Initial Stage Of Reaction Research Articles

Synergistic effect of anion and cation in oxalic acid for graphene surface engineering and its enhanced pseudocapacitance performance

The reduced graphene oxide (rGO-oxalic) with rich carbonyl and hydroxyl groups was prepared by using oxalic acid as reducing agent, and the structure of rGO-oxalic was characterized by XRD, Raman, TEM, AFM, XPS and BET. The anion and cation in oxalic acid play an important role in the removal of oxygen groups on GO surface, but the chemical reaction and mechanism are different. The further study indicated that the GO was reduced rapidly and effectively in the initial stage of reaction, and it is selective reduction in the middle and final stage of the reaction, showing that more carbonyl and hydroxyl groups were retained. The supercapacitor with rGO-oxalic as electrode material exhibited the superior specific capacitance (301.1 F·g−1 and 217.0 F·g−1 at 1 A·g−1 in three- and two-electrode systems, respectively). Meanwhile, the capacitance retention was as high as 89.5% after 10,000 cycles at 5 A·g−1 for the symmetric supercapacitor. The research on the reduction mechanism of rGO-oxalic is beneficial to its potential application in energy storage and other fields.

Effect of Oxygen Vacancies on Adsorption of Small Molecules on Anatase and Rutile TiO2 Surfaces: A Frontier Orbital Approach

Adsorption is a critical step in the initial stage of a catalytic reaction. Oxygen vacancies often become a central topic of discussion with respect to the reaction mechanism on metal oxide surface...

Studies on Epoxidation of Tung oil with Hydrogen Peroxide Catalyzed by Sulfuric Acid

Tung oil with an iodine value (IV) of 99.63 g I2/100 g was epoxidized in-situ with glacial acetic acid and hydrogen peroxide (H2O2), in the presence sulfuric acid as catalyst. The objective of this research was to evaluate the effect of mole ratio of H2O2 to unsaturated fatty acids (UFA), reaction time and catalyst concentration in Tung oil epoxidation. The reaction kinetics were also studied. Epoxidation was carried out for 4 h. The reaction rates and side reactions were evaluated based on the IV and the conversion of the epoxidized Tung oil to oxirane. Catalytic reactions resulted in higher reaction rate than did non-catalytic reactions. Increasing the catalyst concentration resulted in a large decrease in the IV and an increase in the conversion to oxirane at the initial reaction stage. However, higher catalyst concentration in the epoxidation reaction caused to a decrease in reaction selectivity. The mole ratio of H2O2 to UFA had an influence identical to the catalyst concentration. The recommended optimum mole ratio and catalyst concentration in this study were 1.6 and 1.5%, respectively. The highest conversion was 48.94% for a mole ratio of 1.6. The proposed kinetic model provided good results and was suitable for all variations in reaction temperature. The activation energy (Ea) values were around 5.7663 to 76.2442 kcal/mol. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Dry reforming of CH4 over NiCo/Ce0.75Zr0.25O2-δ: The effect of Co on the site activity and carbon pathways studied by transient techniques

The effects of cobalt in the CeZrO2-supported NiCo (3 wt%, Co/ :Ni=3/2) on the DRM at 750oC were investigated by the transient method and use of 18O2 and 13CO2. Transient kinetic rates of carbon deposition and gasification by the support’s oxygen, TOF (s-1) and concentration of active carbon were determined. Higher TOF and reduced carbon accumulation rates were measured on NiCo than Ni at the initial stage of reaction. However, oxidation of Co with time-on-stream led to lower and higher concentration of active metal sites and deposited carbon, respectively. These results appear important for catalyst design improvements (e.g. metal alloy composition).

The deterioration of bio-oil and catalyst during the catalytic upgrading of biomass pyrolysis volatiles

ABSTRACT The tin (Sn)-modified HZSM-5 was employed to upgrade biomass pyrolysis volatiles to prepare bio-oil, and the deterioration of bio-oil and catalyst was focused. A new parameter indicating the physicochemical properties was defined as the comprehensive fuel-grade index (CFI). The catalyst initially demonstrated the better performance to transform oxygen-containing organics to hydrocarbons; consequently, the bio-oil had a higher CFI value. The fresh catalyst produced 33.43% of bio-oil with the higher hydrocarbon content of 41.60%, and the proportions of monocyclic aromatic hydrocarbons (MAHs) and light aliphatic hydrocarbons (LAHs) reached 74.59% and 20.02%, respectively. However, with the extension of catalyst using-time, the obvious decrease of hydrocarbons caused the significant decrease of CFI. Furthermore, the cracking and reforming diffusion performance supported by the acid and textural properties of the catalyst deteriorated severely, which contributed to the proportion increase of polycyclic aromatic hydrocarbons (PAHs). The decrease of the acid and textural properties were attributed to the coke generated and deposited into the pores and on the surface of the catalyst. The deposited cokes could be divided into two types including semihydrogenated coke and carbonaceous coke, and the former was the main one. The carbonaceous coke was formed in the initial stage of catalytic reaction, gradually inducing more precursors to cover active sites and block pores, and then generated more semihydrogenated coke, eventually causing the catalyst performance deterioration. This study provided an insight for improving sustainability in terms of understanding process deterioration.

Dosing effect of nano zero valent iron (NZVI) on the dark hydrogen fermentation performance via lake algae and food waste co-digestion

The effect of nano zero valent iron (NZVI) on hydrogen production by the co-digestion of dry lake algae and food waste was investigated. The results showed that 10 mg.gTS−1 addition of NZVI improved the performance of the co-digestion system, with the cumulative hydrogen increased by 29.20% to 40.04 mL.gVS−1, compared to that of the control. However, the cumulative hydrogen yield decreased to 14.77 and 5.37 mL.gVS−1 when the NZVI dosage was increased to 20 and 40 mg.gTS−1, respectively. The oxidation reduction potential (ORP) of the reaction system was decreased dramatically to -331∼-490 mV at the initial reaction stage. The degradation rates of carbohydrate and protein also reached their peaks at the NZVI dosage of 10 mg.gTS−1. The concentration of end product in the liquid phase and the dehydrogenase activity was first increased then decreased when enhancing the NZVI dosage. Analysis of the transmission electron microscopy images revealed that excessive NZVI dosage could destroy the cells of microorganisms.

Effect of alkalis on enforced carbonation of cement paste: Mechanism of reaction

AbstractIn the present research, an alternative approach to produce supplementary cementitious materials (SCMs) based on the carbon capture and utilization is developed. The approach focuses on enforced carbonation of cement pastes obtained from recycled concrete and its application as SCM. This work focuses on the effect of alkalis in the starting solution on the carbonation mechanism of ground hydrated cement pastes in a wet reactor. The enforced carbonation of cement paste is a rapid process at ambient temperature and pressure being close to complete reaction within a few hours of carbonation, independently on alkali concentration. However, alkalis have a complex impact on the carbonation reaction as they accelerate the initial stages of the carbonation reaction, while the kinetics of the middle stages is retarded. The final degree of carbonation is only slightly affected by the alkali concentration in the solution. The origin of these effects can be explained by relating them to the evolution of solid and solution properties. Additionally, the alkali concentration has an impact on the morphology of the main carbonation products, that is, calcite and the alumina‐silica gel.

Preparation and characterization of ferrous oxalate cement—A novel acid‐base cement

AbstractFerrous oxalate cement (FOC), a new type of acid‐base cement, is prepared at room temperature through reactions between iron‐rich copper slag (CS) and oxalic acid (OA). In this work, the influences of precursor proportions, including the copper slag‐to‐oxalic acid mass ratio (CS/OA), borax‐to‐cement mass ratio (B/C), and water‐to‐cement mass ratio (W/C), on the setting behavior and compressive strength of FOC paste are investigated. Furthermore, the evolutions of pH and ions concentrations are traced to understand the reaction mechanism of FOC. The results show that the compressive strength decreases with an increase in W/C; when W/C is fixed, with an increase in CS/OA, the compressive strength first increases and then decreases, giving an optimal value. The compressive strengths of specimens at 3, 7, and 28 days can reach 33, 41, and 55 MPa, respectively, under the optimal conditions (CS/OA = 3.6, B/C = 0.03, and W/C = 0.18). The setting time is also a function of W/C and CS/OA, and can be extended by adding borax. Iron oxalate hydrate (FeC2O4·2H2O) has been identified as the exclusive hydration product of FOC due to the chemical reaction between Fe2SiO4 or Fe3O4 contained in CS and OA solution. At the initial stage of reaction, OA is dissolved to release protons, HC2O4− and C2O42−, which facilitate the dissolution of Fe2SiO4 and Fe3O4 and the release of Fe2+ in the aqueous phase. Then the Fe2+ ions combine with HC2O4− and C2O42− to precipitate FeC2O4·2H2O, acting as the cementitious phase to bond the unreacted CS particles.

Structure and physiochemical characteristics of whey protein isolate conjugated with xylose through Maillard reaction at different degrees

The purpose of this study is to prepare Maillard reaction products (MRPs) with both good emulsification and antioxidant activity, and the relationship between the Maillard reaction degree and structural changes of whey protein isolate (WPI) conjugated with xylose through wet-heating was explored. Browning intensity didn’t change while the free amino groups reduced significantly at the initial stage of Maillard reaction (MR). Amino acid analysis indicated that the lysine and arginine reduced significantly. The antioxidant property of the MRPs was significantly improved. The best emulsifying properties could be obtained in the middle degree of MR. The sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis illustrated that WPI and xylose formed high molecular weight conjugates. The circular dichroism spectra suggested that α-helix and random coil were increased while the β-sheet and β-turns were decreased after the MR. All of the MRPs exhibited a marked red shift in the maximum fluorescence intensity, indicating that the hydrophilicity of MRPs was enhanced.

Factors influencing dissolution of carbonaceous materials in liquid Fe\u2013Mn

Carbon dissolution from four types of metallurgical cokes and graphite was investigated by using immersion rods in a resistance furnace to clarify the influence of factors governing the rate of carbon dissolution from carbonaceous materials into Fe–Mn melts at 1550 °C. The factors studied were the microstructure of carbonaceous materials, roughness, porosity and the wettability between carbonaceous materials and the melt. Carbon/metal interface was characterised by scanning electron microscopy accompanied with energy-dispersive X-ray spectrometry to investigate the formation of an ash layer. The results showed that coke E had the highest dissolution rate. Surface roughness and porosity of the carbonaceous materials seemed to be dominant factors affecting the dissolution rates. Further, crystallite size did not have a significant effect on the dissolution rates. Solid/liquid wettability seemed to affect the initial stage of dissolution reaction. The dissolution mechanism was found to be both mass transfer and interfacial reactions.

The nature of active Ni sites and the role of Al species in the oligomerization of ethylene on mesoporous Ni-Al-MCM-41 catalysts

Although nickel dispersed in mesoporous aluminosilicates are efficient catalysts for the oligomerization of ethylene, the nature of the active nickel sites still remains controversial. Here we applied in situ FTIR-CO spectroscopy during reaction with ethylene combined with reaction kinetics with online MS analysis of reaction products to unravel the nature of the active nickel species in working mesoporous Ni-Al-MCM-41 catalysts. The results revealed that isolated ion-exchanged Ni2+ cations are irreversibly blocked during the initial reaction stages leaving unsaturated Ni2+ cations grafted on silanols and at the surface of small (confined) NiO nanoparticles as the active species in the pseudo-steady state. The low activity of these species in pure silica materials suggested a promotional role of aluminum in the Al-MCM-41 matrix on enhancing the activity of Ni2+ sites, probably through a close interaction between Al species and nearby Ni2+ sites, as inferred from quantitative 27Al MAS NMR and FTIR spectroscopies.

Effects of Fe and Al ions during hydrogen sulphide (H2S)-induced corrosion of tetracalcium aluminoferrite (C4AF) and tricalcium aluminate (C3A)

With high concentration and toxic H2S gas found in sewage facilities, it has ultra-high leakage risk and great environment impact, once the sealing material failure. In this study, hydrogen sulphide (H2S)-induced corrosion effects of tetracalcium aluminoferrite (C4AF) and tricalcium aluminate (C3A) phases of cement were evaluated during the initial stages of reaction. Both phase changes and bond structures were examined by techniques including Fourier transform infrared spectroscopy (FTIR). The results indicate that corrosion occurred through a stepwise reaction promoted by Fe ions. The effects of Fe and Al ions were further quantitatively investigated by X-ray photoelectron spectroscopy (XPS) and 27Al solid-state nuclear magnetic resonance (SSNMR). Compared with hydrated samples, the Fe ions were changed with Fe(II) ions increasing and Fe(III) ions reducing, and the AlOx group was observed to be transformed form AlO4 to AlO6 after H2S corrosion. Changes obtained will be benefit the further development of hazardous H2S control material and risk management operations.

Breakthrough synthesis of 2,3,3,3-tetrafluoropropene via hydrogen-assisted selective dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane over nickel phosphides

Herein, we report a hydrogen-assisted selective dehydrochlorination of 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb) to 2,3,3,3-tetrafluoropropene (HFO-1234yf) over nickel phosphides (Ni2P, Ni12P5 and Ni3P) catalysts. The Ni3P catalyst exhibited higher activity and HFO-1234yf selectivity than Ni12P5 and Ni2P catalysts. An induction period over Ni3P was observed during the initial 15 h under reaction conditions of 300 °C and H2/HCFC-244bb of 1.5, then a steady HCFC-244bb conversion ~ 42% and HFO-1234yf selectivity ~ 88% was obtained within the rest of 105 h. The catalysts were characterized by in situ temperature-programmed desorption analysis, X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The in situ H2-TPD results reveal that Ni3P was capable of forming larger amount of active hydrogen species than the other nickel phosphides, but by comparing the desorption temperature the reactivity of active hydrogen species on Ni3P was weaker than those formed on Ni12P5 and Ni2P, leading to higher activity and HFO-1234yf selectivity of Ni3P. The theoretical calculations also find that the adsorption energy of H2 over Ni3P is lower than those over Ni12P5 and Ni2P. XPS and TEM-mapping show that a surface chlorination occurred on Ni3P during the initial stage of reaction, resulting in an increase of surface acidity. Thus, the enhanced catalytic efficiency of Ni3P during the induction period can be attributed to a synergism between the metal sites and the in situ formed weak acid sites, further promoting the C-Cl bond scission by active H species and inhibiting the deep-hydrogenation.

Changes in structure and surface properties of Si-based agent during hydrogen generation reaction

Si-based agent which can generate a high amount of hydrogen by the reaction with weak alkaline solutions (e.g., pH8.3) has been investigated using SEM, XRD, DLS, XPS and FT-IR. Si-based agent consists of crystalline Si with the average crystallite size of ~20 nm, and Si nanocrystals form agglomerate with ~150 nm average size. The size of agglomerate slightly decreases from ~150 nm to ~130 nm during the initial hydrogen generation reaction stage up to 500 min in pH8.3 solutions at 36 °C and then the agglomerate size stays constant. The observed curve of the generated hydrogen volume vs. the reaction time is reasonably well expressed by the observed size change of Si crystallites, and also by the thickness of the silicon oxide layer. Before the hydrogen generation reaction, hydrogen atoms are present at the Si/silicon oxide interface as SiH, SiH2, and SiH3, and also at the surface and in the silicon oxide layer, as HSiO, HSiO2, and HSiO3. The concentrations of all hydrogen-containing species increase in the initial reaction stage, and then, decrease with the hydrogen generation reaction time, indicating that generated hydrogen atoms attack SiH bonds, leading to desorption as H2.

Study on the Sulfuration Mechanism of Concrete: Microstructure and Product Analysis.

This paper presents an experimental investigation of the sulfuration mechanism of concrete. The microstructure, mineral phase composition, substance content, and pH of the concrete were determined using scanning electron microscopy, X-ray diffraction, comprehensive thermal analysis, and pore-solution pH test. It was observed that light-grey spots appeared on the surface of the specimen, and a large amount of powdery precipitated substances appeared. At the initial stage of sulfuration reaction, the formation of ettringite blocked the concrete pores and densified its cracks and voids. Subsequently, ettringite reacted with H+ to form gypsum, and the continuous increase in gypsum in the pores increased the number of cracks and broadened their width. Gypsum was the final product of the sulfuration reaction, and the mass percentage of gypsum in the powdery precipitated substances at different water–cement ratios was more than 50%. When the water–cement ratios was 0.37, 0.47, and 0.57, the highest Ca(OH)2 content was found for the lowest water–cement ratio. As the water–cement ratios increased, the amount of powdery precipitated substances decreased and the CaCO3 content and pH increased.

Removal of 1,4-Naphthoquinone by Birnessite-Catalyzed Oxidation: Effect of Phenolic Mediators and the Reaction Pathway.

This study investigated the birnessite (δ-MnO2) catalyzed oxidative removal of 1,4-naphthoquinone (1,4-NPQ) in the presence of phenolic mediators; specifically, the kinetics of 1,4-NPQ removal under various conditions was examined, and the reaction pathway of 1,4-NPQ was verified by liquid chromatography–tandem mass spectrometry (LC–MS/MS). The removal rate of 1,4-NPQ by birnessite-catalyzed oxidation (pH = 5) was faster in the presence of phenolic mediators with electron-donating substituents (pseudo-first-order initial stage rate constant (k1) = 0.380–0.733 h−1) than with electron-withdrawing substituents (k1 = 0.071–0.244 h−1), and the effect on the substituents showed a positive correlation with the Hammett constant (Σσ) (r2 = 0.85, p < 0.001). The rate constants obtained using variable birnessite loadings (0.1–1.0 g L−1), catechol concentrations (0.1–1.0 mM), and reaction sequences indicate that phenolic mediators are the major limiting factor for the cross-coupling reaction of 1,4-NPQ in the initial reaction stages, whereas the birnessite-catalyzed surface reaction acts as the major limiting factor in the later reaction stages. This was explained by the operation of two different reaction mechanisms and reaction products identified by LC-MS/MS.

Novel Pd-loaded urchin-like (NH4)xWO3/WO3 as an efficient visible-light-driven photocatalyst for partial conversion of benzyl alcohol

Photocatalytic oxidation of organic compounds by solar light is a promising strategy for environmentally benign conversion processes. Herein, we first report an urchin-like Pd/(NH4)xWO3/WO3 with three-dimensional hierarchical microstructure prepared through a thiourea-assisted solvothermal method followed by calcination under the reductive atmosphere. The Pd/(NH4)xWO3/WO3 exhibits higher selectivity in comparison to Pd/WO3 nanorods in the partial conversion of aqueous benzyl alcohol into benzaldehyde (e.g., 80% selectivity for benzaldehyde production with ca. 84% conversion of benzyl alcohol) under visible light irradiation. The preferential generation of hydroxyl radicals from water on the (NH4)xWO3/WO3 surface in the initial reaction stage was responsible for the high selectivity for benzaldehyde production because hydroxyl radicals react with benzyl alcohol much more efficiently than benzaldehyde. DFT calculations demonstrate that the energy barrier of the reaction between benzyl alcohol and hydroxyl radicals largely decreased due to the photo-excited triplet states of (NH4)xWO3/WO3, while such a trend in the energy barrier was not observed for other photocatalysts. On the other hand, with extended irradiation time, a large amount of hydrogen peroxide, which was produced by the multi-electron reduction of oxygen molecules, accumulates on the Pd/(NH4)xWO3/WO3 due to the low activity of the Pd cocatalyst. The generated hydrogen peroxide preferentially eliminated the photoexcited holes when the concentrations of benzaldehyde increased, thus inhibiting the peroxidation of benzaldehyde by holes. The Pd/(NH4)xWO3/WO3 may provide a feasible strategy for the photocatalytic oxidation of various other organic compounds due to its unique reactivity shown in this study.

Flammability limit behavior of methane with the addition of gaseous fuel at various relative humidities

The lower flammability limit (LFL) of methane is 5 % in volume. Usually, in the relevant industry, the methane leakage monitoring threshold is set on the basis of the LFL from the perspective of safety precautions. When small amounts of other combustible gases coexist with methane, setting the monitoring threshold according to 5% vol may cause a large deviation and lead to a potential explosion accident. To investigate the effects of flammable gases and the relative humidity (RH) on the methane flammability limit behavior, the flammability limits of methane-air mixtures with the addition of gaseous fuels were experimentally measured in a standard cylindrical setup at various relative humidities. A theoretical model based on the adiabatic flame temperature method was employed to obtain reasonable estimates of the flammability limits of binary mixtures of methane and vapor. The combustion hazards of methane-air mixtures were evaluated. The results showed that both the LFL and the upper flammability limit (UFL) of methane were diminished with the addition of gaseous fuel at the same RH, while these parameters increased with an increase in the RH. The flammable range of methane-air mixtures was slightly narrowed by increasing the RH but was extended by the addition of gaseous fuel. The combustion hazard of methane increases as the volume fraction of added gases increases but drops with an increase in the RH. These phenomena were ascribed to the dual roles of water vapor and the influence of the added gaseous fuel on the initial stage of the methane-air chain reactions. The obtained data could supplement the flammability limits database and help to prevent potential explosion hazards.

Excess oxygen in delafossite CuFeO2+δ: Synthesis, characterization, and applications in solar energy conversion

As an alternative to high-temperature oxidation, the present study demonstrates a new approach to the intercalation of excess O into 3R-delafossite CuFeO2, based on a non-equilibrium hydrothermal synthesis. At lower temperatures, or during the initial stage of this hydrothermal reaction, a large amount of excess O remains between the self-assembled block layers, owing to the incomplete reduction of propionaldehyde in the hydrothermal process. This work not only confirmed the presence of this excess O and quantified the excess O concentrations, but also established the mechanism by which non-stoichiometric CuFeO2+δ is generated, on the basis of experimental observations and theoretical calculations. Normally, highly crystalline CuFeO2+δ prepared using the conventional hydrothermal process only contains low levels of excess O, but the present work shows that this problem can be mitigated by employing a microwave-assisted hydrothermal reaction. This technique can rapidly synthesize high quality 3R-delafossite CuFeO2+δ containing elevated concentrations of excess O. Electronic structures calculated based on density functional theory showed that CuFeO2+δ should exhibit half-metallic ferromagnetism and multiple band gaps. Systematic experimental characterization and theoretical calculations were used to elucidate the manner in which excess O significantly affects the microstructure of this material, while enhancing the electrical, optical and electrochemical properties of CuFeO2. As a result of these enhancements, this material is suitable for the improvement of solar energy conversion. Photoelectrochemical trials and data from the photocatalytic performances confirm these properties, suggesting that non-stoichiometric 3R-delafossite CuFeO2+δ compounds have potential applications in solar energy conversion.

Effect of Pore Structure and Ion Concentration of Solution on the Formation of Ettringite in Composite Cement Paste

Under the background of shrinkage cracking of cement and concrete, ettringite is regarded as the most effective expansion source because of its outstanding expansion characteristics. In order to study the expansion mechanism of ettringite, the growth process and formation conditions of ettringite in composite cement system were studied by means of SEM, MIP and ICP. The effects of pore structure and ion concentration of pore solution on the morphology and expansion properties of ettringite were also analysed in this paper. The results show that the pore structure of cement paste directly affects the expansion properties of ettringite. It is verified that there is no obvious linear relationship between the expansion rate of ettringite and its quantity. The concentration of SO42- and Al(OH)4- in pore solution is the determinant of ettringite formation rate and quantity in composite cement system at the initial stage of hydration reaction. The change of crystallinity of ettringite will be directly caused by pH.