Gadi Rothenberg

Desulfurisation of oils using ionic liquids: selection of cationic and anionic components to enhance extraction efficiency

Extraction of dibenzothiophene from dodecane using ionic liquids as the extracting phase has been investigated for a range of ionic liquids with varying cation classes (imidazolium, pyridinium, and pyrrolidinium) and a range of anion types using liquid–liquid partition studies and QSPR (quantitative structure–activity relationship) analysis. The partition ratio of dibenzothiophene to the ionic liquids showed a clear variation with cation class (dimethylpyridinium > methylpyridinium > pyridinium ≈ imidazolium ≈ pyrrolidinium), with much less significant variation with anion type. Polyaromatic quinolinium-based ionic liquids showed even greater extraction potential, but were compromised by higher melting points. For example, 1-butyl-6-methylquinolinium bis{(trifluoromethyl)sulfonyl}amide (mp 47 °C) extracted 90% of the available dibenzothiophene from dodecane at 60 °C.

Palladium-free and ligand-free Sonogashira cross-coupling

Copper nanoclusters catalyse the cross-coupling of alkynes and aryl halides to give the corresponding disubstituted alkynes. No palladium, ligand, or co-catalyst is needed, and products are isolated in good yields (80–85%) and high selectivity. The clusters are simple to prepare, stable and can be applied to a variety of iodo- and bromoaryls. Mechanistic pathways for homocoupling and cross-coupling of alkynes are examined by comparing the activity of different catalyst and co-catalyst combinations. The copper clusters show different catalytic properties than their homogeneous analogues.

Mesoporous Silica with Site‐Isolated Amine and Phosphotungstic Acid Groups: A Solid Catalyst with Tunable Antagonistic Functions for One‐Pot Tandem Reactions

Coniuga et impera: A bifunctional solid catalyst is prepared by combining acid and base functions on mesoporous silica supports (see picture). The co-existence of these functions is shown by a two-step reaction sequence in one pot. Excellent product yields, which cannot be obtained by separated acid and base functions in one pot, show the validity of our concept.

The pros and cons of lignin valorisation in an integrated biorefinery

This short critical review outlines possible scenarios for using lignin as a feedstock in a biorefinery environment. We first explain the position of biomass with respect to fossil carbon sources and the possibilities of substituting these in tomorrows transportation fuels, energy, and chemicals sectors. Of these, the conversion of biomass to chemicals is, in our opinion, the most worthy. Focusing on lignin, we describe the four main processes for its industrial separation (the Sulfite, Soda, Kraft, and Organosolv processes). Then, we detail several short- and long-term perspectives for its valorisation to aromatics, polymers and materials, as well as new products and in-the-pipeline processes. Finally, we examine the limitations in current lignin valorisation and suggest possible ways forward. Combining the chemical aspects with up-to-date data from economic analyses gives a pragmatic and realistic overview of the commercial applications and possibilities for lignin in the coming decades, where biomass will join shale gas and crude oil as a valid and economical carbon source.

Catalytic routes towards acrylic acid, adipic acid and ε-caprolactam starting from biorenewables

The majority of bulk chemicals are derived from crude oil, but the move to biorenewable resources is gaining both societal and commercial interest. Reviewing this transition, we first summarise the types of todays biomass sources and their economical relevance. Then, we assess the biobased productions of three important bulk chemicals: acrylic acid, adipic acid and e-caprolactam. These are the key monomers for high-end polymers (polyacrylates, nylon 6.6 and nylon 6, respectively) and are all produced globally in excess of two million metric tons per year. The biobased routes for each target molecule are analysed separately, comparing the conventional processes with their sustainable alternatives. Some processes have already received extensive scientific attention. Other, more novel routes are also being considered. We find several common trends: For all three compounds, there are no commercial methods for direct conversion of biobased feedstocks. However, combinations of biotechnologically produced platform chemicals with subsequent chemical modifications are emerging and showing promising results. We then discuss several distinct strategies for implementing biorenewable processes. For each biotechnological and chemocatalytic route, current efficiencies and limitations are presented, but we urge that these routes should be assessed mainly on their potential and prospects for future application. Today, biorenewable routes cannot yet compete with their petrochemical equivalents. However, given that most of them are still in the early stages of development, we foresee their commercial implementation in the next two decades.

De Novo Design of Nanostructured Iron–Cobalt Fischer–Tropsch Catalysts

Audio cassettes hold the key to enhancing Fischer–Tropsch catalysis. Catalysts based on ultra‐thin cobalt shells surrounding cheap iron oxide cores (see picture) are developed, an approach previously optimized for preparing magnetic tape for audio cassettes. These particles are easily made on a large scale, and are excellent Fischer–Tropsch catalysts, giving good diesel fractions.

Sustainable selective oxidations using ceria-based materials

This Perspective covers sustainable oxidation processes using doped cerias, ceria-supported catalysts and ceria-based mixed oxides. Firstly, we consider the general properties of ceria-based catalysts. We outline the advantages of the ceria redox cycle, and explain the dynamic behaviour of these catalysts in the presence of metal additives and dopants. We then review three types of catalytic oxidation processes: preferential CO oxidation (PROX), oxidative dehydrogenation and the selective oxidations of hydrocarbons and inorganics. The preferential oxidation of CO from hydrogen-rich mixtures is interesting for fuel cell applications. Copper-ceria catalysts, where the copper species are well dispersed and interact strongly with the ceria surface, show good selectivity and activity. The oxidative dehydrogenation of small alkanes is another important potential application. To avoid mixing oxygen and hydrocarbons at high temperatures, one can run the dehydrogenation over a conventional Pt/Sn catalyst while burning the hydrogen formed using the ceria lattice oxygen. This safer redox process allows separate tuning of the dehydrogenation and hydrogen combustion stages. A combinatorial screening showed good results for ceria doped with Pb, Cr or Bi, amongst others. Finally, we also discuss the catalytic selective oxidation of various hydrocarbons, oxygenates and inorganic molecules (H2S, H2 and NH3). The goal here is either product valorisation or waste stream purification. Ceria-based materials show promise in a variety of such selective oxidations.

Palladium-catalyzed aryl-aryl coupling in water using molecular hydrogen: kinetics and process optimization of a solid-liquid-gas system

Abstract Coupling of substituted chlorobenzenes to the respective biphenyls is effected in water, using hydrogen gas and NaOH in the presence of catalytic PEG-400 and Pd/C. The catalyst can be efficiently recycled. The competing reduction process ( e.g. of chlorobenzene to benzene) can be minimized by altering reaction conditions. The roles of the hydrogen, the hydroxide, the Pd catalyst, and the PEG are discussed.

Optimising an artificial neural network for predicting the melting point of ionic liquids

We present an optimised artificial neural network (ANN) model for predicting the melting point of a group of 97 imidazolium salts with varied anions. Each cation and anion in the model is described using molecular descriptors. Our model has a mean prediction error of 1.30%, a regression coefficient of 0.99 and a mean P-value of 0.92. The ANNs prediction performance depends mainly on the anion size. In particular, the prediction error decreases as the anion size increases. The high statistical relevance makes this model a useful tool for predicting the melting points of imidazolium-based ionic liquids.

Bimetallic catalysts for the Fischer–Tropsch reaction

This short critical review summarises and analyses the developments in Fischer–Tropsch catalysis using bimetallic alloys. We introduce a simple notation for such catalysts, and monitor the reports of synergistic effects and composition/performance relationships. Special attention is given to CoFe alloys on a variety of supports, and to the effects of catalyst preparation methods and pre-treatment conditions. The key drawbacks in comparing the large amount of data available on Fischer–Tropsch catalysis are the high dimensionality of the problem and the lack of long time-on-stream studies. Based on the new understanding coming from characterisation studies of supported bimetallic particles, we propose a structured approach for effectively studying Fischer–Tropsch catalysis.