Journal
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
Volume 42, Issue 34, Pages 21686-21696Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijhydene.2017.07.096
Keywords
In-situ; K; Ca; H2O; Tar reforming; Biochar structure
Categories
Funding
- National key R&D program of China [2016YFE0102500]
- National Natural Science Foundation innovation research group Heat Transfer and Flow Control [51421063]
- CSC [201606120135, 201606120136]
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In order to obtain the catalytic effects of K and Ca species on the biochar structure during in-situ tar H2O reforming over nascent biochar, the H-form/K-loaded/Ca-loaded rice husks were studied for the in-situ tar reforming in the two-stage fluidized bed/fixed bed reactor. The specific reaction pathway of K and Ca for tar reforming was investigated, associated with the changes of biochar structures, through the methods of ICP-AES, Raman, FTIR and XPS. The results indicate that the in-situ volatiles (tar and free radicals) H2O reforming over nascent biochar could be conducted by three possible ways: occupying reactive sites on biochar, changing biochar structures and/or changing the total/surface concentration of AAEM species. The mechanisms of in-situ tar H2O reforming by K and Ca species were different: tar cracking into low-quality tar or small-molecule gas may be catalyzed by K, while the combination of tar with biochar would be promoted by Ca. The volatilizations of K and Ca with the presence of volatiles were to a large extent in accordance with their valences (monovalent K+ and divalent Ca2+) and their boiling points. The subsequent transformation from the small aromatic ring systems to the larger ones occurred due to the volatile-biochar interaction. During the in-situ tar H2O reforming over biochar, K and Ca act as the active sites on biochar surface to promote the increase of active intermediates (C-O- bonds and C-O-K/Ca), which promotes the tar-biochar interactions. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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