In Ukrainian

Abstract

The features of the interaction of hydrogen molecules with graphene-like planes in which two carbon atoms are replaced by nitrogen or boron atoms are investigated by methods of quantum chemistry (DFT, B3LYP, 6-31G**). To take into account the dispersion contributions to the energy of the formation of intermolecular complexes that arise in the formation of adsorption supramolecular structures, the dispersion correction Grimme-D3 is used. To study the influence of the size of the graphene-like cluster on the molecular hydrogen chemisorption energy in the model of graphene nanoparticles, polyaromatic molecules (PAM) pyrene, coronene (Cor) and that of 54 carbon atoms, as well as their nitrogen and boron-containing analogues, in which the atoms of nitrogen and boron are placed in a para-position in relation to one another, in the so-called piperazine configuration of the atoms of nitrogen or boron. Equilibrium spatial structures of reagent molecules, formed complexes and products of dissociative chemisorption of hydrogen molecules were found by minimizing the norm of a gradient of total energy. An important stage in the transformation of physically sorbed H2 molecules on the surface of the most carbon materials is its decomposition into two hydrogen atoms that can bind to different carbon atoms of model molecules. In this case, a significant number of different reaction products of the same gross composition is formed. The lowest energy among them is related to one where the atoms of the hydrogen are bound to carbon atoms that are adjacent to the nitrogen or boron atoms. It has been found that, regardless of the size of the carbon PAM, the value of the chemisorption energy in all cases has a positive value and is greater than 100 kJ/mol. The chemisorption energy of the hydrogen molecule by PAM with heteroatoms depends on the size of the model, the position of the atoms of nitrogen and boron and, for the most part, has a small negative value (up to -35 kJ/mole), which indicates the spontaneity of the corresponding process. Calculations have shown that the lowest activation energy of the reaction of the H2 molecule with boron PAM, and the most - for pure carbon PAM, regardless of the size of the models. The nature of the heteroatom changes the structure of the transition state and the mechanism of chemisorption. Analysis of the results of quantum chemical calculations showed the highest exothermicity of dissociative adsorption of H2 molecule on boron-containing graphene-like molecules. For nitrogen-containing surfactants, the reaction is slightly less exothermic, as well as the possibility of desorption of atomic hydrogen from the surface of the latter with subsequent recombination in the gas phase. At the same time, for the models of pure graphene-like layer, these data indicate that chemosorption of molecular hydrogen is impossible. Without a total analysis of the results of all possible placements of a pair of hydrogen atoms (formed by the dissociation of the H2 molecule) when they are bound to nitrogen-containing polyaromatic molecules, it can be noted that the dissociation chemisorption of the H2 molecule, regardless of the nature of the heteroatom in the PAM, is thermodynamically more probable at the periphery of the model molecules than in their center.