Absence Of Propene Research Articles

Impact of Propene on Secondary Organic Aerosol Formation fromm-Xylene

Propene is widely used in smog chamber experiments to increase the hydroxyl radical (OH) level based on the assumption that the formation of secondary organic aerosol (SOA) from parent hydrocarbon is unaffected. A series of m-xylene/NO(x) photooxidation experiments were conducted in the presence of propene in the University of California CE-CERT atmospheric chamber facility. The experimental data are compared with previous m-xylene/N0(x) photooxidation work performed in the same chamber facility in the absence of propene (Song et al. Environ. Sci. Technol. 2005, 39, 3143-3149). The result shows that, for similar initial conditions, experiments with propene have lower reaction rates of m-xylene than those without propene, which indicates that propene reduces OH in the system. Furthermore, experiments with propene showed more than 15% reduction in SOA yield compared to experiments in the absence of propene. Additional experiments of m-xylene/ NO(x) with CO showed similar trends of suppressing OH and SOA formation. These results indicate that SOA from m-xylene/NO(x) photooxidation is strongly dependent on the OH level present, which provides evidence for the critical role of OH in SOA formation from aromatic hydrocarbons.

Rhenium(VII) Oxide/Aluminum Oxide: More Experimental Evidence for an Oxametallacyclobutane Intermediate and a Pseudo‐Wittig Initiation Step in Olefin Metathesis

AbstractReactivity studies of the rhenium(VII) oxide/aluminum oxide olefin metathesis catalyst with various olefins show that initiation does not require an olefin with an allylic CH bond, and therefore probably takes place via a pseudo‐Wittig reaction. While it does not react with ethene in the absence of propene, Re2O7/Al2O3 catalyses the self‐metathesis of Z‐stilbene and its cross‐metathesis with ethene. Additionally, reaction of Re2O7/Al2O3 with Z‐2‐butene followed by 13C di‐labelled ethene shows that it contains only 2 % of active sites.

Catalytic propene polymerization: determination of propagation, termination, and epimerization kinetics by direct NMR observation of the (EBI)Zr(MeB(C6F5)3)propenyl catalyst species.

Treatment of (EBI)ZrMe2 with B(C6F5)3 and 100 equiv of 1-hexene in toluene-d8 at -40 degrees C for 1 h, followed by addition of >5 equiv of propene, generates a living polypropene catalyst (3) with a polyhexene "tail". Upon further addition of propene, speciation of the catalyst and propagation kinetics are measured directly by NMR, yielding a propagation rate law that is first order in [propene] and [living catalyst] with a rate constant of 2.6 M-1 s-1 at -40 degrees C and the activation parameters DeltaH = 3.4(0.2) kcal/mol and DeltaS = -42(2) cal/(mol K). In the absence of propene, elimination of vinylidene-terminated polymer is observed with a first-order rate constant of 3.3 (0.5) x 10-5 s-1 at -40 degrees C and DeltaH = 12.9(1.4) kcal/mol and DeltaS = -23(5) cal/(mol K). Use of 1-13C-propene and 1,1-2H-2,3-13C-propene and 1H, 19F, and 13C NMR spectroscopy provide rigorous characterization of the living catalyst and enable the first direct observation of both 1,3-isomerization and chain-end epimerization processes at a metallocene catalyst. Isomerization and epimerization occur with rates that are similar to that of vinylidene termination and are consistent with previous mechanistic hypotheses featuring isomerization via a tertiary alkyl intermediate and switching between enantiofaces of the coordinated alkene.

Catalytic Conversion of N2O to N2 over Metal-Based Catalysts in the Presence of Hydrocarbons and Oxygen

The catalytic conversion of N2O to N2 in the presence or the absence of propene and oxygen was studied. The catalysts examined in this work were synthesized impregnating metals (Rh, Ru, Pd, Co, Cu, Fe, In) on different supports (Al2O3, SiO2, TiO2, ZrO2 and calcined hydrotalcite MgAl2(OH)8·H2O). The experimental results varied both with the type of the active site and with the type of the support. Rh and Ru impregnated on γ-alumina exhibited the highest activity. The performance of the above most promising catalysts was studied using various hydrocarbons (CH4, C3H6, C3H8) as reducing agents. These experimental results showed that the type of reducing agent does not affect the reaction yield. The temperature where complete conversion of N2O to N2 was measured was independent of the reductant type. The activity of the most active catalysts was also measured in the presence of SO2 and H2O in the feed. A shift of the N2O conversion versus temperature curve to higher temperatures was observed when SO2 and H2O were added, separately or simultaneously, to the feed. The inhibition caused by SO2 was attributed to the formation of sulfates and that caused by water to the competitive chemisorption of H2O and N2O on the same active sites.

Catalytic properties of La0.8A0.2MnO3 (A = Sr, Ba, K, Cs) and LaMn0.8B0.2O3 (B = Ni, Zn, Cu) perovskites: 2. Reduction of nitrogen oxides in the presence of oxygen

The selective catalytic reduction of nitrogen oxides in the presence of oxygen and water vapor was investigated over perovskite-type mixed oxides La0.8A0.2MnO3 (A=Sr, Ba, K, Cs) and LaMn0.8B0.2O3 (B=Ni, Zn, Cu) with propene as the reductant, in the temperature range of 150–550°C. The catalysts were contacted with a reactant mixture containing 1000ppm NO, 500ppm C3H6, 5% O2 and 5% H2O in helium at a space velocity of 14.4cm3/gs. A maximum was observed in the conversion of nitrogen oxides to nitrogen with temperature in the range of 300–400°C. In the absence of propene, the activity of these perovskites for NO removal in the 300–550°C range increased from approximately 20% (with propene) to 40% (without propene). Water inhibited the NOx removal process as well, the conversion levels in the propene and water-free gas mixtures rising to about 50–55%. The removal of nitrogen oxides did not take place in the absence of oxygen. Two different reaction mechanisms were postulated: (i) the selective reduction with propene at 150–300°C; (ii) the direct decomposition, which is inhibited by the presence of propene and water, at 300–550°C. The nitrogen dioxide formed by the perovskite-catalyzed oxidation of nitrogen monoxide appears to play a key role in both mechanisms.

Transient Surface Processes of Storage and Conversion of NO x Species on Pt–Me/Al2O3 Catalysts (Me = Ba, Ce, Cu)

The transient reactivity and surface phenomena of storage and conversion of NOx species on Pt(1%)–Me/Al2O3 catalysts, where Me = Ba, Ce and Cu, were studied by the RWF (rectangular wavefront) method. The Me component has a relevant influence on the processes of surface storage and transformation. The reduction of NOx by propene in the presence of oxygen is promoted by adding Cu to a Pt/Al2O3 catalyst, while cerium promotes transient conversion of NO in the absence of propene, but inhibits the reduction of NOx in the presence of propene. Copper is suggested to be a promising element to add together with Ba for new NOx storage-reduction catalysts due to its capacity to act both as a storage element and as promoter for NOx reduction.

Kinetics of metabolism of propene and covalent binding to macromolecules in the mouse

The rate of uptake of propene from air was studied by exposing CBA mice to various concentrations of the gas in a closed, recirculating all-glass chamber. The rate curves showed a saturable dependence on the propene concentration. The inhalational K m and V max were calculated to be 800 ± 60 ppm and 8 ± 0.5 mg (kg body wt) −1 hr −1, respectively, from a Lineweaver-Burk plot of the rate data. The homologous compound ethene is known to be metabolized in the mouse to ethene oxide. When a trace amount of 14C-labeled ethene was administered in combination with a high concentration of propene, the uptake of [ 14C]ethene was lower than in the absence of propene, suggesting a competitive interaction in their metabolic pathways. One group of animals were exposed at 20,000 ppm of propene 4 hr/day during 8 consecutive days. Hemoglobin was isolated from the treated group and a control group. After hydrolysis of the protein, two diastereomers of N τ-(2-hydroxypropyl)histidine were identified in the hydrolysate from treated animals, suggesting that propene, analogous to ethene, is metabolized to the corresponding epoxide and showing that the oxidation is not stereospecific. 2-Hydroxypropylated products were found in hemoglobin from mice treated with 14C-labeled propene. The amounts of alkylated products in DNA were below the detection limit.