Metal catalysed reactions in ionic liquids

This book represents first non-edited book on the subject of metal catalysed reactions in ionic liquids and covers the literature from its origins until early 2005. Following a general introduction to the field of biphasic/mutliphasic catalysis, the synthesis, functionalisation and fundamental properties of ionic liquids relevant to catalysis are described. In the ensuing chapters catalysed reactions are discussed according to their type, encompassing hydrogenation, hydroformylation, oxidation, C-C coupling reactions, metathesis, dimerisation, polymerisation and more. Trends, generalisations, advantages and disadvantages of ionic liquids for specific reaction types are discussed. Specific processes such as supported ionic liquid phase catalysis, continuous processes using CO2 extraction and nanoparticle catalysis are covered. The book should be of interest to all those working in catalysis/green chemistry, in particular, to advanced level undergraduate and graduate students and all those researching or contemplating research in bi- or multiphasic catalysis using ionic liquids.

Solvent effects in catalysis: rational improvements of catalysts via manipulation of solvent interactions

Paul Joseph Dyson, Philip Gregory Jessop

In homogeneous catalysis, the main emphasis on improving catalyst performance (rate, yield and selectivity) is directed towards manipulation of the ligands. The steric and electronic effects of ligands are extremely well understood and the rational design of new ligands that leads to improved catalysts is feasible. Similarly, in heterogeneous catalysis structural changes to the catalyst are used to improve their properties. In contrast, the role that solvents play in catalytic processes is often given cursory attention. The environmental impact of solvents is often considered, as it should be, and the use of organic-immiscible solvents, e.g. water, ionic liquids, etc., is frequently considered with respect to catalyst recovery, product isolation, and recycling. Nevertheless, the direct role of solvents in reactions is often overlooked, although solvents interact directly with the catalyst, the substrates and products, and all these interactions can increase or decrease reaction rate and/or selectivity. Herein we consider the role of solvents in catalysis and illustrate the critical role of solvents viewed from a mechanistic approach. In particular, we focus largely, but not exclusively, on hydrogenation reactions and cross-coupling reactions as the main types of solvents used for these two classes of reactions tend to be very different and illustrate different functions of solvents in catalysis.

2016

Decreasing the Stability of Borohydride with Ionic Liquids for Hydrogen Storage and Carbon Dioxide Conversion

Loris Giovanni Lombardo

The world needs to move from a fossil fuel to a renewable energy based society. With the increasing electricity production from wind and PV, short and long term energy storage are becoming one of challenge of the 21st century. While batteries are the preferred method for short term storage, another technology is required for seasonal storage. Hydrogen is a valuable energy carrier owning its high energy density (122 kJ/g). However, compact and safe storage of H2 is challenging. The current solution is to compress hydrogen up to 700 bar for mobile application (fuel cell cars), and metal hydrides for stationary application. Material-based H2 storage avoids using high-pressure cylinder. Complex hydrides are especially attractive for solid-state H2 storage due to their high gravimetric and volumetric hydrogen density. Sodium borohydride (NaBH4) contains 10.6 mass% of H2, but high temperatures are needed to release H2 (505 Â°C) and the reaction is not reversible under moderate conditions. To apply complex hydrides in real applications, they must be modified to improve the kinetics and thermodynamics of H2 desorption. Several possibilities exist such as confinement into scaffolds, catalyst addition, or combination of several hydrides to modify the dehydrogenation pathway. The stability of complex hydrides is determined by the localization of the charge on the central atom of the complex. Therefore, in this thesis the interaction of highly polar or ionic compounds with complex hydrides were investigated. We combine NaBH4 with a special class of organic salts: ionic liquids (IL). Considering their chemical and thermal stability, IL are attractive additive. Using organic additives instead of expensive metal catalysts is another advantage. Two different techniques were employed to combine the IL and NaBH4. The first one consists of mechanochemically milling them to create an interaction between BH4- and IL. The second one is to directly synthesized IL borohydrides ([IL][BH4]) by metathesis reaction. Different ILs, such as vinylbenzyltrimethylammonium chloride ([VBTMA][Cl]), 1-butyl-3-methylimidazolium chloride ([bmim][Cl]), and 1-ethyl-1-methylpyrrolidinium bromide ([EMPY][Br]) were tested. [bmim][BH4] was able to release H2 below 100 Â°C. The hydrogen content ranges between 2.4 mass% and 2.9 mass%. The second challenge of this century is the CO2 problematic. Atmospheric CO2 concentration linearly increases, leading to greenhouse effect. Carbon capture and sequestration (CCS) and utilization (CCU) are primordial research topic to stabilize the CO2 emission. Hydrides are primary reducing agents, thus reduction of CO2 can be accomplished with them. Direct CO2 reduction at ambient conditions is challenging for classical borohydrides. With our [IL][BH4], gaseous CO2 can be captured and reduced under ambient conditions (1 bar, RT). Three CO2 bounds with boron to give triformatoborohydride ([HB(OCHO)3]â. Dilute CO2 (6 vol%) can be used as well. The reaction was followed in real time with a magnetic suspended balance (MSB). Further, CO2 reduction happened when air is used as a carbon dioxide source. Formic acid can be obtained by adding HCl. Thus, ionic liquid borohydrides have great potential as a CO2 absorber and reducer to alternative fuels. In short, we applied ionic liquid to destabilized borohydrides. The resulting materials exhibited potential for solid-state hydrogen storage, as well as CO2 capture and transformation.

EPFL2021

Decreasing the Stability of Borohydride with Ionic Liquids for Hydrogen Storage and Carbon Dioxide Conversion

Loris Giovanni Lombardo

EPFL2021