Examinando por Autor "Melero, Juan A."

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A novel photoanaerobic process as a feasible alternative to the traditional aerobic treatment of refinery wastewater
(Elsevier, 2022) San Martín, Javier; Puyol, Daniel; Segura, Yolanda; Melero, Juan A.; Martínez, Fernando
Refinery wastewater (RWW) treatment is outdated since new wastewater management and reuse challenges require more environmental-friendly and cheap alternatives. Conventional biological treatments focused on activated sludge are highly energy-intensive and resource-dissipating processes. However, anaerobic treatments are an excellent alternative to reduce costs derived from aeration and carbon footprint. This work proposes a novel strategy for the treatment of RWW involving a photoanaerobic membrane bioreactor (PAnMBR) with a mixed culture of purple phototrophic bacteria (PPB). PPB upcycles the organic matter, nitrogen, and phosphorus in an assimilative way, leading to a much higher biomass yield and nutrient removal than aerobic cultures. The enriched PPB culture was generated from the RWW as the sole substrate without specific PPB inoculation. The RWW (exempted from sufficient nutrients) was successfully treated with additional ammonium and phosphates provided by domestic wastewater (DWW). Preliminary batch tests determined the best DWW/RWW volumetric mixing ratio at 25:75. The PAnMBR was operated for 144 days under different specific loading rates (SLR) by modifying hydraulic and solid retention times. The maximum specific loading rate (SLR) for the efficient RWW/ DWW mix treatment was 0.3 mgCODinlet/mgCODbiomass⋅d. The COD consumption was mainly mediated by Rhodopseudomonas sp. and Rhodobacter sp. PPB genera. The PPB-based photo-anaerobic membrane reactor was able to comply with regulated parameters for wastewater discharge for the more restrictive use of reclaimed water according to the European legislation in force.
Acid-catalyzed production of biodiesel over arenesulfonic SBA-15: insights into the role of water in the reaction network
(Elsevier, 2014) Melero, Juan A.; Bautista, L. Fernando; Morales, Gabriel; Iglesias, Jose; Sánchez-Vázquez, Rebeca
This work presents a systematic approach to understand the effect of the presence of water in highly acidic crude palm oil-typical conditions of low grade oleaginous feedstock- on the performance of arene-SO3H-SBA-15 catalyst in the batch-production of biodiesel. The addition of small amounts of water (1 wt%) to the reaction medium led to a clear reduction of the observed yield to fatty acid methyl esters (FAME), being this decay usually attributed to the highly hydrophilic nature of arenesulfonic acid groups, and the associated difficulties of hydrophobic substrates to access these catalytic acid sites. However, the addition of larger amounts of water -up to 10 wt%- did not cause a proportional decay in the yield to FAME, but a higher production of free fatty acids (FFA). This is attributed to the promotion of acid-catalyzed hydrolysis of both starting triglycerides and formed FAME. The net result is not only a significant reduction of the final FAME yield, but also the appearance of high acid values, i.e. FFA contents, in the final biodiesel. Consequently, the overall process is simultaneously affected by transesterification, esterification and hydrolysis reactions, all of them catalyzed by Brønsted acid sites and dependent on the reaction conditions -temperature and water concentration- to different extents. Several strategies devoted to manage such behavior of sulfonic acid-modified SBA-15 catalysts in presence of water, aiming to maximize FAME yield while minimizing FFA content, have been explored: (1) minimization of the water content in the reacting media by pre-drying of feedstock and catalyst; (2) addition of molecular sieves to the reacting media as water scavengers, (3) hydrophobization of the catalyst surface to minimize the water uptake by the catalyst; and (4) use of a decreasing reaction temperature profile in order to first promote transesterification at high temperature and then reduce the temperature to keep at a minimum the hydrolysis of formed FAME. All these strategies resulted in an improvement of the catalytic performance, especially the use of a decreasing temperature profile. The results showed by the latter strategy open new possibilities and reaction pathways in which readily available, low-grade, cheap oleaginous feedstock with high water and FFA contents can be efficiently converted into biodiesel.
Agglomeration of Ti-SBA-15 with clays for liquid phase olefin epoxidation in a continuous fixed bed reactor.
(ELSEVIER, 2008) Melero, Juan A.; Iglesias, Jose; Sainz-Pardo, Javier; Frutos, Pilar de; Blázquez, Sandra
Titanium-containing SBA-15 material has been agglomerated with bentonite clay to form macroscopic structured catalyst particles with the purpose of being used in continuous epoxidation processes on a fixed bed reactor. The binding conditions, the mass ratio catalyst to binding agent as well as the calcination temperature of the material were studied to improve as much as possible the catalytic behavior and mechanical strength of the titanium-based catalyst. The binded material has been finally tested in the liquid epoxidation of 1-octene with ethyl benzyl hydroperoxide in a continuous up-flow fixed bed reactor. Reaction results reveal a better catalytic performance of this catalyst, both regarding to the conversion of the olefin and efficient use of the oxidant, than conventional commercially available TiO2-SiO2, specially when pellet surface hydrophobization is performed by silylation treatment.
Aldol condensation of furfural and methyl isobutyl ketone over Zr-MOF-808/silica hybrid catalysts
(Elsevier, 2023) Morales, Gabriel; Paniagua, Marta; Flor, Daniel de la; Sanz, María; Leo, Pedro; López-Aguado, Clara; Hernando, Héctor; Orr, Samantha A.; Wilson, Karen; Lee, Adam F.; Melero, Juan A.
Mesoporous silica-supported Zr-MOF-808 catalysts have been synthesised and tested in the aldol condensation of (biomass-derived) furfural and methyl isobutyl ketone to bio-jet fuel precursors. Growth of Zr-MOF-808 nanocrystals over silica scaffolds results in well-dispersed Zr species which confer strong Lewis acidity as determined by FTIR of chemisorbed pyridine. Hybrid Zr-MOF-808/silica materials exhibit higher condensation activity than the unsupported crystalline Zr-MOF-808 (which is also prone to rapid deactivation). Textural properties of the silica support strongly influence the catalytic performance, with a high surface area and sufficiently large mesopore desirable. In the screening, the optimum Zr-MOF-808/MCM-41 catalyst delivered 68 % furfural conversion and 90 % selectivity to the C11 aldol adduct, 1-(furan-2-yl)-5-methylhex-1-en-3-one, at 130 ◦C and a furfural:Zr mass ratio of 150:1. Although more stable than the pure Zr-MOF-808, the Zr-MOF-808/MCM-41 also suffered significant deactivation over successive condensation reactions due to strongly adsorbed organic residues, however this was largely ameliorated by decreasing the furfural:Zr ratio to 75:1, which also led to an outstanding catalytic performance (100 % furfural conversion and adduct selectivity), likely because of the suppression of furfural polymerization.
Aqueous-sensitive reaction sites in sulfonic acid-functionalized mesoporous silicas
(ELSEVIER, 2008) Morales, Gabriel; Athens, George; Chmelka, Bradley F.; van Grieken, Rafael; Melero, Juan A.
Local differences in surface hydrophilicities/hydrophobicities of propyl- and arene-sulfonic-acid modified mesoporous silica and organosilica catalysts have been compared and correlated with their bulk catalytic properties for aqueous-sensitive organic reactions. Syntheses of propyl- and arene-SO3H-modified mesoporous silicas and organosilicas yield materials with different hydrophilicities, especially when ethylsiloxane moieties are incorporated into the silica frameworks. Solid-state two-dimensional (2D) 13C{1H} and 29Si{1H} heteronuclear correlation (HETCOR) NMR spectra prove that the incorporation of hydrophobic ethylsiloxane groups into functionalized mesoporous silica frameworks result in reduced interactions of adsorbed water with the silica framework in general and, importantly, in the immediate vicinities of the SO3H active sites. The hydrophilic/hydrophobic character of the surface, as well as the active site properties depend on the functional species attached. Propyl-sulfonic acid moieties are less acidic but more hydrophobic than arene-SO3H species, leading to superior overall activities for water-mediated acid-catalyzed organic reactions. The etherification of vanillyl alcohol (4-hydroxy-3-methoxybenzylalcohol) with 1-hexanol to yield 4-hydroxy-3-methoxybenzyl-1-hexyl ether is shown to proceed significantly more effectively on SO3H-modified mesoporous organosilicas, compared to wholly siliceous mesoporous supports. The correlation of macroscopic adsorption and reaction results with 2D NMR measurements allows the hydrophilic/hydrophobic surface properties of the mesoporous support to be optimized with respect to water-retention capacities and activities for water-sensitive organic reactions.
Beta zeolite as an efficient catalyst for the synthesis of diphenolic acid (DPA) from renewable levulinic acid
(Elsevier, 2022) Morales, Gabriel; Melero, Juan A.; Paniagua, Marta; López-Aguado, Clara; Vidal, Nora
The solvent-free production of diphenolic acid (DPA) from levulinic acid (LA) and phenol is studied using readily accessible commercial acid zeolites like Beta, ZSM-5 and USY. Acid zeolites are cost-effective catalysts, and they are herein benchmarked against the sulfonic acid resins Amberlyst-15 and Nafion®, and sulfonic acidfunctionalized SBA-15 silicas. Beta zeolite with a moderate aluminum content (H-Beta 19, Si/Al=23) presents the best catalytic performance, owing to the right combination of the shape selectivity effect conferred by the BEA structure, and the adequate balance of acidity (Al content and speciation). The optimization of the reaction conditions is tackled by the response surface methodology using as optimization factors the temperature, the PhOH:LA molar ratio, and the catalyst loading. Thus, under the optimized reaction conditions (12 mmol LA, 140 ᵒC, 0.30 g catalyst loading, PhOH:LA = 6:1 mol), over 70% yield to DPA with LA conversion around 77% is obtained after 72 h. Despite the catalyst shows a progressive activity decay in successive uses because of fouling, removal of the formed organic deposits by calcination in air allows restoring the starting catalytic performance.
Biodiesel production from crude palm oil using sulfonic acid-modified mesostructured catalysts
(ELSEVIER, 2010) Melero, Juan A.; Bautista, L. Fernando; Morales, Gabriel; Iglesias, Jose; Sánchez-Vázquez, Rebeca
Biodiesel production from crude palm oil containing high percentage of free fatty acids over sulfonic acid-functionalized SBA-15 materials (propyl-SO3H, arene-SO3H, perfluoro-SO3H) has been studied. The catalytic results showed that sulfonic acid-modified mesostructured materials were more active than conventional ion-exchange sulfonic resins (Amberlyst-36 and SAC-13) in the simultaneous esterification of free fatty acids and transesterification of triglycerides with methanol. The reusability of the catalysts was also investigated showing high stability for propyl-SO3H and arene-SO3H-modified mesostructured materials. In contrast, ionic exchange sulfonic acid resins displayed low conversion rates, being stronger this decay of activity in the second consecutive catalytic run. Interestingly, perfluorosulfonic acid-functionalized SBA-15 sample yielded a dramatic loss of activity indicating that Si-O-C bonding is not stable under the reaction conditions as compared with Si-C bond present in propyl-SO3H and arene-SO3H catalysts. Further functionalization of arene-SO3H SBA-15 catalyst with hydrophobic trimethylsilyl groups enhanced its catalytic performance. This material was able to produce a yield to FAME of ca. 95 % as determined by 1H NMR in four hours of reaction with a moderate methanol to oil molar ratio (20:1), 140 ºC and a catalyst concentration of 6 wt% referred to starting oil.
Boosting the activity of UiO-66(Zr) by defect engineering: efficient aldol condensation of furfural and MIBK for the production of bio jet-fuel precursors
(Royal Society of Chemistry, 2024-05-30) Sanz, María; Leo, Pedro; Palomino, Carlos; Paniagua, Marta; Morales, Gabriel; Melero, Juan A.
The production of jet-fuel precursors from furfural via aldol-condensation with methyl-isobutyl ketone (MIBK) over defect-engineered UiO-66(Zr) catalysts is presented. The catalysts are prepared using formic acid (FA), trifluoroacetic acid (TFA) and HCl as synthesis modulators, leading to the incorporation of defects on the microcrystalline structure of the metalorganic framework (MOF) material, which dramatically boosts the catalytic performance. An extensive characterization of the modified catalysts by means of X-ray diffraction (XRD), argon adsorption isotherm, thermogravimetry (TGA), transmission electron microscopy, and FTIR spectroscopy of adsorbed acetonitrile, confirmed the incorporation of missing-linker and missing-node defects within the MOF structure, enabling the explanation of the enhancement in the catalytic process. The analysis of the reaction kinetics evidences that, working under moderate temperature conditions, conversion of furfural and selectivity to the desired adduct (FuMe) close to 100% can be achieved, avoiding the formation of degradation and bulkier compounds. Finally, despite the generation of defects within the UiO-66(Zr) structure, the resultant catalyst displays good reusability in low furfural concentration mediums.
Continuous production of biodiesel from low grade feedstock in presence of Zr-SBA-15: Catalyst performance and resistance against deactivation
(Elsevier, 2014) Iglesias, Jose; Melero, Juan A.; Bautista, L. Fernando; Morales, Gabriel; Sánchez-Vázquez, Rebeca
Zirconium-containing SBA-15 materials have been used in the production of fatty acid methyl esters from low grade oleaginous feedstock. Its resistance against deactivation has been assessed by means of studying the effect of conventional impurities present in lipid wastes over the catalytic performance of this material. Alkaline metal cations like potassium could interact with Brønsted acid sites, causing their neutralization by ion exchange and a limited, but not complete, deactivation of the material. Additionally, organic unsaponifiable compounds like retinoids or phospholipids - being studied in this work as retinol and lecithin, respectively - strongly interact with the catalyst surface, leading to a strong deactivation of the material, though reversible, since they are fully regenerated by calcination in air. Catalytic assays in continuous mode in a fixed bed reactor suggest a higher resistance of Zr-SBA-15/bentonite pellets against catalyst deactivation. Bentonite clay, which has been used as binding agent for the preparation of the particulate catalyst, seems to be responsible for this behavior, acting as poison scavenger and preventing the access of the impurities to the catalytic acid sites and consequently their deactivation.
Dehydration of C6-monosaccharides to 5-hydroxymethylfurfural in dimethyl sulfoxide using sulfonic acid heterogeneous catalysts
(Elsevier, 2014) Morales, Gabriel; Melero, Juan A.; Paniagua, Marta; Iglesias, Jose; Hernández, Blanca; Sanz, María
The use of sulfonic acid-functionalized heterogeneous catalysts in conjunction with the use of dimethyl sulfoxide (DMSO) as solvent in the catalytic dehydration of C6 monosaccharides into 5-hydroxymethylfurfural (HMF) has been shown as an interesting alternative route for the production of this platform molecule. Amberlyst-70 was selected as the most active catalyst, ascribing its higher catalytic performance to its higher concentration of sulfonic acid sites, as compared with the rest of the evaluated catalysts. Starting from fructose, the use of Amberlyst-70 led to 93 mol% yield to HMF after just 1h. For glucose, a much more difficult reaction, reaction conditions (time, temperature and catalyst loading) where optimized for Amberlyst-70 via response surface methodology leading to a maximum HMF yield of 33 mol% at 147ºC, 23 wt% catalyst loading based on glucose loading and 24h. Noticeably, DMSO promotes the dehydration of glucose into anhydroglucose, which acts as a reservoir of substrate facilitating the production of HMF, since it reduces the extent of side-reactions. A study of catalyst¿s reuse, without regeneration treatment, evidenced a gradual decay in catalytic activity, though not very significant.
Direct synthesis of organically modified Ti-SBA-15 materials
(ELSEVIER, 2008) Iglesias, Jose; Melero, Juan A.; Sainz-Pardo, Javier
Organically-modified Ti-SBA-15 materials have been prepared through a direct synthesis procedure based on the co-condensation of tetraethyl orthosilicate (TEOS), alkyltriethoxysilanes (R-TES) and titanocene dichloride as silicon, organic species and titanium sources respectively. The prehydrolysis time for the TEOS and the amount and type of alkyl functionality were studied in order to achieve mesostructured organic-modified Ti-SBA-15 materials. The synthesized samples were assayed in the catalytic epoxidation of 1-octene with TBHP as oxidant. The catalytic results reveal a direct correlation between the activity of the catalyst per titanium site and the length of the alkyl chain. Higher lengths of the alkyl chain induce a significant increase of the activity of the titanium sites due to the enhancement of their hydrophobic microenvironment. Likewise, improved efficiency in the use of the oxidant has also been observed when using organic modified Ti-SBA-15 materials, being correlated this effect with the reduction of the non-oxidative decomposition of TBHP. Finally, the reutilisation tests indicate very high stability of the prepared catalysts in epoxidation reactions with TBHP.
Direct synthesis of titanium substituted mesostructured materials using non-ionic surfactants and titanocene dichloride
(2005) Melero, Juan A.; Arsuaga, Jesús M.; Frutos, Pilar de; Iglesias, José; Sainz, Javier; Blázquez, Sandra
Titanium-substituted mesoporous molecular sieves have been successfully synthesized using non-ionic surfactants and titanocene dichloride under strong acidic conditions. Structure-textural parameters of the synthesized materials were characterized by using X-ray diffraction and nitrogen adsorption techniques. The increasing of the gel solution pH allows an enhancement of titanium within the mesostructure without damage of textural properties and presence of extra-framework species. The high accessibility and dispersion of titanium centres has been proved by means of NH3 adsorption and DR UV-Vis spectroscopy, being compared with TS-1 material. The synthesized materials show high activity and selectivity in the selective epoxidation of 1-octene with ethylbenzylhydroperoxide as oxidant. Moreover, silylated samples promoted an increase of epoxide selectivity.
Effect of the solvent in the liquid phase rearrangement of 1,2-epoxyoctante over Al-MCM-41 and Al-TS-1 catalysts
(ELSEVIER, 2004) van Grieken, Rafael; Serrano, David P.; Melero, Juan A.; García, Alicia
The role of solvent nature in the liquid phase rearrangement of 1,2-epoxyoctane over Al-TS-1 and Al-MCM-41 catalysts is reported. The main reaction product is the aldehyde, while other rearrangement products, mainly allylic alcohols and diol, are obtained. The solvent polarity influences strongly on the activity and product selectivity. The catalytic activity decreases with the increasing of solvent polarity especially for Al-MCM-41 materials. The use of acetonitrile as solvent yields a low conversion of epoxide as a consequence of its basic character. Formation of bulky by-products was detected when dimethylcarbonate was used as solvent over Al-MCM-41. Toluene displays the best catalytic performance in regards to activity and selectivity towards valuable products, with both Al-TS-1 and Al-MCM-41 catalysts, in comparison to those obtained with more polar solvents.
Efficient Self-Condensation of Cyclohexanone into Biojet Fuel Precursors over Sulfonic Acid-Modified Silicas: Insights on the Effect of Pore Size and Structure
(ACS, 2024) Martín, Antonio; Arribas-Yuste, Esther; Paniagua, Marta; Morales, Gabriel; Melero, Juan A.
Mesoporous silica materials with different pore structures and sizes have been used for supporting aryl sulfonic acid catalytic sites via a postsynthetic grafting approach. The synthesized materials have been evaluated in the solventless acid-catalyzed self-condensation of cyclohexanone (CHO) to obtain the corresponding C12 adducts. These compounds display great potential as oxygenated fuel precursors as they can be transformed into jet fuel range alkanes in a subsequent hydrodeoxygenation process. In this work, the synthesized catalysts have displayed high selectivity values toward monocondensed compounds (>95%), thus limiting the formation of undesired heavier condensation products, together with CHO conversion values in the range 20–40% after 2 h of reaction at 100 °C. The structural and textural properties of the supports play an important role in the catalytic performance. Moreover, the activity per acid center is correlated with the textural properties of the supports, indicating that a lower surface density of the anchored aryl sulfonic groups affords an improvement in their specific activity. Finally, the benefit of using supports with large pore sizes and open structures, which limit the fouling of the catalysts by organic deposits, is demonstrated in a stability and reusability test.
Friedel Crafts acylation of aromatic compounds over arenesulfonic containing mesostructured SBA-15 materials
(ELSEVIER, 2004) Melero, Juan A.; van Grieken, Rafael; Morales, Gabriel; Nuño, Vanesa
Arenesulfonic modified mesostructured SBA-15 is shown as an active catalyst for acylation of aromatic compounds using acetic anhydride as acylating agent. The arenesulfonic acid-centers located within the mesostructured SBA-15 show a greater reaction rate (normalised on the concentration of sulfonic groups) as compared to other sulfonated catalysts and even in solventless conditions. This high activity is accompanied with a remarkable stability without leaching of sulphur species during the reaction. Moreover, an increase of the amount of acid centres does not modify the activity of the material per acid center. Thus, this work introduces a new application of these sulfonated mesostructured materials, not described in literature up to now, and in an important organic reaction.
Fries rearrangement of phenyl acetate over sulfonic modified mesostructured SBA-15 materials
(ELSEVIER, 2005) van Grieken, Rafael; Melero, Juan A.; Morales, Gabriel
Arenesulfonic modified mesostructured SBA-15 is shown as an active catalyst in the liquid-phase Fries rearrangement of phenyl acetate. The arenesulfonic acid-centers located within the structure of SBA-15 show high catalytic performance as compared to other homogeneous and heterogeneous acid catalysts. This high activity is accompanied with a remarkable stability without leaching of sulphur species during the reaction. Reaction conditions have been investigated in order to optimize production of hydroxyacetophenones. Strong adsorption of reaction products and/or coke deposition on the sulfonic acid sites rapidly deactivates the catalyst. Interestingly, when dichloromethane is used as solvent the deactivation process is slowed down drastically. Finally, this contribution supports a new application of these sulfonated mesostructured materials in the production of fine chemicals.
Highly Ti-loaded MCM-41: Effect of the metal precursor and loading on the titanium distribution and on the catalytic activity in different oxidation processes
(ELSEVIER, 2010) Iglesias, Jose; Melero, Juan A.; Sanchez-Sanchez, Manuel
Ti-MCM-41 materials have been prepared by co-condensation of tetraethylorthosilicate with two different titanium sources: titanocene dichloride and titanium isopropoxide. The hydrophobic nature of cyclopentadienyl rings has been used to enhance the interaction between the titanocene dichloride starting compound and the surfactant micelles leading to, after calcination, titanium centers finally located in the surface of the mesopores. In this way, increasing the content of titanocene dichloride in the synthesis gel causes the formation of titanium dioxide nanofibers inside the mesoporous system ¿ clearly visible by TEM analysis ¿ for high metal loadings. Such Ti distribution, which has not been observed when using titanium isopropoxide, confers to these Ti-MCM-41 materials a different catalytic behavior to that of conventional Ti-MCM-41 materials for a given Ti content. Thus, samples prepared with titanocene dichloride display higher catalytic activity in the epoxidation of 1-octene and in the oxidative bromination of phenol red than samples prepared with titanium isopropoxide. Besides, in both reactions, the maximum of catalytic activity is reached for lower titanium loading when titanocene dichloride is the starting Ti source as a consequence of a better accessibility of reactants to the final Ti centres.
Insights into the influence of feed impurities on catalytic performance in the solvent-free dimerization of renewable levulinic acid
(Elsevier, 2023) Paniagua, Marta; Morales, Gabriel; Melero, Juan A.; García-Salgado, Daniel
Bio-jet fuel precursors can be produced from the solvent-free aldol dimerization of levulinic acid. The influence of the most common impurities accompanying the levulinic acid produced in lignocellulosic biorefineries (sulfuric acid, water, formic acid, and furfural) has been studied on the catalytic performance of different kinds of heterogeneous acid catalysts: (i) sulfonic acid-based materials, such as propyl-sulfonic acid-modified SBA-15, and the sulfonic acid resin Amberlyst-70, and (ii) commercial acid zeolites, such as H-Beta-19 and H-Beta-75. Furfural is the impurity that produces the greatest detrimental effect on the performances of all the catalysts tested. Catalyst deactivation is observed due to the formation of organic deposits on the catalyst surface (identified by TGA and acid-base titration), phenomenon that is accentuated when furfural is present in the reaction medium. Amberlyst-70 can recover almost totally the initial catalytic activity with a regeneration step based on washing with an acid solution under reflux. For Beta zeolites, the original activity of the catalyst can be easily and totally recovered through a regeneration process by calcination. H-Beta-19 zeolite is shown as the most suitable catalyst for the aldol dimerization of renewable LA, as its activity is not significantly affected by the presence of most of the impurities in the levels herein analyzed. In addition, a simultaneous mixture of all the impurities produces a synergistic effect, even improving the initial activity of the H-Beta-19 zeolite as a consequence of the sulfuric acid contribution to the catalytic effect.
Liquid phase isophorone oxide rearrangement over mesoporous Al-MCM-41 materials
(ELSEVIER, 2005) van Grieken, Rafael; Serrano, David P.; Melero, Juan A.; García, Alicia
The rearrangement of isophorone oxide has been investigated over Al-MCM-41 type mesostructured catalysts having different Si/Al molar ratios. The main rearrangement products are the ¿-diketone and the keto aldehyde, whereas the product coming from the decarbonylation of the latter is detected in minor amounts. The textural properties and the number of acid sites of Al-MCM-41 materials influence the extent of isophorone oxide rearrangement reaction. The best catalytic performance in regards to epoxide conversion is obtained for a catalyst having a molar Si/Al ratio around 40 due to a right contribution of acid site concentration and pore size. However, irrespective to the aluminium content of the catalysts and the reaction temperature, the selectivity to the desired keto aldehyde was around 80%. Al-MCM-41 materials are superior catalysts compared to zeolites in terms of both activity and aldehyde selectivity. As a consequence of its large pore size, the use of Al-containing mesostructured materials as catalyst in isophorone oxide rearrangement allows the diffusional problems present in zeolites to be avoided.
Nanocomposite of crystalline Fe2O3 and CuO particles and mesostructured SBA-15 silica as an active catalyst for wet peroxide oxidation processes
(ELSEVIER, 2006) Melero, Juan A.; Calleja, Guillermo; Martinez, Fernando; Molina, Raul
Crystalline Fe2O3 and CuO particles have been incorporated into surfactant-templated SBA-15 materials by direct synthesis. Activity and stability of this material were evaluated on the wet peroxide oxidation of phenol under mild reaction conditions. Its catalytic performance was monitored in terms of total organic carbon (TOC) conversion. The stability was determined by careful measurements of metal leaching into the aqueous solution. The presence of copper prevents the leaching of iron species and increases TOC degradation as compared with those materials containing only crystalline Fe2O3 particles. Moreover, the treatment of iron-copper composite materials under controlled acidic conditions in the presence of hydrogen peroxide leads to the stabilization of metallic species, maintaining TOC degradation rates similar to the fresh catalyst. Thus, this work introduces a new material with interesting properties as Fenton-like catalysts in advanced oxidation processes for pollutant abatement in wastewaters.