Incorporation of nanoparticles in metal-organic frameworks materials for selective catalysis

• Main Author: Zhang, Weina
• Other Authors: Huo Fengwei
• Format: Theses and Dissertations
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Materials
• Online Access: http://hdl.handle.net/10356/62223
• Institution: Nanyang Technological University

Permanently microporous metal-organic frameworks (MOFs), as a new member of heterogeneous catalyst, have shown great promise for catalysis due to their flexible as well as designable structure and outstanding properties. Further, the potential catalysis application of MOFs can be extended by incorporation varieties of nanoparticles (NPs). The traditional heterogeneous catalysts always show the lower selectivity in catalysis due to the limitation of self structure. How to design the NPs/MOFs as a novel heterogeneous catalyst to overcome the limitation of selective catalysis is still a challenge. In this research, the NPs/MOFs as heterogeneous catalyst for selective catalysis was investigated with assistant of the encapsulation of NPs in MOFs as well as the design of NPs/MOFs structure. The first part of the dissertation explored a facile encapsulation strategy to incorparate NPs into MOFs family. Nobel-metal NPs on porous carriers have been attracting an increasing research interest as the important heterogeneous catalyst. However, the fusion and aggregation of noble-metal NPs is a common observed during catalysis reaction by using existing carrier, such as carbon, zeolites and silica, due to high surface energies of free noble-metal NPs. To the best of our knowledge, the development of a suitable method to overcome the problem of NPs aggregation and ideally, introducing new properties to the catalyst at the same time remains a challenge. Herein, the noble metal NPs was encapsulated in carboxylic acid ligands based MOFs, which is the most enormous branch of MOFs family. MOFs matrix has demonstrated convincing advantages as catalytic carriers, which not only avoid the NPs aggregation but also impart new properties to the catalysts composites. Interestingly, the obtained NPs/MOFs composites as hetergeous catalysts exhibited excellent shape-selectivity in olefin hydrogenation, CO oxidation and reduction of 4-nitrophenol. Furthermore, the present results bring hope to the development of heterogeneous catalysts with high activity by using MOFs as a new host for different NPs. The second part of the thesis explored a facile encapsulation and etching strategy of NPs to craft mesopores in MOFs. Especially, the mesopore structure and space distribution could be designed by control of size, shape of NPs and encapsulation condition. It is well known that porous MOFs can be of a powerful tool for many important applications such as gas storage, catalysis, and separation because of the tunable shape and size selectivity of their pore apertures. Large pore aperture will make MOFs lose the unique selectivity; nevertheless, their small pore aperture inherently limits the diffusion of chemical species within MOFs, giving rise to low efficiency in real applications. To date, the development of a suitable method to enhance the molecular diffusion within MOFs while preserving their selectivity remains a challenge. To solve this issue, here, we reported a facile encapsulation and etching strategy of NPs to craft mesopores with controlled size, shape and space distribution in MOFs. Interestingly, we simultaneously incorporated two kinds of NPs in MOFs, where one kind of NPs were served as the catalytic active sites and another kind of NPs were used as the sacrificial template that was subsequently removed by simple etching, leaving mesopores inside the MOFs. In addition, the hierarchical meso-MOFs were be achieved by flexible design of NPs encapsulation as well as simple etching of NPs. It is worth noticing that the obtained MOFs maintained a well-defined crystal structure, showing good selectivity as well as enhanced conversion in liquid phase hydrogenation reaction. Due to the reason that the methods of incorporating NPs of different kinds, shapes and sizes in MOFs have been well developed, the encapsulation strategy is thus general and universal, and can seek a broad range of applications in the field of sensor, storage, medicine and catalysis. The third part of the thesis describes a simple heterogeneous catalyst, NPs/MOFs, which exhibited the unprecedented site-selectivity for oxidation of diol and hydrogenation of alkadiene by simple physical space limitation of MOFs pore. The selective reaction of one functional group of a molecule with several similar functional groups has been the hot topic and always challenge in the field of heterogeneous catalysis. Historically, homogeneous catalyst has provided the only precedents by specific chemical interactions. Although heterogeneous catalysts that meet some of these challenges became known, a simple solution has remained persistent issue. Selective oxidation of diol and selective hydrogenation of alkadiene provide archetypical examples for this challenge. Here, we describe a simple heterogeneous catalyst, NPs/MOFs, which exhibited the unprecedented site-selectivity for oxidation of diol and hydrogenation of alkadiene by simple physical space limitation of MOFs pore, thereby protecting the secondary functional group. Interestingly, in the case of the selective hydrogenation of unsaturated epoxide, NPs/MOFs not only utilized the Pt NPs completely encapsulated in MOFs matrixes but also limited the stretch and movement of PVP by MOFs matrixes to offer the enough steric effect, thereby perfectly performing 100% of selectivity on C=C hydrogenation and protecting the epoxy group. The results suggested exploiting the NPs/MOFs as a heterogeneous catalyst make the position-selectivity catalysis become easy, further open a new door for heterogeneous catalyst in the field of site-selective catalysis, previously, exclusively belonging to homogenous catalyst. The last part of thesis explores a facile encapsulation strategy to prepare NPs/MOFs hybrid thin films which show the optical, magnetic, and catalytic properties originating from the NPs as well as the size-selectivity deriving from microporous structure of the MOFs thin films. Fabrication of MOFs thin films is the starting point of extending MOFs to practical applications of nano-devices. Recently, the controllable integration of functional NPs with MOFs thin film, has been garnering growing research interests for the reason that hybrid MOFs thin films often exhibit optimized as well as novel properties compare to their intrinsic MOFs and thus, could open promising opportunities for developing novel functional nanomaterials such as sensing devices, electronic, and catalytic. To the best of our knowledge, it remains to be a challenge to develop a general, controlled fabrication technique of hybrid MOFs thin films that could efficiently utilize the pore space of MOFs crystals and the functionalities of the incorporated NPs. To solve this issue, herein, we report a simple method to incorporate several types of NPs in zeolitic imidazolate framework thin films by direct growth and spin coating. The as prepared dense, continuous and tunable NPs/MOFs hybrid thin films exhibited both novel properties and molecules sieve behaviors. The results presented here successfully overcome the difficulties of NPs incorporation into thin films by existing methods and would provide valuable insights for the preparation of MOFs-based nano-devices in the future.