Catalytic SO₃ Decomposition Activity of SiO₂-Supported Alkaline Earth Vanadates for Solar Thermochemical Water Splitting Cycles

Abstract

Alkaline earth vanadates (Ae–V: Ae = Ca, Sr, and Ba) were supported on mesoporous SiO2 by a wet impregnation method. The catalytic activity of the prepared materials for the decomposition of SO3 into SO2 and O2, which is a key step in solar thermochemical water splitting cycles, was investigated. In the temperature range 700–800 °C, the Ae–V/SiO2 catalysts exhibited remarkably high activities, which were superior to those of supported Pt catalysts in a wide range of weight hourly space velocities (55–220 g-H2SO4 g–1 h–1). Despite the melting points of the materials exceeding 1000 °C, the high activity was determined to be closely related to the unusual melting behavior of Ae–V. Under the reaction atmosphere, the Ae–V phase was converted to AeSO4 and molten V2O5 (melting point = 690 °C) via facile solid–gas reactions between SO3 and alkaline earth elements displaying high basicity. Notably, upon contact with the molten V2O5 phase, the as-deposited AeSO4 was immediately decomposed into SO2 and O2 to regenerate the Ae–V phase. The catalyst, which solidified at lower temperatures (<690 °C), could not decompose the sulfate and was therefore unable to drive the catalytic cycles. Consequently, the SO3 decomposition rate at <690 °C was lower than that of an alkaline vanadate (Cs–V) with a melting point as low as 500 °C but higher than that of a rare earth vanadate (La–V) with the highest melting point (>1800 °C).

Unveiling the Catalytic Merits of LaV3O9 over Conventional LaVO4 Polymorphs to Boost Desired Kinetics of Humid NOX Reduction and Poison Disintegration

“…This indicated that the N SO2 values mostly originated from the desorption of SO 2 adsorbates bound to the surfaces. Nevertheless, LaV 3 O 9 and V 2 O 5 were reported to undergo dissociation into monoclinic LaVO 4 /V 2 O 5 and melting, respectively, at ≥650–700 °C. , These in turn might induce reconstruction of the SO Z 2– -modified LaV 3 O 9 /V 2 O 5 surfaces along with the evolution of novel surface phases including SO Z 2– during the SO 2 desorption step at 650–1000 °C, thus rendering comparison of the N SO2 values of the catalysts hardly convincing.…”

SO3 decomposition over silica-modified β-SiC supported CuFe2O4 catalyst: characterization, performance, and atomistic insights

“…31 The sulfur-iodine (S-I) thermochemical water-splitting cycle is widely considered one of the potential mass production ways to produce hydrogen in an efficient, cost-effective and environment-friendly manner. 23,[32][33][34][35][36] The S-I cycle was originally proposed by General Atomics Co. (GA) in the mid-1970s and it is composed of the following chemical reactions: [37][38][39][40][41][42][43][44]…”

“…31 The sulfur–iodine (S–I) thermochemical water-splitting cycle is widely considered one of the potential mass production ways to produce hydrogen in an efficient, cost-effective and environment-friendly manner. 23,32–36 The S–I cycle was originally proposed by General Atomics Co. (GA) in the mid-1970s and it is composed of the following chemical reactions: 37–44 H 2 SO 4 → H 2 O + SO 2 + ½O 2 (∼1123 K) Δ H = 186(±3) kJ mol −1 H 2 SO 4 → SO 3 + H 2 O (∼673–773 K) Δ H = 97.54 kJ mol −1 SO 3 → SO 2 + ½O 2 (>1073 K) Δ H = 98.92 kJ mol −1 2HI → H 2 + I 2 (∼473–773 K) Δ H = 12 kJ mol −1 2H 2 O + I 2 + SO 2 → H 2 SO 4 + 2HI (∼373 K) Δ H = −75(±15) kJ mol −1 …”

Effects of coexisting oxoanions on SO₃ decomposition activity of molten-phase potassium metavanadate catalysts

“…Their reactions with SO 3 immediately produce inactive metal sulfates, being more significant at lower reaction temperatures. In a series of preceding studies, 9) 14) we reported that vanadate-based catalysts such as CuV, KV, and CsV oxides supported on mesoporous SiO 2 are potential catalysts for SO 3 decomposition. Their activity at ¯650 °C are among the highest of metal oxide catalysts and are comparable to those of Pt-based catalysts.…”