Periodic Mesoporous Organosilica with a Basic Urea-Derived Framework for Enhanced Carbon Dioxide Capture and Conversion Under Mild Conditions

Use of Periodic Mesoporous Organosilica-Benzene Adsorbent for CO2 Capture to Reduce the Greenhouse Effect

The CO2 adsorption of a phenylene-bridged ordered mesoporous organosilica (PMO-benzene) was analyzed. The maximum capture capacity was 638.2 mg·g-1 (0 °C and 34 atm). Approximately 0.43 g would be enough to reduce the amount of atmospheric CO2 in 1 m3 to pre-industrial levels. The CO2 adsorption data were analyzed using several isotherm models, including Langmuir, Freundlich, Sips, Toth, Dubinin-Radushkevich, and Temkin models. This study confirmed the capability of this material for use in reversible CO2 capture with a minimal loss of capacity (around 1%) after 10 capture cycles. Various techniques were employed to characterize this material. The findings from this study can help mitigate the greenhouse effect caused by CO2.

Hydrogen Bubbles: Harmonizing Local Hydrogen Transfer for Efficient Plastic Hydro-Depolymerization

Hydro-depolymerization presents a promising avenue for transforming plastic waste into high-value hydrocarbons, offering significant potential for value-added recycling. However, a major challenge in this method arises from kinetic limitations due to insufficient hydrogen concentration near the active sites, requiring optimal catalytic performance only at higher hydrogen pressures. In this study, we address this hurdle by developing "hydrogen bubble catalysts" featuring Ru nanoparticles within mesoporous SBA-15 channels (Ru/SBA). The distinctive feature of Ru/SBA catalysts lies in their capacity for physical hydrogen storage and chemically reversible hydrogen spillover, ensuring a timely and ample hydrogen supply. Under identical reaction conditions, the catalytic activity of Ru/SBA surpassed that of Ru/SiO2 (no hydrogen storage capacity) by over 4-fold. This substantial enhancement in catalytic performance provides significant opportunities for near atmospheric pressure hydro-depolymerization of plastic waste.

Liquid Metal Interfacial Engineering Strategy to Synthesize All-Carbon-Linked Porous Aromatic Frameworks for the Cycloaddition of CO2 with Epoxides

This study explores the room-temperature synthesis of porous materials and the immobilization of CO2 without the use of metals. The porous aromatic frameworks synthesized at room temperature retain the important functional group structure, and the abundance of carbon-chlorine bonds creates an excellent environment for imidazole linkage. Consequently, a catalyst conducive to the cycloaddition of carbon dioxide is obtained. Hexachloro-p-xylene is explored as the precursor, and a catalyst conducive to carbon dioxide cycloaddition is obtained. The functionalized porous aromatic frameworks (PAF-280-I/B) possess a conversion of 99.6% with a selectivity of 98.9% toward styrene carbonate (SC). The findings of this study can help mitigate the impact of greenhouse gases and enable the production of organic compounds in the circular carbonate platform, turning waste into valuable resources.

Hydroxyl and amino dual-functionalized core-shell molecular sieves featuring hydrogen bond donor groups for efficient CO2 cycloaddition

In CO2 cycloaddition reactions, hydrogen bond donor (HBD) groups are considered environmentally friendly substitutes for metals to promote epoxide ring-opening through interactions with nucleophilic anions. A core-shell structured ILs-based catalyst (mSiO2@MCM-NH2-OH) with dual hydrogen bond donors (-OH and -NH2) was synthesized by copolymerization strategy. Through in-depth characterization, it has been demonstrated that the catalyst (mSiO2@MCM-NH2-OH) possesses multiple catalytic active sites including -OH, -NH2, Br- groups, and the synergistic effect of double HBD groups (-OH and -NH2) and Lewis base (Br-) significantly improved the catalytic activity. Meanwhile, the core-shell structure of the catalyst effectively prevents the loss of active components, which makes the yield remain at about 94 % after 10 cycles. Based on Density Functional Theory (DFT) calculations, a synergistic catalytic mechanism, which involves dual hydrogen-bond donors (-OH and -NH2) and Lewis bases (Br-) was proposed. The cooperative interaction between -OH/-NH2 and Br- reduced the ring-opening barrier of epoxide from 58.6 to 32.0 kcal mol-1 significantly, and thereby facilitated the CO2 cycloaddition reaction.

Zirconium Containing Periodic Mesoporous Organosilica: The Effect of Zr on CO2 Sorption at Ambient Conditions

Two series of zirconium-incorporated-periodic-mesoporous-organosilica (Zr–PMO) materials were successfully prepared, via a co-condensation strategy, in the presence of Pluronic P123 triblock copolymer. The first series of Zr–PMO was prepared using tris[3-(trimethoxysilyl)propyl]isocyanurate (ICS), tetraethylorthosilicate (TEOS), and zirconyl chloride octahydrate(ZrCO), denoted as Zr-I-PMO, where I refers to ICS. The second series was synthesized using bis(triethoxysilyl)benzene (BTEE), TEOS, and ZrCO as precursors, named as Zr-B-PMO, where B refers to BTEE. Zr–PMO samples exhibit type (IV) adsorption isotherms, with a distinct H2-hysteresis loop and well-developed structural parameters, such as pore volume, pore width, high surface area, and narrow pore-size distribution. Structural properties were studied by varying the Zr:Si ratio, adding TEOS at different time intervals, and changing the amount of block copolymer-Pluronic P123 used as well as the calcination temperature. Surface characteristics were tailored by precisely controlling the Zr:Si ratio, upon varying the amount of TEOS present in the mesostructures. The addition of TEOS at different synthesis stages, notably, enhanced the pore size and surface area of the resulting Zr-I-PMO samples more than the Zr-B-PMO samples. Changing the amount of block copolymer, also, played a significant role in altering the textural and morphological properties of the Zr-I-PMO and Zr-B-PMO samples. Optimizing the amount of Pluronic P123 added is crucial for tailoring the surface properties of Zr–PMOs. The prepared Zr–PMO samples were examined for use in CO2 sorption, at ambient temperature and pressure (25 °C, 1.2 bar pressure). Zr–PMO samples displayed a maximum CO2 uptake of 2.08 mmol/g, at 25 °C and 1.2 bar pressure. However, analogous zirconium samples, without any bridging groups, exhibited a significantly lower CO2 uptake, of 0.72 mmol/g, under the same conditions. The presence of isocyanurate- and benzene-bridging groups in Zr-I-PMO and Zr-B-PMO samples enhances the CO2 sorption. Interestingly, results illustrate that Zr–PMO materials show potential in capturing CO2, at ambient conditions.

Polymeric ionic liquid with carboxyl anchored on mesoporous silica for efficient fixation of carbon dioxide

The utilization of carbon dioxide (CO₂) has drawn much attention because of the increasing serious environmental problems. In order to promote the cycloaddition reaction of CO₂ to epoxides, a new synthesis strategy for friendly nonmetal catalyst to combine polymeric ionic liquid (PIL) with mesoporous silica (mSiO₂) was proposed. By thorough characterizations, those catalysts (mSiO₂-PIL-n, n = 1, 2, 3, 4) were verified that PIL with multiply catalytic active sites such as carboxyl group, imidazole ring and Br^-, was mainly anchored in mesoporous SiO₂ structures. Therefore, mSiO₂-PIL-n exhibited excellent catalytic activity for CO₂ cycloaddition reaction to epoxides under solventless and cocatalyst-free conditions. Typically, the appropriate PIL loading and specific surface area guaranteed mSiO₂-PIL-2 could efficiently catalyze the cycloaddition reaction with 96% yield and 99% selectivity to the target product of propylene carbonate under the conditions of 120 °C, 2 MPa and 6 h. Additionally, the mSiO₂-PIL-2 catalyst showed superior recyclability and there was no catalytic activity decrease for 10 runs of recycling due to the tightly anchored PIL on mesoporous SiO₂ by copolymerization. And the catalytic activity to other substituted epoxides over mSiO₂-PIL-2 was also expanded. Therefore, PIL anchored on mesoporous SiO₂ by copolymerization could be a promising synthetic strategy for the efficient catalyst to combine multiple active components in a single catalyst, meanwhile, mSiO₂-PIL-n exhibited an appealing catalyst candidate for the effective fixation and utilization of CO₂.

Coupling of CO2 with Epoxides by Bifunctional Periodic Mesoporous Organosilica with Ionic Liquid Frameworks under Solvent, Additive and Metal-Free Conditions

Despite huge catalytic systems which have already been introduced to the direct coupling of CO2 with the epoxide to obtain the corresponding cyclic carbonate, the design of new systems which...

Salen-decorated Periodic Mesoporous Organosilica: From Metal-assisted Epoxidation to Metal-free CO2 Insertion

We clicked a salen ligand onto a thiol-ethane bridged periodic mesoporous organosilica (Salen-PMO) using a photo-initiated thiol-ene click reaction. This process resulted in a covalently bonded salen ligand on the PMO material. The final BET surface area amounts 511 m² /g and the pore size diameter is approximately 7 nm. The functionalized PMO material showed an excellent carbon dioxide uptake capacity of 1.29 mmol/g at 273 K and 1 bar. More importantly, by coordinating a MoO₂ ²⁺ complex onto the Salen-PMO material, we obtained a heterogeneous catalyst with a good catalytic performance for the epoxidation of cyclohexene. The catalyst was highly reusable, as no decrease in its activity was observed for at least four runs (99% conversion). Finally, the metal-free Salen-PMO showed an exceptional catalytic performance in the cycloaddition of CO₂ to epoxides. The obtained results clearly demonstrate the versatility of the Salen-PMO material not only as metal-free catalyst but also as a support material to anchor metal complexes for specific catalytic applications. With the same catalytic platform, we were able to firstly create epoxides out of alkenes, and subsequently turn these epoxides into cyclic carbonates, consuming CO₂ .

Carbamate-Isocyanurate-Bridged Periodic Mesoporous Organosilica for van der Waals CO2 Capture

We synthesized a new organosiloxane bridge on the basis of an isocyanurate derivative through a simple melt-fusion approach by the reaction of 3-isocyanatopropyltriethoxysilane (IPTES) with 1,3,5-tris(2-hydroxyethyl)-1,3,5-triazinane-2,4,6(1H,3H,5H)-trione (THEIC). The obtained carbamate-isocyanurate-based organosiloxane bridge precursor was used for the preparation of chemo- and thermostable periodic mesoporous organosilica (PMO-THEIC) on condensation with tetrathoxysilane silicon precursor through a soft-template approach. Furthermore, the synthesized PMO-THEIC with unique surface functionality was investigated for CO₂ capture. The results show that the PMO-THEIC has higher activity than pure SBA-15 for CO₂ capture due to the high affinity of carbamate functionalities embedded within the pore walls toward CO₂ molecules. The affinity of organosiloxane bridge for CO₂ molecules is mainly facilitated via the van der Waals force with carbamate functional groups rather than the isocyanurate ring, according to the density functional calculations.

Synthesis and Characterization of Novel Pyridine Periodic Mesoporous Organosilicas and Its Catalytic Activity in the Knoevenagel Condensation Reaction

The preparation of novel organic-inorganic hybrid mesoporous organosilica containing pyridinedicarboxamide functional groups uniformly distributed inside the nanostructured pore walls has been addressed. The mesoporosity and uniformity of the synthesized nanomaterials were characterized by different techniques such as nitrogen adsorption/desorption measurements and powder X-ray diffraction (PXRD). Additionally, the presence of the pyridinedicarboxamide in the pore walls of the nanomaterials was assessed by Fourier-transform infrared spectroscopy (FT-IR), as well as ²⁹Si and ¹³C solid-state cross-polarization and magic angle spinning nuclear magnetic resonance (CP/MAS-NMR). The Knoevenagel condensation of aldehydes with active methylene compounds was carried out over the pyridinedicarboxamide functionalized mesoporous organosilica, which has been proven to be an efficient heterogeneous basic catalyst in the presence of ethanol as solvent. The catalytic activity of the investigated materials was investigated in the Knoevenagel condensation between malononitrile and several benzaldehyde derivatives exhibiting a high conversion (>90%) and excellent selectivity toward the final condensation products under very mild reaction conditions. Furthermore, the catalyst stability is noteworthy as it could be recycled and reused at least twelve times without any significant change in the performance.

Ionic-Liquid-Modified Click-Based Porous Organic Polymers for Controlling Capture and Catalytic Conversion of CO2

Capture and catalytic conversion of CO₂ into value-added chemicals is a promising and sustainable approach to relieve global warming and the energy crisis. Nitrogen-rich porous organic polymers (POPs) are promising materials for CO₂ capture and separation, but their application in the additive-free catalytic conversion of CO₂ into cyclic carbonates is still a challenge. Herein, a nitrogen-rich click-based POP (CPP) was developed for the cycloaddition reaction of CO₂ with epoxides in the absence of metal, solvents, and additives. The introduction of imidazolium-based ionic liquids on the CPP host backbone could modulate the porosity, CO₂ adsorption/desorption, CO₂ selectivity over N₂ , and catalytic activity in the chemical transformation. A tentative catalytic pathway was proposed to account for the superior catalytic activity of the catalytic systems, in which the incorporated ionic liquid and porous properties of CPP synergistically contributed to the catalytic reaction. This study provides a platform to understand the cooperative effects of porous properties and nucleophilic anions on the cycloaddition reaction of CO₂ with epoxides.

Facile fabrication of a heterogeneous Co-modified pyridinecarboxaldehyde-polyethylenimine catalyst for efficient CO2 conversion under mild conditions

A heterogeneous Co-modified pyridinecarboxaldehyde-polyethylenimine catalyst with active metal sites and amine groups exhibited high catalytic activity for CO₂ conversion under mild conditions, even at ambient temperature.

Novel porous organocatalysts for cycloaddition of CO2 and epoxides

Three classes of organosilicas (DMO, OMOs and PMOs) containing immobilized multi-hydroxyl bis-(quaternary ammonium) iodide salts were prepared and tested in the cycloaddition of CO₂ and epoxides. Owing to its higher surface area, pore volume and optimum nucleophilicity of the iodide ion, OMO-2 with two hydroxyl groups was found to be the most active catalyst. For substrates that are easy to activate such as propylene oxide, 1,2-epoxybutane and epichlorohydrin, excellent yields and selectivities were obtained under mild reaction conditions (0.5 MPa CO₂, 50 °C and 10-15 h). Moreover, OMO-2 showed very good catalytic properties (yield ≥ 93% and selectivity ≥ 98%), and excellent chemical and textural stability in the synthesis of 1,2-butylene carbonate over 5 cycles.

Ionic Liquids Catalysis for Carbon Dioxide Conversion With Nucleophiles

Carbon dioxide, as a promising C₁ synthon, has attracted great interest in organic synthesis. Due to the thermodynamic stability and kinetic inertness of CO₂, developing efficient strategies for CO₂ activation and subsequent conversion is very crucial. In this context, Ionic liquids (ILs) show great potential for capturing and activating CO₂ owing to their unique structures and properties, making them become ideal alternatives to volatile organic solvents and/or catalysts for CO₂ transformation. This minireview aims at summarizing ILs-promoted reactions of CO₂ with N-nucleophiles (primary amines)/O-nucleophiles (primary alcohols, water). Two catalytic systems i.e., metal/ILs binary systems such as Cu/ILs systems and Ag/ILs systems as well as single ILs systems including anion-functionalized ILs and bifunctionalized ILs have been developed for CO₂ catalytic conversion, for instance, carboxylative cyclization of nucleophiles e.g., propargylic alcohols, amines, 2-aminobenzonitriles and o-aminobenzenethiol, and formylation of amines or 2-aminothiophenols with hydrosilanes to afford various value-added chemicals e.g., cyclic carbamates, unsymmetrical organic carbonates, α-hydroxyl ketones, and benzimidazolones. In a word, IL could provide a powerful tool for efficient CO₂ utilization.

Ambient chemical fixation of CO2 using a highly efficient heterometallic helicate catalyst system

Two novel heptanuclear 3d–4f helicates have been synthesized and characterized.