The adsorption of sulfur by microporous materials

The sorption of sulfur by the zeolites NaX (= 13X) and CaA (= 5A) and an activated charcoal prepared from sugar was investigated at temperatures between 150 and 350°C and relative sulfur pressures between 10−4 and 10−1. The adsorbate-adsorbate interaction indicated by the S-shaped isotherm for the zeolite NaX points to physical or chemical interaction of sulfur molecules in neighboring supercages. In CaA adsorbate-adsorbate interaction between sulfur species in different supercages is negligible. Below 200°C the rate of sulfur uptake by the zeolite CaA is determined by the diffusion rate of a sulfur species through the zeolitic framework. In activated charcoal a strong adsorbate-adsorbent interaction is present and part of the sulfur is chemisorbed at 350°C. The differences in the density of the adsorbed sulfur determined with three different methods indicate that even at full saturation of the micropore volume with sulfur, there is still some residual adsorption volume

The mechanism of pyridine hydrogenolysis on molybdenum-containing catalysts : III. Cracking, hydrocracking, dehydrogenation and disproportionation of pentylamine

The conversion of pentylamine on a MoO3-Al2O3 catalyst was studied between 250 and 350 °C, at various hydrogen pressures. The reactions observed were cracking to pentene and ammonia, hydrocracking to pentane and ammonia, dehydrogenation to pentanimine and butylcarbonitrile, and disproportionation to ammonia and dipentylamine.\ud \ud The equilibrium between pentylamine, dipentylamine and ammonia appeared to be established under most of the experimental conditions. The equilibrium constant is about 9 at 250 °C and about 5 at 320 °C. The disproportionation reaction is zero order in hydrogen and of −1 order in the initial pentylamine pressure.\ud \ud Dehydrogenation was observed at low hydrogen pressures, and especially at higher temperatures; the reaction is first order in pentylamine.\ud \ud Both cracking and hydrocracking take place, mainly above 300 °C. Hydrocracking appears to be half order in hydrogen; the rate of cracking is almost independent of the hydrogen pressure. The hydrocarbon formation is of zero order in pentylamine or dipentylamine.\ud \ud The same type of reactions (except hydrocracking) take place on alumina, but with a far lower reaction rate

The role of sulfur trapped in micropores in the catalytic partial oxidation of hydrogen sulfide with oxygen

The catalytic oxidation of hydrogen sulfide into sulfur with molecular oxygen has been studied in the temperature range 130–200 °C. Active carbon, molecular sieve 13X and liquid sulfur were used as catalysts. Sulfur is adsorbed in the micropores (3 < r < 40 Å) of the catalysts. Experiments with a surface of liquid sulfur demonstrated that sulfur is a catalyst for H2S oxidation.\ud \ud This catalytic function reflects itself in the fact that H2S oxidation rate showed a maximum as a function of the amount of sulfur present in the pores of active carbon and molecular sieve 13X. The kinetics of the reaction and the activation energy are equal on catalysts of different chemical composition.\ud \ud The mechanism of the catalysis by sulfur is discussed as well as the function of traces of iron oxide, present in most catalysts

The mechanism of pyridine hydrogenolysis on molybdenum-containing catalysts : IV. The conversion of piperidine

The conversion of piperidine was investigated on a CoO-MoO3-Al2O3 catalysts as a function of the temperature, reaction time, initial piperidine partial pressure and the hydrogen pressure.\ud \ud At 60 atm of hydrogen and conversions below 50% piperidine is selectively converted to ammonia and N-pentylpiperidine. This reaction appears to be a two-step process, ring-opening to pentylamine followed by a fast alkyl transfer from pentylamine to piperidine. The piperidine conversion is first order in piperidine as well as in hydrogen, and of -1 order in the total pressure of the nitrogen bases.\ud At higher conversions the rate of formation of pentane and ammonia are influenced by the rate of the (hydro)cracking steps, and also by the equilibrium constants of the alkyl transfer equilibria. The rate of a (hydro)cracking reaction is lower when a ring is present in the nitrogen base. The activation energies of these reactions were 160 kJ mol−1, about 60 kJ mol−1 greater than those of alkyl transfer reactions.\ud At 1 atm of hydrogen the product composition was completely different from that observed at higher pressures of hydrogen.\ud The mechanism of the reactions is briefly discussed

The influence of the precipitation rate on the properties of porous chromia

The properties were studied of heated (320°C) chromia samples, prepared by two precipitation methods: \ud \ud 1. (1) addition of ammonia to chromium salt solutions,\ud 2. (2) OH− formation in chromium salt solutions through hydrolysis of urea.\ud \ud Samples formed by means of the first method are macro or mesoporous and have a lower specific surface area (~200 m2·g−1) than those formed by urea hydrolysis (~300 m2·g−1). Only in the case of a very slow addition of the ammonia solution these properties of the chromia's become equal. Experiments show that the micro porous type samples with high surface area are only formed if the pH range 5.1 to 5.7 is passed slowly. The formation of polychromium complexes of uniform size is suggested.\ud \u

On marginally outer trapped surfaces in stationary and static spacetimes

In this paper we prove that for any spacelike hypersurface containing an untrapped barrier in a stationary spacetime satisfying the null energy condition, any marginally outer trapped surface cannot lie in the exterior region where the stationary Killing vector is timelike. In the static case we prove that any marginally outer trapped surface cannot penetrate into the exterior region where the static Killing vector is timelike. In fact, we prove these result at an initial data level, without even assuming existence of a spacetime. The proof relies on a powerful theorem by Andersson and Metzger on existence of an outermost marginally outer trapped surface.Comment: 22 pages, 3 figures; 1 reference added, 1 figure changed, other minor change

The nature of the potassium compound acting as a promoter in iron-alumina catalysts for ammonia synthesis

The chemical form of the potassium promoter on an iron-alumina catalyst during ammonia synthesis has been studied by two methods, viz, (i) the measurement of the equilibrium constant of the process KNH2 + H2 KH + NH3, and (ii) chemical analysis of the used catalyst. The equilibrium constant measurements gave K723 = (12.9 ± 0.5) × 10−3, ΔHf2980(KNH2) = −119 ± 3 kJ mol−1 and S2980(KNH2) = 109 ± 4 J mol−1 K−1. The chemical analysis showed that no KNH2 is present on the catalyst during synthesis. From these results and with the aid of thermodynamic considerations it is concluded that KNH2, K and K2O are not stable compounds under conditions of ammonia synthesis. X-Ray diffraction showed that part of the potassium reacts with Al2O3, probably leaving part of the potassium in the form of KOH which is quite stable under ammonia synthesis conditions

Not the Cleavers Anymore: Third-Party Parental Interests in Minor Children and the Evolving American Family

Not the Cleavers Anymore: Third-Party Parental Interests in Minor Children and the Evolving American Famil