Influence of alkali metals on Pd/TiO2 catalysts for catalytic oxidation of formaldehyde at room temperature

We previously observed that sodium (Na) addition had a dramatic promotion effect on Pd/TiO2 catalysts for formaldehyde (HCHO) oxidation. In this study, a series of alkali metal (Li, Na, K, Cs) doped Pd/TiO2 catalysts were prepared and tested for ambient temperature HCHO oxidation. The results showed that the doped alkali metals have a common promotion effect on the performance of the Pd/TiO2 catalysts for HCHO oxidation under ambient temperature, which followed the order K > Cs > Na > Li. X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), CO chemisorption, Transmission Electric Microscopy (TEM), temperature-programmed reduction by H-2 (H-2-TPR), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption by O-2 (O-2-TPD) methods were used to characterize the alkali metal doped catalysts to investigate the mechanism of the alkali metal promotion effect. The results showed that a negatively charged and well-dispersed Pd species was induced and stabilized by alkali metal addition, which facilitates the activation of chemisorbed oxygen, and then enhances the performance of alkali metal doped Pd/TiO2 catalysts for room temperature HCHO destruction. The K-Pd/TiO2 catalyst in particular possessed the highest Pd dispersion degree with active sites, attributing to the best activity in ambient temperature HCHO oxidation.