**3.3 Effect of HNO3 and/or NaOH treatment on mordenite pore character**

The mordenite pore character analysis was performed using a Gas Sorption Analyzer (GSA). This pore character was carried out in order to determine the impact of the HNO3 and/or NaOH treatment on the pore character of mordenite. The mordenite analyzed is mordenite that has been given alkaline treatment in order to determine the pore distribution of the mordenite. In addition, analysis by GSA provides information regarding the distribution of pore size (diameter), pore volume and specific surface area of mordenite. The specific surface area analysis of mordenite was carried out using the N2 gas adsorption–desorption isotherm data

on the mordenite surface based on the Branauer-Emmett–Teller (BET) method. The BET method describes the phenomenon of gas molecular adsorption on the surface of solids. N2 gas is the most gas often used for analysis of the pore character of a material. The pore character in this study was carried out at a temperature of 77.35 K which is the boiling point of N2.

**Figure 3** below shows that the three mordenites have a type IV adsorption isotherm pattern. This type IV adsorption isotherm pattern indicates the formation of mesoporous characters in the three mordenites as indicated by the presence of loop hysteresis on the mordenite after being treated with NaOH. However, BAM0.5 shows a wide and open hysteresis loop, it is presumed that in BAM0.5 has pore diameter with the highest meso size compared to other mordenites and is followed by partial collapse of the mordenite framework, which is indicated by the presence of decrease in surface area drastically. Based on the shape of the hysteresis loop, it can be seen that the pore size formed in the three mordenites is homogeneous. This is supported by the pore distribution data obtained.

The pore distribution graph shows a relationship between dV (r) and pore diameter. Dv (r) (Differential volume radius) shows the pore distribution in mesoporous materials. The pore distribution in this study used the BJH method. Based on **Figure 4**, it can be seen that the pore distribution in the three materials

**Figure 4.** *Distribution of the desorption mordenite BJH BHM (a), BAM0.1 (b) and BAM0.5 (c).*

### *The Effect of HNO3 and/or NaOH Treatments on Characteristics of Mordenite DOI: http://dx.doi.org/10.5772/intechopen.96444*

is homogeneous. In addition, **Figure 4** also shows that all the pore distributions of the mordenite material are found in the mesoporous region, namely in the 3–30 nm range.

This is also supported by the average pore diameter data in **Table 4**. Based on the data in **Table 4**, it shows that alkaline treatment on mordenite can produce mordenite with a meso pore diameter. The higher the Si/Al ratio of mordenite, the resulting mesoporosity will also increase, this is because NaOH treatment can enlarge the pores than mordenite. The highest average pore diameter is owned by BAM0.5, this is because the Si/Al ratio of BAM 0.5 is the highest compared to other mordenites.

The distribution of micropores and mesopores can be measured using a t-plot. This method can calculate the micropore volume and surface area of mesoporous rather than mordenite. The intercepts obtained from the t-plot method were 71.92 (BHM), 96.94 (BAM0.1) and 13.03 (BAM0.5). Through the intercept of the t-plot method, data on the pore volume composition of the mordenite will be obtained which are presented in **Table 5**.

**Table 5** shows a decrease in the percentage of micro volume in mordenite after being treated with NaOH and followed by an increase in the percentage of volume of meso in the mordenite, along with the increase in the Si/Al ratio. This shows that the higher the Si/Al ratio of mordenite, the resulting mesoporosity will also increase.

The total surface area (SBET) of mordenite was calculated using the multi-point BET method. Mesoporous surface area can also be calculated using the t-plot method. Mesoporous surface area calculations were performed using the slope of the mordenite t-plot chart. This calculation can produce data in the form of mesoporous surface area. The slopes obtained from the t-plot method are 5.259 (BHM), 5.445 (BAM0.1) and 8.174 (BAM0.5). Total surface area, micropore and mesoporous data are shown in **Table 6**.

**Table 6** shows an increase in the percentage of the mesoporous surface area (Smeso) along with the increase in the Si/Al ratio of the mordenite. In addition, it was found a decrease in the total surface area of mordenite, but an increase in the percentage of Smeso. This is due to an increase in the surface area of the mesoporous structure compared to the micropore structure.


#### **Table 4.**

*Data of average pore diameter. Total pore volume and SBET.*


#### **Table 5.**

*Data of Mordenite pore volume composition.*


**Table 6.**

*Data on mordenite surface area composition.*
