Acid-Resistant Catalysis without Use of Noble Metals: Carbon Nitride with Underlying Nickel

Abstract

A nanocomposite able to function as a hydrogenation catalyst under strongly acidic conditions without the presence of noble metals is synthesized and thoroughly studied. This specially designed catalyst possesses a unique structure composed of carbon nitride (CN) with underlying nickel, in which the nickel endows the CN with new active sites for hydrogen adsorption and activation while it itself is physically isolated from the reactive environment and protected from poisoning or loss. The CN is inert for hydrogenation without the help of nickel. The catalyst shows good performance for hydrogenation of nitro compounds under strong acidic conditions, including the one-step hydrogenation of nitrobenzene in 1.5 M H₂SO₄ to produce <i>p</i>-amoniophenol, for which the acid in the reaction system has restricted the catalyst only to noble metals in previous studies. Further characterization has demonstrated that the nickel in the catalyst is in an electron-deficient state because some of its electron has been donated to CN (HRTEM, PES); thus, the hydrogen can be directly adsorbed and activated by the CN (HD exchange, in situ IR and NMR). With this structure, the active nickel is protected by inert CN from the corrosion of acid, and the inert CN is activated by the nickel for catalytic hydrogenation. The assembly of them gives a new catalyst that is effective and stable for hydrogenation even under a strongly acidic environment