The CH4/NO/O2 “Lean-deNOx” Reaction on Mesoporous Mn-Based Mixed Oxides

High surface area Mn-based porous oxides (MANPO) containing additives like Ce, Sr and La were found to be very active and selective materials under 0.67% CH₄/0.2% NO/5% O₂ lean-deNO _x conditions in the 200–300°C low-temperature range. These materials perform also impressively in the presence of 4% H₂O in the feed stream, where a N₂ selectivity of 98% and an excellent stability over 24 h on stream have been observed. The MANPO materials can be considered serious competitors of noble metals for low-temperature lean-deNO _x applications.     

Catalytic behavior of La–Sr–Ce–Fe–O mixed oxidic/perovskitic systems for the NO+CO and NO+CH4+O2 (lean-NOx) reactions

Mixed oxides of the general formula La_0.5Sr_xCe_yFeO_z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO₃ and SrFeO_3−x and oxides -Fe₂O₃ and CeO₂ depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH₄+O₂ (“lean-NO_x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La³⁺ cation at A-site with divalent Sr⁺² and tetravalent Ce⁺⁴ cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La_0.5Sr_xCe_yFeO_z materials to reduce NO by CO or by CH₄ under “lean-NO_x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s⁻¹) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al₂O₃ catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La_0.5Sr_xCe_yFeO_z solids and their catalytic activity. O₂ TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O₂ TPD studies was observed for the La_0.5Sr_0.2Ce_0.3FeO_z and La_0.5Sr_0.5FeO_z solids.     

Transesterification of rapeseed oil for the production of biodiesel using homogeneous and heterogeneous catalysis

In the present work, the transesterification reaction of rapeseed oil with methanol, in the presence of alkaline catalysts, either homogeneous (NaOH) or heterogeneous (Mg MCM-41, Mg–Al Hydrotalcite, and K+ impregnated zirconia), using low frequency ultrasonication (24 kHz) and mechanical stirring (600 rpm) for the production of biodiesel fuel was studied. Selection of heterogeneous catalysts was based on a combination of their porosity and surface basicity. Their characterization was carried out using X-ray diffraction (XRD), Nitrogen adsorption–desorption porosimetry and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The activities of the catalysts were related to their basic strength. Mg–Al hydrotalcite showed particularly the highest activity with conversion reaching 97%). The activity of ZrO₂ in the transesterification reaction increased as the catalyst was doped with more potassium cations, becoming thus more basic. Use of ultrasonication significantly accelerated the transesterification reaction compared to the use of mechanical stirring (5 h vs. 24 h).Given the differences in experimental design, it can be concluded that the homogeneous catalyst accelerated significantly the transesterification reaction, as compared to all heterogeneous catalysts, using both mechanical stirring (15 min vs. 24 h) and ultrasonication (10 min vs. 5 h). However, the use of homogeneous base catalysts requires neutralization and separation from the reaction mixture leading to a series of environmental problems related to the use of high amounts of solvents and energy. Heterogeneous solid base catalysts can be easily separated from the reaction mixture by simple filtration, they are easily regenerated and bear a less corrosive nature, leading to safer, cheaper and more environment-friendly operations.     

The influence of alteration on the engineering properties of dolerites: The examples from the Pindos and Vourinos ophiolites (northern Greece)

The influence of alteration on the physico-mechanical properties of dolerites from the Pindos and Vourinos ophiolites, northern Greece, is investigated. Quantitative petrographic analysis shows that the samples display various percentages of secondary minerals. Two new micropetrographic indices are calculated from the results of petrographic modal analysis for the engineering assessment of dolerites: the micropetrographic strength index I_ps and the replacement index I_rep. The samples are also tested to determine water absorption, apparent density, total porosity, sand equivalent, uniaxial compressive strength, Los Angeles abrasion value, aggregate impact value, aggregate abrasion value and polished stone value. The influence of alteration on the rock quality and especially the relationships between the proposed micropetrographic indices and the engineering parameters are determined using regression analysis and the derived equations were verified by the t-test and the F-test. The relationships between the I_ps and I_rep indices and the engineering properties show that alteration products generally result in mechanically weaker rocks. However, the results of the physico-mechanical tests indicate that dolerites retain their strength and durability due to the low proportions of soft minerals and microcracks, along with the preservation of their igneous textures. The polishing resistance is the only engineering parameter that is positively affected by alteration processes, as expressed by the I_ps index. Particularly, the replacement of the primary mafic minerals by secondary minerals, expressed by the I_rep index, can enhance the polishing resistance of dolerites when used in the wearing surface of a road. The results also indicate strong positive correlations between the chlorite content and the water absorption and total porosity values.     

Cuticular hydrocarbons of the screwworm,Cochliomyia hominivorox (Diptera: Calliphoridae)

A novel series of 2,X-dimethylalkanes were isolated and identified. The nonpolar fraction of the surface lipids secreted by the adult (5-day-old) screwworm,Cochliomyia hominivorax, contains over 130 different hydrocarbons comprising normal alkanes (32% of the total hydrocarbon), branched alkanes (53%), and monoalkenes (11%). Branched alkanes included monomethylalkanes with substitution in all possible positions except for 4-methylalkanes, internally branched dimethylalkanes, and 2,X- and 3,X-dimethylalkanes. At emergence, adults of both sexes of the 009 strain have nearly identical gas Chromatographic profiles, which diverge as the insect ages. Irradiation of pharate pupae does not affect the hydrocarbon produced.Mention of a commercial or proprietary product in this paper does not constitute an endorsement of that product by the USDA.     

Alkanes from surface lipids of sunflower stem weevil,Cylindrocopturus adspersus (LeConte)

The stem weevil,Cylindrocopturus adspersus (LeConte) (Coleoptera: Curculionidae) yields 3% of its body weight as extractable lipids (40 g/ weevil). The alkane fraction was composed ofn-alkanes (38%) and branched alkanes (62%). The compounds were characterized by gas chromatography-mass spectrometry (GC-MS). The chromatogram contained several single-component peaks (9 of 25). Only seven dimethylalkanes were isolated (17.8%): 9,19- and 9,21-dimethylheptacosane; 9,19- and 9,21-dimethylnonacosane; 9,21- and 11,21-dimethylhentriacontane; and 11,21-dimethyltritriacontane. Important methylalkanes were: 2-methyltetra- and hexacosanes and 10-methylhexa- and octacosanes. Late-eluting gas chromatography peaks were composed of simple alkane mixtures or a single component.     

Insect hydrocarbons

Standard mono- and dimethyl-branched hydrocarbons were synthesized from substituted thiophenes for the purpose of comparing their mass spectra to those of hydrocarbons isolated from the tobacco hornworm,Manduca sexta L. The mass spectra of the standard compounds confirmed the structures of the partially characterized natural products.     

Catalytic activity of (CaO)1−x(ZnO)x solids for the N2O decomposition: relation with photoluminescence

(CaO)_1–x (ZnO) _x mixed oxides (x=0–1), heated at 1423 K under atmospheric conditions, were checked for their catalytic activity in the N₂O decomposition in the temperature range of 450–650°C. Although the catalytic activity was measured in the dark, it was found to be linearly related with the photoluminescence intensity of the catalysts.     

Structure and photocatalytic performance of TiO2/clay nanocomposites for the degradation of dimethachlor

In the present study TiO₂/clay composites were synthesized by dispersion of TiO₂ on the surfaces of a natural montmorillonite and a synthetic hectorite in order to increase the sorption ability of TiO₂ and therefore its photocatalytic action. Six materials with different loading in TiO₂ (15, 30 and 55 wt%) were prepared and characterized by several analytical techniques including XRD, BET and SEM analysis. The synthetic procedure allows the development of delaminated layers for hectorite–TiO₂ samples, while in the case of montmorillonite–TiO₂ composites we have the formation of a more lamellar-like aggregation. It was found that, the greater the percentage of TiO₂, the greater the pore volume and the specific surface area of the montmorillonite–TiO₂ samples. On the contrary, in the case of hectorite–TiO₂ samples, as the content of TiO₂ increases, the surface area and pore volume decreases. The photocatalytic efficiency of the nanocomposite catalysts was evaluated using a chloroacetanilide herbicide (dimethachlor) in water as model compound. The primary degradation of dimethachlor followed pseudo-first-order kinetics according to the Langmuir–Hinshelwood model. All supported catalysts exhibit good photodegradation efficiency and their overall removal efficiency per mass of TiO₂ was better than that of bare TiO₂ produced by the sol–gel method. In conclusion, together with their good sedimentation ability the composite materials could be considered as a promising alternative for the removal of organic water contaminants.     

Synthetic methyl- and dimethylalkanes

All possible isomeric mono-methylpentacosanes as well as 2,6-, 2,8-, 2,10-, 2,12-, and 2,14-dimethylheptacosane were synthesized. The [¹³C]NMR shifts and the Kovats indices were determined, and the relationship to separation of isomeric mixtures of insect cuticular waxes are discussed. When several homologous series of hydrocarbon isomeric mixtures are to be separated, it is not practical to attempt complete gas-chromatographic separation of all possible isomers. The mass spectra of the 2,X-dimethylheptacosanes are presented and discussed.