Surface Science Meets Catalysis Research: Iron oxide films for in-situ model catalysis

An in-depth model catalysis study on a complex system is reviewed. Both unpromoted and potassium-promoted iron oxide model catalysts films of single crystalline quality are prepared and characterized in ultrahigh vacuum (UHV) using surface science methods. In order to bridge the pressure and material gap for the catalytic dehydrogenation of ethylbenzene to styrene in presence of steam, this reaction is studied at reactive gas pressures between 10-6 and 36 mbar. The samples are transferred under vacuum into an stagnation point micro-flow reactor where the reaction is studied, followed by post-reaction characterization in UHV. Clean hematite Fe2O3 is an excellent catalyst but deactivates quickly by reduction and by coking. Addition of H2O limits reduction to the oxidation state of magnetite Fe3O4 and counteracts coking. Both deactivation mechanisms can be avoided by addition of some O2 to the feed. Potassium has basically the same functions as O2. It does not seem to be involved in the catalytic dehydrogenation step but rather to block active sites if its concentration is high. Long-term deactivation occurs mainly by potassium removal in form of volatile KOH. Regeneration by “steaming” in pure H2O accelerates this process while ethylbenzene in the feed stabilizes potassium. This is ascribed to the formation of non-volatile K2CO3 which is an intermediate in potassium catalysed coke removal. The addition of O2 instead of K-promotion may be an alternative reaction route

Spatioselective Growth of Metal‐Organic Framework Nanocrystals on Compositionally Anisotropic Polymer Particles

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106850/1/adma201305461-sup-0001-S1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/106850/2/adma201305461.pd

Made-to-order metal-organic frameworks for trace carbon dioxide removal and air capture

International audienceDirect air capture is regarded as a plausible alternate approach that, if economically practical, can mitigate the increasing carbon dioxide emissions associated with two of the main carbon polluting sources, namely stationary power plants and transportation. Here we show that metal-organic framework crystal chemistry permits the construction of an isostructural metal-organic framework (SIFSIX-3-Cu) based on pyrazine/copper(II) two-dimensional periodic 44 square grids pillared by silicon hexafluoride anions and thus allows further contraction of the pore system to 3.5 versus 3.84 Å for the parent zinc(II) derivative. This enhances the adsorption energetics and subsequently displays carbon dioxide uptake and selectivity at very low partial pressures relevant to air capture and trace carbon dioxide removal. The resultant SIFSIX-3-Cu exhibits uniformly distributed adsorption energetics and offers enhanced carbon dioxide physical adsorption properties, uptake and selectivity in highly diluted gas streams, a performance, to the best of our knowledge, unachievable with other classes of porous materials

Photocatalytic Degradation Of Phenolic Compounds

A great challenge for this century lies in cleaning-up the wastewater generated during industrial, domestic and agricultural activities before being released, into the aquatic environment, or reused for another purpose e.g. irrigation. Phenolic compounds among the various organic contaminates found in wastewater require special attention because of their toxic effect on humans and the environment. Their presence has been confirmed in many different industrial wastewaters. These phenolic compounds are refractory ones and the efficiency of their traditional treatment techniques is low. Therefore, the use of an effective and economic elimination technique for phenolic compounds in wastewater becomes an urgent demand. Advanced oxidation processes (AOPs) represents the most recent technology in wastewater treatment. TiO2 is known to be an excellent photocatalyst. However, there are some challenges regarding using TiO2 in the industrial scale. Significant attention is directed towards using carbonaceous nanomaterials as support to enhance photocatalytic behavior of TiO2 due to their unique and controllable structural and electrical properties. In this work, low percentage of reduced graphene oxide (RGO) and graphene oxide (GO) were supported on TiO2 seeking a better catalytic performances. These composites were tested for degrading some phenolic compounds using UV as photoexcitation source in presence of some oxidants e.g. H2O2. It was found that small loadings of GO and RGO decreased the band gap energy for TiO2 and increased the efficiency and decreased the time needed for the photodegradation of phenolic compounds.qscienc

One-dimensional metal-organic framework photonic crystals used as platforms for vapor sorption.

We present the fabrication of one-dimensional photonic crystals (Bragg stacks) based on a microporous metal–organic framework material and mesoporous titanium dioxide. The Bragg stack heterostructures were obtained using two complementary synthesis approaches utilizing the bottom-up assembly of heterogeneous, i.e. two-component photonic crystal multilayer structures. Zeolitic imidazolate framework ZIF-8 and mesoporous titanium dioxide were chosen as functional components with different refractive indices. While ZIF-8 is intended to impart molecular selectivity, mesoporous TiO2 is used to ensure high refractive index contrast and to guarantee molecular diffusion within the Bragg stack. The combination of micro- and mesoporosity within one scaffold endows the 1D-MOF PC with characteristic adsorption properties upon exposure to various organic vapors. In this context, the sorption behavior of the photonic material was studied as a function of partial pressure of organic vapors. The results show that the multilayered photonic heterostructures are sensitive and selective towards a series of chemically similar solvent vapors. It is thus anticipated that the concept of multilayer heterogeneous photonic structures will provide a versatile platform for future selective, label-free optical sensors