35 research outputs found
Fluence and dose measurements with activation and spallation detectors near internal targets at the CERN Proton Synchrotron
Dicyclohexylmethane as a liquid organic hydrogen carrier A model study on the dehydrogenation mechanism over palladium surfaces
We have studied the dehydrogenation of the liquid organic hydrogen carrier (LOHC) dicyclohexylmethane (DCHM) to diphenylmethane (DPM) and its side reactions on a Pd(111) single crystal surface. The adsorption and thermal evolution of both DPM and DCHM was measured in situ in ultrahigh vacuum (UHV) using synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy (HR-XPS). We found that after deposition at 170 K, the hydrogen-lean DPM undergoes C-H bond scission at the methylene bridge at 200 K and, starting at 360 K, complete dehydrogenation of the phenyl rings occurs. Above 600 K, atomic carbon incorporates into the Pd bulk. For the hydrogen-rich DCHM, the first stable dehydrogenation intermediate, a double Ï-allylic species, forms already at 190 K. Until 340 K, further dehydrogenation of the phenyl rings and of the methylene bridge occurs, yielding the same intermediate that is formed upon heating of DPM to this temperature, that is, DPM dehydrogenated at the methylene bridge. The onset for the complete dehydrogenation of this intermediate occurs at a much higher temperature than after adsorption of DPM. This behavior is mainly attributed to coadsorbed hydrogen from DCHM dehydrogenation. The results are discussed in comparison to our previous study of DPM and DCHM on Pt(111) revealing strong material dependencies
Radiation protection considerations in the design of the LHC, CERN's Large Hadron Collider
Growth and electronic structure of boron doped graphene
The doping of graphene to tune its electronic structure is essential for its
further use in carbon based electronics. Adapting strategies from classical
silicon based semiconductor technology, we use the incorporation of heteroatoms
in the 2D graphene network as a straightforward way to achieve this goal. Here,
we report on the synthesis of boron-doped graphene on Ni(111) in a chemical
vapor deposition process of triethylborane on the one hand and by segregation
of boron from the bulk on the other hand. The chemical environment of boron was
determined by x-ray photoelectron spectroscopy and angle resolved photoelectron
spectroscopy was used to analyze the impact on the band structure. Doping with
boron leads to a shift of the graphene bands to lower binding energies. The
shift depends on the doping concentration and for a doping level of 0.3 ML a
shift of up to 1.2 eV is observed. The experimental results are in agreement
with density-functional calculations. Furthermore, our calculations suggest
that doping with boron leads to graphene preferentially adsorbed in the top-fcc
geometry, since the boron atoms in the graphene lattice are then adsorbed at
substrate fcc-hollow sites. The smaller adsorption distance of boron compared
to carbon leads to a bending of the graphene sheet in the vicinity of the boron
atoms. By comparing calculations of doped and undoped graphene on Ni(111), as
well as the respective free-standing cases, we are able to distinguish between
the effects that doping and adsorption have on the band structure of graphene.
Both, doping and bonding to the surface, result in opposing shifts on the
graphene bands
Surface Reactions of Dicyclohexylmethane on Pt 111
We
investigated the surface reaction of the liquid organic hydrogen
carrier dicyclohexylmethane (DCHM) on Pt(111) in ultrahigh vacuum
by high-resolution X-ray photoelectron spectroscopy, temperature-programmed
desorption, near-edge X-ray absorption fine structure, and infrared
reflectionâabsorption spectroscopy. Additionally, the hydrogen-lean
molecule diphenylmethane and the relevant molecular fragments of DCHM,
methylcyclohexane, and toluene were studied to elucidate the reaction
steps of DCHM. We find dehydrogenation of DCHM in the range of 200â260
K, to form a double-sided Ï-allylic species coadsorbed with
hydrogen. Subsequently, âŒ30% of the molecules desorb, and for
âŒ70%, one of the Ï-allyls reacts to a phenyl group between
260 and 330 K, accompanied by associative hydrogen desorption. Above
360 K, the second Ï-allylic species is dehydrogenated to a phenyl
ring. This is accompanied by CâH bond scission at the methylene
group, which is an unwanted decomposition step in the hydrogen storage
cycle, as it alters the original hydrogen carrier DCHM. Above 450
K, we find further decomposition steps which we assign to CâH
abstraction at the phenyl rings