Life cycle impact assessment of airborne metal pollution near selected iron and steelmaking industrial areas in China

Toxic metals in particulate matter pose a significant health risk to humans via inhalation and dermal exposure. Additionally, airborne pollution has negative impacts on terrestrial and aquatic quality as a result of atmospheric deposition. Iron and steelmaking industry is considered as a major contributor to airborne metal pollution. Given that China has been the largest steel producer and consumer since 1996, a detailed investigation of airborne metal pollution is required to assess the potential risks to both human health and ecosystem quality near iron and steelmaking areas in China. This study applied an environmental impact assessment approach to evaluate the freshwater ecotoxicity, terrestrial ecotoxicity, marine ecotoxicity and human toxicity caused by metal concentrations in PM1.1, PM1.1-2.1 and PM2.1-9.0 fractions. Results showed that heavy metals Cu and Zn associated with steelmaking activities were largely responsible for aquatic and terrestrial ecotoxicity. This study also found that As and Pb contamination presented the largest fraction of the impacts on human toxicity. Findings presented in this study showed that more stringent control measures are required to improve the environmental performance of the iron and steelmaking industries in China

Probing the Charge Separation Process on In2S3/Pt-TiO2 Nanocomposites for Boosted Visible-light Photocatalytic Hydrogen Production

A simple refluxing wet-chemical approach is employed for fabricating In2S3/Pt-TiO2 heterogeneous catalysts for hydrogen generation under visible light irradiation. When the mass ratio between Pt-TiO2 and cubic-phased In2S3 (denoted as In2S3/Pt-TiO2) is two, the composite catalyst shows the highest hydrogen production, which exhibits an 82-fold enhancement over in-situ deposited Pt-In2S3. UV-vis diffuse reflectance and valence band X-ray photoelectron spectra elucidate that the conduction band of In2S3 is 0.3 eV more negative compared to that of TiO2, favoring charge separation in the nanocomposites. Photoelectrochemical transient photo-current measurements and optical pump - terahertz probe spectroscopic studies further corroborate the charge separation in In2S3/Pt-TiO2. The migration of photo-induced electrons from the In2S3 conduction band to the TiO2 conduction band and subsequently into the Pt nanoparticles is found to occur within 5 picoseconds. Based on the experimental evidence, a charge separation process is proposed which accounts for the enhanced activity exhibited by the In2S3/Pt-TiO2 composite catalysts

Mechanistische Studien an der Umsetzung von Methanol zu Olefinen an sauren Zeolith-Katalysatoren mittels der in-situ Festkörper-NMR-UV/Vis Spektroskopie

Due to the increasing demand for light olefins, the catalytic conversion of methanol-to-olefins (MTO) on acidic zeolite catalysts continues to be an industrially interesting process in heterogeneous catalysis. During the last decades, increasing efforts were made to clarify the mechanism of the MTO process. Recent progress revealed that, in the MTO process, the conversion of an equilibrium mixture of methanol and dimethyl ether (DME) is dominated by a “hydrocarbon pool” route in which methanol is directly added onto reactive organic compounds, such as polyalkylbenzenes, cyclic carbenium ions, and probably poly-alkylbenzenium cations, while light olefins are formed via an elimination from these compounds. However, the chemistry during the “induction period” leading to formation of the first organic compounds, and the behaviors of reactive hydrocarbon pool formed under the steady-state conditions still remain a matter of debate. In this work, the novel in situ continuous-flow (CF) MAS NMR-UV/Vis technique combined with on-line gas chromatography (GC) offers an interesting approach for studying the detailed mechanism of the MTO process. During the induction period of MTO process, the reactivity of surface methoxy groups on acidic zeolite H-Y and silicoaluminophosphate H-SAPO-34 has been investigated by the solid-state 13C MAS NMR spectroscopy. The obtained spectra give an evidence for the high reactivity of surface methoxy groups, which might be responsible for the initiation of the MTO process. However, it has been suggested that an initiation of the MTO process might be affected by co-feeding of impurities in the methanol feed. In order to clarify whether traces of organic impurities also govern the conversion of surface methoxy groups, the solid-state 13C MAS NMR combined with UV/Vis spectroscopy is applied to study the initiation stage of the methanol conversion on acidic zeolite catalysts via the methoxy route. Both NMR spectra and simultaneously recorded UV/Vis bands indicate that traces of organic impurities present in the methanol do not govern the formation of primary hydrocarbons from surface methoxy groups. Under steady-state conditions of the MTO process, due to the specific effects of the pore architectures and catalytically active Broensted sites in zeolites, the investigation of hydro-carbon pool compounds and coke deposits is obviously a severe and complex task in the field of heterogeneous catalysis. The in situ MAS NMR-UV/Vis offers an approach for characterizing the nature of “hydrocarbon pool” on H-SAPO-34 under continuous-flow conditions at reaction temperatures of 473 to 673 K. In addition, a quantitative evaluation of the 13C MAS NMR experiments gives the mean numbers of aromatic compounds and of alkyl groups per aromatic ring under reaction conditions. With increasing time on-stream, the deactivation of the working catalysts is accompanied by a decrease of the mean number of methyl groups bound to aromatic hydrocarbon pool compounds, which will lead to a lower selectivity of propylene in the product distribution. The regeneration of spent catalysts at high temperatures by purging with nitrogen led to a decrease of the content of polyalkylaromatics. While a treatment of the used catalyst with synthetic air at high temperatures could remove nearly all neutral polycyclic aromatics acting as coke deposits. As indicated by 13C MAS NMR and UV/Vis spectroscopy, the residual organic deposits on acidic catalysts consist of a small amount of reactive carbenium ions, which indicates that the catalysts get regenerated.Wegen der innerhalb der letzten zehn Jahre stark angewachsenen Nachfrage nach leichten Olefinen, wie z.B. nach Ethen und Propen, konzentrieren sich die gegenwärtigen Forschungen auf die Untersuchung der Umwandlung von Methanol zu Olefinen (methanol-to-olefin: MTO). Der Reaktionsweg des MTO-Prozesses wird wie folgt beschrieben: Der erste Schritt ist die Dehydratisierung des Methanols an den sauren Oberflächenzentren des Zeolith-Katalysators zu Dimethylether (DME). Das hierbei gebildete Gleichgewichtsgemisch aus Methanol, DME und Wasser wird nach einer Induktionsperiode, während der es zur Bildung der ersten Kohlenwasserstoffe kommt, in leichte Olefine umgesetzt. Diese leichten Olefine bilden im weiteren verzweigte Olefine, Aromaten und Naphthene. Es entsteht ein Kohlenwasserstoff Pool in den Poren und Hohlräumen des Zeolith-Katalysators. Hierbei laufen Wasserstofftransfer-, Alkylierungs-, Isomerisierungs-, Polykondensations- und andere Sekundärreaktionen ab. In der letzten Phase des MTO-Prozesses kommt es zur Desaktivierung des arbeitenden Katalysators aufgrund der Bildung von harten Koks.Der detaillierte Reaktionsmechanismus bei der Umsetzung von Methanol zu Olefinen ist bisher noch nicht vollständig geklärt. Die erste Kombination der In situ-MAS-NMR-Spektroskopie mit einer weiteren spektroskopischen Methode führte in den Gruppen von Hunger zur Entwicklung der In-situ-MAS-NMR-UV/Vis-Technik. Mit dieser neuartigen spektroskopischen Technik ist eine direkte Untersuchung der Bildung und Transformation von Komplexen an den Oberflächen von Feststoffkatalysatoren unter Gleichgewichtsbedingungen mit hoher Auflösung mittels Festkörper-NMR-Spektroskopie und, in einigen Fällen, mit einer gleichzeitigen gas-chromatographischen Analyse der Reaktionsprodukte möglich. Anderseits ist es möglich geworden, gleichzeitig Olefine mit konjugierten Doppelbindungen, Aromaten und ungesättigte Carbeniumionen mit hoher Empfindlichkeit mittels UV/Vis-Spektroskopie zu untersuchen. Durch die Einführung und Entwicklung der Kombination verschiedener spektroskopischer Methoden ist es möglich geworden, offene Fragestellungen zum MTO-Prozess zu bearbeiten: (1) Einfluss von organischen Verunreinigungen im Methanol-Feed auf die Bildung von Kohlenwasserstoffen durch die chemische Umsetzung von Oberflächen-Methoxy-Spezies; (2) Reaktivität von Oberflächen-Methoxy-Spezies als Voraussetzung für ihren Beitrag zur Bildung des Kohlenwasserstoff-Pool an sauren Zeolith-Katalysatoren; (3) Zusammensetzung des Kohlenwasserstoff-Pools und des während der stationären Phase des MTO-Prozesses gebildeten Kokses; (4) Mechanismus der Desaktivierung des arbeitenden Katalysators und Natur des Kokses. Einfluss von organischen Verunreinigungen im Methanol-Feed auf die Bildung von Kohlenwasserstoffen durch die chemische Umsetzung von Oberflächen-Methoxy-Gruppen an sauren Zeolith-Katalysatoren

Selective synthesis of TiO₂-based nanoparticles with highly active surface sites for gas-phase photocatalytic oxidation

This work demonstrated the absence of surface terminal hydroxyl groups plays a key role in the photocatalytic oxidation of low concentration volatile organic compounds. Probed by ¹H MAS NMR spectroscopy, we showed the synthesis of bare and F-TiO₂ nanoparticles with undetectably low content of terminal hydroxyl groups (TiOH) on the surface of TiO₂ could be obtained through a sol-gel process. The characterization results by N₂ adsorption, XRD, HRTEM, Raman, and XPS show that the bare TiO₂ and F-TiO₂ have almost identical bulk and surface structural properties. The photocatalytic activity was evaluated by photocatalytic oxidation of acetaldehyde and ethanol. Due to the absence of terminal TiOH in the bare TiO₂ and F-TiO₂, both materials exhibit 100% photodegradation of acetaldehyde and ethanol. No deactivation was observed during the experimental period of 8 days. The activities surpassed the photodegradation performance of the benchmarking Aeroxide P25 TiO₂ under similar conditions (93%). On the bare TiO₂, only stoichiometric CO₂ production was observed and no detectable by-product existed in the product stream, resulting in no expanded off-odor problems. On the contrary, ethanol photodegradation on F-TiO₂ produced minor acetaldehyde as a by-product, but the amount of acetaldehyde produced was still lower than that produced on Aeroxide P25.8 page(s

Proximate determinants of particulate matter (PM2.5) emission, mortality and life expectancy in Europe, Central Asia, Australia, Canada and the US

publishedVersio

Production of formic acid from CO₂ reduction by means of potassium borohydride at ambient conditions

The present study provides an efficient process for the high-yield production of formic acid (24%) by reduction of carbon dioxide (CO₂) with potassium borohydride at ambient conditions. The effects of reaction temperature, CO₂ pressure and borohydride concentration have been investigated. For a 0.5M borohydride solution, 0.15mol/L of formic acid were produced at room temperature and ambient pressure with yields increasing at higher pressures. A time-resolved in situ¹H and ¹¹B nuclear magnetic resonance (NMR) technique was firstly developed to monitor the elementary reaction processes under real working conditions. Direct evidence is given for the formation of H₂, HD and a hydroxyborohydride intermediate (BH₃OH⁻) formed during borohydride decomposition indicating that the source of the hydrogen gas comes from both the borohydride anion and water, while borohydride works as a water-splitting reagent. Consequently, a reaction mechanism involved in both borohydride hydrolysis and CO₂ reduction has been established.7 page(s

Effect of reactant density inside supercages of zeolite La,Na-Y on the mechanism of the ethylbenzene conversion

Zeolites La,Na-Y are important catalysts for industrial FCC units due to their acidic properties and stability. The ethylbenzene disproportionation on this zeolite was suggested as a standard test reaction for acidic zeolites by the Catalysis Commission of the International Zeolite Association (IZA). The present work provides solid-state ¹³C NMR spectroscopic evidence that various amounts of reactants inside the supercages of zeolites La,Na-Y obviously affect the catalytic behavior of ethylbenzene reaction. At 453 K, diphenylethane was only detected on zeolite La,Na-Y with three ethylbenzene molecules per supercage. This intermediate, however, did not occur on samples with low loading (1 or 2 EB molecules per supercage). On zeolite La,Na-Y loaded with one molecule ethylbenzene per supercage, dealkylation and realkylation of ethylbenzene occurred at 548 K without any side-reactions. However, side-reactions of oligomerization, hydride transfer, and aromatization were observed on samples with high ethylbenzene loading, which promotes the catalyst deactivation. In addition, the zeolites La,Na-Y with high loadings of ethylbenzene show a higher reactivity and more complex reaction mechanisms.5 page(s

Exploring the relationship between surface structure and photocatalytic activity of flame-made TiO₂-based catalysts

Bare titanium dioxides (TiO₂) and doped with metal (Cu) or non-metal ion (F) were synthesized by a single-step flame spray pyrolysis (FSP) method. According to the BET, XRD, and TEM results, the Cu- and F-doped TiO₂ nanoparticles synthesized by FSP possess comparable features in terms of surface area, crystallite size and phase composition, and morphology. However, the F-doped TiO₂ exhibited the highest photocatalytic activity for the complete oxidation of acetaldehyde (ACE) even surpassing benchmarking Aeroxide TiO₂ (P25). In contrast, Cu-doped TiO₂ had a detrimental effect on the ACE photocatalytic oxidation. The proportion of native terminal hydroxyl groups, evaluated using high-field ¹H MAS NMR, on the particle surface was varied by doping the TiO₂ with either Cu or F ions during FSP synthesis. A relationship, whereby decreased terminal hydroxyl group content corresponded to elevated acetaldehyde photodegradation, was subsequently uncovered. The findings were reinforced by studying the XPS O 1s photopeaks in the region attributed to surface hydroxyl groups.8 page(s