Interaction between zeolites and cluster compounds. Part 2.—Thermal decomposition of iron pentacarbonyl on zeolites

Thermal decomposition in a thermobalance of Fe(CO)5 adsorbed on alkali-metal, hydrogen-Y, dealuminated Y, L and omega zeolites proceeds stepwise via slow decarbonylation at low and high temperatures, separated by a fast endothermic reaction. Average CO/Fe ratios have been determined after each step. From i.r. results the former intermediates are assigned to species bearing bridging CO, whereas reaction products with CO/Fe < 1 are associated with highly unsaturated carbonyl clusters in strong interaction with the zeolite.The thermal stability of zeolite/Fe(CO)5 adducts as well as of the intermediates increases with the electron-donor properties of the matrix and can be rationalized using the Sanderson electronegativity concept. Iron loadings ranging from 2.4 wt % in zeolite L up to 10 wt % with NaY and HY are obtained by decomposition in inert atmosphere. Under vacuum conditions loss of metal up to 50% is observed. Metallic iron clusters are the final decomposition products in alkali-metal zeolites, as probed by NO adsorption. In HY part of the metallic iron is oxidized to FeII ions, which are located at cation positions

Interaction between zeolites and cluster compounds. Part 1.—Adsorption of iron pentacarbonyl on zeolites

The adsorption isotherms of Fe(CO)5 on NaY, HY and Linde L zeolites obtained in McBain balances show micropore adsorption, whereas additional capillary condensation is found with zeolite omega and Na-mordenite. The pores and/or cages of the zeolites studied are completely filled with the complex upon saturation, with the exception of Na-mordenite. Their behaviour is explained, respectively, by pore blocking and the occurrence of channel openings that are too narrow. The silicalite channel system also is too narrow to accept Fe(CO)5 molecules.Infrared results show that an increasing interaction of the complex with faujasites exists in the sequence: dealuminated Y < CsY < HY < NaY. This is derived from the increasing band half-width of the adsorbed complex in the CO stretching region and from the increasing intensity of the v1 vibration, which upon adsorption becomes i.r. active. The interaction is assumed to be influenced mainly by electrostatic fields in the cages or pores, which can lead to a very restricted mobility for the encaged complex. The complex seems to remain intact upon adsorption at 293 K in all the zeolites studied

Multiphase smoothed-particle hydrodynamics

We adapt the smoothed-particle hydrodynamics (SPH) technique to allow a multiphase fluid in which SPH particles of widely differing density may be freely intermixed. Applications include modelling of galaxy formation and cooling flows

Flood modelling with hydraTE: 2+1-dimensional smoothed-particle hydrodynamics

We present HydraTE, our own implementation of the smoothed-particle hydrodynamics technique for shallow water that uses the adaptive size of the smoothing kernel as a proxy for the local water depth. We derive the equa- tions of motion for this approach from the Lagrangian before demonstrating that we can model the depth of water in a trough, implement vertical walls, recover the correct acceleration and terminal velocity for water flowing down a slope and obtain a stable hydraulic jump with the correct jump condition. We demonstrate that HydraTE performs well on two of the UK Environ- ment Agency flood modelling benchmark tests. Benchmark EA3 involves flow down an incline into a double dip depression and studies the amount of water that reaches the second dip. Our results are in agreement with those of the other codes that have attempted this test. Benchmark EA6 is a dam break into a horizontal channel containing a building. HydraTE again pro- duces results that are in good agreement with the other methods and the experimetal validation data except where the vertical velocity structure of the flow is expected to be multi-valued, such as the hydralic jump where the precise location is not recovered even though the pre- and post- jump water heights are. We conclude that HydraTE is suitable for a wide range of flood modelling problems as it preforms at least as well as the best available commercial alternatives for the problems we have tested

Characterization of a new iron-on-zeolite Y Fischer-Tropsch catalyst

Iron pentacarbonyl adsorbed on dry Na-Y zeolite can be oxidized at subambient temperatures into Fe203 located in the zeolite supercages (catalyst I). When catalyst I is hydrogen reduced at 575 K most of the iron has agglomerated externally to the zeolite (catalyst 11). When the iron carbonyl is thermally decomposed in vacuo at 525 K, an iron phase with a very low degree of dispersion is again obtained (catalyst 111). During a Fischer-Tropsch reaction most of the iron is transformed into a Hagg-type carbide phase, located externally to the zeolite. Catalysts I1 and 111 rapidly reach steady state and show a Schulz-Flory-type of product distribution, the Hagg carbide being the active phase. Catalyst I slowly moves to steady state and Schulz-Flory behavior. Product selectivity is only found on this catalyst during transient conditions. The physical information on the three catalysts before and after reaction was obtained with transmission electron microscopy and Mossbauer and EXAFS spectroscopies. These techniques supplied consistent and complementary evidenc

Supporting Data mining of large databases by visual feedback queries

In this paper, we describe a query system that provides visual relevance feedback in querying large databases. Our goal is to support the process of data mining by representing as many data items as possible on the display. By arranging and coloring the data items as pixels according to their relevance for the query, the user gets a visual impression of the resulting data set. Using an interactive query interface, the user may change the query dynamically and receives immediate feedback by the visual representation of the resulting data set. Furthermore, by using multiple windows for different parts of a complex query, the user gets visual feedback for each part of the query and, therefore, may easier understand the overall result. Our system allows to represent the largest amount of data that can be visualized on current display technology, provides valuable feedback in querying the database, and allows the user to find results which, otherwise, would remain hidden in the database

The Bowl Championship Series: A Mathematical Review

We discuss individual components of the college football Bowl Championship Series, compare with a simple algorithm defined by random walks on a biased graph, attempt to predict whether the proposed changes will truly lead to increased BCS bowl access for non-BCS schools, and conclude by arguing that the true problem with the BCS Standings lies not in the computer algorithms, but rather in misguided addition.Comment: 12 pages, 2 figures, submitted to Notices of the AM

MEGA: merger graphs of structure formation

When following the growth of structure in the Universe, we propose replacing merger trees with merger graphs, in which haloes can both merge and split into separate pieces. We show that this leads to smoother mass growth and eliminates catastrophic failures in which massive haloes have no progenitors or descendants. For those who prefer to stick with merger trees, we find that trees derived from our merger graphs have similar mass growth properties to previous methods, but again without catastrophic failures. For future galaxy formation modelling, two different density thresholds can be used to distinguish host haloes (extended galactic haloes, groups and clusters) from higher-density subhaloes: sites of galaxy formation