Rational Functionalization of UiO-66 with Pd Nanoparticles: Synthesis and In Situ Fourier-Transform Infrared Monitoring

Abstract

Functionalization of metal−organic frameworks (MOFs) with noble metal nanoparticles (NPs) is a challenging task. Conventional impregnation by metals often leads to agglomerates on the surface of MOF crystals. Functional groups on linkers interact with metal precursors and promote the homogeneous distribution of NPs in the pores of MOFs, but their uncontrolled localization can block channels and thus hinder mass transport. To overcome this problem, we created nucleation centers only in the defective pores of the UiO-66 MOF via the postsynthesis exchange. First, we have introduced defects into UiO-66 using benzoic acid as a modulator. Second, the modulator was exchanged for amino-benzoic acid. As a result, amino groups have decorated mainly the defective pores and attracted the Pd precursor after impregnation. The interaction of the metal precursor with amino groups and the growth of NPs were monitored by in situ infrared spectroscopy. Three processes were distinguished: the gaseous HCl release, NH 2 reactivation, and growth of extended Pd surfaces. Uniform Pd NPs were located in the pores because of the homogeneous distribution of the precursor and pore diffusion-limited nucleation rate. Our work demonstrates an alternative approach of controlled Pd incorporation into UiO-66 that is of great importance for the rational design of heterogeneous catalysts.

The structure of Pd-functionalized UiO-67 during CO2 hydrogenation

“…1) may originate from the coexistence of the particles inside the pores and at the outer surface of MOF crystallites. 21,32,36 Fig. 2 shows details of operando FT-IR spectra of UiO-67-Pd, namely the formate region (2800-2700 cm À1 ) and COÁ Á ÁMe interaction region (2150-1910 cm À1 ) collected during CO 2 hydrogenation reaction.…”

“…Since these nodes are active by themselves only in a limited number of MOF structures, it is proposed to carry out additional functionalization for catalytic purposes. [17][18][19][20][21] Some of the most promising MOFs are the Zr-based UiO family, displaying exceptional thermal and chemical stability up to the required reaction temperatures. [22][23][24][25][26] Also, in the case of UiO-66/67/68, functionalization has played an important role in enhancing the material potentialities, by insertion of other metals in the inorganic cornerstones 27,28 and by functionalization of linkers with additional metals.…”

Defect-containing metal–organic framework materials for sensor applications

“…These clusters are subsequently orchestrated into the nal 3D structure through reversible ligand exchange with covalently linked acids. 49,50 In this process, the applied modulators actively participate in the reaction and become integrated into the resultant MOF structure, giving rise to the emergence of structural defects. However, in specic scenarios, these defect-inducing modulators can be eliminated post-synthesis through thermal activation, thereby unveiling the exposed metal sites of the Lewis acid.…”

Scaling-Up Microwave-Assisted Synthesis of Highly Defective Pd@UiO-66-NH2 Catalysts for Selective Olefin Hydrogenation under Ambient Conditions

“…28 These defects considerably attract Pd(II) cations that can easily diffuse throughout the network within a few seconds by a simple wet impregnation. 29 On the other hand, the use of 2-aminoterephthalic acid as the organic ligand (i.e. UiO-66-NH 2 ) enhances, even more, the stability of Pd species with the aid of −NH 2 moieties.…”

“…UiO-66 shows a wide flexibility in terms of defect generation, even allowing up to 67% ligand replacement without collapsing . These defects considerably attract Pd­(II) cations that can easily diffuse throughout the network within a few seconds by a simple wet impregnation . On the other hand, the use of 2-aminoterephthalic acid as the organic ligand (i.e.…”