Confirmation of NH species in the framework of nitrogen-incorporated ZSM-5 zeolite by experimental and theoretical studies

Nitrogen-incorporated zeolites have drawn much attention as a new family of basic solid materials and N atoms are expected to be introduced into the frameworks of zeolites. In this study, nitrogen-incorporated ZSM-5 zeolites were prepared by temperature-programmed nitridation and their physicochemical properties were characterized by means of XRD, SEM and BET techniques. Combined a detailed IR characterization with a theoretical IR simulation, the bands relating to bridging Si–N(H)–Si groups at 1151 and 985 cm−1 were observed in the IR fingerprint region of nitrogen-incorporated zeolites. The results confirmed that N atoms have been introduced into the framework of ZSM-5 zeolites by nitridation to form basic –NH– species, which was also supported by results of 29Si MAS NMR characterization. Furthermore, the basic catalytic properties of nitrogen-incorporated ZSM-5 zeolites were evaluated by Knoevenagel condensation of benzaldehyde and malononitrile and enhanced conversion of benzaldehyde was achieved.