Solvent free liquid phase oxidation of benzyl alcohol using Au supported catalysts prepared using a sol immobilization technique

Solvent free oxidation of benzyl alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for benzyl alcohol oxidation.     

Green Catalysis with Alternative Feedstocks

The use of renewable feedstocks, derived from biomass, for the chemical industry is discussed. The modern chemical industry is based around platform chemicals, e.g. ethene, propene, benzene and xylenes, which are readily derived from oil, and using these intermediates a broad range of finished products can be derived. While it is feasible that biomass can be converted to syngas and hence to existing key platform chemicals, this loses all of the chemical complexity that is inherent in bio-derived molecules. In this paper some of the options are considered and, in particular, the oxidation of glucose and glycerol using gold nanoparticles supported on carbon is described. We also contrast the oxidation of glycerol using supported gold and gold–palladium alloys prepared using an impregnation technique, since the gold–palladium alloys have been shown to be highly effective for the oxidation of alcohols and the synthesis of hydrogen peroxide.     

Screening of Soluble Rhodium Nanoparticles as Precursor for Highly Active Hydrogenation Catalysts: The Effect of the Stabilizing Agents

We report the preparation of rhodium nanoparticles (NPs) stabilized by 1-octadecanethiol (ODT), polyvinyl alcohol (PVA), and tetraoctylammonium bromide (TOAB), and their application for hydrogenation catalysis. The three metal–ligand systems correspond to different mechanism of NPs stabilization via strong covalent linkage, chemisorbed atoms and electrostatic interactions, respectively. We found a strong effect of the interaction between the stabilizer and the surface of the metal nanoparticle on the catalytic activity. The Rh NPs were studied as soluble nanoparticle catalysts and as precursors for the synthesis of supported catalysts. All catalysts were tested in the hydrogenation of cyclohexene under similar conditions as a model reaction. Generally, Rh–ODT NPs were inactive, Rh–PVA NPs exhibited distinct activities in solution (aqueous biphasic catalysis) and as a supported catalyst, and Rh–TOAB NPs exhibited similar activities in solution and after immobilization. This last result opens the opportunity for the preparation of highly active Rh NP catalysts both in solution and as a heterogeneous catalyst. Additionally, the stability of the nanoparticles depends on the choice of ligand and on the functionalization of the support surface before immobilization. By optimizing the catalyst synthesis and reaction conditions, turnover frequencies as high as 700,000 h^?1 where observed for stable and recyclable catalyst.     

Effect of Particle Size on Monometallic and Bimetallic (Au,Pd)/C on the Liquid Phase Oxidation of Glycerol

The influence of metal particle size of monometallic and bimetallic supported catalysts (Au, Pd, Au–Pd)/C was studied using as a model reaction the liquid phase oxidation of glycerol. By tuning the metal particle size from 2 to 16 nm a progressive decrease of activity and simultaneously an increase in the selectivity to sodium glycerate was observed. Moreover, the influence of the temperature was studied and it was found that by increasing the temperature, only with a large particle size the formed glycerate was retained and not over-oxidized to tartronate.     

Oxidation of benzyl alcohol using supported gold–palladium nanoparticles

A key discovery in the last two decades has been the realisation that gold, when prepared as supported nanoparticles, is exceptionally effective as an oxidation catalyst, particularly for the oxidation of alcohols. The catalytic efficacy is enhanced further by the alloying of gold with palladium. In this paper we study the effect of the method preparation of gold–palladium alloy nanoparticles supported on titania and investigate the activity of the materials for the selective oxidation of benzyl alcohol. We contrast impregnation and deposition–precipitation methods and demonstrate that the most active catalysts are prepared using the deposition–precipitation method.     

Polarimetric radar interferometry for improved mine detection andsurface clutter rejection

A recently developed technique, polarimetric radar interferometry, is applied to tackle the problem of the detection of buried objects embedded in surface clutter. An experiment with a fully polarimetric radar in an anechoic chamber has been carried out using different frequency bands and baselines. The processed results show the ability of this technique to detect buried plastic mines and to measure their depth. This technique enables the detection of plastic mines even if their backscatter response is much lower than that of the surface clutter     

High pressure homogenization increases the in vitro bioaccessibility of α- and β-carotene in carrot emulsions but not of lycopene in tomato emulsions

Abstract: The correlation between food microstructure and in vitro bioaccessibility of carotenes was evaluated for tomato and carrot emulsions (5% olive oil) subjected to high pressure homogenization (HPH) at varying degrees of intensity. The aim was to investigate whether additional mechanical disruption of the food matrix could be utilized to further increase the carotene bioaccessibility of an already pre‐processed material. The carotene bioaccessibility of the samples was measured after simulated in vitro digestion, carotene release to the oil phase was estimated by Confocal Raman spectroscopy and, to measure active uptake of carotenes, Caco‐2 cells were incubated with the digesta of selected samples. HPH did not notably affect the retention of carotenes or ascorbic acid but significantly increased both the release and micellar incorporation of α‐ and β‐carotene in carrot emulsions 1.5‐ to 1.6‐fold. On the other hand, in vitro bioaccessibility of lycopene from tomato was not increased by HPH under any of the conditions investigated. Instead, the results suggested that lycopene bioaccessibility was limited by a combination of the low solubility of lycopene in dietary lipids and entrapment in the cellular network. Carotene uptake by Caco‐2 cells appeared to be mainly dependent upon the carotene concentration of the digesta, but cis‐trans isomerization had a significant impact on the micellarization efficiency of carotenes. We therefore conclude that HPH is an interesting option for increasing the bioaccessibility of carotenes from fruits and vegetables while maintaining a high nutrient content, but that the results will depend on both food source and type of carotene. Practical Application: A better understanding of the correlation between the processing of fruits and vegetables, microstructure and nutrient bioaccessibility can be directly applied in the production of food products with an increased nutritional value.     

Rheology and microstructure of carrot and tomato emulsions as a result of high-pressure homogenization conditions

High-pressure homogenization, as a way to further mechanically disrupt plant cells and cell walls compared to conventional blending, has been applied to thermally treated and comminuted carrot and tomato material in the presence of 5% olive oil. Mixes of both vegetables in a 1:1 ratio were also included. Both the effect of homogenization pressure and the effect of multiple process cycles were studied. The different microstructures generated were linked to different rheological properties analyzed by oscillatory and steady state measurements. The results showed that while carrot tissue requires a high shear input to be disrupted into cells and cell fragments, tomato cells were broken across the cell walls already at moderate shear input, and the nature of the tomato particles changed to amorphous aggregates, probably composed of cell contents and cell wall polymers. All the plant stabilized emulsions generated were stable against creaming under centrifugation. While for tomato a low-pressure multiple cycle and a high-pressure single-cycle process led to comparable microstructures and rheological properties, carrot showed different rheological properties after these treatments linked to differences in particle morphology. Mixes of carrot and tomato showed similar rheological properties after homogenizing in a single or in a split-stream process. Practical Application: Following consumers' demand, the food industry has shown a growing interest in manufacturing products free of gums and stabilizers, which are often perceived as artificial. By tailored processing, fresh plant material could be used to structure food products in a more natural way while increasing their nutritional quality.     

Retrieval of biophysical parameters of agricultural crops using polarimetric SAR interferometry

An existing two-layer model for forest height estimation is adapted for agricultural crops in order to develop a retrieval algorithm based on polarimetric synthetic aperture radar interferometry. This new inversion scheme is specifically tailored for vertically oriented agricultural crops, with extinction coefficients dependent on the wave polarization. Physical parameters of the vegetation scene are estimated from the location of the measured coherences in the complex plane. The proposed inversion scheme is validated experimentally with indoor wide-band polarimetric measurements on samples of corn and rice fields. Results show that the estimates of the thickness of the vegetation layer and the ground topography are reasonably accurate for a wide range of frequencies and baselines. Moreover, some interesting results are also obtained when using only dual-polarized data, which brings up new applications for present and future spaceborne missions.