Doris Ruiz

The environmental impact of water contamination has driven the search for sustainable materials for wastewater treatment, especially in the textile industry. The production of carbonaceous materials from biomass stands out as a low-cost and accessible alternative, promoting sustainable development and environmental preservation. This study aimed to produce biochar from leucaena (Leucaena leucocephala) pods and seeds impregnated with Black Liquor and evaluate its performance in removing methylene blue as a model cationic dye. The materials (original and carbonized) were characterized using several techniques, including thermogravimetry, infrared spectroscopy, X-ray diffraction, scanning electron microscopy, ammonia desorption, specific surface area analysis, point of zero charge determination, and Raman spectroscopy, and tested as adsorbents for methylene blue removal. The original materials exhibited a residual mass of 25–54% after pyrolysis up to 600 °C and maintained thermal stability in the range of 400 and 1000 °C. Regarding the total acidity, the results of ammonia desorption at programmed temperature showed that the samples obtained from the leucaena and liquor mixture exhibited higher acidity. The leucaena-black liquor mixture materials efficiently removed methylene blue at alkaline pH (>7.0–9.0), achieving removal efficiencies of 94.08% (pod) and 87.17% (seed). The adsorption kinetics followed a pseudo-second order model, with adsorption capacities of 3.64 mg.g–1 (seed-liquor) and 4.40 mg·g–1 (pod-liquor).

Reductive amination of cyclohexanone with NH₃ and H₂ over Rh and Rh-Ni catalysts on SiO₂ has been studied. Research has focused on the catalytic efficiency of monometallic and bimetallic catalysts in the production of cyclohexylamine, a key intermediate in the synthesis of numerous fine chemicals. Through the wet impregnation method, Rh and Rh-Ni catalysts with varying nickel loadings (1, 2, 5, and 10 wt.%) were synthesized and characterized using techniques such as N₂ physisorption, TEM, HAADF-STEM, XRD, XPS, H₂-TPR, and NH₃-TPD. The catalytic reactions were conducted under controlled conditions using a glass-coated reactor, using ammonia as nitrogen source. Rh-Ni bimetallic catalysts exhibited the highest conversion rates on reductive amination, attributed to enhanced dispersion and advantageous surface properties. High metal dispersion and small particle sizes were confirmed by TEM, HAADF-STEM, and XRD. XPS analysis confirmed the reduced state of Rh and mainly oxidized state of Ni, while H₂-TPR and NH₃-TPD results indicated improved reducibility and acidity, respectively, which are critical for catalytic activity. Monometallic Rh/SiO₂ catalyst showed 83.4% of conversion after 300 min and selectivity of 99.1% toward the desired product cyclohexylamine. The addition of nickel, a cheap and easily available metal, increases the activity without compromising selectivity. At 300 min of the reaction, the 2 wt.% NiRh/SiO₂ catalyst exhibited the highest conversion, yield, and selectivity for the desired product cyclohexylamine, 99.8%, 96.4%, and 96.6% respectively. Additionally, this catalyst is recyclable after the fourth cycle, showing 99.5% selectivity and 74.0% yield for cyclohexylamine at 75.7% conversion. Recycling tests confirmed the stability of bimetallic catalysts, maintaining performance over multiple cycles without significant deactivation.

In this work, partial reductive amination of 5‐hydroxymethylfurfural (HMF) with gaseous ammonia over iridium supported on γ‐Al₂O₃, TiO₂, SiO₂ and carbon has been studied. The influence of the support and pressure was investigated in the valorization under mild conditions of HMF to 5‐(aminomethyl)‐2‐furanmethanol (AMFM). The catalysts were characterized by TEM, SEM‐EDS, N₂ sorption Isotherms, TGA, CO‐Chemisorption, TPR, XRD, NH₃‐TPD, ICP‐AES and XPS. The maximum activity and high rates were obtained for all catalytic systems. At 50 minutes of the reaction the Ir/C catalyst achieved 93 % of conversion and exhibited the highest yield and selectivity of 92 % and 99 % respectively, to the desired product 5‐(aminomethyl)‐2‐furanmethanol. The main properties that influence activity and selectivity are related to the amount of iridium on the surface and catalyst acidity. After the third cycle, 63 % and 59 % of selectivity and yield to AMFM respectively at 93 % of conversion were obtained.

Catalytic pyrolysis is an attractive alternative for converting biomass into energy and chemicals, replacing fossil sources. Efficient catalysts can be used to remove compounds containing oxygen during pyrolysis, improving the bio-oil properties and thus being an important route towards sustainability. Catalytic pyrolysis of medium-density fiberboard (MDF) residues over platinum (1%) supported on beta zeolite was carried out using a biomass/catalyst ratio of 1.0/0.2. The catalysts were characterized via Fourier transform infrared spectroscopy, flame atomic absorption spectrometry, X-ray diffraction, nuclear magnetic resonance, temperature-programmed reduction, and temperature-programmed desorption of ammonia. The thermokinetic and thermodynamic parameters were determined using the isoconversional and non-isothermal methods of Friedman, Flynn-Wall-Ozawa (FWO), and Kissinger-Ahakira-Sunose (KAS). The Friedman method was the most adequate to describe the reaction and thermodynamic parameters. The results show that the catalysts promote the reduction in activation energy compared to non-catalytic pyrolysis. Non-impregnated and impregnated catalysts showed different activation energies and thus different reactions. The addition of platinum slightly increased the activation energy due to the promotion of reactions that require more energy, for example, cracking and coke deposition.