Jinchao Wang,Wenfeng Han,Shucheng Wang,Haodong Tang,Wucan Liu,Ying Li,Chunshan Lu,Jianjun Zhang,Eric M. Kennedy,Xiaonian Li
Catalytic coupling of CH4 with potent greenhouse gas CHF3 to vinylidene fluoride (VDF) was investigated over composite catalysts. Carbon-partitioned LaF3–BaF2 catalysts were prepared by PVDF (polyvinylidene fluoride)-mediated calcination. During catalyst preparation, PVDF functions as the fluorine source and carbon source. Compared with the catalysts prepared by the conventional HF co-precipitation method, the transformation of LaF3 and BaF2 to Ba1−xLaxF2+x solid solution is inhibited as Ba and La are separated by carbon layers derived from the decomposition of PVDF. The Ba1−xLaxF2+x phase is not favorable for the coupling of CH4 with CHF3 to VDF. In addition, PVDF-mediated calcination facilitates the formation of LaOF which is one of the key species for coupling of CH4 with CHF3 to VDF. O− species, which is the most active oxygen species for the activation of CH4, increases significantly following PVDF-mediated calcination due to the formation of LaOF. Consequently, the formation rate of VDF over the catalyst derived from PVDF-mediated calcination is 3.6 times higher than the HF co-precipitation catalyst at a reaction temperature of 700 °C. The formation rate of the HF co-precipitated catalyst declines to nearly half of the initial rate in a time-on-stream of 15 h. By contrast, only slight deactivation is observed over the catalyst prepared by PVDF-mediated calcination. The present work provides a promising strategy for the preparation of composite catalysts.
Transforming carbon-containing wastes into useful porous carbon materials is highly desired. The strategy can not only relieve environmental pollution but obtain porous carbon electrodes for energy storage devices. Herein we report an efficient method to transform the ozone-depleting gas of Freon (CCl 3 F) into 3D graphene (3DG) frameworks for supercapacitor electrode materials . The 3DG possesses self-supporting interconnected meso- and macropore channels supported by the multilayer graphene frameworks, which can be well kept in actual 3DG electrodes. This characteristic, together with high conductivity, enables 3DG supercapacitors to present high rate performance through the effective synergy between ion and electron transports , thus achieving the high capacitance retention of 76.1% (156 F g −1 at 100 A g −1 ) relative to the original capacitance (205 F g −1 at 1 A g −1 ), as well as high energy density retention (42.3% at 100 A g −1 ). The capacitance retention is much higher than that of typical reduced graphene oxide , and comparable to those of the reported state-of-the-art carbon-based materials. This study provides new strategy to dispose carbon-rich environmental pollutants for useful porous carbon electrode materials.
Jiahong Wen,Yaxin Wang,Ruoning Chu,Jinhai Li,Ze Chen,Yongjun Zhang,Xiaoyu Zhao,Qi-Qi Fu
Freon refrigerants, whose leakage will cause serious safety and environmental issues, have an urgent need of developing leakage detection technologies. Conventional metal oxide semiconductor (MOS) gas sensors exhibit limited efficacy in detecting halogenated Freons due to their chemical inertness and weak charge-transfer interactions. While recent innovations employing mesoporous γ-Al 2 O 3 overlayers have enabled Freon detection via catalytic decomposition sensing mechanism, the achieved sensing performance remains suboptimal. In this work, this issue is addressed by engineering a Pd-doped mesoporous γ-Al 2 O 3 /SnO 2 (Pd-γ-Al 2 O 3 /SnO 2 ) gas sensor. The doped Pd atoms not only accelerate the decomposition of Freon molecules on the catalytic layer but also induce the Schottky-barrier effect in the SnO 2 sensing layer. Benefiting from the synergistic effect, the Pd-γ-Al 2 O 3 /SnO 2 gas sensor shows outstanding response, good stability, repeatability, selectivity, and rarely-reported universality in sensing different Freon gases. Notably, a valuable solution is demonstrated in the leakage detection of next-generation refrigerants, Freon R1234yf. The sensing mechanism is deduced by exhaust gas components identification. These results highlight the promising potential for addressing the real-world needs of Freon refrigerant leakage detection technology.
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