Yufei He

Flower-like Au/Ni–Al hydrotalcite with hierarchical pore structure as a multifunctional catalyst for catalytic oxidation of alcohol

Flower-like hierarchical Au/NiAl-LDH catalysts were synthesized for selective oxidation of alcohols. The abundant hydrogen vacancies at the edge of the flowers as nucleation centers contributed to the uniform dispersion of Au NPs. The confinement effect of the hierarchical pores promoted 60% higher activity than the common Au/NiAl-LDH nanoparticle catalyst in the oxidation of benzyl alcohol by heightening the effective collisions between substrates and active sites. The evolution process of the hierarchical pores in the support was further proposed. Moreover, the reaction mechanism of the cooperation among Bronsted base sites, NiIII coordinatively unsaturated metal sites and isolated gold cations was concretely proved. In the oxidation of other typical alcoholic substrates, the flower-like catalyst showed higher activity than the common nanoparticle one except for linear alcohols, which could be attributed to the shape selectivity of straight macropores.

Catalytic performance of Pd-promoted Cu hydrotalcite-derived catalysts in partial hydrogenation of acetylene: effect of Pd–Cu alloy formation

Aiming at the preparation of catalysts with well-controlled structures, bimetallic PdCu catalysts containing only small amounts of Pd were prepared by two different methods for partial hydrogenation of acetylene. The highly dispersed and stable PdCu catalyst with the Pd:Cu atomic ratio of 1:40 was obtained from a Pd(OH)2/CuMgAl hydrotalcite (HT) precursor by a modified co-precipitation method. The obtained PdCu catalyst possessed uniform PdCu nanoalloys with an average size of 1.8 ± 0.3 nm. As a comparison, the impregnation method was also employed to prepare bimetallic PdCu catalysts and it was confirmed that the Pd-rich(core)–Cu-rich(shell) structure was dominant. Under identical reaction conditions, approximately 100% conversion and 82% selectivity at 100 °C were achieved using the PdCu nanoalloy catalyst which were 23% and 12% higher than those of the Pd-rich(core)–Cu-rich(shell) catalyst. The preferable activity was ascribed to the homogeneous nanoalloy structure and small size effect. The enhanced selectivity was attributed to the strong synergistic effect of PdCu. More significantly, this superior catalytic performance can be retained after 48 h of continuous reaction due to the excellent resistibility against carbon deposition and the confinement effect.

Hybrid Ni–Al layered double hydroxide/graphene composite supported gold nanoparticles for aerobic selective oxidation of benzyl alcohol

In this work, a Ni–Al layered double hydroxide/graphene (NiAl-LDH/RGO) nanocomposite which was synthesized by introducing NiAl-LDH on the surface of graphene oxide (GO) and simultaneously reducing graphene oxide without any additional reducing agents was utilized as the support for Au nanoparticles. Raman spectroscopy and XPS analysis revealed that the NiAl-LDH/RGO composite had both defect sites and oxygenic functional groups in RGO to control the directional growth of Au nanoparticles and lead to a small particle size. Compared to an Au catalyst supported on single GO and RGO or NiAl-LDH, this composite-supported Au catalyst (Au/NiAl-LDH/RGO) exhibited superior catalytic activity and stability in the selective oxidation of benzyl alcohol using molecular oxygen under low pressure. Improved activity was mainly ascribed to the small Au particle size effect caused by RGO and the contribution of basic sites in NiAl-LDH. Moreover, the preferable catalytic stability of the Au/NiAl-LDH/RGO catalyst was attributed to the defect sites and oxygenic functional groups in RGO which anchored the Au NPs and prevented the agglomeration, meanwhile, the agglomeration of RGO was inhibited by the introduction of NiAl-LDH.

Partial hydrogenation of acetylene over a NiTi-layered double hydroxide supported PdAg catalyst

NiTi-layered double hydroxide (NiTi-LDH) with rich defective sites was synthesized and used as the support for the preparation of a novel supported PdAg nanoalloy catalyst for the partial hydrogenation of acetylene. The obtained PdAg/NiTi-LDH catalyst exhibited a remarkable catalytic performance. When the conversion of acetylene reached 90%, the selectivity towards ethene maintained 82%. Superior hydrogenation activity was ascribed to two key factors. Small particle size and high dispersion of PdAg nanoparticles were responsible for boosting the catalytic activity. In addition, Ti3+ defective sites in the support also played an important role in the enhancement of activity. The interface at the Ti3+ species and active metals acting as new active sites enhanced the activation and dissociation of hydrogen and therefore further improved the catalytic activity. Preferable selectivity was assigned to the electronic effect between the NiTi-LDH support and the PdAg nanoalloys. The electron transfer from the Ti3+ species to the Pd resulted in the increase of electron density and the linearly coordinated sites of Pd and therefore facilitated the desorption of ethene. Moreover, due to the reducibility of NiTi-LDH, the selectivity and stability over the reduced PdAg/NiTi-LDH catalyst were further enhanced on account of the strong metal–support interaction.

Oxidation of Aliphatic Alcohols by Using Precious Metals Supported on Hydrotalcite under Solvent- and Base-Free Conditions

Precious metal nanoparticles supported on magnesium-aluminum hydrotalcite (HT), TiO2 , and MgO were prepared by sol immobilization and assessed for the catalytic oxidation of octanol, which is a relatively unreactive aliphatic alcohol, with molecular oxygen as the oxidant under solvent- and base-free conditions. Compared with the TiO2 - and MgO-supported catalysts, platinum HT gave the highest activity and selectivity towards the aldehyde. The turnover number achieved for the platinum HT catalyst was >3700 after 180 min under mild reaction conditions. Moreover, the results for the oxidation of different substrates indicate that a specific interaction of octanal with the platinum HT catalyst could lead to deactivation of the catalyst.

Facile and surfactant-free synthesis of supported Pd nanoparticles on hydrotalcite for oxidation of benzyl alcohol

We report a facile modified deposition–precipitation method that permits reproducible preparation of a supported Pd catalyst with small particle size and narrow size distribution but without the protection of a surfactant and any additional treatment. The pH value in this technique plays a key role in controlling the size of the Pd nanoparticles as well as the electronic environment of the surface Pd atoms. With the increasing pH (4.0–12.0), the average size of the Pd nanoparticles decreases gradually, meanwhile, the peak area ratio for CO adsorbed on bridge-bonded Pd to that adsorbed on threefold-coordinate Pd increases. Stronger support–metal interaction (electron transfer from Pd0 to support) is observed at pH values of 7.0 and 10.0. Both the small particle size and the electron-deficient surface metallic Pd contribute to enhancement in the activity for the solvent-free oxidation of benzyl alcohol. Therefore, compared with supported Pd catalysts prepared by sol immobilization, impregnation and deposition–precipitation methods, Pd/hydrotalcite synthesized by this modified deposition–precipitation approach shows a higher TOF value (5330 h−1). This enhanced catalytic performance can also be maintained in five cycles. Under the considerations of green chemistry, a number of Pd catalysts were then prepared on alternative supports using this method without the addition of alkali in the preparation process.

The role of various oxygen species in Mn-based layered double hydroxide catalysts in selective alcohol oxidation

Precise identification of oxygen species in LDH-based catalysts was investigated for the first time for alcohol oxidation. Assisted by surface O2−, O2 molecules were activated in various oxidation states. Labile oxygen species could react with alcohol except for the O22− immobilized by unsaturated metals, while other oxygen species only transferred oxygen species as mediators.

Fabrication of Pd-based metal-acid-alkali multifunctional catalysts for one-pot synthesis of MIBK

Abstract The one-pot synthesis of methyl isobutyl ketone (MIBK) from acetone using multifunctional catalysts is an important sustainable organic synthesis method with high atom and energy efficiency. Herein. we report a series of Pd supported on mixed metal oxide (MMO) catalysts with controllable acidic/basic/metallic sites on the surface. We study the relationship between the nature, synergy, and proximity of active sites and the catalytic performance of the multifunctional catalyst in the tandem reaction, in detail. In the existence of Lewis acid and base sites, the catalysts with medium-strength acidic/basic sites show preferred activity and/or MIBK selectivity. For multifunctional catalysts, the catalytic properties are more than just a collection of active sites, and the Pd/Mg3Al-MMO catalyst possessing 0.1% Pd loading and ~0.4 acid/base molar ratio exhibits the optimal 42.1% acetone conversion and 37.2% MIBK yield, which is among the best reported so far for this tandem reaction under similar conditions. Moreover, the proximity test indicates that the intimate distance between acidic/basic/metallic sites can greatly shorten the diffusion time of the intermediate species from each active site, leading to an enhancement in the catalytic performance.

Synthesis of Efficient Ce Modified CuO/CoAl-HT Catalysts for Styrene Epoxidation

The controllable synthesis of efficient supported non-noble with fitting chemical state for styrene epoxidation is of great significance to save scarce resources and improve the atom economy. Herein, a series of Ce modified CuO/CoAl-hydrotalcite catalysts was prepared using deposition–precipitation (DP) method. The appropriate addition of Ce (Ce/Cu = 0.2) could contribute to the dispersion of CuO on the surface of support. Moreover, the chemical state of CuO could be finely tuned by the introduction of Ce additives: Ce interacted with CuO and maked CuO surface enrichment of electrons, while CeO2 weakened the interaction between CuO and CoAl-HT support, increasing the percentage of Cu2+ ions (CuA2+) in metal oxides. Therefore, the obtained CuO–0.2CeO2/CoAl-HT catalyst, possessing maximum CuA2+, exhibited optimal styrene oxide yield in styrene epoxidation reaction at similar condition to date, achieving 79.5% selectivity at 99.6% styrene conversion.Graphical Abstract

Fabrication of Supported Pd–Ir Mesocrystal Catalyst for Hydrogenation of 2-Ethylanthraquinone

Pd–Ir mesocrystals with rough surface and highly branched structure were synthesized through a facile co-reduction method. The morphology evolution shows the mesocrystals were formed by oriented attachment of nanoparticles, and abundant defects sites as well as synergetic effect between building units were formed during mesocrystals oriented attachment process. Therefore, the supported Pd–Ir mesocrystals show a significant enhancement in catalytic performance in hydrogenation of 2-ethylanthraquinone compared with conventional Pd–Ir nanoparticles. The high activity can be ascribed to high densities of defect sites in Pd–Ir MCs catalyst, which facilitated H2 activation. In addition, the geometric effect of Pd–Ir MCs catalyst was responsible for inhibiting further hydrogenation of eAQH2 to undesired consecutive byproducts.Graphical Abstract