Origin of high stability of Pt/anatase-TiO2 catalyst in sulfuric acid decomposition for SI cycle to produce hydrogen

Abstract

Here, anatase- and rutile TiO2 supported Pt catalysts are prepared for sulfuric acid (SA) decomposition in 650∼850 °C. The anatase-supported Pt catalysts (Pt/G5) retains the pure anatase phase even at 850 °C and rutile-supported catalyst (Pt/P25) is prepared by thermal treatment using P25. The prepared Pt/G5 catalyst is highly stable at the temperature of 650 °C–850 °C and a WHSV of 85 gH2SO4 gcat−1 h−1 and there is no Pt loss even in SA decomposition at both 650 °C and 850 °C for 100 h. However, the Pt/P25 is steadily deactivated and 35 % Pt loss is observed at 850 °C for 100 h. On both Pt/G5 and Pt/P25, Pt is encapsulated by TiO2 during the thermal heat treatment and SA decomposition occurs through the exposure of Pt by SA: encapsulation → anchored Pt exposure by SA → sulfuric acid decomposition on Pt anchored to anatase TiO2. The encapsulation of Pt by TiO2 and no CO chemisorption, resulted from typical strong metal support interaction (SMSI) phenomena, are observed. The stronger binding of Pt to anatase TiO2 is pronounced in the condition of SMSI. The reported DFT calculation shows that the binding strength between Pt and TiO2 is pronounced under the condition of the thermal treatment at the temperature higher than 450 °C or the H2 reduction. Therefore, it is proposed that the strong binding of Pt to anatase TiO2 is the origin of the high stability of anatase-TiO2 supported catalysts in SA decomposition. These findings afford a practical solution for the catalysts developments in SA decomposition in a wide reaction temperature ranges of 650∼850 °C.