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Synthesis and application of lanthanum aluminate perovskites obtained from aluminum saline slags as catalysts for dry reforming of methane and other environmental uses
(2024) Muñoz Alvear, Helir Joseph; Gil Bravo, Antonio; Korili, Sophia A.; Ciencias; Zientziak; Universidad Pública de Navarra / Nafarroako Liburutegi Publikoa
In this work, the aluminum was successively extracted from saline slags using an acidic medium (HCl or citric acid). The aluminum solutions obtained were used as precursors in the synthesis of lanthanum aluminate perovskite supports (LaAlO3), and various synthesis methods, including MOF-gel precursor, Pechini, and modified citrate, were evaluated to obtain the perovskite. The parameters in the synthesis of lanthanum aluminate were studied, and the physicochemical properties of the resulting functional materials were characterized, with the purpose to optimize the synthesis process and choose the most promising materials. The chosen materials were evaluated, either as catalytic supports or as catalysts, for the dry reforming of methane or the degradation of carbofuran (CBF) in water doped with synthetic dissolved natural organic matter (NOM). The catalytic behavior was compared with that of catalysts prepared by conventional methods and using commercial aluminum saline. The first two chapters of this thesis correspond to the introduction and focus on the theory related to the subject. The First Chapter (I) refers to lanthanum aluminate perovskite, its physicochemical parameters, synthesis methods, and some of its applications. This chapter focuses on the review of studies from the past ten years related to all the synthesis methods employed in the preparation of lanthanum aluminate. It discusses the synthetic challenges, advantages, and limitations associated with these methods, as well as the most significant catalytic applications. The Second Chapter (II) is related to Ni-perovskites-based catalysts for the dry reforming of methane. This chapter delves into the thermodynamic and kinetic aspects of the DRM, highlighting that the properties of A and B can affect catalytic performance. It discusses recent advancements in the substituting of the B cation to enhance catalytic efficiency through synergistic effects. Similarly, the substitution of cation A is explored for its ability to control acid- base properties and the consequent impact on coke formation and deposition. The chapter also reviews progress in improving the low textural properties of perovskites, either directly or by deposition of the perovskites on a support. Finally, new lines of research focused on softening DRM reaction conditions and promoting the process at lower temperatures are also highlighted. The next three chapters (Chapter III to Chapter V) are related to the results and analysis of the experimental part developed in this work. Chapter III is related with a novel and simple strategy developed for synthesizing the pure perovskite phase of lanthanum aluminate (LaAlO3). This involves the calcination of a highly porous, dry MOF precursor gel, which is prepared using commercial precursors, and its subsequent application in the dry reforming of methane. This study revealed that the textural properties of the materials can be modulated by the solvothermal treatment time. Additionally, it identified the main factors that contribute to enhancing the catalytic performance in the dry reforming of methane (DRM) using the Ni/LaAlO3 catalyst. Chapter IV corresponds to the first synthesis of nickel-modified lanthanum aluminate (Ni/LaAlO3) perovskite catalysts using aluminum extracted from saline slag via acid leaching with HCl or citric acid. Three preparation methods (Pechini, modified citrate, and metal–organic gel) were evaluated to obtain the pure lanthanum aluminate (LaAlO3) phase. This study also investigated the effects of several factors, with some variations observed depending on the methodology used. The most promising materials were evaluated as catalytic supports for Ni active sites in the dry reforming of methane. The catalytic performance of the catalysts was compared with a reference catalyst prepared by a conventional method and using commercial aluminum salt. The annex in this document is related to this part of the study. Given the novelty of preparing lanthanum aluminate perovskite from HCl- and citric acid-extracted aluminum from saline slag, and due to the resulting enhancement in the physicochemical properties of the final functional materials, a patent application has been submitted (details provided in the annex). Chapter V corresponds to the first synthesis of LayAl1–xCuxO3–δ perovskite catalysts using Al extracted from saline slag residue (previously extracted with HCl). This study investigates the effect of parameters such as the La/Al molar ratio during the synthetic process. The best catalyst was used to optimize the degradation of carbofuran (CBF) in water doped with synthetic dissolved natural organic matter (NOM) using the Fenton-like catalytic wet peroxide oxidation (CWPO) approach. Lastly, this work investigates the optimal conditions for maximizing pesticide degradation. Finally, Chapter VI corresponds to the general conclusions that can be obtained from this work.
Open Access
Recent advances in the application of Ni-perovskite-based catalysts for the dry reforming of methane
(Taylor & Francis, 2024-09-17) Muñoz Alvear, Helir Joseph; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Ni-based catalysts have been reported to be very efficient in methane reforming processes, surpassing some noble metals. In the particular case of methane reforming in the presence of carbon dioxide (dry reforming of methane, DRM), modifying and controlling the initial properties of the catalyst becomes crucial to resist carbon deposition and Ni metal sintering. This is because the DRM process is carried out at high temperatures. In this sense, perovskite-based catalysts are of special interest given that they are synthesized at high temperatures and, therefore, can conserve their properties during the reaction. Perovskites are represented by the general formula ABO3 or A2BO4. The properties of these oxides depend on the nature of metals A and B and their possible partial substitution, which allows control of their redox and acid/basic properties. This review delves into the thermodynamic and kinetic aspects of the DRM, highlighting that the properties of A and B can affect catalytic performance. Following this, the focus shifts to B-cation substitution, which can increase the catalytic performance of the catalyst via synergistic effects due to the formation of Ni metal alloys. Next, in an analogous manner, the analysis will examine A-cation substitution, which allows control over the acid/basic properties and, therefore, coke formation and deposition. Given the inherently low textural properties of perovskites, methods for enhancing these properties are also summarized. These methods encompass both direct improvements and deposition of the perovskites on a support. Finally, new lines of research focused on softening DRM reaction conditions and promoting the process at lower temperatures are also highlighted.
Open Access
Optimal carbofuran degradation via CWPO in NOM-doped water by a framework Cu-doped aluminate perovskite catalyst derived from aluminum saline slags
(Elsevier, 2024-09-19) Muñoz Alvear, Helir Joseph; Galeano, Luis Alejandro; Vicente, Miguel Ángel; Korili, Sophia A.; Gil Bravo, Antonio; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This study is the first to propose the synthesis of LayAl1–xCuxO3–δ perovskite catalysts using Al recovered from acid leaching of saline slags. The effect of parameters such as the La/Al molar ratio was explored during the synthetic process. A suite of characterization techniques¿including XRF, XRD, N2 adsorption, H2-TPR, FTIR, TGA-DTA, TEM, SEM, EDX, and XPS¿confirmed the successful synthesis of high-purity (up to 90 %) perovskites with La and O vacancies, and a high concentration of Cu(I) active sites dispersed within the perovskite lattice. The best catalyst was used to optimize the degradation of carbofuran (CBF) in water doped with synthetic dissolved natural organic matter (NOM) using the Fenton-like catalytic wet peroxide oxidation (CWPO) approach. The effects of catalyst concentration, H2O2 dose, and pH on catalytic performance were investigated. Degradation, mineralization (COD removal), and H2O2 consumption were maximized, while Cu leaching was minimized using a statistical desirability function for multiple responses. Optimal conditions were found to be a catalyst concentration (mg Cu/mg H2O2) of 0.234 (2.0 g L-1), an H2O2 dose of 73.3 % (0.73 times the stoichiometric dose for full COD mineralization), and a remarkable circumneutral pH of 6.2. Under these conditions, degradation reached 94.1 %, and COD mineralization was 51 % under room temperature. Notably, the perovskite catalyst exhibited remarkable stability during reuse in up to three cycles, as demonstrated by the low Cu leaching (<1.30 mg L-1).
Open Access
Synthesis of MOF@aluminum saline slag-based composites for CO2 capture at moderate temperatures
(Elsevier, 2025-09-01) Muñoz Alvear, Helir Joseph; Vicente, Miguel Ángel; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa; Gobierno de Navarra / Nafarroako Gobernua
Combining metal–organic framework (MOF) materials and aluminum-containing saline slag residues opens a promising research avenue. This approach reduces the environmental impact of aluminum production by integrating industrial waste in the development of advanced materials that adhere to circular economy principles. It also addresses some inherent stability issues observed in pure MOFs. This study is the first to propose the use of this industrial by-product as a cost-effective and environmentally friendly modulator for controlling the phase transition between MIL-96(Al) and MIL-110(Al). For the first time, novel MOFs composites (MOF@RW1*-n; n = 25, 50, 75% waste) and saline slag waste (RW1*)—a by-product of initial aluminum extraction in an acidic medium—were synthesized in situ by preparing the MOF on RW1* via hydrothermal treatment and subsequently tested as CO2 adsorbents at up to 225 ◦C and 80 kPa. The optimized RW1* content in the composite proved critical in determining the formation of specific crystalline structures (MIL-96(Al) or MIL-110(Al)), ultimately yielding hybrid materials with enhanced textural properties and thermal stability.
Open Access
Facile synthesis of an Ni/LaAlO3 - perovskite via an MOF gel precursor for the dry reforming of methane
(Elsevier, 2024) Muñoz Alvear, Helir Joseph; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
A simple strategy to prepare the pure perovskite phase of lanthanum aluminate (LaAlO3) by calcination of a highly porous, dry MOF precursor gel has been developed. This study demonstrates that the structural and textural properties, such as specific surface area, pore volumes and pore sizes, of precursor-like metal-organic gels (MOG) (MOG-Al-La) based on metal-organic framework (MOF) structures can be modulated by optimizing the solvothermal treatment time. The perovskite obtained after solvothermal treatment at 120º C for 12 h and calcination at 750º C maintained the mesoporous characteristics of the MOF precursor, with a small particle size due to the decrease in crystallization temperature. These properties in the support allowed a good dispersion of the active Ni sites, low reducibility, and a strong interaction between them and the support, thus suppressing sintering under the severe catalytic reaction conditions evaluated (GHSV = 120,000 cm3/g-h) for the dry reforming of methane. The resulting MOX-(12 h)-LaAlO3-750-Ni catalyst gave a CH4 average conversion of 75% and CO2 average conversion of 80% after 20 h of reaction. The improved stability of the catalyst was attributed to suppression of the formation of the dense network of carbon filaments that can stress and subsequently fracture the support, cause attrition of the catalyst granules and hinder diffusion of the reactants both through the pores of the support and the interparticle spaces.
Open Access
Progress and recent strategies in the synthesis and catalytic applications of perovskites based on lanthanum and aluminum
(MDPI, 2022) Muñoz Alvear, Helir Joseph; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Lanthanum aluminate-based perovskite (LaAlO3) has excellent stability at high temperatures, low toxicity, and high chemical resistance and also offers wide versatility to the substitution of La3+ and Al3+, thus, allowing it to be applied as a catalyst, nano- dsorbent, sensor, and microwave dielectric resonator, amongst other equally important uses. As such, LaAlO3 perovskites have gained importance in recent years. This review considers the extensive literature of the past 10 years on the synthesis and catalytic applications of perovskites based on lanthanum and aluminum (LaAlO3). The aim is, first, to provide an overview of the structure, properties, and classification of perovskites. Secondly, the most recent advances in synthetic methods, such as solid-state methods, solutionmediated methods (co-precipitation, sol–gel, and Pechini synthesis), thermal treatments (combustion, microwave, and freeze drying), and hydrothermal and solvothermal methods, are also discussed. The most recent energetic catalytic applications (the dry and steam reforming of methane; steam reforming of toluene, glycerol, and ethanol; and oxidative coupling of methane, amongst others) using these functional materials are also addressed. Finally, the synthetic challenges, advantages, and limitations associated with the preparation methods and catalytic applications are discussed.
Open Access
Preparation of Al/Fe-pillared clays: effect of the starting mineral
(MDPI, 2017) Muñoz Alvear, Helir Joseph; Blanco, Carolina; Gil Bravo, Antonio; Vicente, Miguel Ángel; Galeano, Luis Alejandro; Química Aplicada; Kimika Aplikatua
Four natural clays were modified with mixed polyoxocations of Al/Fe for evaluating the effect of the physicochemical properties of the starting materials (chemical composition, abundance of expandable clay phases, cationic exchange capacity and textural properties) on final physicochemical and catalytic properties of Al/Fe-PILCs. The aluminosilicate denoted C2 exhibited the highest potential as starting material in the preparation of Al/Fe-PILC catalysts, mainly due to its starting cationic exchange capacity (192 meq/100 g) and the dioctahedral nature of the smectite phase. These characteristics favored the intercalation of the mixed (Al13􀀀x/Fex)7+ Keggin-type polyoxocations, stabilizing a basal spacing of 17.4 Å and high increase of the BET surface (194 m2/g), mainly represented in microporous content. According to H2-TPR analyses, catalytic performance of the incorporated Fe in the CatalyticWet Peroxide Oxidation (CWPO) reaction strongly depends on the level of location in mixed Al/Fe pillars. Altogether, such physicochemical characteristics promoted high performance in CWPO catalytic degradation of methyl orange in aqueous medium at very mild reaction temperatures (25.0 1.0 C) and pressure (76 kPa), achieving TOC removal of 52% and 70% of azo-dye decolourization in only 75 min of reaction under very low concentration of clay catalyst (0.05 g/L).
Embargo
Surface tuning of a highly crystalline Ni/LaAlO3 perovskite catalyst obtained from aluminum saline slags using various synthesis methods for the dry reforming of methane
(Elsevier, 2025-03-01) Muñoz Alvear, Helir Joseph; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
This research presents the first synthesis of nickel-modified lanthanum aluminate (Ni/LaAlO3) perovskite from aluminum (Al) saline slag waste involving acid extraction. Two methods were employed to extract Al: a 2 M HCl aqueous solution (AH) and various citric acid (CA) aqueous solutions (0.5, 1.0, or 2.0 M). Three preparation methods (Pechini, modified citrate, and metal–organic gel) were evaluated to obtain the pure lanthanum aluminate (LaAlO3) phase. This study also investigated the effects of several factors, with some variations being observed depending on the methodology used. The factors analyzed were: (i) preparation method; (ii) type of Al precursor solution (either extracted using HCl or CA); (iii) ligand/cations molar ratio (La3 + + Al3+), ranging from 0.3 to 3.0; (iv) CA concentration; (v) molar ratio (La/Al), between 0.5 and 1.0; (vi) calcination temperature; and (vii) acid etching of the final materials with aqueous dilute nitric acid (HNO3). The results indicated that it is possible to obtain LaAlO3 perovskite using all three methodologies and the Al extracted from saline slags. For the Pechini and metal–organic gel methods, ligand/cations molar ratios (La3+ + Al3+) of 3.0 and between 0.3 (with CA) and 1.5 (with AH), respectively, were obtained, while a CA concentration of 1.0 M was used for the modified citrate method. The optimal molar ratio (La/Al) for obtaining the perovskite was 1.0 in all three methods. The perovskite was synthesized at low temperatures, starting from 650 °C, and was obtained in a completely pure form at between 950 and 1050 °C. Treatment with aqueous dilute acid had a marked effect, especially on the materials obtained when using the initial solution extracted with 2.0 M HCl. This treatment was particularly beneficial for the material prepared using the Pechini method, which induced a 2.5-fold increase in the specific surface area and total pore volume without affecting the crystalline structure, and allowed the specificity of the nickel (Ni) active sites incorporated to be directed, particularly towards a higher proportion of β1 reducible species. This result improved the catalytic performance in the dry reforming of methane (DRM) reaction, achieving conversions of up to 73 % in CO2 and up to 70 % in CH4, with average selectivity of 0.93 after 20 h of reaction. These outcomes even surpassed the reference catalyst, which was entirely prepared using commercial-grade reagents. Factors such as the presence of other metals in the slag and the versatility of cationic substitution contributed to enhancing the physicochemical properties of the catalysts. Ultimately, all of this led to suppression of the formation of double-walled filamentous carbon deposits, which tend to deactivate the catalyst due to sintering and deformation of the active phase.