Ignition of CO2 methanation using DBD-plasma catalysis in an adiabatic reactor

In this work, a novel strategy of the use of dielectric barrier discharge (DBD) plasma-catalysis for exothermic reactions is presented. DBD-plasma is used as reaction ignitor, rather than the classical approach of continuous operation, by taking advantage of the synergy between catalytic plasma activation from room temperature and a self-sustained exothermic reaction. CO2 methanation reaction was performed in a thermal insulated reactor using an active nickel-based catalyst loaded in two catalytic bed sections, with electrodes implemented solely in the first section. DBD plasma was employed to activate the reaction from cold conditions with the subsequent increase in reactor temperature and, finally, reaction was self-sustained by thermal-catalysis. The experimental results pointed out the sensitive dependence of the reactor temperature on the gas flow rate during the plasma operation. Low-energy conditions were found in which the reaction could operate in autothermal mode, after plasma shut-off. Power and start-up time were optimized, obtaining a considerable low start-up time from cold conditions (25 ◦C) of only 3 min. Besides, the autothermal operation mode was maintained for 8 h without any energy input. This proof-of-concept work demonstrates that plasma can be implemented as initial power ignition in exothermic reactions using proper reactor design and conditions, and then, the reactor can operate in autothermal mode

CeO2-promoted Cu2O-based catalyst sprayed on the gas diffusion layer for the electroreduction of carbon dioxide to ethylene

The development of efficient and selective catalysts for the carbon dioxide reduction reaction (CO2RR) is crucial for sustainable energy and chemical synthesis. In this work, CeO2-y (y = C (cubic) and R (rod)) was incorporated into Cu2O nanocube electrocatalyst as a promoter for ethylene (C2H4) production. The results demonstrate that the catalyst with a loading of 5 wt% crystalline CeO2-C exhibits competitive activity and stability for ethylene production compared to pristine Cu2O. Under optimized reaction conditions of −250 mA cm−2 current density and 1 M KOH electrolyte, the Cu2O–5CeO2-C catalyst achieved a faradaic efficiency (FE) of ∼53% for C2H4 production, while maintaining stability over a period of 120 minutes. In contrast, non-promoted Cu2O exhibited a lower FE for C2H4 (∼38%) and experienced partial deactivation after 45 minutes. The characterization of the catalysts before and after the reaction revealed that the interaction between Cu2O and CeO2-C creates intrinsic sites (Cux–CeO2−x; Cux = Cu2+, Cu+, and Cu0) for the binding of CO2 and H2O molecules. Moreover, the Cu2O–5CeO2-C catalyst outperforms other reported systems in terms of FE and partial current density for C2H4 production. It requires a lower potential (−0.98 V vs. RHE) to operate at the same electrolyte concentration. This finding highlights the promising nature of Cu2O–5CeO2-C as an efficient and cost-effective catalyst for C2H4 production

Design of a Multi-Tubular Catalytic Reactor Assisted by CFD Based on Free-Convection Heat-Management for Decentralised Synthetic Methane Production

A simple reactor design for the conversion of CO2 methanation into synthetic methane based on free convection is an interesting option for small-scale, decentralised locations. In this work, we present a heat-management design of a multi-tubular reactor assisted by CFD (Ansys Fluent®) as an interesting tool for scaling-up laboratory reactor designs. The simulation results pointed out that the scale-up of an individual reactive channel (d = 1/4′, H = 300 mm) through a hexagonal-shaped distribution of 23 reactive channels separated by 40 mm allows to obtain a suitable decreasing temperature profile (T = 487-230 °C) for the reaction using natural convection cooling. The resulting heat-management configuration was composed of three zones: (i) preheating of the reactants up to 230 °C, followed by (ii) a free-convection zone (1 m/s air flow) in the first reactor section (0-25 mm) to limit overheating and, thus, catalyst deactivation, followed by (iii) an isolation zone in the main reactor section (25-300 mm) to guarantee a proper reactor temperature and favourable kinetics. The evaluation of the geometry, reactive channel separation, and a simple heat-management strategy by CFD indicated that the implementation of an intensive reactor cooling system could be omitted with natural air circulation

Structural Influence of the Anode Materials towards Efficient Zn Deposition/Dissolution in Aqueous Zn-Iodide Flow Batteries

Zinc-iodide flow battery (ZIFB) is one of the best potential candidates for future grid-scale energy storage, due to its eye-catching features of benign, high energy density and non-corrosive nature. However major investigations have not done yet on the negative electrode of this battery where the Zn deposition/dissolution mechanism takes place, which may have an impact on the battery performance. Herein, we have reported a comparative study of different carbon-based anodes which are conventional graphite felt, carbon paper and graphite foil. Single-cell charge/discharge performances among these three different anodes depicts that the cell with planar, hydrophilic graphite foil anode is showing the best energy efficiency and the lowest cell resistance among the carbonaceous electrodes. Zinc dissolution process during discharge process seems to be the bottleneck for having a stable cell, which was corroborated by the use of a Zn foil anode that shows excellent efficiencies along the successive cycles

Suppressing water migration in aqueous Zn-iodide flow batteries by asymmetric electrolyte formulation

Zinc-iodide flow battery (ZIFB) is under research for the last years due to its suitability as a potential candidate for future electrochemical energy storage. During cycling, one of the biggest challenges that affect the reliable performance of ZIFB is the substantial water migration through the membrane because of differential molar concentrations between anolyte and catholyte that imbalance the osmotic pressures in each compartment. Considering the mass balances, herein we propose to equalize the total ionic concentration of electrolytes by the addition of extra solute into the compartment of lower ion concentration as a way to restrict the water crossover. Experimental validation of this electrolyte concentrations balancing strategy has been carried out by assessing the post-cycled electrolytes, and half-cell charged electrolytes, which confirms the efficient suppression of water migration from catholyte to anolyte. Besides, in-depth analysis of ions and water transport mechanism through Nafion 117 membrane confirms that solvated K+ ions of lower ionic radius compared to solvated Zn2+ ions, are the dominant migrating carrier. Therefore, the addition of extra KI solute is beneficial to suppress the major transport of large hydrated Zn2+ ions along with the higher amount of water. Finally, the improved ZIFB cell behaviour with enhanced electrical conductivity, discharge capacity, and voltage efficiency in the cell assembled with the electrolytes of balanced molar concentrations concludes our present study, proving that tuning the electrolytes concentrations is an effective way to suppress water migration as an appealing method in the prospect of upscaling ZIFB application

Fischer-Tropsch synthesis: Towards a highly-selective catalyst by lanthanide promotion under relevant CO2 syngas mixtures

The role of lanthanides as promoters on cobalt-based catalysts for Fischer-Tropsch synthesis was evaluated under relevant biomass-derived syngas mixtures. Cerium, lanthanum and a combination of them were impregnated on an industrial cobalt-based micro-catalyst. Lanthanide incorporation did not affect significantly the morphology of the catalyst, although it reduced the available surface cobalt. Catalytic tests revealed that both the presence of carbon dioxide in the feed and lanthanides in the catalyst led to similar outcomes; higher selectivity to long-chain hydrocarbons, at the expense of reactivity. Reaction experiments were well aligned with in-situ DRIFTS measurements, which evidenced the modification of the initial reaction mechanism, CO2 conversion and the presence of lower CO-cobalt coverages. This work reports two relevant findings for FTS development. Firstly, the presence of carbon dioxide is beneficial for long-chain hydrocarbon production. Secondly, the incorporation of lanthanides increases the production of gasoline, kerosene and diesel fractions

Passivation of Co/Al2O3 Catalyst by Atomic Layer Deposition to Reduce Deactivation in the Fischer-Tropsch Synthesis

The present work explores the technical feasibility of passivating a Co/γ-Al2O3catalyst byatomic layer deposition (ALD) to reduce deactivation rate during Fischer-Tropsch synthesis (FTS).Three samples of the reference catalyst were passivated using different numbers of ALD cycles (3, 6and 10). Characterization results revealed that a shell of the passivating agent (Al2O3) grew aroundcatalyst particles. This shell did not affect the properties of passivated samples below 10 cycles, inwhich catalyst reduction was hindered. Catalytic tests at 50% CO conversion evidenced that 3 and6 ALD cycles increased catalyst stability without significantly affecting the catalytic performance,whereas 10 cycles caused blockage of the active phase that led to a strong decrease of catalytic activity.Catalyst deactivation modelling and tests at 60% CO conversion served to conclude that 3 to 6 ALDcycles reduced Co/γ-Al2O3deactivation, so that the technical feasibility of this technique was provenin FTS

Effect of Thermal Treatment on Nickel-Cobalt Electrocatalysts for Glycerol Oxidation

Nickel-cobalt electrocatalysts with atomic ratios of 2 : 1 and 1 : 2 were synthesized on nickel foam (NF) substrates by cathodic electrodeposition, further evaluating the performance of the pristine and thermally-treated materials as anodes for glycerol oxidation in alkaline medium. The electrodes were characterized by cyclic and linear sweep voltammetry at alkaline pH, showing an indirect oxidation of glycerol mediated by the metal oxyhydroxides. Under the selected conditions, a favourable potential window of 0.2 V upon comparison of water and glycerol oxidation was found. In addition, the increase in nickel content and the thermal treatment enhanced the anode polarization. After galvanostatic electrolysis at 10 mA cm−2, the products were analysed by HPLC, formate ion being the primary product, with a faradaic efficiency (FE) higher than 70 % in most cases. Both the FE to formate and the glycerol conversion were substantially enhanced using the thermally-treated anodes, whereas the effect of the Ni/Co ratio on these two parameters did not follow a clear trend

Bimetallic cobalt catalysts promoted by La2O3 for the production of high-calorie synthetic gas

A new catalytic route for the production of a high-calorie synthetic gas (40-60 MJ/Nm3), composed by C1-C4 hydrocarbons, has industrial interest for gas applications and locations with high heating requirements. In this work, a series of bimetallic Co-X (X = Ni, Pt and Fe) catalysts supported on La2O3 promoted Al2O3 micro-spheres were evaluated using both CO2 and CO carbon sources under mild temperature (T = 200-300 °C), moderate pressure (P = 10 bar·g) and relatively high gas hourly space velocity (40,000 N mL/gcat·h). Experimental results proved that the incorporation of nickel as a second metal is beneficial for high-calorie gas application. Besides, catalytic results showed that the utilization of CO as carbon source is beneficial in both conversion and C1-C4 hydrocarbon selectivities. Co-Ni presented the most interesting results, leading to a heating value of 57.9 MJ/Nm3 (40.01 % CH4 and 50.04 % C2-C4 hydrocarbon) at 250 °C through CO hydrogenation. The enhanced catalytic performance achieved over bimetallic Co-Ni was attributed to CoNi alloy catalytic activity, high reducibility (73.82 %), active metal content (9.65x10-4 mmol/g) and appropriate acid-basic sites for COx activation. In contrast, the conversion of CO2 to high-calorie gas was found to be more challenging and lower gas heating values were achieved (39.73 MJ/Nm3). In this case, an adapted reactor concept using a dual bimetallic catalyst and different reaction conditions is hereby proposed to shift selectivity towards the targeted products. This findings represent a step forwards in catalytic engineering for the development of high-calorie synthetic gas reactors

Direct Operando Visualization of Metal Support Interactions Induced by Hydrogen Spillover During CO2 Hydrogenation

The understanding of catalyst active sites is a fundamental challenge for the future rational design of optimized and bespoke catalysts. For instance, the partial reduction of Ce4+ surface sites to Ce3+ and the formation of oxygen vacancies are critical for CO2 hydrogenation, CO oxidation, and the water gas shift reaction. Furthermore, metal nanoparticles, the reducible support, and metal support interactions are prone to evolve under reaction conditions; therefore a catalyst structure must be characterized under operando conditions to identify active states and deduce structure-activity relationships. In the present work, temperature-induced morphological and chemical changes in Ni nanoparticle-decorated mesoporous CeO2 by means of in situ quantitative multimode electron tomography and in situ heating electron energy loss spectroscopy, respectively, are investigated. Moreover, operando electron energy loss spectroscopy is employed using a windowed gas cell and reveals the role of Ni-induced hydrogen spillover on active Ce3+ site formation and enhancement of the overall catalytic performance