摘要
采用共沉淀法制备了Mo/Sn物质的量比为1∶3的MoO_3-SnO_2催化剂,考察了焙烧气氛(O_2、air、N_2和H_2)对催化剂结构及二甲醚(DME)低温氧化制甲酸甲酯(MF)性能的影响。结果表明,在O_2中焙烧的催化剂上DME转化率高达25.10%,MF选择性为72.21%,催化剂具有较高的反应活性。而在H_2中焙烧催化剂上DME转化率仅为7.01%,MF选择性为75.82%。不同气氛焙烧催化剂上DME转化率由大到小的顺序:O_2>air>N_2>H_2。采用XRD、Raman、XPS及ESR等对催化剂进行深入表征。结果表明,共沉淀制备Mo1Sn3催化剂中钼物种以高分散MoOx形式存在。O_2中焙烧催化剂表面Mo=O及存在于Mo-Sn界面处五配位钼氧化物中Mo^(5+)含量均高于其他三种催化剂,即低聚态MoOx末端Mo=O可能是反应活性位点之一,五配位钼氧化物中Mo5+的存在有利于催化剂活性的提高,也有助于MF的生成。结合in suit DRIFTS证实了吸附于Mo^(5+)上的CH_3O,在催化剂表面Mo=O作用下氧化为HCHO后与另一分子CH_3O耦合为MF。
MoO3- SnO2 catalysts with a Mo/Sn molar ratio of 1 ：3 was prepared by the co-precipitation method and calcined in different atmospheres （O2, air, N2 and H2）; the effect of calcination atmosphere on the catalytic performance of MoO3 - SnO2 in the oxidation of dimethyl ether （ DME ） to methyl formate （ MF ） was investigated. The results show that the MoO3- SnO2 catalyst prepared by calcination in O2 exhibits the highest activity; the conversion of DME reaches 25. 10%,with the selectivity of 72. 21% to MF. Over the catalyst calcined in H2, the conversion of DME is only 7. 01%, with the selectivity of 75. 82% to MF. The activity of the MoO3- SnO2 catalysts calcined at different atmospheres follows the order of O2〉 air 〉 N2〉 H2. The results of XRD, Raman,XPS and ESR characterization indicate the presence of MoOx domains on the surface of the MoO3- SnO2 catalyst with a Mo/Sn molar ratio of 1：3. The terminal Mo =O groups of oligomeric MoO3 may be the active sites for the methoxy intermediate and the penta-coordinated Mo5＋ species in the Mo-Sn interface may be able to promote the oxidation of DME to MF. Consequently,methoxy species are absorbed on the Mo5＋ species in the Mo-Sn interfaces,which are oxidized to HCHO on the terminal Mo =O groups; after that,the absorbed HCHO may then react with the neighboring absorbed methoxy species, forming MF.
出处
《燃料化学学报》
EI
CAS
CSCD
北大核心
2017年第5期572-580,共9页
Journal of Fuel Chemistry and Technology
基金
国家自然科学基金(21373253
20903114)
中国科学院青年创新促进会(2014155)资助~~
