Ian J. Shannon

Microbial engineering of nanoheterostructures: Biological synthesis of a magnetically recoverable palladium nanocatalyst

Precious metals supported on ferrimagnetic particles have a diverse range of uses in catalysis. However, fabrication using synthetic methods results in potentially high environmental and economic costs. Here we show a novel biotechnological route for the synthesis of a heterogeneous catalyst consisting of reactive palladium nanoparticles arrayed on a nanoscale biomagnetite support. The magnetic support was synthesized at ambient temperature by the Fe(III)-reducing bacterium, Geobacter sulfurreducens , and facilitated ease of recovery of the catalyst with superior performance due to reduced agglomeration (versus conventional colloidal Pd nanoparticles). Surface arrays of palladium nanoparticles were deposited on the nanomagnetite using a simple one-step method without the need to modify the biomineral surface, most likely due to an organic coating priming the surface for Pd adsorption, which was produced by the bacterial culture during the formation of the nanoparticles. A combination of EXAFS and XPS showed the Pd nanoparticles on the magnetite to be predominantly metallic in nature. The Pd(0)-biomagnetite was tested for catalytic activity in the Heck reaction coupling iodobenzene to ethyl acrylate or styrene. Rates of reaction were equal to or superior to those obtained with an equimolar amount of a commercial colloidal palladium catalyst, and near complete conversion to ethyl cinnamate or stilbene was achieved within 90 and 180 min, respectively.

SSZ‐23: An Odd Zeolite with Pore Openings of Seven and Nine Tetrahedral Atoms

Single-crystal X-ray diffraction with synchrotron radiation enabled the structure of microcrystalline SSZ-23 (see drawing on the right), the first zeolite with channels bounded by seven- and nine-membered rings, to be solved.

Synthesis of functionalised porous network silsesquioxane polymers

Porous polyhedral silsesquioxane (POSS)-based network polymers are prepared using hydrosilation copolymerisation reactions of a silyl-functionalised POSS molecule with a vinyl-functionalised moiety. Characterisation of these solids show them to possess pore structures in the mesoporous regime, and polymers with longer organic linking groups showing evidence of flexible wall structures. Functionalisation of the polymers is carried out by reaction with triflic acid or sodium hydroxide, followed by incorporation of CpTiCl3. EXAFS spectroscopy results are consistent with the titanium being coordinated to the oxygen atoms that make up part of a POSS unit.

Imaging the structure, symmetry, and surface-inhibited rotation of polyoxometalate ions on graphene oxide

Atomic-resolution imaging of discrete [γ-SiW10O36]8- lacunary Keggin ions dispersed onto monolayer graphene oxide (GO) films by low voltage aberration corrected transmission electron microscopy is described. Under low electron beam dose, individual anions remain stationary for long enough that a variety of projections can be observed and structural information extracted with ca. ± 0.03 nm precision. Unambiguous assignment of the orientation of individual ions with respect to the point symmetry elements can be determined. The C2v symmetry [γ-SiW10O36]8- ion was imaged along its 2-fold C2 axis or orthogonally with respect to one of two nonequivalent mirror planes (i.e., σv). Continued electron beam exposure of a second ion imaged orthogonal to σv causes it to translate and/or rotate in an inhibited fashion so that the ion can be viewed in different relative orientations. The inhibited surface motion of the anion, which is in response to H-bonding-type interactions, reveals an important new property for GO in that it demonstrably behaves as a chemically modified (i.e., rather than chemically neutral) surface in electron microscopy. This behavior indicates that GO has more in common with substrates used in imaging techniques such as atomic force microscopy and scanning tunneling microscopy, and this clearly sets it apart from other support films used in transmission electron microscopy.

Hydrotalcite-derived mixed oxides containing copper: catalysts for the removal of nitric oxide

Hydrotalcite structures containing copper, magnesium and aluminium in the metal hydroxide layers have been investigated for their potential as precursors to the formation of catalysts for the decomposition and reduction of nitrogen oxides. These CuIIMgIIAlIII hydrotalcites are catalytically active towards both the decomposition of nitric oxide and its reduction in the presence of an appropriate coreductant, such as propane. The copper centred active species, identified using EXAFS spectroscopy and combined EXAFS/XRD under operating conditions, have been found to be CuI for the decomposition and Cu0 for the reduction.

Metallocene-derived, isolated MoVI active centres on mesoporous silica for the catalytic dehydrogenation of methanol

Isolated MoVI active sites have been grafted onto the inner surfaces of MCM-41 mesoporous silica via a molybdocene dichloride precursor, to generate a catalyst which has been tested for the oxidative dehydrogenation of methanol. Mo K-edge X-ray absorption spectroscopy shows that, after calcination, at low Mo loadings (ca. 1 mol% with respect to SiO2), isolated MoO4 species are generated on the surface, whereas at higher loadings (ca. 4 mol%) there is some evidence for the formation of polymeric oxo-molybdenum species. Catalysis tests show that lower Mo loadings on the MCM-41 silica lead to higher selectivity for the production of formaldehyde, in contrast to the results of previous studies of isolated Mo species on pure silica, which report that methyl formate is the major product.

Control of structure, pore size and morphology of three dimensionally ordered mesoporous silicas prepared using the dicationic surfactant [CH3(CH2)15N(CH3)2(CH2)3N(CH3)3]Br2

The synthesis of mesoporous silicas in the presence of the dicationic gemini surfactant [CH3(CH2)15N(CH3)2(CH2)3N(CH3)3]Br2 (C16-3-1) has been investigated at low temperatures (−4 °C) under basic and acidic conditions. Under basic conditions, the SBA-2 phase (based on a close-packed arrangement of micelles and exhibiting frequent stacking faults) is observed, with hollow sphere morphology. Under strongly acidic conditions, the phase SBA-1 (Pmn) and the SBA-2 family of phases (based on the close packing of micelles) are observed, depending on the surfactant and silicate content of the original gel. Conditions under which the pure hexagonally close-packed end member of the family (P63/mmc) is formed have been identified. SBA-1 and the pure hexagonally close-packed end member are prepared with well-defined morphologies. The adsorption of nitrogen and the hydrocarbons cyclopentane and mesitylene reveal that SBA-2 prepared in basic media has a cage structure where the cages are linked through small (<4 A) micropores, whereas the silicas prepared in acidic media have larger pores after calcination. SBA-1 and a poorly ordered SBA-2, prepared using C16-3-1 under acidic conditions, are able to adsorb mesitylene (diameter ca. 8 A), whereas the hexagonal end member of the SBA-2 series prepared under acidic conditions is able to adsorb cyclopentane (diameter ca. 5 A) but not mesitylene.

Synthesis, structure and thermal transformations of aluminophosphates containing the nickel complex [Ni(diethylenetriamine)2]2+ as a structure directing agent

Abstract [Ni(diethylenetriamine)2]2+, (Ni(deta)2), acts as a structure directing agent for aluminophosphates and metalloaluminophosphates with the CHA and AFI framework topologies. In the presence of ammonium fluoride, triclinic Ni(deta)2-UT-6; P 1 , a=9.289(1) A, b=9.095(1) A, c=9.356(1) A, α=88.35(1)°, β=78.91(1)°, γ=89.21(1)°, with the CHA topology and orthorhombic Ni(deta)2-AlPO(F)-5; Ccc2, a=13.8603(5) A, b=23.1285(5) A, c=8.5420(4) A with the AFI topology are prepared, the latter being favoured by higher water contents in the synthesis gel. Upon heating in nitrogen or oxygen at temperatures of 500 °C and above, Ni(deta)2-UT-6 is transformed reconstructively to an aluminophosphate with the AFI topology whereas heating at lower temperatures followed by heating in oxygen at 600 °C removes the organic and gives a solid with the CHA topology. Calcination of all samples prepared in the absence of fluoride leaves the original frameworks intact. Ni K-edge X-ray spectroscopy of Ni(deta)2-UT-6 calcined in oxygen at 600 °C reveals the formation of nanoparticulate NiO.

Structural and dynamic properties of the 1,10-dibromodecane/urea inclusion compound, investigated by variable-temperature powder X-ray diffraction, solid-state 2H NMR lineshape analysis and solid-state 2H NMR spin–lattice relaxation time measurements

Powder X-ray diffraction and solid-state 2H NMR lineshape analysis and spin–lattice relaxation time measurements have been used to investigate structural and dynamic properties of the 1,10-dibromodecane/urea inclusion compound. This solid has the characteristic urea ‘host’ tunnel structure of conventional urea inclusion compounds and the 1,10-dibromodecane ‘guest’ molecules are located within these tunnels.Variable-temperarture powder X-ray diffraction studies have demonstrated that a phase transition (at ca. 140–146 K) in 1,10-dibromodecane is associated with a change in the (average) symmetry of the urea tunnel structure from hexagonal (high-temperature phase) to orthorhombic (low-temperature phase) and is associated with only a minor structural distortion. From 2H NMR spectroscopy of [2H20]1,10-dibromodecane/urea, the dynamic properties of the guest molecules are best described as rotational diffusion in a six-fold cosine potential, and there is no significant discontinuity in this dynamic process at the phase-transition temperature. The results suggest that the dynamic properties of all CD2 groups in the guest molecule are indistinguishable (on the timescale of the 2H NMR technique). 2H NMR spectroscopy of 1,10-dibromodecane/[2H4]urea indicates that, at sufficiently high temperature, the urea molecules undergo 180° jumps about their CO bonds. Activation parameters have been determined for the reorientational motions of the 1,10-dibromodecane and urea molecules.The structural and dynamic properties of the 1,10-dibromodecane/urea inclusion compound, determined in this work, are compared in detail with the corresponding properties determined previously for alkane/urea inclusion compounds.

Theoretical prediction of the guest periodicity of alkane/urea inclusion compounds

A mathematical model of one-dimensional inclusion compounds, developed previously, is applied here to predict and rationalize structural properties of the alkane/urea family of inclusion compounds. Within this model, the one-dimensional inclusion compound is considered as a linear infinite host tunnel (with periodic repeat distance ch) containing a finite periodic arrangement (with periodic repeat distance cg) of identical guest molecules. This mathematical model provides a formalism that allows potential-energy functions (describing host–guest interaction, guest–guest interaction and intramolecular potential energies) computed for any one-dimensional inclusion compound to be used to predict and rationalize structural properties of the inclusion compound. Using this approach, the optimum cg has been determined for the series of urea inclusion compounds containing the alkane guest molecules CH3(CH2)rCH3, with r= 2–18, and the question of whether these inclusion compounds exhibit commensurate or incommensurate behaviour has been assessed. It is predicted and demonstrated that the heptadecane/urea inclusion compound is commensurate (6cg= 13ch). The butane/urea inclusion compound is also predicted to be commensurate, whereas all of the other alkane/urea inclusion compounds investigated are predicted to exhibit incommensurate behaviour. The wider issue of assessing the commensurate vs. incommensurate nature of such inclusion compounds by this theoretical approach is discussed.The alkane/urea inclusion compounds with guest molecules CH3(CH2)rCH3(r= 7–15, 18) have been studied by single-crystal X-ray diffraction, and from these data the value of cg at room temperature has been determined. The values of cg predicted theoretically for these inclusion compounds are in good agreement with the values of cg determined experimentally. For all the urea inclusion compounds studied, the optimum cg is ca. 0.5 A shorter than the value of cg corresponding to the minimum guest–guest interaction energy; this fact substantiates the claim that, at the optimum guest periodicity in alkane/urea inclusion compounds, the interaction between adjacent guest molecules is repulsive.