Mixture Of H2 Research Articles

Photocatalytic Upcyclingof Plastic Waste into Syngas by ZnS/Ga2O3 Z-scheme Heterojunction.

The photocatalytic conversion of plastic waste into value-added products using solar energy presents a promising approach for promoting environmental sustainability. Nonetheless, the emission of CO2 during the conventional photocatalytic degradation process remains a major hurdle that impedes its further development. In this study, we propose an efficient photocatalytic conversion of polyethylene plastic into syngas (CO + H2 mixtures) by using a ZnS/Ga2O3 Z-scheme heterojunction photocatalyst. It is found that the strong redox capability of photogenerated holes and electrons in the Z-scheme heterojunction photocatalyst can promote the oxidative depolymerization of PE plastic, concurrently enabling the efficient reduction of the intermediate product CO2 into syngas. Furthermore, this system also demonstrates applicability in the conversion and upcycling of other polyolefin plastics including polypropylene and polyvinyl chloride. Our findings highlight the potential of polyolefin plastics photoreforming for the production of syngas under environmentally benign conditions.

Flame Speed Measurements of Ammonia–Hydrogen Mixtures for Gas-Turbines

Abstract Recent findings from the U.S. Energy Information Administration project an increase in domestic fossil fuel consumption (e.g., petroleum and natural gas) and global greenhouse gas emissions through 2050 (Nalley, S., 2021, “International Energy Outlook 2021 (IEO2021),” IEO2021 Release, CSIS, Center for Strategic and International Studies, Washington, DC, Technical Presentation, pp. 2–12). Consequently, advanced combustion research aims to identify fuels to mitigate fossil fuel consumption while minimizing exhaust emissions. Ammonia (NH3) is one of these candidates, as it has historically been shown to provide high energy potential and zero-carbon emission (CO and CO2) (Hayakawa, A., Goto, T., Mimoto, R., Arakawa, Y., Kudo, T., and Kobayashi, H., 2015, “Laminar Burning Velocity and Markstein Length of Ammonia/Air Premixed Flames at Various Pressures,” Fuel, 159, pp. 98–106). As a hydrogen (H2) carrier, NH3 serves as a possible solution to the U.S. Department of Energy's Hydrogen Program Plan by providing efficient H2 storage and conservation capabilities (U.S. Department of Energy, 2020, “Department of Energy Hydrogen Program Plan,” U.S. Department of Energy, Washington, DC, Report No. DOE/EE-2128). As a result, applied turbine-combustion research of NH3 and H2 fuel has been conducted to identify combustion performance parameters that aid in the design of sustainable turbomachinery (Chiong, M.-C., Chong, C., Ng, J., Mashruk, S., Chong, W., Samiran, N., Mong, G., and Medina, A., 2021, “Advancements of Combustion Technologies in the Ammonia-Fuelled Engines,” Energy Convers. Manage., 244, p. 114460). One of these key combustion parameters is the laminar burning speed (LBS). While abundant literature exists on the combustion of NH3 and H2 fuels, there is not sufficient evidence in high-pressure environments to provide a comprehensive understanding of NH3 and H2 combustion phenomena in turbine-combustor settings. To advance the state of the knowledge, NH3 and H2 mixtures were ignited in a spherical chamber across a range of equivalence ratios at 296 K and 5 atm to understand their flame characteristics and LBS which was determined using a multizone constant volume method. The experimental conditions were selected according to primary turbine-combustor conditions, as much research is needed to support NH3–H2 applicability in turbomachinery for power generation. The effect of H2 addition to NH3 fuel was observed by comparing the LBS for various NH3–H2 mixture compositions. Experimental results revealed increased LBS values for H2 enriched NH3, with the maximum LBS occurring at stoichiometry. The experimental data were accurately predicted by the University of Central Florida (UCF) NH3–H2 mechanism developed for this investigation, while NUI 1.1 simulations overestimated recorded LBS data by a significant margin. This study demonstrates and quantifies the enhancing effect of H2 addition to NH3 fuels via LBS and strengthens the literature surrounding NH3–H2 combustion reactions for future work.

Energetic and Exergoeconomic Evaluation of a Stig Cycle and Cooled Inlet Air Gas Turbine Powered by Mixtures of Natural Gas and H2 in Tropical Climates

Energetic and Exergoeconomic Evaluation of a Stig Cycle and Cooled Inlet Air Gas Turbine Powered by Mixtures of Natural Gas and H2 in Tropical Climates

In Situ Exsolved CuZn Alloy Electrocatalysts for CO2 Conversion to Tunable Syngas Production

AbstractAlloying is considered as a promising method for syngas (H2 and CO mixture gas) generation. However, it is challenging to elucidate the relationship between the ratios of syngas and alloy components for CO2 reduction reaction. Herein, through tuning the Cu/Zn ratio on CuZn alloy, the H2/CO ratios in CuZn‐2 (Cu/Zn = 0.77) can be tuned in a noticeable range between 0.8 and 5.8 at −0.88 to −1.28 V versus RHE, and a durable stability of 12 h. The CuZn‐2 displays better performance and enhanced dynamics than other samples. Electrochemical impedance spectroscopies and Tafel results reveal that CuZn‐2 behaves kinetically optimized performance. Density functional theory calculations results reveal that CuZn alloy exhibits middle desorption intensity of *H for HER compared with pure Zn and Cu. CuZn alloy effectively decreases the energy barrier of CO2 molecules activated to *COOH relative to Zn, and also the alloy renders it easier for *CO desorb to generate CO for Cu. In situ Fourier transform infrared spectroscopies also observe a significant intensity of *CO on CuZn‐2. This work demonstrates that alloying Cu and Zn can create active sites, in which Cu acts as an auxiliary active site further facilitating *CO generation.

Durable electrocatalysts based on barium niobates doped with Ca, Fe, and Y: Enhancing catalytic activity and selectivity for oxidative coupling of methane

Effective conversion of methane into value added products such as olefins, is a major research area for the past 40 years. Electrochemical oxidative coupling of methane (E-OCM) is recently gaining attention due to its ability to control the product selectivity by oxide ion flux and applied potential. We report a new series of catalysts, Ca, Fe, and Y co-doped barium niobate perovskites (BCNFY) for E-OCM application. BCNFY perovskites show chemical stability under 4 % H2, CH4, and high CH4-O2 mixtures at high temperatures up to 900 °C. Under reducing conditions, BCNFY perovskites form excess oxygen vacancies that is supported by Nb4+/5+ oxidation state changes that help retain the crystal structure. Temperature programmed reaction (TPR) measurements under 95 % CH4:5% O2 reveal methane activation properties from 600 °C with a high C2+ selectivity of 82 % at 850 °C. TPR measurements further reveal the nature of active sites for methane activation. Cyclic voltammetry measurements show a unique relationship between product selectivity and applied potential as at applied biases close to open circuit potential, CO and H2 are the major products while at high applied biases ethylene and CO2 are the major products. Our results show the advantages of E-OCM over conventional OCM although improvements in terms of electronic conductivity of the electrode and overall current densities are required for commercial viability for these perovskite electrodes.

Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2.

Oil has long been the dominant feedstock for producing fuels and chemicals, but coal, natural gas and biomass are increasingly explored alternatives1-3. Their conversion first generates syngas, a mixture of CO and H2, which is then processed further using Fischer-Tropsch (FT) chemistry. However, although commercial FT technology for fuel production is established, using it to access valuable chemicals remains challenging. A case in point is linear α-olefins (LAOs), which are important chemical intermediates obtained by ethylene oligomerization at present4-8. The commercial high-temperature FT process and the FT-to-olefin process under development at present both convert syngas directly to LAOs, but also generate much CO2 waste that leads to a low carbon utilization efficiency9-14. The efficiency is further compromised by substantially fewer of the converted carbon atoms ending up as valuable C5-C10 LAOs than are found in the C2-C4 olefins that dominate the product mixtures9-14. Here we show that the use of the original phase-pure χ-iron carbide can minimize these syngas conversion problems: tailored and optimized for the process of FT to LAOs, this catalyst exhibits an activity at 290 °C that is 1-2 orders higher than dedicated FT-to-olefin catalysts can achieve above 320 °C (refs. 12-15), is stable for 200 h, and produces desired C2-C10 LAOs and unwanted CO2 with carbon-based selectivities of 51% and 9% under industrially relevant conditions. This higher catalytic performance, persisting over a wide temperature range (250-320 °C), demonstrates the potential of the system for developing a practically relevant technology.

Reduction of CO2 emissions by recycling low-potential heat from the Benfield CO2 removal process at a natural gas hydrogen production plant

AbstractThe EU policies related to CO2 emission strictly define the stages of carbon neutrality achieving. According to these regulations, all production installations that emit carbon dioxide will be charged additional emission fees from 2026 to fully in 2035. Analysis of the increasing emission fees shows that in some industries incurring such additional costs will result in a lack of profitability of the products. Industries directly related to the food sector, such as nitrogen fertiliser production, are strategic in the economies of all countries. Nitrogen fertilisers are produced from ammonia, which is synthesised on a large scale from hydrogen and nitrogen. Hydrogen is produced by natural gas reforming with water vapour resulting in syngas (mixture of H2, CO, CO2, H2O), which CO in the next step reacts with water vapour (water gas shift reaction) producing H2 and CO2. CO2 is separated from hydrogen using the Benfield method. The analysis of the Benfield process (one process of hydrogen production) shows a possible way to reduce CO2 emission by optimising heat balance. It was shown that in the proposed technology the heat recovery reaches 89%, while the level below 30% was reported for other available technologies. The proposed solution is based on recirculation and reuse of heat, which is lost in other technologies. The analysis is for a process balance in a medium-sized hydrogen production installation. The analysis considers also the correlations with other installations thermally linked to hydrogen production. The economic balance showed the great financial benefits of this solution. In the scenario discussed, the CO2 emission factor was reduced by 20%. Graphical Abstract

Fine-tuning syngas composition using laser surface modified silver electrode for CO2 electroreduction

Electrochemical reduction of CO2 and H2O to synthesize gas (H2 and CO mixture) is of significant interest due to established industrial pathways to tune the H2 to CO composition to generate an array of valuable products including methanol, synthetic fuel, synthetic natural gas, and hydrogen. However, controlled H2:CO ratios are challenging on CO-active electrocatalysts like silver. We demonstrate that applying laser engineering to adjust the surface wetting state of a silver electrocatalyst with water contact angles θw ranging from 47° and 135°, H2:CO ratios can be tuned from 1 to 4 at modest potentials (−0.7 V versus RHE, RHE—reversible hydrogen electrode) with almost total unity Faradaic efficiency. Both hydrophilic (θw = 47°) and more hydrophobic (θw = 135°) samples showed an increasing H2:CO trend with rising potentials (0.7–1.2 V versus RHE) due to mass transport. Conversely, silver electrocatalyst with θw = 110° exhibited a constant H2:CO ratio of 4. This indicates catalyst wettability potentially affects *H and *HOCO intermediates’ adsorption, impacting H2:CO ratios. Our results show the feasibility of syngas composition control on silver catalysts via surface wettability, providing a simpler alternative to complex multicomponent electrocatalytic systems.

Lower NO emission conditions of NH3–H2 mixtures under the oxygen-enriched premixed combustion mode

Compared with pure NH3 fuel, the lower NO emission conditions of NH3–H2 mixtures under the oxygen-enriched combustion mode have been identified quantitatively. Furthermore, the effects of the H2 addition on the NO productions of premixed oxygen-enriched NH3–H2 flames are studied numerically, while the major reactions responsible for the variation of total NO are identified. Results show that the H2 addition is eligible to reduce the NO emissions of the oxygen-enriched NH3 combustion if the laminar burning velocity is fixed to a larger value (>23 cm/s). The quantitative equations are obtained to determine the optimum oxygen-enriched conditions of the NH3–H2 mixture, aiming to achieve lower NO emission and similar or improved combustion stability compared to pure NH3 fuel by restricting the minimum and maximum O2 percentages for the NH3–H2 mixtures. Based on the rate of production (ROP) analysis, for the oxygen-enriched NH3–H2 combustion, R144 (HNO + H<=>H2+NO) is consistently the most significant NO production reaction, while R85 (NH + NO<=>N2O + H) and R91 (N + NO<=>O + N2) play significant roles in the NO consumption. When the laminar burning velocity (SL) is kept to a lower value, the increased total NO of the oxygen-enriched NH3 flames with the H2 addition is ascribed to more efficient suppressions on the NO consumption reactions of R85, R91 and R77 (NH2+NO<=>NNH + OH). In contrast, thanks to the extra impact of the higher O2 percentage on the H/O/OH radical pool at larger SL, the NO production reactions begin to suffer stronger suppressions of the H2 addition, resulting in the reduced total NO of NH3–H2 mixtures. Furthermore, R144 is identified as the key reaction influencing the variation trend of total NO at both lower and higher SL values.

Reducing CO[formula omitted] emissions, energy consumption, and decarbonization costs in manganese production by integrating fuel-assisted solid oxide electrolysis cells in two-stage oxide reduction

Manganese is one of the most consumed metals due to its use in iron and steel making, which generates between 7%–9% of all CO2 emissions produced globally per annum. For the first time, this work explores the potential of a novel process concept to reduce CO2 emissions, energy consumption, and decarbonization costs in manganese production, which involves integrating fuel-assisted solid oxide electrolysis cells (FASOECs) in a two-stage scheme for the reduction of raw manganese ores. In this scheme, higher oxides that are present in raw manganese ores (MnO2, Mn2O3, Mn3O4) are pre-reduced using CO, yielding manganese monoxide (MnO) that is further reduced to Mn in a submerged arc furnace (SAF) using coke and electricity. In the proposed FASOEC integration concept, off-gas from the manganese ores after pre-reduction (a mixture of H2, CO, and CO2) is supplied to the FASOECs’ anode as fuel, in order to produce high-purity H2 in the cathode that is directed to the first stage of manganese reduction. H2 has enhanced reaction kinetics for reducing higher manganese oxides in comparison to CO; therefore, integrating FASOECs can improve manganese oxide conversion rates during pre-reduction, resulting in lower consumption rates of coke and energy in the SAF. The off-gas supplied to the FASOECs’ anode also lowers the amount of energy required for H2 production in the cathode (can also generate electricity, simultaneously) and produces anode exhaust gas containing only CO2 and steam. Since steam can be easily condensed from this stream, the integration of FASOECs also enables efficient decarbonization of the manganese production process, thus eliminating the need for a designated CO2 capture system. The techno-economic analysis performed herein demonstrates that directing the full supply of off-gas produced by the SAF to the FASOECs’ anode at 800 °C reduces the overall energy consumption of manganese production by up to 18% in comparison to conventional processes. This results in decarbonization cost reductions by as much as 3%–15% and a corresponding decarbonization price range of $4-32 per ton of manganese product for plant capacities of 50 and 200 kt, respectively.

The energy metabolism of Cupriavidus necator in different trophic conditions.

The "knallgas" bacterium Cupriavidus necator is attracting interest due to its extremely versatile metabolism. C. necator can use hydrogen or formic acid as an energy source, fixes CO2 via the Calvin-Benson-Bassham (CBB) cycle, and grows on organic acids and sugars. Its tripartite genome is notable for its size and duplications of key genes (CBB cycle, hydrogenases, and nitrate reductases). Little is known about which of these isoenzymes and their cofactors are actually utilized for growth on different substrates. Here, we investigated the energy metabolism of C. necator H16 by growing a barcoded transposon knockout library on succinate, fructose, hydrogen (H2/CO2), and formic acid. The fitness contribution of each gene was determined from enrichment or depletion of the corresponding mutants. Fitness analysis revealed that (i) some, but not all, molybdenum cofactor biosynthesis genes were essential for growth on formate and nitrate respiration. (ii) Soluble formate dehydrogenase (FDH) was the dominant enzyme for formate oxidation, not membrane-bound FDH. (iii) For hydrogenases, both soluble and membrane-bound enzymes were utilized for lithoautotrophic growth. (iv) Of the six terminal respiratory complexes in C. necator H16, only some are utilized, and utilization depends on the energy source. (v) Deletion of hydrogenase-related genes boosted heterotrophic growth, and we show that the relief from associated protein cost is responsible for this phenomenon. This study evaluates the contribution of each of C. necator's genes to fitness in biotechnologically relevant growth regimes. Our results illustrate the genomic redundancy of this generalist bacterium and inspire future engineering strategies.IMPORTANCEThe soil bacterium Cupriavidus necator can grow on gas mixtures of CO2, H2, and O2. It also consumes formic acid as carbon and energy source and various other substrates. This metabolic flexibility comes at a price, for example, a comparatively large genome (6.6 Mb) and a significant background expression of lowly utilized genes. In this study, we mutated every non-essential gene in C. necator using barcoded transposons in order to determine their effect on fitness. We grew the mutant library in various trophic conditions including hydrogen and formate as the sole energy source. Fitness analysis revealed which of the various energy-generating iso-enzymes are actually utilized in which condition. For example, only a few of the six terminal respiratory complexes are used, and utilization depends on the substrate. We also show that the protein cost for the various lowly utilized enzymes represents a significant growth disadvantage in specific conditions, offering a route to rational engineering of the genome. All fitness data are available in an interactive app at https://m-jahn.shinyapps.io/ShinyLib/.

Impact of Diluents on Flame Stability With Blends of Natural Gas and Hydrogen

Abstract Two potential decarbonization pathways for natural gas (NG)-fueled gas turbine engines include blending hydrogen (H2) into NG and postcombustion carbon capture. H2 blending changes several combustion properties, including flame speed and stretch sensitivity. The use of post-combustion carbon capture systems is typically facilitated by the implementation of exhaust gas recirculation (EGR), where exhaust gases are injected into the inlet of the engine, increasing carbon dioxide (CO2) concentration at the outlet and, hence, increasing the efficiency of carbon capture technologies. In this work, we explore the impact of H2 blending and EGR on the stability of a swirl-stabilized, central-piloted flame. Mixtures of NG and H2 are tested at a range of different diluent compositions, with oxygen varied from 21% to 15% by volume in the oxidizer. In all cases, a constant adiabatic flame temperature is maintained to mimic the operation of a gas turbine at a given turbine inlet temperature. A variable-length combustor is used for testing, where combustor length is varied to understand the dynamic stability characteristics of the system. Results show that EGR and H2 work in opposition to each other, where higher levels of EGR result in poor flame holding and higher levels of H2 result in better flame holding. Increasing H2 generally increases the amplitude of thermoacoustic instability at each condition, a result of the change in flame position in this particular combustor. Importantly, H2 can be added to NG to improve flame holding without significantly decreasing CO2 levels in the products, showing that H2 blending can be a method for counteracting combustor operability issues that arise from high levels of EGR necessary to improve the efficiency of typical carbon capture systems.

The Technical and Economic Aspects of Integrating Energy Sectors for Climate Neutrality

With the development of an energy sector based on renewable primary sources, structural changes are emerging for the entire national energy system. Initially, it was estimated that energy generation based on fossil fuels would decrease until its disappearance. However, the evolution of CO2 capture capacity leads to a possible coexistence for a certain period with the renewable energy sector. The paper develops this concept of the coexistence of the two systems, with the positioning of green hydrogen not only within the renewable energy sector but also as a transformation vector for carbon dioxide captured in the form of synthetic fuels, such as CH4 and CH3OH. The authors conducted pilot-scale research on CO2 capture with green H2, both for pure (captured) CO2 and for CO2 found in combustion gases. The positive results led to the respective recommendation. The research conducted by the authors meets the strict requirements of the current energy phase, with the authors considering that wind and solar energy alone are not sufficient to meet current energy demand. The paper also analyzes the economic aspects related to price differences for energy produced in the two sectors, as well as their interconnection. The technical aspect, as well as the economic aspect, of storage through various other solutions besides hydrogen has been highlighted. The development of the renewable energy sector and its demarcation from the fossil fuel energy sector, even with the transcendent vector represented by green hydrogen, leads to the deepening of dispersion aspects between the electricity sector and the thermal energy sector, a less commonly mentioned aspect in current works, but of great importance. The purpose of this paper is to highlight energy challenges during the current transition period towards climate neutrality, along with solutions proposed by the authors to be implemented in this phase. The current stage of combustion of the CH4−H2 mixture imposes requirements for the capture of the resulting CO2.

Advancing spectroscopic understanding of HOCS+: Laboratory investigations and astronomical implications

Sulphur-bearing species play crucial roles in interstellar chemistry, yet their precise characterisation remains challenging. Here, we present laboratory experiments aimed at extending the high-resolution spectroscopy of protonated carbonyl sulphide (HOCS+), a recently detected molecular ion in space. Using a frequency-modulated free-space absorption spectrometer, we detected rotational transitions of HOCS+ in an extended negative glow discharge with a mixture of H2 and OCS, extending the high-resolution rotational characterisation of the cation well into the millimetre wave region (200–370 GHz). Comparisons with prior measurements and quantum chemical calculations revealed an overall agreement in the spectroscopic parameters. With the new spectroscopic dataset in hand, we re-investigated the observations of HOCS+ towards G+0.693−0.027, which were initially based solely on Ka = 0 lines contaminated by HNC34S. This re-investigation enabled the detection of weak Ka ≠ 0 transitions, free from HNC34S contamination. Our high-resolution spectroscopic characterisation also provides valuable insights for future millimetre and submillimetre astronomical observations of these species in different interstellar environments. In particular, the new high-resolution catalogue will facilitate the search for this cation in cold dark clouds, where very narrow line widths are typically observed.

Low-NOx thermal plasma torches: A renewable heat source for the electrified process industry

Industrial thermal plasma torches can heat a gas up to 5000–20,000 K, i.e., well above the temperature needed to replace the heat generated from the combustion of traditional fossil fuels (e.g., coal, oil, and natural gas) in large-scale process industry furnaces producing construction materials (e.g., iron, steel, lime, and cement). However, there is a risk for significant NOx emissions when air or N2 are used as plasma-forming gas since the temperature somewhere in the furnace always will be higher compared to the threshold NOx formation temperature of ∼1800 K. Torch NOx forms inside the high temperature region of the plasma torch (>5000 K) when air is used as gas. Process NOx forms instead when the hot gas (when air or nitrogen is used as plasma forming gas) from the plasma torch mixes with process air downstream the torch. By analysing the complex chemistry of both the torch- and process NOx formation with thermodynamic equilibrium and one-dimensional chemical kinetic calculations it was shown that adding H2 to the plasma-forming N2 gas significantly reduces the NOx emissions with more than 90 %. Verifying experiments with air, pure N2, and mixtures of H2 and N2 as plasma-forming gas were performed in a laboratory scale insulated laboratory furnace with different pre-heating temperatures of process air (293, 673, and 1073 K) which the plasma gas mixes with downstream the torch. Depending on the pre-heating temperature the NOx emissions were between 12,000–14,000 mg NO2/MJfuel when air was used as plasma forming gas. Substantial NOx emission reduction occurs both when N2 replaces air, where the NOx emissions was in the span of 8000–11,500 mg NO2/MJfuel and furthermore when H2 was mixed into the N2 gas stream. For the highest degree of H2 mixing (28.6 vol-%), the NOx emissions were between 450–1700 mg NO2/MJfuel depending on the pre-heat temperature of the process air, i.e., a reduction of 88–96 % and 85–94 %, respectively when air or N2 was used as plasma forming gas. The measured NOx emissions are then of the same order of magnitude as would be expected from the combustion of traditional fuels (coal, oil, biomass and pure H2). Finally, by analysing the aerodynamics in an axisymmetric furnace with an experimentally validated computational fluid dynamics (CFD) model using reduced chemistry for the NOx formation (19 species and 70 reactions), further guidelines into the process of NOx reduction from thermal plasma torches are given.

Understanding the heat release fluctuations and combustion noise characteristics of non-premixed co/counter-swirl syngas flames at MILD conditions

The heat release fluctuations and combustion noise of co/counter-swirl non-premixed syngas (mixture of CO and H2) and air flames at moderate or intense low-oxygen dilution (MILD) conditions has been investigated experimentally using simultaneous OH∗-chemiluminescence (5 kHz) and microphone measurements (50 kHz). Furthermore, the similarities and differences between co and counter-swirl flames are elucidated using proper orthogonal decomposition (POD), spectrogram, and frequency distributions. At a high O2 concentration (21% by volume), noise measurements for both co/counter-swirl flames comprise both high-amplitude periodic and low-amplitude aperiodic oscillations, revealing signatures of intermittency. Interestingly, for periodic oscillations, the global luminosity (Ifluc) obtained from OH∗-chemiluminescence and noise (Pfluc) are found to be in phase, indicating a strong coupling between noise and heat-release rate. Moreover, POD modes indicate that the global heat release fluctuation occurring in the central region of the combustor is the source of these periodic fluctuations. Besides global fluctuation, the heat release region undergoes rotation around the combustor axis with differing frequencies for co and counter-swirl flames. Furthermore, the global fluctuation is found to be prominent for co-swirl flames, while precession motion is more pronounced in counter-swirl flames. When O2 is reduced to 13.13%, the combustion becomes stable, as suggested by low-amplitude aperiodic oscillations in the noise measurement. Heat release of co and counter-swirl flames respond differently to this reduction in O2 concentration. The precession motion remains unaffected for co-swirl flames upon O2 reduction. In contrast, precession motion alters significantly for counter-swirl. Regarding global fluctuations, low oxygen concentration suppresses all periodic fluctuations, mitigates noise, and Pfluc and Ifluc become entirely decoupled for both flames. Hence, the present study demonstrates for the first time the applicability of a low-oxygen dilution strategy in the context of co/counter-swirl flames for decoupling heat release and noise measurements. Furthermore, the study also indicates the varied response of complex co and counter-swirl flames to different oxygen concentrations.

Photo-Thermal Dry Reforming of Methane with PGM-Free and PGM-Based Catalysts: A Review.

Dry reforming of methane (DRM) is considered one of the most promising technologies for efficient greenhouse gas management thanks to the fact that through this reaction, it is possible to reduce CO2 and CH4 to obtain syngas, a mixture of H2 and CO, with a suitable ratio for the Fischer-Tropsch production of long-chain hydrocarbons. Two other main processes can yield H2 from CH4, i.e., Steam Reforming of Methane (SRM) and Partial Oxidation of Methane (POM), even though, not having CO2 as a reagent, they are considered less green. Recently, scientists' challenge is to overcome the many drawbacks of DRM reactions, i.e., the use of precious metal-based catalysts, the high temperatures of the process, metal particle sintering and carbon deposition on the catalysts' surfaces. To overcome these issues, one proposed solution is to implement photo-thermal dry reforming of methane in which irradiation with light is used in combination with heating to improve the efficiency of the process. In this paper, we review the work of several groups aiming to investigate the pivotal promoting role of light radiation in DRM. Focus is also placed on the catalysts' design and the progress needed for bringing DRM to an industrial scale.

A Comprehensive Review of Syngas Production, Fuel Properties, and Operational Parameters for Biomass Conversion

This study aims to provide an overview of the growing need for renewable energy conversion and aligns with the broader context of environmentally friendly energy, specifically through producing syngas from biomass. Unlike natural gas, which is mainly composed of methane, syngas contains a mixture of combustible CO, H2, and CnHm. Therefore, optimizing its production requires a thorough examination of various operational parameters such as the gasifying agent, the equivalence ratio, the biofuel type, and the state, particularly in densified forms like pellets or briquettes. As new biomass sources are continually discovered and tested, operational parameters are also constantly evaluated, and new techniques are continuously developed. Indeed, these techniques include different gasifier types and the use or non-use of catalysts during biofuel conversion. The present study focuses on these critical aspects to examine their effect on the efficiency of syngas production. It is worth mentioning that syngas is the primary gaseous product from gasification. Moreover, it is essential to note that the pyrolysis process (prior to gasification) can produce, in addition to tar and char, a mixture of gases. The common feature among these gases is their versatility in energy generation, heat production, and chemical synthesis. The analysis encompasses the resulting gas features, including the yield and composition, mainly through the hydrogen-to-carbon monoxide ratio and the carbon monoxide-to-carbon dioxide ratio, as well as the lower heating value and considerations of the tar yield.

Modulating the coordination environment and metal choice in carbon buckypapers supported metal phthalocyanines for enhanced electrocatalytic carbon dioxide reduction

In the search of versatile electrocatalysts for the electrochemical reduction of carbon dioxide (CO2RR), different transition metal phthalocyanines (MPc, where M=Fe, Co, Ni and Cu) have been immobilized by an easy and scalable wet impregnation on carbon nanotubes (CNTs) in the form of buckypaper (BP). Both the nature of the metal and the surface chemistry of the carbon support were found to play a pivotal role in determining their CO2RR efficiency and selectivity. We disclose here a potentiodynamic strategy for the controlled surface modification of BP with N- and P-containing polymeric species as a simple heterogenization strategy for molecular catalysts, enabling to easily tune their electrocatalytic performance. Syngas (mixture of H2 and CO) was obtained as the main product from CO2RR using FePc, CoPc and NiPc as electrocatalysts on functionalized (BPf) or non-modified BP. In contrast, CuPc was found to mainly catalyze the hydrogen evolution reaction (HER), with small amounts of formate as the only CO2RR product. It is possible to modulate the H2/CO ratio in the final product through the appropriate selection of the metal in MPc, the modification of the coordination environment by the controlled functionalization of the carbon support and the adjustment of the operating conditions. In particular, H2/CO ratios in a range between 0.17 and 1.28 have been obtained with good stability during electrolysis. Among all the MPc studied, CoPc surfaced as the most promising candidate for the reduction of CO2 to CO and H2 production, a finding substantiated by computational studies highlighting the positive impact of phosphate ligands on CoPc. This strategy outlines the starting line of a potential route toward the controlled generation of CO2RR-related products.

Effect of composition and processing conditions on the direct reduction of iron oxide pellets

In this paper, HSC software is used to estimate the effects of composition and processing conditions on the reduction behavior of iron oxide pellets, i.e., hematite (Fe2O3), magnetite (Fe3O4), wustite (FeO), pure iron (Fe), and iron carbide (Fe3C), in a wide temperature range from room temperature (RT) to 1000°C in the presence of H2 and CO mixtures. The reducibility of iron ores, in particular Fe2O3, Fe3O4, FeO, Fe is discussed. The choice of reducing agents CO and H2 is explained, with CO proving to be the more effective reducing agent at high temperatures from a thermodynamic point of view. However, the free Gibbs energy of iron reduction is lowest in the presence of a 100% H2 atmosphere. In addition, H2 reduces tortuosity and increases porosity by reducing it at cooler temperatures and promoting diffusion. In contrast, CO increases tortuosity and reduces initial porosity because it requires higher temperatures for effective reduction and causes structural changes. The presence of impurities other than iron oxides has been shown to impair the activity of reduced pure iron by acting as catalyst poisons or participating in competing reactions. CaO accelerates the reduction of FeO, which is due to the formation of calcium ferrite, but the effect decreases at higher temperatures. MgO can either promote or hinder reduction, depending on its concentration and its influence on pellet porosity. The presence of several non‑iron oxides has been shown to affect the overall direct reduction of iron ore pellets, resulting in a significant impact of the overall process.