Pt stabilization on Pt/SBA-15 through surface modification using MPTMS for sulfuric acid decomposition in SI cycle to produce hydrogen

Abstract

Catalysts for the sulfuric acid (SA) decomposition, one of three reactions in Sulfur Iodine (SI) cycle to produce hydrogen, should be active and stable in wide temperature ranges of 650-850 degrees C. Pt based catalysts are explored for SA decomposition, but they suffered from the severe Pt loss at the high temperature of 850 degrees C. Uniform platinum nanoparticles (NPs) are physically trapped within mesopores of the mesoporous SBA-15 prepared in a "one pot" method (Pt-x.x-NTS, x.x: loaded Pt wt%). Other Pt catalysts are prepared to stabilize Pt-x.x particles using 3-mercaptopropyletrimethoxysilane (MPTMS) as a stabilizing agent (Pt-x.x-TS, x.x: loaded Pt wt%). The co-assembly method in the one pot is based on the I+M-S+ scheme in which S+ (Protonated block copolymer) and I+ (Cationic inorganic precursor) are assembled together through the M- (PtCW mediator. The MPTMS containing thiol group is used to modify the cationic precursors (I+) in order to hold the Pt nanoparticles in mesochannels as the reduced platinum metal is easy to bond with thiol groups. The prepared samples are characterized by XRD, TEM, CO Chemisorption, N-2 adsorption desorption, and ICP-OES techniques. The TEM images show that the small Pt NPs of an average size of 7.0 (+/- 0.84 nm) are uniformly dispersed within the mesopores on the mesoporous SBA-15. The thiol stabilized Pt-TS catalysts display the exceptional catalytic stability for sulfuric acid decomposition at the high temperature of 850 degrees C for 50 h. The overall average metal loss is 67% for the Pt-2.0-NTS for 50 h at 76,000 m(cat)(-1).h(-1), while it is 16% for the Pt-2.0-TS. The metal loss of Pt/SBA-15 is significantly suppressed by the surface functionalization using MPTMS in the catalyst preparation step. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.