Simple preparation routes towards novel Zn-based catalysts for the solventless synthesis of propylene carbonate using dense carbon dioxide

CeO2-ZrO2 Solid Solution Catalyzed and Moderate Acidic–Basic Sites Dominated Cycloaddition of CO2 with Epoxides: Halogen-Free Synthesis of Cyclic Carbonates

For the production of cyclic carbonates from the cycloaddition of CO2 with epoxides, halogen pollution and product purity are two of the most common problems due to the usage of homogeneous halogen-containing catalysts such as ammonium salt and alkali metal halide. Hence, the development of a novel, halogen-free and efficient catalyst for the synthesis of high-purity cyclic carbonates is significant. Here, a series of acid–base bifunctional Ce1-xZrxO2 nanorods were successfully prepared. The Ce1-xZrxO2 nanorods could catalyze the cycloaddition of CO2 with epoxides efficiently without any halogen addition. Especially for the Ce0.7Zr0.3O2 catalyst, a conversion of 96% with 100% 1,2-butylene carbonate selectivity was achieved. The excellent catalytic performance of Ce1-xZrxO2 nanorods is attributed to the formation of the CeO2-ZrO2 solid solution, which contributes to abundant moderate acidic–basic active sites on the catalyst surface. It is the synergistic effect of moderate acidic–basic sites that dominates the conversion of CO2 with epoxides, which will supply important references for the synthesis of efficient metal oxide catalyst for the cycloaddition of CO2 with epoxides.

Bifunctional Catalysts Containing Zn(II) and Imidazolium Salt Ionic Liquids for Chemical Fixation of Carbon Dioxide

Zn(II) can efficiently promote the catalytic performance of imidazolium salt ionic liquids (imi-ILs) for the chemical fixation of CO₂ into epoxides. To obtain sustainability, immobilized bifunctional catalysts containing both imi-ILs and Zn(II) were prepared using bimodal mesoporous silica (BMMs) as carrier, through grafting of Zn(OAc)₂ and 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride (Si-imi) separately in the nanopores. The catalysts, named as BMMs-Zn&ILs, were identified as efficient catalysts for cycloaddition reaction of CO₂ into epoxides under solvent-free conditions. BMMs-Zn&ILs showed good catalytic activity, which increased with the increase of the molar ratio of Zn(II) to Si-imi. As a comparison, different catalytic systems including homogeneous imi-IL, BMMs-ILs and BMMs-Zn were studied to demonstrate different cooperation behaviors. Furthermore, the kinetics studies of homogeneous and heterogeneous bifunctional catalysts were employed to confirm the differences, as well as to support the proposed cooperative catalysis mechanism in the nanopores.

Heterostructural design of I-deficient BiOI for photocatalytic decoloration and catalytic CO2 conversion

I⁻ vacancies in BiOI play a major role in governing the photocatalysis and catalysis.

Metal-Organic Framework-Templated Catalyst: Synergy in Multiple Sites for Catalytic CO2 Fixation

The types and quantities of active sites play a critical role in catalysis. Herein, ZnO nanoparticles encapsulated into N-doped porous carbon has been rationally prepared by the pyrolysis of a metal-organic framework (MOF) followed by a moderate oxidation treatment. The resulting catalyst exhibits excellent activity, selectivity, and recyclability in the CO₂ cycloaddtion reactions with epoxides owing to the synergy of multiple sites inherited from the MOF and generated by the oxidation process.

CO2 fixation at atmospheric pressure: porous ZnSnO3 nanocrystals as a highly efficient catalyst for the synthesis of cyclic carbonates

Self-assembled, ultra small, porous zinc stannate nanocrystals have been synthesized, which catalyzes the formation of cyclic carbonates from various epoxide and CO₂ under very mild reaction conditions.

Influence of single- and double-flame spray pyrolysis on the structure of MnOx/γ-Al2O3 and FeOx/γ-Al2O3 catalysts and their behaviour in CO removal under lean exhaust gas conditions

Manganese and iron oxides on alumina prepared by two-nozzle flame synthesis show improved CO-oxidation activity due to minimized composite formation.

Pentaerythritol and KI: An Efficient Catalytic System for the Conversion from CO2 and Epoxides to Cyclic Carbonates

An efficient reaction of epoxides with carbon dioxide to generate the corresponding cyclic carbonates employing pentaerythritol/KI, does not need solvent.

Cyclic carbonate synthesis catalysed by bimetallic aluminium-salen complexes

The development of bimetallic aluminium-salen complexes [{Al(salen)}(2)O] as catalysts for the synthesis of cyclic carbonates (including the commercially important ethylene and propylene carbonates) from a wide range of terminal epoxides in the presence of tetrabutylammonium bromide as a cocatalyst is reported. The bimetallic structure of one complex was confirmed by X-ray crystallography. The bimetallic complexes displayed exceptionally high catalytic activity and in the presence of tetrabutylammonium bromide could catalyse cyclic carbonate synthesis at atmospheric pressure and room temperature. Catalyst-reuse experiments demonstrated that one bimetallic complex was stable for over 60 reactions, though the tetrabutylammonium bromide decomposed in situ by a retro-Menschutkin reaction to form tributylamine and had to be regularly replaced. The mild reaction conditions allowed a full analysis of the reaction kinetics to be carried out and this showed that the reaction was first order in aluminium complex concentration, first order in epoxide concentration, first order in carbon dioxide concentration (except when used in excess) and unexpectedly second order in tetrabutylammonium bromide concentration. Further kinetic experiments demonstrated that the tributylamine formed in situ was involved in the catalysis and that addition of butyl bromide to reconvert the tributylamine into tetrabutylammonium bromide resulted in inhibition of the reaction. The reaction kinetics also indicated that no kinetic resolution of racemic epoxides was possible with this class of catalysts, even when the catalyst was derived from a chiral salen ligand. However, it was shown that if enantiomerically pure styrene oxide was used as substrate, then enantiomerically pure styrene carbonate was formed. On the basis of the kinetic and other experimental data, a catalytic cycle that explains why the bimetallic complexes display such high catalytic activity has been developed.

Flame spray pyrolysis: An enabling technology for nanoparticles design and fabrication

Combustion of appropriate precursor sprays in a flame spray pyrolysis (FSP) process is a highly promising and versatile technique for the rapid and scalable synthesis of nanostuctural materials with engineered functionalities. The technique was initially derived from the fundamentals of the well-established vapour-fed flame aerosols reactors that was widely practised for the manufacturing of simple commodity powders such as pigmentary titania, fumed silica, alumina, and even optical fibers. In the last 10 years however, FSP knowledge and technology was developed substantially and a wide range of new and complex products have been synthesised, attracting major industries in a diverse field of applications. Key innovations in FSP reactor engineering and precursor chemistry have enabled flexible designs of nanostructured loosely-agglomerated powders and particulate films of pure or mixed oxides and even pure metals and alloys. Unique material morphologies such as core-shell structures and nanorods are possible using this essentially one step and continuous FSP process. Finally, research challenges are discussed and an outlook on the next generation of engineered combustion-made materials is given.

Mechanism of cyclic carbonate synthesis from epoxides and CO2

Three interconnected catalytic cycles account for the title reaction catalyzed by a bimetallic aluminum(salen) complex and Bu(4)NBr. In the first, Bu(4)NBr acts as a nucleophile to activate the epoxide. In the second, Bu(3)N generated in situ serves to activate CO(2). In the third, the aluminum(salen) complex brings the two activated species together so that the key bonds can be formed intramolecularly.

Cycloaddition of CO2 to Epoxides Catalyzed by Polyaniline Salts

The catalytic activity of polyaniline-HX (X=I, Br, Cl) (PANI-HI, PANI-HBr, PANI-HCl) for the cycloaddition of CO2 to propylene oxide (PO) to produce propylene carbonate (PC) was studied for the first time. It was shown that all the PANI salts were active for the reaction, and PANI-HI was most active and selective. On the basis of the preliminary results, the effect of the reaction conditions on the cycloadditions of CO2 to propylene oxide and epichlorohydrin was further investigated by using PANI-HI as the catalyst. The results indicated that the optimized temperature was around 115 degrees C. The maxima occurred in yield versus pressure curves at about 5 MPa for both substrates. Complete conversion was achieved in 3 h for epichlorohydrin and 6 h for propylene oxide at 115 degrees C and 5 MPa. With propylene oxide as the substrate, the reusability of PANI-HI was evaluated and no loss of catalytic activity was detectable after the catalyst had been reused five times. The catalyst was characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), which provided further evidence for the high stability of the catalyst. We believe that the catalyst has great potential for industrial applications because it has some unusual advantages, such as its easy preparation, high activity, selectivity, stability, low cost, and simple separation from products.