Making the most of precious metal nanoparticles in the purification of industrial wastewater by catalytic wet air oxidation

The aim of catalytic wet air oxidation is to use air to remove organic contaminants from wastewater through their complete oxidation, without having to vaporise the water. To date, the widespread exploitation of this process has been held back by the low activity of available catalysts, which means that it has to be operated at above-atmospheric pressure in order to keep the water in the liquid phase at the elevated temperatures required to achieve complete oxidation. Here we present an overview of an ongoing study examining the key requirements of both the active phase and the support material in precious metal catalysts for wet air oxidation, using phenol as the model contaminant. The major outcome to date is that the results reveal a synergy between platinum and hydrophobic support materials, which is not apparent when the active phase is ruthenium

Multifunctional Role of Magnetic Nanoparticles in Efficient Microalgae Separation and Catalytic Hydrothermal Liquefaction

In this work, the efficiency of extracting algae from culture medium using magnetic nanoparticles (MNPs), converting the algal/particle slurry to biocrude using hydrothermal liquefaction (HTL), and successfully recycling the MNPs from the char phase was fully demonstrated for the first time. MNPs were synthesized by coprecipitation and used to extract algae from aqueous phase at a separation efficiency (SE) of 99%. The SE was optimized at pH 4. Liquefaction of algal/MNPs slurry gave a biocrude yield of 37.1% while algae only yielded 23.2%. The percentage areas in the GC-MS chromatogram corresponding to hydrocarbons (HCs) in Zn-ferrite catalyzed and uncatalyzed biocrude were 46.5% and 19.9%, respectively, while the percentage areas of heptadecane from Zn-ferrite catalyzed and uncatalyzed biocrude were 37.8% and 10%, respectively. Furthermore, the percentage area of heteroatom compounds in biocrude reduced substantially when liquefaction was done in the presence of Zn/Mg ferrites. The nanoparticles were recovered from biochar by sonication and recycled at a SE of 96.1%. Recycling of MNPs for magnetic separation of algae and catalytic HTL could lower the cost of microalgae harvesting and improve the yield and quality of biocrude. This could potentially reduce the cost of advanced biofuel processing from microalgae, making them more affordable in comparison to petroleum-derived fuels.</p

Multifunctional Role of Magnetic Nanoparticles in Efficient Microalgae Separation and Catalytic Hydrothermal Liquefaction

In this work, the efficiency of extracting algae from culture medium using magnetic nanoparticles (MNPs), converting the algal/particle slurry to biocrude using hydrothermal liquefaction (HTL), and successfully recycling the MNPs from the char phase was fully demonstrated for the first time. MNPs were synthesized by coprecipitation and used to extract algae from aqueous phase at a separation efficiency (SE) of 99%. The SE was optimized at pH 4. Liquefaction of algal/MNPs slurry gave a biocrude yield of 37.1% while algae only yielded 23.2%. The percentage areas in the GC-MS chromatogram corresponding to hydrocarbons (HCs) in Zn-ferrite catalyzed and uncatalyzed biocrude were 46.5% and 19.9%, respectively, while the percentage areas of heptadecane from Zn-ferrite catalyzed and uncatalyzed biocrude were 37.8% and 10%, respectively. Furthermore, the percentage area of heteroatom compounds in biocrude reduced substantially when liquefaction was done in the presence of Zn/Mg ferrites. The nanoparticles were recovered from biochar by sonication and recycled at a SE of 96.1%. Recycling of MNPs for magnetic separation of algae and catalytic HTL could lower the cost of microalgae harvesting and improve the yield and quality of biocrude. This could potentially reduce the cost of advanced biofuel processing from microalgae, making them more affordable in comparison to petroleum-derived fuels.</p

Robust and reusable supported palladium catalysts for cross-coupling reactions in flow

Two novel polymer encapsulated silica supported palladium catalysts have been prepared and shown to be highly active, robust and recyclable catalysts for Heck and Suzuki–Miyaura cross coupling reactions under continuous flow conditions. They were demonstrated to give excellent conversions of both electron rich and electron deficient substrates and the catalysts were used for over 50 hours continuous operation without any appreciable decrease in catalytic activity and low levels of Pd leaching measured by ICP-MS.<br/

Sustainable catalytic epoxidation of biorenewable terpene feedstocks using H₂O₂as an oxidant in flow microreactors

Solvent-free continuous flow epoxidation of the alkene bonds of a range of biorenewable terpene substrates have been carried out using a recyclable tungsten-based polyoxometalate phase transfer catalyst and aqueous H2O2 as a benign oxidant. These sustainable flow epoxidation reactions are carried out in commercial microreactors containing static mixing channels that enable common monoterpenes (e.g. untreated crude sulfate turpentine, limonene, etc.) to be safely epoxidized in short reaction times and in good yields. These flow procedures are applicable for the flow epoxidation of trisubstituted and disubstituted alkenes for the safe production of multigram quantities of a wide range of epoxides. This journal i

Continuous-flow liquid-phase dehydrogenation of 1,4-cyclohexanedione in a structured multichannel reactor

A highly selective, scalable and continuous-flow process is developed for the liquid-phase dehydrogenation of 1,4-cyclohexanedione to hydroquinone in a millimetre-scale structured multichannel reactor. The square shaped channels (3 mm × 3 mm) were filled with 10 wt% Pd/C catalyst particles and utilized for the dehydrogenation reaction in single-pass and recycle modes. For the purpose to enhance process understanding and to maximize conversion and selectivity by process optimization, Design of Experiment (DoE) methodology was utilized by studying the effect of operating parameters on the catalytic performance in kinetic regime. The results demostrated the strong influence of temperature and liquid feed flow on the conversion and selectivity, with liquid feed and N₂ flows influencing pressure drop significantly. A multi-objective optimization methodology was used to identify the optimum process window with the aid of sweet spot plots, with design space plots developed to establish acceptable boundaries for process parameters. In single-pass mode, complete conversion per pass per channel was not achievable whereas conversion increased from 59.8% in one-channel to 78.3% for two-channel-in-series while maintaining selectivity (&gt; 99%) with intermediate hydrogen removal. However, for without intermediate H₂ removal step, selectivity was declined from &gt; 99% in one-channel to 82.3% at the outlet of second-channel. In recycle mode, dehydrogenation reaction was resulted in almost complete conversion (&gt; 99%) with very high selectivity (&gt; 99%) and yield (&gt; 98%). This combination of mm-scale multichannel reactor and DoE methodology opens the way to developing highly selective and scalable dehydrogenation proocesses in the fine chemical and pharmaceutical industries

Ruthenium-catalyzed <i>O</i>- to S-alkyl migration:a pseudoreversible Barton-McCombie pathway

A practical ruthenium-catalyzed O- to S-alkyl migration affords structurally diverse thiooxazolidinones in excellent yields. Our studies suggest this catalytic transformation proceeds through a pseudoreversible radical pathway drawing mechanistic parallels to the classic Barton-McCombie reaction. A radical step in a new direction: A practical ruthenium-catalyzed O- to S-alkyl migration affords structurally diverse thiooxazolidinones in excellent yields. Experimental and computational studies suggest a pseudoreversible radical pathway drawing mechanistic parallels to the classic Barton-McCombie reaction.</p

Exploring the feasibility of continuous CWAO of bisphenol A at near-ambient temperature and pressure through use of hydrophobic Pt catalysts

Hydrophobic Pt CWAO-catalysts can achieve complete removal of bisphenol A from a flow of contaminated water in a trickle-bed reactor at an operating temperature of 120°C, total air pressure of 8 bar and a liquid-hourly space velocity of 26.6 h−1. Although increasing the throughput of contaminated water while lowering the operating temperature results in bisphenol A conversions below 100%, these more demanding conditions allow structurally similar catalyst formulations to be differentiated from one another. At 60°C and 8 bar total pressure of air, 2%Pt supported on a SiC-TiC composite material has the highest initial activity from a group of three hydrophobic catalysts with similar surface areas and Pt particle diameters, but it begins to deactivate progressively after 15 hours on stream. This catalyst contains some localised hydrophilicity arising from the presence of surface TiO2, which forms when the exposed TiC component of the support material oxidises during catalyst preparation. At 80 °C and ambient air pressure, the activity is lower but there are no signs of deactivation during 24 hours on stream. The results are consistent with metallic platinum providing the active sites for CWAO of bisphenol A, with oxygen being directly activated from the gas phase at elevated pressures, but with dissolved oxygen also contributing to the reaction particularly at ambient air pressure. Continuous and irreversible deactivation, which occurs at air pressures ≥4 bar, appears to be associated with high occupancy of the active sites by adsorbed oxygen, resulting in leaching of platinum into the aqueous phase

Effect of support of Co-Na-Mo catalysts on the direct conversion of CO₂ to hydrocarbons

This study of the effect of support of Co-Na-Mo based catalysts on the direct hydrogenation of CO2 into hydrocarbons (HC) provides guidelines for the design of catalysts for CO2 conversion. We demonstrate that the surface area of the support and the metal-support interaction have a key role determining the cobalt crystallite size and consequently the activity of the system. Cobalt particles with sizes 2 and ZSM-5 supports not only substantially increases the CO2 conversion but it also provides high HC selectivities. Further increase of the cobalt particle size to 25-30 nm has a detrimental effect on the global CO2 conversion with HC:CO ratios below 1, however, lower methane selectivity and enhanced formation of unsaturated HC products are achieved. Additionally, the metal-support interaction potentially also has a strong effect on the growth chain probability of the formed hydrocarbons, increasing as the metal-support interaction increases. These evidences demonstrate that CO2 conversion and hydrocarbon distribution can be tuned towards desired products by controlled catalyst design.</p

Reconstruction of primary vertices at the ATLAS experiment in Run 1 proton–proton collisions at the LHC

This paper presents the method and performance of primary vertex reconstruction in proton–proton collision data recorded by the ATLAS experiment during Run 1 of the LHC. The studies presented focus on data taken during 2012 at a centre-of-mass energy of √s=8 TeV. The performance has been measured as a function of the number of interactions per bunch crossing over a wide range, from one to seventy. The measurement of the position and size of the luminous region and its use as a constraint to improve the primary vertex resolution are discussed. A longitudinal vertex position resolution of about 30μm is achieved for events with high multiplicity of reconstructed tracks. The transverse position resolution is better than 20μm and is dominated by the precision on the size of the luminous region. An analytical model is proposed to describe the primary vertex reconstruction efficiency as a function of the number of interactions per bunch crossing and of the longitudinal size of the luminous region. Agreement between the data and the predictions of this model is better than 3% up to seventy interactions per bunch crossing