Catalytic performance of molybdate and sulfated molybdate-supported mesoporous TiO₂ nanocomposites in the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene and 3,4-dihydropyrimidinones

From both environmental and economic perspectives, our focus has been on developing simple catalysts that offer key advantages, including ease of isolation and preparation, high stability, and strong catalytic performance. In the present work, a series of MoO₃-supported mesoporous TiO₂ nanocomposites with different MoO₃ contents (15, 25, 35, and 50 wt%) was prepared by an impregnation method. The surface properties of the 35Mo/Ti-III nanocomposite were improved by the addition of sulfate. The synthesized materials were characterized in detail using XRD, FTIR, SEM, TEM, S_BET, and XPS techniques. XRD measurement revealed that a mesoporous ordered structure was present in all samples. It also showed some peaks due to orthorhombic α-MoO₃ that increased in intensity with increasing MoO₃ content and decreased after sulfate loading. In the case of pure mesoporous TiO₂, TEM images revealed the presence of fine nanoparticles within the size range between 10 and 14 nm. While the aggregation of MoO₃ nanosheets caused the formation of larger particles by incorporating MoO₃ into the framework of TiO₂, sulfur loading led to the formation of new particles <10 nm, which means successful incorporation of sulfur into the Mo/Ti nanocomposite. Surface acidity of the prepared nanocomposites was estimated by non-aqueous potentiometric titration with n-butylamine and FTIR spectra of chemisorbed pyridine. All the nanocomposites displayed both Brønsted and Lewis acid sites. All the nanocomposites were screened for their catalytic efficiency and reusability toward the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene and 3,4-dihydropyrimidinones. Among these, the nanocomposite 25S-35Mo/Ti-III presented the highest acidity, Ei = 520 mV, which afforded 92 % of 14-aryl-14H-dibenzo[a,j]xanthene and 94 % of 3,4-dihydropyrimidinones, demonstrating remarkable catalytic activity.