Catalytic performance of modified kaolinite in pyrolysis of benzyl phenyl ether: A model compound of low rank coal

A serials of modified kaolinites were prepared by calcination and further acid treatment and charac-terized by in-situ XRD, N-2 adsorption, NH3-TPD, Py-IR and Al-27 MAS-NMR. And their catalytic performance in pyrolysis of methanol/benzyl phenyl ether (MeOH-BPE), a model compound of low-rank coal, were investigated at 400 degrees C in a fixed-bed reactor to explore the correlation between the structure of modified samples and their catalytic performances. The results show that calcination temperature above 500 degrees C causes the collapse of kaolinite structure. Further acid leaching facilitates the formation of micropores and mesopores. The calcination of kaolinite leads to the transformation of six-coordinate Al atoms (Al-VI) into four and five coordinate species (Al-IV and Al-V), while the subsequent acid treatment increases the contents of Al-IV and Al-VI and removes Al-V. Total acid sites exhibit a first increase and then decrease tendency with the raising calcination temperature. In the presence of the modified kaolinites, BPE conversion significantly enhances and reaches the highest value of 91.41% over K-A-70 0 prepared by calcination at 700 degrees C of kaolinite and further acid leaching. Besides, the maximum content of phenol and toluene is also achieved due to the highest acid sites and Al-IV content of K-A-700, which favors the generation of H-center dot, thus resulting in an obvious inhibition of bibenzyl formation but a significant increase of 2-benzylphenol. In-situ pyrolysis by time-of-flight mass spectrometry suggests that the cleavage of C-al-O bond of BPE to form phenol radicals and benzyl radicals is the primary way, while insufficient H-center dot results in the formation of dominant product of 2-benzylphenol. (C) 2020 Energy Institute. Published by Elsevier Ltd. All rights reserved.