Catalytic Behavior of K-doped Fe/MgO Catalysts for Ammonia Synthesis Under Mild Reaction Conditions.

An important part of realizing a carbon-neutral society using ammonia will be the development of an inexpensive yet efficient catalyst for ammonia synthesis under mild reaction conditions (<400 °C, <10 MPa). Here, we report Fe/K(3)/MgO, fabricated via an impregnation method, as a highly active catalyst for ammonia synthesis under mild reaction conditions (350 °C, 1.0 MPa). At the mentioned conditions, the activity of Fe/K(3)/MgO (17.5 mmol h-1 gcat -1 ) was greater than that of a commercial fused iron catalyst (8.6 mmol h-1 gcat -1 ) currently used in the Haber-Bosch process. K doping was found to increase the ratio of Fe0 on the surface and turnover frequency of Fe in our Fe/K(3)/MgO catalyst. In addition, increasing the pressure to 3.0 MPa at the same temperature led to a significant improvement of the ammonia synthesis rate to 29.6 mmol h-1 gcat -1 , which was higher than that of two more expensive, benchmark Ru-based catalysts, which are also potential alternative catalysts. A kinetics analysis revealed that the addition of K enhanced the ammonia synthesis activity at ≥300 °C by changing the main adsorbed species from NH to N which can accelerate dissociative adsorption of nitrogen as the rate limiting step in ammonia synthesis.

Co Nanoparticle Catalysts Encapsulated by BaO-La2O3 Nanofractions for Efficient Ammonia Synthesis Under Mild Reaction Conditions.

Ruthenium catalysts may allow for realization of renewable energy-based ammonia synthesis processes using mild reaction conditions (<400 °C, <10 MPa). However, ruthenium is relatively rare and therefore expensive. Here, we report a Co nanoparticle catalyst loaded on a basic Ba/La2O3 support and prereduced at 700 °C (Co/Ba/La2O3_700red) that showed higher ammonia synthesis activity at 350 °C and 1.0-3.0 MPa than two benchmark Ru catalysts, Cs+/Ru/MgO and Ru/CeO2. The synthesis rate of the catalyst at 350 °C and 1.0 MPa (19.3 mmol h-1 g-1) was 8.0 times that of Co/Ba/La2O3_500red and 6.9 times that of Co/La2O3_700red. The catalyst showed ammonia synthesis activity at temperatures down to 200 °C. Reduction at the high temperature induced the formation of BaO-La2O3 nanofractions around the Co nanoparticles by decomposition of BaCO3, which increased turnover frequency, inhibited the sintering of Co nanoparticles, and suppressed ammonia poisoning. These strategies may also be applicable to other non-noble metal catalysts, such as nickel.

Effects of changes in polycyclic aromatic hydrocarbons (PAHs) emissions and degradation on their concentrations in Tokyo from 2007 and 2016.

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in aerosol were measured in Shinjuku, which is central Tokyo, Japan, for 10 years from 2007 to 2016. The effects of changes in emission sources and their degradation by reaction with ozone were assessed in this study. There was no significant increasing or decreasing trend of the PAH concentrations during 10 years (P > 0.05). The average selected seven the PAH concentrations (0.88 ng m-3) during 10 years was lower than those in New York and Paris. However, the trend of ozone concentrations is increasing in central Tokyo. This inconsistency raises a question. Did the fact that the ozone concentration was higher than the PAH concentrations promote PAH degradation? To apportion the PAH sources, we used PAH concentration profiles and positive matrix factorization analysis. The contribution of vehicle emissions to the PAHs ranged from 40 to 80%. Ozone concentrations increased by 3.70%/year during 10 years. The theoretical degradation rates of PAHs by ozone, which were calculated using a pseudo-first-order rate equation, suggested that the lifetimes of benzo[a]pyrene (BaP) decreased by 1 min from 2007 to 2016. We investigated the aging of BaP using the profile of the isomer ratios. We found that the aging of BaP at the urban and roadside sites were nearly identical indicating aging regardless of the season. Although the decomposition of BaP is promoted by the photochemical oxidation reaction, this result suggests that a certain threshold value exists as the degree of the decomposition. This degradation of PAH can improve chemical loss processes in air quality model.

Multifunctional Catalytic Surface Design for Concerted Acceleration of One-Pot Hydrosilylation-CO2 Cycloaddition.

Silica-supported Rh-ammonium iodide catalyst showed high performance for hydrosilylation-CO2 cycloaddition reaction sequences. The catalyst was prepared by surface grafting of Rh and the silane-coupling reaction of the ammonium iodide moiety. The acceleration of each catalytic reaction was realized due to the concerted catalysis between Rh species, immobilized organic functions, and surface Si-OH groups. As a result, good to excellent yields of silyl carbonates were obtained from epoxyolefins, hydrosilanes, and CO2 under mild reaction conditions.

Prediction of rate constants for the gas phase reactions of triphenylene with OH and NO3 radicals using a relative rate method in CCl4 liquid phase-system.

The kinetics of CCl(4) liquid-phase reactions of ten kinds of polycyclic aromatic compounds (PACs) including triphenylene (TP) with NO(3) radicals have been investigated at 273K by a relative rate method using naphthalene (NA) as a reference compound. The obtained relative reaction rates of the tested PACs to NA in CCl(4) were as follows: 2.57±0.24 (acenaphthene), 2.11±0.30 (2,3-dimethylnaphthalene), 1.21±0.13 (fluoranthene), 0.56±0.07 (fluorene), 1.85±0.19 (1-methylnaphthalene), 1.77±0.12 (2-methylnaphthalene), 0.11±0.03 (1-nitronaphthalene), 1.59±0.23 (phenanthrene), 2.40±0.29 (pyrene), 0.22±0.04 (TP). TP is a semi-volatile PAC with four aromatic rings and it is chemically changed into mutagenic 2-nitrotriphenylene (2-NTP) via the gas-phase OH or NO(3) radical-initiated reactions. On the basis of the relative reactivity of the PACs in the CCl(4) liquid phase-system, the rate constants of the gas-phase reactions of TP with OH and NO(3) radicals at 298 K were predicted to be (8.6±1.2)×10(-12) cm(3) molecule(-1) s(-1) and (6.6±1.5)×10(-29)[NO(2)] cm(3) molecule(-1) s(-1), respectively. Based on the ambient concentrations of TP and 2-NTP and the obtained rate constant for the reaction of TP with OH radicals, the atmospheric loss rate of 2-NTP was also evaluated.

Dichlorodifluoromethane decomposition to CO2 with simultaneous halogen fixation by calcium oxide based materials.

The decomposition of CCl2F2 to CO2 and accompanying halogen fixation by a CaO based material was studied. To improve the low reactivity of CaO, a consequence of its low surface acidity, transition metal oxides were added. Impregnation of metal acetylacetonate followed by removal of the ligand under vacuum was found to be an effective method. This method resulted in the formation of carbonaceous species and the reduction of metal oxide to metal, both of which were thought to initiate the decomposition reaction. The reactivity of these materials (MOx(a)/CaO-vac) was found to be in the following order: M = Ni > Cu > V = Fe > Mn > Co > Ca. In particular, nickel supported on CaO was most effective for the decomposition of CCl2F2. During the preparation, nickel oxide was reduced to the metal phase. CCl2F2 was decomposed to CO2 with a small amount of CO, and halogens were fixed as CaFCl, without significant deactivation at 723 K.

Catalytic transformation of methane over in-loaded ZSM-5 zeolite in the presence of ethene.

Methane is shown to react with ethene over In-loaded ZSM-5 to higher hydrocarbons such as propene and toluene at around 673 K. Such methane conversion is not catalyzed by proton-exchanged ZSM-5 (H-ZSM-5) under the same conditions, only C2H4 being converted to higher hydrocarbons. By using 13C-labeled methane (13CH4) as a reactant, the reaction paths for the formation of propene, benzene and toluene were examined. 13C-labeled propene (13CC2H6) is formed by the reaction of 13CH4 with C2H4. The lack of 13C-labeled benzene revealed that propene is not transformed to benzene, which instead originates entirely from C2H4. The 13C atom is inserted both into the methyl group and benzene ring in the toluene formed. This indicates that toluene is formed by two reaction paths; the reaction of 13CC2H6 with butenes formed by the dimerization of C2H4 and the reaction of benzene with 13CH4. The existence of the latter path was proved by the direct reaction of 13CH4 with benzene. The reaction of methane with benzene was also carried out in a continuous flow system over In-loaded ZSM-5. The reaction afforded 7.6% and 0.9% yields of toluene and xylenes, respectively, at 623 K.

Selective wet-air oxidation of diluted aqueous ammonia solutions over supported Ni catalysts.

Wet-air oxidation (WAO) of diluted aqueous ammonia solutions over Ni supported on Al(2)O(3) catalysts was investigated. A nitrogen selectivity of approximately 90% was achieved by the WAO of ammonia over the 20-wt% Ni/Al(2)O(3) catalyst at 503K, a reaction time of 2h and air-feed pressure of 2.0MPa without the dissolution of Ni during the reaction. Ni/Al(2)O(3) pretreated by calcinations in air at 1173K for 4h showed high stability due to the formation of a NiAl(2)O(4) phase.

Metal nanowire arrays by electrodeposition.

We describe two related methods for preparing arrays of nanowires composed of molybdenum, copper, nickel, gold, and palladium. Nanowires were obtained by selectively electrodepositing either a metal oxide or a metal at the step edges present on the basal plane of highly oriented pyrolytic graphite (HOPG) electrodes. If a metal oxide was electrodeposited, then nanowires of the parent metal were obtained by reduction at elevated temperature in hydrogen. The resulting nanowires were organized in parallel arrays of 100-1000 wires. These nanowires were long (some > 500 microns), polycrystalline, and approximately hemicylindrical in cross-section. The nanowire arrays prepared by electrodeposition were also "portable": After embedding the nanowires in a polymer or cyanoacrylate film, arrays of nanowires could be lifted off the graphite surface thereby facilitating the incorporation of metal nanowire arrays into devices such as sensors.