Catalytic SO₃ Decomposition Activity and Stability of Pt Supported on Anatase TiO₂ for Solar Thermochemical Water-Splitting Cycles

Abstract

Pt-loaded anatase TiO 2 (Pt/TiO 2 -A) was found to be a highly active and stable catalyst for SO 3 decomposition at moderate temperatures (∼600 °C), which will prove to be the key for solar thermochemical water-splitting processes used to produce H 2 . The catalytic activity of Pt/TiO 2 -A was found to be markedly superior to that of a Pt catalyst supported on rutile TiO 2 (Pt/TiO 2 -R), which has been extensively studied at a higher reaction temperature range (≥800 °C); this superior activity was found despite the two being tested with similar surface areas and metal dispersions after the catalytic reactions. The higher activity of Pt on anatase is in accordance with the abundance of metallic Pt (Pt 0 ) found for this catalyst, which favors the dissociative adsorption of SO 3 and the fast removal of the products (SO 2 and O 2 ) from the surface. Conversely, Pt was easily oxidized to the much less active PtO 2 (Pt 4+ ), with the strong interactions between the oxide and rutile TiO 2 forming a fully coherent interface that limited the active sites. A long-term stability test of Pt/TiO 2 -A conducted for 1000 h at 600 °C demonstrated that there was no indication of noticeable deactivation (activity loss ≤ 4%) over the time period; this was because the phase transformation from anatase to rutile was completely prevented. The small amount of deactivation that occurred was due to the sintering of Pt and TiO 2 and the loss of Pt under the harsh reaction atmosphere.

Stability of Molten-Phase Cs–V–O Catalysts for SO3 Decomposition in Solar Thermochemical Water Splitting

“…A reference catalyst, K–V–O/SiO 2 was also prepared in a similar manner. Another reference catalyst, 1 wt % Pt/TiO 2 , was prepared by impregnation using an aqueous solution of Pt­(NO 2 ) 2 (NH 3 ) 2 (Tanaka Precious Metals) and anatase TiO 2 (JRC-TIO-8, supplied by Catalysis Society of Japan), as reported previously . Prior to catalytic measurement, all the catalysts were aged under the catalytic reaction atmosphere (14 vol % SO 3 , 18 vol % H 2 O, and N 2 balance) for 3 h.…”

“…It has been reported that two classes of materials are candidates for active SO 3 decomposition catalysts that work at around 600 °C. One is precious metals, the following sequence of their activities was reported: Pt > Pd > Rh > Ir > Ru. ,− Because metallic Pt promotes the dissociation of adsorbed SO 3 into SO 2 and O and the subsequent desorption these decomposition products most efficiently, supported Pt catalysts are promising for the required temperature range. ,− Stable Pt catalysts can be prepared by depositing Pt onto SO 3 -resistant support materials, including TiO 2 , ,,, SiO 2 , , SiC, − and Ta 2 O 5 . Although these supported Pt catalysts demonstrate excellent catalytic activities, their widespread use should be limited due to the high cost and rarity.…”

Heat- and corrosion-resistant catalytic materials for environmental and energy applications

“…5(a)]. 33) At this temperature, Pt is mainly present in the active metallic state on anatase TiO 2 , whereas less-active Pt oxides (PtO 2 and PtO) are dominant on rutile TiO 2 . This stark contrast can be attributed to the greater interfacial formation energy, which stabilizes the oxidized states of Pt on rutile.…”

A Review on Recent Progress in the Integrated Green Hydrogen Production Processes

“…The increased activity of Pt on anatase is related to the abundance of metallic platinum, which facilitates the dissociative adsorption of sulfur trioxide as well as SO 2 and O 2 removal from the surface. A slight activity loss has been observed in these catalysts attributed to the slow sintering and loss of platinum [130]. The catalytic activity of non-platinum-based catalysts has also been studied.…”