126 research outputs found
Functionalized carbophenes as high-capacity versatile gas adsorbents: An ab initio study
This study employs density functional theory (DFT) and density functional
tight-binding theory (DFTB) to determine the adsorption properties of carbon
dioxide (CO), methane (CH), and dihydrogen (H) in carbophenes
functionalized with carboxyl (COOH), amine (NH), nitro (NO), and
hydroxyl (OH) groups. We demonstrate that carbophenes are promising candidates
as adsorbents for these gasses. Carbophenes have larger CO and CH
adsorption energies than other next-generation solid-state capture materials.
Yet, the low predicted desorption temperatures mean they can be beneficial as
air scrubbers in confined spaces. Functionalized carbophenes have H
adsorption energies usually observed in metal-containing materials. Further,
the predicted desorption temperatures of H from carbophenes lie within the
DOE Technical Targets for Onboard Hydrogen Storage for Light-Duty Vehicles
(DOEHST) operating temperature range. The possibility of tailoring the degree
of functionalization in combination with selecting sufficiently open carbophene
structures that allow for multiple strong interactions without steric hindrance
(crowding) effects, added to the multiplicity of possible functional groups
alone or in combination, suggests that these very light materials can be ideal
adsorbates for many gases. Tailoring the design to specific adsorption or
separation needs would require extensive combinatorial investigations
Interaction of Hydrogen with Graphitic Surfaces, Clean and Doped with Metal Clusters
ProducciĂłn CientĂficaHydrogen is viewed as a possible alternative to the fossil fuels in transportation.
The technology of fuel-cell engines is fully developed, and the outstanding
remaining problem is the storage of hydrogen in the vehicle. Porous materials,
in which hydrogen is adsorbed on the pore walls, and in particular nanoporous
carbons, have been investigated as potential onboard containers. Furthermore,
metallic nanoparticles embedded in porous carbons catalyze the dissociation of
hydrogen in the anode of the fuel cells. For these reasons the interaction of
hydrogen with the surfaces of carbon materials is a topic of high technological
interest. Computational modeling and the density functional formalism (DFT)
are helping in the task of discovering the basic mechanisms of the interaction
of hydrogen with clean and doped carbon surfaces. Planar and curved graphene
provide good models for the walls of porous carbons. We first review work on
the interaction of molecular and atomic hydrogen with graphene and graphene nanoribbons, and next we address the effects due to the presence of metal clusters
on the surface because of the evidence of their role in enhancing hydrogen
storage.Ministerio de EconomĂa, Industria y Competitividad (Grant MAT2014-54378-R
Identification of active sites on supported metal catalysts with carbon nanotube hydrogen highways
Catalysts consisting of metal particles supported on reducible oxides exhibit promising
activity and selectivity for a variety of current and emerging industrial processes. Enhanced
catalytic activity can arise from direct contact between the support and the metal or from
metal-induced promoter effects on the oxide. Discovering the source of enhanced catalytic
activity and selectivity is challenging, with conflicting arguments often presented based on
indirect evidence. Here, we separate the metal from the support by a controlled distance
while maintaining the ability to promote defects via the use of carbon nanotube hydrogen
highways. As illustrative cases, we use this approach to show that the selective transformation
of furfural to methylfuran over Pd/TiO2 occurs at the Pd-TiO2 interface while anisole
conversion to phenol and cresol over Cu/TiO2 is facilitated by exposed Ti3+ cations on the
support. This approach can be used to clarify many conflicting arguments in the literatureWe acknowledge financial support from the National Science Foundation, Grant CAREER1653935. Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract DE-AC02-06CH11357. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. E.C.W. and J.T.M. were supported in part by Center for Innovative Transformation of Alkane Resources (CISTAR) by the National Science Foundation under Cooperative Agreement No. EEC-1647722.
Open access fees fees for this article provided whole or in part by OU Libraries Open Access Fund.Ye
Atomic Hydrogen Diffusion on Doped and Chemically Modified Graphene
To explore hydrogen mobility on graphene, density functional calculations are used to determine the magnitude of binding energy versus the diffusion barrier for graphene, considering the effects of hole and electron doping, B and N substitutional dopants, and oxygen heteroatoms. Although C-H binding energy and the barrier for chemical diffusion are not correlated, the binding energy of H in the lowest energy site on top of a C atom correlates with the binding energy of H over a bridge C-C bond, which is the transition state for chemical diffusion. Using this framework, we demonstrate that both B substitutionally doped graphene and hydoxylated graphene have the potential to simultaneously meet thermodynamic and kinetic constraints for reversible room-temperature hydrogenation. The constraints demonstrate that reversible room-temperature hydrogenation is possible only when H diffuses in a chemically bound state
Transition to oscillatory Marangoni convection in liquid bridges of intermediate prandtl number
Atomic Hydrogen Diffusion on Doped and Chemically Modified Graphene
To explore hydrogen
mobility on graphene, density functional calculations
are used to determine the magnitude of binding energy versus the diffusion
barrier for graphene, considering the effects of hole and electron
doping, B and N substitutional dopants, and oxygen heteroatoms. Although
C–H binding energy and the barrier for chemical diffusion are
not correlated, the binding energy of H in the lowest energy site
on top of a C atom correlates with the binding energy of H over a
“bridge” C–C bond, which is the transition state
for chemical diffusion. Using this framework, we demonstrate that
both B substitutionally doped graphene and hydoxylated graphene have
the potential to simultaneously meet thermodynamic and kinetic constraints
for reversible room-temperature hydrogenation. The constraints demonstrate
that reversible room-temperature hydrogenation is possible only when
H diffuses in a chemically bound state
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