*2.2.4 Catalyst activity test*

Hydrotreating reaction of α-cellulose in three variations of conditions, namely thermal hydrotreating, catalytic hydrotreating with mordenite catalyst before and after NaOH alkaline treatment. The hydrotreating reaction with a mordenite catalyst was carried out on cellulose with a catalyst/feed ratio of 1/60 (w/w). The

#### *Advances in Geopolymer-Zeolite Composites - Synthesis and Characterization*

feed and catalyst are put into the sleeve with the feed position under the catalyst, then the sleeve is inserted into the reactor. The hydrotreating reaction was carried out with hydrogen gas with a flow rate of 20 mL min−1 at a temperature of 450 °C for 2 hours. In comparison, a thermal hydrotreating reaction is also carried out. The product formed is flowed through a condenser (cooler) to a flask which is cooled with an ice bath.

The percentage (%) conversion of the hydrotreating reaction results is determined by the following formula:

$$\text{Liquid product} \left(\text{wt.}\,\text{\textdegree}\right) = \frac{M\_{\,\,j1} - M\_{\,\,j0}}{M\_{\,\,s} - \left(M\_{\,\,u1} - M\_{\,\,u0}\right)} \times \mathbf{100}\,\text{\textdegree} \tag{1}$$

$$\text{Coke}\left(\text{wt.}\,\%\right) = \frac{M\_{k1} - M\_{k0}}{M\_s - \left(M\_{u1} - M\_{u0}\right)} \times 100\,\% \tag{2}$$

$$\mathbf{Gas}\left(\mathbf{wt.\%}\right) = \mathbf{100\%} - \left(\text{liquid product} + \text{coke}\right) \tag{3}$$

Where Ms = mass of α-cellulose; Mj0 = mass of an empty flask; Mj1 = flask mass after hydrotreating; Mu0 = mass of the feed container before hydrotreating; Mu1 = mass of the feed container after hydrotreating; Mk0 = mass of catalyst before hydrotreating; Mk1 = mass of catalyst after hydrotreating.

### **3. Results and discussion**

### **3.1 The effect of HNO3 and/or NaOH treatment on Si/Al ratio and acidity of mordenite**

The Si/Al mol ratio in zeolites is ones of the most important character which affected the acidity, thermal stability, and activity in catalytic reactions. The dealumination process towards zeolite generally increases activity and thermal stability [17].

Based on the ICP measurement results, there was a change in the Si/Al ratio in the mordenite before and after the NaOH treatment (**Table 1**). The change in the Si/ Al ratio indicates that the dealumination and desilication processes of mordenite are going well.

Based on **Table 1**, it shows an increase in Si/Al ratio of mordenite with the higher concentration of HNO3. The increase in Si/Al ratio is due to the dealumination process in mordenite. In the dealumination process, previous experiment [18] stated


**Table 1.**

*The Si-Al ratio and acidity of mordenite after HNO3 and or NaOH treatment.*

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

that the presence of H+ ions resulting from the ionization of HNO3 in water will cause H+ ions to tend to be bound by O atoms that have bound Si and Al. This causes the O atom to have three unstable bonds. The stability of the O atom will be achieved if it breaks a bond that has the lowest dissociation energy. It can be seen that the dissociation energy of Al-O (116 kcal/mol) is much lower when it compared to the dissociation energy of Si-O (190 kcal/mol) so that the Al-O bond will be broken more easily than Si-O [19]. Therefore, the number of Al atoms in the framework will be reduced to non-framework Al due to the bond between Al atoms and NO3 − ions.

The NaOH treatment was then carried out on mordenite HM, AM0.1 and AM0.5. This treatment can cause desilication which results in a decrease in the Si/Al ratio. In **Table 1**, it is shown that after NaOH treatment, Si/Al ratio of mordenite (AM) has decreased compared to that of mordenite (HM). The mordenite is in contact with NaOH which causes the silicon to be extracted from the mordenite framework, causing the Si/Al ratio decreased.

However, there were differences in mordenite BAM0.1 and BAM0.5, where there were an increase in Si/Al ratio compared to Si/Al ratio before being treated with NaOH as shown in **Table 1**. This is due to the low Si/Al ratio in mordenite before being treated with NaOH. The low Si/Al ratio causes of Si and Al distance to be close, so that when silicon is extracted, aluminum is also extracted due to its amphoteric nature [17].

The mordenite that has been treated with NaOH, then the ion exchange process is carried out with the ammonium ion. The exchange of cations in mordenite with NH4 + aims to remove impurities in the form of alkaline or cations such as K<sup>+</sup> , Na+ , Ca2+, Mg2+ which act as a counterweight to mordenite which can be exchanged with other cations so that the cations will be exchanged into NH4 + by pushing the cations. Then, the calcination process is carried out at high temperatures which aims to remove water molecules bound to the mordenite so that the surface area increases.

Besides the Si/Al ratio, another aspect that must be considered in mordenite is acidity. The calculation of the acid centre on the surface of a solid relates to the theory of Brønsted and Lewis acids, namely Brønsted acid (proton giver) and Lewis acid (an empty orbital capable of accepting an electron pair) present on the solid surface.

A simple method that can be used to determine acidity in solids or catalysts is by average of gravimetry, namely by weighing the solids before and after adsorbing the base. One of the bases that can be used as adsorbed substances is ammonia [20]. Ammonia base was chosen as the adsorbate because it has small molecular size so that it can be adsorbed into all mordenite pores.

Based on **Table 1**, it shows a decrease in the number of total acid sites (acidity) along with the increase in the Si/Al ratio of mordenite. The decrease in the total number of acid sites is due to a reduction in the number of Brønsted acid sites which present in the mordenite. The Brønsted acid site will decrease as the aluminum content in a zeolite decreases [4].

Increasing Si/Al ratio can lead the increase of acid strength. This is due to changes in the distribution of aluminum atoms in the zeolite framework. The farther of distance between the aluminum atoms, the less interference between the aluminum atoms, which causes an increase in the acid strength of the Brønsted acid sites possessed by aluminum atoms [21].

However, mordenite AM0.1 was found to increase the number of acid sites when compared to mordenite HM. This could be due to the appearance of Lewis acid sites on the mordenite AM0.1 framework. Lewis acid sites can occur if there are aluminum atoms bonded outside the main zeolite framework which is known as extraframework aluminum (EFAL). This phenomenon also occurs in a study conducted by [6] who showed an increase in the number of acid sites on zeolites.
