Presence Of Steam Research Articles

Unlocking the Value of Phosphogypsum Waste: Steam Calcination for Efficient Decomposition and Resource Recovery

ABSTRACT Phosphogypsum is a waste by-product of phosphate fertilizer production. It contains calcium sulfate (CaSO4.xH2O), which can be decomposed to produce calcium oxide (CaO) and sulfur dioxide (SO2). Steam calcination is a process that uses steam to decompose CaSO4. This study represents the first comprehensive investigation of steam calcination applied to phosphogypsum, comparing its performance to pure CaSO4 at various temperatures (1050–1200 °C) and steam molar ratios (0, 4%, and 30%). The results showed that steam calcination can significantly lower the calcination temperature of both CaSO4 and phosphogypsum. The presence of steam can significantly accelerate the decomposition reaction of pure CaSO4 and phosphogypsum when compared to decomposition in nitrogen or air. It was found that the decomposition reaction in steam follows the contracting cylinder reaction model in the case of CaSO4 and the first-order reaction model for the phosphogypsum. Additionally, the activation energy for the steam calcination of CaSO4 and phosphogypsum were found to be 421.2 kJ/mol and 418.6 kJ/mol, respectively, which are lower than the activation energy for the calcination in oxyfuel combustion products (O2, CO2, SO2, and H2O gases) 531.4 kJ/mol demonstrating its potential for enhanced energy efficiency. As a result, steam calcination emerges as a promising sustainable solution for valorizing phosphogypsum while reducing energy consumption and greenhouse gas emissions.

Efficient integration of calcium looping with methane Bi-reforming using Pd-enhanced Ni-CaO dual functional nanomaterials

Integration technology of methane bi-reforming (BRM; a combination of methane steam and dry reforming) with calcium looping (CaL-BRM) offered a novel solution to reduce CO2 emission, enabling direct capture and conversion of low-concentration CO2 from sources into value-added products (H2, syngas) within the same reactor. In this study, Ni-CaO-based dual-functional material (DFM), with a small quantity of palladium in the nanostructure, was developed via a continuous two-stage aerosol process and employed in the CaL-BRM. Experimental results demonstrate that Pd-Ni-CaO exhibited high activity and cyclic stability over multiple cycles, maintaining effective CO2 capture (12.0 mmolCO2/gCaO) and BRM performance (>98 % CO2 conversion; H2/CO = 2) at a relatively low temperature (600 °C). Density functional theory calculations reveal that the presence of Pd lowered the activation energy of CH* dissociation, the rate-determining step, from 1.14 to 0.67 eV. The higher adsorption energy (−0.87 eV) of H2O on the Ni-Pd surface and the lower energy barrier (0.62 eV) for subsequent dissociation contributed to the promising catalytic performance in the presence of steam. These findings underscore the significance of utilizing appropriate DFM and demonstrate the potential of CaL-BRM for efficient integrated carbon capture and utilization.

Investigating the Impact of Steam Enhancement on Combustion in a Swirl-Assisted Jet-Stabilized Gas Turbine Combustor

Abstract A newly developed gas turbine combustor system based on the swirl-assisted jet-stabilized concept using Jet A-1 and natural gas as reference fuel is tested under wet conditions to evaluate its combustion characteristics in the presence of steam. The effect of steam injection into the gas turbine combustor under both spray and superheated liquid fuel injection conditions is studied experimentally on an atmospheric test rig. To evaluate the effect of steam injection on combustion performance, the water-to-gas ratio (WGR) is varied from 0 to 32%. With increasing WGR = 0 to 16% and at stoichiometric condition, NOx reductions of -82% to -100% were observed during Jet A-1 and natural gas combustion, respectively. It is shown that the reduction of the combustion zone temperature due to the steam acting as a heat sink is the main cause of the NOx decrease. The operating range of the burner remained fairly constant for Jet A-1 until WGR = 20%, while it decreased significantly with increasing WGR for natural gas combustion. While the effect of the WGR on CO was modest, the greatest effect of the WGR was on the heat release zone intensity at a constant air to fuel ratio. In reducing the NOx levels of Jet A-1 and natural gas combustion, both thermal and chemical effects of steam injection were observed. However, steam acting as a heat sink and lowering the flame temperature, thereby reducing the thermal NO formation rate, was the dominant factor in NOx reduction.

Syngas Purpose Pyrolysis-Gasification of Organic Fractions of MSW over Metal-Loaded Y-Zeolite Catalysts

The increasing environmental consideration and the growth of instability of the energy market call for methods that can process the organic fraction of municipal solid waste (OFMSW) into fuel instead of disposal. Due to the pyrolysis and gasification that are efficient procedures to achieve valuable products, gasification of OFMSW with different particle sizes and compositions was carried out in the presence of Ni and Ni-Ce-loaded Y-zeolite in a multizone tubular kiln reactor. During the experiments, 500°C was applied in the first reactor zone, while the 2nd zone was at an elevated temperature of 600°C or 900°C in the presence of steam. The combined pyrolysis and gasification experiments were also carried out without a catalyst with the same operating conditions. The feedstock was collected from the organic fraction of a Hungarian mechanical-biological treatment (MBT) plant and was separated into four different fractions based on particle size: <1 cm dry biomass and fine particles, 1-2 cm paper-rich, 2-6 cm paper and plastic-rich feedstocks, and <6 cm mixture of these fractions. During the experimental work, product yields; gaseous product composition; the ratio of H2/CO, CO2/CO, and CH4/CO; and lower heating value were determined in the function of feedstock composition, the applied temperature, and catalysts. It was found that the hydrogen content and H2/CO ratio of gaseous products were increased due to catalyst application and temperature elevation in the 2nd reactor zone. The addition of Ce to the Ni/Y-zeolite catalyst was advantageous in the case of hydrogen formation at a lower temperature (600°C). The hydrogen and methane content of products obtained from the catalytic pyrolysis-gasification of paper and plastic-rich OFMSWs on elevated temperatures were higher, which increased the lower heating value of those products. Based on the elemental analysis of the obtained solid residues, it was found that paper/plastic-rich feedstock released hydrogen and carbon with a higher extent. 1-2 cm feedstock-related solid residues had the highest H/C ratio which caused a 12.5-12.8 MJ/kg gross heating value. As a result, combined pyrolysis and gasification appear to be an efficient method to attain valuable outputs from OFMSW not only in gas but also in solid products.

Enhanced Catalytic Hydrogenation of Olefins in Sulfur-Rich Naphtha Using Molybdenum Carbide Supported on γ-Al2O3 Spheres under Steam Conditions: Simulating the Hot Separator Stream Process.

Spheres comprising 10 wt.% Mo2C/γ-Al2O3, synthesized through the sucrose route, exhibited unprecedented catalytic activity for olefin hydrogenation within an industrial naphtha feedstock that contained 23 wt.% olefins, as determined by supercritical fluid chromatography (SFC). The catalyst demonstrated resilience to sulfur, exhibiting no discernible deactivation signs over a tested 96 h operational period. The resultant hydrogenated naphtha from the catalytic process contained only 2.5 wt.% olefins when the reaction was conducted at 280 °C and 3.44 × 106 Pa H2, subsequently blended with Athabasca bitumen to meet pipeline specifications for oil transportation. Additionally, the carbide catalyst spheres effectively hydrogenated olefins under steam conditions without experiencing any notable hydrogenation in the aromatics. We propose the supported carbide catalyst as a viable alternative to noble metals, serving as a selective agent for olefin elimination from light petroleum distillates in the presence of steam and sulfur, mitigating the formation of gums and deposits during the transportation of diluted bitumen (dilbit) through pipelines.

Investigation of regeneration cycles with different catalysts on steam gasification of biomass

In this work, agricultural biomass waste was gasified in a two-zone tubular reactor in the presence of steam. Firstly, during preliminary experiments the effect of temperature in the 1st and 2nd reactor zone, as well as the influence of catalysts and steam/raw material ratio was investigated, then the reusability of catalysts was also studied during ten regeneration cycles. Based on the preliminary results, in the 1st reactor zone a lower temperature was used (400 °C), where the yield of carbon dioxide was ∼55 %, which has a positive effect on numerous reactions, also it can be converted to carbon monoxide with proper catalysts with in-situ process. Regarding the temperature, it is important to be mentioned that a significant difference was observed in the yield of synthesis gas at 700 °C thus, the experiments were carried out using 700 °C in the 2nd reactor zone. A natural (Clinoptilolite) and a synthetic zeolite (ZSM-5), a mesoporous alumina (Al2O3) and a carbon dioxide capturing carrier (CaO) were selected and impregnated with nickel for further use and for enhancing the yield of synthesis gas and hydrogen during the gasification process. The utilization of catalysts helped the in-situ reduction of carbon dioxide while their performance in the gasification process during the regeneration cycles was also investigated. Henceforward, the tested Ni/ZSM-5, Ni/Al2O3 and Ni/Clinoptilolite, reduced the amount of carbon monoxide from the 5th regeneration cycles, while the amount carbon dioxide with the four mentioned catalysts was decreased by 15–35 mmol/g raw material, compared to the results obtained during thermal degradation.

Sodium acetate-based thermochemical energy storage with low charging temperature and enhanced power density

The electrification of heat necessitates the development of innovative domestic heat batteries to effectively balance energy demand with renewable power supply. Thermochemical heat storage systems show great promise in supporting the electrification of heating, thanks to their high thermal energy storage density and minimal thermal losses. Among these systems, salt hydrate-based thermochemical systems are particularly appealing. However, they do suffer from slow hydration kinetics in the presence of steam, which limits the achievable power density. Additionally, their relatively high dehydration temperature hinders their application in supporting heating systems. Furthermore, there are still challenges regarding the appropriate thermodynamic, physical, kinetic, chemical, and economic requirements for implementing these systems in heating applications. This study analyzes a proposal for thermochemical energy storage based on the direct hydration of sodium acetate with liquid water. The proposed scheme satisfies numerous requirements for heating applications. By directly adding liquid water to the salt, an unprecedented power density of 5.96 W/g is achieved, nearly two orders of magnitude higher than previously reported for other salt-based systems that utilize steam. Albeit the reactivity drops as a consequence of deliquescence and particle aggregation, it has been shown that this deactivation can be effectively mitigated by incorporating 10 % silica, achieving lower but stable energy and power density values. Furthermore, unlike other salts studied previously, sodium acetate can be fully dehydrated at temperatures within the ideal range for electrified heating systems such as heat pumps (40 °C – 60 °C). The performance of the proposed scheme in terms of dehydration, hydration, and multicyclic behavior is determined through experimental analysis.

Large-scale PANDA facility – radiation experiments and CFD calculations

Abstract CFD modelling of the thermo-hydraulic phenomena in the containment during the various phases of a severe accident necessarily requires consideration of radiative heat transfer – in the presence of steam. These radiative phenomena include (i) energy transfer within the gas mixture and (ii) between the gas and surrounding structures. Preliminary calculations carried out for these types of experiments within the OECD/NEA HYMERES-2 project with the CFD code containmentFOAM using a Monte Carlo solver for thermal radiation, demonstrated that the radiative heat transfer is significant even for very small amounts of vapour in the range of ≈0.1 % to ≈2 %. For this reason, the test matrix was tailored to the two opposite extremes: either gas compositions with a low vapour/steam content, where radiative heat transfer can be neglected, or gas mixtures with higher vapour contents, so that radiative heat transfer plays a dominant role. For the selected experiments of the H2P2 series and the corresponding CFD calculations, a vessel with a diameter of 4 m and a height of 8 m was preconditioned with different air-vapour mixtures (a) at room temperature and (b) elevated temperatures. A stable helium layer was then built-up in the upper part of the vessel. The gas was then compressed by injecting helium from above which resembles with best efforts a compression with a piston in a cylinder. This results in a height-dependent and transient increase of the gas temperature. These experiments and the associated CFD calculations were developed to isolate the phenomena of thermal radiation as good as possible from convective and diffusive effects – within the always present experimental limitations. For the reference experiment with ‘dry conditions’ corresponding to the lowest experimentally possible humidity of ≈0.1 %, we show that the use of a model without radiation provides the best agreement between the experimental and numerical results. For the much higher steam content of ≈60 %, the statistical narrow band correlated-k model (SNBCK), non-gray gas model, is the best candidate for future calculations – with computationally forgivable additional effort. We also provide with the Filtered Rayleigh Scattering technique (FRS) an outlook for a possible future instrumentation approach to better meet the requirements of the CFD community.

Investigating the behavior of six limestones in presence of steam in dual interconnected fluidized beds, under operating conditions relevant for sorption-enhanced gasification

This paper presents results on the behavior, in terms of CO2 capture capacity and attrition/fragmentation tendency, for six limestones processed in a dual interconnected fluidized beds system under operating conditions simulating those of sorption-enhanced gasification in presence of water vapor. Ten calcination/carbonation cycles have been carried out for each sorbent; in particular, carbonation has been carried out at two temperature levels (650 °C and 700 °C), with a CO2 and H2O inlet concentration of 10% for both gases. Degree of CaO carbonation (with related modelling) along the cycles, and particle size distribution at the end of the cycles, have been analyzed and discussed, together with results coming from ex situ impact fragmentation tests carried out in a specifically devoted apparatus. The discussion has been extended to particular cases in which the system was operated in the absence of steam, to analyze the role of this species on the sorbent behavior.

Pyrolysis and catalytic steam gasification of olive oil waste in two stages

A study of the pyrolysis and catalytic gasification of a waste from the extraction of olive oil has been carried out. The work objective was to characterize the solid and gaseous phases generated in the process for their possible utilization in energy generation. The experimental system consists of two cylindrical stainless steel reactors connected in series. A conventional pyrolysis is produced in the first reactor. In the second reactor, the gases and liquids generated in the first one pass through a dolomite catalytic bed where the cracking of the heavier components is produced. Also, in this second reactor, a steam stream is continuously introduced. The influence of temperature (500-700 ºC), quantity of catalyst (25-100 g) and steam flow rate (0-1.40 mL/min) has been determined. Also, the dolomite effectiveness as catalyst was evaluated For this motive, experiments, without reactivating dolomite, were carried out (0-6 runs), and the yields of solids, liquids and gases were determined. An increase in reaction temperature leads to a decrease in solid and liquid yield and to an increase in the gas phase yield. The presence of catalyst and the quantity of the same, originate an important decrease in the liquid phase yield and a high increase in the gas phase yield, especially important in the case of hydrogen. On the other hand, the catalyst is very stable and does not lose activity during at least six cycles of reaction. The presence of steam, increase the yield of hydrogen, but the increase of the steam flow rate, do not generate significant changes in the products distribution.

Morphology of uranium oxides reduced from magnesium and sodium diuranate

Abstract Morphological analysis of uranium materials has proven to be a key signature for nuclear forensic purposes. This study examines the morphological changes to magnesium diuranate (MDU) and sodium diuranate (SDU) during reduction in a 10 % hydrogen atmosphere with and without steam present. Impurity concentrations of the materials were also examined pre and post reduction using energy dispersive X-ray spectroscopy combined with scanning electron microscopy (SEM-EDX). The structures of the MDU, SDU, and UO x samples were analyzed using powder X-ray diffraction (p-XRD). Using this method, UO x from MDU was found to be a mixture of UO2, U4O9, and MgU2O6 while UO x from SDU were combinations of UO2, U4O9, U3O8, and UO3. By SEM, the MDU and UO x from MDU had identical morphologies comprised of large agglomerates of rounded particles in an irregular pattern. SEM-EDX revealed pockets of high U and high Mg content distributed throughout the materials. The SDU and UO x from SDU had slightly different morphologies. The SDU consisted of massive agglomerates of platy sheets with rough surfaces. The UO x from SDU was comprised of massive agglomerates of acicular and sub-rounded particles that appeared slightly sintered. Backscatter images of SDU and related UO x materials showed sub-rounded dark spots indicating areas of high Na content, especially in UO x materials created in the presence of steam. SEM-EDX confirmed the presence of high sodium concentration spots in the SDU and UO x from SDU. Elemental compositions were found to not change between pre and post reduction of MDU and SDU indicating that reduction with or without steam does not affect Mg or Na concentrations. The identification of Mg and Na impurities using SEM analysis presents a readily accessible tool in nuclear material analysis with high Mg and Na impurities likely indicating processing via MDU or SDU, respectively. Machine learning using convolutional neural networks (CNNs) found that the MDU and SDU had unique morphologies compared to previous publications and that there are distinguishing features between materials created with and without steam.

(Invited) Understanding the Performance Limits of Solid Acid Fuel Cells with Pt Electrocatalysts

Solid acid fuel cells (SAFCs) confer unique functional benefits over nearby technologies due to the solid state nature and intermediate temperature operability of the electrolyte. Amongst candidate solid acids, the electrolyte of choice in fuel cell applications is almost exclusively cesium dihydrogen phosphate (CDP), CsH2PO4. The material displays excellent proton conductivity (~2 ∗ 10-2 S/cm) at moderate temperatures (228 – 300 °C) with no detectable electronic conductivity. The elevated temperature of operation relative to polymer electrolyte membrane (PEM) fuel cells (< 90 °C), suggests that the kinetics for the oxygen reduction reaction will be elevated, and that SAFCs should provide higher power densities at reduced catalyst loadings. In practice, however, these advantages have not been realized. State-of-the-art SAFCs produce peak power densities of ~200 mW/cm2 with Pt loadings of 1.75 mg/cm2.1 In comparison, PEMFCs have demonstrated peak power densities >1 W/cm2 with Pt loadings of only 0.1 mg/cm2.2 In this work, we begin to unravel the question of why the anticipated thermal activation of reaction kinetics has not resulted in superior SAFC performance. We measure fundamental microstructural and material parameters of SAFC cathodes, and use these to predict fuel cell polarization curves. We find that, while the exchange current density for the oxygen reduction reaction is high in SAFCs, the Tafel slope is steep. Thus, the fundamental steps in the ORR reaction on Pt follow a different and unfavorable pathway under SAFC conditions than PEMFC conditions.We further employ the experimentally informed and validated physical model (see figure) to assess the role of microstructural, operational, and material parameters on SAFC polarization curves. The model suggests that a 10-fold increase in active Pt surface area would be required to approach the DOE fuel cell target of 300 mA/cm2 at 0.8 V (even without accounting for voltage drops through the ~ 50 mm thick electrolyte). In turn, this would require a decrease in CDP particle size in the cathode, where CDP serves as the support onto which Pt nanoparticles are deposited, from 500 to 50 nm, and would be accompanied by an untenable increase in Pt loading to over 30 mg/cm2. We further find that the Pt catalytic activity is strongly inhibited by the presence of steam, required to maintain stability of the electrolyte against dehydration. The humidification requirement moreover increases polarization losses at higher temperatures of operation, at which higher steam levels are required for electrolyte stabilization, overcoming the expected benefits of thermally activated catalysis. These insights motivate prioritization of the development and deployment of alternative catalyst materials and advanced electrolytes with greater thermodynamic stability over attempts to modify electrode microstructure, cell architecture, or operational conditions using today’s material set in order to advance SAFC technology towards commercial realization.1. Papandrew, A. B., Chisholm, C. R. I., Elgammal, R. A., Özer, M. M. & Zecevic, S. K. Advanced Electrodes for Solid Acid Fuel Cells by Platinum Deposition on CsH2PO4. Chemistry of Materials 23, 1659-1667, (2011).2. Zhao, Z. et al. Graphene-nanopocket-encaged PtCo nanocatalysts for highly durable fuel cell operation under demanding ultralow-Pt-loading conditions. Nat Nanotechnol, (2022). Figure 1

Revealing the mechanism of oxygen vacancy defect for CO2 adsorption and diffusion on CaO: DFT and experimental study

The calcium looping is a promising technology to achieve industrial CO2 capture, and the introduction of oxygen vacancy can promote the CO2 capture reactivity of CaO-based sorbents. In this work, DFT calculations were performed to investigate the CO2 adsorption by CaO in the presence of oxygen vacancy defect. The presence of oxygen vacancy reduces the band gap of CaO surface, which results from the delocalization of Ca 2p orbital. Besides, the electron accumulation at the oxygen vacancy occurs due to the unsaturated Ca-O bonds, and the reaction possibility is promoted neighbouring the defect. The top site of oxygen vacancy defect of CaO is favourable for CO2 adsorption. The adsorption energy of CO2 on CaO with oxygen vacancy achieves − 2.52 eV, which is 1.81 times as high as that on pristine CaO. Due to strong interaction between CO2 and CaO with oxygen vacancy, CO2 migration from this site is more difficult, while the following diffusion is more prone to occur. In the presence of steam, CO2 adsorption energy is enhanced to − 2.70 eV on CaO with oxygen vacancy, and the distance from CO2 radical to surface is intuitively reduced, which results from the electrons donated from defect and neighbouring Ca atoms, while CO2 diffusion difficulty is increased. This work provides an incisive investigation for structural, electronic, and thermodynamic characteristics of CO2 adsorption and diffusion on CaO in the presence of oxygen vacancy defect, and it can shed light on rational synthesis and functional design of surface-active sites of CaO-based sorbents.

Variation of pore development scenarios by changing gasification atmosphere and temperature

Finding a good replacement for the commercially produced activated carbons among the residual biochars should begin with a thorough evaluation of their pore size distribution and its development under different gasification conditions. Materials of various pore structures may be found useful depending on the applications. For some applications, ultramicroporous or supermicro-mesoporous materials may be optimal, but in general, a specific pore size distribution should be evaluated to find the best for a given application. We investigated different pore formation scenarios in several biochars gasified with steam, CO2, and diluted O2 using gas adsorption measurement and the dual gas analysis using the 2D-NLDFT model calculation. The detailed characteristics of the ultramicro-, supermicro-, and mesopore volumes showed a consistent trend of pore widening in the presence of steam at 800 °C, regardless of the steam concentration. On the other hand, steam gasification at elevated temperature (1000 °C) created highly ultramicroporous materials, and so did the reaction with diluted oxygen. We conclude that different pore formation patterns can be achieved with the modification of the gasification process and the dual gas analysis can assist in formulating guidance for tailoring chars for specific applications.

Investigation into application of biochar as a catalyst during pyrolysis-catalytic reforming of rice husk: The role of K specie and steam in upgrading syngas quality

This study investigated the role of K and steam in upgrading syngas quality over biochar in a two-stage fixed-bed reactor. The integration of K-char catalyst and steam greatly increased syngas (H2+CO) and H2 production. The syngas products yield (19.76 mmol/gbiomass) and a H2 yield (11.14 mmol/gbiomass) were achieved when K-char was used as catalyst in the presence of steam. In general, four ways could be concluded to promote volatiles reforming to improve syngas quality by K and steam: Firstly, K and steam interaction with biochar increased the surface area and developed the porous structure of biochar, providing the pyrolytic intermediates with full complete contact with the char surface, and improving the chance of contact with the active sites. Secondly, the condensation reactions of biochar were inhibited by K and steam, thus preventing the reduction of active groups on the aromatic ring of biochar. Thirdly, K and steam promoted the formation of O-containing groups with high reactive activity on the char surface, such as –COO and –CO. Moreover, volatile K migrated in biochar matrix during catalytic reforming, and steam inhibited the release of K in biochar, resulting in more K retaining on the char surface in the form of -COK and -COOK acting as the active sites, which ultimately improved the catalytic activity of biochar, and promoted tar destruction and hydrocarbon reforming.

Effect of steam on the barium sulfate reduction by methane

Methane gas decomposes at high temperatures and produces carbon as a result. The deposited carbon causes problems during the process. In this study, the reduction of barium sulfate powder using methane was studied and steam was used to remove the carbon produced during the reaction. The effect of temperature and methane concentration on the reaction rate was investigated at two different conditions, using 20 vol % steam and without steam at operating temperatures in the range 850–1000 °C. When steam was used, methane concentration was selected in the range 19–40 vol %, while it was 21–78 % in the absence of steam. The experimental data was interpreted using the "shrinking unreacted core model" and intrinsic kinetic parameters of the reactions were determined. The reaction order and activation energy were calculated to be 1 and 145.5 kJ/mol in the absence of steam and 1.5 and 179.6 kJ/mol in its presence, respectively. From the obtained rate equations, it was found that the reaction rate without steam was always faster than the reaction rate in the presence of steam.

Comparison of Carbon Deposition and Removal from Ni-YSZ and Ni-BCZY Composites Using Operando Optical Methods

Solid oxide fuel cells (SOFCs) are attractive devices for power generation because they can operate with a variety of fuels, including H2, hydrocarbon fuels, biogas, and syngas. Conventional SOFC anode composites comprised of Ni-YSZ (YSZ = yttria-stabilized zirconia), however, suffer from performance degradation due to surface accumulation of carbon from hydrocarbon cracking. Alternative electrolyte materials such as yttria-doped barium cerate/zirconate mixtures (BCZY) offer the promise of reduced carbon formation over the Ni-BCZY electrode and lower operating temperatures by the conduction of protons instead of oxide ions. In this study, 50%-50% Ni-8YSZ and 50%-50% Ni-BCZY27 composites were exposed to CH4 in the absence and presence of either CO2 or H2O. The degree of carbon deposition and mechanism of carbon removal in the absence of fuel was estimated in the presence of steam using operando Fourier transform infrared emission spectroscopy (FTIRES) and near-infrared thermal imaging (NIRTI) at 750 °C. Upon exposure to each fuel condition, carbon removal using steam results in more CO2 + CO product formation from Ni-8YSZ implying more carbon formation on Ni-8YSZ compared to Ni-BCZY27. Carbon removal of cells exposed to CH4 alone indicate limited formation and fast depletion of CO over Ni-BCZY27; depletion of CO2, however, happens more slowly. Depletion of CO and CO2 in the Ni-8YSZ system happens more gradually suggesting the deposition of carbon over Ni-BCZY27 occurs less readily and its removal is more facile through gasification. Interestingly, the cracking of CH4 over Ni-8YSZ is accompanied by a larger degree of cooling compared to Ni-BCZY27 whereas both dry and wet reforming result in similar cooling over Ni-8YSZ and Ni-BCZY27. The results will be discussed in the context of recent work using operando spectroscopies to characterize CH4 fuel utilization in Ni-8YSZ based SOFCs in the absence and presence of various reformers.

Solid-State Schikorr Reaction from Ferrous Chloride to Magnetite with Hydrogen Evolution as the Kinetic Bottleneck.

The selective formation of meta-stable Fe3O4 from ferrous sources by suppressing its oxidative conversion to the most stable hematite (α-Fe2O3) is challenging under oxidative conditions for solid-state synthesis. In this work, we investigated the conversion of iron(II) chloride (FeCl2) to magnetite (Fe3O4) under inert atmosphere in the presence of steam, and the obtained oxides were analyzed by atomic-resolution TEM, 57Fe Mössbauer spectroscopy, and the Verwey transition temperature (Tv). The reaction proceeded in two steps, with H2O as the oxide source in the initial step and as an oxidant in the second step. The initial hydrolysis occurred at temperatures higher than 120 °C to release gaseous HCl, via substituting lattice chloride Cl- with oxide O2-, to give iron oxide intermediates. In the first step, the construction of the intermediate oxides was not topotactic. The second step as a kinetic bottleneck occurred at temperatures higher than 350 °C to generate gaseous H2 through the oxidation of FeII by H+. A substantially large kinetic isotope effect (KIE) was observed for the second step at 500 °C, and this indicates the rate-determining step is the hydrogen evolution. Quantitative analysis of evolved H2 revealed that full conversion of ferrous chloride to magnetite at 500 °C was followed by additional oxidation of the outer sphere of magnetite to give a Fe2O3 phase, as supported by X-ray photoelectron spectroscopy (XPS), and the outer phase confined the conductive magnetite phase within the insulating layers, enabling kinetic control of magnetite synthesis. As such, the reaction stopped at meta-stable magnetite with an excellent saturation magnetization (σs) of 86 emu g-1 and Tv > 120 K without affording the thermodynamically stable α-Fe2O3 as the major final product. The study also discusses the influence of parameters such as reaction temperature, initial grain size of FeCl2, the extent of hydration, and partial pressure of H2O.

Insight into performance over IM-5, ZSM-5 and ZSM-11 zeolites for n-heptane cracking to light olefins in the absence & presence of steam

The three dimension (3D) 10-membered ring channels zeolite has a unique advantage in increasing light olefins for catalytic cracking reaction. Herein, zeolites IM-5, ZSM-5 and ZSM-11 were synthesized hydrothermally to achieve comparable texture properties and SiO2/Al2O3 ratios. The acid content and acid strength of the three zeolites were as follows: IM-5 > ZSM-5 > ZSM-11. Meanwhile, 1H DQ MAS NMR confirmed that there was a synergistic effect between Brønsted and Lewis acids in IM-5 zeolite. However, IM-5 zeolite with lots of strong BAS had an unexpected low TOF in n-heptane cracking. Furthermore, the light olefins selectivity was as follows: IM-5 > ZSM-11 > ZSM-5 at 550–650 ℃ in the absence of steam. IM-5 zeolite had the particular advantage in ethylene, and its selectivity was up to 44.9 %. After steam was introduced, the monomolecular cracking reaction, the aromatization of propylene and the deep cracking of C3 and C4 hydrocarbons were inhibited over the three zeolites. Steam could prolong the activity of IM-5 zeolite, but accelerate the deactivation of ZSM-5 and ZSM-11 zeolites. The primary cause for the rapid deactivation of ZSM-5 and ZSM-11 zeolites was dealuminization in steam, whereas for the IM-5 zeolite, it was the rapid formation of coke on its surface, thereby blocking its micropore channels.

Preparation of morph-genetic aluminum-doped calcium oxide templated from cotton and the calcium looping performance for energy storage in the presence of steam

Calcium looping (CaL), which can be combined with concentrated solar power (CSP) plants, is considered a promising technology for energy storage. To overcome the deactivation of calcium based materials with increasing cycles, a novel morph-genetic aluminum doped calcium oxide was prepared by a biomass template method using limestone, aluminum nitrate and cotton as raw materials. The effects of preparation parameters and heat storage conditions (especially in presence of steam) on the energy storage performance were studied. The results showed that the hollow tubular structure of the biomass template was preserved in the synthesized material and stabilized by the support of Ca12Al14O33. The presence of the hollow microtubular structure resulted in an increased pore volume of the synthesized materials and a change of the pore distribution, promoting the diffusion of CO2. This phenomenon also explained the superior performance of the synthesized material in terms of the apparent kinetic properties and resistance to sintering. The optimal synthesized material had a high energy storage density and carbonation fraction, which were more than three times those of limestone. The presence of steam during calcination served to reduce the calcination temperature and mitigate the sintering effect of CaO. An optimization route combining solar steam system and CaL-CSP system was proposed based on the positive effect of steam, which was promising for high-efficiency energy storage.