NF_3在Mn/MgO和Cr/MgO上的分解反应

NF_3 Decomposition over Mn/MgO and Cr/MgO Without Water

用Mn(NO_3)_2和Cr(NO_3),溶液浸渍MgO制备了Mn/MgO和Cr/MgO系列脱氟剂;考察了无水条件下,NF_3在Mn/MgO和Cr/MgO上的分解反应,并对反应前后的脱氟剂进行了XRD、N_2吸附-脱附和EDX表征,分析了影响脱氟活性的原因。实验结果表明,Mn/MgO的脱氟活性显著高于MgO,但Cr/MgO的脱氟活性比MgO低;在反应气体积组成2%NF_3/98%He、流量50 mL/min、脱氟剂用量2 g、400℃的条件下,NF_3在10%(Mn原子与MgO的质量比)Mn/MgO上的全转化时间达460 min。依据表征结果和热力学计算数据,认为NF,与Mn/MgO反应生成的表层MnF_3可与MgO进行氟/氧交换,促进了MgO的氟化反应,提高了Mn/MgO的脱氟活性;而NF,与Cr/MgO反应生成的表层CrF_3不能与MgO进行氟/氧交换反应,且低比表面积、低孔体积的CrF_3致密层附着在MgO表面,限制了NF_3扩散至MgO孔中进行分解反应,降低了Cr/MgO的脱氟活性。

Two defluorinating agents, Mn/MgO and Cr/MgO, were prepared by impregnating MgO powder with Mn（NO3）2 and Cr（NO3）a separately. The decomposition of NF3 on the defluorinating agents without water was investigated. The fresh and spent defluorinating agents were characterized by means of XRD, N2 adsorption-desorption and EDX. The results showed that Mn/MgO and Cr/ MgO were more and less active than MgO, respectively. The time for the full conversion of NF3 over 10%（mass ratio of Mn to MgO）Mn/MgO was 460 min under the conditions of reactant gases 2%NF3/98%He（φ）, flow rate 50 mL/min, defluorinating agent 2 g and reaction temperature 400 ℃. On the basis of the characterization and thermodynamic calculation, it was suggested that the fluorine/ oxygen exchange reaction occurred between the formed surface layer MnF3 and MgO in Mn/MgO during the NF3 decomposition, which could promote the fluorination of MgO. On the contrary, the fluorine/oxygen exchange reaction between the formed surface layer CrF3 and MgO in Cr/MgO did not occur. In addition, the CrF3 layer with low specific surface area and low pore volume restrained the diffusion of NF3 into MgO pores, so the defluorination activity of Cr/MgO was lower.