Meilin Jia

Aerobic Oxidation of Alcohols on Au Nanocatalyst: Insight to the Roles of the Ni–Al Layered Double Hydroxides Support

Au nanoparticles (NPs) supported on Ni–Al layered double hydroxides (LDHs) were shown to be efficient heterogeneous catalysts for the highly selective oxidation of alcohols to the corresponding aldehydes or ketones under base‐free or even solvent‐free conditions with O2 as the sole oxidant. The Au NPs can be uniformly distributed on Ni–Al LDHs support, which is beneficial to the catalytic activity. In addition, the weak Brønsted basic property of the support enables the aerobic oxidation of alcohols under base‐free conditions. More importantly, unlike Al2O3, which is inert, Ni–Al–LDHs are redox‐actively involved in prompting the electron transfer to O2 via the Au nanocatalyst because of the presence of NiII. Both of the basic and the redox properties of Ni–Al–LDHs can be tuned by adjusting the ratio of Ni:Al to achieve the best synergistic effects between Au NPs and the supports. The activity of the obtained Au catalysts was found to be structurally associated with the arrangements of NiO6 and AlO6 octahedra in the surface hydroxide layers which were different from the bulk Ni:Al ratio.

Synthesis of imines from amines in aliphatic alcohols on Pd/ZrO2 catalyst under ambient conditions

Synthesis of imines from amines and aliphatic alcohols (C1–C6) in the presence of base on supported palladium nanoparticles has been achieved for the first time. The catalytic system shows high activity and selectivity in open air at room temperature. As an example of the isostructural Ln3Sb3Co2O14 (Ln: La, Pr, Nd, Sm—Ho) series with an ordered pyrochlore structure, the La variant is prepared by a citrate complex method employing stoichiometric amounts of La(NO3)3, Co(NO3)2, and Sb tartrate together with citric acid with a metal/citrate molar ratio of 1:2

Heterogeneous recyclable nano-palladium catalyzed amidation of esters using formamides as amine sources

Catalyzed by supported palladium nanoparticles, a decarbonylative amidation reaction between various aryl esters and formamides by C–O bond activation has been developed for the synthesis of amides. The catalyst can be reused and shows high activity after five cycles. The XPS analysis of the catalyst before and after the reaction suggested that the reaction might be performed via a Pd0/PdII/PdIV catalytic cycle that began with Pd0. The hot filtration test strongly suggests that the present reaction would proceed in a heterogeneous manner.

Replacing Pd(OAc)2 with supported palladium nanoparticles in ortho-directed CDC reactions of alkylbenzenes

Supported palladium nanoparticles are used as efficient catalysts for the synthesis of aromatic ketones via cross dehydrogenative coupling reactions of 2-arylpyridines with alkylbenzenes. The catalyst can be reused for five cycles without significantly losing activity. Mechanism research showed that alkylbenzenes were oxidized to their corresponding aldehydes and subsequently coupled with 2-arylpyridines to generate aryl ketones through a Pd0/PdII/PdIV catalytic cycle.

Hydrotalcite-supported Pd–Au nanocatalysts for Ullmann homocoupling reactions at low temperature

Hydrotalcite-supported Pd–Au nanocatalysts were found to be efficient heterogeneous catalysts for Ullmann homocoupling reactions of aryl bromides or chlorides at 25 or 40 °C, which could be due to the ensemble effect and increased electron density of Pd sites on Pd–Au nanoparticles, and the assistant role of the hydrotalcite for the reversion of the catalytic active center, Pd(0).

Recyclable CuMgAl hydrotalcite for oxidative esterification of aldehydes with alkylbenzenes

ABSTRACT A series of hydrotalcite-like compounds with various Cu:Mg:Al molar ratios were prepared by the co-precipitation method. The catalytic performance for oxidative esterification of aldehydes was investigated. X-ray diffraction, N2 adsorption–desorption (BET), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy, the scanning electron microscope (SEM), the transmission electron microscope and atomic absorption spectrometry were used to characterize the catalysts. The results showed that the benzyl benzoate product was obtained in good to excellent yield using tert-butyl peroxybenzoate as oxidant at 90°C under air atmosphere over Cu2Mg1Al1-LDH catalyst. The catalyst can be recovered and used with 45% conversion after recycling five times. The oxidative esterification reaction in the heterogeneous system is environmentally friendly. The Cu2Mg1Al1-LDH catalyst prepared by co-precipitation method showed high catalytic activity for oxidative esterification of aldehydes. 81.0% yield of benzyl benzoate with benzaldehyde and toluene as reactants was obtained using tert-butyl peroxybenzoate as oxidant at 90°C under air atmosphere over Cu2Mg1Al1-LDH catalyst. The catalyst can be recovered and used with 45% conversion after recycling five runs. The oxidative esterification reaction in the heterogeneous system is environmentally friendly. GRAPHICAL ABSTRACT

Catalytic oxidation of glyoxal to glyoxalic acid over Au-Pd alloy nanoparticles on hydrotalcite

Synthesis of glyoxalic acid by selective oxidation of glyoxal at ambient temperatures with O2 as an oxidant is an important problem. We found that gold nanoparticles supported on hydrotalcite (Au/HT) exhibit an appreciable catalytic activity for this reaction in the liquid phase. Moreover, Au-Pd/HT, prepared by the deposition-precipitation method is superior in the catalytic behavior to monometallic Au/HT and Pd/HT catalysts. Introduction of palladium enhances ability of the catalysts to oxidize carbonyl to carboxyl, weakens the power to rupture C-C bond and in this way improves the catalytic performance. Furthermore, the Au: Pd ratio also influences the properties of the alloy catalysts. The 1.5Au-1.5Pd/HT catalysts show the highest activity for the selective oxidation at ambient temperature producing glyoxalic acid in 13.4% yield at pH 7.7. Moreover, due to basic properties of hydrotalcite, glyoxalic acid could be synthesized over 1.5Au-1.5Pd/HT in 8.0% yield without adding a base. It is hoped that results of this study can fuel further research in designing new catalysts with alloy nanoparticles supported by hydrotalcite that can be used for the selective oxidation of other useful compounds.

Low-Temperature CO Oxidation over Pd/SAPO-34 Catalyst: Low-Temperature CO Oxidation over Pd/SAPO-34 Catalyst

SAPO-34, MnSAPO-34, and CuSAPO-34 were synthesized by the hydrothermal method. A series of supported Pd catalysts were prepared by the impregnation method. The effects of calcination temperature, Pd content, prereduction of the catalyst, and reaction tempera- ture on CO oxidation were studied. The catalytic activity decreased with increasing calcination temperature. The higher reaction temperature or Pd content resulted in the higher catalytic performance for CO oxidation; however, H2 prereduction of the catalyst led to a lower catalytic performance. The results of X-ray diffraction and transmission electron microscopy analysis showed that Pd species are highly dispersed on SAPO-34 zeolite, and the Pd dispersion of the catalysts depends on the pretreatment temperature and reaction conditions. The characteriza- tion of X-ray photoelectron spectroscopy and H2 temperature-programmed reduction reveals that Pd 2+ species are the active sites for CO