Failures and successes in the quest of hybrid systems for efficient catalysis

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Inorgánica. Fecha de lectura: 13-03-2015This thesis has been carried out in the Department of Inorganic Chemistry at the Autonomous University of Madrid and focused on the study of hybrid systems with potential use in a variety of catalytic processes. After the general introduction, in the second chapter is presented a comprehensive analysis of the H2 activation process achieved by active species generated by the reaction of H2O2 with non-heme iron compound [Fe (BPMCN) (OTf)2] (BPMCN= N,N’-bis(2-pyridylmethyl)-1,2-diaminocyclohexane). This study was derived from the original idea of designing a tandem catalytic process from H2 + O2 mixture until the formation of epoxides and H2O from reaction with olefins. However, what was observed is that depending on the presence of acetic acid in the reaction medium, H2 molecule is activated with varying efficiency by the non-heme iron species with high oxidation state. In the third chapter of this thesis, different strategies for supramolecular or covalent functionalization of graphene oxide (GO) designing for GO- porphyrin hybrids are presented. In the fourth chapter, a procedure of sonication of graphite is reported in various mixtures of water and organic solvent, producing stable suspensions of few layers graphene. Optimized spray deposition processes of these graphene suspensions resulted in transparent coatings with excellent electrical conductivity vs transparency ratios. In the fifth chapter is presented the design of electrodes with high surface area, based on carbon microfibers, which can be chemically modified (by an oxidation process using H2SO4 / H2O2) to make them active in electrocatalytic processes for H2 generationEsta tesis se ha llevado a cabo en el departamento de Química Inorgánica en la Universidad Autónoma de Madrid y se ha centrado en el estudio de sistemas híbridos con potencial uso en diversos procesos catalíticos. Después de la introducción general, en el segundo capítulo se ha presentado un análisis exhaustivo del proceso de activación de H2 logrado por las especies activas generadas por reacción de H2O2 con el compuesto de hierro no hemo [Fe(BPMCN)(OTf)2] (BPMCN= N,N’-bis(2-pyridylmethyl)-1,2-diaminocyclohexane). Este estudio se derivó de la idea original de diseñar un proceso catalítico tipo tándem desde la mezcla H2 + O2 hasta la formación de epóxidos y H2O a partir de reacción con olefinas. Sin embargo, lo que se observó fue que en función de la presencia de ácido acético en el medio de reacción, se activa con más o menos eficiencia la molécula de H2 por la correspondiente especie de hierro no hemo con elevado estado de oxidación. En el tercer capítulo de esta tesis se presentan diferentes estrategias de funcionalización supramolecular o covalente de óxido de grafeno para obtener híbridos de GO-porfirina. En el cuarto capítulo se reporta un procedimiento de sonicación de grafito en varias mezclas de agua y disolvente orgánico que produce suspensiones muy estables de grafeno de pocas capas. La optimización de procesos de deposición por pulverización de estas suspensiones de grafeno ha resultado en recubrimientos transparentes con una excelente relación transparencia vs conductividad eléctrica. En el quinto capítulo se presenta el diseño electrodos de elevada área superficial, basados en fibra de carbono, los cuales pueden ser químicamente modificados (mediante un proceso de oxidación usando H2SO4/H2O2) para hacerlos activos en procesos electrocatalíticos para la generación de H2

Highly concentrated and stable few-layers graphene suspensions in pure and volatile organic solvents

Highly stable graphene suspensions in pure organic solvents, including volatile solvents such as ethanol, tetrahydrofurane, chloroform, acetone or toluene have been prepared by re-dispersion of a graphene-powder. Such re-dispersable solid is produced by precipitation or solvent elimination from graphene suspensions obtained by sonication of graphite in several organic solvent-water mixtures. Re-dispersion is feasible in a wide range of pure organic solvents, obtaining high quality few-layers graphene flakes stable in suspension for months. As a proof-of-concept, on-glass spray deposition of some of these suspensions, e.g. ethanol or tetrahydrofuran, results on electrically conductive transparent coatings. These results suggest industrial potential use of the scalable technology here developed to fabricate low-cost devices with many different potential applicationsThis research was financially supported by Abengoa Co., the Spanish Ministry of Economy and Competitiveness (MAT2013-46753-C2-1-P and RYC2012-09864) and Comunidad de Madrid (CAM 09-S2009_MAT-1467

H2 oxidation versus organic substrate oxidation in non-heme iron mediated reactions with H2O2

Herein we show that species generated upon reaction of α-[Fe(CF3SO3)2(BPMCN)] (BPMCN = N,N′-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane) with H2O2 (putatively [FeV(O)(OH)(BPMCN)]) is able to efficiently oxidize H2 to H2O even in the presence of organic substrates, while species formed in the presence of acetic acid (putatively [FeV(O)(OAc)(BPMCN)]) prefer organic substrate oxidation over H2 activation. Mechanistic implications have been analysed with the aid of computational methodsThis work was supported by Spanish Ministerio de Economia y Competitividad (CTQ2012-37420-C02-02 and 01) European Research Council (StG 239910), and Generalitat de Catalunya (2014 SGR 862 and ICREA Academia award to MC). J.Ll.-F. thanks the CELLEX foundation for the starting career program for financial suppor