Five MFI-type zeolite catalysts, which were aluminosilicate ZSM-5 (Z5), gallium-substituted silicalite-1 (Ga-S1), mesoporous ZSM-5 (MZ5), gallium-substituted mesoporous silicalite-1 (Ga-MS1) and gallium-substituted mesoporous ZSM-5 (Ga-MZ5), were hydrothermally synthesized with combined using of TPAOH and TPOAC as micropore and mesopore structure-directing agents respectively, followed by the application in the catalytic upgrading of volatiles from low-rank coal fast pyrolysis. The obtained results indicated that significant improvements with the yield of high value-added products of BTEXN (benzene, toluene, ethylbenzene, xylene and naphthalene) increased from 5.4 mg.g −1 to 11.9–26.4 mg.g −1 , as well as the content of light fractions (<300 °C) in coal tars increased from 51% to 65–88% were realized by using the representative MFI-type zeolite catalysts in contrast to non-catalyst pyrolysis. Moreover, the possible mechanism for catalytic upgrading over the best-performing catalyst of gallium-substituted mesoporous ZSM-5 (Ga-MZ5) with the highest yield of aromatics and effective reduction of phenols was proposed on the basis of systematic comparison of structural features and catalytic performances of various MFI-type zeolite catalysts and fundamental study of the synergetic effects dominated by acidity, ratio of Brønsted/Lewis acid sites, intra-/extra-framework gallium species and hierarchical meso-/microporosity.
Shanshan Duan,Can Huang,Min Liu,Zhiwen Cao,Xiaocong Tian,Shuen Hou,Jiangyu Li,Boyuan Huang,Hongyun Jin
NASICON-type solid state electrolytes have attracted great interest in all-solid-state batteries, and many attempts have been applied to enhance the ionic conductivity. It is generally believed that low activation energy governs the high ionic conductivity while the prefactor, particularly migration entropy, is often overlooked. Here, employing a combination of electrochemical strain microscopy, speed of sound measurements, and electrochemical impedance spectra, we investigate the structure–property relationships governing ionic conduction behavior in the Li1−3xGaxZr2(PO4)3 system. A sharp increase in the prefactor upon Ga substitution is attributed to the increased migration entropy while the increase in activation energy can be rationalized in terms of the inductive effect. These two competitive factors determine the final ionic conductivity.
Cr 3+ -doped near-infrared phosphors have recently attracted a wide attention. Here, NIR Ca 1- y Sr y Al 12- x Ga x O 19 :0.12Cr 3+ phosphors are obtained by a high-temperature solid-phase method. First, a series of CaAl 7.88 Ga 4 O 19 :0.12Cr 3+ samples is studied and shows that the crystal field strength can be tuned by cation substitutions, until achieving a sharp emission at 692 nm and a broad emission at 780 nm under a 400 nm excitation, and an internal quantum yield of 90.73%. A further substitution by an appropriate amount of Sr 2+ is suggested to be beneficial to increase the rigidity of the crystal structure by Debye temperature calculations. Experimentally, it is observed that Sr 2+ for Ca 2+ substitutions did not affect the luminescence wavelength and resulted in a significant increase of the thermal stability. When 0.7 Sr 2+ substitute Ca 2+ , the thermal stability at 450 K increased by 28% compared to the samples without Sr 2+ .
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