Percorrer por autor "Serp, Philippe"
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- Amphiphilic carbon nanotubes for catalytic wet peroxide oxidation of 4-nitrophenolPublication . Roman, Fernanda; Sanches, Flávia Kim; Díaz de Tuesta, Jose Luis; Marin, Pricila; Machado, Bruno; Serp, Philippe; Silva, Adrián; Faria, Joaquim; Gomes, HelderCarbon nanotubes (CNTs) were synthesized via chemical vapor deposition (CVD) over an AlCoFeO4 catalyst by a sequential feed of ethylene (E, as carbon source) and acetonitrile (A, as nitrogen source). The resulting samples were noted E20 (hydrophobic), E10A10 (amphiphilic), and A20 (hydrophilic), the number referring to the feed time (minutes) of each precursor, as reported elsewhere1. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of 4-nitrophenol (4-NP). The reaction was monitored by HPLC (to determine the concentration of 4-NP and respective intermediates), TOC analyzer, and UV-vis spectrophotometry (to quantify H2O2) (Figure 1). After 8 h of reaction, A20 led to the highest consumption of H2O2 (90%), followed by E10A10 (61%) and E20 (52%). On the other hand, the highest degradation of 4-NP was observed with the amphiphilic E10A10 material (98%) followed by E20 (95%), whereas A20 only led to a removal of 69%. Similar behavior was found when analyzing the formation of reaction intermediates (data not shown), i.e., while A20 resulted in the accumulation of 4-nitrocatechol (4-NTC) and hydroquinone (HQ) E10A10 and E20 led to the total conversion of formed 4-NTC and HQ. This resulted in a lower TOC removal for A20 (37%) than to E10A10 and E20 (53%). Therefore, the amphiphilic E10A10 material is a promising catalyst for the CWPO of 4-NP.
- Aplicación de MWNT a aguas residuales de alta carga orgánica mediante CWAOPublication . García, Juan; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, JoaquimUna gran parte de los vertidos residuales que genera la Industria Química. y otras industrias relacionadas con ella, están en forma de corrientes acuosas que, en muchos casos, contienen compuestos orgánicos en una concentración demasiado baja para que su recuperación sea rentable, pero es lo suficiente elevada para constituir una fluente de contaminación importante. La utilización de materiales de carbón como soporte catalítico ha sido ampliamente utilizado en procesos de oxidación húmeda catalítica (CWAO) como un pretratamiento efectivo en el tratamiento de este tipo de efluentes. Los materiales de carbono son utilizados tanto como soportes activos como soportes catalíticos debido a sus características específicas que son principalmente la resistencia a medios ácido/básicos, control de la porosidad y la superficie química y la fácil recuperación de metales mediante la combustión del soporte con el resultado de un bajo impacto medioambiental. El gran impacto de los materiales nanoestruturados se debe a que su gran superficie mejora sus propiedades mecánicas y sus únicas propiedades electrónicas. t abre caminos a una amplia diversidad de nuevas aplicaciones En este contexto, el objetivo principal de este trabajo es ilustrar el potencial que presentan los catalizadores de rutenio soportados en nanotubos de carbono de pared múltiple (MWNT) en la oxidación húmeda catalítica (CWAO) de aguas residuales conteniendo anilina.
- Carbon nanotube catalysts for the cwpo of 2-nitrophenol in biphasic systems: kinetic insightsPublication . Díaz de Tuesta, Jose Luis; Machado, Bruno; Serp, Philippe; Silva, Adrián; Faria, Joaquim; Gomes, HelderCarbon nanotubes (CNTs) were used as catalysts in the removal of 2-nitrophenol (2-NP) by catalytic wet peroxide oxidation (CWPO). Different CNTs were synthesized by catalytic chemical vapour deposition (CVD) using Fe/γ-Al2O3, as described elsewhere (Purceno et al., 2015 and Martin-Martinez et al., 2016). A fluidized-bed reactor was employed by feeding a gas mixture of hydrogen and: i) ethylene alone for 30 min (sample E30); ii) acetonitrile for 20 min, followed by ethylene for 20 min (sample A20E20); iii) acetonitrile for 20 min, followed by ethylene for 10 min (sample A20E10); iv) ethylene for 10 min, followed by acetonitrile for 20 min (sample E10A20); and v) acetonitrile alone for 30 min (sample A30). The CNTs were tested for the oxidation of 2-nitrophenol (2-NP) in aqueous-phase (Martin-Martinez et al., 2016) and in biphasic conditions (cyclohexane-water) simulating oily wastewater effluents as described in previous works (Diaz de Tuesta et al., 2018). Both systems were modelled by using kinetic power-law equations, following a methodology presented previously (Diaz de Tuesta et al., 2017).
- Carbon nanotube supported ruthenium catalysts for the treatment of high strength wastewater with aniline using wet air oxidationPublication . García, Juan; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, JoaquimMulti-walled carbon nanotubes (MWCNT) can be efficiently used as support of ruthenium catalysts for the catalytic wet air oxidation of high strength wastewater containing aniline. Catalysts were prepared using different ruthenium precursors, Ruthenocene [Ru(g5-C5H52], Ruthenium (1,5-cyclooctadiene, 1,3,5-cyclooctatriene) [Ru(cod)(cot)] and Ruthenium trichloride (RuCl3.xH2O), different impregnation methods (excess solution and incipient wetness impregnation) and different MWCNT support surface chemistry (nitric acid oxidized MWCNT-COOH and Na2CO3 ion exchanged MWCNT-COONa). The efficiency of the aniline removal obtained with the catalysts prepared with different precursors decreases in the order [Ru(cod)(cot)] > RuCl3.xH2O > [Ru(g5-C5H52], 100% aniline conversion being obtained after 45 min of reaction with the catalyst prepared with [Ru(cod)(cot)]. The influence of the impregnation technique was found to be negligible, while the use of the MWCNT-COONa support led to increased catalyst performances when compared to that obtained with catalysts prepared with the MWCNT-COOH support. Leaching of ruthenium was observed in all cases, but the use of the precursor [Ru(cod)(cot)] and of the support MWCNT-COONa in the preparation of the catalysts seems to improve their stability. A direct relationship between metal load and catalyst stability was found and attributed to the strength of metal-support interactions.
- Carbon nanotubes and xerogels as supports of well dispersed Pt catalysts for environmental applicationsPublication . Gomes, Helder; Samant, Purnakala; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, JoaquimDifferent types of carbon materials including multi-walled nanotubes (MWNT), carbon xerogels (CX) and activated carbon (AC) were used as supports to prepare platinum catalysts (1% w/w), which were tested in the treatment of aqueous aniline solutions by catalytic wet air oxidation (CWAO). The prepared materials and catalysts were characterized by several techniques (SEM/EDS, TEM, N2 adsorption, TPD and H2 chemisorption). All catalysts presented a very high activity for the removal of aniline and total organic carbon (TOC). Catalyst activity and selectivity toward CO2 formation were found to depend on the nature of the support and concentration of oxygen containing functional groups on the surface of the materials.
- Carbon nanotubes as catalysts for wet peroxide oxidation: structure-reactivity relationshipsPublication . Ribeiro, Rui; Martin-Martinez, Maria; Machado, Bruno; Serp, Philippe; Morales-Torres, Sergio; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderMagnetic neat and N-doped carbon nanotubes with different properties have been synthesized by chemical vapour deposiüon and tested in the catalytic wet peroxide oxidation of 4-nitrophenol solutions (5 g L') at relatively mild operating conditions (atmospheric pressure, T = 50 °C, pH = 3)~using a catalyst load = 2.5 g L-' and [H202]o = 17.8 g L-1. The results demonstrate that the catalyst hydrophobicity/ hydrophilicity is a detenninant property in the CWPO reaction, since it affects the rate ofH202 decomposition. The controlled formation ofreactive radicais (HO* and HOO*) at hydrophobic surfaces avoids the formation of non-reactive species (02 and H20), increasing.
- Carbon nanotubes as catalysts for wet peroxide oxidation: the effect of surface chemistryPublication . Martin-Martinez, Maria; Machado, Bruno; Serp, Philippe; Morales-Torres, Sergio; Silva, Adrián; Figueiredo, José; Faria, Joaquim; Gomes, HelderThree magnetic carbon nanotube (CNT) samples, named A30 (N-doped), E30 (undoped) and E10A20 (selectively N-doped), synthesized by catalytic chemical vapor deposition, were modified by introducing oxygenated surface groups (oxidation with HNO3, samples CNT-N), and by heat treatment at 800 °C for the removal of surface functionalities (samples CNT-HT). Both treatments lead to higher specific surface areas. The acid treatment results in more acidic surfaces, with higher amounts of oxygenated species being introduced on Ndoped surfaces. Heat-treated samples are less hydrophilic than those treated with nitric acid, heat treatment leading to neutral or basic surfaces, only N-quaternary and N-pyridinic species being found by XPS on N-doped surfaces. These materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4-nitrophenol solutions (4-NP, 5 g L−1) at atmospheric pressure, T=50 °C and pH=3, using a catalyst load of 2.5 g L−1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4-NP. The high temperature treatment enhanced significantly the activity of the CNTs towards CWPO, evaluated in terms of 4-NP and total organic carbon conversion, due to the increased hydrophobicity of their surface. In particular, E30HT and E10A20HT were able to remove ca. 100% of 4-NP after 8 h of operation. On the other hand, by treating the CNTs with HNO3, the activity of the less hydrophilic samples decreased upon increasing the concentration of surface oxygen-containing functionalities, whilst the reactivity generated inside the opened nanotubes improved the activity of the highly hydrophilic A30 N.
- Carbon nanotubes supported catalysts for selective hydrogenations of unsaturated aldehydesPublication . Machado, Bruno; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Faria, Joaquim
- Carbon supported iridium catalysts in the catalytic wet air oxidation of carboxylic acids: kinetics and mechanistic interpretationPublication . Gomes, Helder; Figueiredo, José; Faria, Joaquim; Serp, Philippe; Kalck, PhilippeCarbon-supported iridium catalysts were prepared by different incipient wetness impregnation methods and by organometallic chemical vapor deposition. The catalysts were characterized by N2 adsorption, TPD, SEM and H2 chemisorption measurements. The results obtained indicate a clear dependency of the metal-phase dispersion on the pre-treatment of the carbon support and the impregnation method. Their activity for catalytic wet air oxidation of butyric and iso-butyric acid aqueous solutions was investigated in a stirred reactor at 473K and 0.69MPa of oxygen partial pressure. The conversions obtained after 2 h were 43 and 52%,with respect to each carboxylic acid, when the most active catalysts were used. The measured conversions and initial reaction rates correlate well with the exposed metal area. A rate equation was determined from measurements of the initial reaction rates at different oxygen partial pressures, temperatures and catalyst mass loads. The results were modeled considering a heterogeneously catalyzed free-radical mechanism.
- Carbon supported noble metal catalysts prepared by photochemical depositionPublication . Faria, Joaquim; Machado, Bruno; Gomes, Helder; Serp, Philippe; Kalck, PhilippePhotochemical deposition of noble metals in different supports is gaining importance because of its simplicity and advantages. Its main advantage is the ability of spreading very effectively the metal throughout the support, thus leading to very high dispersions, resulting in higher molecular control, with a positive effect on both activity and selectivity. This type of catalysts is important for industrial preparation of fine chemicals. A common synthetic route in these processes is the selective catalytic hydrogenation of organic substrates containing unsaturated functional groups, like steroids or α,β-unsaturated aldehydes.