*3.2.1 X-ray diffraction (XRD)*

XRD pattern of Co/NaZSM-5 h and Co/HZSM-5 h in **Figure 5** shows that the ZSM-5 zeolite structure was retained after cobalt impregnation followed by calcination at 823 K on each NaZSM-5 h and HZSM-5 h, but they showed decrease in peak intensity. It is suggested that loading of Co on ZSM-5 h zeolite has caused lowering of its crystallinity. New diffraction peaks of Co3O4 phase (2θ = 38.6° and 47.8°) and Co2SiO4 phase (2θ = 56.07°) [20] are observed in XRD patterns of Co/NaZSM-5 h and Co/HZSM-5 h. This is an evidence of the presence of cobalt oxide species in the NaZSM-5 h and HZSM-5 h, respectively.

### *3.2.2 Surface area analysis*

**Figure 6** shows a decrease in surface area and total pore volume of Co/ NaZSM-5 h and Co/HZSM-5 h compared to NaZSM-5 h and HZSM-5 h. More *Partial Oxidation of Methane to Methanol on Cobalt Oxide-Modified Hierarchical ZSM-5 DOI: http://dx.doi.org/10.5772/intechopen.86133*

**Figure 5.** *XRD pattern of Co oxide-modified ZSM-5 h zeolites.*

**Figure 6.**

*(a) Isotherm adsorption–desorption and (b) pore-size distribution of Co/ZSM-5 h zeolites.*

detailed information is summarized in **Table 1**. This proves that the cobalt species has penetrated into the pores and surface of ZSM-5 structure. Decrease of the mesopore volume was more significant than the micropore volume. It is assumed that due to less available spaces in micropore as they were already occupied by Na + ions, the counter ions, the Co2+ resides in the mesopore area. This reduction was more notable in NaZSM-5 h than HZSM-5 h, which is in accordance with the amount of Co loading shown in **Table 1**. It is suggested that zeolite acidity affects the amount of impregnated cobalt as the lower the acidity of zeolite, the higher the Co loading in zeolite.
