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
Renewable hydrocarbon production from waste cottonseed oil pyrolysis and catalytic upgrading of vapors with Mo-Co and Mo-Ni catalysts supported on γ-Al2O3
(MDPI, 2021) Alves Melo, Josué; Santana de Sá, Mirele; Moral Larrasoaña, Ainara; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Wisniewski, Alberto; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this work, the production of renewable hydrocarbons was explored by the means of waste cottonseed oil (WCSO) micropyrolysis at 500◦C. Catalytic upgrading of the pyrolysis vapors was studied using α-Al2O3, γ-Al2O3, Mo-Co/γ-Al2O3, and Mo-Ni/γ-Al2O3 catalysts. The oxygen removal efficiency was much lower in non-catalytic pyrolysis (18.0%), whilst γ-Al2O3 yielded a very high oxygen removal efficiency (91.8%), similar to that obtained with Mo-Co/γ-Al2O3 (92.8%) and higher than that attained with Mo-Ni/γ-Al2O3 (82.0%). Higher conversion yields into total renewable hydrocarbons were obtained with Mo-Co/γ-Al2O3 (61.9 wt.%) in comparison to Mo-Ni/γ-Al2O3 (46.6%). GC/MS analyses showed a relative chemical composition of 31.3, 86.4, and 92.6% of total renewable hydrocarbons and 58.7, 7.2, and 4.2% of oxygenated compounds for non-catalytic bio-oil (BOWCSO), BOMoNi and BOMoCo, respectively. The renewable hydrocarbons that were derived from BOMoNi and BOMoCo were mainly composed by olefins (35.3 and 33.4%), aromatics (31.4 and 28.9%), and paraffins (13.8 and 25.7%). The results revealed the catalysts’ effectiveness in FFA decarbonylation and decarboxylation, as evidenced by significant changes in the van Krevelen space, with the lowest O/C ratio values for BOMoCo and BOMoNi (O/C = 0–0.10) in relation to the BOWCSO (O/C = 0.10–0.20), and by a decrease in the presence of oxygenated compounds in the catalytic bio-oils.
Open Access
Oxidative steam reforming of glycerol. A review
(Elsevier, 2021) Moreira, Rui; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Ferreira, Abel; Sánchez, José Luis; Portugal, Antonio; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This review article presents the state-of-the-art on the catalytic oxidative steam reforming (OSR) of glycerol to produce syngas. Concerning the different technologies proposed for the catalytic OSR of glycerol, the following key points can be highlighted: (1) the robustness is much higher than other reforming technologies, (2) several catalysts can work with low deactivation, some of which can recover almost full activity by suitable regeneration, (3) syngas production by catalytic OSR of glycerin is higher than with concurrent technologies, (4) their scaling-up remains an unrealized task, (5) the thermodynamics of the process has been sufficiently covered in the literature, (6) there is a significant lack of kinetic and mechanistic studies that could help gaining deeper insight on the process, (7) novel concepts and reactor designs must be proposed for their development at larger scales, (8) new catalyst formulations must be developed for attaining higher resistance against oxidation and (9) process intensification could help developing them at larger scales.
Open Access
Innovative flow-through reaction system for the sustainable production of phenolic monomers from lignocellulose catalyzed by supported Mo2C
(Wiley, 2024) Maisterra Udi, Maitane; Atienza Martínez, María; Hablich Alvarracin, Karina Lissett; Moreira, Rui; Martínez Merino, Víctor; Gandía Pascual, Luis; Cornejo Ibergallartu, Alfonso; Bimbela Serrano, Fernando; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra - Nafarroako Unibertsitate Publikoa
Molybdenum carbide supported on activated carbon (β-Mo2C/AC) has been tested as catalyst in the reductive catalytic fractionation (RCF) of lignocellulosic biomass both in batch and in Flow-Through (FT) reaction systems. High phenolic monomer yields (34 wt.%) and selectivity to monomers with reduced side alkyl chains (up to 80 wt.%) could be achieved in batch in the presence of hydrogen. FT-RCF were made with no hydrogen feed, thus via transfer hydrogenation from ethanol. Similar selectivity could be attained in FT-RCF using high catalyst/biomass ratios (0.6) and high molybdenum loading (35 wt.%) in the catalyst, although selectivity decreased with lower catalyst/biomass ratios or molybdenum contents. Regardless of these parameters, high delignification of the lignocellulosic biomass and similar monomer yields were observed in the FT mode (13-15 wt.%) while preserving the holocellulose fractions in the delignified pulp. FT-RCF system outperforms the batch reaction mode in the absence of hydrogen, both in terms of activity and selectivity to reduced monomers that is attributed to the two-step non-equilibrium processes and the removal of diffusional limitations that occur in the FT mode. Even though some molybdenum leaching was detected, the catalytic performance could be maintained with negligible loss of activity or selectivity for 15 consecutive runs.
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
Exploring a low-cost valorization route for amazonian cocoa pod husks through thermochemical and catalytic upgrading of pyrolysis vapors
(American Chemical Society, 2023) Villasana, Yanet; Armenise, Sabino; Ábrego, Javier; Hablich, Karina; Bimbela Serrano, Fernando; Cornejo Ibergallartu, Alfonso; Gandía Pascual, Luis; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Ecuador as an international leader in the production of cocoa beans produced more than 300 000 tons in 2021; hence, the management and valorization of the 2 MM tons of waste generated annually by this industry have a strategic and socioeconomic value. Consequently, appropriate technologies to avoid environmental problems and promote sustainable development and the bioeconomy, especially considering that this is a megadiverse country, are of the utmost relevance. For this reason, we explored a low-cost pyrolysis route for valorizing cocoa pod husks from Ecuador’s Amazonian region, aiming at producing pyrolysis liquids (bio-oil), biochar, and gas as an alternative chemical source from cocoa residues in the absence of hydrogen. Downstream catalytic processing of hot pyrolysis vapors using Mo- and/or Ni-based catalysts and standalone γ-Al2O3 was applied for obtaining upgraded bio-oils in a laboratory-scale fixed bed reactor, at 500 °C in a N2 atmosphere. As a result, bimetallic catalysts increased the bio-oil aqueous phase yield by 6.6%, at the expense of the organic phase due to cracking reactions according to nuclear magnetic resonance (NMR) and gas chromatography–mass spectrometry (GC–MS) results. Overall product yield remained constant, in comparison to pyrolysis without any downstream catalytic treatment (bio-oil ∼39.0–40.0 wt % and permanent gases 24.6–26.6 wt %). Ex situ reduced and passivated MoNi/γ-Al2O3 led to the lowest organic phase and highest aqueous phase yields. The product distribution between the two liquid phases was also modified by the catalytic upgrading experiments carried out, according to heteronuclear single-quantum correlation (HSQC), total correlation spectroscopy (TOCSY), and NMR analyses. The detailed composition distribution reported here shows the chemical production potential of this residue and serves as a starting point for subsequent valorizing technologies and/or processes in the food and nonfood industry beneficiating society, environment, economy, and research.
Embargo
How bimetallic CoMo carbides and nitrides improve CO oxidation
(Elsevier, 2023) Villasana, Yanet; García Macedo, Jorge A.; Navarro Puyuelo, Andrea; Reyero Zaragoza, Inés; Lara, Hugo; Bimbela Serrano, Fernando; Gandía Pascual, Luis; Brito, Joaquin L.; Méndez, Franklin J.; Institute for Advanced Materials and Mathematics - INAMAT2
CO elimination is an important step for the proper management of gaseous effluents from various processes, thus avoiding adverse impacts on the environment and human health. In this study, different bimetallic Al2O3-supported CoMo catalysts have been developed, characterized, and tested in the CO oxidation reaction, based on their respective oxides, carbides, and nitrides phases. The parent CoMo-oxide catalyst (CoMo) was prepared by impregnation and then transformed to its carburized (CoMoC) and nitrided (CoMoN) forms using temperatureprogrammed reaction methods under controlled atmospheres of CH4/H2 and NH3, respectively. The catalytic results demonstrate that the CoMoC catalyst exhibits higher activity compared to its CoMoN counterpart, and both are more active than the parent CoMo catalyst. Furthermore, the reduction temperature and space velocity were key process factors, which notably influenced activity and kinetic parameters, while the increase of reduction time does not seem to improve catalytic behavior. These results were associated with a better metal dispersion, and relatively higher reduction grade and metallic surface area on the carbides and nitrides, opening the possibility that new adsorption sites may be created. The catalytic results compare favorably with other nonnoble metal catalysts, such as Cr-, Cu-, Fe-, and Ni-based samples, and highlight the potential of using carbides and nitrides as alternative formulations to enhance the performance of CO oxidation.
Open Access
Extraction of phenolic compounds from populus salicaceae bark
(MDPI, 2022) Autor, Elsa; Cornejo Ibergallartu, Alfonso; Bimbela Serrano, Fernando; Maisterra Udi, Maitane; Gandía Pascual, Luis; Martínez Merino, Víctor; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Gobierno de Navarra / Nafarroako Gobernua; Universidad Pública de Navarra / Nafarroako Unibertsitate
Lignocellulosic residues have the potential for obtaining high value-added products that could be better valorized if biorefinery strategies are adopted. The debarking of short-rotation crops yields important amounts of residues that are currently underexploited as low-grade fuel and could be a renewable source of phenolic compounds and other important phytochemicals. The isolation of these compounds can be carried out by different methods, but for attaining an integral valorization of barks, a preliminary extraction step for phytochemicals should be included. Using optimized extraction methods based on Soxhlet extraction can be effective for the isolation of phenolic compounds with antioxidant properties. In this study, poplar bark (Populus Salicaceae) was used to obtain a series of extracts using five different solvents in a sequential extraction of 24 h each in a Soxhlet extractor. Selected solvents were put in contact with the bark sample raffinate following an increasing order of polarity: n-hexane, dichloromethane, ethyl acetate, methanol, and water. The oily residues of the extracts obtained after each extraction were further subjected to flash chromatography, and the fractions obtained were characterized by gas chromatography coupled with mass spectrometry (GC–MS). The total phenolic content (TPC) was determined using the Folin–Ciocalteu method, and the antioxidant activity (AOA) of the samples was evaluated in their reaction with the free radical 2,2-Diphenyl-picrylhydrazyl (DPPH method). Polar solvents allowed for higher individual extraction yields, with overall extraction yields at around 23% (dry, ash-free basis). Different compounds were identified, including hydrolyzable tannins, phenolic monomers such as catechol and vanillin, pentoses and hexoses, and other organic compounds such as long-chain alkanes, alcohols, and carboxylic acids, among others. An excellent correlation was found between TPC and antioxidant activity for the samples analyzed. The fractions obtained using methanol showed the highest phenolic content (608 g of gallic acid equivalent (GAE)/mg) and the greatest antioxidant activity.
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.
Open Access
Clean syngas production by gasification of lignocellulosic char: state of the art and future prospects
(Elsevier, 2021) Moreira, Rui; Bimbela Serrano, Fernando; Gil-Lalaguna, Noemí; Sánchez, José Luis; Portugal, Antonio; Institute for Advanced Materials and Mathematics - INAMAT2
Using lignocellulosic char instead of the original biomass avoids the need for costly cleaning and conditioning stages of the producer gasification gas. However, lignocellulosic char gasification has been less extensively studied than gasification of lignocellulosic biomass, and a review of published works on this topic was missing. In this review the present status of char gasification technologies and their future prospects are critically discussed, including possible research opportunities. To date, most studies on char gasification have been performed in thermogravimetric analyzers (TGA) or TGA-like experimental setups. The major setback of TGA and TGA-like equipment is that they do not mimic the actual reaction conditions occurring in gasification reactors, which impedes a direct extrapolation of the findings during the scale-up of different gasification technologies. For this reason, in this literature review focus was put on studies undertaken in industrially relevant reactors, both in batch and continuous configurations. Overall, char gasification can be deemed a valid alternative for clean syngas production, contributing to an integral valorization of lignocellulosic residues within different biorefinery schemes. Of these, process intensification by microwave heating offers interesting opportunities for research and scaling-up, though efforts must be directed toward developing continuous microwave-assisted gasification processes.