Pd–Rh Alloyed Nanoparticles on Zeolite Imidazolide Framework-67 for Methyl Orange Degradation

Bimetallic or alloyed nanoparticles (NPs) are important materials that often exhibit chemical properties different from those of their monometallic counterparts. However, access to uniformly alloyed bimetallic particles, particularly in the Pd–Rh system, is difficult because of the thermodynamic immiscibility of the individual metals. Herein, we propose a method for accumulating Pd–Rh alloy particles on the surface of zeolite imidazolide framework-67 (ZIF-67), a chemically stable metal–organic framework, under mild conditions at 25 °C. The degradation of methyl orange was used to test the applicability of the resultant material as a heterogeneous catalyst. A turnover frequency of 38.5 h–1 was recorded for Pd0.12Rh0.88/ZIF-67, which is higher than that of catalysts with either Pd (17.2 h–1) or Rh (16.5 h–1). The acceleration of methyl orange decomposition was attributed to electron transfer from Pd to Rh in the alloy particles due to the differences in Pauling electronegativity and an increase in metallic Rh on the catalyst surface. No metal leakage or structural degradation of the ZIF-67 support was observed during the catalytic reaction. Pd0.12Rh0.88/ZIF-67 could actively degrade methyl orange, Congo red, and methylene blue. The structure of the catalyst remained intact even when a mixed solution of all three dyes was circulated for 60 min in a fixed-bed system, and the catalyst conversion rate exceeded 99.7%. Our results collectively demonstrate the successful preparation of Pd–Rh-supported catalysts and their application to the continuous reduction of multicomponent dye mixtures. The metal NP-MOF composites prepared using the proposed approach are free from MOF pore damage and can maintain their specific surface area. Therefore, this strategy could give impetus to research on catalytic applications of NP-MOF composites.