Publications

This paper is aimed to develop ultrananoporous polarized hydroxyapatite (HAp) catalyst and evaluate its performance in transforming CO2 into useable ethanol considering three different scenarios: 1) a batch reaction using a mixture of CO2 and CH4 as feeding gas; 2) a batch reaction using as reactant exhaust gases captured from the fumes of diesel vehicles; and 3) a continuous flow reaction using pure CO2 as feeding gas. Ultrananoporous HAp scaffolds were prepared using a four-step process: 1) as prepared HAp powder was mixed with 60% wt. of a commercial hydrogel at low-temperature; 2) the resulting paste was shaped at low temperature to reduce the adhesion between the metallic tools and the mixture, enhancing the homogeneity of the sample; 3) the shaped paste was calcined in air by applying 1000 ºC during 2 h to eliminate the hydrogel; and 4) an external DC electric field of 3 kV/cm was imposed at 1000 ºC during 1 h to the calcined scaffold. The resulting polarized scaffolds both ultrananoporosity and catalytic activation. Thus, the mass: volume ratio of the ultrananoporous catalyst was much lower than that of conventional HAp catalyst (718 vs 5093 g/L. Furthermore, the ethanol yield was much higher (up to a factor of ×21.4) for the ultrananoporous catalyst than for the compact one, allowing us to conclude that ultrananoporous polarized HAp catalyst is a promising technology for transforming CO2 into valuable chemical products from highly polluted gases, especially those coming from road, sea and air transport. © 2024 Elsevier Ltd

JTD Keywords: A: ceramics, Air pollution, Automotives, Batch reactions, Calcination, Carbon, Carbon dioxide, Co2 fixation, Electric fields, Environmental process, Ethanol, Exhaust gases, Feeding gas, Fumes, Hydrogels, Hydroxyapatite, Lows-temperatures, Nano-catalyst, Nanocatalysts, Polarized catalyst, Scaffolds, Temperature, ]+ catalyst

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

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,

The impact of diet and digestive disorders in flatus composition remains largely unexplored. This is partially due to the lack of standardized sampling collection methods, and the easy atmospheric contamination. This paper describes a method to quantitatively determine the major gases in flatus and their application in a nutritional intervention. We describe how to direct sample flatus into Tedlar bags, and simultaneous analysis by gas chromatography–thermal conductivity detection (GC–TCD). Results are analyzed by univariate hypothesis testing and by multilevel principal component analysis. The reported methodology allows simultaneous determination of the five major gases with root mean measurement errors of 0.8% for oxygen (O2), 0.9% for nitrogen (N2), 0.14% for carbon dioxide (CO2), 0.11% for methane (CH4), and 0.26% for hydrogen (H2). The atmospheric contamination was limited to 0.86 (95% CI: [0.7–1.0])% for oxygen and 3.4 (95% CI: [1.4–5.3])% for nitrogen. As an illustration, the method has been successfully applied to measure the response to a nutritional intervention in a reduced crossover study in healthy subjects. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

JTD Keywords: breath, colonic microbiota, diet effect on flatus, disorders, evacuation, excretion, flatulence, hydrogen gas, major flatus gas components, multilevel principal component analysis, rectal gas collection, systems, volume, Atmospheric contamination, Carbon dioxide, Conductivity detection, Diet effect on flatus, Gas chromatography, Gas collections, Gas component, Gases, Major flatus gas component, Major flatus gas components, Multilevel principal component analyse, Multilevel principal component analysis, Multilevels, Nitrogen, Nutrition, Oxygen, Principal component analysis, Principal-component analysis, Rectal gas collection, Volatile organic-compounds

JTD Keywords: added value chemicals, amino-acids, catalytic-hydrogenation, climate, design, electrochemical reduction, electroreduction, green co2 conversion to ethanol, nitrogen, photocatalytic reduction, polarized hydroxyapatite, recycling co2, sea-level, Acetone, Added value chemicals, Added-value chemicals, C-c coupling, Calcium apatites, Carbon dioxide, Carbon-dioxide, Co 2 reduction, Co2 reduction, Ethanol, Green co2 conversion to ethanol, Hard tissues, Hydroxyapatite, Mixtures, Morphology, Morphology and composition, Naturally occurring, Organic carbon, Phosphate minerals, Polarized hydroxyapatite, Recycling co2

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

The electrophotocatalytic synthesis of Glycine and Alanine from a simple gas mixture containing N2, CO2, CH4 and H2O under mild reaction conditions (95 °C and 6 bar) was recently developed using a catalyst formed by permanently polarized hydroxyapatite, which is achieved using a thermally stimulated polarization process, coated with two layers of aminotris(methylenephosphonic acid) (ATMP) separated by an intermediate layer of zirconyl chloride (ZC). This work reports the optimization of the ATMP- and ZC-coating content by examining the influence of their concentration of each component in each layer on the structural and electrochemical properties of the catalyst. After exhaustive analyses, such properties have been related with the efficiency of the catalysts prepared using different ATMP- and ZC-concentrations to yield Gly and Ala amino acids by fixing nitrogen from N2 and carbon from CO2 and CH4. Results show that, although the concentrations of ATMP and ZC in the first and the intermediate layers are important, the third layer plays a predominant role as is responsible of the apparition of supramolecular structures on the surface and the capacitive behavior of the coating

JTD Keywords: Carbon dioxide fixation, Electrocatalyst, Heterogeneous catalysis, Phosphonic acid, Photocatalyst, Polarized hydroxyapatite, Surface chemistry, Zirconyl chloride