Abstract:The combination of metal modified SBA-15 catalyst with potassium iodide was developed as heterogeneous dual catalysts for chemical fixation of CO2 to cyclic carbonates. It was observed that the binary Zn-SBA-15/KI catalysts were the most efficient among various metal modified SBA-15/KI catalysts and showed excellent synergetic effect in promoting the reaction under mild conditions. Moreover, the effects of reaction parameters on cycloaddition of CO2 with propylene oxide (PO) to propylene carbonate (PC) were optimized. Under the optimal conditions determined, Zn-SBA-15/KI catalytic system was also versatile to CO2 cycloaddition with other epoxides.Additionally, the mechanistic details for the fixation of CO2 into cyclic carbonate catalyzed by SBA-15/KI and Zn-SBA-15/KI were also contrastively elucidated using the density functional theory (DFT) method. The DFT results suggested that zincmodified and unmodified catalysts showed different coupling modes of CO2, and the ‡ These authors contributed equally to this work. -2-ring-opening reaction was the rate-determining step in the SBA-15/KI catalyzed cycloaddition reaction, but the zinc-modified SBA-15/KI catalysts could enhance the CO2 cycloaddition as the formation of a stable complex which was beneficial to CO2 trapping. As a result, the ring-closing reaction became the rate-determining step in the Zn-SBA-15/KI catalyzed cycloaddition reaction, which were promising results to guide the catalyst design for CO2 conversion.

Catalytic coupling of carbon dioxide with epoxides to obtain cyclic carbonates is an important reaction that has been receiving renewed interest. In this contribution, the cycloaddition reaction in the presence of various hydrogen bond donors (HBDs) catalyzed by hydroxyl/carboxyl task-specific ionic liquids (ILs) is studied in detail. It was found that the activity of ILs could be significantly enhanced in the presence of ethylene glycol (EG), and EG/HEBimBr were the most efficient catalysts for the CO2 cycloaddition to propylene oxide. Moreover, the binary catalysts were also efficiently versatile for the CO2 cycloaddition to less active epoxides such as styrene oxide and cyclohexene oxide. Besides, the minimum energy paths for this hydrogen bond-promoted catalytic reaction were calculated using the density functional theory (DFT) method. The DFT results suggested that the ring-closing reaction was the rate-determining step in the HEBimBr-catalyzed cycloaddition reaction but the EG addition could remarkably reduce its energy barrier as the formation of a hydrogen bond between EG and the oxygen atom of epoxides led this process along the standard SN2 mechanism. As a result, the ring-opening reaction became the rate-determining step in the EG/HEBimBr-catalyzed cycloaddition reaction. The work reported herein helped the understanding and design of catalysts for efficient fixation of CO2 to epoxides via hydrogen bond activation.

A new noble gas compound containing a Xe-Mo double bond, FXeMoF, was theoretically constructed and studied based on DFT and ab initio calculations. The CCSD(T)-calculated Xe-Mo bond length of 2.518 Å was comparable to the standard value of 2.56 Å. The bonding energy (32.3 kcal mol) was even higher than that of the Xe-Au bond in the well-known XeAuF complex (24.1 kcal mol). The result of natural bond orbital (NBO) analysis indicates that there is a σ-bond and a π-bond between the Xe and Mo atoms in FXeMoF. The properties of the Xe-Mo double bond were also analyzed with the atoms in molecules (AIM) approach and natural resonance theory (NRT).

The noble gas compound containing a triple bond of xenon and transition metal Os (i.e. F4XeOsF4, isomer A) is predicted using quantum-chemical calculations. At the MP2 level of theory, the...

The Ar-, Kr-, and Xe-insertion compounds into acrylic acid, i.e., C2H3COONgH (Ng = Ar, Kr, and Xe), have been studied by ab initio calculations. The geometry optimization, frequency calculation, and stability were investigated at the MP2/aug-cc-pVTZ (aug-cc-pVTZ-PP) level of theory. Two configuration isomers, i.e., s-cis syn (isomer A) and s-cis anti (isomer B), were optimized for each molecule. Using the s-cis syn structure (isomer A) as an example, we performed natural bond orbital (NBO) analysis, natural energy decomposition analysis (NEDA), and atom-in-molecules (AIM) analysis to investigate the bonding nature of these noble-gas compounds. Our study predicts the existence of Kr- and Xe-derivatives of acrylic acid and the instability of Ar-related compounds.

Reaction induced PdxBiy/SiC catalysts exhibit excellent catalytic activity and stability in the gas phase oxidation of monopolistic alcohols at a low temperature of 240 °C due to the formation of Pd0–Bi2O3 species.

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