Traditional methods of synthesizing inorganic materials, such as hydrothermal, sol-gel, calcination and grinding steps, can typically require use of high temperatures, expensive precursors or use of solvents. Because of the energy-intensive nature or environmental impact these techniques, there is a push, especially from an industrial perspective, to move towards greener approaches. Mechanochemistry is a solvent-free alternative technique that can be used to synthesize a variety of materials under ambient conditions. Due to this, there is an increase in attention towards the use of this approach in both solid-state inorganic and organic chemistry. This dissertation reports the mechanochemical synthesis of a few inorganic materials without the need of using high temperatures or solvents. Additionally, examples are presented in which mechanochemistry is used in conjunction with a secondary technique. This mechanical activation of the precursors lead to a decrease in calcination temperature and reactions times, as well as alteration of properties or unique reaction products. The synthesis of kaolinite, vanadia nanostructures, and spinels were carried out in this fashion. Mechanical activation of the precursors allowed for reduced hydrothermal treatment times in case of both kaolinite and vanadia nanostructures and the spinels are calcined at lower temperature for shorter periods of time. In addition, we report alternative template agents than previously reported for the formation of vanadia nanotubes, and report the formation of nanorods. Choosing the appropriate amine template can alter the structure and size of the material. Isomorphously substituted mixed oxides, kaolinite and spinels (MgAl2O4 and ZnAl2O4) were synthesized through a mechanically assisted process. Kaolinites are treated hydrothermally iv for 1 week at 250 ºC to produce an X-ray pure crystalline material. The spinels undergo calcination as low as 500 ºC to produce a nanocrystalline material. Rare-earth metals and transition metals were used as the substitutional atom. The substituted kaolinites exhibit strong order along the c axis, but less ordering along the a and b axes. Trivalent chromium and trivalent rare-earth metals, such as La, Ce, Pr, Nd, Eu, Gd, Ho, and Er, are used to replace aluminum in the structure. Likewise, divalent and trivalent transition, such as Mn, Ni, Cu and Cr, are used as the substitutional atoms in MgAl2O4 and ZnAl2O4. Cathodoluminescence studies on the substituted Spinel structure show that Mn 2+ ions can occupy both the tetrahedral or octahedral holes to give a green and red emission, respectively. On the other hand, Cr3+ ions only occupy the octahedral holes to yield a red emission, similar to that in ruby. These isomorphously substituted materials may have potential applications in catalysis or glaze materials in ceramics. Oxidized graphite, an alternative to graphite oxide and graphene, can be synthesized rapidly by mechanochemical means. Grinding urea hydrogen peroxide adduct with graphite without the need of a solvent produces a product with an oxygen content of 5-15 wt%. The byproducts of this reaction are urea and water. This material is oxidized along the edges of the sheets, allowing it to be hydrophilic while retaining the conductivity. The material can suspend in water and processing allows for films of resistivities between 50 Ω cm-2 and 10 kΩ cm-2 . It was determined that the edges are fully oxidized to yield –COOH groups. This process offers a scalable, environmentally benign route to large quantities of oxidized graphite. An alternative method for the synthesis of nanostructured vanadia is reported. This process involves mechanical grinding of vanadium pentoxide, V2O5, with an amine template, v such as diphenylamine, theophylline, rhodamine 6G and rhodamine, prior to hydrothermal treatment. This allows for the synthesis of VOx nanotubes and nanorods dependent on which template is used. Diphenylamine, theophylline, and rhodamine B produce nanorods. Use of rhodamine 6G produces asymmetric VOx nanorods. In addition to the mixed metals oxides mentioned above, sodium and calcium tantalates are synthesized mechanically. This route does not require the need of elevated temperatures or expensive and hazardous materials. X-ray diffraction analysis of NaTaO3, Ca2Ta2O7, Ca4Ta2O9 and CaTa2O6 shows that these are the only phases detected after 4 h, 10 h, 27 h and 10 h of milling, respectively. During the synthesis of Ca2Ta2O7, an intermediate phase, Ca4Ta2O9, forms within 1 h, which reacts after 5 h to form the desired product. Reference Intensity Ratio analysis shows that the material synthesized mechanically is nanocrystalline Ca2Ta2O7. Nanocrystalline ZrSi2 can also be obtained through mechanochemical synthesis. This method allows for size control and results in crystallites ranging from 9 to 30 nm. Dilution with CaCl2 enables the size control process. A linear relationship exists between the concentration of CaCl2 and the crystallite size. Contrary to a typical self-propagating metathesis reaction, this process does not allow for self-propagation and requires continuous input of mechanical energy to continue. However, this method allows for non-passivated nanoparticles of ZrSi2, which can be incorporated into composites as a reinforcement material for several applications. Hard and ultra-compressible borides, such as ReB2 and OsB2, can be synthesized mechanically. The traditional synthesis of ReB2 requires excess boron due to treatment at high temperatures. This can lead to amorphous boron aggregating at the grain boundaries, which in vi turn, this would degrade the properties of the material. The mechanochemical approach requires mechanical treatment of Re and B powders in stoichiometric quantities for 80 h. Mechanical synthesis of OsB2 powders requires a 1:3 ratio of Os and B powders. After 12 h of milling time, h-OsB2 begins to form, and is the major phase present after 18 h. The lattice parameters corresponding to the hexagonal OsB2 were determined to be a = b = 2.9047 Å, c = 7.4500 Å, α = β = 90º, γ = 120º. Treatment of the OsB2 powder at 1050 ºC under vacuum for 6 days did not induce a phase change, suggesting the hexagonal phase is very stable. Mechanocatalysis of the depolymerization of cellulose and hydrogenation of olefins over BN are reported as well. Heterogeneous catalysis is difficult to apply to solids, such as cellulose. However, mechanical grinding of kaolin and cellulose allows for the catalysis to occur in the solid state. This process allows for a variety of different biomasses to be used as feedstock without inhibition. Kaolinite was found to be the best acid catalyst due to high surface acidity and its layered structure, allowing for up to 84% conversion of the cellulose to water-soluble compounds. This process allows for reduction of waste, insensitivity of feedstock, multiple product pathways and scalability. Hydrogenation reactions are carried out using transition-metals catalysts. These metals have desirable catalytic properties not seen in main group elements, but there is growing concern over their use. A metal-free heterogeneous hydrogenation catalyst based on frustrated Lewis pairs would significantly reduce the health, environmental, and economic concerns associated with these metal-based catalysts. We report the first metal-free heterogeneous hydrogenation catalyst. Hydrogenation of trans-cinnamic acid is carried out over defect-laden h-BN. The vii reactor we use is designed to maximize the defects produced in BN sheets. The introduction of defects in BN creates frustrated Lewis pairs. DFT calculations show that the carbon double bond is weakened over boron substitution for nitrogen sites, vacancies of both boron and nitrogen, and Stone-Wales defects. A new method for crystalline germanium deposition occurring at lower temperatures (210-260 ºC) is reported. This method involves mechanical treatment of the precursors to reduce the particle size. A ground mixture of Ge and CuI are heated under vacuum to synthesize GeI2. In situ disproportionation of this compound at 210 ºC allows for the deposition of polycrystalline Ge films onto a both glass and polymer substrates. The rate of deposition is found to be 25 ng min-1 . The byproducts of this process are GeI2, GeI4 and Cu3Ge, which are valuable precursors for the synthesis of germanium nanostructures and organogermanium compounds. Mechanochemistry is also utilized for the synthesis of trisubstituted pnictides. Mechanochemical treatment of bromobenzene with either Na3Sb or Na3Bi allows for the formation of triphenylstibine or triphenylbismuthine, respectively. The synthesis of the alkali metals pnictide precursors is reported as well. The synthesis of triphenylstibine produces SbPh3 as the major product from the reaction. The synthesis of triphenylbismuthine produces more Wurtz-type coupling products, which are due to the BiPh3 acting as a catalyst. Tributyl and triphenyl analogues are reported as well. The trialkylated analogues for both Sb and Bi produce more Wurtz type coupling products. This would allow for a more cost effective and scalable, alternative methods than what is currently in use today

Self-assembled nonionic alkyl glycoside surfactants are of interest for creating functional adsorption and catalytic sites at the surface of mesoporous metal oxides, but they typically impart poor long-range order when used as pore templates. Improved order and control over the functional site density may be achieved by mixing them with a cationic surfactant. To confirm this hypothesis, we investigate the lyotropic liquid crystalline (LLC) phase behavior of aqueous solutions of the functional nonionic surfactant n-dodecyl β-D-maltoside (C12G2) and cationic cetyltrimethylammonium bromide (C16TAB). A ternary phase diagram of the C16TAB-C12G2-water system is developed at 50 °C. By replacing the volume of water in the phase diagram with an equivalent volume of silica, ordered mesoporous materials are prepared by nanocasting with variable C12G2/C16TAB ratios. Metal oxide mesophases can almost always be predicted from the ternary phase diagram, except that silica prepared with high C12G2/C16TAB ratios are very weakly ordered, perhaps due to differences in hydrogen bonding or rate of assembly. Based on the ternary phase diagram of the system, a systematic approach is taken to the incorporation of titania sites via complexation to the maltoside headgroup of C12G2. Complexation to a saccharide is expected not only to guide titanium to the pore surface, but also to prevent uncontrolled hydrolysis and condensation of the (usually quite reactive) titanium precursor. Tetrahedrally coordinated titanium atoms incorporated into a silica network are believed to be the active oxidation sites required for heterogeneous silica-supported titania oxidation catalysts. To promote well-ordered materials and to allow control over titania site density, the mixed C12G2 / C16TAB system is used for pore templating. Series of Si-Ti mixed oxide thin films and bulk materials are synthesized with different amounts of titanium loading by utilizing pre-complexation between C12G2 and titanium isopropoxide. The degrees of homogeneity (indicated by tetracoordinated Ti) in these films are superior to those of films synthesized with the same loading of titanium but without C12G2 or without pre-complexation. Transition metal-carbohydrate complexation provides highly dispersed, tetrahedrally coordinated titanium atoms rather than the octahedral sites found without saccharide complexation.

Master of Science / Department of Chemistry / Kenneth Klabunde / Remediation of the indoor environment led to the development of novel catalysts which can absorb light in the visible range. These catalysts were prepared using the wet chemistry method known as sol-gel chemistry because preparation via sol-gel provides a homogeneous gel formation, which can be treated via supercritical drying to produce an aerogel. These aerogels have been found to have high surface areas when a combination of titania/silica is used. The increase in surface area has been shown to enhance the activity of the catalysts. Mixed metal oxide systems were prepared using titanium isopropoxide and tetraethyl orthosilicate to yield a 1:1 system of titania/silica (TiO2/SiO2). These systems were doped during the initial synthesis with transition metals (Mn or Co) to create mixed metal oxide systems which absorb light in the visible light range. These materials were assessed for potential as heterogeneous catalysts via gas-solid phase reactions with acetaldehyde. Degradation of acetaldehyde as well as the formation of CO2 was monitored via gas chromatography-mass spectrometery. To increase the activity, visible light was introduced to the system. Experiments have shown that a 10 mol % manganese doped titania/silica system, in the presence of light, can degrade acetaldehyde. The cobalt doped counterpart showed dark activity in the presence of acetaldehyde resulting in the formation of CO2 without the addition of visible light. In the hope of increasing surface area a mixed solvent (toluene/methanol) synthesis procedure was applied to the manganese doped catalyst. The resulting materials were of a low surface area but showed a significant increase in degradation of acetaldehyde. Examination of the interactions between mixed metal oxide systems and semivolatile organic compounds (SVOCs) was studied. The pollutant, triphenyl phosphate, was dissolved in n-pentane and exposed to 10 mg of a given catalyst. These reactions were monitored using UVVis. All systems but the manganese doped titania/silica system resulted in the observation of no activity with triphenyl phosphate. The manganese doped catalyst shown a peculiar activity, the increase in absorbance of the triphenyl phosphate peaks as well as the formation of a new peak.

No description available.

No description available.

The structural chemistry and magnetic properties of compounds isostructural with La₁₈Li₈Rh₅O₃₉ have been studied. In this cubic structure (space group Pm^{^_}<sub style='position: relative; left: -.5em;'>3</sub>n), [111] chains of alternating RhO₆ octahedra (2a, 8e sites) and LiO₆ trigonal prisms (16i site) occupy channels within a La-O framework. In order to study the consequences of both reducing the dimensions of the channels and introducing paramagnetic cations into both the framework and the polyhedral chains, compositions in the series Nd₁₈Li₈Rh_5-xFe_xO₃₉ (1 &le; x &le; 4) have been synthesised and characterised by magnetometry, neutron diffraction and Mössbauer spectroscopy. Iron preferentially occupies the 2a site as low-spin Fe(IV) and the larger 8e site as high-spin Fe(III). Compositions having x > 1 show spin-glass-like behaviour below ~5 K. The behaviour of this series of compositions has been compared with that of the known series La₁₈Li₈Rh_5-xFe_xO₃₉. In order to facilitate this comparison, the structure of La₁₈Li₈Fe₅O₃₉ has been fully characterised by both neutron diffraction and EXAFS. The use of both techniques has revealed differences between the mean and local environments of iron. In order to explore and extend the range and combinations of elements that can be accommodated in this structure, the Ti-containing compounds Ln₁₈Li₈M₄TiO₃₉ (Ln=La,Nd,Pr,Sm; M=Rh,Fe,Co) have been synthesised. Nd₁₈Li₈Fe₄TiO₃₉ was selected for a detailed study by magnetometry, neutron diffraction, Mössbauer spectroscopy and XANES. Cations were found to be stabilised in unusual oxidation states and disordered over three sites of the Nd₁₈Li₈Fe₄TiO₃₉ polyhedral chains. The 8e site is occupied by high-spin Fe³⁺, Ti³⁺ and Li⁺ in a ratio of 76:20:4; the 2a site by low-spin Fe⁴⁺ and Ti⁴⁺ in a ratio of 79:21 and the trigonal-prismatic 16i site by Li⁺ and Fe³⁺ in a ratio of 98:2. Nd₁₈Li₈Fe₄TiO₃₉ undergoes a transition to a spin-glass state at 4.25(5) K, whereas La₁₈Li₈Fe₄TiO₃₉ revealed a different type of magnetic transition at ~8 K. The nature of this transition is not yet clear. Monophasic samples could not be prepared in the Nd/Rh system and cation vacancies were found in Nd/Co. No pure samples of Sm-containing compositions could be prepared, while the only Pr composition which was obtained pure, according to X-ray diffraction, Pr₁₈Li₈Co₄TiO ₃₉ shows the similar magnetic properties to Pr₁₈Li₈Co₃TiO₃₉. The compositions Ln₁₈Li₈M₃ M'O₃₉ (Ln=La,Nd,Pr,Sm; M,M'=Fe,Co,Ti) with 25% of the 8e sites vacant have been investigated. The Co-containing compositions Nd₁₈Li₈Co₃FeO_39-y, Nd₁₈Li₈CoFe₃O_39-y and Nd₁₈Li₈Co₃TiO_39-y were characterised by neutron diffraction. Cation vacancies on the 8e sites were found to coexist with anion vacancies around the 2a sites. The remaining octahedral sites are occupied by a disordered arrangement of transition-metal cations. The trigonal-prismatic sites are fully occupied by Li except in the case of Nd₁₈Li₈CoFe₃O_39-y where some Fe is present, as confirmed by Mössbauer spectral data. Antiferromagnetic interactions are present on the Nd sublattice in each composition, but a spin glass forms below 5 K when a high concentration of spins is also present on the octahedral sites. The magnetic character of the Ln cations plays an important role in determining the properties of these compounds. Long-range magnetic order of the transition-metal cations was not observed in any compositions. Although this might be partly attributable to the cation disorder in the polyhedral chains, the apparent antiferromagnetic behaviour of Nd-containing compositions in which the transition metals have a low magnetic moment, e.g. Nd₁₈Li₈Co₃TiO_39-y, and the marked contrast between certain La and Nd compositions in which the transition metal content is the same, e.g. Nd₁₈Li₈Fe₄TiO₃₉ and La₁₈Li₈Fe₄TiO₃₉, suggests that the Ln sublattice is fully involved in determining the magnetic behaviour.

The selective catalytic oxidation of NH3 (NH3 -SCO) into N2 and H2O is an efficient technology for NH3 abatement in diesel vehicles. However, the catalysts dedicated to NH3 -SCO are still under development. One of the groups of such catalysts constituted transition metal-based catalysts, including hydrotalcite-derived mixed metal oxides. This class of materials is characterized by tailored composition, homogenously dispersed mixed metal oxides, exhibiting high specific surface area and thermal stability. Thus, firstly, we give a short introduction to the structure and composition of hydrotalcite-like materials and their applications in NH3 -SCO. Secondly, an overview of other transition metal-based catalysts reported in the literature is given, following a comparison of both groups. The challenges in NH3 -SCO applications are provided, while the reaction mechanisms are discussed for particular systems

[ES] En este trabajo se ha llevado a cabo un estudio exhaustivo sobre la síntesis, caracterización y reactividad de óxidos metálicos mixtos que presentan la fase ortorrómbica M1, con el fin de conocer la influencia de la composición en las propiedades catalíticas de dichos materiales para la deshidrogenación oxidativa (ODH) de etano a etileno, una alternativa interesante a la producción industrial de olefinas ligeras, lo cual supondría una drástica disminución en la emisión de gases de efecto invernadero. En primer lugar, se ha estudiado la síntesis hidrotermal de óxidos bimetálicos, Mo-V-O que presentan la fase M1, considerando diferentes parámetros sintéticos como la temperatura de síntesis, atmósfera, pH del gel de síntesis, temperatura de activación o post tratamientos de purificación. Los resultados de caracterización indican que la combinación de estos parámetros es clave en la obtención no solo de la fase M1, si no de catalizadores óptimos en la ODH de etano, observándose diferencia de hasta 25 puntos porcentuales en la selectividad a etileno dependiendo de la composición de las especies en la superficie del catalizador. En segundo lugar, se ha investigado la síntesis y caracterización de óxidos trimetálicos, Mo-V-Te-O, que presentan la fase M1 con diferentes proporciones de teluro en la estructura (0 < Te/Mo < 0,17), con el fin modular la acidez, la estabilidad térmica y el comportamiento catalítico de estos catalizadores. Se ha observado que la incorporación de teluro en la estructura de la fase M1 supone un aumento considerable de la estabilidad térmica de los catalizadores, así como de la selectividad a etileno. Posteriormente, se ha llevado a cabo un estudio comparativo entre catalizadores bi-, tri- y tetrametálicos (Mo-V-Te-Nb-O), de la influencia de la composición y/o la activación térmica de los diferentes materiales sobre las propiedades catalíticas. Los resultados obtenidos sugieren una correlación entre la composición superficial y temperatura de activación de los catalizadores con la selectividad a etileno. Así, se ha encontrado una relación directa entre la concentración relativa de especies V4+ en la superficie del catalizador (obtenida mediante de espectroscopia de fotoemisión de rayos-X, XPS) y la selectividad a etileno. Además, y dado que todos estos óxidos mixtos pueden considerarse como semiconductores, se llevó a cabo un estudio electroquímico de los catalizadores. Estos resultados sugieren que, materiales que mostraron una mayor selectividad a etileno, (el catalizador Mo-V-O activado a 400 ºC; y los catalizadores Mo-V-Te-O y Mo-V-Te-Nb-O activados a 600 ºC), presentan una mayor concentración de especies V4+ en la superficie y mayores valores de resistancia eléctrica. Por último, se ha llevado a cabo un estudio comparativo entre los sistemas catalíticos que, en la literatura, presentan los mejores resultados catalíticos para ODH de etano: i) óxido de vanadio soportado sobre alúmina (VOx/Al2O3); ii) óxido de níquel promovido con estaño (Sn-NiO); y iii) el catalizador Mo-V-Te-Nb-O (M1) optimizado en este trabajo. Los resultados catalíticos obtenidos, así como los resultados de caracterización (mediante técnicas de caracterización convencionales e in situ), muestran importantes diferencias en la selectividad a etileno a altas conversiones de etano, como consecuencia de la mayor o menor degradación de etileno en cada catalizador. En ese sentido, el catalizador basado en óxidos mixtos de Mo-V-Te-Nb-O presenta una muy baja reactividad a la combustión de etileno (lo que favorece una alta selectividad durante la ODH de etano), mientras que los otros dos sistemas catalíticos presentan una reactividad para la combustión de etileno mucho mayor (lo que reduce sustancialmente la selectividad a etileno durante la ODH de etano, especialmente a altas conversiones de etano). Estos resultados se discuten en función de las propiedades de adsorción de etano y etileno en cada catalizador. / [CA] En aquest treball s'ha dut a terme un estudi exhaustiu sobre la síntesi, caracterització i reactivitat d'òxids metàl·lics mixtes que presenten la fase ortoròmbica M1, amb la finalitat de conéixer la influència de la composició en les propietats catalítiques d'aquests materials per a la deshidrogenació oxidativa (*ODH) d'età a etilé, una alternativa interessant a la producció industrial d'olefines lleugeres, la qual cosa suposaria una dràstica disminució en l'emissió de gasos d'efecte d'hivernacle. En primer lloc, s'ha estudiat la síntesi hidrotermal d'òxids bimetàl·lics, Mo-V-O que presenten la fase M1, considerant diferents paràmetres sintètics com la temperatura de síntesi, atmosfera, pH del gel de síntesi, temperatura d'activació o post tractaments de purificació. Els resultats de caracterització indiquen que la combinació d'aquestos paràmetres és clau en l'obtenció no sols de la fase M1, si no de catalitzadors òptims en la ODH d'età, observant-se diferència de fins a 25 punts percentuals en la selectivitat a etilé depenent de la composició de les espècies en la superfície del catalitzador. En segon lloc, s'ha investigat la síntesi i caracterització d'òxids trimetàl·lics , Mo-V-Te-O, que presenten la fase M1 amb diferents proporcions de tel·luri en l'estructura (0 < Te/Mo < 0,17), amb la finalitat de modular l'acidesa, l'estabilitat tèrmica i el comportament catalític dels catalitzadors. S'ha observat que la incorporació de tel·luri en l'estructura de la fase M1 suposa un augment considerable de l'estabilitat tèrmica dels catalitzadors, així com de la selectivitat a etilé. Posteriorment, s'ha dut a terme un estudi comparatiu entre catalitzadors bi-, tri- i tetrametàl·lics (Mo-V-Te-Nb-O), de la influència de la composició i/o l'activació tèrmica dels diferents materials sobre les propietats catalítiques. Els resultats obtinguts suggereixen una correlació entre la composició superficial i temperatura d'activació dels catalitzadors amb la selectivitat a etilé. Així, s'ha trobat una relació directa entre la concentració relativa d'espècies V4+ en la superfície del catalitzador (obtinguda mitjançant espectroscòpia de fotoemissió de raigs-X, XPS) i la selectivitat a etilé. A més, i atés que tots aquestos òxids mixtes poden considerar-se com a semiconductors, es va dur a terme un estudi electroquímic dels catalitzadors. Estos resultats suggereixen que, materials que van mostrar una major selectivitat a etilé, (el catalitzador Mo-V-O activat a 400 °C; i els catalitzadors Mo-V-Te-O i Mo-V-Te-Nb-O activats a 600 °C), presenten una major concentració d'espècies V4+ en la superfície i majors valors de resistència elèctrica. Finalment, s'ha dut a terme un estudi comparatiu entre els sistemes catalítics que, en la literatura, presenten millors resultats catalítics per a ODH d'età: i) òxid de vanadi suportat sobre alumina (VOx/Al2O3); ii) òxid de níquel promogut amb estany (Sn-NiO); i iii) el catalitzador Mo-V-Te-Nb-O (M1) optimitzat en este treball. Els resultats catalítics obtinguts, així com els resultats de caracterització (mitjançant tècniques de caracterització convencionals i in situ), mostren importants diferències en la selectivitat a etilé a altes conversions d'età, a conseqüència de la major o menor degradació de l'etilé en cada catalitzador. En eixe sentit, el catalitzador basat en òxids mixtes de Mo-V-Te-Nb-O presenta una molt baixa reactivitat a la combustió d'etilé (el que afavoreix una alta selectivitat durant la ODH d'età), mentre que els altres dos sistemes catalítics presenten una reactivitat per a la combustió d'etilé molt major (el que redueix substancialment la selectivitat a etilé durant la ODH d'età, especialment a altes conversions d'età). Estos resultats es discuteixen en funció de les propietats d'adsorció d'età i etilé en cada catalitzador. / [EN] Herein an exhaustive study on the synthesis, characterization and reactivity of mixed metal oxides that present the orthorhombic M1 phase has been conducted, aiming to unravel the influence of the composition on the catalytic performance of said materials in the oxidative dehydrogenation (ODH) of ethane to produce ethylene, an interesting alternative for the obtention of light olefins, which could suppose a drastic decrease in the greenhouse gas emissions. In a first place, the hydrothermal synthesis of a bimetallic form of the M1 phase, Mo-V-O, has been explored, taking into account all the possible parameters such as temperature, atmosphere, pH of the synthesis gel, activation temperature and post-synthesis treatments. Results indicate that the combination of these parameters is capital not only for the appropriate formation of the M1 phase, but also to the catalytic performance. This is, a set of differently synthesized Mo-V-O catalysts, all of them presenting the M1 phase, may differ in the activity and selectivity to ethylene by up to 25 % depending on the chemical composition on the surface species of the catalyst. Moreover, it was investigated the synthesis and characterization of trimetallic oxides Mo-V-Te-O presenting the M1 phase with different Te-loadings (0 < Te/Mo < 0.17), trying to modulate the acid properties, as well as the thermal stability and catalytic behavior in the ethane ODH. Accordingly, we observed that the introduction of tellurium into the structure of the M1 phase leads to an enhanced thermal stability, in addition to an increase on the selectivity to ethylene. Subsequently, it was performed a comparative study between bi-, tri- and tetrametallic (Mo-V-Te-Nb-O) catalysts about the influence of composition and/or thermal activation on the catalytic behavior. Obtained results suggest that there is a correlation between surface composition, as well as the thermal activation temperature, with the selectivity of these catalysts to ethylene. Then, it was found a direct relationship between surface V4+ species (results from X-ray photoelectron spectroscopy, XPS) and the selectivity to ethylene. Furthermore, since all these mixed oxides can be considered as semiconducting materials, an electrochemical parallel study was also conducted. Then, these results suggest that the oxides that showed the best selectivity to ethylene (i.e., catalyst Mo-V-O activated at 400 ºC; and Mo-V-Te-O and Mo-V-Te-Nb-O catalysts treated at 600 ºC) are also the ones that present the highest amount of V4+ species on the surface of the solid, in addition to the highest values of electric resistance. Finally, a comparative study was performed between the three catalytic systems that have offered the best properties in the oxidative dehydrogenation of ethane in the literature: i) alumina supported vanadium oxide (VOx/Al2O3), ii) tin promoted nickel oxide (Sn-NiO) and iii) multicomponent Mo-V-Te-Nb-O (M1) catalyst optimized in the present thesis. Thus, both the catalytic and the characterization (by means of conventional and in situ techniques) results indicate important differences in the selectivity to ethylene of these catalysts at high ethane conversion values, as a consequence of a greater or lesser degradation of the ethylene over each catalyst. In this sense, the catalyst based on mixed metal oxides, Mo-V-Te-Nb-O, shows a very low reactivity for ethylene deep oxidation (which favors a high selectivity during ethane ODH), whereas the rest of the catalytic systems display higher reactivity for deep oxidation of ethylene (which drastically reduces the selectivity to ethene during ethane ODH, specially at high ethane conversion). These results will be discussed in terms of the different adsorption properties of both ethane/ethene over the three catalytic systems. / Arriba Mateos, AD. (2024). Synthesis and Characterization of Bronze-Type Mixed Oxides for the Selective Activation of Hydrocarbons [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/202614

No description available.

No description available.