by Keyword: Catalyst selectivity

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, Arnau, M, Sanz, V, Turon, P, Alemán, C, (2022). Hydroxyapatite-based biphasic catalysts with plasticity properties and its potential in carbon dioxide fixation Chemical Engineering Journal 433, 133512

The design of catalysts with controlled selectivity at will, also known as catalytic plasticity, is a very attractive approach for the recycling of carbon dioxide (CO2). In this work, we study how catalytically active hydroxyapatite (HAp) and brushite (Bru) interact synergistically, allowing the production of formic acid or acetic acid depending on the HAp/Bru ratio in the catalyst. Raman, wide angle X-ray scattering, X-ray photoelectron spectroscopy, scanning electron microscopy and electrochemical impedance spectroscopy studies, combined with an exhaustive revision of the crystalline structure of the catalyst at the atomic level, allowed to discern how the Bru phase can be generated and stabilized at high temperatures. Results clearly indicate that the presence of OH– groups to maintain the crystalline structural integrity in conjunction with Ca2+ ions less bonded to the lattice fixate carbon into C1, C2 and C3 molecules from CO2 and allow the evolution from formic to acetic acid and acetone. In this way, the plasticity of the HAp-Bru system is demonstrated, representing a promising green alternative to the conventional metal-based electrocatalysts used for CO2 fixation. Thus, the fact that no electric voltage is necessary for the CO2 reduction has a very favorable impact in the final energetic net balance of the carbon fixation reaction. © 2021

JTD Keywords:

ethanol production & nbsp, brushite, co2 reduction, conversion, electrocatalytic reduction, electrode, formate, heterogeneous catalysis & nbsp, hydrogen evolution, insights, monetite, polarized hydroxyapatite,

, Acetic acid, Acetone, Biphasic catalyst, Brushite, Calcium phosphate, Carbon dioxide, Carbon dioxide fixation, Catalysis, Catalyst selectivity, Co 2 reduction, Co2 reduction, Electrocatalysts, Electrochemical impedance spectroscopy, Electrochemical reduction, Electrochemical-impedance spectroscopies, Ethanol production, Formic acid, Heterogeneous catalysis, Hydroxyapatite, Ph, Polarized hydroxyapatite, Property, Reduction, Scanning electron microscopy, Temperature programmed desorption, Wide angle x-ray scattering, X ray photoelectron spectroscopy, X ray scattering, ]+ catalyst