Characterization and n-heptane cracking/isomerization catalysis of tungsten oxynitrides on EMT zeolite

摘要

Catalysts made of two tungsten precursors (one of them containing phosphorus) impregnated on EMT zeolite were nitridated in flowing pure ammonia and passivated by O_2 (1 vol%) in an Ar stream leading to tungsten oxynitrides/EMT (W_2N/EMT) and phosphotungsten oxynitrides/EMT (PW_2N/EMT). The catalysts were examined by X-ray diffraction, NMR spectroscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The materials were tested for the cracking/isomerization of n-heptane at atmospheric pressure and 623 K. Cracking (C_3 + C_4) was the major (about 90%) n-heptane reaction for all the catalysts. The influence of EMT supercages upon selectivity was observed. The yield of n-heptane isomers was significantly enhanced for W_2N/EMT and principally for PW_2N/EMT showing a higher hydrogenation function.