Publications

We present the use of an ultraporous permanently polarized hydroxyapatite (upp-HAp) catalyst for continuous and highly efficient production of formic acid (predominant) and acetic acid using wet CO2 (i.e. CO2 bubbled into liquid water) as a reagent. In all cases, reactions were conducted at temperatures ranging from 95 to 150 degrees C, using a CO2 constant flow of 100 mL s(-1), and without applying any external electric field and/or UV radiation. Herein, we study how to transfer such a catalytic system from batch to continuous reactions, focusing on the water supply (proton source): (1) wet CO2 or (2) liquid water in small amounts is introduced in the reactor. In general, the reduction of CO2 to formic acid predominates over the C-C bond formation reaction. On the other hand, when liquid water is added, two interesting outcomes are observed: (1) the yield of products is higher than in the first scenario (>2 mmol g(c)(-1)min(-1)) while the initial liquid water remains largely available due to the mild reaction temperature (95 degrees C); and (2) a high yield of ethanol (>0.5 mmol g(c)(-1)min(-1)) is observed at 120 degrees C, as a result of the increased efficiency of the C-C bond formation. Analysis of kinetic studies through temporal and temperature dependence shows that CO2 fixation is the rate limiting step, ruling out the competing effect of proton adsorption on the binding sites and confirming the crucial role of water. The activation energy for the CO2 fixation reaction has been determined to be 66 +/- 1 kJ mol(-1), which is within the range of conventional electro-assisted catalysts. Finally, mechanistic insights on the CO2 activation and role of the binding sites of upp-HAp are provided through isotopic-labeling ((CO2)-C-13) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) studies.

JTD Keywords: Butano, Challenges, Co2 reduction, Fuels, Hydrogenation, Mechanism, Nanomaterials, Noble-metal

This paper is aimed to develop ultrananoporous polarized hydroxyapatite (HAp) catalyst and evaluate its per-formance 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 x21.4) 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.

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

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