Efficient catalytic decomposition of sulfuric acid with copper vanadates as an oxygen-generating reaction for solar thermochemical water splitting cycles

Abstract

Copper pyrovanadate (Cu(2)V(2)O(7)) was found for the first time to achieve the high catalytic activity for the decomposition of sulfuric acid to evolve O(2) at moderate temperatures around 650 °C, which is essential for the development of solar thermochemical water splitting cycles.

Structure and SO3 decomposition activity of CeVO4/SiO2 catalysts for solar thermochemical water splitting cycles

“…where P SO3 is the decomposition SO 3 pressure over sulfates [33]. The T d value is defined as the temperature where P SO3 corresponds to the concentration of SO 3 in the gas feed in the catalytic test (4.6%).…”

“…Considering the low melting point of V 2 O 5 (675 C), the sample at Ce/V ¼ 0.5 forms a molten V 2 O 5 phase during calcination at 800 C, which will penetrate into pore structure of the SiO 2 support. In such a situation, particle growth of CeVO 4 may be significantly accelerated by wetting and/or corrosion effects of the liquid phase [33,43]. This is a possible reason of the highly crystallized CeVO 4 for Ce/V ¼ 0.5 as shown in XRD (Fig.…”

“…Because the formation of these inert sulfates is a well-known deactivation route for the catalytic SO 3 decomposition [33], the Ce/V ratio more than 0.9 is inadequate for the present catalyst system. Fig.…”

“…A cationic surfactant (cetyltrimethylammonium chloride, Tokyo Chemical Industry) was dissolved in distilled water (0.5 mol L À1 ) and mixed by stirring for 2 h, followed by addition of tetraethylorthosilicate (Si(OC 2 H 5 ) 4 , Wako, 98%) and aqueous ammonia until pH reached to 9.5 under stirring at 35 C. After stirring the resulting mixture for 30 h at room temperature and subsequent addition of nitric acid until pH ¼ 7, the product was kept for 60 min under a static condition. The solid product thus obtained was filtered without washing and dried at 100 C, followed by calcination at 800 C for 2 h. Using ascalcined SiO 2 products, supported CeeV oxide catalysts (CeeV/SiO 2 ) with the molar ratio of Ce þ V: Si ¼ 1: 10 with varying Ce/V ratios (0.5e1.0) were prepared by impregnating aqueous solutions of Ce(NO 3 ) 2 (Wako, 99%) and NH 4 VO 3 (Wako, 99%), subsequent calcination at 350 C for 1 h and at 800 C for 5 h. Unsupported vanadates containing various metals were prepared by calcining powder mixtures of corresponding metal oxides and V 2 O 5 at 600 C for 5 h [33]. A reference catalyst, 0.5 wt% Pt/g-Al 2 O 3 (S BET ¼ 134 m 2 g À1 ), was prepared by impregnation using aqueous solutions of Pt(NH 3 ) 2 (NO 2 ) 2 and subsequent calcination at 600 C for 3 h in air.…”

“…Although a wide variety of other metal vanadates also exhibit the catalytic activity for SO 3 decomposition [33], they have not been investigated in detail. In this paper, we report the preparation and SO 3 decomposition activity of silicasupported CeVO 4 .…”