Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb Stabilization of Pt at the inner wall of hollow spherical SiO 2 generated from Pt/hollow spherical SiC for sulfuric acid decomposition Hassnain Abbas Khan a,b , Prakash Natarajan b,c , Kwang-Deog Jung a,b, ⁎ a Clean Energy and Chemical Engineering, University of Science and Technology, 217, Gajeong-ro Yuseong-gu, Daejeon, Republic of Korea b Clean Energy Research Centre, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-791, Republic of Korea c Department of Bio & Nano Chemistry, Kookmin University, 861-1, Jeongneung-dong, Seongbuk-gu, Republic of Korea ARTICLE INFO Keywords: Sulfuric acid decomposition SO 3 Decomposition SiC hollow sphere Core-shell SiO 2 hollow sphere-supported Pt catalyst ABSTRACT Catalysts for sulfuric acid (SA) decomposition, one of three reactions in Sulfur-Iodine (SI) cycle to produce hydrogen, should be active and stable up to 800–900 °C. Here, a SiC hollow sphere supported Pt catalyst (1 wt% Pt/hSiC) is prepared, and its catalytic activity and stability are monitored in SA decomposition at 850 °C. The initial SA conversion with the Pt/hSiC catalyst is ca. 80% at 850 °C and a GHSV of 76,000 mL/g cat /h. For comparison, a core-shell SiO 2 supported Pt catalyst (1 wt% Pt/SiO 2 @mSiO 2 ) is prepared and tested for the reaction. The core-shell SiO 2 support has the structure of a dense core and a mesoporous shell. The initial SA conversion with the Pt/SiO 2 @mSiO 2 catalyst is ca. 54% at 850 °C and a GHSV of 76,000 mL/g cat /h. The Pt/hSiC catalyst is transformed to the SiO 2 hollow sphere supported Pt catalyst (Pt/hSiO 2 ) within 6 h reaction. CO chemisorption and TEM analysis exhibit that Pt particles on the pristine and spent catalysts, pretreated at 850 °C, are encapsulated by SiC or SiO 2 on the surfaces of SiC and SiO 2 supports. When the encapsulated Pt particles are in contact with sulfuric acid vapor, the Pt particles are exposed to the reactants by the removal of SiO 2 en- capsulating Pt during the reaction. Pt particles at the outer wall of the pristine hSiC are partly lost via PtOx evaporation, while Pt particles at the inner wall of the hollow sphere supports are stabilized without the severe Pt loss and Pt sintering. In contrast, the Pt particles on SiO 2 @mSiO 2 with the dense SiO 2 core are severely lost via PtOx evaporation during the reaction resulting in severe Pt sintering. The high stability of Pt particles at the inner wall of the hollow support is attributed to the Pt encapsulation and Pt anchoring of the small Pt particles at the inner walls and the diffusion barrier role of the shell for the migration of Pt at the inner wall to the outer wall. 1. Introduction In the last decades, water splitting using energy sources that have zero CO 2 emission has been considered the most attractive alternative to fossil fuels [1]. The sulfur-iodine (SI) cycle using a very high tem- perature nuclear reactor (VHTR) has been studied, due to its cost ef- fectiveness for massive hydrogen production [2,3]. The SI cycle consists of three reaction steps: SO 2 +I 2 + 2H 2 O ⇌ H 2 SO 4 + 2HI (80–120 °C) (1) HI ⇌ I 2 +H 2 (∼450 °C) (2) H 2 SO 4 ⇌ H 2 O + SO 2 + 1/2 O 2 (550–850 °C) (3) In Eq. (3), the endothermic sulfuric acid (SA) decomposition re- quires energy from a pressurized He gas at the high temperatures of ca. 450–900 °C. Several sulfuric decomposers have been proposed for this reaction [4–8]. Recently, the bayonet-type reactor designed by Sandia National Laboratory has been widely used for the SA decomposition in the bench test of the SI cycle [9]. In these reactors, the recommended temperature range for SA decomposition is 550–900 °C [9,10]. There- fore, the catalysts for SA decomposition should be active and stable in this wide temperature range under the corrosive SA stream. Catalytic activity of metal oxides is reversely correlated with the decomposition temperature of metal sulfates [11–13]. Accordingly, Fe-, Cu-, and Cr- based catalysts or their bimetallic catalysts have been extensively stu- died for SA decomposition, because their corresponding metal sulfates have comparably low SA decomposition temperatures [14–19]. The active metal oxide catalyst with the low decomposition temperature of the metal sulfates (reaction intermediates) can also have the higher catalytic stability at the temperature higher than the corresponding decomposition temperature. Vanadia was also considered as an active metal oxide for sulfuric acid decomposition [20–22]. Recently, it was https://doi.org/10.1016/j.apcatb.2018.03.013 Received 27 November 2017; Received in revised form 2 March 2018; Accepted 5 March 2018 ⁎ Corresponding author at: Clean Energy and Chemical Engineering, University of Science and Technology, 217, Gajeong-ro Yuseong-gu, Daejeon, Republic of Korea. E-mail address: jkdcat@kist.re.kr (K.-D. Jung). Applied Catalysis B: Environmental 231 (2018) 151–160 Available online 05 March 2018 0926-3373/ © 2018 Elsevier B.V. All rights reserved. T