Catalizadores heterogéneos para la síntesis de piperazinas a partir de glicerol

[ES] El objetivo principal del trabajo es el estudio de un proceso para la síntesis de productos nitrogenados de alto valor añadido a partir de glicerol empleando catalizadores heterogéneos sostenibles. En concreto, el trabajo se centra en la transformación del glicerol en compuestos nitrogenados del tipo piperazinas, importantes intermedios en síntesis orgánica. Para ello, se plantea un proceso en dos etapas que comprendería una deshidratación selectiva del glicerol para dar hidroxiacetona (o acetol) y una posterior aminación reductiva del acetol con etilendiamina. El estudio trata de optimizar cada etapa reactiva por separado, teniendo en cuenta la posibilidad de poder diseñar un proceso en una sola etapa. Para la deshidratación selectiva del glicerol, catalizadores basados en óxidos mixtos derivados de hidrotalcitas fueron preparados, caracterizados por DRX, análisis ICP y adsorción de N2 y probados en la reacción de interés, utilizando diversos sistemas de reacción. Por otro lado, Pd y Pt soportados sobre alúmina fueron los catalizadores escogidos en la reacción de aminación reductiva para producir la piperazina deseada, caracterizándose los mismos por análisis ICP y TEM. El trabajo proporciona una nueva ruta catalítica para el aprovechamiento del glicerol, ofreciendo nuevas posibilidades para la obtención de compuestos nitrogenados a partir de esta materia prima.[EN] The main purpose of this work is the study of a process for the synthesis of high-valued nitrogenated chemicals from glycerol by means of sustainable heterogeneous catalysts. Specifically, the work is focused on the transformation of glycerol into piperazines, which are basic chemical intermediates for organic synthesis. For the production of piperazines a two-step process is considered, involving selective dehydration of glycerol into hydroxyacetone (or acetol) and posterior reductive amination of acetol with ethylendiamine. The study intends to develop and optimize each single reaction step separately, taking into account the possibility of reaching a "one-pot" process, which is considered to be the most promising alternative. Mixed oxides derived from hydrotalcites were prepared, characterized by XRD, ICP analysis and N2 adsorption and tested for the selective dehydration of glycerol using different reaction systems. On the other hand, Pd and Pt supported on alumina were chosen as the catalysts to perform the reductive amination in order to yield the desired piperazine, being characterized by ICP analysis and TEM. This work opens up a new catalytic route for taking advantage of glycerol, thus offering new insights and possibilities to obtain nitrogenated compounds from this raw material.Mazarío Santa-Pau, J. (2016). Catalizadores heterogéneos para la síntesis de piperazinas a partir de glicerol. http://hdl.handle.net/10251/149334TFG

Isomerization of Glucose-to-Fructose in Water over a Continuous Flow Reactor using Ca-Al Mixed Oxide as Heterogeneous Catalyst

[EN] This work reports the continuous isomerization of glucose to fructose in aqueous media under mild conditions using a mixed oxide hydrotalcite-derived catalyst based on Ca and Al. Different operational parameters of the continuous flow fix-bed catalytic reactor system were studied. At the optimal conditions, the Ca-Al-based catalyst achieved a very high conversion and almost quantitative selectivity towards fructose, this being one of the few successful examples of a heterogeneous catalyst capable of carrying out this reaction in a continuous process. Importantly, catalytic activity held steady during four hours on stream, and slight deactivation occurring could be practically overcome by thermal regeneration of the catalyst.Grant PGC2018-097277-B-I00 funded by MCIN/AEI/10.13039/501100011033 and "ERDF A way of making Europe", and the financial support by the Spanish Government (SEV-2016-0683) and Generalitat Valenciana (GVA, PROMETEO/2018/006) are gratefully acknowledged. Authors also thank the ITQ for the technical support, and the Electron Microscopy Service of Universitat Politecnica de Valencia for instrumental facilities. J.M. thanks the Spanish Government (CTQ-2015-67592) for his PhD fellowship.Ventura, M.; Mazarío-Santa-Pau, J.; Domine, ME. (2022). Isomerization of Glucose-to-Fructose in Water over a Continuous Flow Reactor using Ca-Al Mixed Oxide as Heterogeneous Catalyst. ChemCatChem. 14(3):1-8. https://doi.org/10.1002/cctc.202101229S1814

Pd supported on mixed metal oxide as an efficient catalyst for the reductive amination of bio-derived acetol to 2-methylpiperazine

[EN] An efficient process for synthesizing a high added-value N-heterocycle (2-methylpiperazine, 2-MP) via reductive amination of hydroxyacetone or acetol (product of the selective dehydration of glycerol) with ethylenediamine by using Pd supported catalysts under mild reaction conditions is here presented. Catalysts based on Pd nanoparticles supported on metallic oxides and mixed oxides were prepared and characterized by ICP analysis, XRD, HR-TEM, and NH3-TPD, among others. Catalytic activity comparisons of Pd-based materials (also including commercial references) were done and obtained results correlated with metal particle morphology (analyzed by CO-FTIR) and its ability to activate the C = N bond. The best results were attained with Pd/TiO2-Al2O3 and Pd/ZrO2-Al2O3, the former yielding >80% of 2-MP. The Pd/TiO2-Al2O3 catalyst successfully enables the activation of the imine group (C = N), due to a larger number of unsaturated Pd sites in its nanoparticles, while keeping a suitable acidity to effectively and selectively carry out the reductive cyclo-amination reaction even with lower catalyst loadings. This research work offers a new and sustainable catalytic route for the synthesis of organo-nitrogen compounds taking advantage of renewable raw materials (i.e. acetol) as a carbon source and using efficient Pd supported catalysts.The authors express their gratitude to the Spanish Government for the funding (MICINN: CTQ2015-67592, PGC2018-097277-B-I00 and Severo Ochoa Program: SEV-2016-0683). J. M. thanks the MICINN (CTQ2015-67592) for his PhD scholarship. Z. R. thanks the Islamic Center Association for Guidance and Higher Education for his PhD scholarship. The authors also thank the Electron Microscopy Service of Universitat Politecnica de Valencia for their support and M. Parreno-Romero for her assistance with the measurements.Mazarío-Santa-Pau, J.; Raad, Z.; Concepción Heydorn, P.; Cerdá-Moreno, C.; Domine, ME. (2020). Pd supported on mixed metal oxide as an efficient catalyst for the reductive amination of bio-derived acetol to 2-methylpiperazine. Catalysis Science & Technology. 10(23):8049-8063. https://doi.org/10.1039/d0cy01423kS804980631023Stöcker, M. (2008). Biofuels and Biomass‐To‐Liquid Fuels in the Biorefinery: Catalytic Conversion of Lignocellulosic Biomass using Porous Materials. Angewandte Chemie International Edition, 47(48), 9200-9211. doi:10.1002/anie.200801476Huber, G. W., Iborra, S., & Corma, A. (2006). Synthesis of Transportation Fuels from Biomass:  Chemistry, Catalysts, and Engineering. Chemical Reviews, 106(9), 4044-4098. doi:10.1021/cr068360dWang, Y., Furukawa, S., Fu, X., & Yan, N. (2019). Organonitrogen Chemicals from Oxygen-Containing Feedstock over Heterogeneous Catalysts. ACS Catalysis, 10(1), 311-335. doi:10.1021/acscatal.9b03744Sato, S., Akiyama, M., Takahashi, R., Hara, T., Inui, K., & Yokota, M. (2008). Vapor-phase reaction of polyols over copper catalysts. Applied Catalysis A: General, 347(2), 186-191. doi:10.1016/j.apcata.2008.06.013Velasquez, M., Santamaria, A., & Batiot-Dupeyrat, C. (2014). Selective conversion of glycerol to hydroxyacetone in gas phase over La2CuO4 catalyst. Applied Catalysis B: Environmental, 160-161, 606-613. doi:10.1016/j.apcatb.2014.06.006Célerier, S., Morisset, S., Batonneau-Gener, I., Belin, T., Younes, K., & Batiot-Dupeyrat, C. (2018). Glycerol dehydration to hydroxyacetone in gas phase over copper supported on magnesium oxide (hydroxide) fluoride catalysts. Applied Catalysis A: General, 557, 135-144. doi:10.1016/j.apcata.2018.03.022Mazarío, J., Concepción, P., Ventura, M., & Domine, M. E. (2020). Continuous catalytic process for the selective dehydration of glycerol over Cu-based mixed oxide. 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Derivatives of Piperazine. XXI. Synthesis of Piperazine and C-Substituted Piperazines. Journal of the American Chemical Society, 69(4), 854-855. doi:10.1021/ja01196a034Bai, G., Fan, X., Wang, H., Xu, J., He, F., & Ning, H. (2009). Effects of the preparation methods on the performance of the Cu–Cr–Fe/γ-Al2O3 catalysts for the synthesis of 2-methylpiperazine. Catalysis Communications, 10(15), 2031-2035. doi:10.1016/j.catcom.2009.07.025Narender, N., Srinivasu, P., Kulkarni, S. ., & Raghavan, K. . (2001). Intermolecular Cyclization of Diethanolamine and Methylamine to N,N′-Dimethylpiperazine over Zeolites under High Pressure. Journal of Catalysis, 202(2), 430-433. doi:10.1006/jcat.2001.3291Nagaiah, K., Rao, A. S., Kulkarni, S. J., Subrahmanyam, M., & Rao, A. V. R. (1994). Intermolecular Cyclization of Diethanolamine and Methylamine to N-Methylpiperazine over Zeolites. Journal of Catalysis, 147(1), 349-351. doi:10.1006/jcat.1994.1147Domine, M. E., Hernández-Soto, M. C., Navarro, M. T., & Pérez, Y. (2011). Pt and Pd nanoparticles supported on structured materials as catalysts for the selective reductive amination of carbonyl compounds. Catalysis Today, 172(1), 13-20. doi:10.1016/j.cattod.2011.05.013Domine, M. E., Hernández-Soto, M. C., & Pérez, Y. (2011). Development of metal nanoparticles supported materials as efficient catalysts for reductive amination reactions using high-throughput experimentation. Catalysis Today, 159(1), 2-11. doi:10.1016/j.cattod.2010.08.011H. Blaser , U.Siegrist , H.Steiner , M.Studer , R.Sheldon and H.van Bekkum , Fine chemicals through heterogeneous catalysis , Wiley/VCH , Weinheim , 1st edn, 2001Baiker, A., & Kijenski, J. (1985). Catalytic Synthesis of Higher Aliphatic Amines from the Corresponding Alcohols. Catalysis Reviews, 27(4), 653-697. doi:10.1080/01614948508064235Baxter, E. W., & Reitz, A. B. (2002). Reductive Aminations of Carbonyl Compounds with Borohydride and Borane Reducing Agents. 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Preparation of non-fused heterocycles in zeolites and mesoporous materials. Journal of Molecular Catalysis A: Chemical, 242(1-2), 195-217. doi:10.1016/j.molcata.2005.07.042Vidal, J. D., Climent, M. J., Concepcion, P., Corma, A., Iborra, S., & Sabater, M. J. (2015). Chemicals from Biomass: Chemoselective Reductive Amination of Ethyl Levulinate with Amines. ACS Catalysis, 5(10), 5812-5821. doi:10.1021/acscatal.5b01113Ueda, W., Yokoyama, T., Moro-Oka, Y., & Ikawa, T. (1984). Catalytic synthesis of vinyl ketones over metal oxide catalysts using methanol as the vinylating agent. Journal of the Chemical Society, Chemical Communications, (1), 39. doi:10.1039/c39840000039Liang, G., Wang, A., Li, L., Xu, G., Yan, N., & Zhang, T. (2017). Production of Primary Amines by Reductive Amination of Biomass-Derived Aldehydes/Ketones. Angewandte Chemie International Edition, 56(11), 3050-3054. doi:10.1002/anie.201610964Mazarío, J., Parreño Romero, M., Concepción, P., Chávez-Sifontes, M., Spanevello, R. A., Comba, M. B., … Domine, M. E. (2019). Tuning zirconia-supported metal catalysts for selective one-step hydrogenation of levoglucosenone. Green Chemistry, 21(17), 4769-4785. doi:10.1039/c9gc01857cBORCHERT, H., JURGENS, B., ZIELASEK, V., RUPPRECHTER, G., GIORGIO, S., HENRY, C., & BAUMER, M. (2007). Pd nanoparticles with highly defined structure on MgO as model catalysts: An FTIR study of the interaction with CO, O2, and H2 under ambient conditions. Journal of Catalysis, 247(2), 145-154. doi:10.1016/j.jcat.2007.02.002Tessier, D., Rakai, A., & Bozon-Verduraz, F. (1992). Spectroscopic study of the interaction of carbon monoxide with cationic and metallic palladium in palladium–alumina catalysts. J. Chem. Soc., Faraday Trans., 88(5), 741-749. doi:10.1039/ft9928800741Bertarione, S., Scarano, D., Zecchina, A., Johánek, V., Hoffmann, J., Schauermann, S., … Freund, H.-J. (2004). 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A tandem process for in situ H2O2 formation coupled with benzyl alcohol oxidation using Pd-Au bimetallic catalysts

[EN] Alcohol oxidation is one of the most important industrial organic reactions. Traditionally, the best-suited catalysts are Pd, Pt and Au supported nanoparticles. The research community has recently started developing strategies for synthesizing carbon-supported Pd/Au bimetallic nanoparticles (NPs), leading to higher activities and selectivities. However, the metallic active species in these catalysts are usually generated using sodium borohydride (NaBH4), which is not synthetically easy to reproduce. In fact, minor modifications in pH, concentration and/or other parameters have a prominent effect on the nature of the promoted material. In this work, a robust process involving dihydrogen flow (H2) at 200 °C as a reducing agent for synthesizing Pd/Au supported bimetallic materials was considered an alternative to the common pathway. The physicochemical properties of the materials derived from different reducing reagents and of varying composition ranges were studied using HR-TEM, XRD, CO chemisorption, and XPS. Their stability and activity were also tested for benzyl alcohol oxidation to benzaldehyde under mild reaction conditions (60 °C, water as the solvent, and PO2 = 1.5 bar). Notably, a catalyst from the hydrogen reduction process with a metal composition of 0.8%Pd¿0.2%Au/C consisting of bimetallic clusters (¿1.5 nm) proved to be the best material (C = 94%, S = 99%). Catalytic performances were strongly correlated with structural properties, such as nanoparticle size and distribution, which, in turn, were affected by the reduction step and the metal composition range. Finally, the influence of oxidants on benzyl alcohol oxidation has also been studied, along with the first approach for the tandem in situ formation of H2O2 coupled with alcohol oxidation.The authors are thankful for the financial support by the Spanish Government (RTI2018-096399-A-I00 and PGC2018-097277-B-I00 funded by MICINN/AEI/10.13039/501100011033) and Junta de Andalucia (P20 01027 and PYC 20 RE 060 UAL). The electron microscopy service of the UPV is acknowledged for their help in sample characterization.Martínez, JS.; Mazarío, J.; Gutiérrez-Tarriño, S.; Galdeano-Ruano, CP.; Gaona Miguélez, JA.; Domine, ME.; Oña-Burgos, P. (2022). A tandem process for in situ H2O2 formation coupled with benzyl alcohol oxidation using Pd-Au bimetallic catalysts. Dalton Transactions. 51(46):17567-17578. https://doi.org/10.1039/D2DT02831J1756717578514

Bimetallic Intersection in PdFe@FeOx-C Nanomaterial for Enhanced Water Splitting Electrocatalysis

Supported Fe-doped Pd-nanoparticles (NPs) are prepared via soft transfor-mation of a PdFe-metal oraganic framework (MOF). The thus synthesized bimetallic PdFe-NPs are supported on FeOx@C layers, which are essential for developing well-defined and distributed small NPs, 2.3 nm with 35% metal loading. They are used as bifunctional nanocatalysts for the electro-catalytic water splitting process. They display superior mass activity for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), both in alkaline and acid media, compared with those obtained for benchmarking platinum HER catalyst, and ruthenium, and iridium oxide OER catalysts. PdFe-NPs also exhibit outstanding stability against sintering that can be explained by the protecting role of graphitic carbon layers provided by the organic linker of the MOF. Additionally, the superior electrocatalytic performance of the bimetallic PdFe-NPs compared with those of monometallic Pd/C NPs and FeOx points to a synergetic effect induced by Fe-Pd interactions that facilitates the water splitting reaction. This is supported by additional characterization of the PdFe-NPs prior and post electrolysis by TEM, XRD, X-ray photoelectron spectroscopy, and Raman revealing that dispersed PdFe NPs on FeOx@C promote interactions between Pd and Fe, most likely to be Pd-O-Fe active centers

Tuning zirconia-supported metal catalysts for selective one-step hydrogenation of levoglucosenone

[EN] Levoglucosenone, directly produced from cellulose-containing residual biomass via pyrolysis treatments, is believed to be a promising bio-renewable platform for both fine and commodity chemicals. In this work, the possibilities given by tuneable catalysts based on Pd and Pt supported on metallic oxides to produce the desired product in the one-pot hydrogenation of levoglucosenone are evaluated. Particularly, the excellent catalytic performance of Pd/ZrO2 and Pt/ZrO2 type materials for the synthesis of dihydrolevoglucosenone (or Cyrene) and levoglucosanol, respectively, during the mild hydrogenation of levoglucosenone is demonstrated. In the Cyrene synthesis, the Pd/t-ZrO2 material showed the best catalytic activity compared to other Pd-supported on metallic oxides. This catalyst achieved nearly 95% yields of Cyrene by working under mild reaction conditions, with very low catalyst loadings (¿3 wt%) and using water as the solvent. On the other hand, the one-pot hydrogenation of levoglucosenone to levoglucosanol is reported for the first time with a Pt-based heterogeneous catalyst (Pt/ZrO2-mix, yield ¿90%), by working at low temperatures and mild H2 pressures with water as the solvent. Comparison of the results attained with other Pt-supported metallic oxides let us to conclude that the metal crystal facets (specifically the 100 facet) play an important role in the hydrogenation process to give levoglucosanol selectively. In addition, the stability and re-usability of both catalysts under operational conditions are also evaluated. Finally, catalytic tests including the use of crude bio-liquids obtained from cellulose-rich biomass pyrolysis and containing ¿66 wt% of levoglucosenone are also assayed, thus demonstrating the possibility of scaling-up the process over these metals supported on zirconia catalysts.Financial support by the Spanish Government (CTQ-201567592, SEV-2016-0683 and PGC2018-097277-B-100) is gratefully acknowledged. R.S. thanks the CONICET financial support (CONICET-CSIC, PVCE Program, RD 4183/15). J.M. thanks MICINN (CTQ2015-67592) for the PhD fellowship. Authors also thank the Electron Microscopy Service of Universitat Politecnica de Valencia for their support.Mazarío-Santa-Pau, J.; Parreño-Romero, M.; Concepción Heydorn, P.; Chávez-Sifontes, M.; Spanevello, RA.; Comba, MB.; Suárez, AG.... (2019). Tuning zirconia-supported metal catalysts for selective one-step hydrogenation of levoglucosenone. 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Competitive CC and CO Adsorption of α-β-Unsaturated Aldehydes on Pt and Pd Surfaces in Relation with the Selectivity of Hydrogenation Reactions: A Theoretical Approach. Journal of Catalysis, 152(2), 217-236. doi:10.1006/jcat.1995.1077Li, H., Calle-Vallejo, F., Kolb, M. J., Kwon, Y., Li, Y., & Koper, M. T. M. (2013). Why (1 0 0) Terraces Break and Make Bonds: Oxidation of Dimethyl Ether on Platinum Single-Crystal Electrodes. Journal of the American Chemical Society, 135(38), 14329-14338. doi:10.1021/ja406655qYamagishi, S., Fujimoto, T., Inada, Y., & Orita, H. (2005). Studies of CO Adsorption on Pt(100), Pt(410), and Pt(110) Surfaces Using Density Functional Theory. The Journal of Physical Chemistry B, 109(18), 8899-8908. doi:10.1021/jp050722iBertarione, S., Scarano, D., Zecchina, A., Johánek, V., Hoffmann, J., Schauermann, S., … Freund, H.-J. (2004). 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MOF-mediated synthesis of supported Fe-doped Pd nanoparticles under mild conditions for magnetically recoverable catalysis

Metal-organic framework (MOF)-driven synthesis is considered as a promising alternative for the development of new catalytic materials with well-designed active sites. This synthetic approach is used here to gradually transform a new bimetallic MOF, with Pd and Fe as the metal components, by the in situ generation of aniline under mild conditions. This methodology results in a compositionally homogeneous nanocomposite formed by Fe-doped Pd nanoparticles that, in turn, are supported on iron oxide-doped carbon. The nanocomposite has been fully characterized by several techniques such as IR and Raman spectroscopy, TEM, XPS, and XAS. The performance of this nanocomposite as an heterogeneous catalyst for hydrogenation of nitroarenes and nitrobenzene coupling with benzaldehyde has been evaluated, proving it to be an efficient and reusable catalyst

Developing and understanding Leaching-Resistant cobalt nanoparticles via N/P incorporation for liquid phase hydroformylation

The ultimate target in heterogeneous catalysis is the achievement of robust, resilient and highly efficient materials capable of resisting industrial reaction conditions. Pursuing that goal in liquid-phase hydroformylation poses a unique challenge due to carbon monoxide-induced metal carbonyl species formation, which is directly related to the formation of active homogeneous catalysts by metal leaching. Herein, supported heteroatom-incorporated (P and N) Co nanoparticles were developed to enhance the resistance compared with bare Co nanoparticles. The samples underwent characterization using operando XPS, XAS and HR electron microscopy. Overall, P- and N-doped catalysts increased reusability and suppressed leaching. Among the studied catalysts, the one with N as a dopant, CoNx@NC, presents excellent catalytic results for a Co-based catalyst, with a 94% conversion and a selectivity to aldehydes of 80% in only 7.5 h. Even under milder conditions, this catalyst outperformed existing benchmarks in Turnover Numbers (TON) and productivity. In addition, computational simulations provided atomistic insights, shedding light on the remarkable resistance of small Co clusters interacting with N-doped carbon patches

Catalytic transformations of glycerol via hydroxyacetone into nitrogen heterocycles of industrial interest

[ES] La presente tesis doctoral aborda el desarrollo de nuevos procesos catalíticos centrados en la valorización del glicerol, subproducto principal en la síntesis de biodiesel. El objetivo principal del trabajo consiste en utilizarlo como fuente de carbono para la producción de heterociclos nitrogenados de interés industrial, en concreto, para la producción de 2-metilpiperazina y 2-metilpirazina. Debido a la baja reactividad del glicerol y las drásticas condiciones de reacción que serían necesarias para llevar a cabo las transformaciones a estos heterociclos, se ha planteado como paso previo el estudio de la optimización y el entendimiento del proceso de deshidratación selectiva de glicerol a hidroxiacetona (o acetol). A través de la obtención de este compuesto intermedio, se han podido desarrollar procesos de producción de los heterociclos nitrogenados eficientes y selectivos, en condiciones de reacción moderadas. A este respecto, los precursores de hidrotalcitas del tipo Cu-Mg-Al dan lugar a una familia de materiales basados en óxidos mixtos Cu-Mg-Al capaces de llevar a cabo la deshidratación selectiva de glicerol a acetol en continuo con rendimientos del ¿40%. Además, estos catalizadores son estables durante más de 8 horas, mostrando también excelente capacidad de regeneración y reusabilidad. Del mismo modo, la combinación de centros ácido-base y redox exhibida por estos materiales ha permitido, a través de la combinación de estudios catalíticos y de caracterización, avanzar en el estado del arte en lo que respecta a la comprensión de esta reacción de deshidratación catalítica de glicerol. De esta forma, se ha podido comprobar el papel fundamental de las especies de Cu y, en concreto de las especies Cu(I) presentes en los catalizadores, en la generación de gliceraldehido como intermedio clave para la producción de acetol. Del mismo modo, los centros ácidos del catalizador facilitan la primera adsorción del glicerol, acelerando así la reacción. No obstante, la necesidad de alcanzar productividades de acetol más elevadas para asegurar el éxito de la estrategia global motivó el desarrollo y estudio, en este proceso de deshidratación selectiva de glicerol en continuo, de una segunda familia de catalizadores basados en óxido de cobre soportado sobre diferentes óxidos metálicos (SiO2, Al2O3 y ZrO2), combinando centros ácidos de Lewis y una alta exposición del Cu. La adecuada selección y optimización de estos materiales lleva a lograr, con varios de ellos, rendimientos del 60% a acetol con concentraciones de glicerol en la alimentación mucho más elevadas. Una vez establecidos varios sistemas catalíticos para la producción de acetol, se abordó la producción de los heterociclos nitrogenados de interés a partir de la combinación de esta molécula con etilendiamina. En concreto, el catalizador Pd/TiO2-Al2O3 tiene alta actividad específica hacia la formación de 2-metilpiperazina (80% de rendimiento), gracias a su elevada exposición de centros de Pd insaturados, crítica para activar el doble enlace C=N y así proceder a la hidrogenación de las iminas intermedias. En segundo lugar, el catalizador CuO/Al2O3-npw, muestra rendimientos del 50% a la 2-metilpirazina, siendo posible alcanzar valores cercanos al 60% cuando se usa el método de precipitación-deposición por micelas en fase reversa para incorporar las nanopartículas de CuO. Finalmente, se llevó a cabo una prueba de concepto para la síntesis de 2-metilpirazina a partir de glicerol en un reactor multi-lecho especialmente diseñado para realizar las dos etapas del proceso en "one-pot" con el mismo catalizador basado en CuO-soportado, obteniéndose resultados prometedores. En definitiva, se han establecido dos nuevas rutas catalíticas para la producción de heterociclos nitrogenados con glicerol como la principal fuente de carbono a través de su derivado acetol, abriéndose así nuevas perspectivas en el campo de la valorización sostenible de moléculas derivadas de biomasa.[CA] La present tesi doctoral aborda el desenvolupament de nous processos catalítics centrats en la valorització del glicerol, subproducte principal en la síntesi de biodièsel, utilitzant-lo com a font de carboni per a la producció d'heterocicles nitrogenats d'interès industrial. En concret, per a la producció de 2-metilpiperazina i 2-metilpirazina. A causa de la baixa reactivitat del glicerol i les dràstiques condicions de reacció que serien necessàries per a dur a terme les transformacions a aquests heterocicles, s'ha plantejat com a pas previ un estudi detallat escometent l'optimització i l'enteniment del procés de deshidratació selectiva de glicerol a hidroxiacetona (o acetol). A través de l'obtenció d'aquest compost intermedi, s'han desenvolupat processos de producció dels heterocicles nitrogenats eficients i selectius, en condicions de reacció moderades. Referent a això, els precursors hidrotalcítics Cu-Mg-Al donen com a resultat una família de materials basats en òxids mixtos Cu-Mg-Al capaços de dur a terme la deshidratació selectiva de glicerol a acetol en continu amb rendiments del 40%. Així mateix, aquests catalitzadors són estables durant més de 8 hores, mostrant a més una excel·lent regenerabilitat i reusabilitat. De la mateixa manera, la combinació de centres àcid-base i redox exhibida per aquests materials ha permès, a través de la combinació d'estudis catalítics i de caracterització, avançar significativament en l'estat de l'art pel que fa a la comprensió d'aquesta reacció catalítica. D'aquesta manera, s'ha pogut comprovar el paper fonamental del Cu i, en concret del Cu(I), en la generació de gliceraldehid com a intermedi de reacció clau. Per altra banda, els centres àcids del catalitzador faciliten la primera adsorció del reactiu, accelerant així la reacció. No obstant això, la necessitat d'aconseguir productivitats de acetol més elevades per a assegurar l'èxit de l'estratègia global va motivar l'ús, en aquest procés de deshidratació selectiva de glicerol en continu, d'una segona família de catalitzadors basats en òxid de coure suportat sobre diferents òxids inorgànics d'alta àrea (SiO2, Al2O3 i ZrO2), combinant centres àcids de Lewis i una alta exposició del Cu. L'adequada selecció i optimització d'aquests materials aconsegueix, amb alguns d'ells, rendiments del 60% a acetol amb concentracions de glicerol en l'alimentació molt més elevades. Una vegada establits diversos sistemes catalítics per a la producció d'acetol, es va abordar la producció dels heterocicles nitrogenats d'interès a partir de la combinació d'aquesta molècula amb etilendiamina. En concret, el catalitzador Pd/TiO2-Al2O3 té una alta activitat específica cap a la formació de 2-metilpiperazina (80% de rendiment), gràcies a la seua elevada exposició de centres de Pd insaturats, crítica per a activar el doble enllaç C=N i així procedir a la hidrogenació de les imines intermèdies. En segon lloc, s'ha pogut comprovar que, en presència d'un catalitzador principalment àcid contenint Cu, és possible realitzar la dehidrociclació d'acetol amb etilendiamina per a obtindre 2-metilpirazina i altres alquilpirazinas. Concretament, el catalitzador CuO/Al2O3-npw, mostra rendiments del 50% a la 2-metilpirazina, sent possible aconseguir valors pròxims al 60% quan s'utilitza el mètode de precipitació-deposició per micel·les en fase revessa per a incorporar les nanopartícules de CuO. Finalment, es va dur a terme una prova de concepte per a la síntesi de 2-metilpirazina a partir de glicerol en un reactor multi-llit especialment dissenyat per realitzar les dues etapes del procés en "one-pot" amb el mateix catalitzador basat en CuO-suportat, amb resultats prometedors. D'aquesta manera, s'han establit dues noves rutes catalítiques per a la producció d'heterocicles nitrogenats amb glicerol com a la principal font de carboni, a través del seu derivat acetol obrint així noves perspectives en l'àmbit de la valorització sostenible de les molècules derivades de la biomassa.[EN] This doctoral thesis addresses the development of new catalytic processes centered on glycerol valorization, which is the main by-product of biodiesel synthesis. In this sense, the main aim focused on using it as a carbon source to generate nitrogen heterocycles of industrial interest, specifically, to produce 2-methylpiperazine and 2-methylpyrazine. Due to the low reactivity of glycerol and the severe reaction conditions necessary to carry out the transformations towards these N-heterocycles, previous detailed research to optimize and understand the selective dehydration process of glycerol to hydroxyacetone (or acetol) was undertaken. Through obtaining this intermediate compound, it has been possible to develop efficient and selective nitrogen heterocycles production processes, under moderate reaction conditions. In this regard, Cu-Mg-Al hydrotalcite precursors give rise to a family of materials based on Cu-Mg-Al mixed oxides capable of carrying out the selective dehydration of glycerol to acetol continuously with yields of 40%. In addition, these catalysts are stable for more than 8 hours under operational conditions, showing excellent regeneration capacity and reusability. In the same way, through the combination of catalytic and characterization studies, the interesting mix of acid-base and redox centers exhibited by these materials has allowed for advancing significantly in the state of the art regarding understanding this glycerol catalytic dehydration reaction. Hence, it has been possible to verify the fundamental role of Cu species and, specifically, Cu(I) species present in the catalysts, in the generation of glyceraldehyde as a critical reaction intermediate for acetol production. Similarly, the acid centers of the catalyst facilitate the first adsorption of glycerol, thus accelerating the reaction. However, the need to achieve higher acetol productivities from glycerol to stand a chance to succeed in the overall strategy motivated the development and study of a second family of catalysts based on copper oxide supported on different metal oxides (SiO2, Al2O3 and ZrO2) combining Lewis acid centers and high Cu exposure. The proper selection and optimization of these materials lead to reaching, with several of them, yields of 60% to acetol with much higher glycerol concentrations in the starting feed. Once several catalytic systems had been established to produce acetol, the generation of the nitrogen heterocycles of interest from the combination of this molecule with ethylenediamine was investigated. Specifically, the Pd/TiO2-Al2O3 catalyst presents high specific activity when forming 2-methylpiperazine (80% yield). These excellent results could be attributed to the enhanced exposure of unsaturated Pd centers observed in this material, critical for activating the C=N double bond and thus proceeding to the hydrogenation of the intermediate imines. Secondly, the CuO/Al2O3-npw catalyst yields 50% to 2-methylpyrazine, reaching values close to 60% when the precipitation-deposition method by micelles in reverse phase is used to incorporate the CuO nanoparticles. Finally, a proof of concept of 2-methylpyrazine synthesis starting from glycerol by using a specially designed multi-bed catalytic reactor to perform the two-steps process in one-pot with the same CuO-supported catalyst was assayed, with promising results. In summary, two new catalytic routes have been established to produce nitrogen heterocycles with glycerol as the main carbon source through its derivative hydroxyacetone, thus opening new perspectives in the field of sustainable valorization of biomass-derived molecules.Mazarío Santa-Pau, J. (2021). Catalytic transformations of glycerol via hydroxyacetone into nitrogen heterocycles of industrial interest [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/179915TESI

Isomerization of Glucose-to-Fructose in Water over a Continuous Flow Reactor using Ca−Al Mixed Oxide as Heterogeneous Catalyst

This work reports the continuous isomerization of glucose to fructose in aqueous media under mild conditions using a mixed oxide hydrotalcite-derived catalyst based on Ca and Al. Different operational parameters of the continuous flow fix-bed catalytic reactor system were studied. At the optimal conditions, the Ca−Al-based catalyst achieved a very high conversion and almost quantitative selectivity towards fructose, this being one of the few successful examples of a heterogeneous catalyst capable of carrying out this reaction in a continuous process. Importantly, catalytic activity held steady during four hours on stream, and slight deactivation occurring could be practically overcome by thermal regeneration of the catalyst.Grant PGC2018-097277-B-I00 funded by MCIN/AEI/10.13039/ 501100011033 and “ERDF A way of making Europe“, and the financial support by the Spanish Government (SEV-2016-0683) and Generalitat Valenciana (GVA, PROMETEO/2018/006) are gratefully acknowledged. Authors also thank the ITQ for the technical support, and the Electron Microscopy Service of Universitat Politècnica de València for instrumental facilities. J.M. thanks the Spanish Government (CTQ-2015-67592) for his PhD fellowship.Peer reviewe