Impacts of the Catalyst Structures on CO2 Activation on Catalyst Surfaces

Utilizing CO2 as a sustainable carbon source to form valuable products requires activating it by active sites on catalyst surfaces. These active sites are usually in or below the nanometer scale. Some metals and metal oxides can catalyze the CO2 transformation reactions. On metal oxide-based catalysts, CO2 transformations are promoted significantly in the presence of surface oxygen vacancies or surface defect sites. Electrons transferable to the neutral CO2 molecule can be enriched on oxygen vacancies, which can also act as CO2 adsorption sites. CO2 activation is also possible without necessarily transferring electrons by tailoring catalytic sites that promote interactions at an appropriate energy level alignment of the catalyst and CO2 molecule. This review discusses CO2 activation on various catalysts, particularly the impacts of various structural factors, such as oxygen vacancies, on CO2 activation.

The Ionic Organic Cage: An Effective and Recyclable Testbed for Catalytic CO2 Transformation

Porous organic cages (POC) are a class of relatively new molecular porous materials, whose concept was raised in 2009 by Cooper’s group and has rarely been directly used in the area of organic catalysis. In this contribution, a novel ionic quasi-porous organic cage (denoted as Iq-POC), a quaternary phosphonium salt, was easily synthesized through dynamic covalent chemistry and a subsequent nucleophilic addition reaction. Iq-POC was applied as an effective nucleophilic catalyst for the cycloaddition reaction of CO2 and epoxides. Owing to the combined effect of the relatively large molecular weight (compared with PPh3+I−) and the strong polarity of Iq-POC, the molecular catalyst Iq-POC displayed favorable heterogeneous nature (i.e., insolubility) in this catalytic system. Therefore, the Iq-POC catalyst could be easily separated and recycled by simple centrifugation method, and the catalyst could be reused five times without obvious loss of activity. The molecular weight augmentation route in this study (from PPh3+I− to Iq-POC) provided us a “cage strategy” of designing separable and recyclable molecular catalysts.

On-Demand Transformation of Carbon Dioxide into Polymers Enabled by Comb Shaped Metallic Oligomer Catalyst

Quantitative transformation of CO2 can greatly elevate the sustainability impact of CO2 chemical utilization, but it is formidably challenging due to the sluggish kinetics requiring overwhelmingly excess usage of CO2. Here, we report an on demand CO2 transformation by a switch polymerization method, that is, all reactants including CO2 are fully converted without any by-product, generating tailor-made poly(ether carbonate) polyols (CO2-polyols) whose composition and chain length exactly correspond to the feed of CO2, epoxide and diacid. This is the first time for CO2 as a countable monomer which is in most cases obscurely considered as “pressure condition”. Studies on the kinetics rate law and the activation parameters of key intermediates disclose that it is the multisite cooperativity from metallic oligomer catalyst that facilitates quantitative insertion of CO2 into polymer backbone without adverse backbiting throughout the polymerization. Hence, this work not only introduces the conception of quantitative CO2 transformation, but engineers exquisite CO2-based polymer which is rarely achieved.<br>

On-Demand Transformation of Carbon Dioxide into Polymers Enabled by Comb Shaped Metallic Oligomer Catalyst

Quantitative transformation of CO2 can greatly elevate the sustainability impact of CO2 chemical utilization, but it is formidably challenging due to the sluggish kinetics requiring overwhelmingly excess usage of CO2. Here, we report an on demand CO2 transformation by a switch polymerization method, that is, all reactants including CO2 are fully converted without any by-product, generating tailor-made poly(ether carbonate) polyols (CO2-polyols) whose composition and chain length exactly correspond to the feed of CO2, epoxide and diacid. This is the first time for CO2 as a countable monomer which is in most cases obscurely considered as “pressure condition”. Studies on the kinetics rate law and the activation parameters of key intermediates disclose that it is the multisite cooperativity from metallic oligomer catalyst that facilitates quantitative insertion of CO2 into polymer backbone without adverse backbiting throughout the polymerization. Hence, this work not only introduces the conception of quantitative CO2 transformation, but engineers exquisite CO2-based polymer which is rarely achieved.<br>

Substituent effects and Mechanism Studies in CO2 Transformation to Benzoxazinone Derivatives as Worthwhile N-containing Heterocycles: insight from DFT simulation

Investigation of CO2 transformation into value-added organic molecules is an interesting purpose in scientific communities. Here, the substitute effect exploration in CO2 incorporation reaction toward benzoxazinones formation, as a bioactive heterocyclic compound, is the main studied issue. A profound understanding of the substituent effect is helpful toward the investigation of the kinetic and thermodynamic aspects of the reaction. The substituted arynes, an imine compound, and atmospheric CO2 have been reported as the starting reactants. The substituted functional groups show substantial consequences on the studied mechanisms. The obtained results show that mechanism A, in which the imine compound is added as a nucleophile to arynes, is the most probable mechanism. The Energetic Span Model (ESM) was used in the kinetic studies, which indicates the turnover-frequency determining intermediate (TDI) and turnover-frequency determining transition state (TDTS) in the reaction progress. Also, Electron localization function (ELF) analyses reveal that the electron density of a developing monosynaptic basin on the carbon atom (V(C)) at the transition state shows a good linear correlation with the calculated energy values of TDTS. Electron-withdrawing and electron-releasing characters of the substituents have the main effects on the electron density of the developing basin at the transition states which change the TDTS energies.

Photo-accelerated Co3+/Co2+ Transformation on Cobalt and Phosphorus Co-doped g-C3N4 for Fenton-like Reaction

Peroxydisulfate (PDS) can be activated by graphitic carbon nitride (g-C3N4) under irradiation, and the generated oxygen reactive species (ROSs) can degrade organic pollutants effectively. However, the photocatalytic activity of pristine...