Nanostructured catalysts for the development of the hydrogen economy

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2015-2016La catalyse joue un rôle essentiel dans de nombreuses applications industrielles telles que les industries pétrochimique et biochimique, ainsi que dans la production de polymères et pour la protection de l'environnement. La conception et la fabrication de catalyseurs efficaces et rentables est une étape importante pour résoudre un certain nombre de problèmes des nouvelles technologies de conversion chimique et de stockage de l'énergie. L'objectif de cette thèse est le développement de voies de synthèse efficaces et simples pour fabriquer des catalyseurs performants à base de métaux non nobles et d'examiner les aspects fondamentaux concernant la relation entre structure/composition et performance catalytique, notamment dans des processus liés à la production et au stockage de l'hydrogène. Dans un premier temps, une série d'oxydes métalliques mixtes (Cu/CeO2, CuFe/CeO2, CuCo/CeO2, CuFe2O4, NiFe2O4) nanostructurés et poreux ont été synthétisés grâce à une méthode améliorée de nanocasting. Les matériaux Cu/CeO2 obtenus, dont la composition et la structure poreuse peuvent être contrôlées, ont ensuite été testés pour l’oxydation préférentielle du CO dans un flux d'hydrogène dans le but d’obtenir un combustible hydrogène de haute pureté. Les catalyseurs synthétisés présentent une activité et une sélectivité élevées lors de l'oxydation sélective du CO en CO2. Concernant la question du stockage d'hydrogène, une voie de synthèse a été trouvée pour le composét mixte CuO-NiO, démontrant une excellente performance catalytique comparable aux catalyseurs à base de métaux nobles pour la production d'hydrogène à partir de l'ammoniaborane (aussi appelé borazane). L'activité catalytique du catalyseur étudié dans cette réaction est fortement influencée par la nature des précurseurs métalliques, la composition et la température de traitement thermique utilisées pour la préparation du catalyseur. Enfin, des catalyseurs de Cu-Ni supportés sur silice colloïdale ou sur des particules de carbone, ayant une composition et une taille variable, ont été synthétisés par un simple procédé d'imprégnation. Les catalyseurs supportés sur carbone sont stables et très actifs à la fois dans l'hydrolyse du borazane et la décomposition de l'hydrazine aqueuse pour la production d'hydrogène. Il a été démontré qu'un catalyseur optimal peut être obtenu par le contrôle de l'effet bi-métallique, l'interaction métal-support, et la taille des particules de métal.Catalysis plays an essential role in many industrial applications such as petrochemical and biochemical industries, as well as in the production of polymers and in environmental protection. Design and fabrication of efficient catalysts in a cost-effective way is an important milestone to address a number of unresolved issues in the new generation of chemical and energy conversion technologies. The objective of the studies in this thesis is the development of facile synthetic routes to prepare efficient catalysts based on non-noble metals, and elucidate fundamental aspects regarding the relationship between structure/composition and catalytic performance, in particular in the case of processes related to production and storage of hydrogen fuel. At first, a series of nanostructured porous mixed metal oxides (Cu/CeO2, CuFe/CeO2, CuCo/CeO2, CuFe2O4, NiFe2O4) have been synthesized via an improved nanocasting method. The porous structure of the nanocast products was tailored by tuning the mesostructure of the mesoporous silica phases used as templates. The obtained Cu/CeO2 materials with controlled composition and porous structure were then tested in preferential oxidation of CO in a hydrogen stream to achieve high purity hydrogen fuel. The synthesized catalysts exhibit high activity and selectivity in selective oxidation of CO to CO2. Regarding hydrogen storage, we reported a cost-effective synthetic way towards bi-component CuO-NiO catalyst showing excellent catalytic performance, which is comparable to noble metal catalysts, in the hydrogen generation from ammonia-borane. Moreover, we demonstrate that the interaction between Cu and Ni species is essential in accelerating hydrogen evolution of ammonia borane. The catalytic activity of the obtained catalyst investigated in this reaction is strongly influenced by the nature of the metal precursors, the composition and the thermal treatment temperature employed for the catalyst preparation. Finally, silica- and carbon-supported Cu-Ni nanocatalysts, with tunable composition and metal particle size, were synthesized by simple incipient wetness method. The carbon supported catalysts are stable, highly active and selective in both ammonia-borane hydrolysis and the decomposition of hydrous hydrazine for hydrogen evolution. We showed that optimal catalysts can be achieved through manipulation of bimetallic effect, metal-support interaction, and adequate metal particle size

Mesoporous silica encapsulated metal nanoparticles in catalysis

Nanosized particles can demonstrate dramatic performance in comparison to bulk materials in heterogeneous catalysis, due to their high density of under coordinate sites associated with altered electronic properties. The structural and compositional design of bimetallic nanoparticles can further afford the precise control of activity and selectivity via the geometric and electronic effects of secondary metals. Intermetallic compounds are one of the special alloys with defined stoichiometry and ordered crystal structure, which exemplifies them as ideal model catalysts for structure-property studies in catalysis. Direct colloidal synthesis of intermetallic nanoparticles requires the presence of organic capping agents, which limits the thermal stability of nanoparticles and complicates their surface structures. Mesoporous silica shells can be used to encapsulate monometallic and bimetallic nanoparticles with high sinter-resistance for high-temperature treatment, and enables their applications for harsh reaction conditions and fundamental mechanism studies. Several examples of silica-encapsulated nanoparticles have been demonstrated in this thesis to study their catalytic properties

Promoting catalytic ozonation of phenol over graphene through nitrogenation and Co3O4 compositing

Catalytic ozonation is progressively becoming an attractive technique for quick water purification but efficient and stable catalysts remains elusive. Here we solvothermally synthesized highly-dispersed Co3O4 nanocrystals over microscale nitrogen-doping graphene (NG) nanosheets and tested it as a synthetic catalyst in the ozonation of phenol in aqueous solutions. Transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectra and X-ray photoelectron spectroscopy were used to determine its morphology, crystallinity, elemental composition and molecular bonds, respectively. The comparative experiments confirmed the highest catalytic activity and oxidation degree (AOSC) of Co3O4/NG among four nanocomposites (G, NG, Co3O4/G, and Co3O4/NG). Co3O4/NG also has exhibited the highest degradation rate: complete conversion of a near-saturated concentration of phenol (941.1 mg/L) was achieved within 30 min under ambient conditions with only a small dosage of Co3O4/NG (50 mg/L) and ozone (4 mg/L, flow rate: 0.5 L/min). It also resulted in 34.6% chemical oxygen demand (CODCr) and 24.2% total organic carbon (TOC) reduction. In this work, graphene nanosheets not only functioned as a support for Co3O4 nanocrystals but also functioned as a co-catalyst for the enhancement in phenol removal efficiency. The surface nitridation and Co3O4 modification treatment further improved the removal rate of the phenol pollutants and brought in the higher oxidation degree. Our finding may open new perspectives for pursuing exceptional activity for catalytic ozonation reaction

Removal of Phenol from Wastewater Using Fenton-Like Reaction over Iron Oxide–Modified Silicates

Iron-containing active phase was deposited on natural layered silicate (vermiculite) using several techniques such as ion exchange, precipitation, and forced hydrolysis during hydrothermal digestion. Tuning of the synthesis conditions resulted in preparation of the catalysts with different loading of active phase and physicochemical properties. The composite materials were characterized with respect to their structure (X-ray diffraction), agglomeration state of Fe (diffuse reflectance UV-vis spectroscopy), and chemical composition. Catalytic tests were performed in semi-batch reactor under atmospheric pressure. Aqueous solution of phenol was used as a model industrial effluent, and hydrogen peroxide was added as an oxidant. Spectral techniques were used for identification of intermediate oxidation products. Spent catalysts were also characterized, and structural and chemical changes were determined, e.g., leaching degree of active phase

Síntesis de nanopartículas asistida por microondas en condiciones batch

The development of intensified processes for the preparation of novel catalytically active nanodimensional materials is a captivating challenge getting more attention day-by-day.1, 2 In fact, nanoparticle systems offer the possibility of combining the high activity of homogenous catalysts with the better recoverability of heterogeneous ones, opening to unlimited application in the chemical industry. The microwave-assisted technique – recognized as one of the most innovative methods for process intensification – makes it possible to both synthesize and test new nanocatalysts exploiting the unique characteristics of microwave heating. These characteristics include reduced reaction times, minimized (or suppressed) side reactions, highly reproducibility, enhanced yields and selectivity as well as selective heating and magnetic loss heating.3-5 The PhD thesis presented has been developed thanks to the experience of the research group FQM-383 (NanoVal) in nanoscale chemistry, heterogeneous catalysis and waste/biomass valorization. More in details, the research studies of the PhD thesis demonstrated the potentiality of microwave-assisted techniques for the development of efficient nanocatalytic systems specifically designed for photochemical applications, fine chemical synthesis and biofuel production.6-10 Most important results obtained during the PhD Thesis have been described in three research articles. In addition, a comprehensive minireview has been included in the introduction section in order to highlight the primary importance of nanocatalysts for the production of biofuels. The first research article, “Microwave-assisted valorization of pig bristles: towards visible light photocatalytic chalcocite composites”, discloses the preparation of nano-Cu2S carbon composites via a fast and low-toxicity microwave-assisted method.11 The synthesis was carried out employing ethylene glycol as solvent, copper chloride as metal precursor and waste pig bristles as sulfur and carbon source, avoiding the use of any toxic sulfur precursor (e.g. H2S, thiourea). The high microwave adsorption and high viscosity of ethylene glycol allowed for the preparation of homogeneous Cu2S carbon composites within a few minutes (4 minutes at 200°C operating in a multimode microwave oven). By contrast, conventional heating needed longer reaction times and formed inhomogeneous, low-active Cu2S carbon material. The so-produced composite has been characterized by X-ray diffraction (XRD), nitrogen physisorption (BET model), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX) and UV-Vis spectroscopy. Cu2S carbon composite has been successfully used for the photo degradation of methyl red, a common pollutant dye, under visible LED light irradiation, leading to ca. 40% of degradation within 3 hours. In the second research article, “Heterogeneously Catalyzed Synthesis of Imidazolones via Cycloisomerizations of Propargylic Ureas Using Ag and Au/Al SBA-15 Systems”, a study of environmentally friendly paths for the cycloisomerization of propargylic ureas has been explored.12 Specifically, different nanogold and nanosilver catalsyts have been prepared by supporting the metal nanoparticles over mesoporous silica (AlSBA-15) through mechanochemistry and microwave-assisted approaches. The catalysts have been used as heterogeneous systems in the microwave assisted synthesis of a library of imidazolones via a sequential study aimed to shift the reaction to greener operative conditions. The employed systems avoided the utilization of strong bases, such as NaOH, or expensive homogeneous metal catalysts. The best conditions have been combined in order to catalyse the cycloisomerization of propargyl ureas using only water as solvent and promoter of the reaction. The results demonstrated that the selected solvent highly influenced the reactions, where toluene promoted N-cyclization reactions, ethanol favoured the cyclization of propargylic ureas characterized by more electron withdrawing groups and water favoured the cyclization of propargylic ureas containing electron donor compounds in the structure. The third research article, “Efficient and Environmentally Friendly Microwave-Assisted Synthesis of Catalytically Active Magnetic Metallic Ni Nanoparticles” describes the preparation of pure magnetic metallic nickel by a simple and fast microwave-assisted method using a monomode microwave reactor (CEM Discover, CEM Corp.).13 The synthesis has been carried out using nickel chloride as metal precursor and a mixture of ethylene glycol and ethanol (or isopropanol) as solvent and reducing agent. A fine study carried out varying the molar ratio of ethylene glycol and ethanol in function of the reaction temperature has highlighted the reaction conditions where the reduction of nickel occurred. The best performance (71% yield) has been achieved operating at 250°C for 5 minutes under microwave irradiation. The mechanism of reaction for oxidation of ethylene glycol and reduction of Ni2+ has been demonstrated by gas chromatography–mass spectrometry (GC-MS) analysis, while the behaviour of the mixture and its bubble point in function of the recorder pressure has been simulated by PRO/II software (Schneider Electric Group). The nanoparticles have been analysed by X-ray diffraction (XRD), scanning emission microscopy (SEM), transmission electron microscopy (TEM) and magnetic mass susceptibility. The surface area has been determined by nitrogen physisorption (BET model). The nanoparticles have showed good activity in the hydrogenolysis of benzyl phenyl ether (BPE), a lignin model compound, with a maximum conversion of 24%, and reusability up to 5 cycles without sensible loss of activity.El desarrollo de procesos destinado a la preparación de nuevos materiales con dimensiones nanométricas y, a su vez, catalíticamente activos, es un desafío fascinante que llama cada vez más la atención1, 2. De hecho, los sistemas compuestos de nanopartículas ofrecen la posibilidad de combinar la alta actividad de los catalizadores homogéneos con la mejor capacidad de recuperación de los heterogéneos, ofreciendo de esta manera un número ilimitado de aplicaciones en la industria química. La técnica asistida por microondas, reconocida como uno de los métodos más innovadores para la intensificación de procesos, permite sintetizar y probar nuevos nanocatalizadores que exploten las características únicas del calentamiento por microondas. Estas características incluyen tiempos de reacción reducidos, reacciones secundarias minimizadas (o suprimidas), alta reproducibilidad, rendimientos y selectividad mejorados, así como calentamiento selectivo y calentamiento por pérdida magnética.3-5 La presente tesis doctoral se ha desarrollado gracias a la experiencia del grupo de investigación FQM-383 (NanoVal) en química a nanoescala, catálisis heterogénea y valorización de residuos/biomasa. Más en detalle, los estudios de investigación de la tesis doctoral demostraron la potencialidad de las técnicas asistidas por microondas para el desarrollo de sistemas nanocatalíticos eficientes diseñados específicamente para aplicaciones fotoquímicas, síntesis química fina y producción de biocombustibles.6-10 Los resultados más importantes obtenidos durante la tesis doctoral se han descrito en tres artículos de investigación. Además, en la sección de introducción, un apartado va dedicado a resaltar la gran importancia de los nanocatalizadores en la producción de biocombustibles. El primer artículo de investigación, Microwave-assisted valorization of pig bristles: towards visible light photocatalytic chalcocite composites”, describe la preparación de compuestos nano-Cu2S de carbono mediante un método asistido por microondas rápido y de baja toxicidad.11 La síntesis se llevó a cabo empleando etilenglicol como disolvente, cloruro de cobre como precursor de metal y pelos de cerdo de desecho como fuente de azufre y carbono, evitando el uso de cualquier precursor de azufre tóxico (por ejemplo, H2S, tiourea). La alta adsorción por microondas y la alta viscosidad del etilenglicol permitieron la preparación de compuestos de carbono Cu2S homogéneos en pocos minutos (4 minutos a 200 ° C trabajando en un horno de microondas multimodo). Por el contrario, el calentamiento convencional necesitó tiempos de reacción más largos, dando como resultado un material de carbono Cu2S poco homogéneo y poco activo. El compuesto así producido se ha caracterizado por difracción de rayos X (XRD), fisisorción de nitrógeno (modelo BET), microscopía electrónica de barrido / espectroscopía de rayos X dispersiva de energía (SEM-EDX) y espectroscopía UV-Vis. El compuesto de carbono Cu2S se ha utilizado con éxito para la foto degradación del rojo de metilo, un colorante contaminante común, bajo irradiación de luz LED visible, que conduce a ca. 40% de degradación en 3 horas. En el segundo artículo de investigación, “Heterogeneously Catalyzed Synthesis of Imidazolones via Cycloisomerizations of Propargylic Ureas Using Ag and Au/Al SBA-15 Systems”, se han estudiado diversos caminos ecológicos para la cicloisomerización de ureas propargílicas12. Específicamente, diferentes nanocatalizadores de oro y plata se han preparado soportando las nanopartículas metálicas sobre sílice mesoporosa (AlSBA-15) utilizando mecanoquímica y radiación microondas. Los catalizadores se han utilizado como sistemas heterogéneos en la síntesis asistida por microondas de una biblioteca de imidazolonas a través de un estudio secuencial destinado a cambiar la reacción a condiciones operativas más ecológicas. Los sistemas empleados evitaron la utilización de bases fuertes, como NaOH, o catalizadores metálicos homogéneos y caros. Las mejores condiciones se han combinado para catalizar la cicloisomerización de las propargilureas utilizando solo agua como disolvente y promotor de la reacción. Los resultados demostraron que el disolvente seleccionado tiene una gran influencia en las reacciones, en concreto el tolueno promovió las reacciones de N-ciclación, el etanol favoreció la ciclación de las ureas propargílicas caracterizadas por más grupos de extracción de electrones y el agua favoreció la ciclación de la urea propargílica que contiene compuestos donadores de electrones en la estructura. El tercer artículo de investigación, “Efficient and Environmentally Friendly Microwave-Assisted Synthesis of Catalytically Active Magnetic Metallic Ni Nanoparticles” describe la preparación de níquel metálico y magnético mediante un método simple y rápido asistido por microondas utilizando un reactor monomodo (CEM Discover, CEM Corp .) 13 La síntesis se ha llevado a cabo utilizando cloruro de níquel como precursor metálico y una mezcla de etilenglicol y etanol (o isopropanol) como disolvente y agente reductor. Un buen estudio llevado a cabo variando la relación molar de etilenglicol y etanol en función de la temperatura de reacción ha llevado a las condiciones de reacción donde se produjo la reducción de níquel. El mejor rendimiento (71%) se ha logrado operando a 250 ° C durante 5 minutos bajo irradiación de microondas. El mecanismo de reacción para la oxidación de etilenglicol y la reducción de Ni2 + se ha demostrado mediante el análisis de cromatografía de gases-espectrometría de masas (GC-MS), mientras que el comportamiento de la mezcla y su punto de burbuja en función de la presión del registrador se ha simulado con PRO/II software (Grupo Schneider Electric). Las nanopartículas han sido analizadas por difracción de rayos X (XRD), microscopía de emisión de barrido (SEM), microscopía electrónica de transmisión (TEM) y susceptibilidad de masa magnética. El área superficial ha sido determinada por la fisisorción de nitrógeno (modelo BET). Las nanopartículas han mostrado una buena actividad en la hidrogenolisis del bencil fenil éter (BPE), un compuesto modelo de lignina, con una conversión máxima del 24%, y reutilización de hasta 5 ciclos sin aparente pérdida de actividad

Magnetic nanoparticulate catalysts in flow processes

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Exploiting the optical properties of earth abundant cuprous oxide nanocatalysts for energy and health applications

In this dissertation, we explore the optical properties of semiconductor materials, for energy and photocatalytic applications. In the past semiconductor materials used in photocatalytic reactions are prominently known through electron transfer mechanisms such as redox reactions, and local surface plasmon resonance (LSPR). In this work, we show substantial understanding and advantages of Mie resonances-based photocatalysis. Mie resonance-based photocatalytic mechanisms can find various applications in chemical manufacturing, pollution mitigation, and pharmaceutical industries. We developed an understanding that Mie resonances of metal-oxide nanoparticles are affected by material properties such as absorption and scattering coefficients, dielectric permittivity physical properties like geometry, size of these nanoparticles, and wavelength, and intensity of the incident light. In this work, we experimentally, demonstrate that the dielectric Mie resonances in cuprous oxide (Cu2O) spherical and cubical nanostructures can be used to enhance the dye-sensitization rate of methylene blue dye. The Cu2O nanostructures exhibit dielectric Mie resonances up to an order of magnitude higher dye-sensitization rate and photocatalytic rate as compared to Cu2O nanostructures not exhibiting dielectric Mie resonances. We further established structure-property-performance relationships of these nanostructures and experimentally found evidence, that rate of dye sensitization is directly proportional to the overlap of absorption characteristics of the nanocatalyst, absorption of the dye, and the wavelength of incident light. This work has the potential to be used in pollution mitigation applications, Dye-Sensitized Solar Cells, etc. Gaining a deeper understanding of the characteristics of Cu2O nanostructures, we have experimentally observed that tuning selectivity and activity of reactions can be achieved by modulating the incident wavelength of light. We performed intensity-dependent studies for methylene blue degradation for gaining mechanistic insights into selective photocatalysis. We explored C-C coupling reactions with small molecules which find applications majorly in the chemical and health industry. Carbon-carbon (C-C) coupling reactions are widely used to produce a range of compounds including pharmaceuticals, aromatic polymers, high-performance materials, and agrochemicals. For these reactions industrially, homogenous palladium (Pd) catalysts are used at high temperatures and are a solvent-intensive process. Palladium is expensive, toxic, and rare earth metal. However, the identification of truly heterogeneous versus homogeneous catalytic conditions remains an ongoing challenge within the field. In this research, we gained insights into the homogenous versus heterogeneous pathways using various analytical, experimental, and computational techniques. In this work, we found that Cu2O nanoparticles can catalyze C-C coupling reactions under ligandless and base-free conditions via a truly heterogeneous pathway paving the way for the development of highly efficient, robust, and sustainable flow processes