Extending the range of liquids available for NMR cryoporometry studies of porous materials

Nuclear magnetic resonance (NMR) cryoporometry, although well established, can be limited by the inability of any one liquid to probe a broad range of pore sizes, a relatively small number of commonly-used probe liquids and the requirement to match the probe liquid to the chemistry of the material being studied. Here we demonstrate, for the first time, the use of menthol and t-butanol as probe liquids in NMR cryoporometry measurements. Using appropriate estimates for the values of the melting point depression constant, kc, and the non-freezing surface layer, 2sl, NMR melting data was converted into pore size distributions. The melting point depression constant for t-butanol is similar to that of cyclohexane; however due to its functionality, t-butanol may be the preferred liquid used to study the porosity of hydrophilic materials. Menthol, having a larger value of kc, can accurately analyze larger pore sizes up to 100 nm. This represents the first use of menthol and t-butanol to accurately probe pore dimensions in NMR cryoporometry

Highly selective hydrogenation of furfural over supported Pt nanoparticles under mild conditions

The selective liquid phase hydrogenation of furfural to furfuryl alcohol over Pt nanoparticles supported on SiO₂, ZnO, γ-Al2O₃, CeO₂ is reported under extremely mild conditions. Ambient hydrogen pressure, and temperatures as low as 50 °C are shown sufficient to drive furfural hydrogenation with high conversion and >99% selectivity to furfuryl alcohol. Strong support and solvent dependencies are observed, with methanol and n-butanol proving excellent solvents for promoting high furfuryl alcohol yields over uniformly dispersed 4 nm Pt nanoparticles over MgO, CeO₂ and γ-Al₂O₃. In contrast, non-polar solvents conferred poor furfural conversion, while ethanol favored acetal by-product formation. Furfural selective hydrogenation can be tuned through controlling the oxide support, reaction solvent and temperature

NMR cryoporometric measurements of porous silica:A method for the determination of melting point depression parameters of probe liquids

Nuclear magnetic resonance (NMR) cryoporometry is a non-invasive method for determining the pore size distributions of materials such as porous silica. Cryoporometry has several advantages over other porometric techniques. It is able to measure the melting process in a series of discrete steps, whereas transient heat flow techniques, such as differential scanning calorimetry (DSC), have a minimum rate of measurement, and, secondly, NMR cryoporometry can analyze pore shapes with any geometry, where nitrogen porosimetry is complicated for samples with spherical pores with narrow necks. However, one key drawback of the method is that, for any one liquid observed in any one material, there is a lack of consensus in the two parameters, kckc andView the MathML source2sl , used to convert experimental NMR melting point depression data into a pore size distribution. By considering two decades worth of literature data, values for both were obtained for water in porous silica supports, in particular an estimate of a non-freezing layer between the solid ice and the inner surface of the pore. These values were used to produce pore size distributions for three silica materials, SBA-15 and KIT-6, both with cylindrical pores but possessing different structures, and SBA-16, which has spherical pores. This represents the first time KIT-6 has been characterized by the NMR method. Furthermore, this work demonstrates a general method for obtaining values for kckc and View the MathML source2sl which can be applied to any liquid for which suitable literature data is available

Beyond the simple Proximity Force Approximation: geometrical effects on the non-retarded Casimir interaction

We study the geometrical corrections to the simple Proximity Force Approximation for the non-retarded Casimir force. We present analytical results for the force between objects of various shapes and substrates, and between pairs of objects. We compare the results to those from more exact numerical calculations. We treat spheres, spheroids, cylinders, cubes, cones, and wings; the analytical PFA results together with the geometrical correction factors are summarized in a table.Comment: 18 pages, 19 figures, 1 tabl

Platinum catalysed aerobic selective oxidation of cinnamaldehyde to cinnamic acid

Aerobic selective oxidation of allylic aldehydes offers an atom and energy efficient route to unsaturated carboxylic acids, however suitable heterogeneous catalysts offering high selectivity and productivity have to date proved elusive. Herein, we demonstrate the direct aerobic oxidation of cinnamaldehyde to cinnamic acid employing silica supported Pt nanoparticles under base-free, batch and continuous flow operation. Surface and bulk characterisation of four families of related Pt/silica catalysts by XRD, XPS, HRTEM, CO chemisorption and N2 porosimetry evidence surface PtO2 as the common active site for cinnamaldehyde oxidation, with a common turnover frequency of 49,000 ± 600 h−1; competing cinnamaldehyde hydrogenolysis is favoured over metallic Pt. High area mesoporous (SBA-15 or KIT-6) and macroporous-mesoporous SBA-15 silicas confer significant rate and cinnamic acid yield enhancements versus low area fumed silica, due to superior platinum dispersion. High oxygen partial pressures and continuous flow operation stabilise PtO2 active sites against in-situ reduction and concomitant deactivation, further enhancing cinnamic acid productivity

Tailored mesoporous silica supports for Ni catalysed hydrogen production from ethanol steam reforming

Mesoporous silica supported Ni nanoparticles have been investigated for hydrogen production from ethanol steam reforming. Ethanol reforming is structure-sensitive over Ni, and also dependent on support mesostructure; three-dimensional KIT-6 possessing interconnected mesopores offers superior metal dispersion, steam reforming activity, and on-stream stability against deactivation compared with a two-dimensional SBA-15 support

Selective oxidation of allylic alcohols over highly ordered Pd/meso-Al2 O3 catalysts

Highly ordered mesoporous alumina was prepared via evaporation induced self assembly and was impregnated to afford a family of Pd/meso-Al2O3 catalysts for the aerobic selective oxidation (selox) of allylic alcohols under mild reaction conditions. CO chemisorption and XPS identify the presence of highly dispersed (0.9–2 nm) nanoparticles comprising heavily oxidised PdO surfaces, evidencing a strong palladium-alumina interaction. Surface PdO is confirmed as the catalytically active phase responsible for allylic alcohol selox, with initial rates for Pd/meso-Al2O3 far exceeding those achievable for palladium over either amorphous alumina or mesoporous silica supports. Pd/meso-Al2O3 is exceptionally active for the atom efficient selox of diverse allylic alcohols, with activity inversely proportional to alcohol mass

Acción : diario de Teruel y su provincia: Año II Número 116 - (06/04/33)

The selective aerobic oxidation of crotyl alcohol to crotonaldehyde was investigated by time-resolved synchronous DRIFTS/MS/XAS over silica and alumina supported Pd nanoparticles. Alcohol and oxygen reactant feeds were cycled through the catalyst bed while dynamic measurements of the palladium oxidation state, molecular adsorbates and evolved product distribution were made simultaneously on a sub-second timescale. Highly dispersed palladium nanoparticles remained in a partially oxidised state <100 degrees C, independent of the redox environment, and were selective for crotonaldehyde formation. Higher temperatures facilitated rapid catalyst reduction on exposure to crotyl alcohol, with palladium metal driving crotonaldehyde decarbonylation to propene and CO, while slower (surface diffusion-limited) reoxidation on exposure to oxygen re-opened selective oxidation pathways. Surface palladium oxide is identified as the desired active species

Producing carbon nanotubes from thermochemical conversion of waste plastics using Ni/ceramic based catalyst

As the amount of waste plastic increases, thermo-chemical conversion of plastics provides an economic flexible and environmental friendly method to manage recycled plastics, and generate valuable materials, such as carbon nanotubes (CNTs). The choice of catalysts and reaction parameters are critical to improving the quantity and quality of CNTs production. In this study, a ceramic membrane catalyst (Ni/Al2O3) was studied to control the CNTs growth, with reaction parameters, including catalytic temperature and Ni content investigated. A fixed two-stage reactor was used for thermal pyrolysis of plastic waste, with the resulting CNTs characterized by various techniques including scanning electronic microscopy (SEM), transmitted electronic microscopy (TEM), temperature programmed oxidation (TPO), and X-ray diffraction (XRD). It is observed that different loadings of Ni resulted in the formation of metal particles with various sizes, which in turn governs CNTs production with varying degrees of quantity and quality, with an optimal catalytic temperature at 700 °C

Development of Ca/KIT-6 adsorbents for high temperature CO2 capture

The incorporation of CaO into an inert porous solid support has been identified as an effective approach to improve the stability of adsorbents for CO2 capture. In this work, we focus on enhancing the capacity of carbon capture and cyclic stability of CaO by impregnating CaO particles into a three-dimensional mesoporous silica (KIT-6) support. At a low CaO loading, the three-dimensional mesoporous support was filled with CaO nano-particles. The further increase of CaO loading resulted in the aggregation of CaO particles on the external surface of the support material, as identified by electron microscopy analysis. These CaO/KIT-6 adsorbents show excellent high-temperature CO2 carbonation/calcination stability over multiple cycles of CaO carbonation and calcination. The enhancement of the performance of carbon capture is attributed to the interaction between CaO and the silica skeleton of KIT-6 through the formation of interfacial CaSiO3 and Ca2SiO4 which enhanced the resistance of CaO sintering