Rizhi Chen

Immobilized palladium nanoparticles within polymers as active catalysts for Suzuki–Miyaura reaction

A highly active and reusable catalyst Pd@PNP was developed for Suzuki–Miyaura reaction of aryl chlorides and bromides with aryl boronic acids, and the corresponding biphenyl compounds were obtained in good to excellent yields. Triphenylphosphine and palladium nanoparticles were immobilized in situ in the polymer formed from Pd catalyzed coupling of tris(4-bromophenyl)amine and benzene-1,4-diboronic acid. The immobilized triphenylphosphine enhanced the activity and the stability of the catalyst Pd@PNP, and the catalyst Pd@PNP can be reused at least 5 times with good activity. Functional groups, such as methoxyl, nitrile, tert-butyl, nitro, acyl and formyl groups, were well tolerated under the reaction conditions, and the corresponding products were obtained in high yields.

Selective and recyclable rhodium nanocatalysts for the reductive N-alkylation of nitrobenzenes and amines with aldehydes

Rhodium nanocatalysts were prepared and applied for the reductive N-alkylation of nitrobenzenes and amines to the corresponding secondary amines with aldehydes and ketones. Functional nitrobenzenes, such as nitrobenzenes with F, Cl, Br, CH3O and CH3 were transformed to the corresponding secondary amines in good to excellent yields. Moreover, the Rh@CN catalyzed N-alkylation of a series of primary amines with aldehydes and ketones also gave the corresponding secondary amines in high yields. The Rh@CN is heterogeneous, and can be reusable several times (at least 4 times) for the reductive N-alkylation of nitroarenes.

Heterogeneous cobalt catalysts for selective oxygenation of alcohols to aldehydes, esters and nitriles

Efficient and green oxygenation of alcohols to the corresponding aldehydes, esters and nitriles was developed with high selectivity. Functional alcohols, including some heterocyclic and allylic alcohols can be oxygenated to the corresponding aldehydes, esters and nitriles respectively. Moreover, the catalyst can be recycled and reused without significant deactivation. Noteworthy, the Co@NC (800-2h) catalyzed oxygenation of alcohols can be regulated easily by changing the reaction conditions, and then the corresponding aldehydes, esters and nitriles can be obtained in high yields respectively.

Enhanced catalytic properties of Pd nanoparticles by their deposition on ZnO-coated ceramic membranes

An efficient and reusable catalyst was developed by loading palladium (Pd) nanoparticles on a ceramic membrane modified with a ZnO nano-coating. The microstructures of the as-prepared Pd-loaded ceramic membranes were characterized by FESEM, EDS, ICP, XPS and HRTEM. Their catalytic properties in liquid-phase p-nitrophenol reduction to p-aminophenol were evaluated. A comparative study was also made with the Pd nanoparticles deposited onto the ceramic membrane without any modification. The XPS and HRTEM results indicate that the ZnO coating can provide strong Pd–Zn interactions on the ceramic membrane, resulting in higher catalytic stability with similar catalytic activity as compared to that without modification. It was found that the leaching and agglomeration of Pd nanoparticles should be responsible for the deactivation of Pd-loaded ceramic membranes. This work would aid the development of membrane catalysts with higher catalytic performance.

Controllable synthesis of Pd@ZIF-L catalysts by an assembly method

The Pd@ZIF-L catalysts with uniform crosshair-star shape and a size of about 20 μm were fabricated by an assembly method that enables the crystallization of ZIF-L in water with the presence of polyvinylpyrrolidone (PVP)-stabilized Pd nanoparticles (NPs). The physical and catalytic properties of the Pd@ZIF-L catalysts are greatly affected by the molar ratios of 2-methylimidazole (2-MeIM)/Zn2+ and PVP/Zn2+. Their catalytic activities were evaluated by the catalytic reduction of p-nitrophenol to p-aminophenol. The results indicate that a lower molar ratio of 2-MeIM/Zn2+ is beneficial for the increase of Pd loading and p-nitrophenol conversion, but a suitable molar ratio (≥20) of 2-MeIM/Zn2+ is helpful to the crystallization of ZIF-L and the encapsulation of the Pd NPs within the ZIF-L framework. The Pd@ZIF-L catalyst synthesized at a lower PVP/Zn2+ molar ratio has higher Pd loading and p-nitrophenol conversion due to the easy adsorption of PVP–Pd NPs onto the ZIF-L surfaces. This work would aid the development of high-performance Pd@ZIF-L catalysts.

Efficient recovery of ultrafine catalysts from oil/water/solid three-phase system by ceramic microfiltration membrane

A submerged ceramic membrane filtration system was constructed for the filtration of oil/water/solid three-phase mixture, where hexane acted as the oil phase and beta zeolite as the solid phase. The effects of the phase composition and transmembrane pressure on the filtration performance of ceramic membrane were investigated. The liquid composition in the feed and transmembrane pressure greatly affected the filtration rate and the proportion of oil/water in the permeate. Only aqueous phase passed through the membrane at lower pressures, both water and oil phases could permeate through the membrane with a lower water yield at higher pressures, and the lower water content in the feed promoted the earlier discharge of oil. The hydrophilic nature of ceramic membrane should be responsible for the filtration behavior. A combined process applying low pressure for water permeation and high pressure for oil permeation was proposed for the filtration of oil/water/solid three-phase mixture, and an efficient separation of oil/water/solid three phases was achieved.