Bimetallic AgPd/UiO-66 Hybrid Catalysts for Propylene Glycol Oxidation into Lactic Acid

Abstract

Different methods (the wetness impregnation of Ag and Pd precursors dissolved in water or acetonitrile solution, and the double solvent impregnation technique) were employed to immobilize Ag–Pd nanoparticles (NPs) into the pores of the microporous zirconium-based metal-organic framework known as UiO-66. The obtained materials were characterized by using nitrogen adsorption-desorption at −196 °C, powder X-ray diffraction, UV-Vis diffusion reflectance spectroscopy, and transition electron microscopy measurements. Special attention was paid to the acid and redox properties of the obtained materials, which were studied by using temperature-programmed desorption of ammonia (TPD-NH3) and temperature-programmed reduction (TPR-H2) methods. The use of a drying procedure prior to reduction was found to result in metallic NPs which, most likely, formed on the external surface and were larger than corresponding voids of the metal-organic framework. The formation of Ag–Pd alloy or monometallic Ag and Pd depended on the nature of both metal precursors and the impregnation solvent used. Catalytic activity of the AgPd/UiO-66 materials in propylene glycol oxidation was found to be a result of synergistic interaction between the components in AgPd alloyed NPs immobilized in the pore space and on the external surface of UiO-66. The key factor for consistent transformation of propylene glycol into lactic acid was the proximity between redox and acid-base species.

NH2-Modified UiO-66: Structural Characteristics and Functional Properties

“…The unmodified UiO-66 sample is characterized by a bimodal distribution of micropores with maxima at ~0.9 nm and ~0.6 nm (Figure 4c) that is typical for the UiO-66 [33][34][35]. The observed bimodal distribution is consistent with a change in the size of the pore entrance formed by the terephthalate bridges between the Zr 6 O 4 (OH) 4 sites as a result of a change in the orientation of benzene rings due to the flips around the C 2 symmetry axis [36].…”

Synergistic promotion of Ag nanoparticles supported on magnetic Cu based metal organic framework for A3-coupling and synthesis of benzopyranopyrimidines

“…MOFs have been employed as support for the incorporation of various metallic and bimetallic nanoparticles. [15][16][17][18][19][20] The tunable pores of MOFs not only prevent the aggregation of metal NPs but also ensure their uniform dispersion. In addition to this, the synergistic effect between metal NPs and MOFs improves the overall stability, selectivity, and activity of the catalysts.…”

Modifier Effect in Silica-Supported FePO4 and Fe-Mo-O Catalysts for Propylene Glycol Oxidation

“…Experimental studies of the PG selective oxidation into carbonyl/carboxylic compounds (methylglyoxal, hydroxyacetone, etc.) are known in the literature for catalysts with supported metal nanoparticles, including Ag [ 5 , 6 , 7 ], Pt [ 8 ] and Pd [ 9 , 10 , 11 , 12 ]. The mechanism of PG conversion was theoretically studied over the Ag 4 cluster [ 13 ].…”

“…[ 16 ], it was suggested that in the case of using the metal/bimetallic catalysts in the oxidation of polyatomic alcohols (e.g., PG and glycerol), the key role of the modifying metal was connected with controlling the reagent bond strength with the catalyst surface without a sharp change in the preferred geometry of the adsorbate, and such changes of binding energies can have a strong impact on the catalytic properties. Transition metals, such as Bi for Pd-Bi supported catalysts [ 12 ], are often used as a modifying metal added to those of the Pt or Au subgroups.…”