Steam reforming of acetic acid over Ni/biochar of low metal-loading:Involvement of biochar in tailoring reaction intermediates renders superior catalytic performance

Biochar is a reactive carrier as it may be partially gasified with steam in steam reforming,which could influence the formation of reaction intermediates and modify catalytic behaviors.Herein,the Ni/biochar as well as two comparative catalysts,Ni/Al_(2)O_(3) and Ni/SiO_(2),with low nickel loading(2%(mass))was conducted to probe involvement of the varied carriers in the steam reforming.The results indicated that the Ni/biochar performed excellent catalytic activity than Ni/SiO_(2) and Ni/Al_(2)O_(3),as the biochar carrier facilitated quick conversion of the -OH from dissociation of steam to gasify the oxygen-rich carbonaceous intermediates like C=O and C-O-C,resulting in low coverage while high exposure of nickel species for maintaining the superior catalytic performance.In converse,strong adsorption of aliphatic intermediates over Ni/Al_(2)O_(3) and Ni/SiO_(2) induced serious coking with polymeric coke as the main type(21.5%and 32.1%,respectively),which was significantly higher than that over Ni/biochar(3.9%).The coke over Ni/biochar was mainly aromatic or catalytic type with nanotube morphology and high crystallinity.The high resistivity of Ni/biochar towards coking was due to the balance between formation of coke and gasification of coke and partially biochar with steam,which created developed mesopores in spent Ni/biochar while the coke blocked pores in Ni/Al_(2)O_(3) and Ni/SiO_(2) catalysts.

Mechanistic insights into the active intermediates of 2,6-diaminopyridine dinitration

Mechanistic understanding of the active intermediates of 2,6-diaminopyridine(DAP) dinitration in the concentrated nitric-sulfuric acid system is of crucial importance for the selectivity control of target product, i.e., 2,6-diamino-3,5-dinitropyridine(DADNP). The active intermediates determining the product selectivity are theoretically studied. The HSO_(4)^(-)-NO_(2)^(+) complex is proposed as the dominant active nitrating intermediate for the first time, which shows low energy barrier(i.e., 10.19 kcal·mol^(-1),1 kcal = 4.186 k J) for direct dinitration of DAP to DADNP. The formed water during the reaction results in not only the formation of less active SO_(4)^(2-)-NO_(2)^(+) complex, but also the occurance of DAP sulfonation(DAP-SO_(3)H intermediate)to facilitate the formation of mononitration byproduct. Meanwhile, the accompanied thermal effects cause the generation of undesirable pyridine-NHNO_(2) intermediate, which is difficult to be rearranged to yield DADNP, inhibiting the reaction and thus giving low DAP conversion. The insights reported here elucidates the importance of thermal effects elimination and water content control, confirmed experimentally in the batch-and micro-reaction systems.

High Performance Hydrophobic Interaction Chromatography-A New Approach to Separate Intermediates of Protein Folding──Ⅰ.Separation of Intermediates of Urea-unfolded α-Amylase

Based on the different hydrophobicities of the intermediates of proteins the various conformational intermediates of the refolding of a-amylase originally denatured with 8.0 mol/L urea solution were separated with high performance hydrophobic interaction chromatography(HPHIC). Compared to the separation of the same intermediates with weak anion exchange chromatography and size-exclusion chromatography the result obtained with HPHIC is the best It would be expected that HPHIC may be a strongly potential tool to separate intermediates of some proteins which cannot be, or cannot completely be refolded by HPHIC.

Chlorobenzene degradation by electro-heterogeneous catalysis in aqueous solution:intermediates and reaction mechanism

This study was performed to investigate the variables that influence chlorobenzene (CB) degradation in aqueous solution by electro-heterogeneous catalysis.The effects of current density,pH,and electrolyte concentration on CB degradation were determined.The degradation effciency of CB was almost 100% with an initial CB concentration of 50 mg/L,current density 15 mA/cm2,initial pH 10,electrolyte concentration 0.1 mol/L,and temperature 25°C after 90 min of reaction.Under the same conditions,the degradation eff...

Steam reforming of acetic acid over Ni-Ba/Al2O3 catalysts:Impacts of barium addition on coking behaviors and formation of reaction intermediates

The influence of barium addition to a Ni/Al2O3 catalyst on the reaction intermediates formed,the activity,resistance of the catalyst to coking,and properties of the coke formed after acetic acid steam reforming were investigated in this study.The results showed the drastic effects of barium addition on the physicochemical properties and performances of the catalyst.The solid-phase reaction between alumina and BaO formed BaAl2O4,which re-constructed the alumina structure,resulting in a decrease in the specific surface area and an increase in the resistance of metallic Ni to sintering.The addition of barium was also beneficial for enhancing the catalytic activity,resulting from the changed catalytic reaction network.The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study of the acetic acid steam reforming indicated that barium could effectively suppress the accumulation of the reaction intermediates of carbonyl,formate,and C=C functional groups on the catalyst surface,attributed to its relatively high ability to cause the gasification of these species.In addition,coking was considerably more significant over the Ba-Ni/Al2O3 catalyst.Moreover,the Ba-Ni/Al2O3 catalyst was more stable than the Ni/Al2O3catalyst,owing to the distinct forms of coke formed (carbon nanotube form over the Ba-Ni/Al2O3 catalyst,and the amorphous form over the Ni/Al2O3 catalyst).

Computational Characterization of Reactive Intermediates of Carbon Monoxide Dehydrogenase

The catalytic oxidation of CO to CO2 by carbon monoxide dehydrogenases has been explored theoretically, and a large C-cluster model including the metal core [Ni-4Fe-4S] and surrounding residues and crystal water molecules was used in density functional calculations. The key species involved in the oxidation of CO at the C-cluster, Cred1, Cred2 and Cint, have been elucidated. On the basis of computational results, the plausible enzymatic mechanism for the CO oxidation was proposed. In the catalytic reaction, the first proton abstraction from the Fe（1）-bound water leads to a precursor to accommodate CO binding and the subsequently consecutive proton transfers from the metal-bound carboxylate to the amino acid residues facilitate the release of CO2. The hydrogen-bond network around the C-cluster formed by conserved residues His93, His96, Glu299, Lys563, and four water molecules in the active domain plays an important role in proton transfer and intermediate stabilization. Predicted geometries of key species show good agreement with the reported crystal structures.

Regulating the radical intermediates by conjugated units in covalent organic frameworks for optimized lithium ion storage

Organic active units often transform into radical intermediates during the redox processes but exhibit poor cycling stability due to the uncontrollable redox of the radicals. Herein, we report a facile and efficient strategy to modulate the molecular orbital energies, charge transport capacities, and spin electron densities of the active units in covalent organic frameworks(COFs) via regulating the conjugated unit size to optimize the redox activity and stability of the organic radicals. COFs based on different imide conjugated units exhibit tunable discharge voltages, rate performance and cycling stabilities. Detailed characterizations and theoretical calculation reveal that imide radicals are the important active intermediates during the redox processes of these COFs. Specifically, increasing the size of the imide conjugated units could effectively delocalize the radical electrons and improve the stability of the COFs electrodes. This study offers a very effective strategy to modulate the redox chemistry of organic materials for electrochemical energy storage.

FREE RADICAL INTERMEDIATES THEIR POLARIZATION DURING REDOX PROCESSES OF BILE PIGMENTS

The investigation of bile pigments (bilirubin (BR), biliverdin (BV), purpurin (Pu), choletelin (Ch) etc.) by cyclic voltammetry, in-situ rapid scanning thin layer spectroelectrochemistry and ESR spectroscopy indicates that many free radical intermediates and polymers are produced during oxidation and reduction processes.

Adsorption of cyclohexene and its dehydrogenation intermediates on nAu/Pt(100)(n = 0, 1, 2) surfaces: A DFT study

Adsorption of cyclohexene and its dehydrogenation intermediates on the nAu/Pt（100） （n = 0, 1, 2 means clean Pt, one monolayer and two layers of Au covered Pt surfaces, respectively.） has been investigated by self-consistent （GGA-PW91） density functional theory combined with periodic slab model. It is found that on the clean platinum, there are two kinds of favorable adsorption sites, i.e., hollow sites and bridge sites, and the adsorption energy at the hollow site is larger than that at the bridge site. However, on the Au/Pt and 2Au/Pt surfaces, there are three kinds of adsorption sites, and the adsorption energies are alike at both the bridge site and the top site. The magnitude order of the adsorption energies is as follows： clean Pt Au/Pt 2Au/Pt. The configurations of cyclohexene molecule have been distorted a little during the geometry optimizations. The lengths of C–M （M = Pt or Au, on the top layer of the slab） bonds are closely related to the corresponding adsorption energies.

DETECTION OF INTERMEDIATES IN REACTION BETWEEN N , N'-DI (P-METHYL) PHENYL MONOTHIOXAMIDES AND 1, 3-DIAMINE TRIMETHYLENE USING RAMAN SPECTROSCOPY

Reman spectroscopy is used as a tool to monitor the reaction between N,N'-di(pmethyl)monothioxamides and 1,3-diamine trimethylene and to detect the reaction intermediate. By observing changes of 1024 cm^(-1) C=S band and appearance of a new bend at around 1720 cm^(-1), the reaction mechanism is discussed.

PHOTOCHEMICAL[2+2]CYCLOADDITION VIA RADICAL ION INTERMEDIATES.A CIDNP EVIDENCE

The photochemical[2+2]cycloaddition reaction of carbonyl compunds and alkenes was studied by photochemical induced dynamic nuclear spin polarization.

How Trade Liberalization of Intermediates Contributes to China's Technology Upgrade

Under a heterogeneous firm analysis framework,this paper creates a theoretical model to investigate how trade liberalization of intermediates influences the technology choice of firms based on the data of Chinese manufacturers during 2000-2006.According to our empirical result,after China's WTO entry,trade liberalization of intermediates significantly induced Chinese exporters to apply advanced technologies.In our further consideration of the differentiated productivity of firms,we found that such an effect is related to the initial productivity of firms and only significantly induces mediumproductivity firms to upgrade their technologies.In addition,the technology-promotion effect of trade liberalization of intermediates is the most significant for technology-intensive exporters and the least significant for labor-intensive exporters.

Intermediates transformation for efficient perovskite solar cells

Perovskite materials have made a great progress in terms of the power conversion efficiency(PCE), rising from 3.8% to 25.2%. To obtain pinhole-free, superior crystal, and high-quality perovskite films with less defect, intermediates transformation is important, which has been clearly studied and widely applied.In this review, we systematically summarize the commonly formed intermediates and detailedly analyze their mechanisms from five aspects:(1) Solvent-induced intermediate;(2) HI-induced intermediate;(3)CH3NH2-induced intermediate;(4) MAAc-induced intermediate;(5) other intermediates. Finally, we also provide some prospects on high-quality perovskite fabrication based on using intermediates prudently.

In-situ monitoring of dynamic behavior of catalyst materials and reaction intermediates in semiconductor catalytic processes

Semiconductor photocatalysis, as a key part of solar energy utilization, has far-reaching implications for industrial, agricultural, and commercial development. Lack of understanding of the catalyst evolution and the reaction mechanism is a critical obstacle for designing efficient and stable photocatalysts. This review summarizes the recent progress of in-situ exploring the dynamic behavior of catalyst materials and reaction intermediates. Semiconductor photocatalytic processes and two major classes of in-situ techniques that include microscopic imaging and spectroscopic characterization are presented. Finally, problems and challenges in in-situ characterization are proposed, geared toward developing more advanced in-situ techniques and monitoring more accurate and realistic reaction processes, to guide designing advanced photocatalysts.

Rational Manipulation of Intermediates on Copper for CO_(2)Electroreduction Toward Multicarbon Products

Excess greenhouse gas emissions,primarily carbon dioxide(CO_(2)),have caused major environmental concerns worldwide.The electroreduction of CO_(2)into valuable chemicals using renewable energy is an ecofriendly approach to achieve carbon neutrality.In this regard,copper(Cu)has attracted considerable attention as the only known metallic catalyst available for converting CO_(2)to high-value multicarbon(C_(2+))products.The production of C_(2+)involves complicated C-C coupling steps and thus imposes high demands on intermediate regulation.In this review,we discuss multiple strategies for modulating intermediates to facilitate C_(2+)formation on Cu-based catalysts.Furthermore,several sophisticated in situ characterization techniques are outlined for elucidating the mechanism of C-C coupling.Lastly,the challenges and future directions of CO_(2)electroreduction to C_(2+)are envisioned.

Stabilization and detection of labile reaction intermediates in supramolecular containers

Detection and observation of reactive intermediates is an essential step in investigation of reaction pathways.However,most reactive intermediates are unstable and present at low concentrations;their short lifetimes make them difficult to detect and characterize.Supramolecular containers offer opportunities for the stabilization and characterization of those labile species,through isolation from the media and protection inside the cavity of the host.In this review,we summarize the examples of labile reaction intermediates that are stabilized and characterized with the help of supramolecular containers.The container compounds include carcerands,deep cavitands and amide naphthotubes.We focus on unstable guest species-cyclobutadiene,benzocyclopropenone,o-benzyne,1,2,4,6-cycloheptatetraene,anti-Bredt's olefin,fluorophenoxycarbene,O-acylisoamide,and hemiaminalthat act as intermediates in certain organic reactions.

Mg-Al-hydrotalcite with alkaline sites protects Ni/KIT-6 from formation of amorphous coke in glycerol steam reforming via tailoring reaction intermediates

During steam reforming,the performance of a catalyst and amount/property of coke are closely related to reaction intermediates reaching surface of a catalyst.Herein,modification of reaction intermediates by placing Mg-Al-hydrotalcite above Ni/KIT-6 catalyst in steam reforming of glycerol was conducted at 300 to 600°C.The results revealed that the catalytic activity of Ni/KIT-6 in the lower bed was enhanced with either Mg1-Al5-hydrotalcite(containing more acidic sites)or Mg5-Al1-hydrotalcite(containing more alkaline sites)as upper-layer catalyst.The in situ infrared characterization of steam reforming demonstrated that Mg-Al-hydrotalcite catalyzed the deoxygenation of glycerol,facilitating the reforming of the partially deoxygenated intermediates over Ni/KIT-6.Mg-Al-hydrotalcite as protective catalyst,however,did not protect the Ni/KIT-6 from formation of more coke.Nonetheless,this did not lead to further deactivation of Ni/KIT-6 while Mg5-Al1-hydrotalcite even substantially enhanced the catalytic stability,even though the coke was much more significant than that in the use of single Ni/KIT-6(52.7%vs.28.6%).The reason beneath this was change of the property of coke from more aliphatic to more aromatic.Mg5-Al1-hydrotalcite catalyzed dehydration of glycerol,producing dominantly reaction intermediates bearing C=C,which formed the catalytic coke of with carbon nanotube as the main form with smooth outer walls as well as higher aromaticity,C/H ratio,crystallinity,crystal carbon size,thermal stability,and resistivity toward oxidation on Ni/KIT-6 in the lower bed.In comparison,the abundance of acidic sites on Mg1-Al5-hydrotalcite catalyzed the formation of more oxygen-containing species,leading to the formation of carbon nanotubes of rough surface on Ni/KIT-6.

Advances in Intermediates for the Solution-Processing of Perovskite Films

Owing to its superior efficiency and low cost,the solution-processable perovskite has rapidly become the latest favorite material in the field of photovoltaics.Although solution processing significantly reduces the threshold and cost of perovskite solar cells,the intricate composition and nonequilibrium nucleation of the perovskite precursor can result in leaky film.The precise control of perovskite nucleation and orientation is a fundamental prerequisite for achieving high-quality perovskite photoactive layers.In this process,the intermediate species that widely exists either in the precursor or the asprepared film acts as a transitional state for perovskite nucleation and growth from solution to solid,presenting an opportunity for controlling perovskite crystallization.Herein,we present an overview of the advancements in intermediates for solution-processing perovskite films to gain insights into the growth and manipulation of polycrystalline perovskite films.

Strategic regulation of nitrogen-containing intermediates for enhanced nitrate reduction over Co_(3)O_(4)/SiC catalyst having multiple active centers

Regulating the intermediates involved in the electrocatalytic nitrate reduction reaction(NO_(3)RR)is crucial for the enhancement of reaction efficiency.However,it remains a great challenge to regulate the reaction intermediates through active site manipulation on the surface of the catalyst.Here,a family of n%-Co_(3)O_(4)/SiC(n=5,8,12,20)catalysts with a delicate percentage of Co^(2+)and Co^(3+)were prepared for NO_(3)RR.We found that Co^(3+)primarily acts as the active site for NO_(3)^(−)reduction to NO_(2)^(−),while Co^(2+)is responsible for the conversion of NO_(2)^(−)to NH_(3).Moreover,the conversion of these intermediates over the active sites is autonomous and separately controllable.Both processes synergistically accomplish the reduction of nitrate ions to synthesize ammonia.Combining the experimental studies and density functional theory(DFT)calculations,it is discovered the pathway(^(*)NHO→^(*)NHOH→^(*)NH_(2)OH→^(*)NH_(2)→^(*)NH_(3))is more favorable due to the lowerΔG value(0.25 eV)for the rate-limiting step(^(*)NO→^(*)NHO).The NH_(3)yield rate of 8%-Co_(3)O_(4)/SiC reached 1.08 mmol/(cm^(2)h)with a Faradaic efficiency of 96.4%at−0.89 V versus the reversible hydrogen electrode(RHE),surpassing those of most reported non-noble NO_(3)RR catalysts.This strategy not only provides an efficient catalyst for NO_(3)RR but also serves as an illustrative model for the regulation of multi-step reaction intermediates through the design of distinct active sites,thereby presenting a new approach to enhance the efficiency of intricate reactions.

Multiple evaluations of atmospheric behavior between Criegee intermediates and HCHO: Gas-phase and air-water interface reaction

Given the high abundance of water in the atmosphere,the reaction of Criegee intermediates(CIs)with(H_(2)O)_(2) is considered to be the predominant removal pathway for CIs.However,recent experimental findings reported that the reactions of CIs with organic acids and carbonyls are faster than expected.At the same time,the interface behavior between CIs and carbonyls has not been reported so far.Here,the gas-phase and air-water interface behavior between Criegee intermediates and HCHO were explored by adopting high-level quantum chemical calculations and Born-Oppenheimer molecular dynamics(BOMD)simulations.Quantum chemical calculations evidence that the gas-phase reactions of CIs+HCHO are submerged energy or low energy barriers processes.The rate ratios speculate that the HCHO could be not only a significant tropospheric scavenger of CIs,but also an inhibitor in the oxidizing ability of CIs on SO_(x) in dry and highly polluted areas with abundant HCHO concentration.The reactions of CH_(2)OO with HCHO at the droplet’s surface follow a loop structure mechanism to produce i)SOZ(■),ii)BHMP(HOCH_(2)OOCH_(2)OH),and iii)HMHP(HOCH_(2)OOH).Considering the harsh reaction conditions between CIs and HCHO at the interface(i.e.,the two molecules must be sufficiently close to each other),the hydration of CIs is still their main atmospheric loss pathway.These results could help us get a better interpretation of the underlying CIs-aldehydes chemical processes in the global polluted urban atmospheres.