CF4在Al2O3基金属氧化物上的分解反应

考察了在无水条件下γ-Al2O3基金属氧化物M-Al2O3(M=Mg、La、Ba、Ce、Ni、P)与CF4反应转化为金属氟化物的反应. 结果表明, 在所筛选的金属氧化物中, γ-Al2O3的初活性较高, 但由于CF4分解时产生的强放热效应使未反应的γ-Al2O3发生了α相变, 致使CF4转化率急剧下降, 反应温度越高, γ-Al2O3的α相变越快, 活性下降就越快. CF4在MgO-Al2O3上分解时, Mg物种比Al优先氟化生成了MgF2, Mg物种的氟化反应及其产生的强放热效应使MgAl2O4结构发生了解体. 在Al2O3表面负载助剂P、Ni,提高了其热稳定性, 抑制了CF4高温分解时未反应的Al2O3发生α相变, 使更多的γ-Al2O3参与了CF4分解反应.

Decomposition of CF4 over Al2O3-Based Metal Oxides

The decomposition of CF4 in the absence of water on γ-Al2O3-based metal oxides was carried out to destruct the disposal perfluoro-carbons (PFCs) from industrial processes. In the present work, the conversion of CF4 was tested over bare γ-Al2O3 at different temperatures of 825, 850 and 900 ℃. It was found that the initial activity of Al2O3 increased in the order of 825 ℃<850 ℃<900 ℃CO2 yield declined quickly with time on stream because the un-reacted γ-Al2O3 was transformed into inactive α-Al2O3 phase that resulted from the highly exothermic effect of Al2O3-fluorination reaction. As for the CF4 decomposition on MgO-Al2O3, fluorination of Mg species and the highly exothermic effect produced led to the collapse of MgAl2O4 structure, in which the magnesium element was fluorinated into MgF2. Al2O3 modified with P or Ni could inhibit the transformation of un-reacted γ-Al2O3 into α-Al2O3 during CF4 decomposition, and consequently CF4 conversion reached a stable level with time on stream.