides. Unfortunately, no binary metal hydride satisfies all requirements regarding storage density and hydrogen release and uptake. Increasingly complex hydride systems are investigated, but high thermodynamic stabilities as well as slow kinetics and poor reversibility are important barriers for practical application. Nanostructuring by ball‐milling is an established method to reduce crystallite sizes and increase reaction rates. Since five years attention has also turned to alternative preparation techniques that enable particle sizes below 10 nanometers and are often used in conjunction with porous supports or scaffolds. In this Review we discuss the large impact of nanosizing and ‐confinement on the hydrogen sorption properties of metal hydrides. We illustrate possible preparation strategies, provide insight into the reasons for changes in kinetics, reversibility and thermodynamics, and highlight important progress in this field. All in all we provide the reader with a clear view of how nanosizing and ‐confinement can beneficially affect the hydrogen sorption properties of the most prominent materials that are currently considered for solid‐state hydrogen storage.
Light metal hydrides are an important option for compact, safe, and efficient on‐board hydrogen storage. However, slow kinetics, poor reversibility, and low equilibrium pressures hamper their practical application. We review the impact of nanosizing and ‐confinement; recent strategies with a large impact on the hydrogen sorption properties of relevant light metal hydrides.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid is an important transformation for the production of bio-based polymers. Carbon-supported gold catalysts hold great promise for ...this transformation. Here we demonstrate that the activity, selectivity, and stability of the carbon-supported gold nanoparticles in the oxidation of 5-hydroxymethylfurfural strongly depend on the surface properties of the carbon support. Gold nanoparticles supported on basic carbon materials with a low density of functional groups demonstrate higher activity in 5-hydroxymethylfurfural oxidation (TOFAu up to 1195 h–1), higher selectivity to 2,5-furandicarboxylic acid, and better stability in comparison to gold nanoparticles supported on carbon materials with acidic surface groups. Surface groups of basic carbon supports that are positively charged under the reaction conditions result in a higher adsorption and local concentration of hydroxyl ions, which act as cocatalysts for gold and enhance gold-catalyzed dehydrogenation. Negatively charged surface groups of acidic carbons repel hydroxyls and the intermediate monoacid anions, which leads to lower reaction rates and a high selectivity toward 2,5-hydroxymethylfurancarboxylic acid. Understanding the role of support surface charge and local hydroxyl anion concentration provides a basis for the rational design of the optimal carbon support surface chemistry for highly active, selective, and stable catalysts for the oxidation of 5-hydroxymethylfurfural and related reactions.
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IJS, KILJ, NUK, PNG, UL, UM
Combining quantum‐mechanical simulations and synthesis tools allows the design of highly efficient CuCo/MoOx catalysts for the selective conversion of synthesis gas (CO+H2) into ethanol and higher ...alcohols, which are of eminent interest for the production of platform chemicals from non‐petroleum feedstocks. Density functional theory calculations coupled to microkinetic models identify mixed Cu–Co alloy sites, at Co‐enriched surfaces, as ideal for the selective production of long‐chain alcohols. Accordingly, a versatile synthesis route is developed based on metal nanoparticle exsolution from a molybdate precursor compound whose crystalline structure isomorphically accommodates Cu2+ and Co2+ cations in a wide range of compositions. As revealed by energy‐dispersive X‐ray nanospectroscopy and temperature‐resolved X‐ray diffraction, superior mixing of Cu and Co species promotes formation of CuCo alloy nanocrystals after activation, leading to two orders of magnitude higher yield to high alcohols than a benchmark CuCoCr catalyst. Substantiating simulations, the yield to high alcohols is maximized in parallel to the CuCo alloy contribution, for Co‐rich surface compositions, for which Cu phase segregation is prevented.
Coupling DFT simulations, microkinetic modeling and synthesis tools allowed the development of supported CuCo bimetallic nanoparticles as highly efficient catalysts for the selective conversion of synthesis gas (CO+H2) into ethanol and longer‐chain alcohols. As predicted by theory, maximizing the contribution from mixed Cu–Co sites, while preventing Cu phase segregation, results in superior yields to high alcohols.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage/conversion and as catalysts for the sustainable production of fuels and chemicals. However, the ...tendency of nanoparticles to grow into larger crystallites is an impediment for stable performance. Exemplarily, loss of active surface area by metal particle growth is a major cause of deactivation for supported catalysts. In specific cases particle growth might be mitigated by tuning the properties of individual nanoparticles, such as size, composition and interaction with the support. 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/Al(2)O(3) 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.
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IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The proximity of nanoparticles may affect the performance, in particular the stability, of supported metal catalysts. Short interparticle distances often arise during catalyst preparation by ...formation of aggregates. The cause of aggregation of cobalt nanoparticles during the synthesis of highly loaded silica-supported catalysts was found to originate from the drying process after impregnation of the silica grains with an aqueous cobalt nitrate precursor. Maximal spacing of the Co3O4 nanoparticles was obtained by fluid-bed drying at 100 °C in a N2 flow. Below this temperature, redistribution of liquid occurred before and during precipitation of a solid phase, leading to aggregation of the cobalt particles. At higher temperatures, nucleation and growth of Co3O4 occurred during the drying process also giving rise to aggregation. Fischer–Tropsch catalysis performed under industrially relevant conditions for unpromoted and Pt-promoted cobalt catalysts revealed that the size of aggregates (13–80 nm) of Co particles (size ∼9 nm) had little effect on activity. Large aggregates exhibited higher selectivities to long chain alkanes, possibly related to higher olefin formation with subsequent readsorption and secondary chain growth. Most importantly, larger aggregates of Co particles gave rise to extensive migration of cobalt (up to 75%) to the external surface of the macroscopic catalyst grains (38–75 μm). Although particle size did not increase inside the silica support grains, migration of cobalt to the external surface partly led to particle growth, thus causing a loss of activity. This cobalt migration over macroscopic length scales was suppressed by maximizing the distance between nanoparticles over the support. Clearly, the nanoscale distribution of particles is an important design parameter of supported catalysts in particular and functional nanomaterials in general.
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IJS, KILJ, NUK, PNG, UL, UM
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 subsurface layers play a crucial role in the catalytic performance, and rationalize this finding using density functional theory calculations. Our results open up an alternative avenue for the structural design of bimetallic catalysts.
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Controlling the size and uniformity of metal clusters with atomic precision is essential for fine‐tuning their catalytic properties, however for clusters deposited on supports, such control is ...challenging. Here, by combining X‐ray absorption spectroscopy and density functional theory calculations, it is shown that supports play a crucial role in the evolution of monolayer‐protected clusters into catalysts. Based on the acidic nature of the support, cluster‐support interactions lead either to fragmentation of the cluster into isolated Au–ligand species or ligand‐free metallic Au0 clusters. On Lewis acidic supports that bind metals strongly, the latter transformation occurs while preserving the original size of the metal cluster, as demonstrated for various Aun sizes. These findings underline the role of the support in the design of supported catalysts and represent an important step toward the synthesis of atomically precise supported nanomaterials with tailored physico‐chemical properties.
Small and shiny: X‐ray absorption spectroscopy and density functional theory computations show that the acidity of the support defines the fate of gold–phospine clusters after deposition.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Working at the Y: Zeolite Y crystals with micropores (ca. 1 nm), small mesopores (ca. 3 nm), and large mesopores (ca. 30 nm) were obtained by base leaching of previously steamed and acid‐leached ...material. The zeolite Y crystals with trimodal porosity (see electron‐tomographic picture) displayed close to ideal hydrocracking selectivity and enhanced yields of kerosene and diesel.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Liquid hydrogen carriers are considered to be attractive hydrogen storage options because of their ease of integration into existing chemical transportation infrastructures when compared with liquid ...or compressed hydrogen. The development of such carriers forms part of the work of the International Energy Agency Task 32: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia-based and liquid organic hydrogen carriers, with a particular focus on the challenge of ensuring easily regenerable, high-density hydrogen storage.
•Ammonia and cyclic organic molecules can help overcome H2 infrastructure issues.•Ease of storage and distribution are key advantages of liquid H2 carriers.•Coupling NH3 production to renewables for H2 storage requires new catalysts/methods.•New approaches to low-temperature NH3 synthesis and decomposition using M-NH systems.•Kinetic and thermodynamic methods for tailoring H2 storage in cyclic organics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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