Hydrogen production via sulfur-based thermochemical cycles: Part 2: Performance evaluation of Fe 2O (original) (raw)
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Through our previous studies it was established that non-precious Fe 2 O 3 based catalyst has the potential to replace Pt based catalyst for high temperature sulfuric acid decomposition, the energy conversion step in iodine-sulfur or hybrid-sulfur thermochemical cycles for water splitting (Banerjee et al. [11] and [25]). However, issues like agglomeration and grain growth during prolonged operation still remain to be fully resolved. With an aim to develop low cost, abundant transition metal oxide catalyst with high activity and stability, Fe 2 O 3 nanoparticles immobilized on SiO 2 support is explored, anticipating that the Fe 2 O 3-SiO 2 interactions may prevent self agglomeration of Fe 2 O 3 nanoparticles. Several catalysts with varying Fe 2 O 3 content ranging from 5 to 20 wt% were synthesized, characterized and their catalytic activity evaluated. Structural investigations by XRD and Mössbauer spectroscopy revealed that the 1000 • C calcined samples contained-Fe 2 O 3 as the major phase in addition to minor and-Fe 2 O 3 phases.-Fe 2 O 3 were found to be dispersed as nanorods with typical width of 5 nm from HRTEM images. Analysis of surface features by N 2-BET surface area, pore size distribution, pore volume and XPS indicated that the majority of Fe 2 O 3 was encapsulated within the mesoporous structure of SiO 2 upto 15 wt.%, beyond which Fe 2 O 3 was deposited outside the porous network in an enhanced quantity. The surface area of Fe 2 O 3 (15 wt.%)/SiO 2 was found to be 99.6 m 2 /g. Presence of Fe-O-Si linkages was confirmed by XPS, and supported by successive TPR/TPO studies. The extent of reducibility measured via TPR increased with increasing loading and was found to be maximum for the 15 wt.% dispersed samples. The catalytic activity was found to increase with an increase in loading of active Fe 2 O 3 content upto a SO 2 yield of ∼ 92% at 900 • C at a WHSV of 27 g acid g −1 h −1 , for 15 wt.% and then decreased. Further evaluation of the 15 wt.% sample revealed the durability (100 h) and practical applicability of the composition. The surface morphology, structure and composition underwent modifications during the 100 h operation in order to adapt to the reaction environment (high temperature, steam, oxides of sulfur) and the Fe 2 O 3 (15 wt.%)/SiO 2 catalyst exhibited iron sulfate formation and significant surface reorganization. The high catalytic activity can be ascribed to nanoparticulate nature of Fe 2 O 3 and stability due to its anchored structure on SiO 2. These findings would inspire the design of active and stable catalyst for high temperature catalytic reactions.
High Thermal Stability Fe2O3-Al2O3 System to Produce Renewable Pure Hydrogen in Steam Iron Process
2021
The use of H2 as fuel of the future is closely linked to the development of Fuel Cells, among them Proton Exchange Membrane Fuel Cells (PEMFCs) are the most attractive. To avoid the irreversible poisoning of the platinum-based catalyst placed on the PEMFC electrodes, pure H2 (CO < 10 ppm) is required. Steam iron process (SIP) is a cyclical process which allows, at high temperature and low pressure, the direct production of pure H2 by redox cycles of iron. Syngas is generally used as reducing agent while steam water is used to oxidize iron and to produce pure H2. However, iron oxides powders suffer from deactivation in few redox cycles due to their low thermal stability. The aim of this study is to improve iron oxides resistance adding Al2O3 as high thermal stability material. Bioethanol is used as renewable sources of syngas to makes the process totally sustainable. To evaluate the effect of Al2O3 addition, different Fe2O3 / Al2O3 ratios were tested (40 wt%, 10 wt%, 5 and 2 wt%)....