Helir Joseph Muñoz

Metal-organic framework (MOF) materials combined with aluminum saline slag wastes represent a relatively novel research direction. This innovative approach not only leverages industrial waste for the development of advanced materials but also promotes a circular economy and reduces the ecological footprint of aluminum production. Furthermore, it addresses the inherent stability challenges of pure MOFs. Notably, this study is the first to propose that this industrial by-product can serve as a novel, cost-effective, and environmentally friendly modulator, enabling the selective transition between the MIL-96(Al) and MIL-110(Al) phases. For the first time, novel composites of MOFs and the saline slag waste resulting from the initial aluminum extraction in an acidic medium (RW1*), have been developed. These composites, designated as MOF@RW1*-n (n = 25, 50, 75), were synthesized via the in-situ preparation of the MOF on RW1* using a hydrothermal treatment method and were subsequently evaluated as CO2 adsorbents. The optimized content of RW1* in the composite significantly affect its role as a modulator in the formation of specific crystalline structures, whether MIL-96(Al) or MIL-110(Al), leading to hybrid materials with excellent textural properties and thermal stability.

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.

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-adsorbent, 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, solution-mediated 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.

In this work, the significant intensification of a bentonite pillaring process was achieved by using a novel methodological approach, leading to an intercalating Al/Fe mixed oligomeric precursor, around 100 times more concentrated than usually reported. In addition, the intercalating step was achieved directly on the clay with no previous swelling of the mineral being required; this allowed the successful scaled-up preparation of the Al/Fe-PILC, by a factor of one thousand, from the lab (10 g) to the pilot scale (10 kg). Intercalating solutions prepared under either concentrated (13 cm³) or diluted (widely reported, 2.0 dm³) conditions for lab-scale preparations were both translucent, displaying similar final pH values (close to 4.0) typical of highly oligomerized Al-pillaring solutions. The clay modified from concentrated precursors at the 10 g scale reached a high basal spacing (18.3 Å) and specific surface area (198 m² g⁻¹) with very comparable fractions of Fe forming truly mixed Al/Fe pillars in comparison to a reference material (H₂-TPR analyses). This promoted high performance in the catalytic wet peroxide oxidation of phenol in aqueous solution as a toxic model organic molecule at very mild temperature (25.0 °C ± 1.0 °C) and pressure (76 kPa), exhibiting the highest catalytic efficiency as a function of both parameters (full conversion of phenol together with 45.2% of TOC mineralization) with low iron leaching using a very low catalyst concentration (0.25 g dm⁻³). Particle size refining of the starting clay, the speed of stirring and conditions for the final washing of the interlayered precursor are the main factors influencing successful pillaring at scales higher than 1.0 kg.