Rational engineering of porous materials for bifunctional catalysis : probing the structure-activity relationships

Abstract

The rational design of metal-doped bifunctional porous materials has emerged as a prominent subject in heterogeneous catalysis due to their potential for synergistic cooperativity and scalability in tandem or cascade reactions. Various metal catalysts, such as isolated single atoms, clusters, and nanoparticles supported on different matrices, have been developed. By employing the aforementioned catalyst strategies, it is possible to create tailor-made bifunctional catalysts suitable for diverse applications. This thesis aims to concentrate on the precise synthesis of bifunctional catalysts falling into two primary categories: (1) bimetallic catalysts and (2) dual active site catalysts incorporated within the porous supports of zeolites and metal-organic frameworks (MOFs). The preparation of desirable bifunctional catalysts will involve employing diverse synthesis and modification strategies for the porous materials. By utilizing cutting-edge techniques for structural elucidation, the electronic and geometric structure of the active species confined within the porous materials can be unveiled, facilitating a comprehensive discussion on the atomic-level structure-activity relationship. Chapter 1 will introduce the strategies for the synthesis and modification of metal-doped catalysts, as well as the recent advances in bifunctional catalysts. In Chapter 2, the raw materials, catalyst preparation strategies, and characterization techniques employed in this thesis will be provided. Chapter 3 presents the preparation of atomic dispersed 3d metal bimetallic dual-atom catalysts. By utilizing a di-basic imidazole linker, a linker-bridged 3d bimetallic dual atom can be assembled within the zeolite support. Three distinct synergistic advantages have been revealed in a probe superoxide dismutation reaction: (1) neighboring bimetallic active motifs, (2) tertiary structure around the zeolite support, and (3) the local coordination environment. These findings unravel a reliable approach for the precise engineering of novel bimetallic catalysts. In Chapter 4, the preparation of Cu-Fe dual-atom catalysts (DACs) on the Zr6O4 secondary building unit (SBU) of UiO-66-NH2 is presented. The Cu-Fe DACs are initially positioned on the framework linker using the strategies mentioned in Chapter 3, and further immobilized on the SBU through O2 activation. The peroxyl group bridged Cu-Fe DACs facilitate the selective oxidation of styrene, achieving a selectivity of higher than 92% towards benzaldehyde, based on the well-balanced synergy between the electronic and steric characteristics. Chapter 5 reports the preparation of a bifunctional metal/Bronsted acid zeolite catalyst through one-pot hydrothermal synthesis. By performing systematic investigations of the strength of the active species (Lewis acidity of metal species and Bronsted acidity) using two probe reactions, namely styrene oxidation and GVL decarboxylation, the synergistic cooperativity between the two active species is revealed.