The ZSM-5 samples prepared by different synthesis routes have different
acid properties. The surface acid properties of four ZSM-5 samples were
investigated by NH3-TPD and pyridine FT-IR experiments.
As shown in Fig. 9, all ZSM-5 samples have two NH3desorption peaks at 186-189 ℃ and 387-405 ℃, which correspond to weak
acid sites and strong surface acid sites, respectively [44]. The
acid amount and acid strength of samples are reflected by peak area and
peak position of the TPD profile, respectively [45]. As shown in
Table 3, acid amount and strong surface acid strength of ZSM5-RS and
ZSM5-RD increase significantly compared with ZSM5-SS and ZSM5-SD.
Moreover, the desorption temperature of ammonia from the strong acid
sites shifted to higher temperatures as inducing RPB in the premix
process, which indicates the increase of Al content in extra-framework
positions [34]. In comparison with ZSM5-SS, the acid amount and acid
strength of ZSM5-SD have a slight growth. A possible reason is that the
enhancement of micromixing in the STR affects the acid properties of
zeolites in the crystallization process.