Novel Carbon Nitride/Metal Oxide Nanocomposites as Efficient and Robust Catalysts for Coupling of CO2 and Epoxides

Defect-engineered indium-organic framework displays the higher CO2 adsorption and more excellent catalytic performance on the cycloaddition of CO2 with epoxides under mild conditions

In order to achieve the high adsorption and catalytic performance of CO2, the direct self-assembly of robust defect-engineered MOFs is a scarcely reported and challenging proposition. Herein, a highly robust nanoporous indium(III)-organic framework of {[In2(CPPDA)(H2O)3](NO3)·2DMF·3H2O}n (NUC-107) consisting of two kinds of inorganic units of chain-shaped [In(COO)2(H2O)]n and watery binuclear [In2(COO)4(H2O)8] was generated by regulating the growth environment. It is worth mentioning that [In2(COO)4(H2O)8] is very rare in terms of its richer associated water molecules, implying that defect-enriched metal ions in the activated host framework can serve as strong Lewis acid. Compared to reported skeleton of [In4(CPPDA)2(μ3-OH)2(DMF)(H2O)2]n (NUC-66) with tetranuclear clusters of [In4(μ3-OH)2(COO)10(DMF)(H2O)2] as nodes, the void volume of NUC-107 (50.7%) is slightly lower than the one of NUC-66 (52.8%). However, each In3+ ion in NUC-107 has an average of 1.5 coordinated small molecules (H2O), which far exceeds the average of 0.75 in NUC-66 (H2O and DMF). After thermal activation, NUC-107a characterizes the merits of unsaturated In3+ sites, free pyridine moieties, solvent-free nanochannels (10.2 × 15.7 Å2). Adsorption tests prove that the host framework of NUC-107a has a higher CO2 adsorption (113.2 cm3/g at 273 K and 64.8 cm3/g at 298 K) than NUC-66 (91.2 cm3/g at 273 K and 53.0 cm3/g at 298 K). Catalytic experiments confirmed that activated NUC-107a with the aid of n-Bu4NBr was capable of efficiently catalyzing the cycloaddition of CO2 with epoxides into corresponding cyclic carbonates under the mild conditions. Under the similar conditions of 0.10 mol% MOFs, 0.5 mol% n-Bu4NBr, 0.5 MP CO2, 60 °C and 3 h, compared with NUC-66a, the conversion of SO to SC catalyzed by NUC-107a increased by 21%. Hence, this work offers a valuable perspective that the in situ creation of robust defect-engineered MOFs can be realized by regulating the growth environment.

Experimental and Theoretical Investigation of Interfacial Engineering in Fe2O3/NiFe2O4 Heterostructures toward the Cycloaddition of CO2 with Styrene Oxide

The chemical fixation of CO2 into epoxides for the synthesis of cyclic carbonates is an appealing solution to both reduce global CO2 emission and produce fine chemicals, but it is still a prime challenge to develop a low-cost, earth-abundant, yet efficient solid catalyst. Herein, Fe2O3/NiFe2O4 heterostructures are facilely constructed for the highly efficient cycloaddition of CO2 with styrene oxide (SO) to produce styrene carbonate (SC). Both experimental findings and density functional theory (DFT) calculations substantiate the prominent electron transfer and charge redistribution within the heterointerfaces between the biphasic components, which induce a unique interfacial microenvironment that can facilitate the adsorption and activation of SO. This endows the biphasic catalyst with a substantially higher reactivity than the individual components. This study sheds new insights into the establishment of heterostructured catalysts consisting of transitional metal oxides for the high-efficiency production of SC from the cycloaddition of CO2 with SO.

N/Se co-doped porous carbon catalyst derived from a deep eutectic solvent and chitosan as green precursors: Investigation of catalytic activity for metal-free oxidation of alcohols

Heteroatom-doped porous carbon-based materials with high surface area compared to their metal-based homologs are considered environmentally friendly and ideal catalysts for organic reactions. In this paper, a new method for the convenient fabrication, cost-effective, and high efficiency of nitrogen/selenium co-doped porous carbon-based catalysis (marked as N/SePC-T) was designed. The N/SePC-T catalysts were created from the direct pyrolysis of a eutectic solvent containing choline chloride/urea as the nitrogen-rich carbon source, selenium dioxide as a source of heteroatom and chitosan as a secondary carbon source in different temperatures (T). The efficacy of the carbonization temperature on the pore structure, morphology, and catalytic activity of the N/SePC-T materials was investigated and displayed, the N/SePC-900 (having a surface area of 562.01 m2/g and total pore volume of 0.2351 cm3 g-1) has the best performance. The morphology, structure, and physicochemical properties of N/SePC-900 were characterized using various analyses including XRD, TEM, TGA, FE-SEM, EDX, FT-IR, XPS, and Raman. The optimized N/SePC-900 catalyst indicated excellent catalytic performance in the oxidation of benzylalcohols to corresponding aldehydes in very mild conditions.

Efficient synthesis of cyclic carbonates from CO2 under ambient conditions over Zn(betaine)2Br2: experimental and theoretical studies

It is very interesting to synthesize high value-added chemicals from CO₂ under mild conditions with low energy consumption. Here, we report that a novel catalyst, Zn(betaine)₂Br₂, can efficiently promote the cycloaddition of CO₂ with epoxides to synthesize cyclic carbonates under ambient conditions (30 °C, 1 atm). DFT calculations provide important insights into the mechanism, particularly the unusual synergistic catalytic action of Zn²⁺, Br^- and NR⁴⁺, which is the critical factor for the outstanding performance of Zn(betaine)₂Br₂. The unique features of the catalyst are that it is cheap, green and very easy to prepare.

Experimental and theoretical investigation for the cycloaddition of carbon dioxide to epoxides catalyzed by potassium and boron co-doped carbon nitride

Much endeavor has been devoted to efficient heterogeneous catalysts for carbon dioxide (CO₂) conversion to high-value chemicals. Meanwhile, the cycloaddition of CO₂ to epoxides is considered as a green and atom-economy reaction to produce cyclic carbonates. Herein, a series of K, B co-doped CN with various doping contents (K, B-CN-X) were developed by simple one-step calcination of melamine and KBH₄. B was confirmed to replace the C site and KN bond was formed, which was verified by XPS (X-ray photoelectron spectroscopy) and DFT (density functional theory) calculation. Particularly, K, B-CN-4 displayed the optimal catalytic performance in the presence of Bu₄NBr (tetrabutylammonium bromide) cocatalyst for the CO₂ cycloaddition with propylene oxide. Besides, K, B-CN-4/Bu₄NBr catalyst exhibited good substrate versatility to various epoxides and excellent recycling performance. According to the DFT calculation on CO₂ adsorption and experimental results, K, B-CN-4 presented satisfactory catalytic activity due to the enhanced CO₂ adsorption after K and B dopings then the possible reaction mechanism was proposed. The promising K, B-CN-X catalyst presented an attractive application due to the simple, eco-friendly synthesis route for the efficient fixation of CO₂.

Pyrene-based ammonium bromides combined with g-C3N4 for the synergistically enhanced fixation reaction of CO2 and epoxides

A new type of pyrene-based ammonium bromides (PABs) was synthesized via the reaction of bromomethyl pyrene and tertiary amines with different alkyl chains combined with graphitic carbon nitride (g-C3N4) through π-π stacking interactions. The new pyrene-based ammonium bromides were investigated both in homogenous phase and heterogeneous phase combining with g-C3N4 for the CO2 fixation reaction of epoxides under mild conditions. Obviously, the combination was proved to be an efficient system for the conversion of epoxides. The interaction between g-C3N4 and PABs was confirmed by quantum chemical calculations. g-C3N4/Py-C12 exhibited an excellent yield of cyclic carbonates (above 93%) at 80 °C, atmospheric pressure and solvent-free conditions. A preliminary kinetic study was performed using g-C3N4/Py-C12 and the activation energy was calculated to be 61.5 kJ mol-1.