The synthesized samples are identified from their XRD patterns. The XRD patterns of the zeolite samples MFI match with those of standard sample obtained from literature [18] and it is found that all the samples are highly crystalline. Figure 1 shows the XRD patterns of MFI samples synthesized without and with carbon black particles except ZC4 for which the same is shown in figure 2. From Fig 2 it is not clear whether MFI phase was really materialized or not, although IR spectra show the formation of required T-O bonds and basic units. The variation of full width at half maxima (FWHM) value with different SiO2 /carbon ratio is given in figure 3.
For a particular crystallographic plane (hkl), the crystallinity of MFI samples are calculated by using relation 1.
See relation 1 and 2 in the supplementary files.
Here β is the full width at half maximum (FWHM); K is the shape factor (taken to be 0.9 ); θhkl is the Bragg angle and λ is the wavelength of CuKα1 (1.5418Ǻ ). The factor 5.73 is used to convert the value of β from degree to radian order to obtain Dhkl value in nanometer unit. The average crystallite size ranges from 28-58 nm. The Crystallite size, percentage of Crystallinity (%C)hkl of the synthesized samples is shown in table 2. From the table 2, it is found that as the carbon content in the gel increases, the crystallite sizes of the MFI zeolites decreases. Crystal size of zeolite decreases with increase in mesoporosity. According to Thangaraj et.al [20], crystal size of zeolite decreases with increase in mesoporosity. In the present study mesoporosity of the synthesized samples increases as the carbon content increases (Table 2).
FT-IR spectra of parent (ZP) MFI and MFI samples synthesized in presence of C (ZC) is shown in figure 4. FT-IR results also confirm the formation of MFI zeolites in all cases showing absorption bands near 1080 (internal symmetric stretch), 790 (external symmetric stretch), 540 (double ring vibration) and 450 cm-1 (T-O bending.) [21]. The size and shape of the crystalline MFI zeolites were investigated by SEM analysis. The SEM micrographs of different samples such as parent, ZC1, ZC2 and ZC3 are shown in figures 5 (a), (b), (c) and (d) respectively. From the micrograph it is seen that the particles are cubic in shape and particle sizes ranges from 2.8 to 7.3 µm and is given in table 3. Some cracks are shown in the particle as the carbon content increases. Moreover, it is found that the particle size increases with the increase in carbon content.
The TGA curves of ZC1, ZC2 and ZC3 are shown in figures 6(a), (b) and (c) respectively. The TGA curves show the initial mass loss up to 423 K. This may be due to adsorbed water in the porous materials which means that the endothermic peak in the region 373-423 K can be assigned to the desorption of water in zeolite [22]. The second and third weight loss is due to the degradation of TPA+ cations inside the zeolite structure [23]. The percentages of mass loss in the different regions of temperature are given in table 4.
Nitrogen adsorption-desorption isotherms of parent, ZC1, ZC2 and ZC3 samples are shown in figures 7(a), 7(b), 7(c), and 7(d). Significant changes in the N2 adsorption-desorption isotherms are observed for ZC1, ZC2 and ZC3 samples. The adsorption-desorption isotherms of N2 of each sample show the typical type IV isotherm. At high pressure capillary condensation loops are observed for carbon containing samples ZC1, ZC2 and ZC3. Correspondingly bimodal pore systems are suggested for ZC1, ZC2 and ZC3 as there are mesopores in these samples.The first capillary loops on the isotherms at p/po nearly in the ranges 0.20-0.5 is characteristics of framework confined mesoporosity [24, 25]. The second loops at p/po = 0.6-1.0 in the isotherm indicates the presence of secondary mesopores arising from intracrystalline voids in the packing of smaller crystals [26]. The carbon black particles produce mesoporosity in the MFI samples. The BET surface area and the average pore diameter of the synthesized MFI samples in different solvent are listed in table 5. As the carbon content increases in the gel, the micropore volume decreases from 0.15 to 0.05 cm3g-1 [table 5] and total pore diameter increases from 20.64 to 27.51 Ǻ. On the contrary mesopore volume is found to increase. This may be due to the conversion of some micropores into mesopores. The variation of BET surface area with the amount of SiO2/carbon ratio is shown in figure 8.
Esterification of benzyl alcohol by acetic acid was carried out over parent ZSM-5 and samples ZC1, ZC2 and ZC3 under 373 K temperature and up to duration of 10 h. Benzyl alcohol reacts with acetic to produce benzyl acetate. The reaction is shown in scheme 2.The samples were collected at different time intervals such as 2 h, 4 h, 6 h, 8 h and 10 h. The results for benzyl alcohol esterification on different catalysts under similar conditions at 373 K are summarized in table 6 and figure 9. When the progress of the reaction was studied in different time intervals, it was observed that the conversion of the reaction increased in all cases with increase of reaction time. It has been observed that the conversion increases from 20.5 to 33.9%, from 20.7 to 50.4%, from 21.3 to 54.3%, from 23.2 to 56.9% for the catalysts ZP, ZC1, ZC2 and ZC3 respectively. When time of reaction is increased from 2 to 4 h, there is a difference of pattern in increase of conversion in case of catalyst ZP than other catalysts for increase of time of reaction from 4 to 6 h under similar conditions. It appears from the plot that the reaction tends to equilibrate after 8 h of reaction. Reaction conditions maintained in the reaction are temperature = 373 K, catalyst amount = 0.2 g, benzyl alcohol: acetic acid = 1:2 (molar ratio) and substrate volume 16 mL. It is found that with the increase in carbon content, the % conversion of the samples also increases, this may be due to increase in pore volume with the increase in carbon content.