Browsing by Author "Leal Villarroel, Edgardo Adolfo"
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Item Conversión catalítica del ácido levulínico sobre catalizadores del tipo perovskitas de Ru/AZrO3 A, Ba, Sr.(Universidad de Concepción, 2021) Leal Villarroel, Edgardo Adolfo; Sepúlveda Muñoz, Catherine Valeria; Pecchi Sánchez, GinaEn el presente trabajo se estudió la conversión catalítica de ácido levulínico, sobre catalizadores de rutenio soportados en zirconatos básicos de bario y estroncio, Ru/SrZrO3 y Ru/BaZrO3, para la obtención de γ-valerolactona. Los soportes SrZrO3, BaZrO3 se prepararon por coprecipitación, empleando oxicloruro de circonilo, citrato de amonio dibásico y los cloruros de los metales, el metal se depositó por impregnación seca y se empleó cloruro de rutenio(III) como precursor. Los materiales se caracterizaron por DRX, fisisorción de N2(g) a -196 °C, DTP-NH3, RTP-H2, quimisorción de H2(g), ReTP-MeOH. Las medidas de actividad catalítica se efectuaron en un reactor Parr tipo batch, con una concentración de ácido de 0.46 mol L-1 , 80 mL de solvente 1,4-dioxano y 250 mg de catalizador reducido-pasivado. Para determinar los parámetros cinéticos, se estudió la conversión a diferentes temperaturas entre 175 °C y 250 °C y presiones de H2(g) entre 10-50 atm. Se determinó que el catalizador Ru/SrZrO3 posee menor energía de activación (87,9 kJ mol-1 ) que Ru/BaZrO3 (134,7 kJ mol-1 ), y que a menor temperatura predomina la cantidad de sitios básicos y a mayor temperatura.Item Single site-nanoparticles of noble metal supported on titanium nanotubes as catalysts for the production of aromatic amines from the catalytic hydrogenation of nitroarenes.(Universidad de Concepción, 2026) Leal Villarroel, Edgardo Adolfo; Arteaga Pérez, Luis Ernesto; Campos Figueroa, Cristian H. A; Serp, PhilippeMetal-based heterogeneous catalysis is fundamental to around 80 per cent of industrial production processes, creating a demand for more efficient and sustainable catalytic materials. Since most reactions occur on metal surfaces, it is crucial to maximise the number of accessible metal atoms. In that context, single site catalysts (SSCs), consisting of isolated metal atoms or subnanometric metallic sites (less than 1.0 nm) stabilised on supports, have emerged as an effective strategy. Compared to traditional nanoparticle-based catalysts, these catalysts provide maximum metal utilisation and improved selectivity, resulting in higher efficiency. Hydrogenation is a widely used heterogeneous catalytic process that relies on metal nanoparticles (NPs) to activate H2 and facilitate hydrogen spillover. Synergistic interactions between NPs and single site species enable catalytic pathways that would be difficult to achieve with only NP system. This cooperativity involves H2 activation on the NPs, hydrogen spillover through the support to form H–single site species and the reaction occurring on these highly active and selective sites. The intrinsic instability of isolated atoms and metal sites poses major challenges due to agglomeration and metal leaching. Therefore, robust coordination environments are required to stabilize single sites in SSCs. This study focused on partially reducible titania nanotubes (TNTs), which generate oxygen vacancies (OV) and provide confinement effects through their tubular structure, enabling the effective stabilization of individual sites. To increase the number of OV, TNTs were reduced using NaBH4-assisted pyrolysis to produce TNT-R. This process OV and paramagnetic Ti³⁺ defects, which create electron-deficient anchoring sites for cationic metal precursors. These sites stabilize isolated Pt atoms and prevent their migration and coalescence. Furthermore, the tubular morphology of the TNTs provides nano-confinement effects that promote the homogeneous dispersion of the active phase and may facilitate the diffusion of molecules through its internals channels. The central hypothesis of this thesis is “the combination of Pt single site and nanoparticle catalysts supported on TiO2 nanotubes will exhibit enhanced activity, selectivity, and recyclability in the hydrogenation of nitroarenes to obtain the corresponding aromatic amines, compared with traditional catalysts that are constituted mainly by metal nanoparticles. The chemical nature of the nanotube and its respective OV, as well as the nominal metal loading, will control the single site-to-metal nanoparticle ratio on the support surface and their respective catalytic properties”. A series of Pt(%)/TNT-R catalysts were synthesized with different metal loadings (0.125 wt% to 1.000 wt%) to systematically control the population of isolated sites to nanoparticles. Comprehensive characterization was performed to confirm the successful formation and stabilization of the dual active phase. Atomic force microscopy confirmed that the synthesis achieved the desired single site configuration. The Pt(0.125)/TNT-R catalyst exhibited a distribution dominated by Pt single sites and sub-nanometre clusters (<1.0 nm), whereas Pt(1.000)/TNT-R primarily contained larger Pt NPs. XPS analysis of Pt(1.000)/TNT-R revealed Ti3+ (457.83 eV) and Pt2+ (72.29 eV) species, which supports the stabilization of isolated Pt atoms through coordination with TNT-R defects. EPR spectroscopy confirmed the presence of engineered defects in TNT-R by showing a strong signal at g = 1.9797 G, which is associated with an increase in OV and the presence of paramagnetic Ti3+ centres. Low-temperature FTIR-CO (−80°C) revealed a 2151 cm−1 band for Pt(0.125)/TNT-R, which is characteristic of highly oxidized Ptδ⁺ species. This confirms the formation and electronic isolation of Pt sites. The catalysts were evaluated in the hydrogenation of nitrobenzene to produce aniline. Despite its low metal loading, the Pt(0.125)/TNT-R catalyst, which contains both single sites and NPs, showed the highest activity (TOF: 164 min−1), outperforming the Pt(1.000)/TNT-R catalyst, which mainly contains NPs (TOF: 44 min−1). These results confirm the presence of a cooperative effect between single sites and NPs that enhances catalytic performance. The proposed mechanism involves H2 activation on Pt NPs, followed by hydrogen spillover onto the support where hydrogenation occurs on highly active H–single site species. The reaction follows pseudo-first-order kinetics, with an apparent activation energy of 40.74 kJ mol−1 for Pt(0.125)/TNT-R. Tests with para-substituted nitrobenzenes showed that electron-withdrawing groups increase the hydrogenation rate, while electron-donating groups decrease it. This strong electronic dependence indicates an electron-deficient rate-determining intermediate, consistent with the Haber mechanism. Tests on catalyst recyclability showed moderate deactivation upon reuse. The main cause of deactivation was the agglomeration of Pt single sites into larger NPs, while no metal leaching was detected during nitrobenzene hydrogenation. The water produced as a by-product of the reaction was found to promote Ostwald ripening by dissolving OV that anchor single sites, thereby enabling their mobility and subsequent aggregation into larger Pt NPs. The valorisation of biomass was investigated through the one-pot synthesis of N-furfurylaniline (FFA) from nitrobenzene (NB) and furfural (FUR), using an optimized Pt(0.125)/TNT-R catalyst. This process involves the hydrogenation of NB to aniline, the AN/FUR condensation to an imine and subsequent hydrogenation to FFA. FTIR-Py analysis revealed that TNT-R possesses a higher concentration of weak Bronsted acid sites than the TNT-C control, enhancing FUR reactivity and achieving a maximum FFA selectivity of 66.3%. Temperature studies revealed no competition between NB and FUR for hydrogenation sites. The catalyst remained active for up to six cycles, with deactivation primarily resulting from the agglomeration of single sites into larger NPs, which was promoted by water formation. The synthesis of the pharmaceutical scaffold 3-methylindole (3-ML) was achieved through the reductive amination of nitrobenzene and acetol in a one-pot process, which highlights the challenge of controlling selectivity in cascade reactions. The Pt(1.000)/TNT-R catalyst exhibited the greatest 3-ML selectivity, at 55.8%. In comparison to Pt(1.000)/TNT-C, TNT-R provided the weak acid sites required to promote cyclisation, xxxi whereas TNT-C's high Lewis’s acidity inhibited the reaction by strongly adsorbing acetol and reducing 3-ML formation. Recyclability tests for 3-ML synthesis revealed moderate deactivation resulting from the combined impact of high temperatures (100°C) and substantial water production (4 mol H2O per mol of 3-ML). These conditions caused Pt to sinter, resulting in a mean particle size of 7.1 ± 3.6 nm after 10 cycles. This confirms that hydrothermal environments generated by water production are the main limitation to catalyst durability. These results demonstrate the advantages of cooperative catalysis between single sites and NPs for nitroarene hydrogenation and the one-pot reductive amination of biomass-derived aldehydes, establishing a simple methodology for preparing Pt single site–NP catalysts supported on defect-engineered TNTs. The main deactivation pathway involves the agglomeration of sites into larger NPs, which disrupts cooperativity and reduces the number of active hydrogenation sites. This process is promoted by the formation of water through the solvation of OV. Overall, this work promotes the use of TiO2-nanotube-based catalysts and provides insights into developing recyclable mono- or bimetallic SSCs stabilised by OV for organic transformations.