Infrared study of the selective oxidation of toluene and o-xylene on vanadium oxide/TiO2

Infrared spectroscopy was used to obtain information on the mechanism of the selective oxidation of toluene and o-xylene over vanadium oxide catalysts. The interaction of these aromatic hydrocarbons and the products benzaldehyde and o-tolualdehyde with the surface of a V2O5/TiO2 monolayer catalyst was investigated at different temperatures under conditions comparable to those of the catalytic reaction. The infrared results obtained for each of these compounds showed a great resemblance, indicating that their oxidation proceeds along the same reaction path. Coordinatively adsorbed aldehydes, carboxylate-like structures, and benzoate species could be identified as intermediates on the surface of the catalysts. On the basis of the spectroscopic observations a possible reaction mechanism has been proposed

Influence of phosphorus and potassium impurities on the properties of vanadium oxide supported on TiO2

The catalytic properties of vanadium oxide catalysts supported on TiO2 from Tioxide were strongly affected by phosphorus and potassium, present as impurities in the TiO2 support. The effects observed were stronaly dependent on the type of hydrocarbon oxidised. In the oxidation of toluene to benzoic acid the impurities had a large negative influence on the activity and maximum yield. For the oxidation of o-xylene to ohthalic anhydride this negative effect was only observed at relat- ively low vanadium contents. At higher contents (above monolayer coverage) improved catalytic properties were obtained for catalysts supported on the contaminated TiO2 support. When the phosphorus and potassium impurities were both largely removed by extraction with water optimum catalytic behaviour was achieved at much lower vanadium contents in both oxidation reactions. The effect of each of the two impurities separately was also investigated using vanadium oxide catalysts deliberately contaminated with various amounts of either phosphorus or potassium. From the results of the catalytic oxidation experiments it was concluded that the addition of phosphorus resulted in an increase of the surface acidity of vanadium oxide/TiO2 catalysts. The effect of potassium was much larger and was attributed to an alternation of the nature of the reactive sites, possibly because of the formation of amorphous bronzes

Preparation of supported vanadium and molybdenum oxide catalysts using metal acetylacetonate complexes

Supported vanadium and molybdenum oxide catalysts were prepared by reaction of the corresponding acetylacetonate complex in a non-aqueous solution with the surface hydroxyl groups of the carrier. Continuous or batch adsorption of the metal acetylacetonate from toluene, as well as wet impregnation from ethanol, resulted in a uniform coverage of the support. The applied metal oxide was probably present on the surface as a monomolecular dispersion. When readsorption or reimpregnation from toluene was carried out with TiO2 as support, metal oxide crystallites were formed, which could readily be detected with laser Raman spectroscopy. Reimpregnation from ethanol led to a complete occupancy of the surface hydroxyl groups of the carrier without the formation of metal oxide multilayers or crystallites

Foraminifera in elevated Bermudian caves provide further evidence for +21 m eustatic sea level during Marine Isotope Stage 11

Two hypotheses have been proposed to explain the origin of marine isotope stage (MIS) 11 deposits in small Bermudian caves at +21 m above modern sea level: (1) a +21 m MIS 11 eustatic sea-level highstand, and (2) a MIS 11 mega-tsunami event. Importantly, the foraminifera reported in these caves have yet to be critically evaluated within a framework of coastal cave environments. After statistically comparing foraminifera in modern Bermudian littoral caves and the MIS 11 Calonectris Pocket A (+21 m cave) to the largest available database of Bermudian coastal foraminifera, the assemblages found in modern littoral caves – and Calonectris Pocket A – cannot be statistically differentiated from lagoons. This observation is expected considering littoral caves are simply sheltered extensions of a lagoon environment in the littoral zone, where typical coastal processes (waves, storms) homogenize and rework lagoonal, reefal, and occasional planktic taxa. Fossil protoconchs of the Bermudian cave stygobite Caecum caverna were also associated with the foraminifera. These results indicate that the MIS 11 Bermudian caves are fossil littoral caves (breached flank margin caves), where the total MIS 11 microfossil assemblage is preserving a signature of coeval sea level at +21 m. Brackish foraminifera (Polysaccammina, Pseudothurammina) and anchialine gastropods (w95%, >300 individuals) indicate a brackish anchialine habitat developed in the elevated caves after the prolonged littoral environmental phase. The onset of sea-level regression following the +21 m highstand would first lower the ancient brackish Ghyben-Herzberg lens (<0.5 m) and flood the cave with brackish water, followed by drainage of the cave to create a permanent vadose environment. These interpretations of the MIS 11 microfossils (considering both taphonomy and paleoecology) are congruent with the micropaleontological, hydrogeological and physical mechanisms influencing modern Bermudian coastal cave environments. In conclusion, we reject the mega-tsunami hypothesis, concur with the +21 m MIS 11 eustatic sea-level hypothesis, and reiterate the need to resolve the disparity between global marine isotopic records and the physical geologic evidence for sea level during MIS 11

Sea level controls sedimentation and environments in coastal caves and sinkholes

Quaternary climate and sea-level research in coastal karst basins (caves, cenotes, sinkholes, blueholes, etc.) generally focuses on analyzing isotopes in speleothems, or associating cave elevations prior sea-level highstands. The sediments in coastal karst basins represent an overlooked source of climate and sea-level information in the coastal zone, but to accurately interpret these sediments first requires an understanding of the forcing mechanisms that emplace them. In this study, we hypothesize that coastal karst basins transition through vadose, littoral, anchialine, and finally into submarine environments during sea-level rise because groundwater and sea level oscillate in near synchrony in the coastal zone, causing each environment to deposit a unique sedimentary facies. To test this hypothesis, the stratigraphy in twelve sediment cores from a Bermudian underwater cave (Green Bay Cave) was investigated and temporally constrained with twenty radiocarbon dates. The results indicate that we recovered the first succession spanning the entire Holocene from an underwater cave (~ 13 ka to present). The sediments were characterized with X-radiography, fossil remains, bulk organic matter, organic geochemistry (δ13Corg, C:N), and grain size analysis. Four distinct facies represent the four depositional environments: (i) vadose facies (> 7.7 ka, calcite rafts lithofacies), (ii) littoral facies (7.7 to 7.3 ka: calcite rafts and mud lithofacies), (iii) anchialine facies (7.3 to 1.6 ka: slackwater and diamict lithofacies), and (iv) submarine facies (< 1.6 ka: carbonate mud and shell hash lithofacies). The onset and duration of these sedimentary depositional environments are closely linked to Holocene sea-level rise in Bermuda, indicating that sea level controls environmental development in coastal karst basins. Finally, we present a conceptual model for interpreting the sediments and environments in coastal karst basins as a result of sea-level change

Exceptionally preserved Late Albian (Cretaceous) Arcellaceans (Thecamoebians) from the Dakota Formation near Lincoln, Nebraska, USA

Thousands of exceptionally well-preserved Arcellaceans (Thecamoebians) have been recovered from a Late Albian (Cretaceous) deposit. Sedimentary samples were obtained from a clayey-silt leaf bed in the Dakota Formation, outcropping in a clay pit excavated by the Yankee Hill Brick Company, located near Lincoln, Nebraska. Based on recovered freshwater macrophyte spore and fossil remains, the leaf bed is a lagerstätten of paleobotanical remains in which the paleoenvironment has been interpreted as a quiescent freshwater setting. The large number of recovered thecamoebians revealed a high intraspecific variability in test morphology that is comparable to Holocene thecamoebian populations. Consequently, we employ the thecamoebian strain taxonomic framework, a first for ancient thecamoebians. Extant species contained in this collection include Difflugia oblonga, Difflugia protaeiformis, Difflugia urens, Pontigulasia compressa, Lagenodifflugia vas, Cucurbitella tricuspis, Lesquereusia spiralis and the cysts of environmentally stressed protozoans—with only one new species reported, Difflugia baukalabastron. The well-preserved nature of the taxa, suggesting little taphonomic bias, and the lack of significant new species supports the current hypothesis of minimal evolution in thecamoebian lineages through geologic time

The preparation of supported oxidic catalysts by adsorption of metal acetylacetonates, M(acac)n, on different supports

The adsorption of metal acetylacetonates on different supports has been studied with particular reference to Fe(acac)3 on Ti02. The adsorption takes place by reaction of the M(acac)n with the surface -OH groups of the support. It is possible in this way to prepare well-dispersed supported oxidic catalysts. By continuous adsorption of Fe(acac)3 an almost complete monolayer of Fe203 can be achieved on Ti02