Chem4Energy: a consortium of the Royal Society Africa Capacity-Building Initiative.

The Africa Capacity-Building Initiative is a Royal Society programme funded by the former UK Department for International Development to develop collaborative research between scientists in sub-Saharan Africa and the UK. Initially, four institutions were involved in the Chem4Energy consortium: Cardiff University in the UK and three African partners, the Kwame Nkrumah University of Science and Technology, Ghana, the University of Namibia and the University of Botswana, soon also including the Botswana International University of Science and Technology. The Chem4Energy research programme focused on 'New materials for a sustainable energy future: linking computation with experiment', aiming to deploy the synergy between state-of-the-art computational and experimental techniques to design and optimize new catalysts and semiconductor materials for renewable energy applications, based on materials that are abundant and readily available in African countries.

Ruthenium ion catalysed C-C bond activation in lignin model compounds - towards lignin depolymerisation.

Lignin is the most abundant renewable feedstock to produce aromatic chemicals, however its depolymerisation involves the breaking of several C-O and C-C inter-unit linkages that connect smaller aromatic units that are present in lignin. Several strategies have been reported for the cleavage of the C-O inter-unit linkages in lignin. However, till today, only a few methodologies have been reported for the effective breaking or the conversion of the recalcitrant C-C inter unit linkages in lignin.

Sustainable Synthesis of Dimethyl- and Diethyl Carbonate from CO in Batch and Continuous Flow-Lessons from Thermodynamics and the Importance of Catalyst Stability.

Equilibrium conversions for the direct condensation of MeOH and EtOH with CO to give dimethyl- and diethyl carbonate, respectively, have been calculated over a range of experimentally relevant conditions. The validity of these calculations has been verified in both batch and continuous flow experiments over a heterogeneous CeO catalyst. Operating under optimized conditions of 140 °C and 200 bar CO, record productivities of 235 mmol/L·h DMC and 241 mmol/L·h DEC have been achieved using neat alcohol dissolved in a continuous flow of supercritical CO.

The role of surface oxidation and Fe-Ni synergy in Fe-Ni-S catalysts for CO hydrogenation.

Increasing carbon dioxide (CO) emissions, resulting in climate change, have driven the motivation to achieve the effective and sustainable conversion of CO into useful chemicals and fuels. Taking inspiration from biological processes, synthetic iron-nickel-sulfides have been proposed as suitable catalysts for the hydrogenation of CO. In order to experimentally validate this hypothesis, here we report violarite (Fe,Ni)S as a cheap and economically viable catalyst for the hydrogenation of CO into formate under mild, alkaline conditions at 125 °C and 20 bar (CO : H = 1 : 1).

The Role of Growth Directors in Controlling the Morphology of Hematite Nanorods.

The control of the growth of hematite nanoparticles from iron chloride solutions under hydrothermal conditions in the presence of two different structure promoters has been studied using a range of both structural and spectroscopic techniques including the first report of photo induced force microscopy (PiFM) to map the topographic distribution of the structure-directing agents on the developing nanoparticles. We show that the shape of the nanoparticles can be controlled using the concentration of phosphate ions up to a limit determined to be ~6 × 10 mol. Akaganéite (β-FeOOH) is a major component of the nanoparticles formed in the absence of structure directors but only present in the very early stages (< 8 h) of particle growth when phosphate is present.

Effect of support acidity during selective hydrogenolysis of glycerol over supported palladium-ruthenium catalysts.

We report the role of the acidity of support during the selectivity hydrogenolysis of glycerol over supported bimetallic palladium-ruthenium (PdRu) catalysts. The PdRu nanoparticles were supported on a series of metal oxides and zeolitic supports via the modified impregnation method and tested for the liquid-phase hydrogenolysis of glycerol using gaseous hydrogen. The relative acid site densities of selected catalysts were determined by ammonia temperature-programmed desorption and pyridine desorption experiments.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts.

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO hydrogenation, C-C coupling, and methane oxidation.

Synthesis of highly uniform and composition-controlled gold-palladium supported nanoparticles in continuous flow.

The synthesis of supported bimetallic nanoparticles with well-defined size and compositional parameters has long been a challenge. Although batch colloidal methods are commonly used to pre-form metal nanoparticles with the desired size-range in solution, inhomogeneous mixing of the reactant solutions often leads to variations in size, structure and composition from batch-to-batch and even particle-to-particle. Here we describe a millifluidic approach for the production of oxide supported monometallic Au and bimetallic AuPd nanoparticles in a continuous fashion.

Supported Bimetallic AuPd Nanoparticles as a Catalyst for the Selective Hydrogenation of Nitroarenes.

The solvent-free selective hydrogenation of nitrobenzene was carried out using a supported AuPd nanoparticles catalyst, prepared by the modified impregnation method (M), as efficient catalyst >99% yield of aniline (AN) was obtained after 15 h at 90 °C, 3 bar H₂ that can be used without any further purification or separation, therefore reducing cost and energy input. Supported AuPd nanoparticles catalyst, prepared by M, was found to be active and stable even after four recycle experiments, whereas the same catalyst prepared by S was deactivated during the recycle experiments. The most effective catalyst was tested for the chemoselective hydrogenation of 4-chloronitrobenzene (CNB) to 4-chloroaniline (CAN).

Synergistic Effect of Segregated Pd and Au Nanoparticles on Semiconducting SiC for Efficient Photocatalytic Hydrogenation of Nitroarenes.

Efficient catalytic hydrogenation of nitroarenes to anilines with molecular hydrogen at room temperature is still a challenge. In this study, this transformation was achieved by using a photocatalyst of SiC-supported segregated Pd and Au nanoparticles. Under visible-light irradiation, the nitrobenzene hydrogenation reached a turnover frequency as high as 1715 h at 25 °C and 0.

Mechanistic Insights into Selective Oxidation of Polyaromatic Compounds using RICO Chemistry.

Ruthenium-ion-catalyzed oxidation (RICO) of polyaromatic hydrocarbons (PAHs) has been studied in detail using experimental and computational approaches to explore the reaction mechanism. DFT calculations show that regioselectivity in these reactions can be understood in terms of the preservation of aromaticity in the initial formation of a [3+2] metallocycle intermediate at the most-isolated double bond. We identify two competing pathways: C-C bond cleavage leading to a dialdehyde and C-H activation followed by H migration to the RuO complex to give diketones.

Oxidation of Polynuclear Aromatic Hydrocarbons using Ruthenium-Ion-Catalyzed Oxidation: The Role of Aromatic Ring Number in Reaction Kinetics and Product Distribution.

Oxidation of aromatic hydrocarbons with differing numbers of fused aromatic rings (2-5), have been studied in two solvent environments (monophasic and biphasic) using ruthenium-ion-catalyzed oxidation (RICO). RICO reduces the aromaticity of the polyaromatic core of the molecule in a controlled manner by selective oxidative ring opening. Moreover, the nature of the solvent system determines the product type and distribution, for molecules with more than two aromatic rings.

High performing and stable supported nano-alloys for the catalytic hydrogenation of levulinic acid to γ-valerolactone.

The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method.

Selective oxidation of alkyl-substituted polyaromatics using ruthenium-ion-catalyzed oxidation.

Ruthenium-ion-catalyzed oxidation of a range of alkylated polyaromatics has been studied. 2-Ethylnaphthalene was used as a model substrate, and oxidation can be performed in either a conventional biphasic or in a monophasic solvent system. In either case the reaction rates and product selectivity are identical.

The benzaldehyde oxidation paradox explained by the interception of peroxy radical by benzyl alcohol.

Benzaldehyde readily undergoes autoxidation to form benzoic acid on exposure to air at room temperature. Yet it can be formed in high yield from, for example, benzyl alcohol by oxidation using a variety of procedures and catalysts. Here we report the evidence to resolve this apparent paradox.

Switching-off toluene formation in the solvent-free oxidation of benzyl alcohol using supported trimetallic Au-Pd-Pt nanoparticles.

Trimetallic Au-Pd-Pt nanoparticles have been supported on activated carbon by the sol-immobilisation method. They are found to be highly active and selective catalysts for the solvent-free aerobic oxidation of benzyl alcohol. The addition of Pt promotes the selectivity to the desired product benzaldehyde at the expense of toluene formation.

In situ spectroscopic investigation of oxidative dehydrogenation and disproportionation of benzyl alcohol.

In the solvent free oxidation of benzyl alcohol, using supported gold-palladium nanoalloys, toluene is often one of major by-products and it is formed by the disproportionation of benzyl alcohol. Gold-palladium catalysts on acidic supports promote both the disproportionation of benzyl alcohol and oxidative dehydrogenation to form benzaldehyde. Basic supports completely switch off disproportionation and the gold-palladium nanoparticles catalyse the oxidative dehydrogenation reaction exclusively.

Designing bimetallic catalysts for a green and sustainable future.

This Critical Review provides an overview of the recent developments in the synthesis and characterization of bimetallic nanoparticles. Initially the review follows a materials science perspective on preparing bimetallic nanoparticles with designer morphologies, after which the emphasis shifts towards recent developments in using these bimetallic particles for catalysing either oxidation or reduction. In the final part of this review we present an overview of the utilization of bimetallic catalyst systems for the transformation of bio-renewable substrates and reactions related to the realization of a bio-refinery.

Synthesis of stable ligand-free gold-palladium nanoparticles using a simple excess anion method.

We report a convenient excess anion modification and post-reduction step to the impregnation method which permits the reproducible preparation of supported bimetallic AuPd nanoparticles having a tight particle size distribution comparable to that found for sol-immobilization materials but without the complication of ligands adsorbed on the particle surface. The advantageous features of the modified impregnation materials compared to those made by conventional impregnation include a smaller average particle size, an optimized random alloy composition, and improved compositional uniformity from particle-to-particle resulting in higher activity and stability compared to the catalysts prepared using both conventional impregnation and sol immobilization methods. Detailed STEM combined with EDX analyses of individual particles have revealed that an increase in anion concentration increases the gold content of individual particles in the resultant catalyst, thus providing a method to control/tune the composition of the nanoalloy particles.

Controlling the duality of the mechanism in liquid-phase oxidation of benzyl alcohol catalysed by supported Au-Pd nanoparticles.

In the solvent-free oxidation of benzyl alcohol to benzaldehyde using supported gold-palladium nanoparticles as catalysts, two pathways have been identified as the sources of the principal product, benzaldehyde. One is the direct catalytic oxidation of benzyl alcohol to benzaldehyde by O(2), whereas the second is the disproportionation of two molecules of benzyl alcohol to give equal amounts of benzaldehyde and toluene. Herein we report that by changing the metal oxide used to support the metal-nanoparticles catalyst from titania or niobium oxide to magnesium oxide or zinc oxide, it is possible to switch off the disproportionation reaction and thereby completely stop the toluene formation.

Recycling nanocatalysts by tuning solvent quality.

Catalytic surfactant stabilized gold-containing nanoparticles have been recovered by a new isothermal low-energy approach, by controlled and reversible changes in colloid stability based on fine-tuning of solvent quality. Once recovered, the nanoparticles can be re-dispersed in the solvent, or indeed dispersed into a different solvent. The morphology of the nanoparticles is not significantly affected by the recovery process and they can be used and reused as oxidation catalysts.

Oxidation of glycerol to glycolate by using supported gold and palladium nanoparticles.

Glycolic acid is an important chemical that has uses as a cleaning agent as well as a chemical intermediate. At present glycolic acid is manufactured from either chloroacetic acid or from formaldehyde hydrocyanation, both routes being nongreen and using nonsustainable resources. We investigate the possibility of producing glycolate from the oxidation of glycerol, a sustainable raw material.