Encapsulation of Metal Nanoparticle Catalysts Within Mesoporous Zeolites and Their Enhanced Catalytic Performances: A Review.

Dongdong Xu,Hao Lv,Ben Liu

doi:10.3389/fchem.2018.00550

Abstract

Metal nanoparticles (NPs) exhibit desired activities in various catalytic reactions. However, the aggregation and sintering of metal NPs usually cause the loss of catalytic performance in practical reaction processes. Encapsulation of catalytically active metal NPs on/within a high-surface-area inorganic support partially resolve such concerns. Microporous zeolites, owing to their rigid frameworks and porous structural features, have been considered as one of ideal inorganic supports. Metal NPs can be easily encapsulated and stabilized within zeolitic frameworks to prevent unwished aggregation during the catalysis. Unfortunately, sole microporous nanochannels (generally <1 nm) in conventional zeolites are not easy to be accessed. The introduction of another set of nanochannel (e.g., mesopore), known as mesoporous zeolites, can greatly improve the mass-transfer efficiency, which is structurally beneficial for most catalytic reactions. The coexistence of micropores and mesopores in inorganic supports provides the synergetic advantages of both fine confinement effect for metal NPs and easy diffusion for organic reactants/intermediates/products. This review focuses on the recent advances in the design and synthesis of mesoporous zeolites-encapsulated metal NP catalysts as well as their desired catalytic performances (activity and stability) in organic reactions. We first discuss the advantages of mesoporous zeolites as the supports and present general strategies for the construction of mesoporous zeolites. Then, the preparation methods on how to encapsulate NP catalysts within both microporous and mesoporous zeolites are clearly demonstrated. Third, some recent important cases on catalytic applications are presented to verify structural advantages of mesoporous zeolite supports. Within the conclusion, the perspectives on future developments in metal NP catalysts encapsulated within mesoporous zeolites are lastly discussed.

Highlights

Nanocatalysis by metal nanoparticles (NPs) have always attracted sufficient attention from both scientific researches and industrial applications (Astruc et al, 2005; Narayanan and El-Sayed, 2005; Astruc, 2008; Campelo et al, 2009; Cuenya, 2010)
Mesoporous zeolite is a type of ideal inorganic supports for the encapsulation of metal NPs to produce composite catalysts for various organic reactions
The advantages of mesoporous zeolites as the supports are presented in detail with the comparison to other nanomaterials like metal or nonmetallic oxides, carbon, polymers, and porous frameworks

Summary

INTRODUCTION

Nanocatalysis by metal nanoparticles (NPs) have always attracted sufficient attention from both scientific researches and industrial applications (Astruc et al, 2005; Narayanan and El-Sayed, 2005; Astruc, 2008; Campelo et al, 2009; Cuenya, 2010). For purpose of overcoming this shortcoming, massive efforts have been made to construct zeolitic frameworks with larger aperture (Li and Yu, 2014) or create a new set of pore system (known as mesopores) inside the conventional bulk zeolites (Egeblad et al, 2008; Perez-Ramirez et al, 2008; Lopez-Orozco et al, 2011; Möller and Bein, 2013; Parlett et al, 2013; Perego and Millini, 2013; Serrano et al, 2013) Speaking, the latter is simpler to implement. In mesoporous zeolites-encapsulated metal NPs catalysts, metal surfaces (providing the catalytic active sites), the micropores or mesopores (immobilizing and stabilizing the metal NPs) and interconnected mesopores (accelerating the transfer of reactants and products) together built an excellent catalysis system. Stabilized metal NPs within mesoporous zeolites and how to tune the catalytic performances based on the distinct supports media

CONSTRUCTION OF MESOPOROUS

METAL NPS

In situ Confinement Strategy

CATALYTIC APPLICATIONS

SUMMARY AND PERSPECTIVES