Open Access
Bimetallic (Pt-Ni) La-hexaaluminate catalysts obtained from aluminum saline slags for the dry reforming of methane
(Elsevier, 2021) Torrez Herrera, Jonathan Josué; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work describes the synthesis of platinum-nickel/lanthanum hexaaluminates (PtNi/LHA) and their performance in terms of stability and catalytic activity in the dry reforming of methane (DRM) at 973 K. An Al solution (9.40 g/L) obtained from an Al saline slag waste by acid extraction was used to synthesize the hexaaluminate by mixing with a stoichiometric amount of lanthanum nitrate and methanol/Peg400/PegMn400 under hydrothermal conditions at 493 K for 16 h. After calcination at 1473 K for 2 h, the presence of LHA was confirmed. Wet impregnation of the synthesized support was used to obtain an initial Ni/LHA catalyst (10 wt% NiO) and the modified PtNi/LHA catalysts (0.2–1 wt% Pt). The support and catalysts were characterized by X-ray diffraction (XRD), N2 adsorption at 77 K, temperature- programmed reduction (TPR), scanning electron microscopy (SEM) and transmission electron microscopy (HR- TEM). The analysis of the TPR patterns for the catalysts allowed the type of metal support interaction and NiO species to be determined, with a weak interaction with the support being observed in all cases. The presence of Pt promoted NiO reducibility. The PtNi/LHA catalysts synthesized were found to be active and very stable in the DRM reaction after reaction for 50 h. The catalytic behavior was evaluated from the CO2 and CH4 conversions, as well as the H2/CO selectivity, with values of between 89% and 92% in almost all the time range evaluated. The presence of Pt improved the stability and catalytic performance of Ni/LHA thus improving resistance to coke formation.
Open Access
On the application of an in situ catalyst characterization system (ICCS) and a mass spectrometer detector as powerful techniques for the characterization of catalysts
(MDPI, 2023) Yunes, Simón; Kenvin Jeffrey; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
The in situ characterization of catalysts provides important information on the catalyst and the understanding of its catalytic performance and selectivity for a specific reaction. Temperature programmed analyses (TPX) techniques for catalyst characterization reveal the role of the support on the stabilization and dispersion of the active sites. However, these can be altered at high temperatures since sintering of active species can occur as well as possible carbon deposition which hinders the active species and deactivates the catalyst. The in situ characterization of the spent catalyst, however, may expose the causes of catalyst deactivation. For example, a simple temperature programmed oxidation (TPO) analysis on the spent catalyst may produce CO and CO2 via a reaction with O2 at high temperatures and this is a strong indication that deactivation may be due to the deposition of carbon. Other TPX techniques such as temperature programmed reduction (TPR) and pulse chemisorption are also valuable techniques when they are applied in situ to the fresh catalyst and then to the catalyst upon deactivation. In this work, two Ni supported catalysts were considered as examples to elucidate the importance of these techniques in the characterization study of catalysts applied to the reaction of hydrogenation of CO2.
Open Access
Effect of gold nanoparticles on SiO2@g-C3N4 catalyst for the degradation of amoxicillin
(Elsevier, 2024-08-05) Santamaría Arana, Leticia; Korili, Sophia A.; Gil Bravo, Antonio; López de Luzuriaga Fernández, José Manuel; Monge Oroz, Miguel; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Gold nanoparticles in different proportions (0.5 and 1 %) have been grafted at the surface of a SiO2@g-C3N4 nanotube-based composite (SiO2 nanotubes obtained from halloysite clay) and also g-C3N4 (for comparison purposes) to test their degradation capacity over the antibiotic amoxicillin proving that the introduction of these nanoparticles on the catalyst modifies the degradation mechanism followed by the pollutant. Results obtained show that the introduction of the appropriate percentage of gold NPs in the composite improves amoxicillin degradation efficiency and establish a direct correlation between the presence of gold NPs and the production of ∙O2.
Open Access
Feasibility to producing second generation bioethanol in Bolivia
(Universidad Nacional del Sur (Argentina), 2021) Beltrán Siñani, Magaly Inés; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
Bioethanol produced worldwide is mostly obtained from agricultural crops such as sugarcane and corn. However, it has negative environmental effects, so opportunity for producing bioethanol from agricultural waste arises. This study evaluates the feasibility to produce second generation bioethanol from orange waste (peel and bagasse) generated in the province of Chapare, Bolivia. Bioethanol production yield estimation is carried out by theoretical and experimental ways, DNS and HPLC methods are used for the quantification of reducing sugars, produced by acidic and enzymatic hydrolysis of the waste. Regarding the results obtained, the best alternative in terms of bioethanol production is the enzymatic hydrolysis. An economic and environmental impact evaluation are also included considering the production of bioethanol from real orange residues. The determined price of bioethanol production is USD 0.78 per liter.
Open Access
Progress and perspectives in the catalytic hydrotreatment of bio-oils: effect of the nature of the metal catalyst
(American Chemical Society, 2024) Gil Bravo, Antonio; Sancho Sanz, Iris; Korili, Sophia A.; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In recent years, there has been a surge of interest in transforming biomass into fuel, driven by its potential as the only realistic renewable carbon resource. Several conversion methods have been explored to achieve this, including gasification for producing synthesis gas, fast pyrolysis or hydrothermal liquefaction for obtaining bio-oils, and hydrolysis for generating aqueous sugars. Bio-oils offer environmental benefits due to their lower CO2 emissions, but their direct use as fuels is hindered by limitations such as thermal instability, high viscosity and acidity, and low calorific value. Consequently, advancements in treatment methods are necessary before bio-oils can be used as direct fuels. This review focuses on the catalytic hydrotreatment of bio-oils, which has been shown to be an effective approach for the removal of heteroatoms at moderate temperatures (between 300 and 450 °C) but at high pressures (up to 20 MPa). Oxygenated compounds are transformed into H2O, and N and S are transformed into NH3 and H2S, respectively. The analysis examines how process temperature, residence time, hydrogen pressure, solvent selection, and type of catalyst influence the properties of the improved bio-oil. Mo/W sulfide-supported catalysts have been traditionally used as active phases in hydrotreatment processes, as the presence of S limits catalyst deactivation, while the presence of Ni or Co as promoters enhances hydrogenation reactions. New research trends are exploring alternative catalyst formulations, such as metal phosphides, carbides, nitrides, and mesoporous materials as supports with controlled acid-basic properties.
Open Access
Progress and perspectives on pillared clays applied in energetic and environmental remediation processes
(Elsevier, 2020) Gil Bravo, Antonio; Vicente, Miguel Ángel; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
Pillared interlayered clays (PILCs) are materials that show a two-dimensional layered porous structure with properties that could be interesting alternatives to zeolites and other microporous solids. Some of the properties that make these materials interesting are specific surface area, high exchange capacity, low permeability, swelling ability, relatively good heat resistance stability, high acidic properties, and relatively low price. PILCs have attracted intense research among several years in relation to the possible control of these properties and environmental applications. The current short work is devoted to the tendencies and new insights in to the last five years of PILCs as adsorbents and heterogeneous catalysts. The work finishes considering the future application prospects.
Open Access
Special issue: feature papers in Eng 2022
(MDPI, 2023) Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
The aim of this second Eng Special Issue is to collect experimental and theoretical re-search relating to engineering science and technology. The general topics published in Eng are as follows: electrical, electronic and information engineering; chemical and materials engineering; energy engineering; mechanical and automotive engineering; industrial and manufacturing engineering; civil and structural engineering; aerospace engineering; biomedical engineering; geotechnical engineering and engineering geology; and ocean and environmental engineering. This editorial is an overview of the selected representative studies on these topics. This book contains 33 papers, including 2 Review papers and 1 Communication, published by several authors interested in new cutting-edge developments in the field of engineering. Recently, a subcategory of nanotechnology—nano- and microcontainers—has developed rapidly, with unexpected results. Nano- and microcontainers refer to hollow spherical structures in which the shells can be organic or inorganic. These containers can be filled with substances released when excited and can be used in corrosion healing, cancer therapy, cement healing, antifouling, etc. In the first review, the author summarizes the various innovative technologies that have beneficial effects on improving people’s lives [1].
Open Access
Effect of the synthesis method on the morphology, textural properties and catalytic performance of La-hexaaluminates in the dry reforming of methane
(Elsevier, 2021) Torrez Herrera, Jonathan Josué; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This work describes the synthesis of nickel/lanthanum hexaaluminates (NiO/LHA), optimizing the LHA synthesis method, as well as their performance in terms of stability and catalytic activity in the dry reforming of methane (DRM). The synthesis methods studied include co-precipitation, nitrate decomposition and freeze drying, using a La/Al molar ratio of 1:11 in all methods. Drying methods, namely oven drying (4 h at 353 K), vacuum drying (8 h at 353 K) + oven drying (2 h at 423 K) and heat treatment (12 h at 473 K) + oven drying (2 h at 373 K), were also optimized during selection of the final catalyst support. After calcination at 1473 K for 2 h, the presence of lanthanum aluminate (LaAlO3) and traces of LHA were found in all cases. Specific surface areas of 50, 32 and 30 m(2)/g were obtained for the samples AD1 (nitrate decomposition), FD1 (freeze drying), CP1 (co-precipitation). The nitrate decomposition method was selected and optimized to obtain the LHA structure at low temperature in the presence of Ni(II), using a La/Al/Ni molar ratio of 1/15/0.2. The results showed the formation of pure-phase hexaaluminate at 1473 K. The solids obtained were used as supports for nickel catalysts (10 wt%) for DRM at 973 K. The supports and catalysts were characterized by X-ray diffraction (XRD), N-2 adsorption at 77 K, temperature-programmed reduction (TPR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The simulation of the TPR patterns of the catalysts allowed determining the type of metal support interaction and the activation energy of the system as well as the rest of the kinetic parameters. A cumulative mean activation energy of 100.7 kJ/mol was determined for the catalysts. The metallic morphologies, dispersion and distribution of NiO on the surface of the LHA support were analyzed considering a theoretical simulation of the reduction profiles, obtaining an average growth factor of 1.4, which indicates that the metallic phase is growing in one and two dimensions. The NiO/LHA catalysts synthesized were found to be active and very stable in the DRM reaction after 20 h of reaction with an average selectivity H-2/CO upper than 0.90. The differences observed can be related to the textural properties developed during the optimized nitrate decomposition method. The characterization analysis by simulation, TPR, XRD, TEM, SEM allowed us to establish the effect of the textural properties, the metal interaction, the growth of the nickel grains and their distribution in the support on the catalytic performance in DRM. The better performance was obtained with the catalysts with higher porosity and greater support metal interaction, which allowed obtaining a better distribution of the metallic phase, thus generating less harmful carbonaceous species for the activity of the catalyst and therefore showing the best values of catalytic stability and conversion. Finally, three types of coke were identified from HR-TEM and EDS analysis: graphitic, filamentous and CNT, showing different effects on the catalytic behavior deactivation being the presence of graphitic more aggressive than the other two species.
Open Access
Evidence for the synthesis of La-hexaaluminate from aluminum-containing saline slag wastes: correction of structural defects and phase purification at low temperature
(Elsevier, 2021) Torrez Herrera, Jonathan Josué; Fuentes Ordóñez, Edwin Gustavo; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The synthesis of a lanthanum hexaaluminate from the aluminum extracted from a saline slag waste is presented for the first time. Briefly, a refluxing 2 M solution of HCl is used to extract the aluminum, giving 8.9 gAl/dm3 along with other metals in lower concentrations. This solution is used to synthesize the hexaaluminate by mixing with a stoichiometric amount of lanthanum nitrate. The results showed the formation of pure phase hexaaluminate at 1473 K, as well as predominance of the hexaaluminate phase at temperatures of 1273 and 1373 K. These results also indicate that the pure hexaaluminate phase can be obtained at a much lower temperature than when commercial aluminum solutions are used improving the applications as catalyst and thermal barrier material. It was also found that the presence of other metals in solution allows the structural problems and purity of the La-hexaaluminate phase to be corrected when working with stoichiometric ratios.
Open Access
A comparative study of the catalytic performance of nickel supported on a hibonite-type La-hexaaluminate synthesized from aluminum saline slags in the dry reforming of methane
(Elsevier, 2022) Torrez Herrera, Jonathan Josué; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this work, a hibonite-type Ni/La-hexaaluminate (Ni/LHA) synthesized from an industrial waste is used and compared as catalyst in the dry reforming of methane (DRM) at 973 K. The structure, catalytic behavior, and stability during a run time of at least 50 h of three Nicatalysts obtained from two commercial supports and two preparation methods were used for comparison. An aluminum solution (9.40 g/L) obtained from an aluminum saline slag waste by acid extraction was used to synthesize the hexaaluminate by mixing with a stoichiometric amount of lanthanum nitrate and methanol/Peg400/PegMn400 under hydrothermal conditions at 493 K for 16 h. The Ni/LHA catalyst (10 wt% NiO) was obtained by impregnation of the synthesized support, calcined previously at 1473 K for 2 h. The resulting solids were characterized by several techniques as: X-ray diffraction (XRD), N2 adsorption at 77 K, temperature-programmed reduction (TPR), scanning electron microscopy (SEM) and transmission electron microscopy (HR-TEM). In order to compare the catalytic behavior and properties of the Ni/LHA catalyst, three Ni catalysts obtained from two commercial supports (g-Al2O3 and SiO2) and two preparation methods (wet impregnation (I) and precipitation-deposition (PD)) were synthesized. Analysis of the TPR patterns for the catalysts allowed the type of metal support interaction and NiO species to be determined, with a weak interaction with the support being observed in Ni/LHA and NieI/ SiO2. The NiO species observed, with crystallite sizes between 9.7 and 40.4 nm, confirm the X-ray structural analyses. The Ni/LHA catalyst was found to be active and very stable in the DRM reaction after 50 h. The catalytic behavior was evaluated from the CO2 and CH4 conversions, as well as the H2/CO selectivity, with values of 99% over almost all the time range evaluated. The behavior of this catalyst is comparable to that of NieI/Al2O3 and NiPD/SiO2. The results found indicating that the strong interaction of nickel with the support favors the stability of the catalysts in the DRM reaction.