Explore the vast range of titles available.

Carbonates deserve to be pursued in the exploration of candidate systems for birefringent crystalline materials. Recently, we successfully obtained a novel example of a mixed-metal carbonate, Cs.sub.2Pb(CO.sub.3).sub.2, using a high-temperature solution method in a closed system. Structural analysis shows that the rare Pb-C-O one-dimensional chain structure is formed by interconnecting the fundamental building blocks of PbC.sub.2O.sub.8. Detailed structural analyses and comparisons suggest a non-coplanar arrangement of CO.sub.3 due to the highly distorted polyhedra formed by Pb.sup.2+. Theoretical calculations indicate that Cs.sub.2Pb(CO.sub.3).sub.2 exhibits an average calculated birefringence of 0.037 @ 1.64 nm, which is consistent with the conclusions deduced from the structure. The source of the properties is further elucidated through real-space atom cutting. This work provides a good reference idea for designing and synthesizing new carbonate optical crystal materials.

The cycloaddition of CO[sub.2] to epoxides to afford versatile and useful cyclic carbonate compounds is a highly investigated method for the nonreductive upcycling of CO[sub.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 CO[sub.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 (CeO[sub.2]) was pretreated with reduction and reoxidation under different conditions in order to elucidate the role of surface Ce[sup.4+] and oxygen vacancies in the catalytic activity for direct synthesis of dimethyl carbonate (DMC) from CO[sub.2] and methanol. The corresponding catalysts were comprehensively characterized using N[sub.2] physisorption, XRD, TEM, XPS, TPD, and CO[sub.2]-FTIR. The results indicated that reduction treatment promotes the conversion of Ce[sup.4+] to Ce[sup.3+] and improves the concentration of surface oxygen vacancies, while reoxidation treatment facilitates the conversion of Ce[sup.3+] to Ce[sup.4+] and decreases the concentration of surface oxygen vacancies. The catalytic activity was linear with the number of moderate acidic/basic sites. The surface Ce[sup.4+] rather than oxygen vacancies, as Lewis acid sites, promoted the adsorption of CO[sub.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 Ce[sup.4+] but negatively correlated with the surface concentration of oxygen vacancies. The surface Ce[sup.4+] and lattice oxygen were active Lewis acid and base sites respectively for CeO[sub.2] catalyst, while surface oxygen vacancy and lattice oxygen were active Lewis acid and base sites, respectively, for metal-doped CeO[sub.2] catalysts. This may result from the different natures of oxygen vacancies in CeO[sub.2] and metal-doped CeO[sub.2] catalysts.

Shale oil resources are abundant, but reservoirs exhibit strong heterogeneity with extremely low porosity and permeability, and their development is challenging. Carbon dioxide (CO[sub.2]) injection technology is crucial for efficient shale oil development. When CO[sub.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 CO[sub.2] displacement are investigated by combining static and dynamic tests. The results reveal that the injection of CO[sub.2] into the core leads to reactions between CO[sub.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 CO[sub.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).

The synthesis of dimethyl carbonate (DMC) from methanol and CO[sub.2] has also received widespread attention, and K[sub.2]CO[sub.3] is usually used as a catalyst in the synthesis of DMC. In this work, the role of K[sub.2]CO[sub.3] in synthesizing dimethyl carbonate (DMC) from methanol and CO[sub.2] was revisited. Interestingly, NMR results indicated that K[sub.2]CO[sub.3] can react with methanol to form carbonate CH[sub.3]OCOO[sup.−], an essential intermediate in the synthesis of DMC, which can be transformed into DMC in the presence of CH[sub.3]I. In other words, K[sub.2]CO[sub.3] can act as not only a catalyst but also a reactant to synthesize DMC from methanol and CO[sub.2].

Calcium carbonate formation is the primary pathway by which carbon is returned from the ocean–atmosphere system to the solid Earth 1 , 2 . The removal of dissolved inorganic carbon from seawater by precipitation of carbonate minerals—the marine carbonate factory—plays a critical role in shaping marine biogeochemical cycling 1 , 2 . A paucity of empirical constraints has led to widely divergent views on how the marine carbonate factory has changed over time 3 – 5 . Here we use geochemical insights from stable strontium isotopes to provide a new perspective on the evolution of the marine carbonate factory and carbonate mineral saturation states. Although the production of carbonates in the surface ocean and in shallow seafloor settings have been widely considered the predominant carbonate sinks for most of the history of the Earth 6 , we propose that alternative processes—such as porewater production of authigenic carbonates—may have represented a major carbonate sink throughout the Precambrian. Our results also suggest that the rise of the skeletal carbonate factory decreased seawater carbonate saturation states. Geochemical insights from a dataset of carbonate stable strontium isotopes suggest that porewater production of authigenic carbonates may have been an overlooked carbonate sink for much of Earth’s history.