Two nickel alumina catalysts containing 60 wt. % Ni were synthesized by wet impregnation and co-precipitation in order to study the effect of preparation methods on the catalytic efficiency concerning the transformation of sunflower oil into green diesel. The effect of activation temperature on the catalytic efficiency of the most active catalyst was also studied. The catalysts were characterized using various techniques and which were evaluated in the aforementioned reaction using a semi-batch reactor. The catalyst prepared by co-precipitation exhibited a higher specific surface area and smaller mean crystal size of the nickel nanoparticle (higher nickel metallic surface). These justify its higher efficiency with respect to the corresponding catalyst synthesized by wet impregnation. The increase in the activation temperature from 400 to 600 °C increased the size of the nickel nanoparticles through sintering, thus destroying the small pores. These led to a decrease in the nickel surface and specific surface area and, thus, to a decrease in the catalytic efficiency. The optimization of the reaction conditions over the most active catalyst (prepared by co-precipitation and activated at 400 °C) leads to the complete transformation not only of the sunflower oil (edible oil) but also of waste cooking oil (non-edible oil) into green diesel. The liquid produced after the hydrotreatment for these two feedstocks for 7 h, at H₂ pressure 40 bar and temperature 350 °C using 100 mL of oil and 1 g of catalyst was composed of 97 and 96 wt. % of green diesel, respectively.

This study aims to utilize biochars derived from residual biomass as supports for Ni-based catalysts. For the preparation of the biochars, byproducts of agro-industrial activities were used, such as espresso coffee residue (C) and rice husks (R). Sufficient quantities of the respective biochars (BioC and BioR) were prepared via pyrolysis at 850 °C of the aforementioned materials under limited oxygen conditions. The biochars were further treated with hot water (WBioC, WBioR), H₃PO₄ or H₂SO₄ solution (BioC-P, BioC-S, BioR-P, BioR-S), and NaOH solution (BioC-A and BioR-A), and the obtained solids were characterized using various physicochemical techniques. The biochars produced were microporous with high surface areas (367–938 m²g⁻¹). The most promising biochars were selected as supports for the preparation of nickel catalysts (10 wt.% Ni) with high Ni dispersion (mean crystal size: 8.2–9.8 nm) and suitable acidity. The catalysts were evaluated in a high-pressure semi-batch reactor for the transformation of waste cooking oil (WCO) into green diesel. The 10Ni_BioC-P catalyst exhibited the best performance, resulting in a complete conversion of the WCO but a low hydrocarbon yield (7.5%). Yield improvement was achieved by promoting this catalyst with molybdenum. The addition of Mo increased the hydrocarbon yield by almost three times (19.5%).

Biowaste raw materials were used for biochar preparation through pyrolysis at 850 °C under a limited oxygen atmosphere. Raw materials and the corresponding biochar samples were characterized by XRD, FTIR, SEM, TGA, N₂-sorption, pH-equilibrium, and ash content measurements. These samples were evaluated as sustainable sorbents for use in methylene blue (MB) removal from artificial fresh water. All biochar samples exhibited high specific surface areas (367–870 m²·g⁻¹), low crystallinity, and low population of functional groups (C–O–C, –COOH, –N–O, –N–H, and –OH) on their surfaces. They were mainly micro-porous materials with a significant fraction of pores in the meso-porous range. The specific surface area of the latter pores proved very important for the physical adsorption of MB from aqueous solution. Although the raw materials exhibited low MB sorption capacity, ranging from 29 to 54 mg·g⁻¹, the corresponding biochar samples exhibited important MB sorption efficiency ranging from 58 to 370 mg·g⁻¹. Among the biochar samples studied, those produced from coffee residues proved most promising for MB removal from water solution (sorption capacity: 280–370 mg·g⁻¹), addressing the United Nations Sustainability Development Goal (SDG) 6: Clean Water and Sanitation by improving the index related to anthropogenic wastewater that has received treatment.