Br--intercalated ZnMgAl-LDH Heterogeneous Catalyst for Efficient Cycloaddition of CO2 with Propylene Oxide

Carbon dioxide (CO2) is the greenhouse gas which is generated by the consumption of petrochemicals or fossil resources. CO2 is an abundant and renewable C1 building block. The utilization of CO2 as a C1 raw material in organic synthesis is an environmentally friendly method, which can not only solve the environmental and climate problems, but also facilitates the energy transformation from fossil materials to renewable resources. Thus, the research to transform CO2 into valuable chemicals has attracted attention in the field of green and sustainable chemistry. In the field, cyclic carbonates generated from CO2 and epoxides has been widely investigated. Cyclic carbonate is an important chemical raw material, which is widely applied in high-boiling polar aprotic solvents and electrolytes in batteries. The method of preparing cyclic carbonate with CO2 and epoxides as raw materials is a green synthetic transformation of 100% atomic economy for the utilization of greenhouse gas CO2. There are two kinds of catalysts for cycloaddition, including metal-based catalysts and organocatalysts. Compared with metal catalyst, organic catalysts have the advantages of low cost, simple synthesis steps and no metal contaminants, but harsh reaction conditions and/or higher catalyst loading are often needed. In order to overcome this problem, introduction of hydrogen bond donor to catalytic systems has been prevalent and has provided a simple and efficient protocol for synthesis of cyclic carbonates from CO2 and epoxides. Recent developments in the area of hydrogen bond donor functionalized organocatalysts have demonstrated that the acidity of hydrogen bond donor is crucial for achieving the boosting activity of catalysts in the cycloaddition of CO2 with epoxides. Hydroxyl functionalized organocatalysts are one of the earliest and most widely studied organocatalysts promoted by hydrogen bond donors in the cycloaddition reaction of CO2 with epoxides. The literature results showed that the organocatalysts bearing phenol hydroxyl group showed higher catalytic activity than those with alcohol hydroxyl group, which may be the reason of the stronger acidity of phenol hydroxyl group compared with alcohol hydroxyl group. Increasing the acidity of hydrogen bond donor in certain scale can effectively improve its catalytic activity, but further to increase acidity of hydrogen bond donor may lead to the decrease of catalytic activity. This is because properly increasing the acidity of hydrogen bond donor is beneficial for enhancing the hydrogen bond interaction between hydrogen bond donor and epoxide, thus promoting the ring-opened step of epoxide. However, the excessive enhancement of acidity will lead to too strong hydrogen bond interaction to induce the finally ring-closed step of intermediates. Therefore, the acidity of hydrogen bond donor is very important to the activity of catalyst. In addition to the traditional hydrogen bond donors, some special hydrogen bond donors, such as water and azaphosphatranes, are also employed as hydrogen bond donors in the cycloaddition reaction of CO2 with epoxides. It is particularly noteworthy that water is a kind of abundant and environmentally friendly hydrogen bond donor. All these indicate that the development of a kind of abundant, commercially available, and environmentally friendly hydrogen bond donor is one of the hot topics in the design and synthesis of high efficiency organocatalysts in the future. In this review, the advancement on cycloaddition of CO2 with epoxide promoted by hydroxyl group, carboxyl group, amino group, multi-hydrogen bond donor and special hydrogen bond donor has been summarized over the years. We expected the knowledge from these literatures to provide insight to the rational design of highly active organocatalysts.

Facet and dual vacancy engineering-boosting BiOBr for enhanced CO2 and epoxide cycloaddition reaction under mild and cocatalyst-free conditions: Double substrate active sites and activated surface bromine ions synergy

Facile construction of bifunctional porous ionic polymers for efficient and metal-free catalytic conversion of CO2 into cyclic carbonates

The conversion of CO2 into value-added chemicals has become an imminent research topic and the cycloaddition of CO2 with a C1 resource to produce cyclic carbonates is a promising pathway for CO2 utilization. Herein, a series of POSS-based polyionic liquids (PILs) were synthesized by the copolymerization of octavinyl polyhedral oligomeric silsesquioxane (POSS) with an imidazolium ion linker. The prepared PILs have the characteristics of hydrogen bond donors, halogen atom sites, stable pore structures, and thermal stability, and are used as heterogeneous catalysts for the cycloaddition of epoxides with carbon dioxide. The effect of linkers on the cycloaddition is investigated by tuning the ratio of POSS units to imidazolium ions. Under the optimized conditions, the conversion of epichlorohydrin can reach 99.18% at atmospheric pressure with neither co-catalysts nor solvents. It is concluded that the reaction of the cycloaddition of epoxides with carbon dioxide follows pseudo-first-order kinetics. Moreover, the presence of the catalysis of PILs leads to a significant decrease in the activation energy barrier for cycloaddition. The catalyst can be facilely recovered due to its high stability, and only a slight decrease in conversion was observed after five successive runs. In addition, the mechanism of PILs catalyzing the cycloaddition reaction of epoxides with CO2 is proposed. This work not only provides a sustainable and green process for CO2 cycloaddition, but also highlights the potential of using PILs for CO2 utilization.

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation, which is currently accomplished by modified palladium catalysts. Herein, we rep...

The chemical fixation of carbon dioxide (CO2) into value-added chemicals is a pivotal research direction toward achieving carbon neutrality and sustainable chemistry. Herein, a biomass-derived poly(ionic liquid) (BPIL) was designed from renewable chitin and low-cost pyridinium. The as-prepared catalyst exhibits excellent performance in the cycloaddition of CO2 with various epoxides under mild/solvent-free/cocatalyst-free conditions. Furthermore, the catalyst demonstrates remarkable stability and recyclability with no significant loss of activity over five consecutive cycles. More importantly, a combination of in situ FTIR experimental studies and density functional theory (DFT) calculations reveals a crucial synergistic effect between the hydroxyl groups on the biomass support, acting as hydrogen bond donors (HBDs), and the iodide anions. This synergy effectively activates the epoxide and significantly lowers the energy barrier of the rate-determining step. This work not only provides an efficient and green catalytic system for CO2 valorization but also offers a strategy for the rational design of multifunctional catalysts from renewable biomass.

The development of green solid polymer materials bearing multiple active sites as highly efficient heterogeneous catalysts with cooperative effects toward the conversion of carbon dioxide (CO2) to high-value-added cyclic carbonate is highly in need. Here a novel cationic polymer based on the moieties of 1-bromomethyl-4-hydroxy calix[4]arene and tri(4-imidazolylphenyl)amine has been synthesized, characterized, and used as a metal-free bifunctional heterogeneous catalyst for CO2 utilization. The presence of abundant phenolic OH groups as hydrogen bond donors and bromide anions as nucleophilic agents provides this polymer with brilliant activities in catalyzing the epoxides into cyclic carbonates under atmospheric pressure and solvent-free conditions. More importantly, this bifunctional catalyst can be conveniently recycled and keeps catalytic ability well. This work not only offers a new method to synthesize a competitive green heterogeneous catalyst but also provides the first example of an ionic polymer that contains calixarene for synthesizing cyclic carbonate through the CO2 cycloaddition reaction.

Implanting multi-functional ionic liquids into MOF nodes for boosting CO2 cycloaddition under solventless and cocatalyst-free conditions

The integration of synergic hydrogen bond donors and nucleophilic anions that facilitates the ring-opening of epoxide is an effective way to develop an active catalyst for the cycloaddition of CO2 with epoxides. In this work, a new heterogeneous catalyst for the cycloaddition of epoxides and CO2 into cyclic carbonates based on dual hydroxyls-functionalized polymeric phosphonium bromide (PQPBr-2OH) was presented. Physicochemical characterizations suggested that PQPBr-2OH possessed large surface area, hierarchical pore structure, functional hydroxyl groups, and high density of active sites. Consequently, it behaved as an efficient, recyclable, and metal-free catalyst for the additive and solvent free cycloaddition of epoxides with CO2. Comparing the activity of PQPBr-2OH with that of the reference catalysts based on mono and non-hydroxyl functionalized polymeric phosphonium bromides suggested that hydroxyl functionalities in PQPBr-2OH showed a critical promotion effect on its catalytic activity for CO2 conversion. Moreover, PQPBr-2OH proved to be quite robust and recyclable. It could be reused at least ten times with only a slight decrease of its initial activity.

Ionic polymers functionalized with hydroxyl, carboxyl, and amino groups can enhance the catalytic activity of catalysts. However, the straightforward preparation of bifunctional ionic polymers containing abundant ionic active sites and hydrogen bond donors remains challenging. In this study, a series of porous ionic polymers (BZIs) containing different hydrogen bond donors (-NH2, -OH, -COOH) were prepared through a simple one-pot Friedel-Crafts alkylation using benzimidazole derivatives and benzyl bromide. The structures and properties of BZIs were characterized by various techniques such as Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, solid-state nuclear magnetic resonance, and scanning electron microscopy. Among the prepared catalysts (BZI-NH2, BZI-OH, and BZI-COOH), BZI-NH2 exhibited the highest catalytic activity and recyclability, achieving a yield of 97% in the CO2 cycloaddition. The synergistic effect of Br-, hydrogen bond donors (-NH-, -NH2), and N+ in BZI-NH2 was found to contribute to its superior catalytic performance. DFT calculations were employed to study the effect of hydrogen bonds, Br-, and N+ in BZI-NH2 and BZI-OH on the CO2 cycloaddition. Using BZI-NH2 as an example, a mechanism was proposed for the synergistic effect between amino groups and bromide ions in catalyzing the CO2 cycloaddition reaction.

The potential energy surface of l-homoselenocysteine (HSEC) has been explored through the use of B3LYP/6-311+G(d,p) calculations. In this survey, seventy-seven different conformers have been located. These local minima can be classified in four groups, A–D. Structures A, B, and D are stabilized by intramolecular hydrogen bonds (IMHBs) with the amino group acting as the hydrogen bond (HB) donor and the carbonyl group (structures A and D) or the hydroxyl group (structure B) as HB acceptors. The structures in set C present an IMHB with the amino group acting as the HB acceptor and the hydroxyl group as the HB donor. The stability order decreases in the following order: A > B > C > D. From their relative stabilities it can be concluded that only three of these conformers, namely A1, A4, and A5, would exist in the gas phase at room temperature. The most stable deprotonated form corresponds to a Se-deprotated species stabilized by a strong IMHB between the hydroxyl group and the Se atom. However, a direct deprotonation of the most stable neutrals lead to O-deprotonated species, which eventually isomerize to yield the global minimum. Hence, we can conclude that, quite unexpectedly, HSEC behaves as a Se acid in the gas phase, its intrinsic acidity being 1374 kJ mol–1at the B3LYP/6-311++G(3df,2p) level of theory. The most stable protonated forms are systematically the N-protonated ones, the global minimum being a structure stabilized through an IMHB involving the protonated amino group as the HB donor and the SeH group as the HB acceptor. The calculated gas-phase proton affinity (PA) at the B3LYP/6-311++G(3df,2p) level of theory is 930 kJ mol–1.

Observation of a potential-dependent switch of water-oxidation mechanism on Co-oxide-based catalysts

Facile integration of hydroxyl ionic liquid into Cr-MIL-101 as multifunctional heterogeneous catalyst for promoting the efficiency of CO2 conversion

The development of bifunctional catalytic materials bearing Lewis acid and base activity sites toward the cycloaddition of CO 2 and epoxides to value‐added cyclic carbonate under cocatalyst‐free conditions is needed in particular. In this work, an imidazolium functionalized Zn (II)‐porphyrin ZnTAEImP was first designed and synthesized. Subsequently, a series of porous organic polymers, named POP‐ZnTAEImP/DVB(1: m ) ( m = 30, 50, 70), were prepared through the free‐radical copolymerization of ZnTAEImP with divinylbenzene (DVB). The obtained POP‐ZnTAEImP/DVB(1: m ) exhibited a high specific surface area and good thermal stability. As bifunctional heterogeneous catalysts, POP‐ZnTAEImP/DVB(1: m ) showed excellent catalytic activities in CO 2 cycloaddition with epichlorohydrin under the condition of solvent‐free. In particular, the POP‐ZnTAEImP/DVB(1:50) demonstrated the highest catalytic activity (TON = 2880) and was applicable to a variety of epoxides. Furthermore, only a slight decrease in catalytic activity was observed after five cycles. Activation energy ( E a ) for this reaction was determined to be 52.4 kJ/mol. This work provides a valuable strategy for designing efficient binary heterogeneous catalysts for the high‐efficiency fixation of CO 2 .

<sec><p indent="0mm">Catalysis, the science of accelerating chemical reactions and regulating the selectivity of reaction products, lies in the heart of modern chemical industry. Typically, catalysis can be categorized into heterogeneous catalysis and homogeneous catalysis. Over the past century, heterogeneous catalytic processes such as ammonia synthesis and Fischer-Tropsch synthesis have become an indispensable part of the chemical industry. In recent years, the rational design of catalysts has gained a lot of attention due to both economic and environmental concerns, which has raised new demands for a deep understanding of the mechanism of catalytic reactions. Machine learning methods as one of the most important areas of artificial intelligence (AI) are becoming more and more popular in practices of theoretical simulations. This review gives an overview on various machine learning methods and their applications in theoretical heterogeneous catalysis. </sec><sec> Starting with statistical learning models on small datasets based on specific physical descriptors, which play an important role in early theoretical heterogeneous research, this review analyzes how they connect linear scaling relationship and catalytic experiments. However, due to the complexity of heterogeneous catalytic systems, sometimes nonlinear models can be essential. In this way, the exact form of equations should be obtained before fitting, which is extremely challenging. This problem can be solved by methods based on symbolic regression like SISSO to obtain a set of expressions, and the researchers can select one by their domain knowledge. This review also shows the applications of some popular machine learning methods (such as SVM, PCA, RF, etc.) in research, most of which are based on specific descriptors, simple but have difficulty transferring to other systems. </sec><sec> First-principle calculations like DFT are crucial in catalysis rational design by computational simulations for surface structure determination and reaction channel exploration, but they are impractical for simulations on large and complex catalytic systems due to high computational costs. In recent years, machine learning potentials (MLPs), as tools to bridge the gap between first-principle accuracy and computational efficiency, have pushed forward the frontier of theoretical heterogeneous catalysis. Popular MLPs (LASP, EANN, DP, GemNet-OC, MACE, DPA, etc.) have numerous applications in this field, from global optimization and molecular dynamics of active surfaces under reaction conditions to automatic reaction network exploration. Recently, universal machine learning potentials have gained much attention and are very promising in heterogeneous catalysis simulations, for their promising capability to encapsulate huge chemical space of the whole periodic table in one pre-trained model, which is easy to fine-tune on a specific chemical system, efficiently deploying a specific MLP with high accuracy and transferability. </sec><sec> Recent advances in generative models have shown considerable promise for heterogeneous catalysis research, and the dramatic emergence of large language models like ChatGPT is especially important in this case. LLMs can incorporate information from massive natural language data, having a huge ability to push forward the understanding of topics in catalytic science. Furthermore, the concept of generative models themselves has much potential in generating novel catalytic information directly without natural language as the intermediate, but their application in heterogeneous catalysis is under limitation due to the lack of large datasets with high quality. </sec><sec> In a nutshell, machine learning methods play a key role in theoretical understanding of heterogeneous catalytic systems. Challenges remain due to the complexity of heterogeneous catalytic systems and lack of high-quality dataset, but the era of AI-driven rational design of surface catalysts is truly coming. </sec>