The role of destabilization of palladium hydride in the hydrogen uptake of Pd-containing activated carbons

Hydrogen spillover effects in the Fischer–Tropsch reaction over carbon nanotube supported cobalt catalysts

Support (CNTs) surface defect-induced hydrogen spillover significantly impacted the catalytic activity (turnover frequency, TOF) and methane selectivity evolution in cobalt-based Fischer–Tropsch synthesis.

Hydrogen Solubility and Atomic Structure of Graphene Supported Pd Nanoclusters

We investigated the atomic structure of graphene supported Pd nanoclusters and their interaction with hydrogen up to atmospheric pressures at room temperature by surface X-ray diffraction and scanning tunneling microscopy. We find that Ir seeded Pd nanocluster superlattices with 1.2 nm cluster diameters can be grown on the graphene/Ir(111) moiré template with high structural perfection. The superlattice clusters are anchored through the rehybridized graphene to the Ir support, which superimposes a 2.0% inplane compression onto the clusters. During hydrogen exposure at 10 mbar pressure and room temperature, a significant part of the clusters gets unpinned from the superlattice. The clusters in registry undergo an out-of-plane expansion only, whereas the detached clusters expand in in- and out-of-plane directions. The formation of a hydrogen rich PdH_x α' phase was not observed. After exposure to 1 bar, the majority of the clusters are unpinned from superlattice sites, due to their surface interaction with hydrogen and possible spill over to the graphene support. Only minor sintering was observed, which is more pronounced for the unpinned clusters. The results give evidence that ultrasmall Pd clusters on graphene are a stable hydrogen storage system with reduced hydrogen storage hysteresis and maintain a large surface area for hydrogen chemisorption.

Biobased Functional Carbon Materials: Production, Characterization, and Applications-A Review

Even though research on porous carbon materials from biomass dates back to at least hundred years, it is still an extremely relevant topic. These materials can be found in applications that range from those that are widely known, such as water treatment, to others that are newer and indispensable for the transition towards environmentally friendly technologies, such as lithium- and sodium-ion batteries. This review summarizes some of the most relevant research that has been published concerning production technologies, insights on the chemical reaction mechanisms, characterization techniques, as well as some examples of the applications and the properties that the carbon materials must fulfil to be used in those applications.

Interfacial charge distributions in carbon-supported palladium catalysts

Controlling the charge transfer between a semiconducting catalyst carrier and the supported transition metal active phase represents an elite strategy for fine turning the electronic structure of the catalytic centers, hence their activity and selectivity. These phenomena have been theoretically and experimentally elucidated for oxide supports but remain poorly understood for carbons due to their complex nanoscale structure. Here, we combine advanced spectroscopy and microscopy on model Pd/C samples to decouple the electronic and surface chemistry effects on catalytic performance. Our investigations reveal trends between the charge distribution at the palladium-carbon interface and the metal's selectivity for hydrogenation of multifunctional chemicals. These electronic effects are strong enough to affect the performance of large (~5 nm) Pd particles. Our results also demonstrate how simple thermal treatments can be used to tune the interfacial charge distribution, hereby providing a strategy to rationally design carbon-supported catalysts.Control over charge transfer in carbon-supported metal nanoparticles is essential for designing new catalysts. Here, the authors show that thermal treatments effectively tune the interfacial charge distribution in carbon-supported palladium catalysts with consequential changes in hydrogenation performance.

Gas adsorption properties of graphene-based materials

Clean energy sources and global warming are among the major challenges of the 21st century. One of the possible actions toward finding alternative energy sources and reducing global warming are storage of H₂ and CH₄, and capture of CO₂ by using highly efficient and low-cost adsorbents. Graphene and graphene-based materials attracted a great attention around the world because of their potential for a variety applications ranging from electronics, gas sensing, energy storage and CO₂ capture. Large specific surface area of these materials up to ~3000m²/g and versatile modification make them excellent adsorbents for diverse applications. Here, graphene-based adsorbents are reviewed with special emphasis on their adsorption affinity toward CO₂, H₂ and CH₄. This review shows that graphene derivatives obtained mainly via "chemical exfoliation" of graphite and further modification with polymers and/or metal species can be very effective sorbents for CO₂ and other gases and can compete with the currently used carbonaceous or non-carbonaceous adsorbents. The high adsorption capacities of graphene-based materials are mainly determined by their unique nanostructures, high specific surface areas and tailorable surface properties, which make them suitable for storage or capture of various molecules relevant for environmental and energy-related applications.

Supercritical CO2 mediated incorporation of Pd onto templated carbons: a route to optimizing the Pd particle size and hydrogen uptake density

Palladium nanoparticles are deposited onto zeolite template carbon (ZTC) via supercritical CO2 (scCO2) mediated hydrogenation of a CO2-phillic transition metal precursor. The supercritical fluid (SCF) mediated metal incorporation approach enabled the decoration of ZTC with 0.2-2.0 wt % of well-dispersed Pd nanoparticles of size 2-5 nm. The resulting Pd-doped ZTCs exhibit enhanced hydrogen uptake and storage density. The ZTC (with surface area of 2046 m(2)/g) had a hydrogen storage capacity (at 77 K and 20 bar) of 4.9 wt %, while the Pd-ZTCs had uptake of 4.7-5.3 wt % despite a surface area in the range 1390-1858 m(2)/g. The Pd-ZTCs thus exhibit enhanced hydrogen storage density (14.3-18.3 μmol H2/m(2)), which is much higher than that of Pd-free ZTC (12.0 μmol H2/m(2)). The hydrogen isosteric heat of adsorption (Qst) was found to be higher for the Pd-doped carbons (6.7 kJ/mol) compared to the parent ZTC (5.3 kJ/mol). The deposition of small amounts of Pd (up to 2 wt %) along with well-dispersed Pd nanoparticles of size of 2-5 nm is essential for the enhancement of hydrogen uptake and illustrates the importance of optimizing the balance between metal loading/particle size and surface area to achieve the best metal/porous carbon composite for enhanced hydrogen uptake.

Hydrogen adsorption on Pd- and Ru-doped C60 fullerene at an ambient temperature

Palladium- and ruthenium-doped C(60) fullerene compounds were synthesized by incipient wetness impregnation of C(60) fullerene with the corresponding metal acetylacetonate precursors. Transmission electron microscopy (TEM) imaging of the metal-doped C(60) fullerene samples showed different dispersion morphologies of palladium and ruthenium particles on the C(60) matrix. Raman spectra revealed a drastic decrease in peak intensity followed by disappearance of several bands indicating the distortion of the C(60) cage structure. The amorphous nature of the C(60) fullerene compounds was confirmed by the X-ray diffraction study. Hydrogen adsorption amount of 0.85 wt % and 0. 69 wt % on Pd-C(60) and Ru-C(60), respectively, as compared to 0.3 wt % on the pure C(60) fullerene were measured at 300 bar and 298 K. The enhancement in the hydrogen uptakes can be attributed to several factors, including adsorption of molecular H(2) on the defect sites, metallic hydride formation, spillover of hydrogen, and bond formation with atomic hydrogen with different active sites of carbon of host fullerene. The hydrogen adsorption isotherms are of type III and can be correlated by the Freundlich (for Ru-C(60)) and modified Oswin equations (for Pd-C(60) and pristine C(60)).

Highly efficient hydrogen storage with PdAg nanotubes

Hydrogen storage is one of the vital and challenging issues for the commercialization of hydrogen-powered fuel cells. In this report, the synthesized PdAg nanotubes exhibit enhanced hydrogen-storage ability. The highest capacity for hydrogen absorption obtained on the PdAg nanotubes with 15% of Pd was over 200 times greater than the pure Pd nanoparticles.