Incorporation of carbon originating from CO2 into different compounds of soil microbial biomass and soil organic matter

In general, soils without the vegetation growing on them are regarded as sources of CO2. However, there are indications that CO2 is also fixed by soil microorganisms. Although this process is not significant from a quantitative point of view, it may change the isotopic composition of soil organic matter. Therefore, we conducted an incubation study with soil and 13C-labeled CO2 to investigate this process. We found that the label was transferred from CO2 into organic compounds in soil. At the end of a 61-day incubation period, 1.3 micromol C g(-1) soil, corresponding to approximately 0.08% of the soil organic carbon, had been fixed. CO2 may, therefore, be an additional source of soil organic carbon. Compound-specific analysis of amino sugars, amino acids, and fatty acids indicated that the label is incorporated into microbial, mainly bacterial, biomass. All groups of microorganisms were involved in the assimilation of CO2, but the relatively high enrichment of mono-unsaturated and mid-chain branched fatty acids indicates that gram negative bacteria and actinomycetes may be slightly more important in this process than other groups of microorganisms.     

Letter to the Editor

Journal of Nanoparticle Research -     

Formation of aromatics during the pyrolysis of oligocyclic naphthenes: Indications for a mechanistic alternative

It is known that aromatics are formed in much higher yields in the pyrolysis of di- and oligocyclic naphthenes than in that of alkanes and monocyclic naphthenes. To study the mechanisms of the formation of aromatics from naphthenes, the thermal decomposition of dicyclohexyl, decalin, dodecahydrofluorene, tetradecahydroanthracene, hexadecahydropyrene and [9,10-¹⁴C]tetradecahydroanthracene was studied in different laboratory tubular furnaces from 800 to 850°C. The reaction products were analysed by conventional and radio gas chromatography. As an important consequence of the results, a new hypothesis for the formation of aromatics via acyclic, multiply unsaturated hydrocarbon species as precursors is presented.     

Principal Limitations in Homogeneous Gas Phase Chemistry in Non-Thermal Plasmas

This study highlights the oxidation of H₂, CH₄, and HCl present in the range of some volume percent in a homogeneous O₂ or air phase in a flow through glass barrier discharge reactor. The oxidation of all three compounds is highly exothermic and exergonic at ambient temperature and proceeds at sufficiently high temperatures as radical chain reaction. The conversion of each compound was below 10% in a non-thermal oxygen plasma under various reaction conditions. Increasing concentrations of H₂ and CH₄ above the lower explosion limit did not lead to higher conversion degrees. It is assumed that only initial radical formation by electron impact dissociation and exothermic steps within the chain process run in a sufficiently fast manner at ambient temperature. For endothermic steps within the radical chain, the necessary activation energy is not available and the chain reaction aborts, most likely, after formation of peroxyl (hydro- or methyl-peroxyl) radicals.     

Guest diffusion in interpenetrating networks of micro- and mesopores

Pulsed field gradient NMR is applied for monitoring the diffusion properties of guest molecules in hierarchical pore systems after pressure variation in the external atmosphere. Following previous studies with purely mesoporous solids, also in the material containing both micro- and mesopores (activated carbon MA2), the diffusivity of the guest molecules (cyclohexane) is found to be most decisively determined by the sample "history": at a given external pressure, diffusivities are always found to be larger if they are measured after pressure decrease (i.e., on the "desorption" branch) rather than after pressure increase (adsorption branch). Simple model consideration reproduces the order of magnitude of the measured diffusivities as well as the tendencies in their relation to each other and their concentration dependence.     

Pyrolysis of [5-14C]-1-pentene–evidence for homoallylic rearrangements at 873 K

It was found that the pyrolysis of [5-¹⁴C]-1-pentene gives radioactive 1,3-butadiene. This result can be explained in terms of a sequence of free radical rearrangements of 1-penten-3-yl radicals. From this and additional information on isotope distribution in butadiene formed from different deuterated 1-pentenes, we conclude that homoallylic rearrangement of 1-penten-4-yl and 2-penten-5-yl radicals is the dominant route for their consumption.     

Hyphenated techniques for characterizing coal wastewaters and associated sediments

Capillary gas chromatography (cGC)-mass spectrometry (MS) and cGC-atomic emission detection (AED) were used for the analysis of extracts from highly contaminated wastewaters and associated sediments. The main extractable constituents in both the lignite wastewater and the sediments include phenols, PAHs, indenols and heterocyclic compounds. Pyrolysis (Py)-GC-MS and Py-GC-AED were used for characterizing the building blocks of the dissolved polymeric organic matter. Polymers of natural and anthropogenic origins could be clearly distinguished. The Py-MS studies performed with humic organic matter at both atmospheric pressure and high vacuum (in-source mode) indicate a high portion of pyrolysis residue (about 40%, w/w) upon heating to 700°C, irrespective of the pressure level. The products released include many low molecular weight compounds which are of limited value for characterizing the polymeric network.     

Influence of Ferroelectric Materials and Catalysts on the Performance of Non-Thermal Plasma (NTP) for the Removal of Air Pollutants

The introduction of ferroelectric and catalytically active materials into the discharge zone of NTP reactors is a promising way to improve their performance for the removal of hazardous substances, especially those appearing in low concentrations. In this study, several coaxial barrier-discharge plasma reactors varying in size and barrier material (glass, Al₂ O₃, and TiO₂) were used. The oxidation of methyl tert-butyl ether (MTBE), toluene and acetone was studied in a gas-phase plasma and in various packed-bed reactors (filled with ferroelectric and catalytically active materials). In the ferroelectric packed-bed reactors, better energy efficiency and CO₂ selectivity were found for the oxidation of the model substances. Studies on the oxidation of a toluene/acetone mixture in air showed an enhanced oxidation of the less reactive acetone related to toluene in the ferroelectric packed-bed reactors. It can be concluded that the change of the electrical discharge behaviour was caused by a larger number of non-selective and highly reactive plasma species formed within the ferroelectric bed. When combining ferroelectric (BaTiO₃) and catalytically active materials (LaCoO₃), only a layered implementation led to synergistic effects utilising both highly energetic species formed in the ferroelectric packed-bed and the potential for total oxidation provided by the catalytically active material in the second part of the packed bed.