by Keyword: Nitrogen fixation

Sans J, Arnau M, Bosque R, Turon P, Alemán C, (2024). Synthesis of urea from CO2 and N2 fixation under mild conditions using polarized hydroxyapatite as a catalyst† Sustainable Energy & Fuels

Polarized hydroxyapatite (p-HAp) has been used as a catalyst for the synthesis of urea coupling N2, CO2 and water under mild reaction conditions when compared to classical nitrogen fixation reactions, such as the Haber–Bosch process. The reaction of 3 bar of N2 and 3 bar of CO2 under UV illumination at 120 °C (for 48 h) results in a urea yield of 1.5 ± 0.1 mmol per gram of catalyst (gc) with a selectivity close to 80%, whereas the reaction is not successful without UV irradiation. However, the addition of small amounts of NO (314 ppm) produces 15.2 ± 0.6 and 4.6 ± 0.4 mmol gc−1 with and without UV illumination, respectively, with the selectivity in both cases being close to 100%. As nitrogen fixation without UV irradiation using p-HAp as a catalyst is a challenge, studies with NO have been conducted varying the reaction conditions (time, pressure and temperature). The results suggest a mechanism based on the production of NH4+ through the oxidation of N2 This journal is © The Royal Society of Chemistry 2024.

JTD Keywords: Carbon dioxide, Catalyst selectivity, Condition, Haber-bosch process, Hydroxyapatite, Irradiation, Metabolism, Mild reaction conditions, Nitrogen fixation, Pressure and temperature, Reaction conditions, Time pressures, Time-temperature, Urea, Uv illuminations, Without uv irradiations, ]+ catalyst

Sans, J, Sanz, V, del Valle, LJ, Puiggali, J, Turon, P, Aleman, C, (2021). Optimization of permanently polarized hydroxyapatite catalyst. Implications for the electrophotosynthesis of amino acids by nitrogen and carbon fixation Journal Of Catalysis 397, 98-107

The enhanced catalytic activity of permanently polarized hydroxyapatite, which is achieved using a thermally stimulated polarization process, largely depends on both the experimental conditions used to prepare crystalline hydroxyapatite from its calcium and phosphate precursors and the polarization process parameters. A mineral similar to brushite, which is an apatitic phase that can evolve to hydroxyapatite, is found at the surface of highly crystalline hydroxyapatite. It appears after chemical precipitation and hydrothermal treatment performed at 150 degrees C for 24 h followed by a sinterization at 1000 degrees C and a polarization treatment by applying a voltage of 500 Vat high temperature. Both the high crystallinity and the presence of brushite-like phase on the electrophotocatalyst affect the nitrogen and carbon fixation under mild reaction conditions (95 degrees C and 6 bar) and the synthesis of glycine and alanine from a simple gas mixture containing N-2, CO2, CH4 and H2O. Thus, the Gly/Ala ratio can be customized by controlling the presence of brushite on the surface of the catalyst, enabling to develop new strategies to regulate the production of amino acids by nitrogen and carbon fixation. (C) 2021 Elsevier Inc. All rights reserved.

JTD Keywords: Amino acids, Brushite, Carbon, Carbon dioxide fixation, Catalyst activity, Catalytic apatites, Chemical precipitation, Crystalline hydroxyapatite, Crystallinity, Decomposition, Enhanced catalytic activity, Experimental conditions, Heterogeneous catalysis, High crystallinity, Hydrothermal synthesis, Hydrothermal treatments, Hydroxyapatite, Lactic-acid, Mild reaction conditions, Molecular nitrogen fixation, Nitrogen, Nitrogen fixation, Phosphate, Polarization, Precipitation (chemical), Process parameters, Thermally stimulated polarization