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3D-printed high-surface carbon monoliths have been fabricated and tested as catalyst supports of CO 2 methanation active phases (NiO-CeO 2 , 12 wt% Ni). The carbon carriers show a developed microporosity and good adherence to the catalytic phases of NiO-CeO 2 , showing great stability and cyclability. Two monolith designs were used: a conventional parallel-channeled structure (honeycomb) and a complex 3D network of non-linear channels built upon interconnected circular sections (circles), where flow turbulences along the reactant gas path are spurred. The effect of the active phases particle size on the catalyst distribution and the overall performance has been assessed by comparing NiO-CeO 2 nanoparticles of 7 nm average (Np), with a reference counterpart of uncontrolled structure (Ref). The improved radial gases diffusion in the circles monolith design is confirmed, and nanoparticles show enhanced CO 2 methanation activity than the uncontrolled-size active phase at low temperatures (< 300 ºC). On the contrary, the Ref catalysts achieve higher CH 4 production at higher temperatures, where the reaction kinetics is controlled by mass transfer limitations (T > 300 ºC). SEM and Hg porosimetry evidence that nanoparticles are deposited at deeper penetration through the narrow micropores of the carbon matrix of the monolithic supports, which tend to accumulate on the channels surface remaining more accessible to the reactant molecules. Altogether, this study examines the impact of the channel tortuosity and the active phase sizing on the CO 2 methanation activity, serving as ground knowledge for the further rational and scalable fabrication of carbon monolith for catalytic applications. [Display omitted] • NiO-CeO 2 /3D-printed carbon monoliths were efficient CO 2 methanation catalysts. • Unconventional circular design improves gas mixing along the monolith. • Nanoparticles show higher activity when intrinsic kinetic control prevails. • Above 300 °C, the reference outperforms in mass transfer rate control. [ABSTRACT FROM AUTHOR]

Vanadium-carbon composites were successfully prepared by sol-gel methods, and their behaviour as NO x -reduction catalysts was tested. Two different synthesis approaches were employed: the distribution of VO x (i) along the carbon matrix and (ii) on the carbon spheres surface. This allows to modify the carbon-VO x interaction and thus, evaluate the role of vanadium oxidation state in the NOx abatement. The distribution of VO x along the carbon matrix favours the dispersion and reducibility of VO x nanoparticles and improves the carbon-VO x contact stabilizing vanadium low oxidation states (V2+), however part of the VO x particles were embedded on the carbon matrix becoming inactive. The distribution of those species on the carbon spheres surface improves the accessibility to the VO x active sites but at the expense of the decrease of the carbon-VO x interaction and VO x dispersion and reducibility. The oxidation state of the active phase is related with the global synthesis procedure and that reducibility depends on the interactions between phases. Catalytic results evidence that the NO reduction is strongly influenced by the oxidation state of vanadium. Commercial V 2 O 5 and carbon-V 2 O 5 physical mixture are poorly reactive whereas a stronger activity improvement activity was observed for C-VO x composites reaching conversion higher than 91% at 450 °C. Image 10 [ABSTRACT FROM AUTHOR]

Isolated mesoporous carbon nanospheres doped with carbon nanotubes or nanohorns were obtained for the first time by a sol-gel synthesis. The presence of nanomaterials improves the electrical conductivity of the catalysts increasing the current storage capacity and the electrocatalytic performance. Ni-catalysts were also prepared by impregnation of the supports and by doping during the synthesis. Better Ni-dispersion was obtained in impregnated samples regarding doped ones where Ni-particles are mainly embedded in the carbonaceous matrix and affects the textural properties, especially the mesopores volume which increases with the spheres size. The presence of mesopores shown a positive effect in both electro-reduction reactions. All materials, present electro-catalytic activity in both O 2 and CO 2 electro-reduction but in very different extension. The presence of carbon nanomaterials clearly improves the electro-activity in ORR even being good free-metal electro-catalysts, however, these nanomaterials does not improve the electro-activity in CO 2 reduction. Ni addition improves the electro-activity in both reactions, however in the case of CO 2 reduction, a good accessibility of Ni particles to the electrolyte is necessary. Finally, despite the very low contents of carbon nanomaterials and Ni the electro-catalytic results obtained are good enough and similar that those available in the literature based in carbon materials. [ABSTRACT FROM AUTHOR]

Abstract A sol-gel synthesis method followed by carbonization is reported to obtain vanadium carbon composites. Samples are exhaustively characterized to correlate their chemical, textural and electrochemical properties with their behaviour as electro-catalysts for oxygen reduction reaction in a three-electrode electrochemical set-up in alkaline medium. The results show a very good electro-catalytic behaviour with large kinetic current densities (>20 mA/cm2) and low activation potentials (E onset = −0.18 V and E 1/2 = −0.24 V). The oxygen reduction reaction study of the catalysts shows that vanadium carbon composites possess a comparable catalytic performance to commercial Pt/C catalyst and that these composites offer a promising route for the activity enhancement of the non-precious metal catalysts. Graphical abstract Clean and sustainable energy conversion systems are needed. Fuel cells are excellent candidates, but the high prize of ORR Pt-based catalysts limits its commercialization. VO x -C composites are good non-precious substitute catalysts with a catalytic performance comparable to commercial Pt C electrodes. Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Acid treatments on cellulose determine the properties of Ti-cellulose composites. • Phosphorus groups generated by H 3 PO 4 treatments hinder the TiO 2 crystal growth. • Anatase microcrystallites with reduced band gap are obtained after HNO 3 treatments. • Cellulose-TiO 2 composites presented high removal of the OG dye by photocatalysis. Abstract Cellulose-TiO 2 composites are developed using microcrystalline cellulose (MCC). The closed MCC structure was solubilized by liquid-phase treatments with nitric (HNO 3) or phosphoric acids (H 3 PO 4) to improve the TiO 2 -dispersion. These pretreatments simultaneously generate different types of oxygen and phosphorus functionalities on the cellulose chains that determine the interactions with Ti-alkoxide precursor during impregnation, leading to composite materials with different Ti-loadings and physicochemical characteristics. The morphological, textural, chemical and crystalline properties of both cellulose derivatives and cellulose-TiO 2 composites were studied by complementary techniques. Microporous composites with round-shaped anatase TiO 2 microcrystals were obtained by using HNO 3 treatments, while H 3 PO 4 favours the formation of mesoporous composites with flat and non-crystalline TiO 2 particles. The photocatalytic efficiency of the obtained cellulose-TiO 2 composites always improve the results obtained with the commercial TiO 2 -photocatalysts used as reference materials; this behaviour was analysed taking into account the physicochemical characteristics of the samples. [ABSTRACT FROM AUTHOR]

Carbon xerogel-ZrO 2 composites (CZrX) were successfully synthesized through a one-pot sol-gel synthesis. The XRD results confirm the presence of well dispersed (<4.5 nm) cubic ZrO 2 on the carbon support, homogeneously distributed on the carbon surface. Gas adsorption and mercury porosimetry measurement pointed out that the increase of ZrO 2 in the carbon matrix produces an increase in the mesopore volume as well as a widening of the microporosity at the expense of the narrow micropores (W 0 (CO 2 )) that decreases causing simultaneously the progressive surface area decrease. The obtained composite materials possess specific surface areas ranging from 423 to 539 m 2 g −1 and a very well-developed micro and mesoporosity with a total pore volume ranging from 0.361 to 0.480 cm 3 g −1 . A two-electrode symmetric supercapacitor based on the carbon xerogel-ZrO 2 composites exhibits a high electrochemical performance better than other similar materials from the literature with high capacitances (up to 180 F g −1 at 0.125 A g −1 for 30% ZrO 2 composite), a high retention capacitance and high energy density, 27.1 Wh kg −1 , at a power density of 140 W kg − 1 in the voltage range of 0 V–1.2 V. The presence of zirconium oxide in the carbon matrix improves in all case the capacitive behavior of samples in spite of the decrease of the surface area and micropore volume of the samples. That has been explained on the base of different textural properties and/or chemical characteristic of the material. [ABSTRACT FROM AUTHOR]

Activated carbons from a mixture of olive-residue, oil and vegetable water, known as alperujo, OR, were prepared by KOH and H 3 PO 4 activation. KOH activations were made following two different methods (carbonization-activation and impregnation-activation) with two different KOH/carbon ratios. Textural characterization with N 2 and CO 2 reveals that a prior carbonization of samples followed by the activation with KOH, produces samples with similar textural and chemical properties to the impregnated ones at low KOH ratio, while at high KOH ratio; more porous samples are obtained by carbonization. However, no differences are observed increasing the KOH ratio for the impregnated samples. As a consequence, similar or even more porous samples are obtained by using an easier preparation method such as carbonization-activation. On the other side, H 3 PO 4 activation leads to samples with less surface area but with a more developed mesoporosity. In addition, the chemical surfaces of KOH and H 3 PO 4 activated samples are very different as shown by XPS and TPD results. XPS data denote a similar chemical texture in KOH activated samples in spite of the different preparation methods and KOH ratio, whereas the H 3 PO 4 method fixed different phosphorus surface groups. Analysing TPD data while on KOH activated samples, oxygenated surface groups (OSG) decompose mainly as CO 2 (carboxylic acid, anhydrides, lactones, etc.) during the TPD experiments, on H 3 PO 4 activated one those OSG ones evolve as CO (semiquinone, carbonyl, etc.) which has been attributed to the presence of C O P species that decompose in the form of CO at around 860 °C. As a consequence, similar electrochemical capacitances are obtained using KOH activated samples, which depend linearly on the surface area while the H 3 PO 4 activated one presents higher capacitance value and capacitance stability in spite of its smaller surface area. This fact was related with the presence and nature of phosphorus surface groups. [ABSTRACT FROM AUTHOR]

Abstract: An activated carbon with developed porosity and surface area (S BET =2387m2 g−1) was prepared by chemical activation and then oxidized with ammonium peroxydisulfate. The oxidation treatment destroyed mesopore walls leading to a severe surface area reduction. Specific thermal treatments were carried out in different portions of the oxidized sample to selectively remove the oxygenated surface complexes. The combination of different techniques revealed that thermal treatment between 300 and 500°C produces a strong reorganization of oxygenated groups on the chemical structure of carbons. CO2-evolving groups (around 75wt.%) are selectively transformed into CO-evolving groups. These processes only occur inside the pores, and involve CO2 desorption and re-adsorption in this temperature range. At a higher treatment temperature (700°C), re-oxidation is prevented and the surface chemistry becomes quite similar to the original activated carbon. [Copyright &y& Elsevier]

Ni/CeO 2 catalysts are very active and selective for total hydrogenation of CO 2 to methane, but the nature of the active sites is still unclear. The surface of a Ni/CeO 2 catalyst has been monitored under CO 2 methanation conditions by Near Ambient Pressure-XPS (NAP-XPS) using synchrotron radiation, and has been concluded that t he species involved in the redox processes taking place during the CO 2 methanation mechanism are the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ pairs. In addition, a small fraction of nickel is present on the catalyst surface forming NiO and Ni2+-carbonates/hydroxyls (around 20% of the total surface nickel), but these species do not participate in the redox processes of the methanation mechanism. Under CO 2 methanation conditions the H 2 reduction rate of the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ couples is much faster than their CO 2 reoxidation rate (2 times faster, at least, at 300ºC), but a certain proportion of nickel always remains oxidized under reaction conditions. The high activity of Ni/CeO 2 catalysts for CO 2 methanation is tentatively attributed to the simultaneous presence of Ni2+-CeO 2 and Ni0 active sites where CO 2 and H 2 are expected to be efficiently dissociated, respectively. [Display omitted] • The redox processes during CO 2 methanation involve the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ pairs. • H 2 reduction rate of the Ni2+-CeO 2 /Ni0 and Ce4+/Ce3+ couples is faster than their CO 2 reoxidation rate. • Ni/CeO 2 catalysts keep simultaneously Ni2+-CeO 2 and Ni0 active sites under reaction conditions. • NiO and Ni2+-carbonates/hydroxyls do not participate in redox processes [ABSTRACT FROM AUTHOR]

[Display omitted] • CO 2 methanation kinetics on low-loaded Ni/Al 2 O 3 catalyst is described based on DRIFTS and kinetic data. • LHHW rate equations are deduced including the role of water, carbonyls and formates. • Formates decomposition as RDS rate equation represents most accurately the kinetic performance. • The participation of both carbonyls and formates in the CO 2 hydrogenation is confirmed. The mechanism and kinetic of CO 2 methanation reaction of 9.5 % Ni/Al 2 O 3 catalyst is analysed under a wide range of operating conditions. Once the catalyst activity is stabilized, the influence of temperature, total pressure and space velocity is studied for kinetic characterisation. A data set comprising of 153 experimental runs has been used to develop a kinetic model capable to accurately predict the reaction rate. Ni/Al 2 O 3 catalyst shows an apparent activation energy of 80.1 kJ mol−1 in CO 2 hydrogenation. Data obtained under differential mode adjust quite precisely to a power-law model with H 2 O inhibition, with a water adsorption constant of 3.1 atm−1 and apparent orders of 0.24 and 0.27 for H 2 and CO 2 , respectively. Based on DRIFTS results, we propose for the first time the H-assisted CO formation route, which is compared with the more conventionally reported carbonyl route, and describe the corresponding reaction rate LHHW equation, resulting in notable improvement for mean deviation (D) of 7.0 % in our model related to that based on the carbonyl route (D = 20.1 %) usually suggested for catalysts with higher Ni loads around 20 %. The H-assisted CO formation route considers the formate species decomposition into carbonyls via H-assisted CO formation mechanism and further carbonyls hydrogenation into CHO as the rate determining step. Thus, the LHHW mechanism, in which carbonyls as well as formate species participate in CO 2 methanation, is capable to reflect the kinetics of lowly-loaded Ni/Al 2 O 3 catalyst with high accuracy under relevant process conditions (315−430 °C, 1−6 bar, H 2 to CO 2 molar ratios between 1–16 and, different reagents and products partial pressures). [ABSTRACT FROM AUTHOR]

• Novel ZrO 2 -TiO 2 covered carbon microspheres composites (Zr-Ti/C) were synthesized. • 3D-structures or nanofilaments were observed on the surface of carbon microspheres. • ZrO 2 was successfully incorporated into TiO 2 to form hybridized ZrO 2 –TiO 2 nanostructures. • The low band gaps of composites (2.60–2.96 eV) provides absorbance of solar light. • These composites open the gate to synthesis of new cost-effective solar harvesting materials. ZrO 2 -TiO 2 /C core-shell composites (CTiXZrYs) were synthesized at different Zr-to-Ti ratios by a facile and economical sol-gel approach to obtain highly efficient solar light-responsive photocatalysts. ZrO 2 -(CZrXs) and TiO 2 -covered carbon microspheres (CTiXs) were also prepared as reference materials. SEM and TEM images reveal a coverage formed mainly by fused nanosized spherical particles in CTiXs and CZrXs composites, while in bimetallic ones (CTiXZrYs) 3D-structures or nanofilaments are observed. Zirconium titanate was identified by XRD corroborating the observation obtained by TEM and SEM. XPS confirm that hybridized ZrO 2 –TiO 2 nanostructures are formed due to the incorporation of ZrO 2 into TiO 2. The low band-gaps of composites (2.60–2.96 eV) provide absorbance of solar light and thus, photoactivity. The photocatalytic activity in the removal of hazardous compounds is enhanced in CTiXZrYs and increases with the amount of zirconium titanate present on the composite due to a synergistic effect between the carbon and coupled-semiconductors phases. These newly synthesized coupled-semiconductor/carbon composites open the gate of the synthesis of new cost-effective light harvesting energy materials for future fuel generation and solar energy devices. [ABSTRACT FROM AUTHOR]

Considering that high-purity fresh water is employed in the green production of hydrogen via commercial water electrolyzers and that over 80% of the global population faces significant water safety risks, it is essential to explore alternative water sources. One such alternative is the use of produced water from oil extraction processes. Hence, the main objective of this study is to evaluate the effect of the oil content of oilfield production water on the production of green hydrogen by electrolysis in the presence of carbon quantum dots (CQDs). For this purpose, various electrochemical techniques, such as linear sweep voltammetry (LSV), cyclic voltammetry (CV), and potentiometry, were used to identify the effect of crude oil during hydrogen production. Thermogravimetric analysis (TGA), mass spectrometry (MS), and Fourier-transform infrared spectroscopy (FTIR) were employed to discern the adsorption of crude oil onto the electrodes, quantify the gas fractions generated during the process and identify the functional groups present after the procedure, respectively. Also, optical microscopy was employed to follow the droplet size in the emulsion. The results show that using CQDs affects the Faradaic efficiency, which increases from 77% to 83% with the incorporation of CQDs. In the presence of CQDs, the effects generated by the presence of the oil are inhibited at low oil concentrations. On the contrary, hydrogen production increases by 10.0% (0.1 mL/min) with a faradaic efficiency of 83% and a half-cell efficiency of 41%, compared to the record obtained with the maximum concentration of emulsified crude oil (400 mg/L). The mean size of the initial emulsion droplets was 3.4 μm. At the end of the test, there was evidence of complete breakage of the emulsion due to the effect of the applied electric field. No evidence of adsorption of crude oil on graphite electrodes during electrolysis is observed based on the tests. It has been shown that green hydrogen production from crude oil production water is feasible due to the proposed disruptive electrolytes in the produced water, which inhibit the effect of oil content in the O/W emulsion. This allows the implementation of a new green energy production initiative aligned with the global goal of achieving net zero emissions (NZE) by 2050. The current investigation presents a prospective alternative for harnessing the 18 kW electrical energy potential employed within emulsion-breaking processes within a Colombian field for treatment of around 1000 bpd. This alternative offers a theoretical potential for hydrogen production, approximating 7.36 kW, thus representing a promising opportunity for practical field deployment. • CQDs in electrolysis enhance green hydrogen production efficiency from oilfield-produced water due to their conductive properties. • CQDs significantly increases Faradaic efficiency, inhibiting crude oil's negative effects on hydrogen generation. • Optimized electrolysis with CQDs result in 10% higher hydrogen production at high concentrations of emulsified crude oil. • CQDs mitigate crude oil's negative effects on the system, such as reduced conductivity and electrode degradation. • Gas analysis demonstrates the feasibility of converting oilfield production water into a valuable resource for green energy. [ABSTRACT FROM AUTHOR]

Activated carbon/Ti x O y nanoparticles (CTi) were synthesized by a controlled hydrolysis method under mild conditions of temperature (170–210 °C) and pressure (8 bar). These new materials are presented as visible-light driven photocatalysts with high performance in the degradation of emerging drugs in wastewater, like amoxicillin and paracetamol. The presence of Ti3+ self-structural modified TiO 2 was corroborated by XPS and Raman. The TiO 2 reduction effectivity and consequently, the photocatalytic activity, is influenced by the treatment temperature and the presence of carbon matrix. The band-gap decreases from 3.1 to 1.7 eV by the addition of carbon during the synthesis of coloured titania at 210 °C and from 3.0 to 1.7 eV by increasing the solvothermal temperature from 170 to 210 °C in the preparation of activated carbon-based coloured titania nanoparticles. The presence of carbon also improves the electron transfer from titania nanoparticles to carbon (confirmed by XPS) minimizing electron-hole recombination. All these factors improve the photocatalytic performance of the synthesized materials under visible irradiation providing a cost-effective method for the degradation of persistent wastewater pollutants. [Display omitted] [ABSTRACT FROM AUTHOR]

CO 2 hydrogenation to CH 4 (or methanation) has been proposed to diminish CO 2 emissions producing a valuable fuel. A catalyst consisting of NiO-CeO 2 mixed oxide 6–7 nm nanoparticles with enhanced properties has been prepared, and compared with other NiO-CeO 2 reference catalysts including a mixed oxide with the same composition but without control of the size, a counterpart NiO-CeO 2 mixed oxide with three dimensionally ordered macroporous (3DOM) structure and an inverse catalyst consisting of bulk NiO-supported CeO 2 nanoparticles among others. At 275 °C the CO 2 methanation rate is near 3 times higher to that achieved with the counterpart reference catalyst prepared without control of the size, being more active than all reference catalysts. The selectivity towards CH 4 formation is ~100% in the whole range of temperature studied (until 500 °C), and kept the same activity and selectivity during a 25 h long-term test. The high activity of this catalyst is related with its high specific surface area (122 m2/g) and with the presence of highly-reducible Ni-O-Ce species on the nanoparticles surface • 6-7 nm NiO-CeO2 with enhanced activity for CO2 methanation has been prepared. • Reaction rate is 3 times higher to that of a catalyst prepared without size control. • Nanoparticles selectivity towards CH4 is near 100 % until 500 °C. • Nanoparticles kept the same activity and selectivity for 25 hours. [ABSTRACT FROM AUTHOR]

Sulfamethoxazole and metronidazole are emerging pollutants commonly found in surface water and wastewater. These compounds have a significant environmental impact, being necessary in the design of technologies for their removal. Recently, the advanced oxidation process has been proven successful in the elimination of this kind of compounds. In this sense, the present work discusses the application of UV/H 2 O 2 and ozonation for the degradation of both molecules in single and binary systems. Experimental kinetic data from O 3 and UV/H 2 O 2 process were adequately described by a first and second kinetic model, respectively. From the ANOVA analysis, it was determined that the most statistically significant variables were the initial concentration of the drugs (0.03 mmol L−1) and the pH = 8 for UV/H 2 O 2 system, and only the pH (optimal value of 6) was significant for degradation with O 3. Results showed that both molecules were eliminated with high degradation efficiencies (88–94% for UV/H 2 O 2 and 79–98% for O 3) in short reaction times (around 30–90 min). The modeling was performed using a quadratic regression model through response surface methodology representing adequately 90 % of the experimental data. On the other hand, an artificial neural network was used to evaluate a non-linear multi-variable system, a 98% of fit between the model and experimental data was obtained. The identification of degradation byproducts was performed by high-performance liquid chromatography coupled to a time mass detector. After each process, at least four to five stable byproducts were found in the treated water, reducing the mineralization percentage to 20% for both molecules. [Display omitted] • Advanced oxidation processes were applied to eliminate pharmaceuticals in aqueous solution. • The UV/H 2 O 2 process eliminated 88–94% of sulfamethoxazole and metronidazole. • Ozonation process degraded 98% of both molecules in short reaction times. • Experimental data were best modeling and predicted using an artificial neural network. • Byproducts were identified, most of them disappear after 30 min of treatment. [ABSTRACT FROM AUTHOR]