Revealing the Mechanism of Dioxin Formation from Municipal Solid Waste Gasification in a Reducing Atmosphere

Gasification is an effective technology for the thermal disposal of municipal solid waste (MSW) with lower dioxin emission compared to the prevailing incineration process. Nevertheless, the mechanism of dioxin formation in the reducing atmosphere during the gasification process was seldomly explored. Herein, the effects of the atmosphere, temperature, and chlorine source were systematically investigated in terms of dioxin distribution. With CO₂ and H₂O as gasification agents, a reducing reaction atmosphere was formed with abundant H₂ which effectively suppressed the generation of C-Cl, contributing to a substantial decrease of dioxin concentration by ∼80% compared to the incineration process. The formation of dioxin was favored at temperatures below 700 °C with its peak concentration achieved at 500 °C. It was unveiled that inorganic chlorine played a dominant role in the reducing atmosphere, with a lower proportion of C-O-C/O-C═O on residual slag compared to an oxidizing atmosphere. Additionally, the generated H₂ reduced the concentration of dioxins by attacking C-Cl and inhibiting the crucial Deacon reaction for dioxin formation, validated by density functional theory calculation. Eventually, the formation route paradigm and the reaction mechanism of dioxin formation from MSW gasification were revealed, facilitating and rationally guiding the control of dioxin emission.

Linking the Electrical Conductivity and Non-Stoichiometry of Thin Film Ce1-xZrxO2-δ by a Resonant Nanobalance Approach

Bulk ceria-zirconia solid solutions (Ce_1−xZr_xO_2−δ, CZO) are highly suited for application as oxygen storage materials in automotive three-way catalytic converters (TWC) due to the high levels of achievable oxygen non-stoichiometry δ. In thin film CZO, the oxygen storage properties are expected to be further enhanced. The present study addresses this aspect. CZO thin films with 0 ≤ x ≤ 1 were investigated. A unique nano-thermogravimetric method for thin films that is based on the resonant nanobalance approach for high-temperature characterization of oxygen non-stoichiometry in CZO was implemented. The high-temperature electrical conductivity and the non-stoichiometry δ of CZO were measured under oxygen partial pressures pO₂ in the range of 10⁻²⁴–0.2 bar. Markedly enhanced reducibility and electronic conductivity of CeO₂-ZrO₂ as compared to CeO_2−δ and ZrO₂ were observed. A comparison of temperature- and pO₂-dependences of the non-stoichiometry of thin films with literature data for bulk Ce_1−xZr_xO_2−δ shows enhanced reducibility in the former. The maximum conductivity was found for Ce_0.8Zr_0.2O_2−δ, whereas Ce_0.5Zr_0.5O_2-δ showed the highest non-stoichiometry, yielding δ = 0.16 at 900 °C and pO₂ of 10⁻¹⁴ bar. The defect interactions in Ce_1−xZr_xO_2−δ are analyzed in the framework of defect models for ceria and zirconia.

Dramatically Improved Thermoelectric Properties by Defect Engineering in Cement-Based Composites

In recent years, the problem of overheating in summer has been of great concern. Pavements are continuously exposed to solar radiation, and because of high temperatures, pavement temperatures reach 60 to 70 °C. This potential low-grade heat has been unused. Cement-based composites with thermoelectric properties can convert this low-grade heat to useful electrical energy. The importance of this green technology for generating renewable energy and sustainable development has been widely accepted and noticed. However, the power factor of current cement-based composites is too low, and harvesting low-grade heat on a large scale and at low cost requires improving the thermoelectric properties of cement-based composites. In this paper, we present a method to increase the electrical conductivity of ZnO and thus improve the thermoelectric properties of cement-based composites by defect engineering, obtaining a high power factor of 224 μWm^-1 K^-2 at 70 °C, a record value recently reported for thermoelectric cement-based composites. Zinc oxide powder was treated with a reducing atmosphere to increase the content of oxygen defects and thus improve the electrical conductivity. Pretreated ZnO powder of 5.0 and 10.0 wt % expanded graphite were added to the cement matrix. The ZnO/expanded graphite cement-based composites were made and tested for their thermoelectric properties using a dry pressing process, which exhibited excellent thermoelectric properties. The result showed high conductivity (12.78 S·cm^-1), a high Seebeck coefficient (-419 μV/°C), a high power factor (224 μWm^-1 K^-2), and a high figure of merit value (8.7 × 10^-3), which facilitate future large-scale applications. Using the cement-based composites to lay a road of 1 km in length and 10 m in width, 35.2 kW·h of electricity can be collected in 8 h. This study will inspire how to improve thermoelectric performance of cement-based composites.

Formation of nucleobases in a Miller-Urey reducing atmosphere

The Miller-Urey experiments pioneered modern research on the molecular origins of life, but their actual relevance in this field was later questioned because the gas mixture used in their research is considered too reducing with respect to the most accepted hypotheses for the conditions on primordial Earth. In particular, the production of only amino acids has been taken as evidence of the limited relevance of the results. Here, we report an experimental work, combined with state-of-the-art computational methods, in which both electric discharge and laser-driven plasma impact simulations were carried out in a reducing atmosphere containing NH₃ + CO. We show that RNA nucleobases are synthesized in these experiments, strongly supporting the possibility of the emergence of biologically relevant molecules in a reducing atmosphere. The reconstructed synthetic pathways indicate that small radicals and formamide play a crucial role, in agreement with a number of recent experimental and theoretical results.