Exploring the Myth of Nascent Hydrogen and its Implications for Biomass Conversions

Iron (and to a lesser extent manganese) in the wall of a 316 stainless steel (SS) reactor is responsible for the hydrogenation of cyclohexanone to cyclohexanol when using an aqueous formic acid solution under high temperature and pressure water (HTPW) conditions. However, not only dilute formic acid but also aqueous solutions of several other organic and mineral acids in the presence of iron are active in this reaction covering a range of aldehydes and ketones, even under ambient conditions. The stoichiometry, kinetics, and the possible mechanisms of both dihydrogen production as well as of the hydrogenation of the model compound cyclohexanone were examined. The reduction is essentially stoichiometric with respect to metallic iron, and the conversions are highly dependent on the speed of stirring as well as temperature and reactant concentrations. Importantly, it is established unequivocally that water participates in dihydrogen gas formation (hydrogen atoms originate from both the acid and water molecules) and facilitates substrate reduction.     

A coupled blade element momentum – Computational fluid dynamics model for evaluating tidal stream turbine performance

A modelling approach based on blade element momentum theory is developed for the prediction of tidal stream turbine performance in the ocean environment. Through the coupling of the blade element momentum method with computational fluid dynamics, the influence of upstream hydrodynamics on rotor performance is accounted for. Incoming flow onto the rotor can vary in speed and direction compared to free-stream conditions due to the presence of obstructions to the flow in the upstream, due to other devices for example, or due to the complexity of natural bathymetries. The relative simplicity of the model leads to short run times and a lower demand on computational resources making it a useful tool for considering more complex engineering problems consisting of multiple tidal stream turbines. Results from the model compare well against both measured data from flume experiments and results obtained using the classical blade element momentum model. A discussion considering the advantages and disadvantages of these different approaches is included.     

CHR‐Insertion (RH,CH3) into Cyclohexyl‐Substituted Silsesquioxanes: Reactivity and Decomposition Studies

Amorphous silica plays an important role in heterogeneous catalysis as a support and is frequently presumed to be “inert”. The structure of the supported catalyst is key to understanding the stability and reactivity of catalytic systems. To provide vital insights into the surface reactivity of silica, Polyhedral oligomeric silsesquioxanes (POSSs) can act as realistic homogeneous molecular models for silica surfaces. Here, we report novel reactivities associated with the silica surface, derived from our insights obtained by means of such model systems with potentially significant implications in catalysis when employing silica‐supported catalysts. In this work, the gas‐phase reactivities of two cyclohexyl‐substituted POSSs, namely the completely condensed triganol prism [Si₆cy₆O₉] (a6b0), and the incompletely‐condensed partial cube [Si₇cy₇O₉(OH)₃] (a7b3), with cy=c‐C₆H₁₁, were studied by using atmospheric pressure chemical ionisation (APCI) and collision‐induced decomposition (CID) spectroscopies. Silsesquioxane a6b0, containing three‐membered rings, was found to be much more reactive, undergoing novel CH₂‐insertion on reaction with gas phase molecules—a reaction not observed for a7b3, containing only four‐membered rings. Both silsesquioxanes displayed the ability to trap ammonia formed in situ within the mass spectrometer from N₂ in the instrument. This work also demonstrates the applicability of APCI and the role of CID in elucidating reactive POSS structures, highlighting novel gas‐phase reactivities of POSS.     

The synthesis and characterization of norbornylsilasesquioxanes

Norbornene reacts with trichlorosilane to generate norbornyltrichlorosilane in high yield. The slow hydrolysis of norbornyltrichlorosilane in acetone yields incompletely condensed norbornyl-silasesquioxanes. The compound C₄₂H₇₀O₁₁Si₆ can be isolated from this reaction. On the basis of elemental analyses, ¹H, ¹³C and ²⁹Si NMR, mass spectroscopy, infrared spectroscopy, and crystallographic analysis, C₄₂H₇₀O₁₁Si₆ is formulated as [(C₇H₁₁)₆Si₆O₇(OH)₄], with the Si₆O₇ framework being composed of two perpendicular Si₄O₄ planes sharing an edge. [(C₇H₁₁)₆Si₆O₇(OH)₄] is a putative model of vicinal [Si(OH)]₂ sites on the surface of partially dehydroxylated silica.     

Crystal forms of hillocks and voids formed by electromigration on ultrapure gold and silver wires

Hillocks and voids (vacancy crystals) which were formed by electromigration on ultrapure gold and silver wires, showed only the combined crystal forms {111} and {100}. These planes are identical with the equilibrium planes G_I, calculated by Stranski and Kaishew for nonpolar substances under the assumption of only nearest neighbor interaction. Hillock and void nucleation occurred on crystal imperfections (heterogeneous nucleation). Hillocks and vacancy crystals (voids) on gold showed twin formation obeying the spinel law. Dedicated to Professor I. N. Stranski on the occasion of his 80th birthday.     

Gas-phase molecular structure of 1,1,1,2-tetrabromo-2,2-dimethyldisilane: theoretical and experimental investigation of a super-halogenated disilane and computational investigation of the F, Cl and I analogues

The molecular structure of 1,1,1,2-tetrabromo-2,2-dimethyldisilane (Br₃SiSiBrMe₂) has been determined in the gas phase by electron diffraction and ab initio molecular-orbital calculations. The computational investigation was used to augment the experimental investigation using the Structure Analysis Restrained by Ab initio Calculations for Electron diffractioN (SARACEN) method. The structure was found to adopt a staggered structure with C _s symmetry by both theory and experiment. Important structural parameters (r _h1) include: rSi–Si 235.6(5) pm, rSi–C 185.4(3) pm, rSi–Br_av 220.3(1) pm, ∠Si–Si–Br(14) 106.1(4)°, ∠Si–Si–C 109.2(8)° and ?Br–Si–Si–Br 180.0°(fixed). These experimental observations are supported by theoretical predictions obtained at the MP2/6-311+G* level. An analogous theoretical investigation was also performed for the series X₃SiSiXMe₂ (X = F, Cl and I) and structural trends identified. The Si–X bond was observed to lengthen as a function of the halogen substituent, with corresponding changes to the Si–Si–X bond angles in the SiX₃ groups. The Si–Si–X bond angle in the SiXMe₂ groups displayed rather different behaviour, and was relatively stable to substitution until X = I. The flexible nature of bond angles about silicon atoms was observed, even in this relatively sterically unhindered system.