Search

We identify many larger organics as products of electrochemical CO2 reduction in high-current GDEs – most interestingly, C4 and C5 isomers. The analysis of selectivity trends allows for deduction of general hypotheses to build a detailed mechanism.

Electrochemical conversion of CO2 (CO2R) into fuels and chemicals can both reduce CO2 emissions and allow for clean manufacturing in the scenario of significant expansion of renewable power generation. However, large-scale process deployment is currently limited by unfavourable process economics resulting from significant up- and down-stream costs for obtaining pure CO2, separation of reaction products and increased logistical effort. We have discovered a method for economically viable recycling of waste CO2 that addresses these challenges. Our approach is based on integration of a CO2R unit into an existing manufacturing process: ethylene oxide (EO) production, which emits CO2 as a by-product. The standard EO process separates waste CO2 from the gas stream, hence the substrate for electroreduction is available at an EO plant at no additional cost. CO2 can be converted into an ethylene-rich stream and recycled on-site back to the EO reactor, which uses ethylene as a raw material, and also the anode product (oxygen) can be simultaneously valorized for the EO production reaction. If powered by a renewable electricity source, the process will significantly (ca. 80%) reduce the CO2 emissions of an EO manufacturing plant. A sensitivity analysis shows that the recycling approach can be economically viable in the short term and that its payback time could be as low as 1–2 years in the regions with higher carbon taxes and/or with access to low-cost electricity sources.

Dry reforming of methane (DRM) has incited significant academic and industrial attention in the past couple of decades. Although Ni-based catalysts have shown good activity for DRM, deactivation due to carbon formation is a serious concern. Several strategies are proposed, including doping by other metals and metalloids, to improve the stability of Ni, and hence we investigated boron-doped Ni (NiB) as a potential catalyst for DRM. In this work, we combined DFT and microkinetic modeling to identify the dominant reaction pathways and kinetically relevant steps of the DRM reaction system on Ni and NiB surfaces. We considered a detailed reaction network involving multiple CO2 and CH4 dissociation routes, side reactions (H2O formation, Boudouard reaction) and desorption of products on both surfaces. Our DFT calculations suggest that both Ni and NiB share similar CO2 (direct dissociation to CO*) and CH4 (sequential dehydrogenation to C*) activation routes. Compared to Ni, the CO2 activation barrier on NiB is higher by 44 kJ mol−1 but the barriers in CH4 activation routes are significantly lower. Subsequently, the DFT-calculated energies were used to derive kinetic rate constants of the elementary reaction steps. These rate constants were employed to develop a microkinetic model of the DRM process over Ni (111) and NiB catalysts. At low CH4 and CO2 partial pressures (

Networks of chemical reactions represent relationships between molecules within chemical supply chains and promise to enhance planning of multi-step synthesis routes from bio-renewable feedstocks. This study aims to identify strategic moleculesin chemical reaction networks that may potentially play a significant role within the future circular economy. We mine a commercially available database in order to assemble a network of chemical reactions. We describe molecules within the network by a portfolio of graph theoretical features, and identify strategic molecules with an isolation forest search algorithm. In this work we have identified a list of potential strategic molecules and indicated possibilities for reaction planning using these. This is exemplified by a potential supply chain of functional molecules from bio-waste streams that could be used as feedstocks without being converted to syngas. This work extends the methodology of analysis of reaction networks to the generic problem of development of new reaction pathways based on novel feedstocks.

George Huber, Alexei Lapkin and Yan Ning introduce the Reaction Chemistry & Engineering themed issue on green chemistry and reaction engineering.

A methodology for chemical routes development and evaluation on the basis of data-mining is presented. A section of the Reaxys database was converted into a network, which was used to plan hypothetical synthesis routes to convert a bio-waste feedstock, limonene, to a bulk intermediate, benzoic acid. The route evaluation considered process conditions and used multiple indicators, including exergy, E-factor, solvent score, reaction reliability and route redox efficiency, in a multi-criteria environmental sustainability evaluation. The proposed methodology is the first route evaluation based on data mining, explicitly using reaction conditions, and is amenable to full automation.

The heterogenisation of a new family of Pd–NHC complexes is reported via a straightforward and efficient synthetic procedure. These silica-immobilised materials were successfully applied as catalysts in the Suzuki–Miyaura coupling of aryl chlorides and bromides under mild conditions. The materials exhibited improved stability when the catalytic reaction was run under anhydrous conditions and could be recycled up to five times without significant loss of activity. When the reaction was run within a continuous flow microreactor, these catalysts showed good activity after at least two hours on stream.

The solubility of artemisinin in a range of conventional and novel solvents was evaluated using the COSMO-RS approach, and verified experimentally as well as against literature data. The computational method was improved by calibrating against a limited set of experimental data, enhancing the accuracy of the calculations. The optimised method was shown to be in reasonable agreement with experimental data; however, lack of reliable experimental data is identified as an issue. Several novel solvents perceived as green alternatives to conventional solvents were targeted and shown to offer good solubility of artemisinin. Extraction from Artemisia annua by carbonate solvents was experimentally verified.

Two new types of phenolic resin-derived synthetic carbons with bi-modal and tri-modal pore-size distributions were used as supports for Pd catalysts. The catalysts were tested in chemoselective hydrogenation and hydrodehalogenation reactions in a compact multichannel flow reactor. Bi-modal and tri-modal micro-mesoporous structures of the synthetic carbons were characterised by N2 adsorption. HR-TEM, PXRD and XPS analyses were performed for characterising the synthesised catalysts. N2 adsorption revealed that tri-modal synthetic carbon possesses a well-developed hierarchical mesoporous structure (with 6.5 nm and 42 nm pores), contributing to a larger mesopore volume than the bi-modal carbon (1.57 cm3 g–1 versus 1.23 cm3 g–1). It was found that the tri-modal carbon promotes a better size distribution of Pd nanoparticles than the bi-modal carbon due to presence of hierarchical mesopore limitting the growth of Pd nanoparticles. For all the model reactions investigated, the Pd catalyst based on tri-modal synthetic carbon (Pd/triC) show high activity as well as high stability and reproducibility. The trend in reactivities of different functional groups over the Pd/triC catalyst follows a general order alkyne >> nitro > bromo >> aldehyde.

A flow system capable of dynamically controlling the synthesis of inorganic nanomaterials in real time switching between different conditions is presented whereby the combination of reactor engineering, ligand design and the employment of two in-line analytical techniques enables the synthesis and rapid characterisation of gold nanoparticles. Furthermore, it has been possible to discover a new type of hyper-branched nanogold-based material directly based on the optical feedback from UV-Vis, without stopping the process and the nanoparticles have been characterised using TEM.

A simple, easy to construct, bench-top plug flow reactor consisting of PTFE tubing with a Cu(0) threaded core (wire) was used to perform SET-LRP of methyl acrylate. The reaction was optimized by changing the residence time within the flow reactor. Both changing the flow reactor length and changing the flow rate was seen to control the resultant polymer molecular weight. Using a 20 cm reactor length, 95% conversion of monomer was seen at a flow rate of 0.1 mL min−1. The polymers formed had narrow molecular weight distributions (PDI< 1.2), and very high ω-chain end fidelity, as seen by both 1H NMR and MALDI-TOF MS.

A novel laser electrodispersion (LE) technique was employed to deposit gold nanoparticles onto Si and SiO(x) surfaces. The LE technique combines laser ablation with cascade fission of liquid metal micro-drops, which results in the formation of nanoparticles upon rapid cooling. The shape and the size distribution of the Au nanoparticles prepared by LE depend on the nature of the support. Gold nanoparticles were also deposited in the channels of microreactors fabricated by wet etching of Si and used as SE(R)RS sensors. The influence of the nanoparticle surface density as well as of the nature of the substrate on the Raman response was studied. At an appropriate surface density of the deposited nanoparticles a significant enhancement of Raman signal was observed showing the possibility to create efficient SERS substrates. Application of microfluidic devices in surface enhanced Raman spectroscopy (SERS) in continuous-flow mode with sensor regeneration is described.

Titanate nanotubes were synthesised using a hydrothermal method in a static and a rotating autoclave (end-over-end) over a range of rotation speeds (0–20 rpm). The control of the average length of the titanate nanotubes by the speed of rotation during their synthesis was revealed. As the rotation speed was increased, longer nanotubes (more than 1 µm at 20 rpm) were produced. This phenomenon was attributed to an increase in the mass transfer, facilitating the formation of longer intermediate titanate nanosheets. Long nanotubes self-assemble, forming secondary structures without transformation into nanowires as confirmed by the high specific surface area, pore size (inner nanotubes diameter) of 3.7 nm, XRD and Raman analyses. The initial phase of dissolution of the ends of the nanotubes was observed at higher rotation speeds. Pre-sonication treatment of the suspension of TiO2 precursor in NaOH solution resulted in a slight increase in the length of the nanotubes in the static synthesis, but did not have any effect in the rotating autoclave syntheses.

Recent discovery of high enhancement of heat transfer in nanofluids may be applicable to the area of process intensification of chemical reactors through integration of the functionalities of reaction and heat transfer in compact multifunctional reactors. This may lead to the reduction in the processes footprint and energy intensity over the process life cycle, allow easier implementation of highly exothermic and endothermic reactions, and enable rapid quenching of reactions. A nanofluid based on benign TiO2 material dispersed in ethylene glycol has been studied in an integrated reactor–heat exchanger. An up to 35% increase in the overall heat transfer coefficient was measured in the steady state continuous experiments. This resulted in a closer temperature control in the reaction of selective reduction of an aromatic aldehyde by molecular hydrogen and very rapid change in the temperature of reaction under dynamic reaction control.

A systematic analysis of the influence of preparation conditions in the alkali hydrothermal synthesis on the morphology of TiO2 nanotubes is performed using HRTEM and low temperature nitrogen adsorption. The possible mechanisms of nanotube formation are reviewed and a mechanism based on the key stage of wrapping of intermediate multilayered titanate nanosheets is suggested. The driving force for wrapping is considered to be the mechanical stress arising during crystallisation/dissolution. The average diameter of the nanotubes was found to depend on the temperature and on the ratio of weight of TiO2 to the volume of sodium hydroxide solution. An increase in the temperature from 120 to 150 °C results in an increase in the average nanotube diameter. Subsequent increases in the temperature result in the formation of non-hollow TiO2 nanofibers with an average diameter of 75 nm, a wide distribution in diameter and a length in excess of 10 µm. The increase of the TiO2 : NaOH molar ratio results in an increase in the average diameter of nanotubes and a decrease of surface area. The average inner diameter of TiO2 nanotubes varied between 2 and 10 nm. The pore-size distribution was evaluated from TEM, and low-temperature nitrogen adsorption data using the BJH method. It was shown that nitrogen adsorption is a suitable method for characterisation of the pore morphology of nanotubes.