Enhanced Catalytic Activity of Platinum Nanoparticles by Exfoliated Metal Hydroxide Nanosheets

Abstract

A novel 2-dimensional catalytic system was developed in which platinum nanoparticles (Pt NPs) were immobilized on exfoliated MgAl-layered double hydroxide (LDH) nanosheets through an electrostatic self-assembly between negatively charged Pt NPs and positively charged LDH nanosheets. The LDH nanosheets effectively provided the large double sides of hydroxide functionality to absorb the Pt NPs, as well as fast diffusion rates of the incoming reactants into catalyst surfaces. This new nanostructure improved the rate of reaction, turnover frequency and reaction durability of Pt NPs on LDH nanosheet without significant loss in conversion efficiencies for the reduction of p-nitrophenol into p-aminophenol by NaBH 4 , maintaining more than 97% of catalytic conversions compared to free Pt NPs as well as commercial Pt/C catalyst.Owing to thermodynamically unstable surface atoms and high surface-to-volume ratio of nanomaterials, transition-metal nanoparticles (NPs) have been used in the field of the heterogeneous catalysts over the past several decades.[1] The unique characteristics of nanomaterials have consistently required developments in the surface stabilization of the individual NPs with organic molecules.[2] However, organic stabilizers could hinder most active surface sites of the metal NPs to block their catalytic functions. Immobilizations of the metal NPs on desired solid supports such as metal oxides, [1c] graphitic carbons, [3] and porous silica [4] prevent agglomeration of the metal NPs, which has led to the poisoning of catalytic activities. [5] Metal NPs on supports function in repeated recycles without organic stabilizers, maintaining high performance as heterogeneous catalysts. Nevertheless, the following common problems still exist in the development of new catalysts: (1) the use of covalent chemical linkers to bind metal NPs on the surface of solid supports, (2) loading of the metal NPs by impregnation onto the limited areas of mesoscopic supports, which produced irregular-size NPs, and (3) low dispersion capability of solid supports in solution that can restrict the practical applications of the metal NPs. Thus, the development of new types of solid supports needs a large open surface and reactive surface functionalities, which could bind to metal NPs, such as layered double hydroxides (LDH).[6] In previous reports, we demonstrated the useful application of surface potentials for the charged particles, such as zeolite crystals, proteins, polymer beads, and surface-modified LDHs, which drove their electrostatic assemblies on the as-prepared or chemically modified LDH surface to produce complex nanostructures. [7] To date, powdery LDHs as catalyst supports have been widely reported with polyoxometalates [8] and transition-metal NPs.[9] Metal NPs (e.g., Pt, Pd) impregnated into the LDHs by in situ chemical reduction of intercalated metal chlorides [9a,b] were formed on the edge surfaces of the LDH particles with an irregular size distribution, which is attributed to restricted interlayer galleries....

Layered Double Hydroxide‐Based Catalysts: Recent Advances in Preparation, Structure, and Applications

“…LDH materials have been widely used as catalyst supports. The structure LDH materials (e.g., 2D surface area, flexible composition, confinement effect) allow a series of supported noble metal (Ru, Pd, Pt, and Au) catalysts to be prepared; the metal particles in these materials have a high degree of dispersity, as well as structural stability resulting from the strong anchoring effect of the support. The presence of surface hydroxyl groups and defect structures (e.g., oxygen vacancies) located in the brucite‐like host layers can significantly influence the particle size, morphology, and electronic structure of the supported metal catalysts.…”

Layered Double Hydroxide‐based Nanomaterials as Highly Efficient Catalysts and Adsorbents

“…The lateral (100) facet with a high density of dangling bonds may have relatively active chemical characteristics, resulting in the preferential deposition of Au NPs on the (100) facet. Most recently, Jung et al reported the synthesis of Pt nanoparticles immobilized on exfoliated MgAl‐LDH nanosheets via an electrostatic self‐assembly between negatively‐charged Pt NPs and positively‐charged LDH nanosheets ( Figure ). The LDH nanosheets provide double sides of hydroxide functionality to stabilize Pt NPs, and facilitate a fast diffusion of reactants into the catalyst surface.…”

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

“…MMOs层板表面高度分散的负载型金属催化剂. 2002 年, Choudary等 [56] 基于LDHs层间的几何限域作用, 将 [60] Jung等 [62] [60] (网络版彩图) 图 13 LBL法制备Au/ZnAl-LDH薄膜催化剂示意图 [61]…”