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Careful analysis of the crystals formed in the reduction of AriPr8AlI2 (AriPr8=C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2) with sodium on sodium chloride showed them to contain the long sought-after dialuminene AriPr8AlAlAriPr8 (1) that forms alongside the previously characterized alanediyl :AlAriPr8. The single crystal X-ray structure of 1 revealed a nearly planar, trans-bent C(ipso)AlAlC(ipso) core with an Al-Al distance of 2.648(2) Å. The molecular and electronic structure of 1 are consistent with an Al-Al double dative interaction augmented with diradical character and stabilized by dispersion interactions. Density functional theory calculations showed that the reactivity of :AlAriPr8 with dihydrogen involves 1, not :AlAriPr8, as the reactive species. In contrast, the reaction of :AlAriPr8 with ethylene gave two products, the 1,4-dialuminacyclohexane AriPr8Al(C2H4)2AlAriPr8 (2) and the aluminacyclopentane AriPr8Al(C4H8) (3), that can both form from the aluminacyclopropane intermediate AriPr8Al(C2H4). Although the [2+2+2] cycloaddition of 1 with two equivalents of ethylene was also calculated to be exergonic, it is likely to be kinetically blocked by the numerous isopropyl substituents surrounding the Al-Al bond. Attempts to fine-tune the steric bulk of the terphenyl ligand to allow stronger Al-Al bonding were unsuccessful, leading to the isolation of the sodium salt of a cyclotrialuminene, Na2[AlAriPr6]3 (4), instead of AriPr6AlAlAriPr6.

To investigate the explosion pressure characteristics of methane-acetylene gas mixtures, explosion pressure evolution curves of methane-acetylene mixture gas under different equivalent ratio and doping ratio was obtained by using a 20L spherical explosion test system. The variation in intermediate reactions during the explosion process was studied through numerical simulation. Parameters such as peak reaction pressure (Pmax), maximum pressure rise rate (dp/dt)max, and combustion duration (tc) were obtained for the gas mixture to analyse the rates of production(ROP) and reaction pathways. The results show that the explosive process of the gas mixture becomes more intense with increasing acetylene volume fraction. Furthermore, according to the acetylene volume fraction of 35% and 80%, the premixed system is divided into three combustion stages: methane combustion stage (I), transition stage (II) and acetylene combustion stage (III). Chemical kinetics analysis based on the USC Mech 2.0 mechanism showed that the addition of acetylene accelerated reactant consumption time, significantly promoted O*-containing elementary reactions during the reaction process, shortened the number of reaction path levels of methane, and therefore promoted the forward progress of the mixed combustible gas reaction and enhanced the intensity of the reaction. The results of the phase division of methane-acetylene mixture gas are of great significance to the accidental explosion suppression of various kinds of leakage in industrial production. [ABSTRACT FROM AUTHOR]

N-heterocyclic carbenes (NHCs) are effective organocatalysts, which are widely used in various cycloaddition reactions. Among them, the [3 + 3] cycloaddition reaction type can be used for the synthesis of six-membered ring, which is also one of the most important methods for the formation of carbon–carbon bonds in organic chemistry. In this paper, a possible reaction pathway for the stereoselective [3 + 3] cycloaddition of bromoenal and β-tetralone have been investigated at the M06-2X/6–31G(d,p)/IEFPCM(THF) level. Our suggested mechanism includes binding of the NHC to bromoenal, 1,2-proton transfer, debromination, 1,3-proton shift, Michael addition, protonation, deprotonation and cyclisation, and NHC regeneration. The stereochemistry of the reaction is determined by the Michael addition step, and the favourable pathway generates the R-configurational dihydropyranone. Furthermore, through the use of global reactivity indexes (GRIs), we are able to demonstrate that the nucleophilicity of the bromoenal is increased by the NHC. The mechanistic insights gained in this work should be helpful in the rational design of potential catalysts for analogous reactions. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Amidst the pressing environmental challenges posed by the prevalent reliance on fossil fuels, it becomes imperative to seek sustainable alternatives and prioritize energy efficiency. Electrocatalysis, which is renowned for its high efficiency and environmental friendliness, has garnered significant attention. Rare earth elements (REEs), distinguished by their unique electronic and orbital structures, play a crucial role in electrocatalysis. The strategic integration of REEs into catalysts allows for the fine‐tuning of atomic structures, which in turn, significantly boosts catalytic performance. Despite substantial advancements in rare earth‐based materials for electrocatalysis, a comprehensive overview of the regulatory mechanisms involving REEs is lacking. In this mini‐review, we systematically explore the regulatory mechanisms of REEs within electrocatalysts and their pivotal roles in essential electrocatalytic processes such as the CO2 reduction reaction, oxygen reduction reaction, and hydrogen evolution reaction. We commence with an elucidation of REEs, proceed to delineate their regulatory impacts on electrocatalysts and delve into their applications in key electroreduction reactions. We conclude with discussions on current limitations and prospects for further advancements in this burgeoning field of research. Key Scientists: [ABSTRACT FROM AUTHOR]

The double aim of leveraging the oxy-fuel combustion to turn environmental pollution of post-harvest metal-rich biomass into environmental benignity and lessen dependence on fossil fuels remains poorly elucidated. This study compared the oxy-fuel versus traditional air combustions of water lettuce (Pistia stratiotes L.) (WL) biomass. The decomposition behavior, gas emission pattern, and ash morphology and mineral transformation of the WL combustion were characterized via the coupling of thermogravimetry, scanning electron microscopy, X-ray fluorescence, X-ray diffraction, and Fourier transform infrared spectroscopy. The WL combustion process consisted of water vaporization, combustion of gaseous substances, and mineral breakdown. Since WL was rich in Cl, alkali metal chlorides volatilized at above 700°C. The Fn model(f(α) = (1-α)n)best described the reaction mechanism of the volatiles combustion. The air combustion of WL exhibited superior combustion kinetics and ash characteristics than did the oxy-fuel combustion. However, the oxy-fuel combustion caused lower HCN and higher CO emissions, which were conducive to reducing NOx production, than did the air combustion. According to the best-fit artificial neural network, the oxy-fuel combustion between 800–936°C exhibited the best performance in terms of both maximum energy generation and minimum air pollution. Findings of this study can offer actionable insights into the environmentally friendly disposal of WL. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Amidst the pressing environmental challenges posed by the prevalent reliance on fossil fuels, it becomes imperative to seek sustainable alternatives and prioritize energy efficiency. Electrocatalysis, which is renowned for its high efficiency and environmental friendliness, has garnered significant attention. Rare earth elements (REEs), distinguished by their unique electronic and orbital structures, play a crucial role in electrocatalysis. The strategic integration of REEs into catalysts allows for the fine‐tuning of atomic structures, which in turn, significantly boosts catalytic performance. Despite substantial advancements in rare earth‐based materials for electrocatalysis, a comprehensive overview of the regulatory mechanisms involving REEs is lacking. In this mini‐review, we systematically explore the regulatory mechanisms of REEs within electrocatalysts and their pivotal roles in essential electrocatalytic processes such as the CO2 reduction reaction, oxygen reduction reaction, and hydrogen evolution reaction. We commence with an elucidation of REEs, proceed to delineate their regulatory impacts on electrocatalysts and delve into their applications in key electroreduction reactions. We conclude with discussions on current limitations and prospects for further advancements in this burgeoning field of research. Key Scientists: [ABSTRACT FROM AUTHOR]

The photophysical and photochemical properties of the sulfonyl azide‐based fluorescent probe DNS–Az and its reduction product DNS by hydrogen sulfide (H2S) have been investigated theoretically. The calculated results indicated the first excited states of DNS–Az was dark state (oscillator strength less than 0.03) and DNS was bright state (oscillator strength more than 0.1), which determined the predicted radiative rate kr of DNS–Az was much smaller than that of DNS, meanwhile, due to more larger reorganization energy of DNS–Az, its predicted internal conversion rate kic was four times larger than that of DNS; moreover, owing to the effect of heavy atom from sulfur atom in DNS–Az, its predicted intersystem crossing rate kisc was seven times larger than that of DNS, thus the calculated fluorescence quantum yield of DNS–Az was only 2.16% and that of DNS was more than 77.2%, the above factors is the basis for DNS–Az molecule to function as a fluorescent probe. Regarding both DNS‐Az and DNS molecules, their maximum Huang‐Rhys factors, which are less than unity, signify the reliability of 0–0 transitions between their S0 and S1 electronic states. In addition, for DNS, our simulated emission peak of the 0–0 transition is 515 nm, a value that exhibits enhanced accuracy and coherence when compared to the experimental datum of 528 nm. The reaction mechanism of DNS‐Az generating DNS by H2S has been investigated too, according to the potential energy profile, we found that the fluorescent probe firstly protonated, then this organic ion broke down into DNS with the aid of a proton. [ABSTRACT FROM AUTHOR]

Context: Antioxidants are known to play a beneficial role in human health. Caffeic acid has been previously recognized as efficient in this context. However, such a capability can be enhanced through structural modification. Thus, 3829 caffeic acid derivatives were computational designed to that purpose by adding functional groups (-OH, -SH, -OCH3, -COOCH3, -F, -CF3, and -N(CH3)(C2H5)) to its framework. Promising candidates were chosen considering drug-like behavior, toxicity, and synthetic accessibility. The best candidates, dCAF-2, dCAF-16, and dCAF-82, were identified by comparison with reference antioxidants. The thermochemistry and kinetics of their reaction with •OOH are provided. The global rate coefficients were estimated to be 1.76 × 109 M−1 s−1, 3.19 × 109 M−1 s−1, and 1.79 × 109 M−1 s−1 in aqueous solution for dCAF-2, dCAF-16, and dCAF-82, respectively. In lipid medium, their total rate coefficients were estimated to be 3.65 × 103 M−1 s−1, 3.73 × 103 M−1 s−1, and 8.63 × 104 M−1 s−1 for dCAF-2, dCAF-16, and dCAF-82, respectively. These values allow predicting the designed caffeic acid derivatives as excellent antioxidants in both environments. The reaction forces for the main reaction path of the dCAF-2, dCAF-16, and dCAF-82 reactions with •OOH were explored. Methods: Three protocols were used: (i) CADMA-Chem (computer-assisted design of multifunctional antioxidants, based on chemical properties) to quantify ADME (absorption, distribution, metabolism, and excretion) properties, toxicity and synthetic accessibility; (ii) eH-DAMA (electron and hydrogen donating ability map) tool, to identify the derivatives expected to behave as the best antioxidants; (iii) QM-ORSA (quantum mechanics–based test for overall free radical scavenging activity), to calculate the rate constants. Electronic structure calculations were performed with Gaussian 09, at the M05-2X/6–311 + g(d,p) level of theory. Both aqueous and lipid environments were considered using the SMD continuous solvation model. Intrinsic reaction coordinate (IRC) calculations, as implemented in Gaussian 09, were used to obtain the reaction force. [ABSTRACT FROM AUTHOR]

This study compared the pyrolysis behaviors of corn stalk (CS) and its torrefied biomass after inert torrefaction (IT), oxidative torrefaction (OT), and wet torrefaction (WT), focused on the kinetic parameters and reaction mechanisms. Inert and oxidative torrefaction reduced volatile matter while increasing ash content and fixed carbon. Wet torrefaction reduced both volatile matter and ash content while increasing fixed carbon. Three pretreatment methods decreased oxygen content, increased carbon content, and had a higher heating value. The materials were pyrolyzed in a thermogravimetric analyzer. For CS, the average activation energy (E) values calculated by the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunosen methods were 62.5 and 60.07 kJ/mol. IT and WT showed increased trend, with values of 81.58, 81.48 kJ/mol and 69.75, 67.58 kJ/mol respectively. Conversely, OT decreased with the E values of 57.39 and 56.2 kJ/mol. Pyrolysis was divided into two stages based on various conversion rates (α) using Malek and Coats–Redfern methods. When α was below 0.5, a one-dimensional diffusion mathematical model described the pyrolysis process. When α was beyond 0.5, the pyrolysis of CS conformed to the cylindrical symmetric three-dimensional diffusion mathematical model, while IT, OT, and WT better fit the spherical symmetric three-dimensional diffusion mathematical model. However, the torrefaction atmosphere’s impact on the pyrolysis kinetic mechanism was limited, exhibiting no alterations in the diffusion model. Different torrefaction samples demonstrated a degree of homogeneity, considering the lower pretreatment temperatures and the economic feasibility of torrefaction atmospheres in oxidative torrefaction, coupled with the lowest activation energy of oxidative torrefaction products indicating more efficient pyrolysis, oxidative torrefaction was recommended as the torrefaction pretreatment process before pyrolysis engineering. [ABSTRACT FROM AUTHOR]

The development of ammonium nitrate (AN)/ammonia borane (AB) as a green propellant is crucial for their applicability in different engines. This study investigates the release patterns of small products, particularly nitrogen‐containing molecules, during the initial pyrolysis of AN/AB at low and high pressures using ReaxFF MD simulations. Compared with pure AN, the addition of AB gives the hybrid system enhanced reactivity, leading to faster decomposition and higher energy release. The results show that the consumption of AN in the S13 system (AB with a mass ratio of 12.6 %) is accelerated at 1.47 MPa. NO2 and NO are produced through HNO3 and NO3. At 6.89 MPa, AN exhibits the fastest decomposition rate in the S15 system. The high pressure enhances more reactions of NO with free radicals such as NH and accelerates the release of N2. As the percentage content of AB increases to 15.3 %, more H2O while more NO2 is generated. The effect of AB on the generation of radicals such as H2 and H, is analyzed. AB not only promotes the initial pyrolysis of AN but also accelerates the conversion of intermediates. [ABSTRACT FROM AUTHOR]

Careful analysis of the crystals formed in the reduction of AriPr8AlI2 (AriPr8=C6H‐2,6‐(C6H2‐2,4,6‐iPr3)2‐3,5‐iPr2) with sodium on sodium chloride showed them to contain the long sought‐after dialuminene AriPr8AlAlAriPr8 (1) that forms alongside the previously characterized alanediyl :AlAriPr8. The single crystal X‐ray structure of 1 revealed a nearly planar, trans‐bent C(ipso)AlAlC(ipso) core with an Al−Al distance of 2.648(2) Å. The molecular and electronic structure of 1 are consistent with an Al−Al double dative interaction augmented with diradical character and stabilized by dispersion interactions. Density functional theory calculations showed that the reactivity of :AlAriPr8 with dihydrogen involves 1, not :AlAriPr8, as the reactive species. In contrast, the reaction of :AlAriPr8 with ethylene gave two products, the 1,4‐dialuminacyclohexane AriPr8Al(C2H4)2AlAriPr8 (2) and the aluminacyclopentane AriPr8Al(C4H8) (3), that can both form from the aluminacyclopropane intermediate AriPr8Al(C2H4). Although the [2+2+2] cycloaddition of 1 with two equivalents of ethylene was also calculated to be exergonic, it is likely to be kinetically blocked by the numerous isopropyl substituents surrounding the Al−Al bond. Attempts to fine‐tune the steric bulk of the terphenyl ligand to allow stronger Al−Al bonding were unsuccessful, leading to the isolation of the sodium salt of a cyclotrialuminene, Na2[AlAriPr6]3 (4), instead of AriPr6AlAlAriPr6. [ABSTRACT FROM AUTHOR]

Reductive proton‐coupled electron transfer (PCET) has important energetic implications in numerous synthetic and natural redox processes. The development of catalytic systems that can mediate such transformations has become an attractive target, especially when light is used to generate the reactive species towards solar‐to‐chemicals conversion. However, such approach becomes challenged by kinetic competition with H2 evolution. Here we describe the excited state reactivity of a molecular Zr‐based platform under visible light irradiation for the efficient reduction of multiple bonds. Mechanistic investigations shine light on a charge separation process that colocalizes an excited electron and an acidic proton to promote selective PCET. We further leveraged this reactivity for the photocatalytic reduction of a variety of organic substrates. Our results demonstrate the promise of this molecular platform to design strong photocatalytic PCET mediators for reductive transformations. More broadly, we also show the potential relevance of PCET mechanisms in the (photo)redox chemistry of Zr‐based molecular materials. [ABSTRACT FROM AUTHOR]