Water has long been assumed to be essential for biological function. To understand the molecular basis of the role of water in protein function, several studies have established a correlation between enzyme activity and hydration level. While a threshold of hydration of 0.2 h (grams of water per gram of dried protein) is usually accepted for the onset of enzyme activity, recent works show that enzyme activity is possible at water contents as low as 0.03 h (Lind et al., 2004). Diffusion limitation in these experiments was avoided by monitoring enzyme-catalyzed hydrolysis of gas-phase esters. However, since water is also a substrate for the enzyme used in these experiments, they cannot be used to probe the possibility of activity at zero hydration. However, the pig liver esterase and C. rugosa lipase B are able to catalyse alcoholysis reactions in which an acyl group is transferred between an ester and an alcohol. Therefore, by following this reaction and using a gas phase catalytic system, we have been able to show that activity can occur at 0 g/g. These results led to the question of the accuracy of determinations of very low water concentrations; i.e., how dry is 0 g/g? Although gravimetric measurements of the hydration level do not allow us to define the anhydrous state of the protein with sufficient sensitivity, using 18O-labeled water, we have been able to quantify the small number of water molecules bound to the protein after drying, using a modification of the method of Dolman et al. (1997). Testing different drying methods, we have been able to determine a level of hydration as low as 2 moles of water per mole of protein (equivalent to 0.0006 h in the case of pig liver esterase) and have shown that in the case of the pig liver esterase, activity can occur at this hydration level. At the molecular level, if the hydration level affects activity, we can expect an effect on the protein dynamics. Neutron scattering spectra of hydrated powders, for instance, show that diffusive motions of the protein increase with the hydration (Kurkal et al., 2005) To address the question of the protein motions involved in the onset of enzyme activity at low hydration, we performed neutron scattering experiments on a pico-second time scale on dried powders. Preliminary results show a dynamical transition at hydration levels as low as 3 h. Molecular dynamic simulations have also been used in this study to access the dynamics of the active site. Overall, the results here show that pig liver esterase can function at zero hydration, or as close to zero hydration as current methods allow us to determine. Since the experimental methodology restricts this work to a small number of enzymes, it is unlikely that it will ever be possible to determine if all enzymes can function in the anhydrous state: however, the results here indicate that water is not an obligatory requirement for enzyme function.

In der vorliegenden Arbeit wurden mesoporöse Materialien erfolgreich mit magnetischen bzw. katalytisch aktiven Nanopartikeln funktionalisiert, wobei zwei unterschiedliche Synthesestrategien verfolgt wurden. Zum einen erfolgte eine direkte Integration der katalytisch aktiven CeO2-Nanopartikel in poröse, thermisch stabile SiC-Matrizes mithilfe der inversen Mikroemulsionsmethode. Die Größe dieses wässrigen, cersalzhaltigen Nanoreaktors konnte über den RW-Wert (molares Wasser-Tensid-Verhältnis) im Bereich von 2,0-9,9 nm mit einer engen Größenverteilung variiert werden. Für katalytische Untersuchungen wurden die Cerhydroxidpartikel aus dem Mikroemulsionssystem ausgefällt und bei 100-600 °C calciniert. Dabei konnte eine größenabhängige Aktivität der Nanopartikel in der Rußverbrennung nachgewiesen werden, wobei eine Herabsetzung der Rußverbrennungstemperatur um bis zu 239 K nachgewiesen werden konnte. Weiterhin konnten polymere CeO2-SiC Vorläuferverbindungen durch Zugabe einer flüssigen, präkeramischen Vorläuferverbindung (Polycarbosilan) zum Mikroemulsionssystem hergestellt werden, wobei flüssig prozessierbare, transparente Lösungen resultierten. Anschließend erfolgte nach Entfernung der flüchtigen Bestandteile die Pyrolyse zur Bildung der CeO2-SiC-Keramiken. In Abhängigkeit von den Pyrolysebedingungen konnten kristalline SiC-Strukturen mit spezifischen Oberflächen von bis zu 240 m2/g nachgewiesen werden. In weiteren Untersuchungen konnte die Modularität dieses neuartigen Synthesekonzeptes demonstriert werden, indem Platin als zusätzliche Aktivkomponente in das bestehende Mikroemulsionssystem integriert wurde. Im Gegensatz zu den platinfreien Systemen erfolgte eine Vernetzungsreaktion infolge der Pt-katalysierten Vernetzungsreaktion des allylgruppenhaltigen Polycarbosilans, mit spezifischen Oberflächen von bis zu 896 m2/g. Anhand von TEM-Untersuchungen konnte eine hohe Dispersion der CeO2-Aktivkomponente mit Partikelgrößen von 2-3 nm gezeigt werden. Durch die Zugabe von Divinylbenzol als Kreuzvernetzungskomponente konnte neben einer weiteren Erhöhung der Oberfläche auf 992 m2/g auch die Hydrophobizität des Polymerkomposits signifikant erhöht werden. In einer zweiten Synthesestrategie wurden intermetallische MPt-Systeme (M=Fe, Co, Ni) durch Infiltration geeigneter Vorläuferverbindungen und anschließender Thermolyse in geordneten mesoporösen SiO2- bzw. Kohlenstoffmaterialien synthetisiert. Die Phasenbildung in Abhängigkeit von den Thermolysebedingungen wurde mithilfe der Röntgenpulverdiffraktometrie untersucht. Dabei wurden nach der Reduktion bei 400 °C ungeordnete fcc-MPt-Legierungen mit superparamagnetischen Eigenschaften erhalten. Dagegen resultierte für FePt-Systeme nach der Reduktion bei 750 °C bis 800 °C eine deutliche Zunahme der Raumtemperaturkoerzitivitäten auf bis zu 28,35 kOe (FePt@CMK-3) bzw. 15,60 kOe (FePt@SBA-15) infolge der Bildung der intermetallischen fct-FePt Verbindung. Weiterhin wurden die strukturellen sowie magnetischen Eigenschaften der FePt-Nanopartikel in Abhängigkeit vom Massenanteil sowie der Porengröße bzw. -geometrie der porösen Silicatemplate untersucht. Dabei konnte eine starke Abhängigkeit der Raumtemperaturkoerzitivität von der Porenstruktur sowie den jeweiligen Reduktionsbedingungen nachgewiesen werden. Ein weiterer Aspekt dieser Arbeit war die Synthese hochporöser CDC-Kohlenstoffmaterialien (CDC: carbide derived carbon) durch die Chlorierung nichtoxidischer SiC-Keramiken. Hierbei wurde das Silicium der mesoskopisch geordneten SiC-Strukturen durch Umsetzung mit Chlor bei unterschiedlichen Thermolysebedingungen extrahiert. Die resultierenden CDC-Materialien wiesen neben sehr hohen spezifischen Oberflächen von bis zu 2865 m2/g bzw. Porenvolumina von 2,21 cm3/g auch eine von der SiC-Struktur sowie den Chlorierungsbedingungen abhängige mesoskopische Ordnung auf. Die mesoporösen CDC-Materialien eignen sich als Sorbentien mit hohen Butan- bzw. Wasserstoffspeicherkapazitäten von 0,692 gButan/gCDC (25 °C: 80 Vol% Butan) bzw. 2,58 gew% (77 K: 1 bar). Daneben resultieren überaus hohe gravimetrische Methanspeicherkapazitäten von 0,191 g Methan/gCDC im Hochdruckbereich (25 °C, 100 bar), die deutlich größer sind als die bekannter Metallorganischer Gerüstverbindungen. / Ordered mesoporous materials were successfully functionalized with magnetic and catalytic active nanoparticles. Two different synthesis strategies were employed. Cerium oxide nanoparticle containing silicon carbide composites were synthesized by direct incorporation of catalytic active CeO2 nanoparticles in preceramic polycarbosilane using inverse microemulsion technique and subsequent pyrolysis. Resulting ceramic composites offer specific surface up to 240 m2/g and a narrow pore sizes in the range of 4-6 nm. Additionally porous Pt containing CeO2-SiC composites were prepared demonstrating the versitibilty of this new synthesis strategy. Catalytic activity of ceria nanoparticles were shown in soot combustion reaction. In a second approach intermetallic MPt nanoparticles (M= fe, Co, Ni) were synthesized inside the pores of ordered mesoporous silica and carbon materials. Crystalline structure and particles size were controlled by the porous template and the annealing conditions. Very high room temperature coercivities up to 28.4 koe were obtained for intermetallic FePt nanoparticles in mesoporus carbon matrices. Catalytic activity of FePt silica composites were demonstrated in selective acetylene hydration. Furthermore high porous, mesostructured carbon materials (CDC: carbide derived carbon) were prepared by chlorination of ordered mesoporous silica resulting extraordinary high specific surface areas up 2865 m2/g, high pore volunina up to 2.21 cm3/g and mesoscopic ordering. These new carbon structures are appropriate as high performance energy storage materials.

La déshydratation du glycérol en acroléine a été étudiée sur de nouveaux catalyseurs à base d'oxydes en vue de mettre au point un nouveau procédé de production de la méthionine. Ces catalyseurs performants sont des zircones niobiées et des zircones tungstées dopées à la silice. Si les catalyseurs proposés dans la littérature jusqu'à présent pouvaient être sélectifs, ils se désactivaient rapidement par cokage. Les nouveaux catalyseurs mis au point sont aussi actifs et sélectifs mais beaucoup plus stables sous flux réactionnel. Les performances des zircones niobiées sont très sensibles à la méthode de préparation; les catalyseurs ont été caractérisés par DRX, spectroscopie Raman, MET, EDX, XPS. Ces analyses ont montré qu'une partie du niobium est incorporée dans la zircone qui est recouverte d'espèces polymères de niobium. Les zircones tungstées performantes sont constituées d'une zircone recouverte de silice et de polytunsgtates. L'acido-basicité des catalyseurs a été étudiée par différentes techniques: réactions modèles de transformation du méthylbutynol et du 2-propanol, TPD-NH3, adsorption de NH3 et SO2étudiée par microcalorimétrie et adsorption de pyridine suivie par IR. Ces études ont permis de montrer que les sites basiques de la zircone sont néfastes pour les performances et que les sites acides de Brönsted avec une large gamme de force acide sont actifs et sélectifs en acroléine. Nous avons montré par microcalorimétrie que même les sites acides très faibles participent à la réaction / Glycerol dehydration to acrolein has been studied over innovative oxide catalysts in order to develop a new methionine production process. These performing catalysts are niobiate zirconia mixed oxides and tungstated zirconia doped with silicium. The catalysts proposed so far in the literature are active and selective but they show fast deactivation under reaction flow due to coke deposition. The new catalysts appear at least as active and selective but much more stable. The niobiate zirconia mixed oxides, which catalytic performances are very sensitive to the preparation method, have been characterized by XRD, Raman spectroscopy, TEM with EDX analyses and XPS. Theses analyses show that niobium cations are partially incorporated into zirconia and covered its surface as polymeric niobium oxide species. The efficient tungstated zirconia catalysts consist of zirconia cover with silicium and polymeric tungstate species. Acid-base properties of the catalysts have been studied by model reaction of methylbutynol and 2-propanol, NH3-TPD, SO2 and NH3adsorption followed by microcalorimetry and IR spectroscopy of pyridine adsorption. These studies show that the zirconia uncovered by silica or containing no niobium are unselective sites and that Brönsted acid sites of the polymeric tungstate or niobium oxide species are the selective sites in acrolein. The strength of these sites does not appear as a key parameter to acrolein selectivity and even weak sites participate to the reaction

In der vorliegenden Arbeit wurden mesoporöse Materialien erfolgreich mit magnetischen bzw. katalytisch aktiven Nanopartikeln funktionalisiert, wobei zwei unterschiedliche Synthesestrategien verfolgt wurden. Zum einen erfolgte eine direkte Integration der katalytisch aktiven CeO2-Nanopartikel in poröse, thermisch stabile SiC-Matrizes mithilfe der inversen Mikroemulsionsmethode. Die Größe dieses wässrigen, cersalzhaltigen Nanoreaktors konnte über den RW-Wert (molares Wasser-Tensid-Verhältnis) im Bereich von 2,0-9,9 nm mit einer engen Größenverteilung variiert werden. Für katalytische Untersuchungen wurden die Cerhydroxidpartikel aus dem Mikroemulsionssystem ausgefällt und bei 100-600 °C calciniert. Dabei konnte eine größenabhängige Aktivität der Nanopartikel in der Rußverbrennung nachgewiesen werden, wobei eine Herabsetzung der Rußverbrennungstemperatur um bis zu 239 K nachgewiesen werden konnte. Weiterhin konnten polymere CeO2-SiC Vorläuferverbindungen durch Zugabe einer flüssigen, präkeramischen Vorläuferverbindung (Polycarbosilan) zum Mikroemulsionssystem hergestellt werden, wobei flüssig prozessierbare, transparente Lösungen resultierten. Anschließend erfolgte nach Entfernung der flüchtigen Bestandteile die Pyrolyse zur Bildung der CeO2-SiC-Keramiken. In Abhängigkeit von den Pyrolysebedingungen konnten kristalline SiC-Strukturen mit spezifischen Oberflächen von bis zu 240 m2/g nachgewiesen werden. In weiteren Untersuchungen konnte die Modularität dieses neuartigen Synthesekonzeptes demonstriert werden, indem Platin als zusätzliche Aktivkomponente in das bestehende Mikroemulsionssystem integriert wurde. Im Gegensatz zu den platinfreien Systemen erfolgte eine Vernetzungsreaktion infolge der Pt-katalysierten Vernetzungsreaktion des allylgruppenhaltigen Polycarbosilans, mit spezifischen Oberflächen von bis zu 896 m2/g. Anhand von TEM-Untersuchungen konnte eine hohe Dispersion der CeO2-Aktivkomponente mit Partikelgrößen von 2-3 nm gezeigt werden. Durch die Zugabe von Divinylbenzol als Kreuzvernetzungskomponente konnte neben einer weiteren Erhöhung der Oberfläche auf 992 m2/g auch die Hydrophobizität des Polymerkomposits signifikant erhöht werden. In einer zweiten Synthesestrategie wurden intermetallische MPt-Systeme (M=Fe, Co, Ni) durch Infiltration geeigneter Vorläuferverbindungen und anschließender Thermolyse in geordneten mesoporösen SiO2- bzw. Kohlenstoffmaterialien synthetisiert. Die Phasenbildung in Abhängigkeit von den Thermolysebedingungen wurde mithilfe der Röntgenpulverdiffraktometrie untersucht. Dabei wurden nach der Reduktion bei 400 °C ungeordnete fcc-MPt-Legierungen mit superparamagnetischen Eigenschaften erhalten. Dagegen resultierte für FePt-Systeme nach der Reduktion bei 750 °C bis 800 °C eine deutliche Zunahme der Raumtemperaturkoerzitivitäten auf bis zu 28,35 kOe (FePt@CMK-3) bzw. 15,60 kOe (FePt@SBA-15) infolge der Bildung der intermetallischen fct-FePt Verbindung. Weiterhin wurden die strukturellen sowie magnetischen Eigenschaften der FePt-Nanopartikel in Abhängigkeit vom Massenanteil sowie der Porengröße bzw. -geometrie der porösen Silicatemplate untersucht. Dabei konnte eine starke Abhängigkeit der Raumtemperaturkoerzitivität von der Porenstruktur sowie den jeweiligen Reduktionsbedingungen nachgewiesen werden. Ein weiterer Aspekt dieser Arbeit war die Synthese hochporöser CDC-Kohlenstoffmaterialien (CDC: carbide derived carbon) durch die Chlorierung nichtoxidischer SiC-Keramiken. Hierbei wurde das Silicium der mesoskopisch geordneten SiC-Strukturen durch Umsetzung mit Chlor bei unterschiedlichen Thermolysebedingungen extrahiert. Die resultierenden CDC-Materialien wiesen neben sehr hohen spezifischen Oberflächen von bis zu 2865 m2/g bzw. Porenvolumina von 2,21 cm3/g auch eine von der SiC-Struktur sowie den Chlorierungsbedingungen abhängige mesoskopische Ordnung auf. Die mesoporösen CDC-Materialien eignen sich als Sorbentien mit hohen Butan- bzw. Wasserstoffspeicherkapazitäten von 0,692 gButan/gCDC (25 °C: 80 Vol% Butan) bzw. 2,58 gew% (77 K: 1 bar). Daneben resultieren überaus hohe gravimetrische Methanspeicherkapazitäten von 0,191 g Methan/gCDC im Hochdruckbereich (25 °C, 100 bar), die deutlich größer sind als die bekannter Metallorganischer Gerüstverbindungen. / Ordered mesoporous materials were successfully functionalized with magnetic and catalytic active nanoparticles. Two different synthesis strategies were employed. Cerium oxide nanoparticle containing silicon carbide composites were synthesized by direct incorporation of catalytic active CeO2 nanoparticles in preceramic polycarbosilane using inverse microemulsion technique and subsequent pyrolysis. Resulting ceramic composites offer specific surface up to 240 m2/g and a narrow pore sizes in the range of 4-6 nm. Additionally porous Pt containing CeO2-SiC composites were prepared demonstrating the versitibilty of this new synthesis strategy. Catalytic activity of ceria nanoparticles were shown in soot combustion reaction. In a second approach intermetallic MPt nanoparticles (M= fe, Co, Ni) were synthesized inside the pores of ordered mesoporous silica and carbon materials. Crystalline structure and particles size were controlled by the porous template and the annealing conditions. Very high room temperature coercivities up to 28.4 koe were obtained for intermetallic FePt nanoparticles in mesoporus carbon matrices. Catalytic activity of FePt silica composites were demonstrated in selective acetylene hydration. Furthermore high porous, mesostructured carbon materials (CDC: carbide derived carbon) were prepared by chlorination of ordered mesoporous silica resulting extraordinary high specific surface areas up 2865 m2/g, high pore volunina up to 2.21 cm3/g and mesoscopic ordering. These new carbon structures are appropriate as high performance energy storage materials.

The path towards mitigation of anthropogenic greenhouse gas emissions lies in the transition from conventional to sustainable energy resources. The Hydrogen Economy, a cyclic economy based on hydrogen as a fuel, is suggested as a tool in the necessary energy transition. Photocatalysis makes use of sunlight to promote thermodynamically non-favoured reactions such as water splitting, allowing for sustainable hydrogen production. Harvesting thermal energy along with photonic energy is an interesting concept to decrease the activation energy of water splitting (i.e. ΔG = + 237.2 kJ∙mol−1). This work aims to confront this hypothesis in a gas phase photo-thermal reactor designed specifically for this study. The photocatalyst chosen is graphitic carbon nitride (g-C3N4), an organic semiconductor possessing a narrow band gap (i.e. 2.7 eV) as well as a band structure which theoretically permits water splitting. The photocatalytic performance of Pt/g-C3N4 for hydrogen evolution was tuned by altering its synthetic temperature. Electron paramagnetic resonance was used to gain insight on the evolution of the photocatalyst activity with synthesis temperature. Then, gold nanoparticles were deposited on g-C3N4 surface. Localized surface plasmon resonance properties of gold nanoparticles are reported in the literature to be influenced by temperature. Therefore Au/g-C3N4 appeared as a promising candidate for photo-thermal water splitting. X-ray spectroscopy unveiled interesting observations on the gold oxidation state. Moreover, under specific reduction conditions, gold nanoparticles with a wide variety of shapes characterized by sharp edges were formed. Finally, the development of the photo-thermal reactor is presented. The design process and the implementation of this innovative reactor are discussed. The reactor was successfully utilized to probe photoreactions. Then, the highly energy-demanding photocatalytic water splitting was proven not to be activated by temperature in the photo-thermal apparatus.

Catalysis using nanostructures has been a topic of substantial interest for fundamental studies and for practical applications in energy and environmental sectors. The growing demand for production of energy and in the cleaning of polluting hazardous vehicles/industrial wastes has led to several studies in catalysis. Despite the substantial growth of heterogeneous catalytic technologies in last decade, they are still far from reaching their full potential in terms of efficiency, selectivity as well as durability. It is often difficult to simultaneously tackle all the mentioned issues with single component catalysts. Most of these challenges are being overcome with heterostructures/supported hybrid catalysts by modifying their interfaces. The properties of heterostructures hybrids arises not only from the individual contributions of the individual components but also from strong synergetic effect arising from the interface. Engineering the interfaces provides pathways to promote the catalytic performance and hence has been explored. In this regard, we have focused on the progress in investigating the active interfaces that affect the performance of metal oxide-metal, semiconductor-metal and coupled semiconductor nanocatalyst hybrids. We explored a wide spectrum of their applications in photo catalytic, electrocatalytic as well as gas-phase reactions and highlighted the importance of the interface for overall performance. The entire study reported in the thesis is organized as follows: Chapter 1 is a general introduction of hybrid nanocatalyst and their role in wide spectra of catalytic reactions in photo/electro catalysis as well as gas-phase reactions. This chapter describes the motivation behind modulating the interface between two or more nanostructures to obtain multifunctional nanocatalysts. Nan catalysts to achieve high throughput with active interfaces are elaborated while indicating the role of morphology, internal induced state, charge transfer, geometric, support, as well as electronic effect for enhanced performance. Motivation behind specific nanocatalyst hybrid, synthesis routes as well as characterization techniques are detailed in the respective chapters. Specific details for different hybrids are described in the following chapters. Chapter 2 describes the synthesis of high dense ultrathin Au wires on ZnO nanorods for electrocatalytic oxidation of ethanol, where the prerequisite step is the formation of amine-modified support. Oleylamine modification not only serves to anchor Au nanowires on ZnO but also passivates surface defects of ZnO, which in turn enhances the photocurrent. In addition to the stability, the support induces electronic effect on Au nanowires, which facilitates redox process at low potential. Most importantly, the support promotes the activity of Au nanowires upon photoirradiation, and thus leading to synergy between electro and photooxidation current. This is of immense importance for photofuel cell technologies. Moreover, the method enabled the first time electrocatalysis on these nanowires that revealed ultrathin nanowires are potentially interesting systems for catalysis applications provided they are stabilized by a suitable support. Chapter 3 deals with the growth of ultrathin Au nanowires on metal oxide (TiO2) coupled with graphene hybrid support in order to overcome the low conductivity of metal oxide. Oleylamine, used for growth of Au nanowires simultaneously functionalizes the support and leads to room temperature GO reduction. With respect to catalytic activity, we also synthesized the binary counterparts (rGO/Au, TiO2/Au ultrathin nanowires) to delineate the contribution of each of the components to the overall electrocatalytic oxidation of ethanol. Comparative analysis of photo and electrocatalytic activity between the different binary and ternary hybrids provides interesting information. Both, electronic effect of TiO2 and electrical conductivity of rGO add their specific beneficial to the nanowires, leading to superior ternary system. Chapter 4 rGO supported ultrathin Au nanowires exhibits high electrocatalytic performance for oxidation of borohydride with a lower onset potential compared to rGO/Au nanoparticles. Electrochemical impedance spectroscopy measurements display abnormal inductive behavior of the synthesized hybrids, indicative of Au surface reactivation. DFT calculations indicate that the origin of the high activity stems from the shift in the position of the Au d-band center. Chapter 5 Different aspect ratio ZnO nanostructures are obtained by varying the solvothermal reaction time. We observed a direct correlation between observed photocatalytic activity, measured photocurrent and length of the ZnO nanorods. Furthermore, photoresponse of the high aspect ratio ZnO nanorods are improved by attaching Au nanoparticles, intimate contact of two components leads to band bending. Thus, the synthesized ZnO/Au heterostructure favors for prominent separation of photogenerated charge carriers. Chapter 6 TiO2 and PbO/TiO2 hybrids are synthesized via non–hydrolytic sol–gel combustion method. Hybrid exhibits higher photocatalytic activity for the degradation of dye than TiO2. The estimated photogenerated species reveals that the origin of enhanced activity stems from the direct oxidization of dye via photogenerated hole rather than radicals. The semiconductors are matched based on their band edge positions, for the formation of energetic radicals to degrade the pollutants. Based on this study, we infer that semiconductors should not neglected (for example Si) based on calculated mismatch of their valence band edges position for photooxidation reaction via radicals. Chapter 7 describes the Pd dopant associated band engineering, a strategy for tuning the optoelectronic properties of ZnO towards enhanced photocatalytic activity. Incorporated Pd heterocation induces internal energy states within the ZnO band gap. The created energy level leads to trends mismatch between photocatalytic activity and measured photocurrent. Formed energy level arrests the photogenerated electrons, which make them not contribute for the photocurrent generation. Hence, the isolated photogenerated hole efficiently oxidizes the pollutants through hydroxyl radicals, and thus leads to enhanced photocatalytic activity. Chapter 8 employed Pd-substituted zinc stannate for CO oxidation as heterogeneous catalyst for the first time. Compared with SnO2 support, zinc stannate based materials exhibits abnormal sudden light-off profiles at selective temperatures. On the basis of DRIFT studies under relevant conditions, we find that the initially formed product gets adsorbed over the catalyst surface. It leads to the accumulation of carbonates as a consequence, both lattice oxygen mobility and further CO interactions are disabled. As soon as Sn redox nature dominates over the accumulated carbonates, this leads to sudden release of lattice oxygen, and thus leads to a sudden full conversion. Therefore, choosing the suitable support material greatly influences the nature of the light-off CO oxidation profile. Chapter 9 Although, reducible oxide supported gold nanostructures exhibits the highest CO oxidation activity; they still suffer from problems such as limited selectivity towards CO in the presence of H2. Both ex-situ and in-situ experiments demonstrate that, Au nanoparticles supported on Zn2SnO4 matrix selectively oxidizes CO. DRIFT experiments revealed that the involvement of OH groups leads to the formation of hydroxycarbonyl under PROX conditions. Chapter 10 This chapter discusses the conclusions for the previous chapters and highlights the possibilities for future scope for the developed nanocatalysts hybrids for energy and environmental applications.

[ES] El panorama industrial actual se enfrenta a desafíos significativos mientras transita hacia la descarbonización y la sostenibilidad, impulsado por el imperativo de lograr emisiones netas cero para 2050. Se espera una importante contribución hacia este objetivo al conectar materias primas no convencionales y renovables, alternativas a los materiales fósiles convencionales como el petróleo, a las cadenas de valor existentes de la industria química. Actualmente, existe un creciente interés industrial en la producción de nitrilos de cadena corta como HCN y acetonitrilo, mientras que se espera que las tasas de demanda global disminuyan en los próximos años en el caso del acrilonitrilo. Como reemplazo para materias primas convencionales para la producción de nitrilos, como las olefinas ligeras C2-3 de origen fósil, el desarrollo de rutas de conversión selectivas a partir de bloques de construcción C1 renovables, como el bio/e-syngas o su derivado metanol, y precursores N1 renovables, como el amoníaco verde, proporciona rutas hacia los productos químicos nitrilos, prospectivamente con una huella de carbono más baja. La presente tesis desarrolla y estudia catalizadores sólidos capaces de dirigir simultáneamente reacciones de acoplamiento C-N y C-C para la producción de nitrilos alifáticos C2+, particularmente acetonitrilo. Se hace hincapié en desvelar la naturaleza y estructura del verdadero catalizador activo, que se desarrolla bajo las condiciones del proceso. Específicamente, la tesis estudia efectos promocionales provocados por la combinación de dos metales en compuestos intersticiales mixtos de metales, aleaciones y compuestos intermetálicos. En primer lugar, se realizan estudios catalíticos y teóricos complementarios de Teoría del Funcional de la Densidad (DFT) sobre la conversión de mezclas de amoníaco (N1) y gas de síntesis (C1, CO+H2) a acetonitrilo con un (pre)catalizador monometálico MoO3. Estos estudios demuestran que MoN1-x, que se desarrolla mediante nitridación superficial, es el catalizador activo real y sugieren que la activación disociativa de HCN, asistida por oxígeno, es el paso controlante de la cinética de formación de acetonitrilo. A continuación, se estudian efectos promocionales de metales de transición divalentes de primera fila en catalizadores basados en molibdeno, utilizando un conjunto de compuestos de molibdato mixto cristalino, estructuralmente análogos, como precursores de catalizador. El dopado con Mn (Mn:Mo ~1) proporciona un catalizador particularmente selectivo y estable para la síntesis de acetonitrilo a partir de mezclas de NH3/gas de síntesis, logrando una tasa de formación de acetonitrilo de 50·10-3 mmol gcat-1 min-1 a 723K. Un conjunto de métodos in situ y operando con sensibilidad bulk y superficial, proporcionan evidencias de que un oxinitruro mixto MnM, con una simetría Fm-3m, y rico en defectos estructurales, representa el catalizador activo. Se sugiere que la mayor oxofilia del oxinitruro mixto MnMo, junto con el papel clave del oxígeno superficial para la activación disociativa de HCN, subyacen al efecto sinérgico de ambos metales. Finalmente, se estudió la conversión de mezclas en fase vapor de metanol (C1) y amoníaco (N1) a compuestos nitrogenados sobre nanocristales bimetálicos GaNi soportados en SiO2. Las aleaciones desordenadas de GaNi (Ga/(Ga+Ni)< 20%) son particularmente selectivas hacia la síntesis de nitrilos, mientras que los compuestos intermetálicos GaNi (Ga/(Ga+Ni)> 40%) catalizan principalmente la aminación de metanol a metilaminas. La difracción de rayos X y espectroscopía de absorción de rayos X, in situ y operando, revelan que el galio es un promotor necesario, el cual contribuye a la estabilización de fases expandidas de fcc Ni(C,N) así como Ni3C, a temperaturas relevantes para la catálisis (673-773K), cuyo desarrollo en la superficie del catalizador corresponde al inicio de la producción de nitrilos C2+ mediante la integración de reacciones de acoplamiento C-N y C-C. / [CA] El panorama industrial actual s'enfronta a desafiaments significatius mentres transita cap a la descarbonització i la sostenibilitat, impulsat per l'imperatiu d'aconseguir emissions netes zero per a 2050. S'espera una important contribució cap a este objectiu en connectar matèries primeres no convencionals i renovables, alternatives als materials fòssils convencionals com el petroli, a les cadenes de valor existents de la indústria química. Actualment, existix un creixent interés industrial en la producció de nitrils de cadena curta com HCN i acetonitril, mentres que s'espera que les taxes de demanda global disminuïsquen en els pròxims anys en el cas del acrilonitrilo. Com a reemplaçament per a matèries primeres convencionals per a la producció de nitrils, com les olefines lleugeres C2-3 d'origen fòssil, el desenvolupament de rutes de conversió selectives a partir de blocs de construcció C1 renovables, com el bio/e-syngas o el seu derivat metanol, i precursors N1 renovables, com l'amoníac verd, proporciona rutes cap als productes químics nitrils, prospectivament amb una petjada de carboni més baixa. La present tesi desenvolupa i estudia catalitzadors sòlids capaços de dirigir simultàniament reaccions d'acoblament C-N i C-C per a la producció de nitrils alifàtics C2+, particularment acetonitril. Es posa l'accent a revelar la naturalesa i estructura del verdader catalitzador actiu, que es desenvolupa sota les condicions del procés. Específicament, la tesi estudia efectes promocionals provocats per la combinació de dos metalls en compostos intersticials mixtos de metalls, aliatges i compostos intermetàl·lics. En primer lloc, es realitzen estudis catalítics i teòrics complementaris de Teoria del Funcional de la Densitat (DFT) sobre la conversió de mescles d'amoníac (N1) i gas de síntesi (C1, CO + H2) a acetonitril amb un (pre)catalitzador monometálico MoO3. Estos estudis demostren que MoN1-x, que es desenvolupa mitjançant nitridació superficial, és el catalitzador actiu real i suggerixen que l'activació dissociativa de HCN, assistida per oxigen, és el pas controlante de la cinètica de formació d'acetonitril. A continuació, s'estudien efectes promocionals de metalls de transició divalentes de primera fila en catalitzadors basats en molibdé, utilitzant un conjunt de compostos de molibdat mixt cristal·lí, estructuralment anàlegs, com a precursors de catalitzador. El dopat amb Mn (Mn:Mo ~1) proporciona un catalitzador particularment selectiu i estable per a la síntesi d'acetonitril a partir de mescles de NH3/gas de síntesi, aconseguint una taxa de formació d'acetonitril de 50·10-3 mmol gcat-1 min-1 a 723 K. Un conjunt de mètodes in situ i operant amb sensibilitat bulk i superficial, proporcionen evidències que un oxinitrur mixt MnM, amb una simetria Fm-3m, i ric en defectes estructurals, representa el catalitzador actiu. Se suggerix que la major oxofilia del oxinitrur mixt MnMo, juntament amb el paper clau de l'oxigen superficial per a l'activació dissociativa de HCN, subjauen a este efecte sinèrgic de tots dos metalls. Finalment, es va estudiar la conversió de mescles en fase vapor de metanol (C1) i amoníac (N1) a compostos nitrogenats sobre nanocristalls bimetàl·lics GaNi suportats en SiO2. Els aliatges desordenats de GaNi (Ga/(Ga+Ni)< 20 %) són particularment selectives cap a la síntesi de nitrils, mentres que els compostos intermetàl·lics GaNi (Ga/(Ga+Ni)> 40 %) catalitzen principalment l'aminació de metanol a metilamines. La difracció de raigs X i espectroscòpia d'absorció de raigs X, in situ i operant, revelen que el gal·li és un promotor necessari, el qual contribuïx a l'estabilització de fases expandides de fcc Ni(C,N) així com Ni3C, a temperatures rellevants per a la catàlisi (673-773 K), el desenvolupament de la qual en la superfície del catalitzador correspon a l'inici de la producció de nitrils C2+ mitjançant la integració de reaccions d'acoblament C-N i C-C. / [EN] The current industrial landscape is facing significant challenges as it transitions towards decarbonization and sustainability, driven by the imperative of achieving net-zero emissions by 2050. An important contribution towards this goal is expected from connecting unconventional and renewable feedstocks, alternative to conventional fossil raw materials such as crude oil, to existing value chains of the chemical industry. There is currently growing industrial interest in the production of short-chain nitriles such as acid cyanide and acetonitrile, while lower global demand rates are expected in the next years for acrylonitrile. Departing from conventional raw materials for nitrile production, such as C2-3 light olefin petrochemicals, the development of selective conversion routes from renewable C1 building blocks, such as bio/e-syngas or its derivative methanol, and renewable N1 precursors, like green ammonia, provides prospectively lower carbon footprint routes towards nitrile commodity chemicals. The present thesis develops and studies solid catalysts able to concomitantly steer C-N and C-C coupling reactions for the production of C2+ aliphatic nitrile N-chemicals, precisely acetonitrile. Emphasis is placed on unveiling the nature and structure or the true working catalyst, which develops under relevant process conditions. Specifically, the thesis studies promotional effects brought about by the combination of two metals in mixed-metal interstitial compounds, alloys and intermetallic compounds. First, complementary catalytic and theoretical Density Functional Theory studies on the conversion of mixtures of ammonia (N1) and syngas (C1, CO and H2) to acetonitrile with a monometallic MoO3 (pre)catalyst show MoN1-x, which develops upon near-surface nitridation, as the actual working catalyst and suggest O-assisted dissociative activation of HCN as a kinetically controlling step towards acetonitrile and higher nitriles. Next, promotional effects by first-row divalent transition metals on molybdenum-based catalysts are studied, using a set of structurally analogous crystalline ammonium mixed-metal molybdate compounds as catalyst precursors. Doping with Mn (Mn:Mo ~1) affords a particularly selective and stable catalyst for acetonitrile synthesis from NH3/syngas mixtures, achieving an acetonitrile formation rate of 50·10-3 mmol gcat-1 min-1 at 723 K. A battery of in situ and operando bulk and near-surface sensitive methods provide evidence that a defective MnMo mixed-metal oxynitride, with a Fm-3m symmetry, best represents the working catalyst. The higher oxophilicity of the mixed-metal MnMo oxynitride, alongside the key role of surface oxygen for HCN dissociative activation, is suggested to underlie the Mn-Mo bimetallic synergistic effect. Finally, the conversion of vapor mixtures of methanol (C1) and ammonia (N1) to N-compounds was studied on SiO2-supported GaNi bimetallic nanocrystals. Disordered GaNi alloys (Ga/(Ga+Ni)< 20 %) show to be particularly selective towards nitrile synthesis, whereas GaNi intermetallic compounds (Ga/(Ga+Ni)> 40 %) catalyzed primarily methanol amination to methylamines. In situ and operando X-ray diffraction and X-ray absorption spectroscopy reveal that Ga is a necessary promoter in nickel-based nanocrystals, contributing to the stabilization of expanded fcc Ni(C,N) and Ni3C phases at catalysis relevant temperatures (673-773 K), whose development on the catalyst surface corresponds to the onset of C2+ nitrile production by integration of C-N and C-C coupling reactions. / Martínez Monje, ME. (2024). Catalytic co-valorization of C1 and N1 compounds towards nitrile chemicals [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/207107