Karina Mathisen

In Situ Infrared Spectroscopic and Gravimetric Characterisation of the Solvent Removal and Dehydroxylation of the Metal Organic Frameworks UiO-66 and UiO-67

Herein, the desolvation, dehydroxylation and rehydroxylation of the metal organic frameworks UiO-66 and -67 are followed by in situ DRIFTS and TG–DSC. The spectra recorded on UiO-66 feature multiple bands corresponding to chemically inequivalent isolated hydroxyl groups, whereas UiO-67 has the expected single μ3-OH band from the Zr6O4(OH)4 cornerstone. Complete rehydration is demonstrated on both materials. Based on further experimental insights, hypotheses are given to explain the observed differences between UiO-66 and -67. Quantum chemical calculations are employed in order to deduce the feasibility of one possible explanation for the observed behaviour on UiO-66.

Selective catalytic reduction of NOx over microporous CuAPO-5: structural characterisation by XAS and XRD

The effects of copper source, copper content, Al : P ratio and silicon content for the hydrothermal synthesis of CuAPO-5 using tetraethylammonium hydroxide as template have been investigated. The copper to phosphorus ratio in the synthesis gel was varied from 0.04 to 0.2, and copper(II) oxide and copper(II) acetate were used as copper sources. The samples were characterised by XAS (XANES, EXAFS), XRD (X-ray diffraction), TGA (thermogravimetric analysis), SEM (scanning electron microscopy) and elemental analysis. Rietveld refinements of the structure of CuAPO-5 were carried out on synchrotron X-ray powder diffraction data. The catalytic properties of CuAPO-5 in selectively reducing NOx in the presence of hydrocarbons (SCR-HC) were studied. The results from EXAFS show that copper is present in a distorted octahedral environment, with 4 or 5 Cu–O distances at 1.95 A and 1 or 2 Cu–Al/P distances at about 3.14 A for the as-synthesised samples. The calcined samples still show the same four Cu–O distances at 1.95 A, but with the composite peak at 3.14 A being significantly reduced. The turquoise colour of the as-synthesised CuAPO-5 is consistent with the copper atoms being complexed by water molecules within the pores as the hexaaquacopper(II) complex. The extraframework complex cation is electrostatically bound to the anionic phosphate sites of the framework. The colour changes to olive green on calcination, indicating tetrahedrally coordinated framework copper. The selective catalytic reduction of NOx by propene is catalysed by CuAPO-5 to the extent of 18% conversion. The Rietveld analysis show that calcined CuAPO-5 belongs to the P6/mcc spacegroup in which Al and P are indistinguishable.

The Methylococcus capsulatus (Bath) secreted protein, MopE*, binds both reduced and oxidized copper.

Under copper limiting growth conditions the methanotrophic bacterium Methylococcus capsulatus (Bath) secrets essentially only one protein, MopE*, to the medium. MopE* is a copper-binding protein whose structure has been determined by X-ray crystallography. The structure of MopE* revealed a unique high affinity copper binding site consisting of two histidine imidazoles and one kynurenine, the latter an oxidation product of Trp130. In this study, we demonstrate that the copper ion coordinated by this strong binding site is in the Cu(I) state when MopE* is isolated from the growth medium of M. capsulatus. The conclusion is based on X-ray Near Edge Absorption spectroscopy (XANES), and Electron Paramagnetic Resonance (EPR) studies. EPR analyses demonstrated that MopE*, in addition to the strong copper-binding site, also binds Cu(II) at two weaker binding sites. Both Cu(II) binding sites have properties typical of non-blue type II Cu (II) centres, and the strongest of the two Cu(II) sites is characterised by a relative high hyperfine coupling of copper (A|| = 20 mT). Immobilized metal affinity chromatography binding studies suggests that residues in the N-terminal part of MopE* are involved in forming binding site(s) for Cu(II) ions. Our results support the hypothesis that MopE plays an important role in copper uptake, possibly making use of both its high (Cu(I) and low Cu(II) affinity properties.

A combined in situ XAS/Raman and WAXS study on nanoparticulate V2O5 in zeolites ZSM-5 and Y

Nanoparticles (NPs) of vanadium pentoxide (V2O5) were introduced into zeolites H–ZSM-5 and H–Y by an ion exchange/co-precipitation procedure. Wide Angle X-ray Scattering confirms the presence of V2O5 NPs in ZSM-5, but the particles formed in zeolite Y were too small to be detected. The local vanadium environment was studied by combined X-ray Absorption Spectroscopy and Raman. The vanadium coordination in V2O5/ZSM-5 is distorted square pyramidal, similar to that in bulk V2O5. The vanadyl group is absent in zeolite Y, which is mainly comprised of symmetrical VO x surface groups. The size of the NPs is clearly limited by the shape selective properties of the chosen 3-D support system. Only V2O5/ZSM-5 is active in oxidising propene over a wide temperature range. Variations in the pre-edge height of the 1s–3d pre-edge feature suggests that continuous breakage and restoration of the V=O bond occurs in V2O5/ZSM-5 during reaction.

CO Oxidation over Au/TiO2–Carbon Catalysts: The Effect of Thermal Treatment, Stability and TiO2 Support Structure

The effect of thermal treatment on the catalyst structure and the CO oxidation performance of a Au/TiO2 catalyst supported on a carbon composite material has been studied. X-ray absorption spectroscopy shows that the carbon composite stabilises the TiO2 and prevent agglomeration of the particles. The activity measurements show that both Au and TiO2 need to be present in order to obtain catalytic activity. The catalytic performance was found to be strongly affected by thermal treatments of the active phase prior to the reaction. The thermal treatments have an effect on the ordering of the TiO2 structure, and on the CO oxidation activity. Heat treatment after Au deposition has a positive effect on the CO oxidation performance. This is attributed to the introduction of a stronger interaction between the oxide and Au which improves the catalytic activity. This also indicates that the TiO2 support and the Au–TiO2 interface play important roles in the CO oxidation reaction.