Effects of thermal aging on the electronic and structural properties of Pt-Pd and toluene oxidation activity.

Catalytic oxidation is a feasible method for remediating volatile organic compounds (VOCs), due to its lower energy consumption and mineralization of VOCs into H2O and CO2. Noble metal-based catalysts are preferred for the catalytic oxidation of VOCs because of their superior activity, but they are usually deactivated by thermal aging which sinters the metal particles. Here, we report that Pt-Pd/Al2O3 thermally aged at 700-900 °C in air showed enhanced catalytic activity for toluene oxidation in humid conditions. There were electronic and structural changes in the thermally aged Pt-Pd/Al2O3, as confirmed by numerous analyses. Both Pt and Pd existed in a metallic rather than oxidized state without additional reduction steps. The noble metal particles were assembled to form Pt-Pd alloy, in the form of isolated Pd atoms surrounded by Pt atoms. This specific alloy structure was found to be crucial to the observed enhancement in catalytic toluene oxidation at low temperature.

Influence of the addition of vanadium to Pt/TiO2 catalyst on the selective catalytic oxidation of NH3 to N2.

In this work, the effect of the addition of vanadium to the Pt/TiO2 catalyst on the selective catalytic oxidation (SCO) of NH3 to N2 was investigated. It was found that the addition of vanadium significantly enhanced catalytic activity at all tested temperatures. The Pt/V/TiO2 catalyst exhibited the highest NH3 conversion (∼100%) and NH3 to N2 conversion (∼81%) at 250°C. The physicochemical characteristics of the catalysts were investigated via Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), NH3 temperature-programmed desorption (TPD), NH3 temperature-programmed oxidation (TPO), and in situ Fourier-transform infrared (FTIR) spectroscopy. It was found that the addition of V to the catalyst enhanced the conversion of NH3 as a result of the formation of new acid sites. The increase in the number of acid sites resulted in increased NH3 to N2 conversion via the internal selective catalytic reduction (i-SCR) mechanism. This mechanism involves the SCR of NOx, which are formed by the oxidation of NH3. Based on experimental results and analyses of the catalysts modified by the addition of V, it was shown that there was a close relation between reaction selectivity and the surface oxygen species of the catalyst and N2 yield. Furthermore, the addition of V increased the durability of SO2 by inhibiting the formation of ammonium bisulfate (ABS).