Transformation of dl Limonene into Aromatic Compounds Using Supported Heteropolyacid Catalysts

The transformation of dl limonene (mixture of d - and l -form ~ 1:1) that came from the pyrolysis of scrap tires rubber was studied using four heteropolyacid catalysts (H 3 PW 12 O 40 , H 3 PMo 12 O 40 , H 4 SiW 12 O 40 and H 4 PMo 11 VO 40 ) supported on Q-10, SBA-15, MCM-41, and KIT-6. The catalyst activity was measured using a py/GC/FID under a nitrogen atmosphere. The active phase and support were characterized using various technical methods (XRD, Raman, TEM, N 2 adsorption–desorption, NH 3 -TPD, and py-FTIR). The highest weak acidity and largest number of Lewis acid sites promoted the conversion of dl limonene. The isomerization reactions seemed to be more favored than disproportionation reactions. The p -cymene yield was favored, with a high weak acidity and high Lewis/Brønsted acid sites ratio. Moreover, the results show that the use of amorphous support with a higher pore size seems to promote the conversion of dl limonene and the production of p -cymene. Graphical Abstract HPA-based catalysts with Si are more favorable for converting dl limonene to p-cymene than those with P. For the HPA-based catalysts with P, the highest acidity favors the highest conversion, especially the Lewis acid sites. In this study, the isomerization reactions seem to be more favored than disproportionation reactions.