Deyanira Angeles-Beltrán

From 1950 to the present, plastic production and use have increased mainly because plastics possess qualities like stability, light weight, versatility, and decreasing production costs. However, most plastics are not biodegradable, and only a small portion is recycled worldwide. Bioplastics serve as an alternative if they are biodegradable and derived from residual materials, promoting a circular economy. PHB is a polymer with characteristics similar to some commercial plastics. It was discovered in the 1920s and has been examined by researchers and engineers since then due to its potential as a biodegradable bioplastic. Some microorganisms can produce PHB under controlled conditions. In this work, PHB production was analyzed using two strains, Bacillus subtilis and Bacillus megaterium, and two byproducts—whey and glycerol—as substrates and varying the culture media compositions. Both byproducts and both strains are suitable for PHB production; the absence of nitrogen and trace element sources enhances PHB yield. Additionally, bacterial growth, substrate uptake, and PHB production were modeled using logistic growth and the Luedeking–Piret models.

From 1950 to the present, plastic production and use have increased mainly because plastics possess qualities like stability, light weight, versatility, and decreasing production costs. However, most plastics are not biodegradable, and only a small portion is recycled worldwide. Bioplastics serve as an alternative if they are biodegradable and derived from residual materials, promoting a circular economy. PHB is a polymer with characteristics similar to some commercial plastics. It was discovered in the 1920s and has been examined by researchers and engineers since then due to its potential as a biodegradable bioplastic. Some microorganisms can produce PHB under controlled conditions. In this work, PHB production was analyzed using two strains: Bacillus subtilis and Bacillus megaterium. Using two byproducts—whey and glycerol—as substrates and varying the culture media compositions. Both byproducts and both strains are suitable for PHB production; the absence of nitrogen and trace element sources enhances PHB yield. Additionally, bacterial growth, substrate uptake, and PHB production were modeled using logistic growth and the Luedeking-Piret models.

Selective catalytic reduction (SCR) of NO using various reducing agents is a critical area of research for mitigating environmental pollution. In this study, the influence of active phase loading was investigated in four bimetallic Pt-Ag/Al₂O₃-WO_x catalysts, one monometallic Ag/Al₂O₃-WO_x catalyst, and one Pt-Ag/Al₂O₃-WO_x catalyst subjected to high-severity air-SO₂ pretreatment. All catalysts were supported on cordierite monoliths, and their performance in NO SCR was evaluated using H₂, C₃H₈, and CO as reducing agents. An increase in the active phase loading (Pt-Ag/Al₂O₃) from 10.7 wt% to 17.4 wt% resulted in higher conversions of NO, C₃H₈, and H₂, as well as improved N₂ selectivity. However, CO conversion decreased as the active phase loading increased, which was attributed to competitive reduction by H₂, since both reactions occur within the same temperature range (100–200 °C). The presence of N₂O below 6 ppm was observed in some catalysts. Furthermore, higher active phase loadings led to increased carbon deposition; the Ag/Al₂O₃-WO_x catalyst exhibited the highest carbon content (5 wt%). The deposited carbon was identified as ordered graphitic carbon. In the Pt-Ag catalysts, the presence of Ag⁺ and Agⁿδ⁺ species, as well as the Ag° plasmon, was identified by UV-Vis spectroscopy. STEM analysis showed Ag-Pt crystallites with an average size of 24 nm, which may have contributed to the higher NO conversion observed at 350 °C and the improved N₂ selectivity at 100 °C in the Pt-Ag bimetal catalysts, compared to the activity of the Ag/Al₂O₃-WOx catalyst.

In this work, the removal of Cu(II) ions from an aqueous effluent was studied using an Mg/Fe layered double hydroxide (LDH) as the adsorbent. The material was synthesized and characterized before and after the adsorption process to identify structural and morphological changes induced by copper uptake. Techniques such as X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, and nitrogen physisorption (BET) were employed to confirm the interaction between the metal ions and the LDH surface. The LDH-Mg/Fe exhibited a high maximum adsorption capacity of 526 mg/g, and the adsorption kinetics followed a pseudo-second-order model, achieving over 90% removal of Cu(II) within 2.5 h. The Cu(II)-loaded material was subsequently evaluated as a sustainable catalyst in two applications: (i) an organic synthesis via “click” chemistry, reaching yields of up to 85%, and (ii) the decoloration of Congo Red via a Fenton-like process, achieving a decoloration efficiency of at least 84%. These dual uses demonstrate the potential of Cu(II)-loaded LDH as a cost-effective and environmentally friendly approach to simultaneous pollutant removal and catalytic valorization.

Ag and Pt-Ag catalysts supported on Al2O3-tungsten oxides (WOx) deposited on cordierite monoliths were prepared for the removal of nitrogen oxides (NOx) from diesel engine ex-haust emissions using C3H8 as well as H2 as reductants in the selective catalytic reduction. The catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), tempera-ture programmed reduction (TPR), scanning electron microscopy (SEM/EDX), transmis-sion electron microscopy (STEM/HAADF), H2 chemisorption, and Raman and UV-vis spectroscopy of the evaluated catalysts. The conversion of NO, C3H8 and CO was studied as a function of three GHSVs 30,000, 70,000 and 100,000 h-1 as well as the reaction tem-perature. The combination of 0.1wt%Pt-2wt%Ag /Al₂O₃-WOx on cordierite monoliths was active in NO reduction and CO and C₃H8 combustion. By STEM, small Pt-Ag bimetallic particles (20 nm) presented a high Pt concentration (58.6 atom%). Separate Ag particles were also detected. The best preparation conditions of boehmite AlO(OH)/cordierite mon-olith were obtained by applying three or four boehmite AlO(OH) impregnations, drying, calcination in air flow, and H₂ reduction at 500 °C and exchange with H₂PtCl₃ and AgNO3. A one-dimensional model of NO conversion as a function of reactor length was proposed considering external mass transfer limitations as dominant.

This study investigates the influence of divalent metals—(Mg(II), Co(II), and Ni(II)) in layered double hydroxides (LDHs), with a constant trivalent Fe(III) component—on the decoloration of crystal violet and methyl blue dyes via a Fenton-type oxidation reaction. The catalysts, synthesized by co-precipitation and hydrothermal treatment, were tested in both hydroxide and oxide forms under varying agitation conditions (0 and 280 rpm). A 2² × 3 factorial design was used to analyze the effect of the divalent metal type, catalyst phase, and stirring. The Mg/Fe oxide, with the highest BET surface area (144 m²/g) and crystallite size (59.7 nm), showed superior performance—achieving up to 98% decoloration of crystal violet and 97% of methyl blue within 1 h. The kinetic analysis revealed pseudo-second-order and pseudo-first-order fits for crystal violet and methyl blue, respectively. These findings suggest that LDH-based catalysts provide a fast, low-cost, and effective option for dye removal in aqueous systems.

This study incorporated expanded polystyrene (PS) from waste packaging into the mesoporous material MCM-41 to obtain PS-MCM-41. Both materials were obtained at room temperature, assisted by the ultrasound technique, and functionalized with sulfonated polystyrene (PSSA, Polystyrene Sulfonic Acid) to obtain MCM-41-PSSA and PS-MCM-41-PSSA. The evolution of the pore structures of the synthesized materials was studied using XRD. The functionalized materials' pore size, specific area, and pore volume were reduced. In addition, the thermal stability of PS-modified MCM-41 was improved concerning the parent material. The NH3-TPD technique showed increased strong acid sites, with MCM-41-PSSA being the most acidic material. Incorporating waste material into a silicon-based mesoporous material and its functionalization with sulfonic groups allows the development of a sustainable heterogeneous material with potential applications in heterogeneous acid catalysis. Resumen. En este estudio se incorporó poliestireno expandido (PS) proveniente de empaques de desecho al material mesoporoso MCM-41 para obtener PS-MCM-41. Ambos materiales fueron obtenidos a temperatura ambiente, asistidos por la técnica de ultrasonido, y funcionalizados con poliestireno sulfonado (PSSA, Polystyrene Sulfonic Acid) para obtener MCM-41-PSSA y PS-MCM-41-PSSA. La evolución de las estructuras porosas de los materiales sintetizados se estudió mediante DRX. Se redujo el tamaño de poro, el área específica y el volumen de poro de los materiales funcionalizados. Además, la estabilidad térmica del MCM-41 modificado con PS mejoró con respecto al material original. La técnica NH3-TPD mostró un aumento de los sitios ácidos fuertes, siendo el MCM-41-PSSA el material más ácido. La incorporación de material de desecho en un material mesoporoso basado en silicio y su funcionalización con grupos sulfónicos permite el desarrollo de un material heterogéneo sostenible con potenciales aplicaciones en catálisis ácida heterogénea. In the present research work, the incorporation of waste polystyrene into a material based on mesoporous silica is proposed, as well as the sulfonation of this waste polymer to obtain MCM-41-PSSA with sulfonated polystyrene. The structural, chemical, and surface properties of the materials MCM-41 with polystyrene and MCM-41 with functionalized polystyrene were studied.

A set of Y-type zeolites with Si/Al atomic ratios between 7–45 were studied as catalysts in the aminocyclization reaction between acrolein and ammonia to produce pyridine and 3-picoline. The catalytic activity tests at 360 °C revealed that the acrolein conversion increased in the order Z45 < ZY34 < ZY7 < ZY17, in agreement with the increase of the total acidity per gram of catalyst. In all cases, pyridine bases and cracking products (acetaldehyde and formaldehyde) were detected in the outflow from the reactor. The total yield of pyridines was inversely proportional to the total acidity for the catalysts, which presented large surface areas and micro- and mesoporosity. The selectivity towards 3-picoline was favored when using catalysts with a Brønsted/Lewis acid sites ratio close to 1. The formation of pyridine occurred more selectively over Lewis acid sites than Brønsted acid sites. The deactivation tests showed that the time on stream of the catalysts depended on the textural properties of zeolites, i.e., large pore volume and large BET area, as evidenced by the deactivation rate constants and the characterization of the spent catalysts. The physicochemical properties of the catalysts were determined by XRD, UV-vis, and Raman spectroscopies, infrared spectroscopy with adsorbed pyridine, N₂ physisorption, and SEM-EDXS. After the reaction, the spent catalysts were characterized by XRD, Raman spectroscopy, TGA, and SEM-EDXS, indicating that the uniform deposition of polyaromatic species on the catalyst surface and within the porous system resulted in the loss of activity.

Thermal and catalytic pyrolysis of waste expanded polystyrene (WEPS) was studied to obtain mainly styrene monomer, which can be recycled in the polystyrene industry. Initially, preliminary experiments were carried out in a static semi-batch glass reactor with basic catalysts and without catalysts, using toluene as solvent at 250 °C, determining their styrene yields to select the best catalyst. MgO turned out to be the best catalyst due to its stability and cost. This catalyst was characterized by XRD, BET area, SEM-EDS, Raman spectroscopy, UV–VIS, and TGA. The kinetic equation for WEPS pyrolysis in the glass reactor was determined as a first-order reaction. The heat of reaction, the Gibbs free energy change, and the entropy change were calculated. Finally, WEPS pyrolysis experiments were carried out using a rotating semi-batch steel reactor, at higher temperatures and without using solvents, evaluating the styrene yield and its performance for its possible industrial application. In this reaction, the activity remained almost constant after four catalyst regenerations. The best styrene yield was 94 wt%, which could be one of the highest reported in the literature. This result may be associated with the back-mixing obtained in the rotary reactor, in contrast to the performance observed in the static glass reactor.