PREPARATION, CHARACTERIZATION, AND CATALYTIC BEHAVIOR OF MOLYBDENUM OXYNITRIDES SUPPORTED ON EMT ZEOLITE (NAEMT AND HEMT) CATALYSTS

EMT zeolite-encaged molybdenum oxynitride clusters were prepared by se veral methods, leading to different dispersions of the molybdenum spec ies. HRTEM and EDX measurements indicated that, when the molybdenum sp ecies were inside of the zeolite porosity, they were homogeneously dis persed in the form of clusters whose diameters were less than 10 Angst rom. Depending on the preparation, it was shown by X-ray diffraction a nd specific surface area measurements that the EMT zeolite crystallini ty was affected to different extents following ammonia treatments used for nitridation. The catalytic behavior of these nitrided compounds w as studied in the n-heptane conversion. Supported on NaEMT, the encage d molybdenum oxynitride showed a reactivity of a bulk material. The mo st active catalyst was the low-temperature (523 K) catalyst, the n-hep tane isomerization appearing as the main reaction. In contrast, for th e catalysts supported on acidic HEMT, n-heptane cracking was mainly ob served and the deactivation of the Mo-oxynitride supported catalysts w as lowered compared to that of HEMT alone. (C) 1997 Academic Press.