Open Access
Extruded catalysts with magnetic properties for biodiesel production
(Hindawi, 2018) Silveira Junior, Euripedes Garcia; Justo, Oselys Rodriguez; Perez, Victor Haber; Reyero Zaragoza, Inés; Serrano Lotina, Ana; Campos Ramírez, Leonardo; Santos Dias, Dayana F. dos; Ciencias; Zientziak
The aim of this work was to evaluate the performance of different extruded catalysts containing K2CO3 as active phase and adding conveniently γ-Al2O3 and/or sepiolite and magnetic particles on the biodiesel production from sunflower oil by the ethanolic route. Firstly, the content of the Fe3O4 on the catalyst (0.1, 0.2, 0.3, and 0.4 g Fe3O4/g of K2CO3/γ-Al2O3), after calcination step, was evaluated to verify the separation facility of the catalysts with magnetic properties from reactional medium, using an external magnetic field, at the end of biodiesel synthesis. After that, three different catalysts were considered for comparative purposes: (a) K2CO3/γ-Al2O3; (b) K2CO3/γ-Al2O3/Fe3O4; (c) K2CO3/γ-Al2O3/Sepiolite/Fe3O4 and subsequently characterized by dynamometry, TGA, SEM, VSM, BET, and XRD to determine their mechanical, structural, magnetic, and textural properties. However, their catalytic activities were determined through biodiesel production that was carried out in a glass volumetric reactor during 4 h, under magnetic stirring with 5% wt. of the catalyst and oil: ethanol molar ratio (1: 12) at 80°C reaction temperature. The best result, i.e., around 88% of biodiesel conversion, was obtained with catalyst K2CO3/γ-Al2O3/Sepiolite/Fe3O4 which showed also satisfactory textural and mechanical strength properties comparatively with the other catalytic derivatives. In addition, no agglomeration of the particles was observed during the reaction, and the magnetic property of this catalytic system was satisfactory for adequate separation from reactional medium seeking further reuse. The attained results are attractive for possible implementation at industrial scale and can be considered to mitigate drawbacks which resulting by using of homogeneous catalysts in the conventional processes.
Open Access
Remarkable performance of supported Rh catalysts in the dry and combined reforming of biogas at high space velocities
(Elsevier, 2024) Navarro Puyuelo, Andrea; Atienza Martínez, María; Reyero Zaragoza, Inés; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Dry and combined (with O2) reforming of synthetic biogas were studied at 700 °C using 0.5 % Rh catalysts prepared by impregnation on different supports: γ-Al2O3, SiO2, TiO2, ZrO2 and CeO2. Gas hourly space velocity (GHSV) was varied between 150 and 700 N L CH4/(gcat·h), and two O2/CH4 molar ratios of 0 and 0.12 were studied. Rh/Al2O3 catalysts (prepared using two different commercial supports here denoted as Sph and AA) presented the highest biogas conversion and syngas yields under both dry and combined reforming conditions. Catalytic activities were as follows: Rh/AA ≈ Rh/Sph > Rh/SiO2 > Rh/ZrO2 ≈ Rh/CeO2 > Rh/TiO2. The effect of catalysts’ calcination pre-treatment at relatively low (200 °C) and high temperatures (750 °C) was also studied. Calcination at high temperatures had a detrimental effect on both dry and combined reforming activities. However, a positive effect on the reforming activities and syngas yields was observed when the catalysts were calcined at 200 °C, especially under biogas combined reforming conditions: higher CH4 conversions and syngas yields could be achieved, as well as increasing CO2 conversions, though at the expense of lower H2/CO molar ratios.
Open Access
Avances en la producción de biodiésel: etanolisis y nuevos catalizadores heterogéneos
(2014) Reyero Zaragoza, Inés; Gandía Pascual, Luis; Arzamendi Manterola, Gurutze; Química Aplicada; Kimika Aplikatua
La síntesis convencional del biodiésel se realiza por transesterificación con metanol de los triglicéridos que constituyen los aceites vegetales en presencia de catalizadores básicos homogéneos. En esta tesis se estudian las implicaciones que supone: i) la sustitución de metanol de origen fósil por etanol para mejorar la sostenibilidad del biodiésel; ii) el empleo de catalizadores de tipo heterogéneo, tanto soportados como estructurados para poder ser reutilizados, simplificando además las etapas de purificación de los productos (biodiésel y glicerina) y reduciendo los costes de operación y el impacto ambiental del proceso. Se ha encontrado que las reacciones de metanolisis y etanolisis de triglicéridos presentan diferencias significativas ya que gracias a la mayor intersolubilidad de los diferentes compuestos, la etanolisis se desarrolla en un medio homogéneo mientras que la metanolisis es una reacción heterogénea bifásica. Se ha formulado un modelo cinético para la etanolisis de aceite de girasol catalizada por NaOH que incluye las tres etapas de la reacción de transesterificación como reacciones reversibles elementales y en el que las ecuaciones cinéticas incluyen de forma explícita la concentración de catalizador con orden de reacción 1. El modelo incluye el equilibrio de interconversión entre los aniones hidróxido y etóxido y reacciones de saponificación. El modelo permite describir la evolución con el tiempo de reacción de la conversión del aceite y de los rendimientos a los productos de reacción, incluyendo diglicéridos y monoglicéridos. También captura el fenómeno de agotamiento del catalizador por formación de jabones que se observa a bajas concentraciones iniciales de NaOH y relaciones molares etanol/aceite. Con respecto a los catalizadores heterogéneos másicos, el esfuerzo se ha centrado en el CaO y sus derivados como catalizadores de metanolisis. El CaO es muy sensible a la contaminación con el CO2 y la humedad atmosféricas, lo que provoca pérdida de su actividad. Además en la propia reacción se transforma en gliceróxido de calcio al reaccionar con el glicerol. El gliceróxido es activo en la reacción de metanolisis, pero también muy soluble en metanol lo que incrementa la contribución de catálisis homogénea. Se ha logrado sintetizar e identificar un nuevo compuesto activo en esta reacción, el glicerolato de Ca, que al ser muy poco soluble en metanol, se constituye en un buen candidato para el desarrollo de catalizadores heterogéneos de síntesis de biodiésel. El empleo de catalizadores estructurados supone un paso importante en las posibilidades de recuperación y reutilización del catalizador. Se han formulado series de catalizadores estructurados a base de monolitos metálicos e hidrotalcita Mg-Al y óxidos Ca-Ce. Los resultados catalíticos han sido buenos desde el punto de vista de la actividad, sin embargo, se han presentado problemas de estabilidad relacionados con la baja adherencia de la fase activa al sustrato. Lograr una mayor interacción Ca-Ce parece ser clave para mejorar la estabilidad.
Open Access
Effect of oxygen addition, reaction temperature and thermal treatments on syngas production from biogas combined reforming using Rh/alumina catalysts
(Elsevier, 2019) Navarro Puyuelo, Andrea; Reyero Zaragoza, Inés; Moral Larrasoaña, Ainara; Bimbela Serrano, Fernando; Bañares, Miguel A.; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Dry reforming and partial oxidation of biogas were studied using 0.5 wt.% Rh/Al2O3 catalysts, both inhouse prepared and commercial. The effects of O2 addition on syngas yield and biogas conversion were studied at 700 C using different O2/CH4 ratios in the gas feeding stream: 0 (dry reforming), 0.12, 0.25, 0.45 and 0.50. The highest CH4 conversion, H2 yield and H2/CO molar ratio were obtained with an O2/CH4 ratio of 0.45, even though simultaneous valorization of both CH4 and CO2 could be best attained when the O2/CH4 ratio was 0.12. Increased biogas conversions and syngas yields were obtained by increasing reaction temperatures between 650 and 750 C. A detrimental influence on catalytic activity could be observed when the catalyst was subjected to calcination. Increasing the hold time of the thermal conditioning of the catalyst under inert flow altered Rh dispersion, though had no significant impact on catalyst performance in the dry reforming of methane at 700 C and 150 N L CH4/(gcat h). Characterization of spent samples after reaction by Raman spectroscopy revealed the presence of carbonaceous deposits of different nature, especially on the commercial(named as Rh com) and calcined (Rh calc) catalysts, though oxygen addition in the biogas feed significantly reduced the amount of these deposits. The Rh catalysts that had not been calcined after impregnation (Rh prep) did not present any noticeable characteristic peaks in the G and D bands. In particular, scanning transmission electron microscopy (STEM) images of the spent Rh prep sample revealed the presence of very highly dispersed Rh nanoparticles after reaction, of particle sizes of about 1 nm, and no noticeable C deposits. Combined oxy-CO2 reforming of biogas using highly dispersed and low metal-loading Rh/Al2O3 catalysts with low O2 dosage in the reactor feed can be used to effectively transform biogas into syngas.
Open Access
CO2 methanation over nickel catalysts: support effects investigated through specific activity and operando IR spectroscopy measurement
(MDPI, 2023) González Rangulan, Vigni Virginia; Reyero Zaragoza, Inés; Bimbela Serrano, Fernando; Romero Sarria, Francisca; Daturi, Marco:; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Renewed interest in CO2 methanation is due to its role within the framework of the Power-to-Methane processes. While the use of nickel-based catalysts for CO2 methanation is well stablished, the support is being subjected to thorough research due to its complex effects. The objective of this work was the study of the influence of the support with a series of catalysts supported on alumina, ceria, ceria–zirconia, and titania. Catalysts’ performance has been kinetically and spectroscopically evaluated over a wide range of temperatures (150–500 °C). The main results have shown remarkable differences among the catalysts as concerns Ni dispersion, metallic precursor reducibility, basic properties, and catalytic activity. Operando infrared spectroscopy measurements have evidenced the presence of almost the same type of adsorbed species during the course of the reaction, but with different relative intensities. The results indicate that using as support of Ni a reducible metal oxide that is capable of developing the basicity associated with medium-strength basic sites and a suitable balance between metallic sites and centers linked to the support leads to high CO2 methanation activity. In addition, the results obtained by operando FTIR spectroscopy suggest that CO2 methanation follows the formate pathway over the catalysts under consideration.
Open Access
Rutas y retos para la valorización de biogás
(Universidad Libre (Colombia), 2017) Navarro Puyuelo, Andrea; Reyero Zaragoza, Inés; Moral Larrasoaña, Ainara; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Química Aplicada; Kimika Aplikatua
Las tecnologías de digestión anaerobia para procesar corrientes residuales (fracción orgánica de residuos de vertedero, lodos de estaciones depuradoras de aguas residuales, purines, etc.) han originado un incremento de la producción de biogás. El biogás está compuesto principalmente por metano y dióxido de carbono, aunque contiene otros componentes minoritarios e impurezas que obligan a efectuar tratamientos para su purificación y acondicionamiento. Existen diversas alternativas para el aprovechamiento y la valorización de este gas, como son: su utilización directa en la generación de energía calorífica y/o eléctrica, su conversión a biometano, y la producción de gas de síntesis (H2+CO), que posteriormente permite producir combustibles líquidos y/o compuestos químicos de interés como el metanol. En este trabajo se presenta una revisión general de las alternativas de valorización de biogás, con énfasis en los procesos de reformado catalítico, tales como el reformado seco o con vapor de agua y procesos de reformado combinado incluyendo la oxidación parcial.
Open Access
Catalytic performance of bulk and Al₂O₃-supported molybdenum oxide for the production of biodiesel from oil with high free fatty acids content
(MDPI, 2020) Navajas León, Alberto; Reyero Zaragoza, Inés; Jiménez Barrera, Elena; Romero Sarria, Francisca; Llorca Piqué, Jordi; Gandía Pascual, Luis; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
Non-edible vegetable oils are characterized by high contents of free fatty acids (FFAs) that prevent from using the conventional basic catalysts for the production of biodiesel. In this work, solid acid catalysts are used for the simultaneous esterification and transesterification with methanol of the FFAs and triglycerides contained in sunflower oil acidified with oleic acid. Molybdenum oxide (MoO₃), which has been seldom considered as a catalyst for the production of biodiesel, was used in bulk and alumina-supported forms. Results showed that bulk MoO3 is very active for both transesterification and esterification reactions, but it suffered from severe molybdenum leaching in the reaction medium. When supported on Al₂O₃, the MoO₃ performance improved in terms of active phase utilization and stability though molybdenum leaching remained significant. The improvement of catalytic performance was ascribed to the establishment of MoO₃Al₂O₃ interactions that favored the anchorage of molybdenum to the support and the formation of new strong acidic centers, although this effect was offset by a decrease of specific surface area. It is concluded that the development of stable catalysts based on MoO₃ offers an attractive route for the valorization of oils with high FFAs content.
Open Access
Reaction monitoring by ultrasounds in a pseudohomogeneous medium: triglyceride ethanolysis for biodiesel production
(MDPI, 2022) Reyero Zaragoza, Inés; Gandía Pascual, Luis; Arzamendi Manterola, Gurutze; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The sound propagation speed measurement us is used for monitoring triglyceride ethanol-ysis in a broad range of reaction conditions (mainly, temperature: 23–50◦C; ethanol/oil: from 6 to 24 mol/mol). Experimentally, us slightly increased with the reaction time in all cases as a result of the contribution of its dynamic mixture components. Nomoto’s expression for homogeneous mixtures offered suitable us estimation but with values notably higher than the experimental ones due to the resistance to sound propagation offered by the ethanol/oil interphase (non-homogeneous medium). Our strategy was based on both the comparison of the experimental us values and the theoretical ones correlated by means of triglyceride conversion and on the estimation of the sound speed of oil/ethanol that could emulate the resistance offered by the interphase. The evolution of the reactions was predicted quite well for all the experiments carried out with very different reaction rates. Nev-ertheless, at the beginning of the reaction, the estimated conversion (outside of industrial interests) showed important deviations. The presence of the intermediate reaction products, diglycerides, and monoglycerides could be responsible for those deviations.
Open Access
Performance comparison between washcoated and packed-bed monolithic reactors for the low-temperature Fischer-Tropsch synthesis
(Elsevier, 2021) Ibáñez Borde, María; Sanz Iturralde, Oihane; Egaña, Ane; Reyero Zaragoza, Inés; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Montes, Mario; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Washcoating and packing of Co-Re catalyst particles have been employed as structuring methods of parallel channel monoliths used in the low-temperature Fischer-Tropsch synthesis (FTS). These methods were compared with regard to catalyst hold-up, heat transfer properties and pressure drop. Reactors output was assessed in terms of CO conversion, CH4 selectivity and productivity of C5+ hydrocarbons. Washcoating led to much lower pressure drops, but also resulted in considerably lower catalyst inventory. As for the reactors performance (volumetric and per catalyst mass C5+ productivities), the washcoated monoliths were more effective than the packed-bed ones. This has been attributed to their more favorable hydrodynamic behavior that facilitates the drainage of the reaction products (liquids and waxes) through the central hollow of the channels thus reducing the extra-pellet diffusional limitations. For both catalyst configurations, it has been found that the productivity of C5+ per catalyst mass unit increases as the characteristic diffusion length increases within the range of values considered in this study (below 150 µm). This indicates that a moderate level of internal mass transport restrictions is beneficial for the low-temperature FTS, which has been explained in terms of the effects of diffusional limitations on the H2/CO molar ratio, and that of this ratio on the FTS kinetics. The possible influence of thermal effects on these results has been numerically and experimentally discarded.
Open Access
Highly selective CO formation via CO2 hydrogenation over novel ceria-based high-entropy oxides (HEOs)
(Elsevier, 2025-03-01) Cortázar, María; Lafuente Adiego, Marta; Navarro Puyuelo, Andrea; García, Xènia; Llorca Piqué, Jordi; Reyero Zaragoza, Inés; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In the present study, new ceria-based high-entropy oxides (HEOs) were investigated as CO2 hydrogenation catalysts. The nominal composition was (Ce0.5Ni0.1Co0.1Cu0.1Zn0.1Mg0.1)Ox and the synthesis was accomplished through the citrate complexing sol-gel method. Characterization techniques utilized including ICP-AES, in situ XRD and in situ XPS, SEM-EDS, HR-TEM and HAADF-STEM, Raman spectroscopy, H2-TPR, CO2-TPD and N2 physical adsorption. The physicochemical characterization and the catalytic results revealed that the conditions of the thermal treatments at which the oxides were subjected critically determined the catalytic performance, especially the CO2 hydrogenation products selectivities. Calcination in air and/or reduction in hydrogen conducted at temperatures below 500 °C led to active but poorly selective catalysts that produced both methane and CO with significant yields. This was mainly attributed to the presence of metallic Cu, Ni and Co on the catalysts that appeared to be supported on ceria doped with the rest of the formulation elements. In contrast, thermal treatments at 750 °C favored the formation of a rocksalt entropy-stabilized (NiCoCuZnMg)Ox HEO supported on ceria that has stood out for showing an excellent selectivity towards the reverse water¿gas shift (RWGS) reaction. This catalyst led to CO selectivities of almost 100 % over a very wide range of reaction temperatures (300-700 °C). Long-term stability tests (100 h) showed only a slight decrease in CO2 conversion, while CO selectivity remained stable at nearly 100 % at 400 °C. XRD characterization of the used catalysts evidenced that, whereas the basic catalyst structure remained, some metallic copper exsolved during reduction and reaction period. These results are relevant and very promising, opening a door to the development of new catalysts for the valorization of CO2 through the RWGS reaction, thus expanding the low-temperature limit at which this process can be carried out selectively.