First-Principles Study on the Mechanism of Greenhouse Gas Generation in Aluminum Electrolysis

Greenhouse gases emitted by the aluminum electrolysis industry have brought great challenges to environmental protection. To address this problem, understanding the micro-generation mechanism of greenhouse gases in the electrolysis process is of great significance to their source suppression. Based on the first principles calculation method, the formation paths of CO, CO2 and COF2 during normal electrolysis were obtained by studying the adsorption behavior of oxygen and fluorine complex anions (short for [O]2−, [F]−) on the anode surface in cryolite alumina molten salt. The calculation results indicate that the O and F atoms prefer to adsorb at bridge site 1 of Model A, with the adsorption energies of −4.82 eV and −3.33 eV. In the [O]2− priority discharge stage, Path 3 is the most likely path for CO2 generation, while in the [O]2−, [F]− co-discharge stage, Path 3 is the most likely path for COF2 generation. It is deduced that the thermal decomposition of COF2 at high temperature should account for the generation of CF4 with a low concentration of the so-called non-anode effect PFC (NAE-PFC). Experiments were also conducted to verify the calculation by disclosing the bonding information of C, O and F, which are in good accordance with the results calculated by the first principle.

Gas-phase formation of acetaldehyde: review and new theoretical computations

ABSTRACT Among all the interstellar complex organic molecules, acetaldehyde is one of the most widely detected species. The question of its formation route(s) is, therefore, of a major interest regarding astrochemical models. In this paper, we provide an extensive review of the gas-phase formation paths that were, or are, reported in the literature and the major astrochemical data bases. Four different gas-phase formation routes stand out : (1) CH3OCH3 + H+/CH3CHOH+ + e−, (2) C2H5 + O(3P), (3) CH3OH + CH, and (4) CH3CH2OH + OH/CH3CHOH + O(3P). Paths (2) and (3) were not studied neither via laboratory nor theoretical works in the low temperature and density regime valid for the interstellar medium (ISM). Thus, we carried out new accurate quantum chemistry computations. A theoretical kinetics study at low temperatures (7 ÷ 300 K), adopting the Rice–Ramsperger–Kassel–Marcus scheme, was also performed. We confirm that reaction (2) is efficient in forming acetaldehyde in the 7–300 temperature range (α = 1.21 × 10−10 cm3 s−1 and β = 0.16). On the contrary, our new computations disprove the formation of acetaldehyde through reaction (3) (α = 1.84 ÷ 0.67 × 10−13 cm3 s−1 and β = −0.07 ÷ −0.95). Path (1) was showed to be inefficient too by recent computations, while path (4) was formerly considered for glycolaldehyde formation, having acetaldehyde as a byproduct. In conclusions, of the four above paths, only two, the (2) and (4), are potentially efficient gas-phase reaction routes for the formation of acetaldehyde and we encourage astrochemical modellers to consider only them. Comparison with astronomical observations suggests that path (4) may actually play the major role.

Insight Into the Formation Paths of Methyl Bromide From Syringic Acid in Aqueous Bromide Solutions Under Simulated Sunlight Irradiation

Methyl bromide (CH3Br) is one of the largest natural sources of bromine in the stratosphere, where it leads to ozone depletion. This paper reported the photochemical production of CH3Br from syringic acid (SA) that has been used as an environmentally relevant model compound for terrestrially-derived dissolved organic matter. The formation of CH3Br increased with the increase of bromide ion concentration ranging from 0.8 to 80 mmol L−1. Ferric ions (Fe(III)) enhanced CH3Br production, while chloride inhibited it, with or without Fe(III). Meanwhile, methyl chloride (CH3Cl) was generated in the presence of chloride and was inhibited by Fe(III). The different effects of Fe(III) on the formation of CH3Cl and CH3Br indicate their diverse formation paths. Based on the intermediates identified by liquid chromatography-mass spectrometry and the confirmation of the formation of Fe(III)-SA complexes, it was proposed that there were two formation paths of CH3Br from SA in the bromide-enriched water under simulated sunlight irradiation. One path was via nucleophilic attack of Br− on the excited state protonation of SA; the other was via the combination of methyl radical and bromine radical when Fe(III) was present. This work suggests that the photochemical formation of CH3Br may act as a potential natural source of CH3Br in the bromide-enriched environmental matrix, and helps in better understanding the formation mechanism of CH3Br.

Evaluation of Policies on Inappropriate Treatment of Dead Hogs from the Perspective of Loss Aversion

Punishment policies on the inappropriate treatment of dead hogs play a key role in safeguarding public health and environmental protection. These policies aim to regulate the behavior of farmers and promote the development of sustainable agriculture. Farmers’ evaluation of a policy can be used to measure its effectiveness, and loss aversion is a factor that has been little studied. This study surveyed 404 hog farmers in China, and analyzed the factors that influenced their evaluation of the penalties for the inappropriate treatment of dead hogs during 2016 and 2017. We used three indicators for the evaluation of the penalties: the degree of necessity, implementation, and effectiveness. Special attention was paid to farmers’ aversion to financial penalties and police detention time, which was elicited using economic experiments. The results show that farmers are more likely to be averse to police detention time than financial penalties, and suggest that the level of each indicator needs to be increased. The results from an ordered Probit model show that there are both similarities and differences between the formation paths of the three indicators. An aversion to financial penalties will help to improve the degree of implementation. An aversion to police detention time will lead to a negative trend in the degree of effectiveness. An in-depth analysis of the factors that influence farmers’ evaluation of policies to punish inappropriate treatment of dead hogs may provide a basis for the design of government policies to improve environmental protection performance.

A new insight into the reaction behaviors of side-chain alkylation of toluene with methanol over CsX

The crucial step for styrene production and the formation paths for the main side-products in the side-chain alkylation of toluene with methanol over CsX were unveiled.

Hydrocarbon growth via ion-molecule reactions: computational studies of the isomers of C4H2+, C6H2+ and C6H4+ and their formation paths from acetylene and its fragments

Structures, vibrational and electronic spectra, and AIMD trajectories of formation paths for C4H2+, C6H2+ and C6H4+ from acetylene ion and its fragments are reported in this article.

Sn-Se Binary and Cu-Sn-Se Ternary Thin Films Grown by Co-Evaporation Process

Unfavorable secondary phases like binaries and ternaries are often observed in synthesizing Cu2ZnSnSe4 (CZTSe) quaternary crystal due to its narrow phase space, which strongly limits the performance of Kesterite solar cells. To identify the growth parameters against the stability of these secondary phases, we systematically studied the growth process of Sn-Se binaries and Cu-Sn-Se ternaries using co-evaporation method. We found that the compositions of Sn-related binary and ternary phases were strongly dependent on the substrate temperature and Se flux during deposition, which will be helpful in designing formation paths for quaternary system. Growth temperature of CZTSe higher than 490 °C will make the thin film free of Cu2SnSe3 phase. Our experiments also suggest that formation pathways in the Cu2SnSe3-ZnSe pseudobinary phase diagram at a slightly lower substrate temperature deserve more experimental and theoretical considerations because of its easier composition control.