Distribution Of Reaction Products Research Articles

Disclose effect and mechanism of external electric field on RP-1 fuel pyrolysis

To explore the combustion efficiency of aviation fuel in an electric field, a ReaxFF molecular dynamics and density functional theory calculation was performed to study the electric field effect on 3-component RP-1 (methylcyclohexane, n-dodecane, and isododecane) pyrolysis. The electrostatic potential, charge natural population analysis and molecular structure were discussed under electric fields of various directions and strengths. The chemical reaction kinetics and species were analyzed under a wide range of electrostatic fields and temperatures. The key reaction energy of RP-1 components and motion statistics were discussed. The analysis revealed significant changes in molecular charge density and structure, which predicted possible cracking sites. Cyclohexane and chain alkanes exhibited opposite trends of decomposition rates depending on the field strength and temperature. The different trends were detail analyzed by reaction pathways and product distribution. Newly cracking way appeared under electric field. The decomposition reaction barrier was reduced by the electric field overall. While the motion of molecules was inhibited with the field increasing, which decrease the molecular potential energy. This work conducted a comprehensive analysis about effect of external electric field on the RP-1 mixture fuel pyrolysis. offering a potential solution for improving combustion efficiency.

Production of dimethyl carbonate by gas-phase oxidative carbonylation of methanol over Cu/Y zeolite: Mechanism and kinetics

Dimethyl carbonate (DMC) has become into an appealing fuel additive for reducing the formation of pollutants during combustion and, together with the post-combustion treatment, allowing to fulfill the most stringent environmental regulations. Although the production of this chemical is still an open issue, the oxidative carbonylation of methanol catalyzed by solids and with reactants and products in the gas phase has been proposed to replace the homogeneous commercial process (CuCl in aqueous phase). In this work, we propose the use of a Cu/Y zeolite (prepared by solid-state ion exchange with copper (I) chloride) as alternative catalyst for this purpose, optimizing the reaction conditions and proposing a rigorous kinetic model for this reaction. For accomplishing this aim, gas phase reaction was performed in a continuous fixed-bed reactor. Temperature (100–200 °C) played a critical role in product distribution, DMC being the main product at 120 °C. The influence of different reactant (CH3OH/CO/O2) concentrations on reaction rate and product distribution was determined at 120 °C. The experimental data have been successfully fitted to a kinetic model, derived from the mechanism of the reaction.

Nascent Vibrational Energy Distribution of CS(X1Σ+) Generated in the S(1D) + CS2 Reaction.

The internal energy distributions of reaction products are important information in clarifying the mechanism of chemical reactions. There are few reports of the nascent vibrational energy distribution of CS(X1Σ+) generated in the S(1D) + CS2 reaction. As long as S(1D) is produced by photodissociation of CS2, CS(X1Σ+), as a product of the chemical reaction and as a photoproduct of CS2 is indistinguishable. In this study, S(1D) was generated by the photolysis of OCS at 248 nm, where CS2 hardly dissociates, and CS(X1Σ+) was generated only by the S(1D) + CS2 reaction. The vibrational levels v″ = 0-6 of CS(X1Σ+) were detected with laser-induced fluorescence (LIF) via the A1Π-X1Σ+ transition. The identical time profiles of the LIF intensities showed that all the vibrational levels were produced by the S(1D) + CS2 reaction. The relative nascent vibrational populations of CS(X1Σ+) determined from the area intensities of the excitation spectra are 1.00 ± 0.11/0.58 ± 0.06/0.31 ± 0.03/0.078 ± 0.009/0.013 ± 0.001/<0.002/<0.002 (the values for v″ = 5 and 6 are the upper limits) for v″ = 0/1/2/3/4/5/6. The distribution agrees well with the statistical (prior) distribution.

Numerical simulation of the transient graphite oxidation process based on a dynamic mesh method

The high-temperature gas-cooled reactor uses graphite-matrix spherical fuel elements to coat the tri-structural isotropic fuel particles (TRISO). In accident conditions, graphite oxidation may cause fuel particle exposure, which further leads to severe radioactive contamination. Therefore, it is very important to study the oxidation behavior of graphite during air-ingress accidents. This work aimed to develop a reaction kinetic model of graphite oxidation based on the Institute of Nuclear and New Energy Technology (INET) experiment correlations and to study the transient process of graphite oxidation using computational fluid dynamics and a dynamic mesh method. The results show that convective diffusion and mass diffusion dominate the distribution of reaction products at different flow rates. The reaction rate in the early stage of oxidation was high and then decreased rapidly until the oxygen consumption rate and supplementation rate reached equilibrium. After that, the oxidation rate decreased slowly due to the reduction of graphite surface area. The fluctuating flow around the graphite leads to anisotropic oxygen concentrations at different inflow angles on the graphite surface. The fluctuations caused a non-uniform ellipsoidal graphite structure, in which graphite has a smaller radius of curvature and pits on the windward side and a larger radius of curvature on the leeward side. The oxidation mass of graphite is in good agreement with the INET experimental data, which shows that this study can provide a method for the estimation of the mass and shape of graphite oxidation.

Kinetic Understanding of Catalytic Selectivity and Product Distribution of Electrochemical Carbon Dioxide Reduction Reaction.

CO2 can be electrochemically reduced to different products depending on the nature of catalysts. In this work, we report comprehensive kinetic studies on catalytic selectivity and product distribution of the CO2 reduction reaction on various metal surfaces. The influences on reaction kinetics can be clearly analyzed from the variation of reaction driving force (binding energy difference) and reaction resistance (reorganization energy). Moreover, the CO2RR product distributions are further affected by external factors such as electrode potential and solution pH. A potential-mediated mechanism is found to determine the competing two-electron reduction products of CO2 that shifts from thermodynamics-controlled product formic acid at less negative electrode potentials to kinetic-controlled product CO at more negative electrode potentials. Based on detailed kinetic simulations, a three-parameter descriptor is applied to identify the catalytic selectivity of CO, formate, hydrocarbons/alcohols, as well as side product H2. The present kinetic study not only well explains the catalytic selectivity and product distribution of experimental results but also provides a fast way for catalyst screening.

Electronic and Steric Effects Control Regioselectivity in Alkyne Migratory Insertion during Ni-Catalyzed Indenone Synthesis

Many useful transition-metal-catalyzed reactions depend on the migratory insertion of an alkyne into a metal–carbon bond. Steric effects, electronic effects, and coordinating directing groups have all been shown to control product distributions in reactions in which this is the regioselectivity-determining step. This study describes how both steric and electronic parameters influence regioselectivity within a previously disclosed Ni-catalyzed indenone synthesis reaction. Steric repulsion determines the overall sense of regioselectivity, and to some extent the magnitude, while electronic effects can also significantly alter the magnitude of the observed regioselectivity. The relationship between alkyne insertion regioselectivity and the electronic character of the migrating aryl group is demonstrated via comparisons with established electronic substituent constants (σ+ values). These observations will aid in the understanding and development of other regioselective alkyne carbofunctionalization reactions.

Surface or Internal Hydration - Does It Really Matter?

The precise location of an ion or electron, whether it is internally solvated or residing on the surface of a water cluster, remains an intriguing question. Subtle differences in the hydrogen bonding network may lead to a preference for one or the other. Here we discuss spectroscopic probes of the structure of gas-phase hydrated ions in combination with quantum chemistry, as well as H/D exchange as a means of structure elucidation. With the help of nanocalorimetry, we look for thermochemical signatures of surface vs internal solvation. Examples of strongly size-dependent reactivity are reviewed which illustrate the influence of surface vs internal solvation on unimolecular rearrangements of the cluster, as well as on the rate and product distribution of ion-molecule reactions.

Kinetic and thermodynamic compensation phenomena in C3 and C4 energy crops pyrolysis: Implications on reaction mechanisms and product distributions

This work provides insight into possibilities of maximum utilization of C3-C4 energy crops for thermo-chemical conversion (slow pyrolysis) into high value biochemicals, platform chemicals, drop-in fuels and combustible gases, using coupled kinetic and thermodynamic analyses. In order to examine the kinetics of decomposition of lignocellulosic components, model-free and model-based methods faded from thermal analysis data were used. Thermodynamic compensation was used for explicatory of entropy controlled process, where conformational changes and chemical exchange directly affect the type and distribution of obtained pyrolytic products. It was shown that external variable (i.e. the heating rate/temperature) does not change either an entire reaction mechanism (mechanistic nature of MG and AD pyrolyses) or transition state, but it changes activation enthalpy and activation entropy which lead to differences in terms of heat energy consumption, pyrolysis favorability and thus rates of generation of activated complex among feedstocks. To investigate the interplay of catalysts (present in feedstocks as minerals) and reactants, selective energy transfer (SET) model was applied. The model showed an activity of catalyst with different outputs towards two reactants, lignin part of the structure in MG and 1,8-cineole in AD. It was shown that AD is more convenient for thermal conversion than MG, regarding to lower transformation energy requirement, higher reactivity, as well as much faster accumulation of products.

Facet-dependent peroxo species regulate product distribution and H2O2utilization in CeO2-catalyzed aniline oxidation

We showed that the coordination structure of the Ce sites affects the configuration (and reactivity) of the surface peroxo species in H2O2activation, which determines the product distribution and H2O2utilization in the aniline oxidation reaction.

Comparison of various catalysts in pyrolysis process: A review

The existence of polarity between production and recycling rates, as well as extravagant fossil fuel consumption has has led to the development of waste plastic to fuel conversion technology. Pyrolysis technology shows great potential in recovering liquid oil from plastic waste through thermal and catalytic degradation processes. Catalytic pyrolysis process has advantages over thermal degradation in terms of energy consumption, reaction time and oil grade. The choice of catalyst plays a dominant role in determinating reaction temperature, time, and product distribution. This paper reviews various types of catalysts, including fluid cracking catalyst (FCC), zeolites based catalysts, silica-alumina catalysts, and reforming catalysts, and the impact of various parameters include the mode of contact with plastic solid wastes - direct phase contact of catalyst (either liquid or solid), and vapor phase contact of catalyst, choice of catalyst, catalyst to polymer ratio, and acid-base nature of the catalyst on the product dispersion. The product distribution obtained from catalytic pyrolysis of different types of plastics such as polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinylchloride using ZSM – 5 and red mud catalysts at different temperatures are as follows: 56.9 wt%(liquid), 40.4 wt%(gases), 3.2 wt%(char) at 450 0C in the presence of 10 wt% of Zeolite Socony Mobil − 5 (ZSM – 5) catalyst and 57 wt% (liquid), 41.3 wt% (gases), 1.7 wt% (char) at temperature 500 0C in the presence of 10 wt% of red mud as a catalyst. When catalytic pyrolysis is applied to municipal plastic waste (a heterogenous plastic waste) using 50% natural zeolite as a catalyst at 450 0C the distribution is 50 wt% (liquid), 34 wt% (gases), and 16 wt% of char Although there is a negligible difference in the product distribution of thermoplastics, the use of red mud as a catalyst results in increased energy consumption., highlighting the impact of the acidic and basic characteristics of catalysts. In case of heterogenous feedstock i.e., mixed plastic highly acidic catalysts are used to achieve the desired product distribution.

13C NMR study of amino acid salts in facilitated transport membranes for post-combustion carbon capture

Some of amino acid salts (AASs) have been demonstrated to be effective mobile carriers in facilitated transport membranes (FTMs) to achieve superior CO2 permeance and CO2/N2 selectivity for CO2 capture from flue gas. Understandings of how the structures of different AASs affect the chemistry of the amine–CO2 reaction are essential for the future development of more efficient AAS mobile carriers. In this study, the reaction chemistry of selected AASs with CO2 was investigated by 13C nuclear magnetic resonance (NMR) spectroscopy. The CO2 loading and the distribution of major reaction products, including carbamate and bicarbonate products of each studied AAS were quantitatively analyzed. The positive correlation between the CO2 loading of AAS (mol CO2/g AAS) and the CO2 permeance of FTMs suggested that AAS with a higher CO2 loading may improve the performance of FTMs. Our results also showed that increasing the steric hindrance of AAS could be a practical way to promote the bicarbonate reaction pathway and thus potentially increase the CO2 loading (mol CO2/mol AAS). Moreover, 2-(1-piperazinyl)ethylamine (PZEA) was found to be a more effective multi-amine than piperazine (PZ) for synthesizing AASs due to the presence of more effective nitrogen sites per molecule. The superior CO2 permeance of the PZEA-Sar membrane is also attributed to its more uniform membrane formation. The knowledge gained from this study will inform the rational design of more effective AAS carriers for CO2 capture.

Inline spectroscopic measurements and LES of competitive consecutive reaction in a confined liquid jet in coflow

Dynamic inline spectroscopic measurements and Large Eddy Simulation (LES) observe the products of a competitive-consecutive test reaction system within a well-characterized coaxial flow. The test reaction is a competitive consecutive chemistry which produces two spectrophotometrically measurable products. For the first time, these products are measured spatially throughout the reactor. Experimental and computational results map the reaction progress and product distribution. The evolution of this chemical process is explained in terms of the inlet, jet, and pipe flow regimes of the confined jet. The inlet and jet regimes were demonstrated to produce the majority of the desired product, whereas the undesired product is predominantly generated in the pipe regime.

Catalytic upgradation of crude glycerol to produce bio-based aromatics over hierarchical MFI zeolite: Effect of bimodal hierarchical porosity enhancement and porosity-acidity interaction

The transformation of renewable biomass derived crude glycerol into value-added BTX aromatics is an attractive approach to facilitate carbon neutrality and recycling economy. Herein, two kinds of hierarchical HZSM-5 with distinct hierarchical porosity and acidity distribution were synthesized based on a seed-induced method by utilizing CTAB and TPOAC as soft mesoporogens, respectively. And the effects of bimodal hierarchical porosity and porosity-acidity interaction on the upgradation efficiency during the conversion of crude glycerol over hierarchical HZSM-5 were investigated. The abundant intra-mesopores and promoted porosity-acidity interaction in hierarchical HZSM-5 facilitated the transformation of macromolecules in crude glycerol into small oxygenated chemicals and olefins, resulting in higher BTX yield and longer catalyst lifetime. Among all catalysts, the hierarchical HZSM-5 sample templated with TPOAC exhibited the maximum carbon yields of BTX (38.5%) and longest lifetime (23 h) due to the better interconnectivity of shape-selective micropores and high mass transfer intra-mesopores. The reaction route and product distribution of upgradation of crude glycerol was strongly dependent on the morphology, bimodal hierarchical porosity and acidity variation resulting from the generation of intra-mesopores in HZSM-5 catalysts by the usage of different soft mesoporogens. The liquid route and side alkylation reaction was accelerated over HZSM-5/TPOAC catalyst while the gas route and secondary coking reaction was promoted over HZSM-5/CTAB sample.

Auto‐thermal chemical looping combustion of sulphur with Fe2O3 oxygen carriers for sulphuric acid production: Thermodynamics

AbstractChemical looping is a novel fuel conversion and material separation technology. It can be applied to obtain sulphur through selective oxidation of H2S. Further, chemical looping combustion (CLC) of sulphur can generate SO2 with a high concentration without NOx formation. The high SO2 concentration is adjustable and facilitates large‐scale H2SO4 production. In this study, we examined the thermodynamics of the CLC of sulphur for H2SO4 production, which has not been reported previously. We analyzed the effects of reactor temperature and sulphur to Fe2O3 oxygen carrier (OC) ratios on sulphur allotrope transformations and on the distributions of reaction products. Moreover, the reactors were operated auto‐thermally. Based on this design, we examined the effects of fuel reactor (FR) and air reactor temperatures on the minimum recirculation of the OC, as well as the gas and solid products and heat released from the air reactor. Our results showed that the CLC of sulphur with Fe2O3 OC could occur through an auto‐thermal process. The FR in a sulphur CLC system should be operated over a temperature range of 800–950°C, with an Fe2O3 OC recirculation between 45 and 143 kg/kgS(s). Furthermore, when the FR was operated in the auto‐thermal mode, we achieved 100% SO2 conversion. The findings of this study may be applied to reactor design for large‐scale H2SO4 production through CLC of sulphur.

Alkali -silica reaction and its dynamic relationship with cement pore solution in highly reactive systems

Despite extensive research, the relationship between the progression of alkali-silica reaction (ASR) and the cement hydration mechanism, particularly the influence of the pore solution composition on the nature of reaction products is not thoroughly understood. A multi-analytical approach was applied to study ASR mechanism under accelerated conditions using a mortar system comprising of fused silica aggregates. For the first time, large field SEM mapping was used to correlate physical expansion with the composition, distribution and amount of ASR reaction products produced over time. A three-stage behavioral model was proposed to explain the dynamic relationship between ASR progression and pore solution composition. The results confirmed the co-existence of two phases within the ASR products: a CSH- type gel and an ASR-type gel. The relative abundance of one gel type over the other was dictated by their accessibility to the pore solution, which in turn influences how ASR propagates through the microstructure.

Solvent Deuterium Isotope Effects of Substrate Reduction by Nitrogenase from Azotobacter vinelandii.

The mechanism of nitrogenase, the enzyme responsible for biological nitrogen fixation, has been of great interest for understanding the catalytic strategy utilized to reduce dinitrogen to ammonia under ambient temperatures and pressures. The reduction mechanism of nitrogenase is generally envisioned as involving multiple cycles of electron and proton transfers, with the known substrates requiring at least two cycles. Solvent kinetic isotope effect experiments, in which changes of reaction rates or product distribution are measured upon enrichment of solvent with heavy atom isotopes, have been valuable for deciphering the mechanism of complex enzymatic reactions involving proton or hydrogen transfer. We report the distribution of ethylene, dihydrogen, and methane isotopologue products measured from nitrogenase-catalyzed reductions of acetylene, protons, and cyanide, respectively, performed in varying levels of deuterium enrichment of the solvent. As has been noted previously, the total rate of product formation by nitrogenase is largely insensitive to the presence of D2O in the solvent. Nevertheless, the incorporation of H/D into products can be measured for these substrates that reflect solvent isotope effects on hydrogen atom transfers that are faster than the overall rate-determining step for nitrogenase. From these data, a minimal isotope effect is observed for acetylene reduction (1.4 ± 0.05), while the isotope effects for hydrogen and methane evolution are significantly higher at 4.2 ± 0.1 and 4.4 ± 0.1, respectively. These results indicate that there are pronounced differences in the sensitivity to isotopic substitution of the hydrogen atom transfer steps associated with the reduction of these substrates by nitrogenase.

Day-night alternation and effect of sulfate ions on photodegradation of triclosan in water

Photodegradation is an essential process for the in-stream elimination of triclosan (TCS). There are still some knowledge gaps concerning reaction kinetics, pathways, and transformation products, which are important for understanding the environmental fate of TCS. For example, the effects of ionic strength and day-night alternation on TCS photodegradation have been barely considered in previous studies. To fill these gaps, this study assesses the effect of sulfate ions (SO42−) on the photodegradation of TCS under day-night shifts. Compound-specific carbon and chlorine isotope analysis were applied to characterize different bond-cleavage pathways. Moreover, variations in TCS reaction products distribution were analyzed by using Fourier transform ion cyclotron resonance mass spectrometry. A numerical model was developed to describe the concentration and stable carbon isotopic evolution of TCS under different conditions. Based on the observed experimental data, we show that SO42− can affect the kinetics and product distribution during the photodegradation of TCS. In particular, sulfate ions (100 mM) inhibited the yield of the toxic product, 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD). Furthermore, day-night alternations lead to different predominant bond-cleavage pathways depending on sulfate concentration. By so doing, we propose a realistic framework for the direct photodegradation of TCS in sunlit natural surface waters.

An efficient and mild recycling of waste melamine formaldehyde foams by alkaline hydrolysis

Melamine formaldehyde foam (MFF) generates many poisonous chemicals through the traditional recycling methods for organic resin wastes. Herein, a high MFF degradation ratio of ca. 97 wt.% was achieved under the mild conditions (160 °C) in a NaOH–H2O system with ammelide and ammeline as the main degradation products. The alkaline solvent had an obvious corrosion effect for MFF, as indicated by scanning electron microscopy (SEM). The reaction process and products distribution were studied by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (NMR). Besides, the MFF degradation products that have the similar chemical structures and bonding performances to those of melamine can be directly used as the raw material for synthesis of melamine urea-formaldehyde resins (MUFs). Moreover, the degradation system demonstrated here showed the high degradation efficiency after reusing for 7 times. The degradation process generated few harmful pollutants and no pre- or post-treatments were required, which proves its feasibility in the safe removal or recovery of waste MFF.

Selectivity control of furfuryl alcohol upgrading to 1,5-pentanediol over hydrotalcite-derived Ni-Co-Al catalyst

1,5-pentanediol (1,5-PeD) is a value-added chemical that can be produced from furfuryl alcohol (FFA) via selective scission of CO bond coupled with following hydrogenation reaction. In this work, a series of hydrotalcite-derived Ni-Co-Al catalysts with different Ni/Co ratios were evaluated for FFA upgrading to 1,5-PeD at a temperature range of 413–473 K and hydrogen pressure from 2 to 5 MPa. The catalytic performance and reaction products distribution were found to be highly sensitive to the Ni/Co ratio in the catalysts as well as reaction conditions. The highest catalytic activity was achieved with the Ni-Co-Al catalyst at a Ni/Co atomic ratio of 1:11 (Ni1Co11Al), which attained a 1,5-PeD yield of 42.5 % after 4 h of reaction. The presence of Ni in the Ni1Co11Al catalyst could significantly improve the BET surface area and suppress the growth of metal nanoparticles, leading to its superior catalytic stability in 5 runs. According to the characterization results, it was supposed that hydrogen spillover occurred from the surface of Ni to that of Co species, which was expected to enhance the hydrogen adsorption/activation capability and surface H concentration. The rapid H transfer was beneficial to the hydrogenolysis of furan ring and in situ hydrogenation of reaction intermediates, thus greatly facilitating the activity of the catalyst. Based on the experimental and characterization results, a plausible reaction mechanism was proposed for the selective generation of 1,5-PeD from FFA over the Ni1Co11Al catalyst. The results attained in this paper demonstrated the possibility of using non-precious mixed metal catalyst for FFA upgrading, and could provide useful insights for the design of efficient catalysts.

Cobalt-Graphene Catalyst for Selective Hydrodeoxygenation of Guaiacol to Cyclohexanol.

Herein, cobalt-reduced graphene oxide (rGO) catalyst was synthesized with a practical impregnation–calcination approach for the selective hydrodeoxygenation (HDO) of guaiacol to cyclohexanol. The synthesized Co/rGO was characterized by transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM (HAADF-STEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), and H2 temperature-programmed reduction (H2-TPR) analysis. According to the comprehensive characterization results, the catalyst contains single Co atoms in the graphene matrix and Co oxide nanoparticles (CoOx) on the graphene surface. The isolated Co atoms embedded in the rGO matrix form stable metal carbides (CoCx), which constitute catalytically active sites for hydrogenation. The rGO material with proper amounts of N heteroatoms and lattice defects becomes a suitable graphene material for fabricating the catalyst. The Co/rGO catalyst without prereduction treatment leads to the complete conversion of guaiacol with 93.2% selectivity to cyclohexanol under mild conditions. The remarkable HDO capability of the Co/rGO catalyst is attributed to the unique metal–acid synergy between the CoCx sites and the acid sites of the CoOx nanoparticles. The CoCx sites provide H while the acid sites of CoOx nanoparticles bind the C-O group of reactants to the surface, allowing easier C-O scission. The reaction pathways were characterized based on the observed reaction–product distributions. The effects of the process parameters on catalyst preparation and the HDO reaction, as well as the reusability of the catalyst, were systematically investigated.