Examinando por Autor "Pizarro, Patricia"

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Hydrogen production by catalytic methane decomposition over rice husk derived silica
(Elsevier, 2021-12-15) Gomez-Pozuelo, Gema; Pizarro, Patricia; Botas, Juan Angel; Serrano, David Pedro
Methane decomposition (DeCH4) over solid catalysts is an interesting route for the production of hydrogen free of CO2 emissions. Moreover, it could lead to a negative carbon balance if biogas/biomethane is used as feedstock. However, it is limited by the huge amounts of carbon that are deposited over the catalyst causing its deactivation and hindering its regeneration, which makes necessary the development of low-cost and durable catalytic systems. This work reports the use of different silica materials fully produced from rice husk, i.e. without incorporating any external phase or component, as DeCH4 catalysts. The highest catalytic activity has been found for the silica samples showing large BET surface area and amorphous nature. These properties favor the generation of the actual DeCH4 active sites (-Si-C- species), shortening the induction time detected at the beginning of the reaction tests. The nano-silica materials produced from acid-washed rice husk exhibit a remarkable resistance against deactivation, affording an almost constant reaction rate at long times on stream. This fact is assigned to the presence of large mesopores that facilitate the growth of the carbons deposits towards the outer part of the catalyst particles. The results here reported show the great potential of rice husk-derived nano-silica to overcome several of the most relevant limitations that currently exist for the commercial deployment of hydrogen production by catalytic DeCH4, as a consequence of the low cost and durable activity of these sustainable materials.
Mesostructured SiO2-doped TiO2 with enhanced thermal stability prepared by a soft-templating sol-gel route
(ELSEVIER, 2008) Calleja, Guillermo; Serrano, David P.; Sanz, Raúl; Pizarro, Patricia
Mesostructured SiO2-TiO2 mixed oxides have been prepared by a soft-templating sol-gel route, using a non-ionic triblock copolymer as structure directing agent. Tetraethylorthosilicate (TEOS) and titanium tetraisopropoxide (TTIP) have been employed as Si and Ti sources, respectively. Using a prehydrolysis TEOS step allows mixed oxides to be produced with a homogeneous porosity and with no phase segregation, in a wide range of Si/Ti compositions. Both the hydrolysis molar ratio and the silicon content have been found to be important factors determining the final properties of these materials. For instance, mixed oxides containing low silicon concentrations exhibit N2 physisorption isotherms typical of mesoporous materials, although with an important contribution of microporosity. On the other hand, increasing the hydrolysis molar ratio makes more difficult to reach a total dispersion of SiO2 through the TiO2 matrix. Even with low SiO2 loadings, the thermal stability is effectively enhanced, when compared to the equivalent pure TiO2 materials, as a consequence of a delay in the titania crystallization to anatase. Thus, after calcination at 300 ºC for 3 h, mixed oxides containing low Si/Ti ratios (¿ 20) show BET surface area in the range 290-346 m2/g, while pure TiO2 materials largely collapse under the same treatment and their BET surface area drop strongly to values around 125 m2/g. This synthesis route, therefore, provides mesoporous TiO2-rich materials with enhanced stability and textural properties, which is of high interest for applications as catalysts and supports.
Scaling-Up Microwave-Assisted Synthesis of Highly Defective Pd@UiO-66-NH2 Catalysts for Selective Olefin Hydrogenation under Ambient Conditions
(American Chemical Society, 2024-04-26) Guerrero, Raúl M.; Lemir, Ignacio D.; Carrasco, Sergio; Fernández-Ruiz, Carlos; Kavak, Safiyye; Pizarro, Patricia; Serrano, David P.; Bals, Sara; Horcajada, Patricia; Pérez, Yolanda
The need to develop green and cost-effective industrial catalytic processes has led to growing interest in preparing more robust, efficient, and selective heterogeneous catalysts at a large scale. In this regard, microwave-assisted synthesis is a fast method for fabricating heterogeneous catalysts (including metal oxides, zeolites, metal–organic frameworks, and supported metal nanoparticles) with enhanced catalytic properties, enabling synthesis scale-up. Herein, the synthesis of nanosized UiO-66-NH2 was optimized via a microwave-assisted hydrothermal method to obtain defective matrices essential for the stabilization of metal nanoparticles, promoting catalytically active sites for hydrogenation reactions (760 kg·m–3·day–1 space time yield, STY). Then, this protocol was scaled up in a multimodal microwave reactor, reaching 86% yield (ca. 1 g, 1450 kg·m–3·day–1 STY) in only 30 min. Afterward, Pd nanoparticles were formed in situ decorating the nanoMOF by an effective and fast microwave-assisted hydrothermal method, resulting in the formation of Pd@UiO-66-NH2 composites. Both the localization and oxidation states of Pd nanoparticles (NPs) in the MOF were achieved using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively. The optimal composite, loaded with 1.7 wt % Pd, exhibited an extraordinary catalytic activity (>95% yield, 100% selectivity) under mild conditions (1 bar H2, 25 °C, 1 h reaction time), not only in the selective hydrogenation of a variety of single alkenes (1-hexene, 1-octene, 1-tridecene, cyclohexene, and tetraphenyl ethylene) but also in the conversion of a complex mixture of alkenes (i.e., 1-hexene, 1-tridecene, and anethole). The results showed a powerful interaction and synergy between the active phase (Pd NPs) and the catalytic porous scaffold (UiO-66-NH2), which are essential for the selectivity and recyclability.
SYNTHESIS OF HIERARCHICAL TS-1 ZEOLITE FROM SILANIZED SEEDS
(ELSEVIER, 2010) Serrano, D.P.; Sanz, Raúl; Pizarro, Patricia; Moreno, Inés
Hierarchical TS-1 zeolites with a bimodal pore architecture, consisting of the typical MFI micropores and an additional mesoporosity, have been synthesized by grafting an organosilane compound to the zeolitic seeds previously prepared from two different raw materials: a liquid gel and an amorphous SiO2-TiO2 xerogel. These hierarchical TS-1 zeolites show an excellent catalytic behavior in olefin epoxidation reactions employing organic hydroperoxides as oxidants due to the presence of the secondary mesoporosity, which makes possible the access and interaction of bulky molecules with the Ti active sites