Figure 7 . (a) Conversion of benzyl alcohol and (b) selectivity of BTMB with time-on-stream on synthesized zeolites; (c) the proposed reaction networks and (d) scheme showing the transformation of benzyl carbocation.
3.5 Coke analysis
A part of spent catalysts was taken for thermogravimetric analysis (TGA) to investigate the coke formed in MEL zeolites. Fig. S16 showed the weight loss curves of spent H-MEL-31, P-MEL@Fe and H-MEL@Fe-20 samples, which exhibited three distinct regions of weight loss for all of samples in temperature ranges of 25‒150oC, 150‒350oC and 350‒700oC, respecively. Generally, the weight loss below 150oC was attributed to the moisture and adsorbed water in zeolite cavities and channels.45 The mass loss observed in the temperature range of 150‒350 oC was assigned to soft coke that occurred at a moderate temperature and can be extracted by organic solvent, 46 and the weight loss of H-MEL-31, P-MEL@Fe and H-MEL@Fe-20 in the temperature range of 350‒700oC can be classified as hard coke or insoluble coke. It was worth noting that the proportion of hard coke in the total coke for H-MEL-31, P-MEL@Fe and H-MEL@Fe-20 was about 35 %, 27% and 48 %, respectively. Therefore, we deduced that the coke formed during the alkylation of mesitylene with benzyl alcohol over the investigated MEL zeolite catalysts was mainly soft coke.47
To further investigate the composition of the soluble coke on the used catalyst, the soft coke in H-MEL-31, P-MEL@Fe and H-MEL@Fe-20 were extracted by 1,3,5-trimethylcyclohexane and subsequently were analyzed by GC-MS,47,48as shown in Fig. S17. It was observed that these soft cokes were mainly composed of raw materials, solvents, products and internal standard substances (dodecane), the polyaromatics and muti-methybenzenes were not detected, which was in agreement with the TGA analysis that the main coke was soluble coke.