Europium Oxybromide Catalysts for Efficient Bromine Looping in Natural Gas Valorization

ISSN:1433-7851ISSN:1521-3773ISSN:0570-083

Halogen-Dependent Surface Confinement Governs Selective Alkane Functionalization to Olefins

The product distribution in direct alkane functionalization via oxyhalogenation strongly depends on the halogen of choice. Herein, we demonstrate that the superior selectivity to olefins over an iron phosphate catalyst in oxychlorination is the consequence of a surface-confined reaction. Oppositely, in oxybromination alkane activation follows a gas-phase radical-chain mechanism, yielding a mixture of alkyl bromide, cracking, and combustion products. Surface coverage analysis of the catalyst and identification of gas-phase radicals in operando mode are correlated to the catalytic performance by a multi-technique approach, which combines kinetic studies with advanced characterization techniques, such as prompt-gamma activation analysis and photoelectron photoion coincidence spectroscopy. Rationalization of gas-phase and surface contributions by density functional theory reveals that the molecular level effects of chlorine are pivotal in determining the stark selectivity differences. These results provide a strategy that enables to unravel a detailed mechanistic picture in a complex reaction network

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Catalytic Processes for Intensified Vinyl Chloride Production

Polyvinyl chloride (PVC) is the third most widely used plastic in today’s society. The industrial production of its monomer, vinyl chloride (commonly denoted as VCM), relies on hydrochlorination of acetylene or thermal dehydrochlorination of 1,2-dichloroethane (known as ethylene dichloride, EDC) forming equimolar amounts of HCl. EDC itself is produced by ethene chlorination with Cl2 or oxychlorination with HCl, enabling its recycling. However, while the state-of-the-art CuCl2-based oxychlorination catalyst is very selective, it suffers from stability issues. In this work, three major areas of research have been targeted, in particular i) the development of a more robust ethene oxychlorination catalyst, ii) the process intensification via combining oxychlorination and dehydrochlorination functions in one material or a dual catalyst system, and iii) the evaluation of a feedstock change from ethene to the much cheaper ethane. To this end, catalytic systems and corresponding mechanistic understanding is developed by assessment of performance and kinetics, combined with in-depth molecular level modeling of the complex reaction network. In a first step, recently discovered HCl oxidation catalysts were tested in ethene oxychlorination and compared to a CuCl2-based benchmark. Among these catalysts, RuO2 exhibited a low yield of EDC and VCM due to strong combustion, while CeO2 exhibited excellent stability and enabled up to 25% VCM and 25% EDC yield in a single pass. The selectivity was attributed to the bifunctional character of ceria, where redox centers oxychlorinate ethene to EDC, which is subsequently dehydrochlorinated to VCM over acid sites generated in situ. However, combustion or the formation of 1,2-dichlorethene (DCE) could not be suppressed, and deeper mechanistic understanding was yet missing. Therefore, first computational studies of the complete ethene oxychlorination and its related combustion network were conducted on the RuO2(110) surface, a relatively simple material for density functional theory (DFT) calculations, revealing that chlorination steps are kinetically controlled, whereas oxidation steps are under thermodynamic control. This enabled a reduction of the overall reaction network for investigation on a CeO2(111) surface. Catalytic evaluation and corresponding characterization revealed that the catalyst surface contains CeOCl, while the bulk phase remains CeO2, regardless of the starting phase. A higher degree of chlorination led to increased selectivity to EDC and VCM, while decreasing the selectivity to DCE and COx (CO+CO2). Combination of DFT with steady-state experiments and temporal analysis of products (TAP) then revealed that the most likely pathway of VCM formation proceeds via a cascade reaction on a chlorinated CeO2(111) surface. In contrast, oxygen vacancies facilitate the formation of DCE, while combustion can originate from reactants and products. To overcome these mechanistic limitations, other lanthanide oxides were investigated in ethene oxychlorination, revealing that the oxide forms of all compounds, except CeO2, transformed into their respective chlorides or mainly oxychlorides. Among those, europium oxychloride (EuOCl) led to a VCM selectivity of up to 96% at 20% conversion, while CeO2 still exhibited about double the activity with 30% VCM selectivity. The outstanding selectivity of EuOCl was attributed to a unique balance of mild redox and enhanced acid properties, which suppresses oxidation and boosts EDC dehydrochlorination. However, the high price and moderate activity of EuOCl motivated further efforts to design a stable and VCM selective CeO2-based ethene oxychlorination catalyst by nanostructuring the active phase onto a suitable carrier. Among the developed materials, CeO2 on monoclinic ZrO2 emerged as an outstanding catalyst, exhibiting 100% EDC selectivity at a 10-fold increased metal efficiency with respect to bulk CeO2. Use of acidic supports, such as Al2O3 or ZSM-5, resulted in high VCM selectivities, yet combustion and coking were pronounced. The observed performances were rationalized by suitable probe reactions, evidencing that a high HCl oxidation ability and low acidity are key for active and selective EDC production catalysts. Accordingly, we implemented a dual-catalyst system, featuring CeO2/ZrO2 for EDC formation and Ca-doped Al2O3 for EDC dehydrochlorination, leading to up to 100% VCM selectivity at 25% ethene conversion. In the quest to utilize ethane instead of ethene as feedstock for VCM production, recent studies reported a wide range of ethane oxychlorination catalysts, which mainly yield ethene, while VCM remains a minor by-product. Strikingly, the same catalysts selectively form VCM under equivalent reaction conditions in ethene oxychlorination. Combining quantitative catalytic tests, TAP, and DFT on iron phosphate, the origin of these diverging selectivity patterns was revealed. In particular, co-feeding ethane in ethene oxychlorination gave evidence that the alkane suppresses VCM formation in ethene oxychlorination, which originates from the hydrocarbon competition for active sites. These observations were extended by ethane co- feeding tests in ethene oxychlorination over a wide range of known oxychlorination catalysts, and corresponding DFT calculations indicated that the described phenomenon is material independent. Overall, the fundamental insight developed in this work exemplifies how an integrated approach of catalytic synthesis, characterization, and evaluation in combination with molecular- level rationalization are able to uncover complex reaction networks, providing guidelines for future developments within industrial VCM production

Fehlende Datensätze in der Meldung: Imputation versus Neuanforderung. Möglichkeiten und Grenzen der Imputation bei der Erhebung zu Tarifinformationen

Die monatliche Verdiensterhebung hat die vierjährlich durchgeführte Verdienststrukturerhebung und die Vierteljährliche Verdiensterhebung abgelöst. Ergänzt wird sie durch eine fünfjährliche Erhebung zum angewandten Tarifvertrag. Es kommt vor, dass Betriebe nicht zu allen Arbeitnehmersätzen der monatlichen Verdiensterhebung Angaben liefern, die Meldung also unvollständig ist. Die hier vorgestellte Studie untersucht, ob es möglich ist, die Angaben zur tarifvertraglichen Bindung durch ein Nearest-Neighbor-Imputationsverfahren mit einer hinreichenden Zuverlässigkeit für das Gesamtergebnis zu schätzen.The monthly earnings survey has replaced the four-yearly structure of earnings survey and the quarterly earnings survey. It is supplemented by a five-yearly survey of the collective agreements applied. Sometimes the reporting companies do not provide information on the relevant collective agreement for all employee records in the monthly earnings survey, and so the report is incomplete. The study presented here examines whether a nearest-neighbor imputation can be used to estimate the information on collective bargaining coverage while ensuring adequate reliability of the overall results

Mechanism of ethylene oxychlorination over ruthenium oxide

ISSN:0021-9517ISSN:1090-269

Lanthanide compounds as catalysts for the one-step synthesis of vinyl chloride from ethylene

ISSN:0021-9517ISSN:1090-269

Mechanistic origin of the diverging selectivity patterns in catalyzed ethane and ethene oxychlorination

In the context of vinyl chloride monomer (VCM) production, an oxychlorination catalyst that allows direct VCM formation from gas-derived ethane instead of expensive oil-derived ethene is intensively sought after. A wide range of stable ethane oxychlorination catalysts for this purpose have recently been reported, yet they mainly yield ethene, while VCM remains a minor by-product. Strikingly, the same catalysts are active in ethene oxychlorination, resulting in selective VCM formation under equivalent reaction conditions. This work reveals the origin of these diverging selectivity patterns by combining quantitative catalytic tests, temporal analysis of products (TAP), and density functional theory (DFT) on iron phosphate. Ethane oxychlorination is found to proceed sequentially through ethyl chloride (EtCl) dehydrochlorination to ethene, while ethene oxychlorination directly yields VCM without formation of the intermediate dichloroethane (EDC) on iron phosphate. Furthermore, by co-feeding ethane in ethene oxychlorination, we demonstrate that the alkane suppresses the formation of VCM in ethene oxychlorination. The reason for this VCM inhibition is found in the hydrocarbon competition for a combination of the active, free and chlorinated iron centers. As ethane activation exhibits half of the barrier of ethene activation, the presence of ethane leads to active site depletion, hindering VCM formation. These observations are extended by ethane co-feeding tests in ethene oxychlorination over a wide range of known oxychlorination catalysts (EuOCl, LaOCl, CeO2, and CuCl2-KCl-LaCl3/c-Al2O3), and corresponding DFT calculations, indicating that the described phenomenon is material independent. The gathered molecular-level understanding explains the major hurdle of using ethane as feedstock for vinyl chloride production