Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Palladium nanoparticles on chitin-derived nitrogen-doped carbon materials for carbon dioxide hydrogenation into formic acid

Utilizing waste carbon resources to produce chemicals and materials is beneficial to mitigate the fossil fuel consumption and the global warming. In this study, ocean-based chitin biomass and waste shrimp shell powders were employed as the feedstock to prepare Pd loaded nitrogen-doped carbon materials as the catalysts for carbon dioxide (CO₂)/bicarbonate hydrogenation into formic acid, which simultaneously converts waste biomass into useful materials and CO₂ into a valuable chemical. Three different preparation methods were examined, and the two-stage calcination was the most efficient one to obtain N-doped carbon material with good physicochemical properties as the best Pd support. The highest formic acid yield was achieved of ∼77% at 100 °C in water with KHCO₃ substrate under optimal condition with a TON of 610. The nitrogen content and N functionalities of the as-synthesized carbon materials were crucial which could serve as anchor sites for the Pd precursor and assist the formation of well-dispersed and small-sized Pd NPs for boosted catalytic activity. The study puts forward a facile, inexpensive and environmentally benign way for simultaneous valorization of oceanic waste biomass and carbon dioxide into valuable products.

Development of Power-to-X Catalytic Processes for CO2 Valorisation: From the Molecular Level to the Reactor Architecture

Nowadays, global climate change is likely the most compelling problem mankind is facing. In this scenario, decarbonisation of the chemical industry is one of the global challenges that the scientific community needs to address in the immediate future. Catalysis and catalytic processes are called to play a decisive role in the transition to a more sustainable and low-carbon future. This critical review analyses the unique advantages of structured reactors (isothermicity, a wide range of residence times availability, complex geometries) with the multifunctional design of efficient catalysts to synthesise chemicals using CO2 and renewable H2 in a Power-to-X (PTX) strategy. Fine-chemistry synthetic methods and advanced in situ/operando techniques are essential to elucidate the changes of the catalysts during the studied reaction, thus gathering fundamental information about the active species and reaction mechanisms. Such information becomes crucial to refine the catalyst’s formulation and boost the reaction’s performance. On the other hand, reactors architecture allows flow pattern and temperature control, the management of strong thermal effects and the incorporation of specifically designed materials as catalytically active phases are expected to significantly contribute to the advance in the valorisation of CO2 in the form of high added-value products. From a general perspective, this paper aims to update the state of the art in Carbon Capture and Utilisation (CCU) and PTX concepts with emphasis on processes involving the transformation of CO2 into targeted fuels and platform chemicals, combining innovation from the point of view of both structured reactor design and multifunctional catalysts development.

Effects of TiO2 structure and Co addition as a second metal on Ru-based catalysts supported on TiO2 for selective hydrogenation of furfural to FA

The TiO2 supported Ru-based catalysts were prepared with 1.5 wt% Ru and 0-0.8 wt% Co on various TiO2 (anatase, rutile, P-25, and sol-gel TiO2) and studied in the liquid-phase selective hydrogenation of furfural to furfuryl alcohol (FA) under mild conditions (50 °C and 2 MPa H2). The presence of high anatase crystallographic composition on TiO2 support was favorable for enhancing hydrogenation activity, while the strong interaction between Ru and TiO2 (Ru-TiOx sites) was required for promoting the selectivity to FA. The catalytic performances of bimetallic Ru-Co catalysts were improved with increasing Co loading due to the synergistic effect of Ru-Co alloying system together with the strong interaction between Ru and Co as revealed by XPS, H2-TPR, and TEM-EDX results. The enhancement of reducibility of Co oxides in the bimetallic Ru-Co catalysts led to higher hydrogenation activity with the Ru-0.6Co/TiO2 catalyst exhibited the best performances in FA selective hydrogenation of furfural to FA under the reaction conditions used.

Enhanced Base-Free Formic Acid Production from CO2 on Pd/g-C3 N4 by Tuning of the Carrier Defects

CO₂ hydrogenation is attracting increasing attention as a sustainable route to produce formic acid, a commodity and potential energy vector. Here, bifunctional catalysts comprising metal nanoparticles deposited on bulk graphitic carbon nitride were assessed under base-free conditions, identifying supported Pd as the best performer. The catalyst productivity was enhanced by maximizing the edge-defects of the g-C₃ N₄ carrier, amino groups able to activate CO₂ , and by generating welldispersed 5 nm Pd particles, required to split H₂ . Bottom-up synthesis methods, that is, hard-templating and carbon enrichment upon polymerization, and top-down strategies, that is, thermal exfoliation of the as-prepared solid, were explored to boost the defects, the nature and density of which were evaluated by thermal and (in situ) spectroscopic techniques. After optimization of temperature, pressure, and reaction time, a 20 times higher turnover frequency compared with the best Pd/g-C₃ N₄ catalyst reported producing formic acid from CO₂ without base was attained. This activity level was retained upon recycling with intermediate catalyst regeneration at mild temperature.

Synthesis and Characterization of Pd exchanged MMT Clay for Mizoroki-Heck Reaction

We successfully synthesized Pd@MMT clay using a cation exchange process. We characterized all the synthesized Pd@MMT clays using sophisticated analytical techniques before testing them as a heterogeneous catalyst for the Mizoroki - Heck reaction (mono and double). The highest yield of the Mizoroki-Heck reaction product was recovered using thermally stable and highly reactive Pd@ MMT-1 clay catalyst in the functionalized ionic liquid reaction medium. We successfully isolated 2-aryl-vinyl phosphonates (mono-Mizoroki-Heck reaction product) and 2,2-diaryl-vinylphosphonates (double-Mizoroki-Heck reaction product) using aryl halides and dialkyl vinyl phosphonates in higher yields. The low catalyst loading, easy recovery of reaction product and 8 times catalyst recycling are the major highlights of this proposed protocol.

Hydrogenation of CO2 to Formate over Ruthenium Immobilized on Solid Molecular Phosphines

Formic acid is a promising hydrogen storage medium and can be produced by catalytic hydrogenation of CO₂ . Molecular ruthenium complexes immobilized on phosphine polymers have been found to exhibit excellent productivity and selectivity in the catalytic hydrogenation of CO₂ under mild conditions. The polymeric analog of 1,2-bis(diphenylphosphino)ethane exhibited the highest activity and turnover numbers up to 13 170 were obtained in a single run. This catalyst was already active at 40 °C and with a catalyst loading of only 0.0006 mol %. Recycling experiments revealed a loss of activity after the first run, followed by a gradual decrease during the subsequent runs. This is attributed to a change in the catalytically active complex during the hydrogenation reaction. High selectivity towards formate and low leaching were maintained in the absence of CO formation. Based on the catalyst characterization, a mechanism for the CO₂ hydrogenation is proposed.