Xiaoli Wei,Yifan Wei,Jiaqin Lu,Yunfan Huang,Yiwei Sun,Yu Wang,Lijia Liu,Bing Liu,Wenfeng Han
Transforming potent greenhouse gasses, hydrofluorocarbons (HFCs) to hydrofluoroolefins (HFOs) is an environmentally friendly and low energy input route compared with traditional incineration method. During the conversion process, Lewis acidity of the catalysts play a vital role in the activity. Here, inspired by the fluorinated metal oxide, a novel nonmetallic catalyst SiC was fabricated via sequentially mechanochemical treatment and fluorination. With series characterizations, it demonstrated that on the super surface of SiC, there are thin layers of graphite, COOH species, SiO 2 and Si 4 C 4-x O 2 substrates. Through the mechanochemical treatment, the layers of graphite, COOH species and partial SiO 2 could be grinded off. Hence, the exposed SiO 2 residue could be removed via the fluorination by HFC-152a and HF forming volatile SiF 4 . At the same time, the transition layer, Si 4 C 4-x O 2 was fluorinated to Si 4 C 4-x F 2 accompanied with enhanced Lewis acidity. As a result, the activity of the treated SiC was significantly superior than the unmilled SiC. These findings provide a feasible way to develop the catalytic performances of nonmetallic catalysts for the dehydrofluorination.
Wenfeng Han,Hong Yang,Linzhe Wang,Bing Liu,Xiaoli Wei,Aimin Chen,Weiyu Song,Haodong Tang,Ying Li
Aluminum fluoride layers (AlFx) were prepared by the in situ etching of Ti 3 AlC 2 with 1,1-difluoroethane at elevated temperatures. During etching, Ti layers were fluorinated to stable TiF 3 interacting with C to confine the Al species and sublimable TiF 4 . Al layers were fluorinated to unsaturated AlFx with relatively weak Lewis acidity. Due to the sublimation of TiF 4 , more AlFx acting as the main active centers were exposed to the reactants, and the surface areas of the confined-AlFx were increased, which contributed to the enhanced activity of the catalyst. The evaluation of the dehydrofluorination reaction showed that confined-AlFx layers presented higher reaction rate than F-γ-Al 2 O 3 and AlF 3 . Besides, it was unexpected that TiF 3 also exhibited activity for the reaction, even though the activity was much lower than confined-AlFx. Finally, the experimental results were confirmed by DFT calculations.
Han Wenfeng,Wang Zhikun,Li Xiaojuan,Tang Haodong,Xi Miao,Li Ying,Liu Huazhang
Nano-Cr 2 O 3 was prepared via solution combustion synthesis (SCS) with Cr(NO 3 ) 3 ·9H 2 O as the Cr precursor and glycine as the fuel. The effect of molar ratio of glycine to Cr in the feed during solution combustion was investigated. Cr 2 O 3 samples were characterized by XRD, SEM, TEM, H 2 -TPR, and XPS. In addition, these catalysts were evaluated for the dehydrofluorination of 1,1-difluoroethane producing vinyl fluoride (VF, CH 2 =CHF). The results confirm that Cr 2 O 3 is in relatively uniform flakes or flat particles via solution combustion synthesis with the particle size of 50–200 nm and composed by the aggregation of 58–77 nm nanoparticles. The specific surface area of higher than 30 m 2 g −1 is achieved, which is comparable to the values obtained by solvothermal route. For the dehydrofluorination of 1,1-difluoroethane, high conversion levels (83 % for commercial catalyst and 93 % for SCS catalyst) are achieved at 350 °C, and the activity of SCS catalyst is at least 2× higher than that of commercial Cr 2 O 3 at reaction temperatures below 300 °C. Compared with commercial Cr 2 O 3 , XPS, and H 2 -TPR reveal the higher CrO 3 contents on the surface of Cr 2 O 3 derived from SCS. It is suggested that CrO 3 plays a major role in the catalytic performance as high-valent Cr species such as Cr(VI) are vital for the reaction because they could be transformed to the active species such as CrO
x
F
y
. In addition to the high activity, compared with commercial Cr 2 O 3 , SCS catalyst also show higher stability. Following the reaction of 120 h at 300 °C, no noticeable deactivation is observed while the activity of commercial Cr 2 O 3 declines with TOS. High surface area and much smaller size of Cr 2 O 3 crystalline favors the formation of CrO
x
F
y
during reaction over Cr 2 O 3 -3.33 catalyst probably contribute to the high activity and stability.
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