无定形MnOx/SiO2催化剂的合成及低温催化氧化甲醛机理

Synthesis of amorphous MnOx/SiO2 catalyst and the mechanism for low-temperature catalytic oxidation of formaldehyde

甲醛因其污染范围广、持续时间长、危害性大等特性被视为室内有害物质的头号"杀手"。本文采用自组装法于SiO2表面原位生长MnOx (MnOx/SiO2催化剂)并用于低温催化氧化甲醛的研究,XRD、SEM-EDS、TEM和BET表征显示,MnOx以无定形态均匀地分布在SiO2载体表面,同时考察了MnOx的负载量以及煅烧温度对甲醛催化活性的影响。实验结果表明,优选的质量分数13%MnOx/SiO2无定形催化剂具有较大的比表面积(高达164.85m^2/g)和丰富的活性位点(Mn3+,75.6%),而较大的比表面积有利于更多的甲醛分子吸附在催化剂表面并进行活化反应。对甲醛进行连续性动态检测,结果显示催化剂在连续催化6h后仍保持80%以上的去除效率,表明无定形催化剂具有良好的低温催化效果。随着温度的升高,催化甲醛过程中间产物(甲酸根)被进一步分解,有利于催化剂的再生使用,当温度达到90℃时,甲醛的去除效果可达90%。

Formaldehyde is regarded as the world’s No.1 indoor hazardous substances because of its wide pollution range, long enduring time and great harm. In this paper, a self-assembly method to fabricate MnOx(MnOx/SiO2 catalyst) onto the surface of SiO2 is presented, and then the catalyst was used for the catalytic oxidation of formaldehyde at low temperature. XRD, SEM-EDS, TEM and BET measurements have shown that the MnOxhad an amorphous structure and were evenly distributed on the surface of SiO2. The effects of the MnOxdosage and calcinating temperature on the activity of the catalysts were evaluated. The optimization results showed that the amorphous catalyst of the 13% MnOx/SiO2 have a higher specific surface area(164.85 m^2/g) with many active sites(Mn3+, 75.6%), which was beneficial for the adsorption and activation of formaldehyde. Continuous tests showed that the catalyst was able to maintain over 80% removal efficiency after 6 hours, which confirmed the good low-temperature catalytic activity of the amorphous catalyst. Moreover, the formate species on the catalyst can decompose at high temperature, which realizes the regeneration of catalyst. The formaldehyde removal efficiency was up to90% when temperature reached 90℃.