Search

Rice straw is an agricultural byproduct primarily produced in Asian regions. It is crucial to discover an effective method for converting this waste into chemicals that can be utilized to substitute goods derived from fossil fuels. Pyrolysis serves as an interesting procedure to obtain bio-oil from this rice straw. The composition of the bio-oil obtained after the pyrolysis procedure contains a small quantity of value-added chemicals in addition to various gas components in the gas product. Therefore, the development of catalytic systems that improve this pyrolytic reaction is mandatory. Herein, the design of a dual catalyst bed (CEM/ZSM-5) that catalyzes the volatiles that it releases has been developed. The highest output of 42.1 wt.% of bio-oil, 29.9 wt.% of gases and 28.0 wt.% of bio-char was obtained. Nevertheless, the inclusion of single zeolites to biomass yields biofuel outputs of 42.8 wt.%, gas yields of 27.7 wt.%, and a bio-char yielding of 29.5 wt.%. Additionally, the addition of cement to biomass results in a bio-oil yield of 40.4 wt.% and 30.5 wt.% of gas, along with 29.1 wt.% of char. Regarding pyrolysis gas products, the H2 yield in the produced biogas was increased from 35.9 mL/g to 45.7 mL/g, and the CH4 output was increased from 21.1 mL/g to 27.4 mL/g. The bioenergy output was evaluated employing GC-FID and GC-MS (gas and biofuel). The dual catalytic bed had a significant impact on the contents of the generated biofuel, increasing the quantity of hydrocarbons and other value-added compounds.

Premio extraordinario de Trabajo Fin de Máster curso 2018/2019. Máster en Profesorado de Enseñanza Secundaria Obligatoria, Bachillerato, Formación Profesional y Enseñanza de Idiomas

A new heterogenous catalyst has been synthesized by immobilization of a copper complex on dipyridyl-pyridazine functionalized periodic mesoporous organosilica (dppz-vPMO). This ordered support was firstly prepared by a co-condensation reaction between vinyltriethoxysilane and 1,2-bis(trimethoxysilyl)ethane and further post-functionalized through a hetero Diels-Alder reaction with 3,6-di-2-pyridyl-1,2,4,5-tetrazine. Techniques such as XRD, N2 isotherms, TEM, 13C NMR, XPS and DRIFT, among others, were employed to characterize the surface functionalized materials. These results have proven the ordered mesostructure of the materials as well as the presence of novel nitrogen-chelating heterocyclic compounds in the pore surface after the post-modification process. Additionally, it has been confirmed the successful anchoring of a copper complex on the dipyridyl-pyridazine (dppz) ligands. The resulting material was evaluated as heterogenous catalyst in the epoxidation of styrene using tert-butylhydroperoxide (TBHP) as oxidant. Under optimized reaction conditions, Cu@dppz-vPMO showed a high styrene conversion (86.0 %) and a remarkable selectivity to styrene oxide (41.9 %). Indeed, this catalyst provided excellent catalytic results in terms of stability, reaction rate, conversion and selectivity compared to other bipyridine-like copper catalysts.

La presente Tesis Doctoral aborda la síntesis, funcionalización, caracterización y aplicaciones de una extensa variedad de materiales híbridos orgánico-inorgánicos. Los resultados obtenidos en esta investigación han sido clasificados en tres secciones atendiendo a la naturaleza híbrida del material diseñado: • Sección 1: Polímeros de coordinación-Metal Organic Frameworks (MOFs): ▪ En el artículo “Zirconium coordination polymers based on tartaric and malic acids as catalysts for cyanosilylation reactions” se han sintetizado polímeros de coordinación que contienen zirconio como nodo metálico y ligandos orgánicos procedentes de productos naturales sencillos que contienen centros quirales como son el ácido L-málico, L-tartárico y dibenzoil-L-tartárico. Los materiales fueron preparados en autoclave bajo presión autógena o en reactor tipo batch bajo presión atmosférica. Tras ser caracterizados por diferentes técnicas, se han evaluado como catalizadores heterogéneos quirales en la reacción asimétrica de cianosililación del benzaldehído con cianuro de trimetilsililo dando como resultado la formación de cianohidrinas. La actividad catalítica en términos de conversión y enantioselectividad fue determinada estudiando el efecto de diferentes variables de reacción como la temperatura, el disolvente, la adición de promotores o el sustrato empleado. ▪ En el artículo “Fast ultrasound-assisted synthesis of highly crystalline MIL-88A particles and their application as ethylene adsorbents” se han sintetizado partículas altamente cristalinas del MOF MIL-88A compuesto por trímeros de octaedros de hierro (III) interconectados a través de dianiones fumarato mediante una metodología rápida asistida por ultrasonidos. La influencia del generador de sonicación y el tiempo de síntesis en la estructura, cristalinidad, morfología y el área superficial fue estudiada detalladamente. Además, los materiales preparados han sido aplicados en procesos de adsorción de etileno. Estos resultados fueron comparados con los obtenidos por otros MOFs comunes ampliamente reportados en literatura. ▪ El artículo “MIL-88A Metal-Organic Framework as a stable sulfur-host cathode for long-cycle Li-S batteries” estuvo en consonancia con el trabajo anterior. Aprovechando las propiedades texturales y morfológicas de las partículas MIL-88A sintetizadas mediante el método de sonda asistida por ultrasonidos en un corto tiempo de 10 minutos, este material fue empleado como anfitrión para la impregnación de azufre con objeto de ser usado como componente catódico en baterías Litio Azufre (Li-S), uno de los sistemas más avanzados de almacenamiento de energía. Además, la estabilidad del sistema electroquímico resultante fue evaluada llevando a cabo experimentos de ciclabilidad a tiempos prolongados. • Sección 2: Materiales híbridos orgánico-inorgánicos basados en sílice-Periodic Mesoporous Organosilicas (PMOs): ▪ El artículo “Catalytic systems mimicking the [FeFe]- hydrogenase active site for visible-light-driven hydrogen production” consistió en una revisión exhaustiva que abordó el campo de la química biomimética de los sistemas catalíticos que imitan el sitio activo de [FeFe]-hidrogenasa aplicados en la producción de hidrógeno dirigida por luz. Los diferentes sistemas fotocatalíticos fueron clasificados por grupos en orden de complejidad creciente y por su desarrollo cronológico: catalizadores moleculares [2Fe2S], díadas de fotosensibilizador - [FeFe]-hidrogenasa, tríadas de donador de electrones - fotosensibilizador - [FeFe]-hidrogenasa, entidades supramoleculares, conjuntos de semiconductores híbridos, soportes heterogéneos y fotocátodos basados en [2Fe2S] para dispositivos fotoelectroquímicos (PEC). ▪ El artículo de revisión citado anteriormente sirvió para llevar a cabo el trabajo “Hydroxyl-decorated diiron complex as a [FeFe]-hydrogenase active site model complex: Light-driven photocatalytic activity and heterogenization on ethylene-bridged periodic mesoporous organosilica” en que un complejo modelo biomimético del sitio activo de [FeFe]-hidrogenasa (FeFeOH) con un puente de etileno y un grupo hidroxilo colgante fue sintetizado y caracterizado detalladamente. La interacción del grupo hidroxilo presente en el complejo con 3- isocianatopropiltrietoxisilano proporcionó un carbamato trietoxisilano portador de un complejo ditiolato de dihierro (NCOFeFe), convirtiéndose así en un precursor potencialmente prometedor para su anclaje sobre soportes heterogéneos. A continuación, el precursor NCOFeFe fue incorporado mediante un procedimiento de “grafting” en una organosílice periódica mesoporosa con puentes etano (EthanePMO@NCOFeFe). Adicionalmente, tanto los complejos moleculares como los heterogeneizados se evaluaron como catalizadores para la generación de hidrógeno en solución acuosa impulsada por la luz, optimizando todas las condiciones fotocatalíticas: tiempo de reacción, pH, cantidad de catalizador o fotosensibilizador, flujo de fotones y tipo de fuente de luz (LED y lámpara Xe). • Sección 3: Materiales híbridos basados en grafeno: ▪ En el artículo “A comparative study of particle size distribution of graphene nanosheets synthesized by an ultrasound-assisted method” se han preparado nanoláminas de grafeno (GNS) mediante la exfoliación de un micrografito comercial (MG) utilizando una sonda de ultrasonido. La caracterización estructural, superficial y morfológica fue realizada por difracción de rayos X (DRX), espectroscopia Raman, espectroscopia de fotoelectrones de rayos X (XPS) y microscopía electrónica de transmisión (TEM). Un estudio exhaustivo de la distribución del tamaño de partícula se llevó a cabo mediante diferentes técnicas analíticas como la dispersión de luz dinámica (DLS), análisis de seguimiento de nanopartículas (NTA) y fraccionamiento en flujo mediante campo de flujo asimétrico (AF4). ▪ En el artículo “Luminescent graphene-based materials via europium complexation on dipyridylpyridazine-functionalized graphene sheets” se sintetizaron materiales híbridos basados en grafeno mediante reacciones Diels-Alder entre grafito (dienófilo) y la molécula orgánica 3,6-di(2-piridil)-1,2,4,5-tetrazina (dieno). Se obtuvieron grafeno de pocas capas (FLG), grafeno multicapa (MLG) y grafito (MG) funcionalizados con unidades de dipiridilpiridazina dependiendo de la metodología de síntesis aplicada. Los aductos superficiales de dipiridilpiridazina generados en las láminas de grafeno han sido empleados para la formación de complejos de europio, como ejemplos de iones lantánidos emisores en el visible. ▪ En el artículo “Surface Diels-Alder adducts on multilayer graphene for the generation of edge-enriched single-atom FeN4 sites for ORR and OER electrocatalysis” se propone una nueva síntesis mecanoquímica a baja temperatura y sin disolventes basada en el uso de grafeno multicapa funcionalizado con dipiridilpiridazina como material de partida para la generación de sitios activos de tipo FeN4. Después de una caracterización exhaustiva, estos materiales fueron aplicados como electrocatalizadores bifuncionales para reacciones electroquímicas de reducción de oxígeno (ORR) y evolución de oxígeno (OER). This Doctoral Thesis deals with the synthesis, functionalization, characterization, and applications of a wide variety of organic-inorganic hybrid materials. The results obtained in this research have been divided into three sections according to the hybrid nature of the designed material: • Section 1: Coordination Polymers-Metal Organic Frameworks (MOFs): ▪ In the article “Zirconium coordination polymers based on tartaric and malic acids as catalysts for cyanosilylation reactions”, coordination polymers containing zirconium as a metallic node and organic ligands from simple natural products containing chiral centers such as L-malic, L-tartaric and dibenzoyl-L-tartaric acids, have been synthesized. The materials were prepared in an autoclave under autogenous pressure or in a batch type reactor under atmospheric pressure. After being characterized by different techniques, they have been evaluated as chiral heterogeneous catalysts in the asymmetric cyanosilylation reaction of benzaldehyde with trimethylsilyl cyanide, resulting in the formation of cyanohydrins. The catalytic activity in terms of conversion and enantioselectivity was determined by studying the effect of different reaction parameters such as temperature, solvent, the addition of promoters or the substrate used. ▪ In the article “Fast ultrasound-assisted synthesis of highly crystalline MIL-88A particles and their application as ethylene adsorbents”, highly crystalline particles of the MOF MIL-88A composed of trimers of iron (III) octahedrons interconnected through fumarate dianions have been synthesized by a fast ultrasound-assisted methodology. The influence of the sonication generator and the synthesis time on the structure, crystallinity, morphology and surface area was studied in detail. In addition, the prepared materials have been applied in ethylene adsorption processes. These results were compared with those obtained by other common MOFs widely reported in the literature. ▪ The article “MIL-88A Metal-Organic Framework as a stable sulfur-host cathode for long-cycle Li-S batteries” was consistent with the previous work. Taking advantage of the textural and morphological properties of the MIL-88A particles synthesized by the ultrasound-assisted probe method in a short time of 10 minutes, this material was used as a sulfur host to be applied as a cathode component in Lithium-Sulfur (Li-S) batteries, one of the most advanced energy storage systems. In addition, the stability of the resulting electrochemical system was evaluated by carrying out long-term cyclability experiments. • Section 2: Silica-based organic-inorganic hybrid materials-Periodic Mesoporous Organosilicas (PMOs): ▪ The article “Catalytic systems mimicking the [FeFe]- hydrogenase active site for visible-light-driven hydrogen production” was an exhaustive review that addressed the field of biomimetic chemistry of catalytic systems mimicking the active site of [FeFe]-hydrogenase applied in the light-driven hydrogen production. The different photocatalytic systems were classified by groups in order of increasing complexity and by their chronological development: [2Fe2S] molecular catalysts, photosensitizer-[FeFe]-hydrogenase dyads, electron donor photosensitizer-[FeFe]-hydrogenase triads, supramolecular entities, hybrid semiconductor arrays, heterogeneous supports and [2Fe2S]-based photocathodes for photoelectrochemical (PEC) devices. ▪ The review article cited above served to carry out the work “Hydroxyl-decorated diiron complex as a [FeFe]-hydrogenase active site model complex: Light-driven photocatalytic activity and heterogenization on ethylene-bridged periodic mesoporous organosilica” in which a biomimetic model complex for the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group was synthesized and characterized in detail. The reaction of the hydroxyl group present in the complex with 3-isocyanatopropyltriethoxysilane provided a triethoxysilane carbamate bearing a complex diiron dithiolate (NCOFeFe), thus becoming a potentially promising precursor for its anchoring on heterogeneous supports. Next, the precursor NCOFeFe was incorporated by a "grafting" procedure in a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Additionally, both molecular and heterogenized complexes were evaluated as catalysts for hydrogen evolution reactions in aqueous solution assisted by visible light, optimizing all the photocatalytic conditions: reaction time, pH, amount of catalyst or photosensitizer, photon flux and light source (LED and Xe lamp). • Section 3: Graphene-based hybrid materials: ▪ In the article “A comparative study of particle size distribution of graphene nanosheets synthesized by an ultrasound-assisted method”, graphene nanosheets (GNS) have been prepared by exfoliating a commercial micrographite (MG) using an ultrasound probe. Structural, surface, and morphological characterization was performed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). An exhaustive study of the particle size distribution was carried out using different analytical techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and asymmetrical flow field - flow fractionation (AF4). ▪ In the article “Luminescent graphene-based materials via europium complexation on dipyridylpyridazine-functionalized graphene sheets”, graphene-based hybrid materials were synthesized by Diels-Alder reactions between graphite (dienophile) and the organic molecule 3,6-di(2-pyridyl)- 1,2,4,5- tetrazine (diene). Few layer graphene (FLG), multilayer graphene (MLG) and graphite (MG) functionalized with dipyridylpyridazine units were obtained depending on the synthesis methodology applied. Surface adducts of dipyridylpyridazine generated in graphene sheets have been used for the formation of europium complexes, as examples of emitting lanthanide ions in the visible. ▪ The article “Surface Diels-Alder adducts on multilayer graphene for the generation of edge-enriched single-atom FeN4 sites for ORR and OER electrocatalysis” proposes a new mechanochemical synthesis at low temperature and without solvents based on the use of multilayer graphene functionalized with dipyridylpyridazine as starting material for the generation of FeN4-type active sites. After extensive characterization, these materials were applied as bifunctional electrocatalysts for electrochemical oxygen reduction (ORR) and oxygen evolution (OER) reactions.