Junting Feng

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.

Co-intercalation of Acid Red 337 and a UV absorbent into layered double hydroxides: enhancement of photostability.

Organic-inorganic hybrid pigments with enhanced thermo- and photostability have been prepared by co-intercalating C.I. Acid Red 337 (AR337) and a UV absorbent (BP-4) into the interlayer of ZnAl layered double hydroxides through a coprecipitation method. The obtained compounds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric-differential thermogravimetric-differential thermal analysis, UV-visible spectroscopy, and the International Commission on Illumination (CIE) 1976 L*a*b* color scales. The results show the successful co-intercalation of AR337 and BP-4 into the interlayer region of layered double hydroxides (LDHs) and reveal the presence of host-guest interactions between LDH host layers and guest anions of AR337 and BP-4 and guest-guest interactions between AR337 and BP-4. The intercalation can improve the thermostability of AR337 due to the protection of LDH layers. Moreover, the co-intercalation of AR337 and BP-4 not only markedly enhances the photostability of AR337 but also significantly influences the color of the hybrid pigment.

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.

Facile synthesis of supported RuO2·xH2O nanoparticles on Co–Al hydrotalcite for the catalytic oxidation of alcohol: effect of temperature pretreatment

RuO2·xH2O supported on a CoAl-LDH catalyst was synthesized by the co-precipitation (CP) method and the deposition–precipitation (DP) method for the selective oxidation of alcohols. The catalyst prepared by the CP method exhibited higher activity compared with that obtained by the DP method due to stronger interaction between RuO2 and the CoAl-LDH support as well as the slightly smaller particle size of the RuO2 nanoparticles. The influence of the temperature pretreatment on catalytic performance was then investigated. Among the catalysts pretreated at different temperature, RuO2/CoAl-LDH treated at 200 °C showed the highest activity with a TOF of 142 h−1, which was nearly 55% higher than that of the untreated catalyst. It could be related to not only the suitable amount of RuO2·xH2O for β-H cleavage, but also the presence of Co3+ species for the activation of O2 molecules and storage of the resulting active O* species. Furthermore, the strong interaction between RuO2 and the support was revealed to promote the adsorption and activation of benzyl alcohol and thus enhance the catalytic performance. Significantly, RuO2/CoAl-LDH treated at 200 °C was found to selectively oxidize various alcohols to the corresponding aldehydes and ketones with respectable activity and had greater advantage comparable to that of some Ru catalysts.

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/Cuu2009=u20090.2) 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