Monodispersed Pd Nanoparticles Supported on Mg–Al Mixed Metal Oxides: A Green and Controllable Synthesis

Abstract

Aimed at the green synthesis of supported noble metal nanoparticles without any additional reducing agents or stabilizers at room temperature, a new strategy in which monodispersed Pd nanoparticles were successfully immobilized on Mg–Al mixed metal oxides derived from layered double hydroxides was developed, and the reduction mechanism was also proposed. It allowed the in situ immobilization of monodispersed Pd nanoparticles with a face-centered cubic structure, using only alcohols with α-hydrogen atom as the solvent and reducing agent. Control over the mean particle size and content of Pd nanoparticles was realized by adjusting the temperature, initial concentration, and type of alcohol. With the content of Pd varied from 6.4 to 42.3 mg/g, the mean particle size of Pd increased from 1.1 to 4.9 nm. The as-prepared catalyst showed high catalytic activity for oxidation of benzyl alcohol: when the Pd content was 6.4 mg/g, conversion of 60.3% and selectivity of 99.2% were obtained with a turnover frequency of 4807 h –1 . Similarly, on the basis of the high stand electrode potentials, immobilized Ag (5.6 nm) and Au (4.7 nm) nanoparticles were also prepared through this methodology. Moreover, the choice of supports was extended to other powder supports that would react with the byproduced acid. Overall, this facile method opens up new opportunities for controllable synthesis of supported nanoparticle catalysts in a green way.

Recent advances in high-dispersed supported metal catalysts based on two-dimension structural effects

“…此外, 利用层板金属离子与负载金属离子间的 相互作用也可在负载过程中实现对活性金属的有效 限域, 从而获得活性组分高分散且稳定分散的负载 金属催化剂. 谭天伟等 [47] 以MgAl-MMO为载体, 乙 醇为溶剂和还原剂, 依据MgO+PdCl2 +CH3CH2OH → Pd+CH3CHO+MgCl2+H2O氧化还原过程, 通过一步还 原制备了Pd/MgAl-MMO催化剂, 由于MgO物种在层 板中的高分散特性, 有效实现了负载过程中对Pd的 http://engine.scichina.com/doi/10.1360/N032017-00094 限域, 所得Pd NPs平均尺寸仅为1.1 nm, 该催化剂在 苯甲醇氧化反应体系中TOF值达4807 h −1 . 何静等 [48] 以球形Al2O3表面原位生长的MgSnAl-LDH为载体前 [50] 采用改性共沉淀法制备了 PdCl4 2− /CuMgAl-LDH前驱体, 系列表征结果表明, 助 图 9 MgAl-MMO (a)和MgO (b)载体表面酸碱性位点对Pd NPs的网阱限域作用 [40] 图 10 Pt/MgSnAl-MMO/Al2O3催化剂的制备示意图(a)和 HAADF-STEM照片(b) [48] [50] (网络版彩图) http://engine.scichina.com/doi/10.1360/N032017-00094 位合成了PdCl4 2− /GaMgAl-LDH前驱体, 还原后获得 高分散负载型PdGa/MgAl-MMO/Al2O3合金催化剂 [51] .…”

Acceptorless Amine Dehydrogenation and Transamination Using Pd-Doped Hydrotalcites

“…We recently developed a synthetic method that readily affords such dispersed species in HTs using coprecipitation under continuous flow conditions . This immobilization strategy is distinct from that previously employed to support Rh, Ru, Ag, Pd, − Au, and Cu by postsynthetic wet deposition on prepared HTs, which typically results only in nanoparticles. Pd incorporation into cationic HT sheets has not previously been targeted to our knowledge.…”

“…There are also two examples of dispersed Pd phases on mixed metal oxides (MMOs), derived by calcining HTs, both synthesized by wet impregnation: Chary et al 54 reported the formation of ∼4 nm PdO nanoparticles, indicating a strong interaction with the MMO support, while Tan et al observed Pd 0 nanoparticle formation following a mild alcohol reduction treatment. 48 Here we describe the synthesis, characterization, and application of Pd-HTs that exhibit distinct physicochemical properties from previously described examples due to the use of a readily scalable process consisting of coprecipitation in a mesoscale continuous flow reactor, followed by aging. These materials exhibit significant catalytic activity for AD of secondary amines (Scheme 1a) and oxidative transamination of primary amines via dehydrogenation (Scheme 1b).…”

“…Sivasanker et al and Ruiz et al reported immobilization of Pd salts on HTs by postsynthetic wet impregnation, but did not characterize the resulting catalysts. There are also two examples of dispersed Pd phases on mixed metal oxides (MMOs), derived by calcining HTs, both synthesized by wet impregnation: Chary et al reported the formation of ∼4 nm PdO nanoparticles, indicating a strong interaction with the MMO support, while Tan et al observed Pd 0 nanoparticle formation following a mild alcohol reduction treatment …”

Accessing 2‐Aryl Quinolines via Acceptorless Dehydrogenation and Transfer Hydrogenation Under Base and Solvent‐Free Reaction Conditions

“…Despite several efficient homogeneous catalysts that have been reported in quinoline synthesis, homogeneous catalysts exhibit several drawbacks such as thermal instability, poor recyclability, and difficulties in separation from the products. [39] On the other hand, metal catalysts decorated on inorganic supports often show excellent performances in a variety of catalytic transformations. Thus, over the years various metal nanoparticles and nanoclusters on appropriate supports have replaced the conventional catalysts.…”