Properties of methane adsorbed in confined geometries are interesting from both fundamental and practical points of view. At ambient temperatures adsorption at the supercritical conditions is usually studied, as it is interesting from the point of view of methane storage. At the same time, the analysis of low temperature adsorption properties is essential for understanding the mechanism of adsorption, as a function of temperature and the pore size. In this work we study phase diagram of methane confined in carbon slit pores of the width between 1nm and 4nm. We analyze the mechanism of the layering transition(s) and capillary condensation at subcritical conditions, for temperatures between 80 K and 180 K, then we study the pore s storage capacity, up to the room temperature. The mechanism of the layers formation is strongly temperature dependent, and changes from a sharp adsorption at low temperature to more continuous one at higher temperatures. The size of pore defines the number of layers adsorbed: 1 nm pore allows adsorbing 2 layers of methane molecules. Capillary condensation is observed in 4 nm pores.

Controlled doping of active carbon materials (viz., graphenes, carbonnanotubes etc.) may lead to the enhancement of their desired properties. The leaststudied case of C/Be substitution offers an attractive possibility in this respect. Theinteractions of Be2 with Be or C atoms are dominated by the large repulsive Pauliexchange contributions, which in turn offsets the attractive interactions leading torelatively small binding energies. The Be2 dimer, e.g., after being doped inside a planarcarbon network, undergoes orbital adjustments due to charge transfer and unusualintermolecular interactions and is oriented perpendicular to the plane of the carbonnetwork with the Be−Be bond center located inside the plane. The present theoreticalinvestigation on the nature of bonding in C/Be2 exchange complexes, using state of theart quantum chemical techniques, reveals a sp2 carbon-like bonding scheme in Be2 arising due to the molecular hybridization of σand two π orbitals. The perturbations imposed by doped Be2 dimers exhibit a local character of the structural and electronicproperties of the complexes, and the separation by two carbon atoms between beryllium active centers is sufficient to considerthese centers as independent sites.

Binding energy between adsorbent and adsorbate strongly affects themechanism of adsorption. Porous systems are usually characterized by a distribution ofthis energy, which is not easy to determine experimentally. A coupled experimentalsimulationprocedure to estimate binding energy directly from experimentaladsorption isotherms is proposed. This new approach combines experimentalinformation (pore size distribution determined from nitrogen adsorption at 77 K)and numerical data (grand canonical Monte Carlo simulations of adsorption in pores)to explain an influence of binding energy on adsorption isotherms. The procedure hasbeen validated by analysis of hydrogen adsorption in a series of carbons activated withKOH:C ratio varying from 3 to 6. These carbons show high capacity of hydrogenstorage both at 80 and 303 K (115 gH2/kgC and 23 gH2/kgC at p = 100 bar,respectively, for carbon activated during 1 h at T = 790 C (T = 1361 K) with KOH:Cratio equal to 3, having the surface area above 2600 m2/g, 0.77 porosity, and largefraction (31%) of pores with average width below 1 nm). An additional energeticparameter has been introduced into the conventional fitting procedure to account for the distribution of adsorption energy inmeasured samples. The observed high consistency between experimental and simulated results validates/correlates thecharacterization procedures and proves the coherence and robustness of both the experimental results and the numericalsimulations.