Solid‐State NMR Study on Phosphorus Species in Phosphorus‐modified ZSM‐5 Zeolite

Chemical changes of phosphorus‐modified ZSM‐5 zeolite in calcining and steaming processes were studied using solid‐state magic angle spinning nuclear magnetic resonance techniques. 1 H → 31 P cross‐polarization magic angle spinning and 31 P– 27 Al rotational‐echo double resonance signals of calcined and steamed P‐ZSM‐5 zeolites were measured and analyzed. Results showed that the average distance between phosphorus and hydrogens in phosphorus compounds was increased while the average distance between aluminum and phosphorus was decreased after the steaming process. Aluminum attached to highly condensed phosphates was protected in the zeolite framework during the steaming process.