A series of Au-Pd/TiO2 catalysts were synthesized in different weight % using sol-immobilization method. Of the range studied 1%Pd/TiO2 catalyst achieved 86.4% conversion of phenol to CO2 in a standard batch-slurry system utilizing UV. However under recycle or continuous operation Pd leaching from catalyst surface led to gradual deactivation. Au-Pd nanoparticles supported on TiO2 P25 were stable and recyclable, here Au species were found to help to anchor Pd species on TiO2, and no observable Pd leaching occurred. Utilizing UV, 1%Pd/TiO2 showed faster rate of phenol degradation in comparison to Au-Pd/TiO2, while 1%Au/TiO2 and 0.5%Au-0.5%Pd/TiO2 showed faster phenol degradation rates under visible light. The TiO2 P25 support was also found to be active, stable and recyclable in phenol degradation utilizing UV; and was hence considered suitable for continuous operation. However poor oxygen mass transfer led to the formation and lay-down of polymeric species when using a Trickle bed approach. Operation in the Taylor flow regime was demonstrated to increase oxygen saturation and significantly reduced deactivation. Hence continuous photocatalytic degradation of phenol could be achieved using TiO2 under Taylor Flow conditions.
Titanium dioxide has proven to be one of the most promising heterogeneous catalyst. This work explores the photocatalytic activity of modified titanium dioxide. Nitrogen was incorporated into mesoporous TiO2 using Sol-gel method. The N-TiO2 was characterized using X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) thermogravimetric analysis (TGA), and U-Vis diffuse reflectance spectroscopy (DRS). 1%wtN-TiO2 expresses the highest photoactivity in UV light compared to 3%wtN-TiO2 and 5%wt N-TiO2 respectively. The photodegradation efficiency of the catalyst follows the following trend 1%wtN-TiO2 >3%wtN-TiO2 >5%wtN-TiO2>PURE-TiO2. The results obtained from the kinetics investigation shows the following trends 1%wtN-TiO2 is 0.049 s-1, 3%wtN-TiO2 is 0.0289 s-1, 5%wtN-TiO2 is 0.0143 s-1, and the PURE-TiO2 is 0.0118 s-1. The consistency in the rate constant values of the phodegradation of methylene blue; it clearly showed that the reaction follows a pseudo-first order kinetics.
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