Rapid, non-invasive characterization of the dispersity of emulsions via microwaves

A rapid and non-invasive method to determine the dispersity of emulsions is developed based on the interrelationship between the droplet size distribution and the dielectric properties of emulsions. A range of water-in-oil emulsions with different water contents and droplet size distributions were analysed using a microwave cavity perturbation technique together with dynamic light scattering. The results demonstrate that the dielectric properties, as measured by non-invasive microwave cavity analysis, can be used to characterise the dispersity of emulsions, and is also capable of characterizing heavy oil emulsions. This technique has great potential for industrial applications to examine the sedimentation, creaming and hence the stability of emulsions

Rapid synthesis of BiOBrxI1-x photocatalysts : insights to the visible-light photocatalytic activity and strong deviation from Vegard’s Law

This work was supported by the Royal Society for international collaboration grants (IE160277 and IE/CNSFC170670) and Sir John Houghton Fellowship in Jesus College at University of Oxford. ZJ appreciated the institutional GCRF fund from EPSRC and JG appreciates the EUSTICE scholarship from University of Southampton.A series of visible-light-responsive BiOBrxI1-x solid solutions were prepared by a rapid and efficient ultrasonication synthesis and applied in photodegradation of Rhodamine B in aqueous solution. The detailed characterisations showed that the lattice parameters and their band structures of the BiOBrxI1-x solid solutions significantly deviated from the well-established Vegard’s law for solid solution materials. The Mulliken electronegativity and valence band XPS analyses revealed that the substitution of Br by less electronegative iodine can simultaneously modulate the edges of conductance and valence band of the BiOBr, leading to nonlinear dependence of bandgap (Eg) on the halogen anion concentrations. Although the solid solution displayed superior RhB photodegration activity to BiOI, only Br-rich BiOBrxI1-x solid solutions (x>0.5) were more active than BiOBr and BiOI, with the optimal one is BiOBr0.75I0.25. The Br-dependence of bandstructure and photocatalytic activity for the BiOBrxI1-x solid solutions as well as their rate-limiting radical species were also clarified based on experimental and theoretical analyses.PostprintPeer reviewe

Methanol-to-hydrocarbons conversion over MoO3/H-ZSM-5 catalysts prepared via lower temperature calcination: a route to tailor the distribution and evolution of promoter Mo species, and their corresponding catalytic properties

A series of MoO3/H-ZSM-5 (Si/Al=25) catalysts were prepared via calcination at a lower-than-usual temperature (400 oC) and subsequently evaluated in the methanol-to-hydrocarbon reaction at that same temperature. The catalytic properties of those catalysts were compared with the sample prepared at the more conventional, higher temperature of 500 oC. For the lower temperature preparations, molybdenum oxide was preferentially dispersed over the zeolite external surface, while only the higher loading level of MoO3 (7.5 wt% or higher) led to observable inner migration of the Mo species into the zeolite channels, with concomitant partial loss of the zeolite Brønsted acidity. On the MoO3 modified samples, the early-period gas yield, especially for valuable propylene and C4 products, was noticeably accelerated, and is gradually converted into an enhanced liquid aromatic formation. The 7.5 wt% MoO3/H-ZSM-5 sample prepared at 400oC thereby achieved a balance between the zeolite surface dispersion of Mo species, their inner channel migration and the corresponding effect on the intrinsic Brønsted acidity of the acidic zeolite. That loading level also possessed the highest product selectivity (after 5h reaction) to benzene, toluene and xylenes, as well as higher early-period valuable gas product yields in time-on-stream experiments. However, MoO3 loading levels of 7.5wt% and above also resulted in earlier catalyst deactivation by enhanced coke accumulation at, or near, the zeolite channel openings. Our research illustrates that the careful adoption of moderate/lower temperature dispersion processes for zeolite catalyst modification gives considerable potential for tailoring and optimizing the system’s catalytic performanc

Size-dependent microwave heating and catalytic activity of fine iron particles in the deep dehydrogenation of hexadecane

Knowledge of the electromagnetic microwave radiation–solid matter interaction and ensuing mechanisms at active catalytic sites will enable a deeper understanding of microwave-initiated chemical interactions and processes, and will lead to further optimization of this class of heterogeneous catalysis. Here, we study the fundamental mechanism of the interaction between microwave radiation and solid Fe catalysts and the deep dehydrogenation of a model hydrocarbon, hexadecane. We find that the size-dependent electronic transition of particulate Fe metal from a microwave “reflector” to a microwave “absorber” lies at the heart of efficient metal catalysis in these heterogeneous processes. In this regard, the optimal particle size of a Fe metal catalyst for highly effective microwave-initiated dehydrogenation reactions is approximately 80–120 nm, and the catalytic performance is strongly dependent on the ratio of the mean radius of Fe particles to the microwave skin depth (r/δ) at the operating frequency. Importantly, the particle size of selected Fe catalysts will ultimately affect the basic heating properties of the catalysts and decisively influence their catalytic performance under microwave initiation. In addition, we have found that when two or more materials─present as a mechanical mixture─are simultaneously exposed to microwave irradiation, each constituent material will respond to the microwaves independently. Thus, the interaction between the two materials has been found to have synergistic effects, subsequently contributing to heating and improving the overall catalytic performance

The decarbonization of coal tar via microwave-initiated catalytic deep dehydrogenation

Coal tar, a major by-product of the coal industry, presents considerable difficulties in its refining and conversion into fuels due to its complex chemical composition and physical properties, such as high viscosity, corrosiveness, thermal instability, etc. Here we report a new route for producing hydrogen-rich gases together with carbonaceous materials, including carbon nanotubes, through the microwave-initiated catalytic deep dehydrogenation of coal tar using inexpensive iron catalysts. The resulting carbonaceous materials generated over the catalyst were investigated using a variety of techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature programmed oxidation (TPO) and Raman spectroscopy. Importantly, we have found that an aqueous emulsion feed of the coal tar enables considerably easier handling and an enhanced hydrogen production whilst also significantly reducing the extent of catalyst deactivation. This behaviour is shown to be assisted by the phenomenon of micro-explosion that enhances mass and heat transfer during the catalytic reactions

The decarbonisation of petroleum and other fossil hydrocarbon fuels for the facile production and safe storage of hydrogen

The importance of extracted and refined fossil carbonaceous fuels (petroleum, diesel etc.) to the development of human society cannot be overestimated. These natural resources have improved billions of lives, worldwide, in providing accessible, relatively inexpensive energy at nearly every scale. Notwithstanding the credible advances in renewable energy production over the past decade or so, the aerial combustion of coal, natural gas and liquid fossil fuels, given humankinds insatiable demand for power, will continue to be the ready source of more than 85% of the world's energy in the foreseeable and possibly the distant future. Human activities based on the combustion of fossil fuels, however, has led to significant anthropogenic emissions of carbon dioxide (CO2) to the atmosphere – and that fact is now seen as the major contributor to global warming and climate change. To stabilise global mean temperatures will depend on the ultimate transformation of humankind's energy system to one that does not introduce CO2 into the atmosphere. The hydrogen economy has long been mooted as a route to achieving the required net-zero emissions energy future. Paradoxically, fossil fuel sources such as petroleum, crude and extra-heavy crude oil, petrol, diesel and methane are reported here to produce high volumes of high-purity hydrogen through their microwave-initiated catalytic dehydrogenation using fine iron particles. The co-product of this dehydrogenation process, solid carbon, can be safely stored underground in perpetuity or converted in future to valuable hydrocarbons and other materials. Through their catalytic dehydrogenation to yield carbon-free hydrogen – rather than through their aerial combustion to produce carbon dioxide – petroleum and other fossil fuels can now serve as an energy pathway to stabilising global mean temperatures