Synthesis of polyoxometalates supported on HZSM-5 for the photocatalytic purification of crude terephthalic acid under mild conditions

Abstract Phosphomolybdic (PMo) and vanadium-containing phosphomolybdic (PV 2 Mo) acids were synthesized and supported on HZSM-5 zeolite via a wet impregnation technique and used as photocatalysts for the purification of terephthalic acid (TA) via an economic process. Nowadays, purified TA can be obtained from crude TA due to their great commercial importance by separating 4-carboxybenzaldehyde (4-CBA), which represents high environmental toxicity and negatively affects the applications of TA. For these reasons, conversion of 4-CBA to TA is highly desirable for both enhancing the efficiency of purified TA production and environmental reasons. The synthesized catalysts were characterized by XRD, FTIR, Raman spectroscopy, BET, SEM, and TEM. The purification process was carried out by under different parameters as VUV irradiation, persulfate (PS), time, and different types of catalysts (PMo or PV 2 Mo)/HZSM-5. This kind of combination showed complete removal of the 4-CBA with a high yield of PTA in 2 h. The high efficiency attributed to the acidity of the polyoxometalates/HZSM-5, which increase the selectivity to oxidize 4-CBA at room temperature and much shorter reaction time compared to other common methods.