Browsing by Author "Kalck, Philippe"
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- 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 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 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.
- Carbon supported platinum catalysts for catalytic wet air oxidation of refractory carboxylic acidsPublication . Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, JoaquimCarbon supported platinum (1% wt) catalysts were prepared by the incipient wetness impregnation method and by organometallic chemical vapor deposition. Catalyst characterization was carried out by means of adsorption and thermogravimetric techniques, and by electron microscopy. The catalyst with higher metal dispersion was produced by incipient wetness impregnation. The catalysts were tested in the catalytic wet air oxidation (200 C and 6.9 bar of oxygen partial pressure) of aqueous solutions containing low molecular weight (C2 to C4) carboxylic acids. Significant conversions (greater than 60% over 2 h) and 100% selectivity towards water and non-carboxylic acid products were observed for both systems. The initial reaction rate was used to compare the performance of the two catalytic materials and direct correspondence to the metal dispersion was found. No metal leaching was observed during reaction and no significant deactivation occurred in three successive catalytic oxidation runs. A kinetic model based on the Langmuir–Hinshelwood formulation was applied and the results were analyzed in terms of a heterogeneously catalyzed free radical mechanism.
- Carbon xerogel as catalytic support for noble metal based selective hydrogenation reactionsPublication . Machado, Bruno; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, JoaquimNitric acid treated carbon xerogel was used as support to prepare Pt, Ir and Ru monometallic catalysts. The introduction of oxygen surface groups was important to increase metal dispersion but proved to limit selectivity to cinnamyl alcohol during the hydrogenation of cinnamaldehyde. After an activation treatment to remove unwanted surface groups, Pt catalysts exhibited the highest selectivity, 73%, followed by Ir with 65% and finally Ru with only 32% (measured at 50% conversion).
- Carbon xerogel supported noble metal catalysts for fine chemical applicationsPublication . Machado, Bruno; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, JoaquimCarbon xerogels are mesoporous materials obtained upon pyrolysis of the dried gels resulting from polycondensation of resorcinol and formaldehyde. Treatment with nitric acid under severe conditions introduces high amounts of oxygen containing functional groups onto the surface of thematerial, leading however to the collapse of its porous structure. The resulting material is then used to support 1 wt.% Pt, Ir and Ru monometallic catalysts by wet impregnation using organometallic precursors. The catalysts are characterized by N2 adsorption–desorption isotherms at 77 K, temperature programmed desorption coupled with mass spectrometry, scanning and transmission electron microscopy, and H2 chemisorption. The liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol is used in order to assess the catalytic performance of the prepared materials. Pt and Ru catalysts are initially very selective towards the hydrogenation of the olefinic double bond, while Ir is mostly selective towards the carbonyl group. After a thermal post-reduction treatment at 973 K, selectivity towards cinnamyl alcohol is significantly improved regardless of the metal nature. The Pt catalyst exhibits the best behavior, a complete shift in C=C to C=O hydrogenation being detected. The improvement in selectivity is rationalized in terms of both an increase in metal particle size and a modification in the surface chemistry of the catalyst after the post-reduction treatment.
- Carbon xerogel supported noble metal catalysts for fine chemical applicationsPublication . Machado, Bruno; Gomes, Helder; Serp, Philippe; Kalck, Philippe; Figueiredo, José; Faria, JoaquimCarbon xerogel, a mesoporous material, was produced by polycondensation of resorcinol and formaldehyde. A concentrated nitric acid solution was subsequently used to introduce high amounts of oxygenated groups on the surface. The carbon xerogel served as a support for Pt, Ir and Ru monometallic catalysts by using organometallic precursors. The catalysts were tested in the liquid-phase selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. The introduction of surface groups was important to increase metal dispersion but proved to limit selectivity towards the unsaturated alcohol. After a thermal treatment at 973 K the catalysts showed excellent thermal stability and a narrow metal size distribution. Regarding the catalytic results measured at 50% conversion, Pt catalysts exhibited the highest selectivity to cinnamyl alcohol (73 %) followed by Ir with 65 % and finally Ru with only 32 %.
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