Examinando por Autor "Botas, Juan Ángel"

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Assessment of Fe2O3/SiO2 catalyst for the continuous treatment of phenol aqueous solutions in a fixed bed reactor
(ELSEVIER, 2010) Botas, Juan Ángel; Melero, J.A.; Martínez, F.; Pariente, M.I.
Different iron-containing catalysts have been tested for the oxidation of phenol aqueous solutions in a catalytic fixed bed reactor in presence of hydrogen peroxide. All the catalysts consist of iron oxide, mainly crystalline hematite particles, over different silica supports(mesostructured SBA-15 silica and non-ordered mesoporous silica). The immobilization of iron species over different silica supports was addressed by direct incorporation of metal during the synthesis or post-synthesis impregnation. The synthesis conditions were tuned up to yield agglomerated catalysts with iron loadings between 10 and 15 wt. %. The influence of the preparation method and the type of silica support was evaluated in a catalytic fixed bed reactor for the continuous oxidation of phenol in terms of its activity (phenol and total organic carbon degradation) as well as its stability (catalyst deactivation by iron leaching). Those catalyst prepared by direct synthesis either in presence (Fe2O3/SBA-15(DS)) or absence(Fe2O3/SiO2(DS)) of template molecules achieved high catalytic performances (TOC reduction of 65 and 52 %, respectively) with remarkable low iron leaching in comparison with the impregnated iron catalysts. Catalytic results demonstrated that the synthesis method plays a crucial role in the dispersion and stability of active species and hence resulting in superior catalytic performances.
Experimental evaluation and energy analysis of a two-step water splitting thermochemical cycle for solar hydrogen production based on La0.8Sr0.2CoO3-δ perovskite
(Elsevier, 2022) Orfila, María; Linares, María; Pérez, Antonio; Barras García, Inés; Molina Gil, Raúl; Marugán, Javier; Botas, Juan Ángel; Sanz, Raúl
A study of the hydrogen production by thermochemical water splitting with a commercial perovskite La0.8Sr0.2CoO3-d(denoted as LSC) under different temperature conditions is presented. The experiments revealed that high operational temperatures for the thermal reduction step (>1000 C) implied a decrease in the hydrogen production with each consecutive cycle due to the formation of segregated phases of Co3O4. On the other hand, the experiments at lower thermal reduction operational temperatures indicated that the material had a stable behaviour with a hydrogen production of 15.8 cm3 STP/gmaterial$cycle during 20 consecutive cycles at 1000 C, being negligible at 800 C. This results comparable or even higher than the maximum values reported in literature for other perovskites (9.80 e10.50 STP/gmaterial$cycle), but at considerable lower temperatures in the reduction step of the thermochemical cycle for the water splitting (1000 vs 1300e1400 C). The LSC keeps the perovskite type structure after each thermochemical cycle, ensuring a stable and constant H2 production. An energy and exergy evaluation of the cycle led to values of solar to fuel efficiency and exergy efficiency of 0.67 and 0.36 (as a percentage of 1), respectively, which are higher than those reported for other metal oxides redox pairs commonly found in the literature, being the reduction temperature remarkably lower. These facts point out to the LSC perovskite as a promising material for full-scale applications of solar hydrogen production with good cyclability and compatible with current concentrating solar power technology.
H2 Production from methane pyrolisis over commercial carbon catalysts: Kinetic and deactivation study
(ELSEVIER, 2009) Serrano, D.P.; Botas, Juan Ángel; Guil Lopez, R.
Hydrogen production from catalytic methane decomposition (DeCH4) is a simple process to produce high purity hydrogen with no formation of carbon oxides (CO or CO2). However, to completely avoid those emissions, the catalyst must not be regenerated. Therefore, it is necessary to use inexpensive catalysts, which show low deactivation during the process. Use of carbon materials as catalysts fulfils these requirements. Methane decomposition catalysed by a number of commercial carbons has been studied in this work using both constant and variable temperature experiments. The results obtained showed that the most active catalyst at short reaction times was activated carbon, but it underwent a fast deactivation due to the deposition of the carbon formed from methane cracking. On the contrary, carbon blacks, and especially the CB-bp sample, present high reaction rates for methane decomposition at both short and long reaction times. Carbon nanotubes exhibit a relatively low activity in spite of containing significant amounts of metals. The initial loss of activity observed with the different catalysts is attributed mainly to the blockage of their micropores due to the deposition of the carbon formed during the reaction.
Heterogeneous catalytic Wet Peroxide Oxidation Systems for the Treatment of an Industrial Pharmaceutical Wastewater
(ELSEVIER, 2009) Melero, J.A.; Martínez, F.; Botas, Juan Ángel; Molina, R.; Pariente, M.I.
The aim of this work was to assess the treatment of a wastewater coming from a pharmaceutical plant through a continuous heterogeneous catalytic wet peroxide oxidation (CWPO) process using a Fe2O3/SBA-15 nanocomposite catalyst. This catalyst was preliminary tested in a batch stirred tank reactor (STR), to elucidate the influence of significant parameters on the oxidation system, such as temperature, initial oxidant concentration and initial pH of the reaction medium. In that case, a temperature of 80ºC using an initial oxidant concentration corresponding to twice the theoretical stoichiometric amount for a complete carbon depletion and initial pH of ca. 3 allow obtaining TOC degradation around 50% after 200 minutes of contact time. Thereafter, the powder catalyst was extruded with bentonite to prepare pellets that could be used in a fixed bed reactor (FBR). Results in the up-flow FBR indicate that the catalyst shows high activity in terms of TOC mineralization (ca. 60% under steady-state conditions), with an excellent use of the oxidant and high stability of the supported iron species. The activity of the catalyst is kept constant, at least, for 55 hours of reaction. Furthermore, BOD5/COD ratio is increased from 0.20 up to 0.30, whereas the Average Oxidation Stage (AOS) changed from 0.70 to 2.35. These two parameters show a high oxidation degree of organic compounds in the outlet effluent, which enhances its biodegradability, and favours the possibility of a subsequent coupling with a conventional biological treatment.
Heterogeneous Photo-Fenton Oxidation of Benzoic Acid in Water Effect of Operating Conditions, Reaction By-Products and Coupling with Biological Treatment
(ELSEVIER, 2008) Pariente, M. Isabel; Martínez, Fernando; Melero, Juan Antonio; Botas, Juan Ángel; Velegraki, Theodora; Xekoukoulotakis, Nikolaos P.; Mantzavinos, Dionissios
The heterogeneous photo-Fenton oxidation of benzoic acid, a precursor of several organic pollutants found in agro-industrial effluents, was studied in model aqueous solutions. UVA irradiation was provided by a 125 W medium pressure mercury lamp, while a nanocomposite material of crystalline iron oxides supported over mesostructured SBA-15 was used as the catalyst. Experiments were conducted at benzoic acid initial concentrations between 25 and 450 mg/L, catalyst concentrations between 0.3 and 1.2 g/L and hydrogen peroxide concentrations between 20% and 100% of the stoichiometric amount needed for complete mineralization. Conversion, which was found to be first order regarding benzoic acid concentration, generally increased with increasing the concentration of Fenton¿s reagents and decreasing substrate concentration. HPLC analysis showed that oxidation was accompanied by the formation of several by-products; of these, the three monohydroxybenzoic acids as well as oxalic acid were successfully identified and quantified. By-products were more resistant to oxidation than benzoic acid since COD reduction was generally lower than substrate conversion. Catalyst stability was assessed measuring the extent of iron leaching in the reaction mixture and was found to be excellent as dissolved iron never exceeded 5% relative to the initial iron content. The aerobic biodegradability of benzoic acid before and after photo-Fenton oxidation was assessed by shake flask tests. Chemical oxidation enhanced the biodegradability of benzoic acid although the oxidized solution was more ecotoxic to marine bacteria than the original one. The feasibility of coupling chemical and biological oxidation was also assessed for an actual olive oil mill effluent.
Modified wacker TBHP oxidation of 1- DODECENE
(ELSEVIER, 2008) Escola, J. M.; Botas, Juan Ángel; Aguado, José; Serrano, D. P.; Vargas, C.; Bravo, M.
A higher 1-olefin (1-dodecene) was oxidized to 2-dodecanone and other ketones in a modified Wacker system featured by omitting the use of copper chloride and employing tert-butylhydroperoxide (TBHP) as oxidant. Acetonitrile was the solvent of choice due to its higher selectivity towards 2-dodecanone, the reaction occurring mostly in the interface. A maximum in conversion and selectivity was measured for a ratio [CH3CN] / [1-dodecene] = 10. The temperature abatement enhances the 2-dodecanone selectivity (61% at 40ºC) because of the lower extent of the competing isomerization reactions. An optimum in 2-dodecanone selectivity was found for a [TBHP] / [1-dodecene] ratio = 7. The use of H2O2 as oxidant led towards slower oxidation rates than TBHP. Other palladium salts (PdSO4 and Pd(CH3COO)2) and several R-CN solvents (propionitrile, benzonitrile, isobutyronitrile) yielded lower performances than palladium chloride and acetonitrile, respectively. On the contrary, ß-ciclodextrin, a phase transfer catalyst, improved the selectivity towards 2-dodecanone.
Novel and Versatile Cobalt Azobenzene-Based Metal-Organic Framework as Hydrogen Adsorbent
(Wiley, 2019-01-18) Montes-Andres, Helena; Leo, Pedro; Orcajo, Gisela; Rodríguez-Dieguez, Antonio; Choquesillo-Lazarte, Duane; Martos, Carmen; Botas, Juan Ángel; Martínez, Fernando; Calleja, Guillermo
A novel URJC-3 material based on cobalt and 5,5′-(diazene-1,2-diyl)diisophthalate ligand, containing Lewis acid and basic sites, has been synthesized under solvothermal conditions. Compound URJC-3, with polyhedral morphology, crystallizes in the tetragonal and P43212 space group, exhibiting a three-dimensional structure with small channels along a and b axes. This material was fully characterized, and its hydrogen adsorption properties were estimated for a wide range of temperatures (77–298 K) and pressures (1–170 bar). The hydrogen storage capacity of URJC-3 is quite high in relation to its moderate surface area, which is probably due to the confinement effect of hydrogen molecules inside its reduced pores of 6 Å, which is close the ionic radii of hydrogen molecules. The storage capacity of this material is not only higher than that of active carbon and purified single-walled carbon nanotubes, but also surpasses the gravimetric hydrogen uptake of most MOF materials.
Oxidation of heavy 1- olefins (C12= - C20=) with TBHP using a modified Wacker system
(ELSEVIER, 2010) Escola, J. M.; Botas, Juan Ángel; Vargas, C.; Bravo, M.
The oxidation of heavy olefins (CB12 B¿ CB20B) was carried out using a modified Wacker system with TBHP as oxidant and acetonitrile as solvent at 80ºC. This system allowed the oxidation of 1-octadecene giving rise to 90% conversion with 60% selectivity towards 2-octadecanone after 2 h while the addition of ß-cyclodextrins did not increase the production of 2-octadecanone. The oxidation of a equimolar mixture of n-dodecane + 1-dodecene enhanced markedly the selectivity towards 2-dodecanone yielding 63% instead of 34% in n-paraffin absence after 2 h, likely due to a dilution effect of the n-dodecane which reduces the extent of the isomerisation reactions. The oxidation of a equimolar mixture CB12PB=P + CB16PB=P + CB20PB=P in presence of equimolar amounts of their corresponding n-paraffins gave rise to practically complete conversion and selectivities towards 2-methylketones within 70 ¿ 90%, enhancing with decreasing chain length due to their higher solubility in the biphasic system. The activity of the catalyst dropped after two reaction cycles, indicating its deactivation by formation of palladium clusters. However, it was possible to obtain similar results in terms of activity and selectivity by decreasing the [1-dodecene]/[PdClB2B] ratio to 100, which is expected to increase the catalyst lifetime by decreasing the extent of palladium aggregation. In this regard, the reported system is rather promising for the oxidation of heavy 1-olefins towards methyl ketones.
Shifting pathways in the phenol/2-propanol conversion over the tandem Raney Ni + ZSM-5 catalytic system
(American Chemical Society, 2020-02-04) García-Minguillán, Alba María; Briones, Laura; Serrano, David Pedro; Botas, Juan Ángel; Escola, José María
This work investigates the effects of both the zeolite accessibility and the reaction temperature on conversion of phenol assisted by 2-propanol over the tandem system Raney Ni + ZSM-5 zeolite. Two different zeolite samples, containing similar Si/Al ratios, were used: nanocrystalline ZSM-5 (n-ZSM-5) and hierarchical ZSM-5 (h-ZSM-5), operating at temperatures of 125, 150 and 175°C. When working with the Raney Ni + n-ZSM-5 system at low and intermediate temperatures the main products were mostly benzene and cyclohexene formed by phenol deoxygenation. In contrast, when increasing the temperature up to 175°C, a shift in the reaction pathways was observed, leading towards a significant share of valuable alkylphenols (mostly cresols and cyclohexylphenols) in the product distribution, generated by the occurrence of alkylation reactions catalyzed by the zeolite acid sites. This effect was enhanced in the case of the h-ZSM-5 sample, due to its improved accessibility and larger mesopore/external surface area.
Synthesis, Structural Features, and Hydrogen Adsorption Properties of Three New Flexible Sulfur-Containing Metal–Organic Frameworks
(American Chemical Society, 2020-08-31) Montes-Andres, Helena; Leo, Pedro; Orcajo, Gisela; Rodríguez-Dieguez, Antonio; Choquesillo-Lazarte, Duane; Martos, Carmen; Botas, Juan Ángel; Calleja, Guillermo
Three novel flexible sulfur-containing MOF materials named Co-URJC-5, Cu-URJC-6 and Zn-URJC-7, based on the 5,5′-thiodiisophthalic acid linker have been synthesized through solvothermal methods and characterized by different physicochemical techniques. Hydrogen adsorption analysis at room temperature reveals that these compounds display a gate-opening type adsorption mechanism at low pressures, attributed to the flexible nature of the H4TBTC ligand. This behavior is even more noticeable for Cu-URJC-6, since the layer arrangement by π–π stacking interactions between the aromatic layers could contribute to the flexibility of the structure. These results can be considered as a representative example to elucidate how MOF structures are built using flexible ligands and more significantly as a promising route for designing materials with selective gas sorption properties.