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Zeolite synthesis from industrial wastes
(Elsevier, 2019) Yoldi Sangüesa, María; Fuentes Ordóñez, Edwin Gustavo; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias; Gobierno de Navarra / Nafarroako Gobernua, PI017 CORRAL
Conventional synthesis conditions for each type of zeolite are tabulated and reported by the International Zeolite Association Structure Commission (IZA) and most of them are synthesized from commercial reagents, but they can also be synthesized from industrial by-products rich in Si and/or Al. In zeolite synthesis from wastes, concentration of alkali source, temperature, reaction time, liquid/solid ratio and type of waste determine the textural properties, crystal structure, Si/Al ratio and ion exchange characteristics of the fabricated zeolite and its applications. This work summarizes the main methods that have been developed to synthesize zeolites using industrial wastes as Al and/or Si sources, the parameters of synthesis and the advantages and limitations of each synthesis process. The main characteristics and the applications of these synthetic waste zeolites are also reported.
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
Catalytic valorization of CO2 by hydrogenation: current status and future trends
(Taylor and Francis, 2021) Sancho Sanz, Iris; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
Terrestrial environmental and biological systems are being threatened by the tremendous amount of human carbon dioxide emissions. Therefore, it is crucial to develop a sustainable energy system based on CO2 as chemical feedstock. In this review, an introduction to the CO2 activation and transformation has been made, together with a more comprehensive study of the catalytical reduction of CO2 to methane, methanol, and formic acid, which are currently contemplated as chemical feedstocks and/or promising energy carriers and alternative fuels.
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
Optimizing the removal of nitrate by adsorption onto activated carbon using response surface methodology based on the central composite design
(Taylor & Francis, 2020) Taoufik, Nawal; Elmchaouri, Abdellah; Korili, Sophia A.; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
This study sheds light on the adsorption process for the removal of nitrate ions from synthetic aqueous solutions. This contaminant pose a potential risk to the environment and can cause health effects including cancers and methemoglobinemia in infants. When the adsorption process is carried out, the effect by the several operating parameters such as initial nitrate concentration, pH, mass of activated carbon, and contact time becomes apparent. The essential process variables are optimized using response surface methodology (RSM) based on the central composite design (CCD) experiments. For this purpose 31 experimental results are required to determine the optimum conditions. The optimum conditions for the removal of nitrates is found to be: initial nitrate concentration = 15 mg/L; initial pH 4.0; mass of activated carbon = 25 mg, and contact time = 70 min. At these optimized conditions, the maximum removal of nitrates is found to be 96.59%.
Open Access
Progress and recent novelties in naphtha reforming catalysts
(Elsevier, 2024) Aznárez Salvatierra, María Aránzazu; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
High octane gasoline and aromatics, such as benzene, toluene, and xylenes, are both produced by the catalytic reforming of naphtha, being aromatics crucial building blocks in the chemical industry. Competing reactions occurring concurrently and catalyst deactivation under specific operating conditions make catalytic reforming of naphtha a very complicated process. This review focuses on the catalytic naphtha reforming process for aromatics production and makes special emphasis on reforming catalysts (evolution and recent novelties, as well as their deactivation, regeneration, and reactivation processes). Various aspects of the catalytic reforming process, such as the major reforming reactions carried out during the reforming process, types of industrial reforming processes, characteristics of the reviewed reforming processes, and the reaction parameters and their effect on the catalytic reforming process, are also considered in order to establish the context. Reforming catalysts are bifunctional, while some reactions just require the Pt site or the acid function to complete, others require both of these types of sites. Platinum is generally combined with one or two metals, such as Re, Ir, Sn, or Ge. The catalyst's acidic function is determined by chlorine, which also contributes to a high dispersion of the metallic phase. Research into naphtha reforming catalysts is looking for ways to improve aromatics yield and catalyst life. It has been noted that low dehydrogenating capacity and high hydrogenolytic capacity, both of which are provided by Pt, as well as low polymerization capacity, which is provided by the strong acid sites in the support, are the characteristics that make a catalyst stable as a result of the lesser formation of coke. Significant differences in the catalysts' basic composition have not been documented because bi- and trimetallic catalysts are still actively researched due to the complexity of their chemistry, with the identification of the wide variety of sites present within them and the understanding of their chemistry being of utmost importance. Even so, some innovation has occurred in recent years, among which are: non-noble metal reforming catalysts based on metal carbides, metal zeolite composite catalysts, the use of metals (In and Ga) other than those commonly used, and Ce3+-modified zeolites as support.
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
Progress in the synthesis and applications of hexaaluminate-based catalysts
(Taylor & Francis, 2020) 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
The development of materials that can exhibit thermal resistance at very high temperatures, thus allowing them to be applied as catalysts and thermal insulators, amongst other possible uses, is a research subject of great interest. This is the case for hexaaluminates, a class of hexagonal aluminate compounds with a unique structure that are stable at very high temperatures up to 1600°C and exhibit exceptional resistance to sintering and thermal shock, thus making them attractive catalysts for high-temperature applications. In this review, the structure of hexaaluminates is presented first. The most recent advances in synthetic methods (sol-gel, reverse microemulsion, hydrothermal synthesis, carbon-templating, solution combustion synthesis, and freeze-drying methods) are discussed subsequently, with the aim of maximizing textural properties and including in their structure metals known to be active in catalytic applications, such as combustion of CH4, partial oxidation, and dry reforming of CH4 to produce synthetic gas, and the decomposition of N2O. Finally, other applications, such as their function as a thermal barrier, are also addressed.
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
Adsorption recovery of Ag(I) and Au(III) from an electronics industry wastewater on a clay mineral composite
(University of Science and Technology Beijing, 2019) Rakhila, Youness; Elmchaouri, Abdellah; Mestari, Allal; Korili, Sophia A.; Abouri, Meriem; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
The aim of this work is to investigate the ability of an adsorbent of a clay mineral composite to remove and recover gold and silver ions from wastewater. The composite was prepared by mixing phosphogypsum (PG), obtained from an industrial waste, and a natural clay mineral. The materials were characterized before and after use in adsorption by several techniques. Batch adsorption experiments were carried out, and the effects of the contact time and the pH and temperature of solution on the removal processes were investigated. The optimum pH for the adsorption was found to be 4. The adsorption of these metal ions reached equilibrium after 2 h of contact. The pseudo-first- and the pseudo-second-order kinetic models, as well as the Freundlich and the Langmuir isotherm equations, were considered to describe the adsorption results. The maximum adsorbed amount of 85 mg·g−1 Ag(I) and 108.3 mg·g−1 Au(III) was found. The recovery of the adsorbed gold and silver ions from the adsorbent was also analyzed. Strong acids appeared to be the best desorption agents to recover gold and silver ions. The use of aqua regia gave regeneration rates close to 95.3% and 94.3% for Ag(I) and Au(III), respectively. Finally, the removal of gold and silver ions from an industrial wastewater was tested in batch experiments, and percentage recoveries of 76.5% and 79.9% for Ag(I) and Au(III), respectively, were obtained. To carry out the industrial application of the proposed methodology, an economic viability study is required.