Insight into the activity of efficient acid–base bifunctional catalysts for the coupling reaction of CO2

Theoretical Insights Into the Depolymerization Mechanism of Lignin to Methyl p-hydroxycinnamate by [Bmim][FeCl4] Ionic Liquid

Depolymerization of lignin into valuable aromatic compounds is an important starting point for its valorization strategies, which requires the cleavage of C-O and C-C bonds between lignin monomer units. The catalytic cleavage of these bonds is still difficult and challenging. Our previous experimental investigation (Green Chem., 2018, 20: 3743) has shown that methyl p-hydroxycinnamate (MPC) can be produced from molecular tailoring of H unit in lignin by the cleavage of the γ-O ester bond. In this study, the mechanism of [Bmim][FeCl4]-catalyzed depolymerization of lignin was investigated by using the density functional theory (DFT) method. The results reveal that [FeCl4]- anion of the catalyst plays a decisive role in the whole catalytic process, where two possible activation modes including three different potential reaction pathways can realize the depolymerization of lignin model compound. The calculated overall barriers of the catalytic conversion along these potential routes show that the third potential pathway, i.e., methanol firstly activated by [Bmim][FeCl4], has the most probability with the lowest energy barrier, while the second pathway is excluded because the energy barrier is too high. Also, the results illustrate that the solvent effect is beneficial to the reduction of the relative energy for the reaction to form the transition states. Hence, the obtained molecular level information can identify the favorable conversion process catalyzed by metallic ionic liquids to a certain extent, and it is desirable to enhance the utilization of biomass as a ubiquitous feedstock.

Imidazolium- and Triazine-Based Porous Organic Polymers for Heterogeneous Catalytic Conversion of CO2 into Cyclic Carbonates

CO₂ adsorption and concomitant catalytic conversion into useful chemicals are promising approaches to alleviate the energy crisis and effects of global warming. This is highly desirable for developing new types of heterogeneous catalytic materials containing CO₂ -philic groups and catalytic active sites for CO₂ chemical transformation. Here, we present an imidazolium- and triazine-based porous organic polymer with counter chloride anion (IT-POP-1). The porosity and CO₂ affinity of IT-POP-1 may be modulated at the molecular level through a facile anion-exchange strategy. Compared with the post-modified polymers with iodide and hexafluorophosphate anions, IT-POP-1 possesses the highest surface area and the best CO₂ uptake capacity with excellent adsorption selectivity over N₂ . The roles of the task-specific components such as triazine, imidazolium, hydroxyl, and counter anions in CO₂ absorption and catalytic performance were illustrated. IT-POP-1 exhibits the highest catalytic activity and excellent recyclability in solvent- and additive-free cycloaddition reaction of CO₂ with epoxides.

Organocatalyzed coupling of carbon dioxide with epoxides for the synthesis of cyclic carbonates: catalyst design and mechanistic studies

The coupling of carbon dioxide (CO₂) with epoxides with the formation of cyclic carbonates is a highly attractive 100% atom economic reaction. It represents a greener and safer alternative to the conventional synthesis of cyclic carbonates from diols and toxic phosgene.