Preparation and Characterization of Pd Modified TiO₂ Nanofiber Catalyst for Carbon-Carbon Coupling Heck Reaction

TiO₂ fibers were prepared through electrospinning of poly methyl methacrylate (PMMA) and titanium isopropoxide (TIP) solution followed by calcination of fibers in air at 500°C. Cetyltrimethylammonium bromide (CTAB) protected palladium nanoparticles (Pd NPs) prepared through reduction method were successfully adsorbed on the TiO₂ nanofibers (NF). Combined studies of X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) indicated that the synthesized Pd/TiO₂ had anatase. BET indicated that the synthesized TiO₂ and Pd/TiO₂ had a surface area of 53.4 and 43.4 m²/g, respectively. The activity and selectivity of 1 mol% Pd/TiO₂ in the Heck reaction have been investigated towards the Mizoroki-Heck carbon-carbon cross-coupling of bromobenzene (ArBr) and styrene. Temperature, time, solvent, and base were optimized and catalyst was recycled thrice. ¹H NMR and ¹³C NMR indicated that stilbene, a known compound from literature, was obtained in various Heck reactions at temperatures between 100°C and 140°C but the recyclability was limited due to some palladium leaching and catalyst poisoning which probably arose from some residual carbon from the polymer. The catalyst was found to be highly active under air atmosphere with reaction temperatures up to 140°C. Optimized reaction condition resulted in 89.7% conversions with a TON of 1993.4 and TOF value of 332.2 hr^-1.