Examinando por Autor "Serrano, David P."

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Catalytic Properties in Polyolefin Cracking of Hierarchical Nanocrystalline HZSM-5 Samples Prepared According to Different Strategies
(ELSEVIER, 2010) Serrano, David P.; Aguado, J.; Escola, J.M.; Rodríguez, J.M.; Peral, Ángel
Two series of hierarchical nanocrystalline ZSM-5 zeolites prepared by different synthesis strategies (at low temperature and from silanized seeds) and with external surface areas ranging from 150 to 250 m2 g-1 were tested in the cracking of pure LDPE and HDPE at 340ºC and of waste polyethylene at 360ºC. Hierarchical zeolites showed quite higher activity, with values even 6 times higher than a standard nanocrystalline sample used as reference (n-HZSM-5). The activity values decreased from LDPE to HDPE due to the occurrence of some degree of branching in the former polymer, which act as preferential cracking sites. The major products were C1 - C4 hydrocarbons (in the range 30 - 70%, mostly C3 - C4 olefins) and C5 - C12 hydrocarbons (20 - 60%), whose share depends on both the polyolefin and the catalyst. The amount of C13 - C40 hydrocarbons was practically negligible (< 1%) due to the high acid strength of the zeolites which promotes end-chain cracking reactions. Likewise, hierarchical nanocrystalline HZSM-5 zeolites prepared from silanized protozeolitic units showed higher activities than the hierarchical nanocrystalline HZSM-5 samples synthesized at low temperature and atmospheric pressure. The differences were especially remarkable in the case of waste polyethylene cracking. These results were ascribed to the stronger acidity of the hierarchical zeolite samples prepared from silanized seeds.
Effect of the solvent in the liquid phase rearrangement of 1,2-epoxyoctante over Al-MCM-41 and Al-TS-1 catalysts
(ELSEVIER, 2004) van Grieken, Rafael; Serrano, David P.; Melero, Juan A.; García, Alicia
The role of solvent nature in the liquid phase rearrangement of 1,2-epoxyoctane over Al-TS-1 and Al-MCM-41 catalysts is reported. The main reaction product is the aldehyde, while other rearrangement products, mainly allylic alcohols and diol, are obtained. The solvent polarity influences strongly on the activity and product selectivity. The catalytic activity decreases with the increasing of solvent polarity especially for Al-MCM-41 materials. The use of acetonitrile as solvent yields a low conversion of epoxide as a consequence of its basic character. Formation of bulky by-products was detected when dimethylcarbonate was used as solvent over Al-MCM-41. Toluene displays the best catalytic performance in regards to activity and selectivity towards valuable products, with both Al-TS-1 and Al-MCM-41 catalysts, in comparison to those obtained with more polar solvents.
Liquid phase isophorone oxide rearrangement over mesoporous Al-MCM-41 materials
(ELSEVIER, 2005) van Grieken, Rafael; Serrano, David P.; Melero, Juan A.; García, Alicia
The rearrangement of isophorone oxide has been investigated over Al-MCM-41 type mesostructured catalysts having different Si/Al molar ratios. The main rearrangement products are the ¿-diketone and the keto aldehyde, whereas the product coming from the decarbonylation of the latter is detected in minor amounts. The textural properties and the number of acid sites of Al-MCM-41 materials influence the extent of isophorone oxide rearrangement reaction. The best catalytic performance in regards to epoxide conversion is obtained for a catalyst having a molar Si/Al ratio around 40 due to a right contribution of acid site concentration and pore size. However, irrespective to the aluminium content of the catalysts and the reaction temperature, the selectivity to the desired keto aldehyde was around 80%. Al-MCM-41 materials are superior catalysts compared to zeolites in terms of both activity and aldehyde selectivity. As a consequence of its large pore size, the use of Al-containing mesostructured materials as catalyst in isophorone oxide rearrangement allows the diffusional problems present in zeolites to be avoided.
Liquid phase rearrangement of long straight-chain epoxides over amorphous, mesostructured and zeolitic catalysts
(ELSEVIER, 2004) Serrano, David P.; van Grieken, Rafael; Melero, Juan Antonio; García, Alicia
A variety of materials with different structural features and acid properties, including amorphous, mesostructured and zeolitic catalysts have been tested in the liquid-phase rearrangement of 1,2-epoxyoctane. The structure and acid strength of the catalysts influence strongly on the activity and product selectivity. The main rearrangement products are the aldehyde, allylic alcohols and diol. Acid sites in the amorphous materials show a poor catalytic activity. Al-TS-1 and Al-Ti-beta, zeolites with medium aluminium content, lead to significant activities and selectivities towards both the aldehyde and the octenols in comparison to those obtained with other zeolitic materials tested. Aluminium-containing mesostructured materials present much higher activities than amorphous and zeolitic catalysts. Al-MCM-41 synthesized by a sol-gel method at room temperature yielded selectivities to octaldehyde and octen-1ols of 40.6% and 44.7%, respectively with a high catalyst activity (TOF of ca. 30.5).
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.
Propane dehydrogenation over Pt and Ga-containing MFI zeolites with modified acidity and textural properties
(Elsevier, 2023) Oliveira, Adriana S.; Cueto, Jennifer; Alonso-Doncel, María del Mar; Kubů, Martin; Čejka, Jiří; Serrano, David P.; García-Muñoz, Rafael A.
A variety of oxides (titanium, tin, calcium, magnesium, and gallium) were supported over nano-crystalline ZSM-5 zeolite (n-ZSM-5) by wet impregnation, characterized and evaluated for propane dehydrogenation (PDH) reaction. To enhance the catalytic performance of the oxide-modified n-ZSM-5, Pt nanoparticles were also dispersed over the oxides-supported zeolite catalysts by wet impregnation. Finally, Ga-containing MFI zeolites were used as catalysts in the PDH. Ga was incorporated into the zeolite by two different methods, via hydrothermal synthesis and via wet impregnation. In the PDH reaction, Pt-containing samples exhibited a high initial catalytic activity although they suffered a fast deactivation by coke deposition. On the contrary, Ga-containing MFI catalysts showed a remarkable stability in the PDH reaction. In particular, the catalyst in which Ga was incorporated into the MFI structure by hydrothermal synthesis (Ga-MFI (nSH)) achieved the highest catalytic performance in PDH (9% conversion and 80% propylene selectivity) due to the synergy between the Brønsted and Lewis acid sites (BAS and LAS) and the optimal strength of its LAS sites. These results denote the great potential of Ga-MFI zeolites as catalysts in PDH reactions.
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.
Selective Decarboxylation of Fatty Acids Catalyzed by Pd-Supported Hierarchical ZSM‑5 Zeolite
(ACS, 2021) Arroyo, Marta; Briones, Laura; Hernando, Héctor; Escola, José M.; Serrano, David P.
Decarboxylation of fatty acids is an interesting route for the production of renewable long-chain hydrocarbons that could replace fossil resources in the formulation of diesel and jet range fuels. The results reported in the present work demonstrate that Pd supported on hierarchical ZSM-5 zeolite allows for the decarboxylation of different fatty acids (stearic, oleic, and palmitic acids) to proceed under mild operation conditions (T = 250 °C and PH2 = 6 bar) with over 90% selectivity toward middle distillate hydrocarbons and conversions in the range of 60–85%. This outstanding performance has been attributed to a combination of high accessibility and tailored acidity in the zeolitic support that favors the metal dispersion and promotes the interaction between Pd and acid sites. The presence of a hydrogen atmosphere, under low-pressure conditions, is required for activating the Pd sites. It is also noteworthy that the catalyst could be reused after washing with n-dodecane, retaining 74% of its initial stearic acid conversion with just a minor variation in the yield of C17 hydrocarbons.
Synthesis of Sn-silicalite from hydrothermal synthesis of SiO2-SnO2 xerogels
(Microporous Mesoporous Mater. 119 (2009) 176-185, 2009) van Grieken, Rafael; Martos, Carmen; Sánchez-Sánchez, Manuel; Serrano, David P.; Melero, Juan A.; Iglesias, José; Cubero, Alvar G.
For the first time, the synthesis of Sn-zeolites starting from SiO2-SnO2 xerogels is described. The influence of several synthesis parameters in the physical-chemical properties of the xerogels and the zeolites subsequently generated has been investigated. Two different tin sources were assayed in the synthesis of xerogels (anhydrous SnCl4 and SnCl4¿5H2O) as well as two gelation agents (NH3 and TPAOH). Though both bases led SiO2-SnO2 xerogels mainly showing tetrahedrally coordinated tin centres, regardless the tin source, only TPAOH derived materials were easily transformed into MFI-type zeolites showing tin incorporation. On the other hand, NH3 gelified xerogels were difficult to crystallize, being this fact attributed to the retention of NH3 species in the xerogels because of the tin Lewis acidity, avoiding its inclusion in the zeolite crystalline framework. Studies on the crystallization time and temperature allowed to optimize the transformation of TPAOH gelified SiO2-SnO2 xerogels into tin-containing MFI zeolites showing isomorphically incorporated tin centres. The so-obtained materials were compared with conventionally synthesized SnS-1 zeolite showing better quality in terms of tin incorporation.