Selective Catalytic Performances of Noble Metal Nanoparticle@MOF Composites: The Concomitant Effect of Aperture Size and Structural Flexibility of MOF Matrices

Abstract

Noble metal nanoparticles embedded in metal-organic frameworks (MOFs) are composite catalysts with enhanced or novel properties compared to the pristine counterparts. In recent years, to determine the role of MOFs during catalytic process, most studies have focussed on the confinement effect of MOFs, but ignored the structural flexibility of MOFs. In this study, we use two composite catalysts, Pt@ZIF-8 [Zn(mIM) , mIM=2-methyl imidazole] with flexible structure and Pt@ZIF-71 [Zn(DClIM) , DClIM=4,5-dichloroimidazole] with rigid structure, and hydrogenation of cinnamaldehyde as model reaction, to show the confinement effect and the structure flexibility of MOF matrices on the catalytic performance of composite catalysts. Both catalysts showed high selectivity for cinnamic alcohol with the confinement effect of the aperture. But, compared to Pt@ZIF-71, Pt@ZIF-8 exhibited higher conversion but lower selectivity owing to the flexible structure. The above results remind us that we will have to consider both the aperture size of MOFs and structure flexibility to select the proper MOF matrices for the composite materials to achieve the optimized performance.

Catalysis in Confined Spaces of Metal Organic Frameworks

“…In another report, encapsulation of Pt NPs within the matrices of ZIF-8 and ZIF-71 provided Pt@ZIF-8 (1 wt%) and Pt@ZIF-71 (1 wt%), respectively and their activity was evaluated in the reduction of cinnamaldehyde to cinnamyl alcohol. [89] Pt@ZIF-8 and Pt@ZIF-71 showed around 88 and 97 % cinnamyl alcohol selectivity at cinnamaldehyde conversion of 58.6 % and 11.2 %, respectively (Figure 20). In addition, due to the operation of confinement catalysis, no further oxidation products were observed.…”

“…Reduction of cinnamaldehyde to cinnamyl alcohol using Pt/C-20 %, Pt-PVP, Pt@ZIF-8-1 % and Pt@ZIF-71-1 % solids. Reproduced with permission from Ref [89]. Copyright 2017 Wiley.…”

The function of metal–organic frameworks in the application of MOF-based composites

“…To solve this problem, Tang et al fabricated MOF-supported metal catalysts by growing additional MOF layers on the catalysts to form a sandwich-like structure. 23,74,75 They rst synthesized MIL-101 loaded with Pt NPs and then epitaxially grew another MIL-101 shell with a different thickness outside the as-prepared Pt@MIL-101 particles. 23 As a result, all Pt NPs were embedded in the very thin MIL-101 layer, which did not affect the diffusion of substances (Fig.…”

“…Thick shells will restrict the diffusions of reactants and products, thereby reducing the reaction conversion signicantly although selectivity should be improved to the same extent. 75 2.5. One-pot synthetic method Each of the above-mentioned methods involves multiple steps.…”

Sequential Deconstruction–Reconstruction of Metal–Organic Frameworks: An Alternative Strategy for Synthesizing (Multi)-Layered ZIF Composites

“…[23][24][25][26] Also, ZIF-8/ZIF-67 particles can be etched (top-down) into novel shapes 27,28 or synthesized as hollow or yolk-shelled particles. [29][30][31][32][33][34] Furthermore, both of these ZIFs can grow on the surface of INPs and biosystems, meaning that a rich variety of core-shell [35][36][37][38][39][40][41][42][43][44] and layered composites 17,23,45 could be designed.…”