FePO 4 and AlPO 4 distribute at intervals, and there exist Lewis base sites (P=O and P-O-Fe) and Lewis acid sites (Fe 3+ and Al 3+) on the catalyst surface.

• FePO4 和AlPO4 间隔分布在催化剂表面 ；形成Lewis碱位 (P =O ；P O Fe)和Lewis酸位 (Fe3 + ；Al3 + ) .