Catalytic Transformation of Positional Nitrophenol Isomers on Highly Active Ag/Linde-Type A4 Zeolite: A Comparative Analysis

The catalytic transformation of ortho-(o-NP), meta-(m-NP) and para-nitrophenols (p-NP) by Ag nanoparticles (Ag-NPs) stabilised on zeolite A4 (ZA4) is presented for the first time. The catalysts are prepared by microwave-assisted synthesis (Ag/ZA4-MW) or ion exchange (Ag/ZA4-IE). The results indicate that the nitrophenol reduction rate depends on the molecule structure and the presence of low-coordinated metallic Ag-NPs (∼2 nm and sub nanometric species). Meanwhile, the reactivity tendency depends on the synthesis methodology (m-NP>p-NP>o-NP and o-NP>m-NP>p-NP for Ag/ZA4-MW and Ag/ZA4-IE, respectively). The turnover frequency (TOF) values estimated for nitrophenols reduction are superior for Ag/ZA4-MW catalyst by several orders of magnitude compared with those obtained for Ag/ZA4-IE catalyst. In addition, the catalyst exhibits remarkable catalytic stability for the reduction of p-NP even after the fifth consecutive catalytic run. The presently prepared catalysts are characterised by superior catalytic activity for the reduction of nitroaromatic compounds than similar Ag-based materials reported in the literature.