c) Periodicity
In applied catalysis, the catalyst reusability is the most important after the catalytic performance. The reusability of the tow employed catalysts was studied at the previously optimized reaction conditions,viz., at 130oC, OA/TMP molar ratio of 3:1, catalyst dosage 3wt. % and reaction time of 20h. At these optimized circumstances, any change in the catalytic behavior will be easily detectable. Figure 6 illustrates the observed results during six consecutive runs where the recorded catalytic activity of each run is slightly less than the previous one. The decrease in catalytic activity most probably attributed to the slight leaching of acidic protons or the adsorption of reactant molecules on the active sites (Li, 2012). In general, the yield of TMPTO is maintained at the level of 83.40% and 65% for IL1/SBA and IL2/SBA-15 referring that the catalysts are relatively stable during the reaction.