The determination of the HOR/HER reaction mechanism from experimental kinetic data

Hydrogen oxidation and evolution are important processes from both a fundamental and applied perspective. In interpreting experimental kinetic data, few studies have explicitly accounted for the impact of H* coverage and mass transport, which lead to discrepancies in the kinetic parameters and the resultant reaction mechanism. Here, we present how to determine the kinetic parameters accounting for both effects. We discuss the use of the kinetic parameters towards mechanistic interpretations for HOR/HER and show that, in general, knowledge of the coverage of H* or activation energies may be required to assign a reaction mechanism. We apply these ideas to activity data of several HOR and HER electrocatalysts, such as Au, Pt, MoS2, and CoP

Breaking linear scaling relationships with transition metal carbides

Transition metal carbides (TMCs) are proposed as catalysts and supports for small metal particles to replace expensive late transition metals as heterogeneous catalysts

Stability and reactivity of metal nanoclusters supported on transition metal carbides

Small particles of transition metals (TM) supported on transition metal carbides (TMC) – TMn@TMC – provide a plethora of design opportunities for catalytic applications due to their highly exposed active centres, efficient atom utilisation and the physicochemical properties of the TMC support. To date, however, only a very small subset of TMn@TMC catalysts have been tested experimentally and it is unclear which combinations may best catalyse which chemical reactions. Herein, we develop a high-throughput screening approach to catalyst design for supported nanoclusters based on density functional theory, and apply it to elucidate the stability and catalytic performance of all possible combinations between 7 monometallic nanoclusters (Rh, Pd, Pt, Au, Co, Ni and Cu) and 11 stable support surfaces of TMCs with 1 : 1 stoichiometry (TiC, ZrC, HfC, VC, NbC, TaC, MoC and WC) towards CH4 and CO2 conversion technologies. We analyse the generated database to unravel trends or simple descriptors in their resistance towards metal aggregate formation and sintering, oxidation, stability in the presence of adsorbate species, and study their adsorptive and catalytic properties, to facilitate the discovery of novel materials in the future. We identify 8 TMn@TMC combinations as promising catalysts, all of them being new for experimental validation, thus expanding the chemical space for efficient conversion of CH4 and CO2

Limitations of free energy diagrams to predict the catalytic activity: the reverse water gas shift reaction catalyzed by Ni/TiC

The temporal evolution at the catalyst surface is a result of an intricate interplay between all involved microscopic events such as adsorption, desorption, diffusion, and bond breaking/formation steps, and the interaction with the surrounding environment. By properly including these effects, kinetic Monte Carlo (kMC) simulations can accurately describe the complexity of real catalysts, unravel the dominant reaction mechanisms and provide fundamental understanding towards the rational design of novel catalysts. In this work, we combine density functional theory (DFT) calculations, statistical thermodynamics and kMC simulations to study the reverse water–gas shift (RWGS) reaction on Ni/TiC, a bifunctional catalyst. The predictions from DFT energy profiles do not coincide with the outcome of the kMC simulations, evidencing the limitations of the former, especially in including the effect of coverage of surface species, which plays a crucial role. The kMC simulations results are in remarkable agreement with the experimental data, proving that the kMC simulations are able to describe the complex chemistry of the RWGS reaction on a bifunctional catalyst

System Dynamics Modeling for Supporting Drought-Oriented Management of the Jucar River System, Spain

[EN] The management of water in systems where the balance between resources and demands is already precarious can pose a challenge and it can be easily disrupted by drought episodes. Anticipated drought management has proved to be one of the main strategies to reduce their impact. Drought economic, environmental, and social impacts affect different sectors that are often interconnected. There is a need for water management models able to acknowledge the complex interactions between multiple sectors, activities, and variables to study the response of water resource systems to drought management strategies. System dynamics (SD) is a modeling methodology that facilitates the analysis of interactions and feedbacks within and between sectors. Although SD has been applied for water resource management, there is a lack of SD models able to regulate complex water resource systems on a monthly time scale and considering multiple reservoir operating rules, demands, and policies. In this paper, we present an SD model for the strategic planning of drought management in the Jucar River system, incorporating dynamic reservoir operating rules, policies, and drought management strategies triggered by a system state index. The DSS combines features from early warning and information systems, allowing for the simulation of drought strategies, evaluating their economic impact, and exploring new management options in the same environment. The results for the historical period show that drought early management can be beneficial for the performance of the system, monitoring the current state of the system, and activating drought management measures results in a substantial reduction of the economic impact of droughts.The data used in this study was obtained from the references included. We acknowledge the European Research Area for Climate Services consortium (ER4CS) and the Agencia Estatal de Investigacion for their financial support to this research under the INNOVA project (Grant Agreement: 690462; PCIN-2017-066). This study has also been partially funded by the ADAPTAMED project (RTI2018-101483-B-I00) from the Ministerio de Ciencia, Innovacion y Universidades (MICIU) of Spain.Rubio-Martin, A.; Pulido-Velazquez, M.; Macian-Sorribes, H.; Garcia-Prats, A. (2020). System Dynamics Modeling for Supporting Drought-Oriented Management of the Jucar River System, Spain. Water. 12(5):1-19. https://doi.org/10.3390/w12051407S119125Mishra, A. K., & Singh, V. P. (2010). A review of drought concepts. Journal of Hydrology, 391(1-2), 202-216. doi:10.1016/j.jhydrol.2010.07.012Momblanch, A., Paredes-Arquiola, J., Munné, A., Manzano, A., Arnau, J., & Andreu, J. (2015). Managing water quality under drought conditions in the Llobregat River Basin. 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Zeolite-encapsulated single-atom catalysts for efficient CO2 conversion

Zeolite-supported single-atom catalysts (SACs) have emerged as a novel class of cheap and tuneable catalysts that can exhibit high activity, selectivity and stability. In this work, we conduct an extensive screening by means of density functional theory calculations to determine the usefulness of 3d, 4d and 5d transition metal (TM) SACs-supported in MFI-type Silicalite-1 zeolite for CO2 conversion. Two reaction mechanisms are considered, namely the redox direct CO2 dissociation and associative hydrogen-assisted CO2 dissociation mechanisms. Early TM SACs exhibit the lowest energy barriers, which follow the redox mechanism. These energy barriers raise when going right in the periodic table up to group 10, where they become prohibitive and the associative mechanism should dominate. By also considering their resistance to aggregation, we support the use of Sc, Y, La, Ru, Rh, Ni, Pd and Pt as potentially active and stable catalysts for CO2 conversion, given their low energy barriers and strong interaction with the zeolite framework

Occurrence and Removal of Priority Substances and Contaminants of Emerging Concern at the WWTP of Benidorm (Spain)

This work is part of the European research project LIFE15 ENV/ES/00598 whose objective was to develop an efficient and sustainable methodology to eliminate Priority Substances (PS) and Contaminants of Emerging Concern (CEC), in Wastewater Treatment Plants (WWTP). The aim was to achieve reduce the concentration of PSs until their concentration was below the quality limit established in the DIRECTIVE 2013/39/EU, and to achieve reductions of 99% of the initial concentration for the selected CECs. The plant selected for the experimentation was the Benidorm WWTP (Spain). This publication studied the appearance and elimination, in the conventional treatment of this plant, of 12 priority substances (EU) and 16 emerging pollutants (5 of them included in the EU watch lists) during a year of experimentation. The analytical methods of choice were High Performance Liquid Chromatography coupled to a Mass Spectrometer (HPLC-MS/MS) and Gas Chromatography coupled to a Mass Spectrometer (GC-MS/MS). Results showed that the PSs atrazine, brominated diphenyl ether, isoproturon, octylphenol, pentachlorobenzene, simazine, terbutryn, tributyltin, and trifluralin, and the CECs 17-α-ethinylestradiol, 17-β-estradiol, imazalil, orthophenylphenol, tertbutylazine, and thiabendazole, were not detected. The micropollutants with the highest a-verage percentages of removal (>90%) are: chloramphenicol (100%), estriol (100%) and ibuprofen (99%). Partially removed were ketoprofen (79%), chlorpyrifos (78%), di(2-ethylhexyl) phthalate (78%), estrone (76%), sulfamethoxazole (68%), and fluoxetine (53%). The compounds with the lowest average percentage of removal (<50%) are diclofenac (30%), erythromycin (1%), diuron (0%) and carbamazepine (0%). For the micropollutants chlorpyrifos, diclofenac, erythromycin, sulfamethoxazole, carbamazepine, fluoxetine, ibuprofen, and ketoprofen, complementary treatments will be necessary in case there is a need to reduce their concentrations in the WWTP effluent below a certain standard. The presence of the different micropollutants in the samples was not regular. Some of them were presented continuously, such as carbamazepine; however, others sporadically such as chloramphenicol and others were associated with seasonal variations or related to remarkable periods of time, such as sulfamethoxazole.This research was funded by European Commission, grant number LIFE15ENV/ES/00598 Development of an Efficient and Sustainable Methodology for Emerging Pollutants Removal in WWTPS

On the Capabilities of Transition Metal Carbides for Carbon Capture and Utilization Technologies

The search for cheap and active materials for the capture and activation of CO2 has led to many efforts aimed at developing new catalysts. In this context, earth-abundant transition metal carbides (TMCs) have emerged as promising candidates, garnering increased attention in recent decades due to their exceptional refractory properties and resistance to sintering, coking, and sulfur poisoning. In this work, we assess the use of Group 5 TMCs (VC, NbC, and TaC) as potential materials for carbon capture and sequestration/utilization technologies by combining experimental characterization techniques, first-principles-based multiscale modeling, vibrational analysis, and catalytic experiments. Our findings reveal that the stoichiometric phase of VC exhibits weak interactions with CO2, displaying an inability to adsorb or dissociate it. However, VC often exhibits the presence of surface carbon vacancies, leading to significant activation of CO2 at room temperature and facilitating its catalytic hydrogenation. In contrast, stoichiometric NbC and TaC phases exhibit stronger interactions with CO2, capable of adsorbing and even breaking of CO2 at low temperatures, particularly notable in the case of TaC. Nevertheless, NbC and TaC demonstrate poor catalytic performance for CO2 hydrogenation. This work suggests Group 5 TMCs as potential materials for CO2 abatement, emphasizes the importance of surface vacancies in enhancing catalytic activity and adsorption capability, and provides a reference for using the infrared spectra as a unique identifier to detect oxy-carbide phases or surface C vacancies within Group 5 TMCs

Solvation of furfural at metal–water interfaces: Implications for aqueous phase hydrogenation reactions

Metal-water interfaces are central to understanding aqueous-phase heterogeneous catalytic processes. However, the explicit modeling of the interface is still challenging as it necessitates extensive sampling of the interfaces' degrees of freedom. Herein, we use ab initio molecular dynamics (AIMD) simulations to study the adsorption of furfural, a platform biomass chemical on several catalytically relevant metal-water interfaces (Pt, Rh, Pd, Cu, and Au) at low coverages. We find that furfural adsorption is destabilized on all the metal-water interfaces compared to the metal-gas interfaces considered in this work. This destabilization is a result of the energetic penalty associated with the displacement of water molecules near the surface upon adsorption of furfural, further evidenced by a linear correlation between solvation energy and the change in surface water coverage. To predict solvation energies without the need for computationally expensive AIMD simulations, we demonstrate OH binding energy as a good descriptor to estimate the solvation energies of furfural. Using microkinetic modeling, we further explain the origin of the activity for furfural hydrogenation on intrinsically strong-binding metals under aqueous conditions, i.e., the endothermic solvation energies for furfural adsorption prevent surface poisoning. Our work sheds light on the development of active aqueous-phase catalytic systems via rationally tuning the solvation energies of reaction intermediates

Unravelling the removal mechanisms of bacterial and viral surrogates in aerobic granular sludge systems

The aerobic granular sludge (AGS) process is an effective wastewater treatment technology for organic matter and nutrient removal that has been introduced in the market rapidly. Until now, limited information is available on AGS regarding the removal of bacterial and viral pathogenic organisms present in sewage. This study focussed on determining the relation between reactor operational conditions (plug flow feeding, turbulent aeration and settling) and physical and biological mechanisms on removing two faecal surrogates, Escherichia coli and MS2 bacteriophages. Two AGS laboratory-scale systems were separately fed with influent spiked with 1.0 × 106 CFU/100 mL of E. coli and 1.3 × 108 PFU/100 mL of MS2 bacteriophages and followed during the different operational phases. The reactors contained only granular sludge and no flocculent sludge. Both systems showed reductions in the liquid phase of 0.3 Log10 during anaerobic feeding caused by a dilution factor and attachment of the organisms on the granules. Higher removal efficiencies were achieved during aeration, approximately 1 Log10 for E. coli and 0.6 Log10 for the MS2 bacteriophages caused mainly by predation. The 18S sequencing analysis revealed high operational taxonomic units (OTUs) of free-living protozoa genera Rhogostoma and Telotrochidium concerning the whole eukaryotic community. Attached ciliates propagated after the addition of the E. coli, an active contribution of the genera Epistylis, Vorticella, and Pseudovorticella was found when the reactor reached stability. In contrast, no significant growth of predators occurred when spiking the system with MS2 bacteriophages, indicating a low contribution of protozoa on the phage removal. Settling did not contribute to the removal of the studied bacterial and viral surrogates.M.L. Barrios-Hernández acknowledges the Technological Institute of Costa Rica for providing the fellowship (Grant Number 007-2014-M) to pursue her PhD programme (2016-2020) at IHE-Delft, the Netherlands. K. Mora-Cabrera acknowledges the Generalitat Valenciana (GRISOLIAP/2017/173) and the European Social Funds (BEFPI/2019/065) for their financial support