High OH Concentrations Research Articles

Characterization of sugar maple and red oak bark: Efficient lignin extraction via the Organosolv and acidic dioxane process

The barks of two wood species, sugar maple (SM) and red oak (RO), were investigated to characterize their chemical composition and isolate the lignins they contain, representing relatively underexplored and underutilized polymers. Characterizing these two barks involved assessing extractive components, Klason and acid-soluble lignin, ash content, and sugars. It was observed that RO bark had a higher concentration of extractive substances and a lower Klason lignin content compared to SM bark. The Klason lignin content in the barks of the SM and RO bark was measured at 35.0% and 26.4%, respectively, higher than values reported for corresponding to wood of the same species, 21.8% and 22.2%, respectively, for RO and SM. Lignin isolation from bark was achieved by utilizing Organosolv catalytic and acid dioxane processes. Notably, the Organosolv process yielded lignins of considerably higher purity. The structural analysis of the bark lignins was peformed by combination of spectroscopic methods: FTIR,13P NMR, and solid-state NMR. Compared to dioxane lignins, a higher concentration of OH bound to syringyl and guayacyl units were found in Organosolv lignins. In contrast, aliphatic OH units are more important in dioxane lignins than in Organosolv lignins. Furthermore, sugar analysis was conducted via HPLC, thermal analysis was conducted through DSC and TGA, and ash composition identification was done using ICP-OES. Notably, higher Mw and Mn values are determined by GPC for dioxane lignins than for Organosolv lignins.

Passivation and depassivation of reinforcement steel in alkali-activated materials—A review

This paper reviews the formation and breakdown of passive film on the surface of reinforcement steel in alkali-activated materials (AAMs) considering the characteristics of reaction product and pore solution chemistry. The literature review shows that the pore solution of AAMs has higher concentrations of OH−, Na+, silica and aluminium compared to Portland cement (PC). This relatively high alkalinity contributes to the generation of a passive film, which has positive effects on the corrosion resistance of reinforcement steel embedded in AAMs. The silica-aluminium zeolite layer present on the surface of passive film adsorbs chloride ions and effectively inhibits chloride-induced depassivation. Generally, lower ratios of [Cl−]/[SO42−] and [Cl−]/[S2O32−] potentially inhibit the depassivation of reinforcement steel. The high pH value and the elevated concentrations of HS− of AAMs contribute to the increase of critical chloride content (Ccrit). However, the higher content of reduced sulfide mainly dissolved from slag results in the consumption of dissolved oxygen, which is necessary for the formation of passive film. Generally, the presence of reduced sulfide forms Fe-S complexes on the surface of reinforcement steel in AAMs. Even so, higher corrosion resistance for AAMs is mostly expected with longer depassivation time due to finer microstructure and lower chloride penetration rates compared to PC-based materials. The decrease in pH value in the pore solution of the AAMs is the main factor affecting carbonation-induced depassivation of reinforcement steel, while high concentrations of bicarbonate and carbonate ions inhibit depassivation.

Magnetically Enhanced Oxygen Evolution Reaction in Mild Alkaline Electrolytes by Building Catalysts on Magnetic Frame.

Under large current densities, the excessive hydroxide ion (OH) consumption hampers alkaline water splitting involving the oxygen evolution reaction (OER). High OH concentration (≈30wt.%) is often used to enhance the catalytic activity of OER, but it also leads to higher corrosion in practical systems. To achieve higher catalytic activity in low OH concentration, catalysts on magnetic frame (CMF) are built to utilize the local magnetic convection induced from the host frame's magnetic field distributions. This way, a higher reaction rate can be achieved in relatively lower OH concentrations. A CMF model system with catalytically active CoFeOx nanograins grown on the magnetic Ni foam is demonstrated. The OER current of CoFeOx@NF receives ≈90% enhancement under 400mT (900mAcm-2 at 1.65V) compared to that in zero field, and exhibits remarkable durability over 120h. As a demonstration, the water-splitting performance sees a maximum 45% magnetic enhancement under 400mT in 1m KOH (700mAcm-2 at 2.4V), equivalent to the concentration enhancement of the same electrode in a more corrosive 2m KOH electrolyte. Therefore, the catalyst-on-magnetic-frame strategy can make efficient use of the catalysts and achieve higher catalytic activity in low OH concentration by harvesting local magnetic convection.

Characteristics of a pre-combustion plasma jet igniter

Plasma ignition technology has delivered good performance in the aerospace industry. In this study, a pre-combustion plasma jet igniter was designed, and its characteristics were examined from three aspects: the morphology, temperature, and discharge characteristics and process of ignition. Images of the OH distribution were obtained by using an OH Planar Laser⁃Induced Fluorescence (OH-PLIF) experimental system. Results have shown that the proposed plasma jet had a higher OH concentration, longer length, and larger area than those of a traditional igniter. The stability of discharge of the igniter was improved as the equivalence ratio φ was increased, and reducing gas flow reduced the pulsation of the plasma jet. When the input current was increased from 15 A to 35 A, the highest average temperature increased from 5127 K to 7987 K. An increase in the equivalence ratio reduced the region of arc ionization, but expanded the regions of the core combustion reaction and the outer flame. Herein, this study has obtained a deep understanding of the jet and ignition law and developed a new idea for the application of plasma in the ignition field. A pre-combustion plasma jet igniter can significantly improve the efficiency of ignition and shorten the ignition process compared with a traditional igniter.

Facet-Controlled Growth of Hydroxyapatite for Effectively Removing Pb from Aqueous Solutions.

To address the growing concerns regarding severe water pollution, effective and environmentally friendly adsorbents must be identified. In this study, we prepared hydroxyapatite (HAp, Ca10(PO4)6(OH)2) as an eco-friendly absorbent via simple precipitation and obtained rod- (r-HAp) and plate-shaped HAp (p-HAp). The approach to obtaining p-HAp involved a low pH titration rate, promoting growth along the c-axis due to the adsorption of OH- on the (110) facet. Conversely, r-HAp was obtained by maintaining a high concentration of OH- during the initial stage through rapid pH titration, leading to a stronger restrictive effect on the growth of positively charged a(b)-planes. p-HAp demonstrated superior adsorption capacity, removing Pb through dissolution and recrystallization, achieving an impressive 625 mg/g within a 60 min reaction time compared to r-HAp. Our findings afford insights into the Pb removal mechanisms of HAp with different morphologies and can aid in the development of water purification strategies against heavy metal contamination.

Fenton-mediated thermocatalytic conversion of CO2 to acetic acid by industrial waste-derived magnetite nanoparticles.

Iron oxide dust, discarded as industrial waste, has been used here to fabricate magnetic iron oxide nanoparticles (Fe3O4-NPs). We have proposed the thermo-catalytic reduction of carbon dioxide (CO2) using Fe3O4-NPs in the presence of H2O2 to get acetic acid (AcOH) at near ambient conditions (100 °C, 10 bar) with a maximum yield of ∼0.4 M in a batch-reactor. The importance of H2O2 can be described as it facilitates the production of higher concentrations of OH˙ and H+/˙, which consequently supports the synthesis of AcOH.

The impact of COVID-19 lockdowns on urban photochemistry as inferred from TROPOMI

Movement restrictions were imposed in 2020 to mitigate the spread of Covid-19. These lock-down episodes provide a unique opportunity to study the sensitivity of urban photochemistry to temporary emission reductions and test air quality models. This study uses Tropospheric Monitoring Instrument (TROPOMI) nitrogen dioxide/carbon monoxide (NO2/CO) ratios in urban plumes in combination with an exponential fitting procedure to infer changes in the NOx lifetime (τNOx) during Covid-19 lock-downs in the cities of Denver, Chicago, New York, Riyadh, Wuhan and Sao Paulo compared with the year before.The strict lockdown policy in Wuhan led to a 65–80% reduction in NO2, compared to 30–50% in the other cities that were studied. In New York and Wuhan, CO concentration was reduced by 10–15%, whereas over Riyadh, Denver, Chicago, and Sao Paulo the CO background concentration increased by 2–5 ppb. τNOx has been derived for calm (0.0 < U (m/s) < 3.5) and windy (5.0 < U (m/s) < 8.5) days to study the influence of wind speed. We find reductions in τNOx during Covid-19 lockdowns in all six megacities during calm days. The largest change in τNOx during calm days is found for Sao-Paulo (31.8 ± 9.0%), whereas the smallest reduction is observed over Riyadh (22 ± 6.6%). During windy days, reductions in τNOx are observed during Covid-19 lockdowns in New York and Chicago. However, over Riyadh τNOx is almost similar for windy days during the Covid-19 lockdown and the year before.Ground-based measurements and the Chemistry Land-surface Atmosphere Soil Slab (CLASS) model have been used to validate the TROPOMI-derived results over Denver. CLASS simulates an enhancement of ozone (O3) by 4 ppb along with reductions in NO (38.7%), NO2 (25.7%) and CO (17.2%) during the Covid-19 lockdown in agreement with the ground-based measurements. In CLASS, decreased NOx emissions reduce the removal of OH in the NO2 + OH reaction, leading to higher OH concentrations and decreased τNOx. The reduction in τNOx inferred from TROPOMI (28 ± 9.0%) is in agreement with CLASS. These results indicate that TROPOMI derived NO2/CO ratios provide useful information about urban photochemistry and that changes in photochemical lifetimes can successfully be detected.

Evolution of organic carbon in the laboratory oxidation of biomass-burning emissions

Abstract. Biomass burning (BB) is a major source of reactive organic carbon into the atmosphere. Once in the atmosphere, these organic BB emissions, in both the gas and particle phases, are subject to atmospheric oxidation, though the nature and impact of the chemical transformations are not currently well constrained. Here we describe experiments carried out as part of the FIREX FireLab campaign, in which smoke from the combustion of fuels typical of the western United States was sampled into an environmental chamber and exposed to high concentrations of OH, to simulate the equivalent of up to 2 d of atmospheric oxidation. The evolution of the organic mixture was monitored using three real-time time-of-flight mass spectrometric instruments (a proton transfer reaction mass spectrometer, an iodide chemical ionization mass spectrometer, and an aerosol mass spectrometer), providing measurements of both individual species and ensemble properties of the mixture. The combined measurements from these instruments achieve a reasonable degree of carbon closure (within 15 %–35 %), indicating that most of the reactive organic carbon is measured by these instruments. Consistent with our previous studies of the oxidation of individual organic species, atmospheric oxidation of the complex organic mixture leads to the formation of species that on average are smaller and more oxidized than those in the unoxidized emissions. In addition, the comparison of mass spectra from the different fuels indicates that the oxidative evolution of BB emissions proceeds largely independent of fuel type, with different fresh smoke mixtures ultimately converging into a common, aged distribution of gas-phase compounds. This distribution is characterized by high concentrations of several small, volatile oxygenates, formed from fragmentation reactions, as well as a complex pool of many minor oxidized species and secondary organic aerosol, likely formed via functionalization processes.

Biocompatible PVTF Coatings on Ti with Improved Bonding Strength

In this work, a poly(vinylidenefluoride-co-trifluoroethylene) (PVTF) coating on a titanium (Ti) substrate was prepared, and Ti metal surfaces were treated by physical or chemical methods to achieve a high bonding strength with PVTF. Scanning electron microscopy (SEM), atomic force microscope (AFM), and static water contact angles (WCA) were used to characterize the Ti metal surfaces. Further, mechanical stretching testing was employed to measure the bonding strength of PVTF coatings. The possible mechanism for the improved bonding strength could be the higher OH concentrations on Ti metal surfaces, which could lead to the formation of chemical bonds with the F atom of PVTF chains. Finally, a CCK-8 analysis of bone marrow mesenchymal stem cells (BMSCs) cultured on the PVTF coatings confirmed that the physical and chemical treatments had no significant differences in biocompatibility. Such a PVTF coating on a Ti substrate showed the potential of biomedical metal implants.

Effect of flammable gases produced from spontaneous smoldering combustion of coal on methane explosion in coal mines

Methane released from underground coal mines forms a highly explosive mixture when combined with air, which can be aggravated by the flammable gases produced from spontaneous smoldering combustion of coal in the mines. In this work, the flammable gases from coal smoldering combustion under conditions close to those in a coal mine are experimentally characterized by a self-designed quartz cylinder. The flammable gases mainly consist of CO at the initial stage of the smoldering combustion while they are composed of CO, H2 and CH4 at temperatures above 300 °C. Then, their effect on explosion of methane-air mixtures is investigated via experiments and simulations. The explosion characteristics and flame propagation of the typical in-mine methane-air mixtures enriched by the smoldering combustion products are studied using a 20 L spherical vessel reactor and a high-speed camera. Among all the methane-air mixtures tested, the addition of the smoldering combustion products to fuel-lean methane-air mixtures most remarkably enhance methane explosion. In the simulations, a sensitivity analysis is conducted to identify the dominant elementary reactions during the explosion process. As the share of the smoldering combustion products added to the methane-air mixture increases, the dominant elementary reaction for methane consumption is found to eventually shift to enhance methane explosion by generating a high concentration of OH and O. The results of this work not only improve the understanding of methane explosion but also benefit the development of new methane explosion suppression technology for coal-mining industry.

Understanding the Oxidative Properties of Nickel Oxyhydroxide in Alcohol Oxidation Reactions.

The NiOOH electrode is commonly used in electrochemical alcohol oxidations. Yet understanding the reaction mechanism is far from trivial. In many cases, the difficulty lies in the decoupling of the overlapping influence of chemical and electrochemical factors that not only govern the reaction pathway but also the crystal structure of the in situ formed oxyhydroxide. Here, we use a different approach to understand this system: we start with synthesizing pure forms of the two oxyhydroxides, β-NiOOH and γ-NiOOH. Then, using the oxidative dehydrogenation of three typical alcohols as the model reactions, we examine the reactivity and selectivity of each oxyhydroxide. While solvent has a clear effect on the reaction rate of β-NiOOH, the observed selectivity was found to be unaffected and remained over 95% for the dehydrogenation of both primary and secondary alcohols to aldehydes and ketones, respectively. Yet, high concentration of OH- in aqueous solvent promoted the preferential conversion of benzyl alcohol to benzoic acid. Thus, the formation of carboxylic compounds in the electrochemical oxidation without alkaline electrolyte is more likely to follow the direct electrochemical oxidation pathway. Overoxidation of NiOOH from the β- to γ-phase will affect the selectivity but not the reactivity with a sustained >95% conversion. The mechanistic examinations comprising kinetic isotope effects, Hammett analysis, and spin trapping studies reveal that benzyl alcohol is oxidatively dehydrogenated to benzaldehyde via two consecutive hydrogen atom transfer steps. This work offers the unique oxidative and catalytic properties of NiOOH in alcohol oxidation reactions, shedding light on the mechanistic understanding of the electrochemical alcohol conversion using NiOOH-based electrodes.

Reagentless electrochemically assisted desorption for selective phosphate recovery from wastewater: Proof of concept and mechanism

Adsorption is a promising technology for removing and recovering phosphorus (P) from wastewater. However, the chemical-intensive regeneration of adsorbents increases carbon emissions and introduces potential secondary pollution. Most existing approaches cannot achieve simultaneous P desorption and selective recovery. For this purpose, a new-type electrochemically assisted phosphate desorption and recovery (EPDR) process was investigated and developed for the efficient desorption and recovery of P and simultaneous regeneration of the adsorbent in situ. In the EPDR process, the adsorbent amorphous zirconium oxide (am-ZrO2) coated carbon felt (CF) was employed as a cathode in an anion-exchange membrane (AEM) water electrolysis cell for P adsorption/desorption and recovery. The P desorption and recovery efficiency from the adsorbent were over 90% at 3.5 V. It was found that the high concentration of OH– at the cathode surface derived from water splitting reaction and electrodialysis under the applied electric field was playing a critical role in the desorption process. Low concentrations of P in actual wastewater were effectively removed, concentrated and recovered under multiple adsorption–desorption cycles with easy-to-scale-up stacked EPDR. The nature of reagent-free, high efficiency and selectivity make EPDR the foundation for developing a cost-effective and green technology for sustainable phosphorus management.

Characterization of products formed from the oxidation of toluene and m-xylene with varying NOx and OH exposure

Aromatic volatile organic compounds (VOCs) are an important precursor of secondary organic aerosol (SOA) in the urban environment. SOA formed from the oxidation of anthropogenic VOCs can be substantially more abundant than biogenic SOA and has been shown to account for a significant fraction of fine particulate matter in urban areas. A potential aerosol mass (PAM) chamber was used to investigate the oxidised products from the photo-oxidation of m-xylene and toluene. The experiments were carried out with OH radical as oxidant in both high- and low-NOx conditions and the resultant aerosol samples were collected using quartz filters and analysed by GC × GC-TOFMS. Results show the oxidation products derived from both precursors included ring-retaining and -opening compounds (unsaturated aldehydes, unsaturated ketones and organic acids) with a high number of ring-opening compounds observed from toluene oxidation. Glyoxal and methyl glyoxal were the major ring-cleavage products from both oxidation systems, indicating that a bicyclic route plays an important role in their formation. SOA yields were higher for both precursors under high-NOx (toluene: 0.111; m-xylene: 0.124) than at low-NOx (toluene: 0.089; m-xylene: 0.052), likely linked to higher OH concentrations during low-NOx experiments which may lead to higher degree of fragmentation. DHOPA (2,3-dihydroxy-4-oxo-pentanoic acid), a known tracer of toluene oxidation, was observed in both oxidation systems. The mass fraction of DHOPA in SOA from toluene oxidation was about double the value reported previously, but it should not be regarded as a tracer solely for oxidation of toluene as m-xylene oxidation gave a similar relative yield.

A Study on Combustion Characteristics of Insensitive Triple-Base Propellant

Research on combustion characteristics can provide basic information and theoretical support for the design of insensitive propellant. This work aims to investigate the combustion characteristics of insensitive triple-base propellant. All propellants were prepared based on same triple-base propellant, but they were desensitized with the same desensitizer in different ways. The high-speed camera, spontaneous luminescence, NO, NH chemiluminescence, and OH-planar laser induction fluorescence (PLIF) methods were employed to capture the combustion flame and derive the distributions of important intermediates. Results show that ignition delay times of insensitive propellants are obviously longer. This indicated that the application of the desensitizer has a partly hindering effect on the early ignition stage. The combustion time of insensitive propellants is mostly similar, which means that the desensitizer has little influence on the intensity of actual combustion. The change in flame height and area of insensitive propellants over time indicated that the combustion progressivity of some insensitive propellants was more prominent, which means that the desensitizer concentration and desensitizing methods all affect the performance of insensitive propellant. The signal intensities of NO and NH show a negative correlation, indicating that a competitive relationship probably exists between the formation of NO and NH radicals during the reaction process. The high concentration of OH mainly locates outside NO, suggesting that there may be a transformation between NO and OH. The maximum signal intensity of NO and NH of different insensitive propellants confirmed that both the concentration of desensitizers and the desensitizing methods exhibit important effect on the reaction process.

Surface hydroxide promotes CO2 electrolysis to ethylene in acidic conditions

Performing CO2 reduction in acidic conditions enables high single-pass CO2 conversion efficiency. However, a faster kinetics of the hydrogen evolution reaction compared to CO2 reduction limits the selectivity toward multicarbon products. Prior studies have shown that adsorbed hydroxide on the Cu surface promotes CO2 reduction in neutral and alkaline conditions. We posited that limited adsorbed hydroxide species in acidic CO2 reduction could contribute to a low selectivity to multicarbon products. Here we report an electrodeposited Cu catalyst that suppresses hydrogen formation and promotes selective CO2 reduction in acidic conditions. Using in situ time-resolved Raman spectroscopy, we show that a high concentration of CO and OH on the catalyst surface promotes C-C coupling, a finding that we correlate with evidence of increased CO residence time. The optimized electrodeposited Cu catalyst achieves a 60% faradaic efficiency for ethylene and 90% for multicarbon products. When deployed in a slim flow cell, the catalyst attains a 20% energy efficiency to ethylene, and 30% to multicarbon products.

Manipulation of the crystallization of SSZ-13 transformed from coal fly ash-derived analcime

Interzeolite transformation (IZT) has been used to produce zeolite with novel structure and composition. However, the complicated interactions between synthesis parameters and the resultant zeolites remained ambiguous. Herein, we synthesized zeolite SSZ-13 via an IZT strategy by using coal fly ash-derived analcime as parent zeolite. The effects of feeding H2O/SiO2, OH-/SiO2, and SiO2/Al2O3 ratios on the crystallization of zeolite SSZ-13 were examined. The crystallinity, pore structure, building units, and chemical environment of the products were investigated by XRD, SEM, XRF, N2 adsorption-desorption, FT-IR, and NMR, respectively. Zeolite SSZ-13 with high crystallinity and regular pore structure can be obtained under feeding H2O/SiO2 ratios of 17.5–25, OH-/SiO2 ratios of 0.2–0.6, and Al2O3/SiO2 ratios of 30–40. The absence of external water limited the mass transfer between reactants. While excessive water lessened the driving force for synthesizing zeolite SSZ-13 with regular structure. Small amounts of OH- ions triggered the dissociation of zeolite analcime. But high concentrations of OH- ions blocked the condensation of Si reactants and nucleation of zeolite SSZ-13. Increasing SiO2/Al2O3 ratio boosted the nucleation frequency. Insufficient contents of external Si species delayed nucleation and formed amorphous aluminosilicate impurities. The superfluous SiO2/Al2O3 ratio caused the overgrowth of zeolite SSZ-13 with irregular structures. Our findings benefited in understanding the interaction among synthesis parameters and the crystallization mechanism of IZT. It also gained new strategies for synthesizing high-silica zeolite using Al-rich natural and industrial aluminosilicate solid wastes.

Synergistic Electric Metal (Ni SAs)‐Semiconductor (CdS NPs) Interaction for Improved H2O‐to‐H2 Conversion Performance under Simulated Sunlight

Single‐atom (SA) cocatalysis has obvious superiority in promoting solar‐to‐chemical energy conversion. However, easy aggregation of SAs is very unfavorable to its catalysis for high surface energy. Herein, a photoreduction procedure is adopted to immobilize Ni SAs on CdS nanoparticles (NPs) to construct the synergistic electric metal–semiconductor interaction (EMSI) for highly promoting the simulated sunlight‐driven H2O‐to‐H2 (HTH) conversion in alkaline condition (pH = 14.0) without any sacrificial agent addition, and the nanocatalyst with 1.25‰ of Ni carrying capacity (CdS–Ni1.25‰) achieves the highest HTH conversion rate (8149.71 μmol h−1 g−1, 13.0‐fold greater of that of CdS NPs) and stable photostability accompanied by 27.60% of apparent quantum yield (AQY400 nm). Characterizations and density functional theory calculations indicate that the EMSI on CdS–Ni1.25‰ nanocatalyst greatly improves the light absorption capacity and promotes the orderly bulk‐to‐surface migration of photoexcitons, effectively suppressing their recombination kinetics for higher photoexciton utilization efficiency. Under alkaline conditions, high concentration of OH− ions is easy to react with photogenerated holes to generate hydroxyl radicals for effectively inhibiting the oxidation half‐reaction and obtaining higher HTH conversion performance due to significantly reduced energy barriers on atomic Ni sites. This study provides an insight for improving the performance of a conventional photocatalyst through non‐noble metallic SAs cocatalysis.

Effect of Promoters on the Catalytic Performance of Ni‐Based Catalysts for Dry Reforming of Methane

AbstractDifferent promoters have a significant impact on the catalyst performance. In this paper, the effects of different promoters on the physical properties and catalytic behavior of methane dry reforming catalysts were investigated. A series of characterizations showed that the Mg, Ba, and Ca promoters increased the basicity of the catalysts. However, their high concentration of OH− leads to the destruction of Ni3Si2O5(OH)4 species, which results in a decrease of catalytic performance. The addition of Ce significantly improves the catalyst stability. After 100 h of Ni‐5Ce‐MSC reaction, there was almost no carbon deposition, exhibiting high activity and resistance to carbon accumulation. These findings provide a new perspective for the design of nickel‐based dry reforming catalysts.

H2 Production by Methane Oxy-Reforming: Effect of Catalyst Pretreatment on the Properties and Activity of Rh-Ce0.5Zr0.5O2 Synthetized by Microemulsion

Green hydrogen introduction in hard-to-abate processes is held back by the cost of substituting steam reforming plants with electrolyzers. However, green hydrogen can be integrated in properly modified reforming processes. The process proposed here involves the substitution of steam reforming with oxy-reforming, which is the coupling of the former with catalytic partial oxidation (CPO), exploiting the pure oxygen coproduced during electrolysis to feed CPO, which allows for better heat exchange thanks to its exothermic nature. With the aim of developing tailored catalysts for the oxy-reforming process, Ce0.5Zr0.5O2 was synthetized by microemulsion and impregnated with Rh. The Ce-based supports were calcined at different temperatures (750 and 900 °C) and the catalysts were reduced at 750 °C or 500 °C. Tuning the calcination temperature allowed for an increase in the support surface area, resulting in well-dispersed Rh species that provided a high reducibility for both the metal active phase and the Ce-based support. This allowed for an increase in methane conversion under different conditions of contact time and pressure and the outperformance of the other catalysts. The higher activity was related to well-dispersed Rh species interacting with the support that provided a high concentration of surface OH* on the Ce-based support and increased methane dissociation. This anticipated the occurrence and the extent of steam reforming over the catalytic bed, producing a smoother thermal profile.

HCCI engine performance using fuel mixture of H2 and H2O2

The main goal of this paper is to study a free carbon combustion engine using H2/H2O2 fuel for the HCCI engine. HCCI engine Combustion phasing, IMEP, and thermal efficiency are analyzed at different effective equivalence ratios (Phi) and engine speeds. A 3D CFD model is developed and validated with available syngas fuel combustion experimental data. This model is used to control the combustion phasing of the HCCI engine by altering the volume fraction of H2O2 in the H2/air-fueled HCCI engine. Therefore, the results show that H2O2 minimizes the inlet mixture temperature; it also helps control combustion phasing and improve combustion and thermal efficiencies at all Phi and engine speeds. Furthermore, the volume fraction of H2O2 increases the reactivity of fuel due to a high concentration of OH, which enhances the combustion rate in the crevice, resultantly high combustion efficiency. Hence, the combustion efficiency reached 97% at a 20% volume fraction of H2O2, whereas the thermal efficiency reached about 45%. On the other side, a design expert tool is used to analyze the interaction between different factors and their effect on the HCCI engine performance. It is reported that enhancement of H2O2 volume fraction and Phi has a linear effect on combustion efficiency at all engine speeds, but H2O2 volume fraction has a dominant effect. Conversely, it shows a quadratic relation between H2O2 volume fraction and Phi for thermal efficiency. It is concluded that the performance of the HCCI engine is improved with zero carbon and limited NOx emissions by using a blended fuel mixture of H2 and H2O2.