Highly efficient and recyclable basic mesoporous zeolite catalyzed condensation, hydroxylation, and cycloaddition reactions

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

For many years, capturing, storing or sequestering CO₂ from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO₂. Moreover, the use of CO₂ as a C1 building block to mitigate CO₂ emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO₂ into valuable chemicals has received much attention in the last decade, since CO₂ is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO₂ is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO₂ requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO₂ conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO₂ into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO₂ into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C₂₊OH), C₂₊ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO₂ into chemicals and fuels.

Understanding the effect of the divalent cations (Ni, Cu, and Zn) exchanged FAU zeolite on the kinetic of CO2 cycloaddition with ethylene oxide: A DFT study

Epoxide ring opening and cycloaddition with CO₂ is one of the promising routes to convert CO₂ to more valuable industrial chemicals. In this work, density functional theory calculations with the M06-L/6-31G(d,p) level of theory have been employed to study the cycloaddition of ethylene oxide (EO) with CO₂ over M(II)-faujasite zeolite (M = Ni, Cu, and Zn) in the absence of a co-catalyst. The influence of the exchanged metals strongly dominates the adsorption of EO. The binding energies of EO on the active site are -39.9 (Ni-FAU), -24.2 (Cu-FAU), and -35.0 (Zn-FAU) kcal/mol, respectively. The reaction mechanism is proposed to occur via the concerted mechanism, in which the metals initiate the EO ring opening and the formation of two new C-O bonds between the adsorbed EO and CO₂ proceed in a single step. The activation energy of the reaction catalyzed by Cu-FAU is 24.2 kcal/mol whereas that of Ni and Zn-FAU is found to be 31.1 and 31.4 kcal/mol, respectively. Moderate adsorption of EO and a larger electron transfer at the transition state are the important keys that reduce the activation energy for the Cu-FAU lower than in the other systems.

A review of the recent progress on heterogeneous catalysts for Knoevenagel condensation

One of the most crucial attributes of synthetic organic chemistry is to design organic reactions under the facets of green chemistry for the sustainable production of chemicals. Thus, due to the intensified environmental and safety concern, the need for new technologies for conducting chemical transformation has grown. In this regard, there is enormous interest in the use of heterogeneous catalysts as they generally avoid the generation of waste, require fewer toxic reagents, as well as entail easier separation and recycling of the catalyst. α,β-Unsaturated acids have been widely used in various industrial applications and have been identified as one of the most promising chemicals obtained via the Knoevenagel condensation reaction. This review aims to discuss the most pertinent heterogeneous catalytic systems such as zeolites, mesoporous silica, ionic liquids, metal oxides, and graphitic carbon nitride-based catalysts in the Knoevenagel reaction. Ultimately, this review focuses not only on the catalyst but also provides an overall idea and guide for the preparation of new catalysts with outstanding properties by looking at the chemical and engineering aspects such as the reaction conditions and the mechanisms.

ZIF-8-Nanocrystalline Zirconosilicate Integrated Porous Material for the Activation and Utilization of CO2 in Insertion Reactions

The conversion of CO₂ to useful chemicals, especially to atom economical products, is the best approach to utilize an excess of CO₂ present in the atmosphere. In this study, a metal-organic framework (ZIF-8) is integrated with nanocrystalline zirconosilicate zeolite to develop an integrated porous catalyst for CO₂ insertion reactions. The catalyst exhibits excellent activity for the CO₂ insertion reaction of epoxide to produce cyclic carbonate in neat condition without the addition of any co-catalyst. The catalyst is stable and recyclable during the cyclic carbonate synthesis. Further, the catalyst also exhibits very good activity in another CO₂ insertion reaction to produce quinazoline-2,4(1H, 3H)-dione.

Zeolites as Acid/Basic Solid Catalysts: Recent Synthetic Developments

The zeolites are porous solid structures characterized by a particular framework of aluminosilicates, in which the incorporation of the Al+3 ions generates an excess of negative charge compensated by cations (usually alkali or alkali earth) or protons. In the latter case, they are employed as catalysts for a wide variety of reactions, such as dehydration, skeletal isomerization and cracking, while the catalytic activity of basic zeolites has not found, up to now, any industrial or whatever relevant application in chemical processes. In the present review, we firstly intend to give an overview of the fundamental chemical composition, as well as the structural features of the zeolite framework. The purpose of this paper is to analyze their key properties as acid, both Lewis and Brønsted, and basic solid support. Their application as catalysts is discussed by reviewing the already published works in that field, and a final remark of their still unexplored potential as green, mild, and selective catalyst is also reported.

Mechanistic insights into CO2 cycloaddition of styrene oxide on paddle-wheel metal clusters: a theoretical study

The reaction mechanisms for the CO₂ cycloaddition of styrene oxide catalyzed by M–BTC clusters have been systematically elucidated by means of the M06-L functional.

A Comparative Study of MFI Zeolite Derived from Different Silica Sources: Synthesis, Characterization and Catalytic Performance

In this paper, a comparative study of MFI zeolite derived from different silica sources is presented. Dry gel conversion (DGC) method is used to synthesize silicalite-1 and ZSM-5 with MFI structure. Two kinds of silica sources with different particle sizes are used during the synthesis of MFI zeolite. The as-prepared samples were characterized by X-ray diffraction (XRD), N2-sorption, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and X-ray fluorescence spectrometer (XRF). From the characterization results, it could be seen that the high-quality coffin-like silicalite-1 was synthesized using silica sphere with particle size of 300 nm as silica source, with crystallization time being shortened to 2 h. The schematic diagram of silicalite-1 formation using silica sources with different particle sizes is summarized. ZSM-5 was obtained by adding Al atoms to raw materials during the synthesis of MFI zeolite. The performance of aqueous phase eugenol hydrodeoxygenation over Pd/C-ZSM-5 catalyst is evaluated.

Structural Studies of Multifunctional SrTiO3 Nanocatalyst Synthesized by Microwave and Oxalate Methods: Its Catalytic Application for Condensation, Hydrogenation, and Amination Reactions

The present study deals with the synthesis of SrTiO₃ (STO) nanocatalysts by conventional oxalate and microwave-assisted hydrothermal methods. Thorough characterization of the nanocatalysts synthesized has been done by using various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, N₂ physisorption, transmission electron microscopy, total acidity by pyridine adsorption method, and acidic strength by n-butylamine potentiometric titration, respectively. Structural parameters were estimated by Rietveld refinement analysis from XRD data which confirms cubic structure of SrTiO₃. Traces of impurities such as TiO₂ and SrCO₃ were found in conventional catalysts, whereas these are absent in microwave catalyst. Brunauer-Emmett-Teller (BET) surface area of the microwave catalyst was enhanced 14-folds compared to conventional catalyst. Increase in Lewis acid sites and their strength were also observed in STO microwave catalyst. Catalytic performance of the catalysts was evaluated for various reactions, such as Knoevenagel condensation of benzaldehyde, catalytic transfer hydrogenation of nitrobenzene, and amination of benzaldehyde. Catalytic results reveal that microwave-synthesized catalyst showed 100% conversion and selectivity (>99% yield) for the chosen reactions than the conventional catalyst. Excellent catalytic activity of the STO microwave catalyst was due to high BET surface area, pore volume, and acidity of the catalyst, as compared to conventional catalyst. The present study marks the first-time application of perovskite-based SrTiO₃ as a potential multitasking cost-effective catalyst for the above reactions and synthesized using environment friendly microwave synthesis method.