The importance of particle-support interaction on particle size determination by gas chemisorption.

ABSTRACT: The interaction of the metal-support and particle shape has a key role on the determination of the particle size by gas chemisorption. This paper demonstrates mathematically that, assuming metal particles with hemispherical shapes (a common assumption in this type of characterisation) can provide misleading results of up to one order of magnitude. Thus, the metal particle sizes are underestimated when the metal strongly interacts with the support and overestimated when there is a weak metal-support interaction. Additionally, we also demonstrate that although the assumption of spherical shapes always underestimates the size of particles, this error is considerably lower with regular geometries than that associated to the effect of the metal-support interaction due to their effect on the particle shape. Herein, it is demonstrated the importance of introducing the particle-support interaction factor in the chemisorption particle size determination.The author would like to acknowledge the UK Engineering and Physical Science Research Council (Grant Number EP/L020432/2) for funding.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s11051-016-3385-

Continuous synthesis of tuneable sized silver nanoparticles: Via a tandem seed-mediated method in coiled flow inverter reactors

Size control of metal nanoparticles is essential to achieve accurate adjustment of their unique chemical and physical properties.</p

Ammonia decomposition over cobalt/carbon catalysts—Effect of carbon support and electron donating promoter on activity

This paper sets the new design parameters for the development of low temperature ammonia decomposition catalysts based on readily available cobalt as an alternative to scarce but highly active ruthenium-based catalysts. By using a variety of carbon materials as catalytic supports, we systematically demonstrate that microporous supports capable of stabilising small cobalt crystallites (~2 nm) lead to high catalytic activities compared to bigger nanoparticles. Additionally, the degree of graphitisation of the carbon support has a detrimental effect on the activity of the cobalt (0) active sites, likely due to their potential as an electron donator. Consequently, the addition of electron donating promoters such as cesium substantially decreases the activity of the cobalt catalysts. This relationship deviates from the trends observed for ruthenium-based catalysts with an optimum 3–5 nm size where an increase of the graphitisation degree of the support and the addition of electron donating promoters increases the ammonia decomposition activity.The authors would like to acknowledge the UK Engineering and Physical Science Research Council (grant number EP/L020432/2) and the Doctoral Training Centre in the Centre for Sustainable Chemical Technologies at the University of Bath (grant number EP/K016334/1) for funding, and SASOL UK Ltd for supporting TEB’s studentship. We would also like to thank the Research Catalysis Group at Harwell(RCaH)for access to the TEM microscopy facilities.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.cattod.2016.05.04

Biphasic Epoxidation Reaction in the Absence of Surfactants - Integration of Reaction and Separation Steps in Microtubular Reactors

This paper presents a paradigm shift with respect to the current direction of biphasic reactions in surfactant-free emulsions. Herein, the contact area between both phases is simply sustained by the reactor design (i.e., diameter of the tubular reactor) compared to the current trend of using reversible/switchable emulsions where the addition of an external agent (e.g., bistable surfactant, magnetic particles, etc.) is required. In this way, temporally stable phase dispersions using microtubular reactors facilitate the integration of reaction and separation steps in biphasic systems without the need for energy-intensive downstream separation steps. In this study, we demonstrate this innovative tool in the epoxidation reaction of sunflower oil with hydrogen peroxide. Using a combination of mechanistic and kinetic studies, we demonstrate that the poor solubility of the catalytic species in the oil phase may be used advantageously, allowing ready recyclability of catalyst (and oxidant) in consecutive runs.The authors thank the UK Engineering and Physical Sciences Research Council for funding via the EPSRC Doctoral Training Centre in Sustainable Chemical Technologies, University of Bath (Grant No. EP/G03768X/1) and a L.T.-M.’s Fellowship award (Grant No. EP/L020432/2).This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/acssuschemeng.6b0028

Effect of nanostructured support on the WGSR activity of Pt/CeO₂ catalysts

Abstract The water gas shift catalytic activity and methane selectivity of Pt/CeO2 catalysts are shown to be strongly dependent on the platinum-ceria interaction. Platinum nanoparticles supported on nanostructured ceria rods present a higher hydrogen yield and lower methane selectivity than its counterpart catalysts supported on ceria nanoparticles or nanocubes, despite the similitude in platinum particle size. Indeed, the constraints of the 1D crystal structure of the ceria nanorods and the selective exposure of the (110) crystal plane are directly related to its superior catalytic activity. Platinum nanoparticles do not only act as active sites for CO adsorption and oxidation but also affect the reducibility of the support.</p

Effect of support of Co-Na-Mo catalysts on the direct conversion of CO<inf>2</inf> to hydrocarbons

This study of the effect of support of Co-Na-Mo based catalysts on the direct hydrogenation of CO$_2$ into hydrocarbons (HC) provides guidelines for the design of catalysts for CO$_2$ 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 nm supported on MgO present low reverse water gas shift conversion with negligible Fischer-Tropsch activity. Increasing the cobalt particle size to ~15 nm supported on SiO$_2$ and ZSM-5 supports not only substantially increases the CO$_2$ 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 CO$_2$ 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 CO$_2$ conversion and hydrocarbon distribution can be tuned towards desired products by controlled catalyst design.University of BathThis is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.jcou.2016.06.00

N-Doped Fe@CNT for Combined RWGS/FT CO ₂ Hydrogenation

The conversion of CO₂ into chemical fuels represents an attractive route for greenhouse gas emission reductions and renewable energy storage. Iron nanoparticles supported on graphitic carbon materials (e.g., carbon nanotubes (CNTs)) have proven themselves to be effective catalysts for this process. This is due to their stability and ability to support simultaneous reverse water-gas shift (RWGS) and Fischer–Tropsch (FT) catalysis. Typically, these catalytic iron particles are postdoped onto an existing carbon support via wet impregnation. Nitrogen doping of the catalyst support enhances particle–support interactions by providing electron-rich anchoring sites for nanoparticles during wet impregnation. This is typically credited for improving CO₂ conversion and product selectivity in subsequent catalysis. However, the mechanism for RWGS/FT catalysis remains underexplored. Current research places significant emphasis on the importance of enhanced particle–support interactions due to N doping, which may mask further mechanistic effects arising from the presence or absence of nitrogen during CO₂ hydrogenation. Here we report a clear relationship between the presence of nitrogen in the CNT support of an RWGS/FT iron catalyst and significant shifts in the activity and product distribution of the reaction. Particle–support interactions are maximized (and discrepancies between N-doped and pristine support materials are minimized) by incorporating iron and nitrogen directly into the support during synthesis. Reactivity is thus rationalized in terms of the influence of C–N dipoles in the support upon the adsorption properties of CO₂ and CO on the surface rather than improved particle–support interactions. These results show that the direct hydrogenation of CO₂ to hydrocarbons is a potentially viable route to reduce carbon emissions from human activities

Synthesis of narrow sized silver nanoparticles in the absence of capping ligands in helical microreactors

Microtubular helical reactors generate secondary flows promoting the synthesis of mono-sized silver nanoparticles in the absence of capping ligands.LTM would like to acknowledge the UK Engineering and Physical Science Research Council for her Fellowship award (grant number EP/L020432/2)