Enhanced catalytic transfer hydrogenation of p-nitrophenol using formaldehyde: MnO-supported Ag nanohybrids with tuned d-band structure.

The catalytic reduction of p-nitrophenol (4-NP) to p-aminophenol (4-AP) is important in fine chemical synthesis, especially in the pharmaceutical, dye, and agrochemical industries. Sustainable methods are increasingly prioritized in these fields. Catalytic transfer hydrogenation (CTH) using formaldehyde (HCHO) as a hydrogen donor presents a safer and more environmentally friendly alternative due to its low-toxicity by-products and ease of handling. In this study, we developed manganese dioxide (MnO)-supported silver (Ag) nanoparticles (NPs) as an efficient catalyst for the CTH of 4-NP using HCHO. The MnO support prevents the agglomeration of Ag NPs and acts as an electron-acceptor matrix, enhancing the adsorption and activation of HCHO and facilitating the formation of active hydrogen (H*). Structural characterization and density functional theory (DFT) simulations confirmed electron transfer from Ag to MnO in the Ag/MnO nanohybrids, driven by their distinct work functions. This electron transfer results in a depletion of electrons in the Ag 4d orbitals, shifting its valence configuration from 4d to 4d, creating electron-deficient Ag sites that promote HCHO activation, thereby improving the CTH process. The optimized 15 % Ag/MnO catalyst demonstrated enhanced catalytic hydrogenation of 4-NP with HCHO, achieving a turnover frequency of 3.83 min. This study highlights the potential of Ag-based nanohybrids in improving catalytic performance for HCHO-assisted CTH by tuning the d-band structure with suitable oxide supports.