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

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,

Smoldering fires are characterized by the production of early gas emissions that can include high levels of CO and Volatile Organic Compounds (VOCs) due to pyrolysis or thermal degradation. Nowadays, standalone CO sensors, smoke detectors, or a combination of these, are standard components for fire alarm systems. While gas sensor arrays together with pattern recognition techniques are a valuable alternative for early fire detection, in practice they have certain drawbacks-they can detect early gas emissions, but can show low immunity to nuisances, and sensor time drift can render calibration models obsolete. In this work, we explore the performance of a gas sensor array for detecting smoldering and plastic fires while ensuring the rejection of a set of nuisances. We conducted variety of fire and nuisance experiments in a validated standard fire room (240 m(3)). Using PLS-DA and SVM, we evaluate the performance of different multivariate calibration models for this dataset. We show that calibration models remain predictive after several months, but perfect performance is not achieved. For example, 4 months after calibration, a PLS-DA model provides 100% specificity and 85% sensitivity since the system has difficulties in detecting plastic fires, whose signatures are close to nuisance scenarios. Nevertheless, our results show that systems based on gas sensor arrays are able to provide faster fire alarm response than conventional smoke-based fire alarms. We also propose the use of small-scale fire experiments to increase the number of calibration conditions at a reduced cost. Our results show that this is an effective way to increase the performance of the model, even when evaluated on a standard fire room. Finally, the acquired datasets are made publicly available to the community (doi: 10.5281/zenodo.5643074).

JTD Keywords: Calibration, Chemical sensors, Co2, Early fire, Early fire detection, En-54, Fire alarm, Fire detection, Fire room, Fires, Gas detectors, Gas emissions, Gas sensors, Pattern recognition, Public dataset, Sensor arrays, Sensors array, Signatures, Smoke, Smoke detector, Smoke detectors, Standard fire, Standard fire room, Support vector machines, Temperature, Toxicity, 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