The cycloaddition of COsub.2 to epoxides to afford versatile and useful cyclic carbonate compounds is a highly investigated method for the nonreductive upcycling of COsub.2. One of the main focuses ...of the current research in this area is the discovery of readily available, sustainable, and inexpensive catalysts, and of catalytic methodologies that allow their seamless solvent-free recycling. Water, often regarded as an undesirable pollutant in the cycloaddition process, is progressively emerging as a helpful reaction component. On the one hand, it serves as an inexpensive hydrogen bond donor (HBD) to enhance the performance of ionic compounds; on the other hand, aqueous media allow the development of diverse catalytic protocols that can boost catalytic performance or ease the recycling of molecular catalysts. An overview of the advances in the use of aqueous and biphasic aqueous systems for the cycloaddition of COsub.2 to epoxides is provided in this work along with recommendations for possible future developments.
A potassium carbonate promoted tandem oxy-Michael addition/cyclization of α,β-unsaturated carbonyl compounds with naphthol derivatives for the synthesis of 2-substituted naphthopyrans was developed. ...Using the readily available, inexpensive potassium carbonate as the promoter, a range of different substituted naphthopyrans were prepared.
Cerium dioxide (CeOsub.2) was pretreated with reduction and reoxidation under different conditions in order to elucidate the role of surface Cesup.4+ and oxygen vacancies in the catalytic activity ...for direct synthesis of dimethyl carbonate (DMC) from COsub.2 and methanol. The corresponding catalysts were comprehensively characterized using Nsub.2 physisorption, XRD, TEM, XPS, TPD, and COsub.2-FTIR. The results indicated that reduction treatment promotes the conversion of Cesup.4+ to Cesup.3+ and improves the concentration of surface oxygen vacancies, while reoxidation treatment facilitates the conversion of Cesup.3+ to Cesup.4+ and decreases the concentration of surface oxygen vacancies. The catalytic activity was linear with the number of moderate acidic/basic sites. The surface Cesup.4+ rather than oxygen vacancies, as Lewis acid sites, promoted the adsorption of COsub.2 and the formation of active bidentate carbonates. The number of moderate basic sites and the catalytic activity were positively correlated with the surface concentration of Cesup.4+ but negatively correlated with the surface concentration of oxygen vacancies. The surface Cesup.4+ and lattice oxygen were active Lewis acid and base sites respectively for CeOsub.2 catalyst, while surface oxygen vacancy and lattice oxygen were active Lewis acid and base sites, respectively, for metal-doped CeOsub.2 catalysts. This may result from the different natures of oxygen vacancies in CeOsub.2 and metal-doped CeOsub.2 catalysts.
In this study, a new and efficient solvent-less procedure was expanded to synthesize cyclic carbonate derivatives by chemical fixation of CO.sub.2 using Cu(II)/hydroxyl terminated triazine-based ...dendrimer (Cu(II)/TD) as a proficient heterogeneous nano-catalyst. The Cu(II)/TD nano-catalyst was characterized using TEM, TGA, FT-IR, SEM, EDS, and ICP techniques. The application of this new nano-catalyst provides the preparation of assorted cyclic carbonate derivatives in the attendance of 0.045 mol% of nano-catalyst and 0.3 MPa of CO.sub.2 pressure at 50 °C under solvent-less situations in outstanding yields. The Cu(II)/TD catalyst was able to be reprocessed and recovered many times without considerable failure of its performance. The findings strongly confirm that Cu(II)/TD can be considered as an environmentally friendly and retrievable catalyst for fixation of CO.sub.2 into the valuable products. Graphical
In this study, a new and efficient solvent-less procedure was expanded to synthesize cyclic carbonate derivatives by chemical fixation of CO.sub.2 using Cu(II)/hydroxyl terminated triazine-based ...dendrimer (Cu(II)/TD) as a proficient heterogeneous nano-catalyst. The Cu(II)/TD nano-catalyst was characterized using TEM, TGA, FT-IR, SEM, EDS, and ICP techniques. The application of this new nano-catalyst provides the preparation of assorted cyclic carbonate derivatives in the attendance of 0.045 mol% of nano-catalyst and 0.3 MPa of CO.sub.2 pressure at 50 °C under solvent-less situations in outstanding yields. The Cu(II)/TD catalyst was able to be reprocessed and recovered many times without considerable failure of its performance. The findings strongly confirm that Cu(II)/TD can be considered as an environmentally friendly and retrievable catalyst for fixation of CO.sub.2 into the valuable products.
Background and Aim: Epithelium in the gastric mucosa has strong triple barrier systems such as pre-epithelial barrier (gastric mucus bicarbonate barrier), epithelial barrier (tight junction), and ...post-epithelial barrier gastric mucosal blood flow (GMBF), thereby protecting the gastric mucosa from infiltration of the gastric acid. Allyl-isothiocyanate (AITC), the pungent ingredient of wasabi, is known to activate transient receptor potential (TRP) cation channels TRPA1. In the present study, we investigated a role of TRPA1 in these gastric barrier systems in rats. Methods: Male SD rats were used after 18 h-fasting. GMBF was measured in the ex vivo stomach of urethane-anesthetized rats by using the laser Doppler flowmeter. GMBF and luminal acid loss were measured simultaneously in response to intragastric AITC or capsaicin. TRPV1- and TRPA1-immunoreactivities were detected by staining with fluorescein-conjugated tyramide amplification. Results: When AITC was intraluminally treated in ex vivo stomach of anesthetized rats, AITC infiltrated mucosa together with the acid by breaking tight junction in epithelium. As a result, shedding of surface mucosal cells was observed histologically, but apparent gastric mucosal injury was not observed macroscopically. Mucosal application of AITC increased GMBF in a concentration-dependent manner. The increased GMBF response to AITC was entirely blocked by a TRPA1 blocker. Chemical ablation of TRPV1-expressing sensory nerves attenuated the GMBF response to AITC without affecting luminal acid loss. The long-lasting increase in GMBF in response to AITC was markedly attenuated by chemical deafferentation, but initial transient increase in GMBF was not. These changes resulted in severe mucosal lesions in sensory deafferented rats. Discussion: These results suggest that (1) AITC breaks tight junction barrier in gastric epithelial cells via TRPA1-independent pathways, and (2) AITC exerts a protective effect on gastric mucosa via an increase of GMBF mediated by activation of TRPA1. It is speculated that TRPA1 channels in TRPV1-expresseing sensory nerves sense the emergency of the gastric mucosa, leading to induction of gastroprotection through the increased GMBF. Thus, the gastric mucosa will be protected against the infiltration of AITC and the acid.
Shale oil resources are abundant, but reservoirs exhibit strong heterogeneity with extremely low porosity and permeability, and their development is challenging. Carbon dioxide (COsub.2) injection ...technology is crucial for efficient shale oil development. When COsub.2 is dissolved in reservoir formation water, it undergoes a series of physical and chemical reactions with various rock minerals present in the reservoir. These reactions not only modify the reservoir environment but also lead to precipitation that impacts the development of the oil reservoir. In this paper, the effects of water–rock interaction on core porosity and permeability during COsub.2 displacement are investigated by combining static and dynamic tests. The results reveal that the injection of COsub.2 into the core leads to reactions between COsub.2 and rock minerals upon dissolution in formation water. These reactions result in the formation of new minerals and the obstruction of clastic particles, thereby reducing core permeability. However, the generation of fine fractures through carbonic acid corrosion yields an increase in core permeability. The COsub.2–water–rock reaction is significantly influenced by the PV number, pressure, and temperature. As the injected PV number increases, the degree of pore throat plugging gradually increases. As the pressure increases, the volume of larger pore spaces gradually decreases, resulting in an increase in the degree of pore blockage. However, when the pressure exceeds 20 MPa, the degree of carbonic acid dissolution will be enhanced, resulting in the formation of small cracks and an increase in the volume of small pores. As the temperature reaches the critical point, the degree of blockage of macropores gradually increases, and the blockage of small pores also occurs, which eventually leads to a decrease in core porosity.
The cycloaddition of CO.sub.2 with epoxides to cyclic organic carbonates using metal-free heterogeneous catalysts is considered as a 100% atom-economic and environmental-friendly route for CO.sub.2 ...utilization. Herein, we developed a metal-free microporous polymeric spheres catalyst (p-TBIB) by a simple Friedel-Crafts alkylation and applied in the cycloaddition of CO.sub.2 to cyclic organic carbonates. The catalyst shows high CO.sub.2 uptake (62.7 cm.sup.3 g.sup.-1, at 298 K and 1 bar), high selectivity over N.sub.2 (46 at 298 K) and perfect cycloaddition activities (66-97%) and selectivities (over 99%) and reusability (at least ten cycles) at ambient conditions (at 298 K and 1 bar).
Metal oxide clusters composed of group 5 metal ions, such as Nb and Ta, exhibit catalytic activities for COsub.2 fixation to styrene oxide (SO) due to the highly negative natural bonding charge of ...the terminal O atoms that could work as COsub.2 activation sites. In this study, tetrabutylammonium (TBA) salts of TaxNbsub.6−xOsub.19sup.8− (TBA-TaxNbsub.6−x, x = 0-6) were prepared and Ta-substitution effect on the catalytic properties of TBA-TaxNbsub.6−x for COsub.2 fixation to SO was investigated. We found that TBA-Tasub.1Nbsub.5 shows the highest styrene carbonate (SC) selectivity (95%) among TBA-TaxNbsub.6−x, although the SO conversion monotonously increases with the incremental Ta substitution amount. The COsub.2 fixation to SO under various conditions and in situ X-ray absorption fine structure measurements reveal that COsub.2 is activated on both terminal O sites coordinated to the Ta (terminal Osub.Ta) and Nb (terminal Osub.Nb) sites, whereas the activation of SO proceeds on the terminal Osub.Ta and/or bridge O sites that are connected to Ta. Density functional theory (DFT) calculations reveal that the terminal Osub.Ta of TBA-Tasub.1Nbsub.5 preferentially adsorbs COsub.2 compared with other Osub.Nb base sites. We conclude that the selective COsub.2 activation at terminal Osub.Ta of TBA-Tasub.1Nbsub.5 without SO activation is a crucial factor for high SC selectivity in the COsub.2 fixation to SO.
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![Selective CO[sub.2] Fixatio...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2073-4344/small "Selective CO[sub.2] Fixation to Styrene Oxide by Ta-Substitution of Lindqvist-Type [[sub.6]O[sub.19]][sup.8−] Clusters")