An effective approach for modifying carbonaceous materials with niobium single sites to improve their catalytic properties

Abstract

In this paper we show a very simple route for the incorporation of catalytically active niobium species on the surface of carbon materials, such as graphene oxide, carbon nanotubes and activated carbon. Some existing methods of incorporating a transition metal on a support have involved co-precipitation or wet impregnation, to obtain the corresponding oxides. These methods, however, cause reduction in the specific area of the support and can also form large metal oxide particles with loss of metal exposure. Therefore, here we present a novel way to add catalytically active species on the surfaces of different types of carbon through the formation of interaction complexes between the metal precursor and the functional groups of the carbon matrix. Because of the excellent catalytic properties exhibited by the niobium species we choose the NH4[NbO(C2O4)2(H2O)2]·2H2O salt as the model precursor. The characterization by XPS reveals the presence of the niobium species indicated by the displacement of the peaks between 206-212 eV related to the oxalate species according to the spectrum from pure niobium oxalate. Images obtained by TEM and SEM show the typical morphologies of carbonaceous materials without the niobium oxide formation signal, which indicates the presence of niobium complexes as isolated sites on the carbon surfaces. This new class of materials exhibited excellent properties as catalysts for pollutant oxidation. The presence of Nb promotes the catalytic activation of H2O2 generating hydroxyl radicals in situ, which allows their use in the organic compound oxidation processes. Tests for DBT oxidation indicate that Nb significantly improves the removal of such pollutants in biphasic reactions with removal around 90% under the tested conditions. Theoretical calculations showed that the most favorable adsorption model is an ionic complex presenting a ΔG = -108.7 kcal mol(-1) for the whole adsorption process.

Niobium oxide prepared through a novel supercritical-CO2-assisted method as a highly active heterogeneous catalyst for the synthesis of azoxybenzene from aniline

“…(n = 1 for nitrosobenzene and nitrobenzene, n = 2 for azobenzene and azoxybenzene) reactions through the formation of active oxygen species, including peroxo, superoxo and hydroxyl radical species. 44,45 The exact form of active oxygen species depends on the active sites of the catalyst and the reaction conditions (e.g. pH, H 2 O 2 concentration).…”

“…pH, H 2 O 2 concentration). Until now, Nb 2 O 5 has been applied as a heterogeneous catalyst in many reactions employing H 2 O 2 as the oxidant, such as the oxidation of organic sulfides, 44,45 glycerol, and alkenes. 46 Carreño et al reported that Nb 2 O 5 prepared by a microwave-assisted hydrothermal method catalysed the oxidation of aniline with H 2 O 2 at 25°C with phenylhydroxylamine and nitrosobenzene as the main products.…”

Nióbio: Um Elemento Químico Estratégico Para O Brasil

“…Diferentes estruturas de carbono como óxidos de grafeno, nanotubos de carbono e carvão ativado têm sido usados como suportes para imobilizar grupos peroxo-nióbio cataliticamente ativos para reações de oxidação. 49 A presença de nióbio na superfície do óxido de grafite resultou no catalisador mais ativo para reações de oxidação de dibenzotiofeno em uma mistura bifásica de hexano/ acetonitrila. Catalisadores à base de Nb 12 O 29 foram usados como um suporte reativo para deposição de Fe 2 O 3 que funcionou como um catalisador do tipo-Fenton em presença de H 2 O 2 para reação de oxidação de azul de metileno em meio aquoso.…”

Production of Reduced Graphene Oxide Platelets from Graphite Flakes Using the Fenton Reaction as an Alternative to Harmful Oxidizing Agents

“…Graphene is a two-dimensional (2D) graphitic structure which is the basic unit for making graphitic materials of other dimensionalities such as 0D fullerene, 1D carbon nanotube, or 3D graphite [1]. Because of its exceptional electronic, thermal, and mechanical properties [2][3][4], graphene has been investigated in several fields of science including catalysis [5][6][7], adsorption [8][9][10], electrocatalysis [11,12], energy storage [13][14][15], and sensors [16,17].…”