(544cw) Preparation of Highly Dispersed Iron Species over ZSM?5 with Enhanced Metal?Support Interaction By Freeze?Drying Impregnation

Preparation of
highly dispersed iron species over ZSM-5 with enhanced metal-support
interaction by freeze-drying impregnation

Lisong Fan, Dang-guo Cheng*, Fengqiu Chen and Xiaoli Zhan

College of Chemical and Biological Engineering, Zhejiang
University, 38 Zheda Road, Hangzhou 310027, China

Abstract:
Impregnation is usually used to prepare supported metal catalysts. However,
during conventional evaporation drying, a large amount of metal precursor along
with solution are transported to the support surface by capillary pressure and
large aggregations are formed, leading to a low activity after subsequent calcination. To get the metal more dispersed in
impregnation, we prepared catalyst via freeze-drying and select iron species
supported on ZSM-5 as a model. Freeze drying is a technique to remove solvent
from frozen sample by sublimation, during which the movement of metal precursor
is greatly reduced. Compared with evaporation-drying catalyst (labeled as
FeZSM-E), the distribution of iron species is much better in freeze-drying
catalyst (FeZSM-F), which is shown in Fig. 1. The different distributions lead
to difference in the location and structure of iron species. In FeZSM-F, most
iron species are confined in ZSM-5, many small Fe_xO_y nanoparticles
in the channel and framework bonded iron species are formed, indicating the
enhanced interactions between metal precursor and support. While for FeZSM-E,
most iron species are located at the surface of ZSM-5 in the form of large Fe₂O₃
clusters. To verify change of iron species in two catalysts, we apply them in N₂O
decomposition and oxidation of CH₄ to oxygenates reactions. The
catalytic activities are illustrated in Table 1. Both reactions testify the
change in iron species and superior activity of freeze-drying catalyst. 

Fig. 1 STEM image
and EDS elemental mapping of catalysts
(a) FeZSM-E (b) FeZSM-F

Table
1 Catalytic activities of FeZSM catalysts for N₂O
decomposition and oxidation
of CH₄ to oxygenates

* Corresponding
author. Tel.: +86 0571 87953382; Fax: +86 0571 87951227

E-mail address: dgcheng@zju.edu.cn (D.G. Cheng) fqchen@zju.edu.cn (F.Q. Chen)

xlzhan@zju.edu.cn (X.L. Zhan)
lsfan@zju.edu.cn
(L.S. Fan)