Generation of hydrogen peroxide on a pyridine-like nitrogen-nickel doped graphene surface
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Generation of hydrogen peroxide on a pyridine-like nitrogen-nickel doped graphene surface E. Rangel1,2, L. F. Magana2 and L. E. Sansores1, G.J. Vázquez2 1
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, C.P. 04510, México, D. F., México. 2 Instituto de Física, Universidad Nacional Autónoma de México, Apartado Postal 20-364, C.P. 01000, México, D. F. México. ABSTRACT Density functional theory and molecular dynamics were used to study the generation of hydrogen peroxide around a nickel atom anchored on a pyridine-like nitrogen-doped graphene (PNG) layer. First, we found that two hydrogen molecules are adsorbed around the nickel atom, with adsorption energy 0.95 eV/molecule. Then we studied the interaction of oxygen molecules with this system at atmospheric pressure and 300 K. It is found that two hydrogen peroxide molecules are formed. However, at 700 K, one hydrogen peroxide molecule, and one water molecule are desorbed. One oxygen atom stays bound to the nickel atom. INTRODUCTION Hydrogen peroxide (H2O2) is a compound that has a strong oxidizing property as well as disinfectant and antiseptic property due to its composition of an extra oxygen compared to water. Hydrogen peroxide is used in agriculture as an insecticide and to harvest a great amount of crops. On the other hand, about 50% of the world's production of hydrogen peroxide in 1994 was used for pulp- and paper-bleaching [1-4]. Most of the catalysts used for the direct synthesis of hydrogen peroxide are prepared by palladium supported on a variety of substrates such as alumina, silica and carbon [5]. However, the management of a colloid is difficult in a commercial process because its recovery is not feasible because of the low dissolved metal concentrations used. Here, we studied by density functional theory, the formation of hydrogen peroxide through a direct catalytic production, a catalyst composed of a nickel atom anchored on a pyridine-like nitrogen-doped defect on a graphene surface. METHOD For the the adsorption energy of the nickel atom on the vacancy we used: ǻE = E[(PNG+Ni)]–[E(PNG)+E(Ni)]. Here E[(PNG+Ni)] is the energy of the final optimized configuration; E(PNG)+E(Ni) is the energy of the initial system, plus the energy of nickel alone with no interaction between them. We used for the adsorption energy of hydrogen molecules: ǻE = E[(PNG+Ni+nH2)]-[E(PNG+Ni)+E(nH2)].
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Here n is the number of hydrogen molecules; E[(PNG+Ni+nH2)] is the energy of the final optimized configuration; E (PNG+Ni)+E (nH2) is the energy of the initial system, which is the nickel doped graphene alone plus the energy of n hydrogen molecules alone with no interaction between them. Density functional theory (DFT) with the local density approximation (LDA) [6], molecular dynamics (MD) [7, 8], within the Born-Oppenheimer approximation and the Quantum Espresso code [9] were used. For a cross check, we repeat part of the calculations with the generalized gradient approximation GGA. For exchange-correlation energies
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