Ammonia decomposition on polycrystalline Pt at pressures between 1.3 and 93 kPa

The kinetics of ammonia decomposition on polycrystalline Pt at temperatures between 600 and 1700 K and at pressures between 1.3 and 93 kPa were measured and correlated with a Langmuir-Hinshelwood unimolecular reaction rate expression. This rate expression had previously been shown to fit data in the same temperature range for pressures between 2 and 1400 Pa.

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Pt 600–1700 1,3 93 , - . , , , 2 1400 .

     

Oxidative dehydrogenation of propane over Mo/g-Al2O3. effect of precursor

Alumina supported molybdenum oxide was prepared using ammonium heptamolybdate and molybdenum acetate as different precursors. The catalysts were characterized by BET, AAS, SEM-EDAX, XRD, TPR and surface acidity measurements. The characterization results and the catalytic behavior in oxydehydrogenation of propane were similar irrespective of precursor. This revised version was published online in August 2006 with corrections to the Cover Date.     

XPS study of the surface properties and Ni particle size determination of Ni‐supported catalysts

The surface properties of Ni/MgAl₂O₄ catalysts doped with Ce or Pr were analyzed by XPS after treatment in an inert and reductive atmosphere at 400 °C. The Ce‐promoted solids presented the Ce³⁺/Ce⁴⁺ couple on the surface even after treatment in a reductive atmosphere, H₂(5%)/Ar. The promotion effect of Ce on these solids could be associated with their participation on the carbon deposition‐removal mechanism. Pr‐doped catalysts showed a very high concentration of Pr³⁺ under a reductive atmosphere and the redox behavior associated with the carbon removal could be partially inhibited or become slower. The size of the Ni⁰ particles after both an inert and a reductive atmosphere was estimated by XPS intensity ratio using the model proposed by Davis. The results obtained from the Davis model showed that an important increase occurred in Ni particle size after treatment in H₂(5%)/Ar for the Pr‐promoted solids. The metal sintering under reductive atmosphere could be the reason for the higher loss of activity of the Pr‐doped solids under reforming conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of 1,1-Diethoxyethane From Bioethanol. Influence of Catalyst Acidity

The surface of an unpoisoned and sulfur-poisoned industrial iron ammonia catalysts is investigated by K, K⁺ thermal desorption. The K⁺ desorption energy increases while the K energy decreases upon poisoning. Presence of sulfur also suppresses the potassium desorption in electronically excited states. This revised version was published online in June 2006 with corrections to the Cover Date.     

Visibility Graphs and Oriented Matroids

Abstract. We describe a set of necessary conditions for a given graph to be the visibility graph of a simple polygon. For every graph satisfying these conditions we show that a uniform rank 3 oriented matroid can be constructed in polynomial time, which if affinely coordinatizable yields a simple polygon whose visibility graph is isomorphic to the given graph.     

Supported choline hydroxide (ionic liquid) as heterogeneous catalyst for aldol condensation reactions

Choline hydroxide was used as a basic catalyst for aldol condensation reactions to produce new C-C bonds between several ketones and aldehydes. Choline supported on MgO exhibits higher TOF values than other well known basic catalysts in these reactions.     

Preparation and characterization of CuZnAl catalysts by citrate gel process

CuZnAl catalysts with different Cu loading (1-23 wt%) and a Zn:Al atomic ratio nearly constant (Zn:Al≅0.6), were prepared by the citrate sol-gel method and characterized by different techniques such as TG, BET, TPR, XRD and FTIR. The final structure obtained was strongly influenced by the calcination temperature and metal precursor composition. XRD and quantitative Rietveld revealed Zn and Al species were mainly incorporated into the normal spinel matrix and copper predominantly forms CuO. The formation of a ZnAl₂O₄ spinel was favored by increasing Cu amounts and/or by increasing calcination temperature (from 500° to 700 °C). The spinel phase of the catalysts calcined at 700 °C, had a good thermal stability and it was preserved after TPR measurements. Under hydrogen atmosphere Cu²⁺ was fully reduced to Cu⁰. Although the composition and the calcination temperature have a strong influence on the phase nature in CuZnAl catalysts, the reducibility of Cu species changes in a non significant way.     

Visibility graphs of staircase polygons and the weak Bruhat order,I: From visibility graphs to maximal chains

The recognition problem for visibility graphs of simple polygons is not known to be in NP, nor is it known to be NP-hard. It is, however, known to be inPSPACE. Further, every such visibility graph can be dismantled as a sequence of visibility graphs of convex fans. Any nondegenerated configuration ofn points can be associated with amaximal chain in the weak Bruhat order of the symmetric groupS _n . The visibility graph ofany simple polygon defined on this configuration is completely determined by this maximal chain via a one-to-one correspondence between maximal chains andbalanced tableaux of a certain shape. In the case of staircase polygons (special convex fans), we define a class of graphs calledpersistent graphs and show that the visibility graph of a staircase polygon is persistent. We then describe a polynomial-time algorithm that recovers a representative maximal chain in the weak Bruhat order from a given persistent graph, thus characterizing the class of persistent graphs. The question of recovering a staircase polygon from a given persistent graph, via a maximal chain, is studied in the companion paper [4]. The overall goal of both papers is to offer a characterization of visibility graphs, of convex fans. The research of J. Abello was supported by NSF Grants Nos. DCR 8603722 and DCR 8896281. This research was done while K. Kumar was at the Department of Computer Science, Texas A & M University.     

Preparation and characterization of a glycyl-l-methioninatocopper(II) complex

Summary A glycyl-L-methioninatocopper(II) complex has been isolated and characterized using x-ray crystallography. Precise details are given about its preparation. Crystal parameters have been determined.