Edgardo Meza-Fuentes

The chemical recycling of poly(ethylene terephthalate) (PET) through glycolysis has emerged as an attractive alternative for recovering high-value monomers while reducing plastic waste accumulation. In this work, ZnMgAl mixed oxide catalysts derived from a hydrotalcite precursor were synthesized by constant-pH co-precipitation and calcined at 400, 500, and 600 °C to investigate the influence of calcination temperature on catalyst structure, PET depolymerization efficiency, and BHET crystallization behavior. Structural evolution of the catalysts was evaluated by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC), and N2 physisorption. Calcination promoted the transformation of the layered precursor into mixed oxides containing ZnO, MgO, and spinel-type phases, together with significant modifications in surface area and pore architecture. ZnMgAl-600 exhibited the highest specific surface area (151 m2·g-1) and the narrowest mesopore distribution. PET glycolysis was performed using ethylene glycol at 180, 190, and 200 °C. Complete PET depolymerization was achieved under most conditions, while BHET selectivity strongly depended on catalyst properties and reaction temperature. ZnMgAl-600 showed the best overall performance, maintaining complete PET degradation and high BHET selectivity (92-98%) over the entire temperature range. The recovered monomers were characterized by FTIR and powder X-ray diffraction (PXRD). FTIR confirmed the formation of BHET-type products in all samples, whereas PXRD revealed temperature, and catalyst-dependent polymorphism involving monoclinic a -BHET and orthorhombic g-BHET phases. ZnMgAl-400 favored a-BHET formation at intermediate temperatures but promoted g -phase crystallization at 200 °C, while ZnMgAl-600 generated mixed a + g systems under highly selective conditions. The combined results demonstrate that catalyst textural properties not only affect PET depolymerization efficiency but also influence the crystalline and supramolecular organization of the recovered monomer, providing insights for the rational design of LDH-derived catalysts for sustainable PET chemical recycling.

This study investigates the catalytic glycolysis of post-consumer poly(ethylene terephthalate) (PET) using Zn-Al and Zn-Ni-Al mixed oxides derived from hydrotalcite-like precursors. The catalysts were synthesized by constant-pH coprecipitation and calcined at 500 °C to generate mixed oxide phases. Structural characterization by XRD revealed the collapse of the layered structure and the formation of ZnO domains together with spinel-type MAl2O4 phases (M = Zn, Ni, or mixed Ni–Zn). Nitrogen physisorption showed a strong composition-dependent evolution of the mesostructure, with the Ni0.44Zn0.22Al0.33 catalyst exhibiting the highest surface area (177 m2·g-1). Control experiments demonstrated that PET depolymerization does not occur in the absence of catalyst, that ZnO promotes polymer degradation but with low selectivity toward BHET, and that bulk NiO is essentially inactive. The best catalytic performance was obtained for Ni0.44Zn0.22Al0.33, reaching 96.4% PET depolymerization and 82.0% selectivity toward bis(2-hydroxyethyl) terephthalate (BHET). The recovered monomer was identified by FTIR spectroscopy, differential scanning calorimetry (DSC), and morphological analysis confirming the formation of crystalline BHET as the main reaction product. The results indicate that catalytic performance is governed by the structural integration of Zn and Ni within the mixed oxide matrix rather than by the simple coexistence of individual oxides. A mechanistic interpretation suggests that Zn-related Lewis acid sites activate the ester carbonyl groups of PET, while the incorporation of Ni into aluminate structures modifies the surface environment and improves site accessibility within the mesoporous framework, leading to enhanced depolymerization and selectivity.

This study evaluates the glycolysis of post-consumer polyethylene terephthalate (PET) using NiZnAl-derived catalysts obtained from hydrotalcite precursors, with a particular focus on the influence of operational variables and catalyst properties. A statistical approach based on response surface methodology (RSM) was applied to analyze the effects of reaction temperature, propylene glycol volume, catalyst mass, and catalyst calcination temperature on PET degradation. The results indicate that reaction temperature is the most influential variable, showing a significant positive effect on PET conversion, while propylene glycol volume and catalyst mass exhibit moderate but statistically relevant effects. In contrast, catalyst calcination temperature was not found to be statistically significant within the studied experimental domain. The fitted quadratic model suggests that the response is primarily governed by linear effects, with limited contribution from interaction and quadratic terms, indicating a system dominated by first-order trends. Experimental observations further suggest that increasing solvent volume and catalyst loading may introduce mass transfer limitations and dilution effects, reducing the efficiency of the depolymerization process. Catalysts calcined at intermediate temperatures showed higher average degradation, which may be related to differences in surface structure and accessibility of active sites, although this effect cannot be considered dominant. The predictive capability of the model was validated through scale-up experiments, where degradation values remained consistent with model predictions, demonstrating the applicability of RSM for process optimization. Overall, PET glycolysis in this system appears to be mainly controlled by thermal activation, while catalyst properties contribute to the efficiency of the reaction without acting as the primary governing factor. Graphical abstract PET Glycolysis with Ni–Zn–Al Catalysts: Optimization via RSM.

Nickel-based catalysts are of great importance for the generation of hydrogen from natural gas. Within this process, the conditions in which commercial NiO/Al2O3 is converted to Ni0/Al2O3 catalyst should be further investigated. A widely used technique to identify Ni2+ reduction conditions and the different compounds or types of particles in which this element is present is temperature-programmed reduction. In this work, the type of nickel oxide particles occurring on Al2O3 and ZnO-Al2O3-based supports were studied by different techniques, such as energy-dispersive X-ray spectroscopy, FTIR, the BET method, X-ray diffraction (XRD), and Temperature Programmed Reduction (TPR). All materials were evaluated in the water gas shift reaction (WGS), and the influence of their characteristics on the catalytic activity was assessed. Solids were prepared at different temperatures and Ni/Zn molar ratios. The results showed the presence of NiO in all materials, as well as the presence of ZnO, NiAl2O4, and ZnAl2O4 in materials prepared at higher temperatures. In all the materials calcined at the lowest temperature, the formation of NiO particles that fail to interact with the supports was prioritized. As the calcination temperature increased, NiO aggregates were formed, which, to a greater degree, interacted with the supports, whereby nickel aluminate was detected in all materials prepared at 750 °C. Zinc increased the selectivity but decreased specific surface area and activity through the WGS reaction. The solid labeled AZ15-500 showed higher activity and selectivity, reaching values of 100% for the water gas shift reaction.

RESUMEN Las hidrotalcitas pueden ser usadas para diferentes aplicaciones debido a sus propiedades químicas y por dar origen a sólidos con elevada área superficial específica, buena estabilidad térmica, alta dispersión y carácter básico. Estas características han conducido a que estos materiales hayan recibido mucha atención y aplicación en áreas como la remoción de contaminantes y en la síntesis de catalizadores. En este estudio se evaluó el efecto de la sustitución de zinc por níquel en hidrotalcitas a base de zinc-aluminio, las cuales han mostrado actividad para la depolimerización catalítica de poli (tereftalato de etileno). La estructura del tipo hidrotalcita fue observada en todos los materiales, notándose que el aumento de zinc conduce a mayores valores del parámetro a de las celdas ortorrómbicas de las hidrotalcitas. La disminución del parámetro c condujo a una mayor interacción CO32-‧ ‧ ‧ OH en la región interlaminar. Los sólidos con mayor contenido de zinc colapsaron a menores temperaturas, efecto contrario al inducido por el níquel. Los sólidos calcinados contienen las fases ZnO, NiO y g-Al2O3, cuya presencia depende de los metales presentes. Los resultados sugieren la presencia de partículas grandes y con alta cristalinidad de la fase ZnO, mientras que los picos definidos y anchos de NiO sugieren la existencia de partículas pequeñas de esta especie, cuya cristalinidad está afectada por la presencia de cationes Zn2+ y Al3+ en la red cristalina cubica del NiO. Los materiales conteniendo dos metales presentaron isotermas características de materiales predominantemente macroporosos, En relación a los materiales con tres metales, las estructuras son mesoporosas y con alta área superficial específica, observándose que el sólido Zn0,44Ni0,22Al0,33 contiene poros en forma de hendidura, mientras que los sólidos Zn0,33Ni0,33Al0,33 y Ni0,44Zn0,22Al0,33 presentaron isotermas propias de materiales con poros estrechos en forma de capilares.

NiO has a variety of applications, mainly in the production of electrochemical sensors and of metallic nickel. In addition, it is widely used as catalysts to produce hydrogen from natural gas. In this work, hydrotalcites based on nickel-aluminum and nickel-zinc-aluminum were synthesized, calcined at 500 °C and studied by different techniques. It was observed that nickel-aluminum hydrotalcites are thermally more stable, collapsing at higher temperatures than hydrotalcites containing zinc. During calcination, aluminum is incorporated into NiO lattice, leading to a decrease in crystallographic parameters. However, zinc decreases this effect, favoring the formation of NiO with lattice parameters close to pure nickel oxide. Zinc also contributes to the formation of smaller NiO particles, which is very useful for its use as a catalyst. In addition, aluminum led to a distortion in NiO lattice, an effect that is minimized by zinc, showing that it hinders the incorporation of Al3+ in the NiO lattice.

Este trabajo trata sobre la comparación de la asignación teórica del espectro vibracional de DADP con los desplazamientos experimentales por marcación isotópica. Para ello, se sintetizaron los isotopómeros DADP-C4 y DADP-C2, los cuales son isotopómeros parcialmente marcados. DADP-C4 y DADP-C2 fueron sintetizados a partir de acetona marcada isotópicamente en los átomos de carbonos del grupo metilo y carbonilo, respectivamente. La acetona y los compuestos isotopómeros de DADP fueron caracterizados usando espectroscopia Raman e Infrarroja. Las asignaciones teóricas fueron tomadas de estudios previos sobre la distribución de energía potencial de un modo vibracional, el cual proporciona una aproximación a las coordenadas internas relacionadas con cada banda vibracional. La marcación isotópica selectiva nos permitió acercarnos a la dependencia de cada banda, debido a que, la energía de una vibración molecular depende también de la masa recíproca de los átomos involucrados. En general, los resultados mostraron que algunas bandas asignadas experimentalmente no coinciden con las asignaciones teóricas mediante simulaciones mecánicas cuánticas.