表面修饰碳纤维负载铱催化剂的结构调控及其催化行为

Structure regulation and catalytic performances of surface modified carbon fiber supported iridium catalyst

以电化学改性和化学改性的碳纤维(CF)为载体制备了负载铱催化剂,通过考察催化剂在甲醇低压羰基化合成醋酸反应中的催化性能,研究了CF表面处理条件对负载铱催化剂性能的影响。XPS测试结果表明,阳极氧化后碳纤维表面出现O、N元素,氧化时间由2min增加到5min,O/N原子比例提高,在随后的负载铱催化剂中,铱的负载量由2.17%增加到4.88%,且双齿配位铱的比例较单齿配位铱增加,对醋酸的选择性由20%提高到30%。对阳极氧化后的CF,分别通过表面羟基缩合引入具有配位基团的N-(β-氨乙基)-γ-氨丙基甲基二甲氧基硅烷后,由于配位基团数量的增加,铱的负载量分别提高到4.49%和6.43%,同时,单齿配位铱/双齿配位铱的比例增大,由于其分子链结构的柔性,明显改善了固载铱的化学微环境,催化剂对醋酸的选择性分别提高到72.5%和77.8%,表现出良好的催化活性和选择性。

Carbon fiber （CF）modified by anodizing （CF-Ox）and silanization （CF-Si）were applied for supported iridium catalyst.The effects of CF modification condition on the performances of the supported iridium catalysts were investigated by studying its catalytic activities in the methanol carbonylation reaction.The loading amount of Ir on CF-Ox was 2.17% and 4.88% for anodizing time of 2 and 5 min respectively,the X-ray photoelectron spectroscopy results indicated that oxygen and nitrogen were introduced to CF surface after anodizing （CF-ox）. The oxygen/nitrogen atomic ratio enhanced as the anodizing time from 2 to 5 min,subsequently,the loading amount of Ir increased from 2.17% to 4.88% in the supported iridium catalyst.Comparing to the monodentate ligand iridium,the proportion of bidentate ligand iridium was increased,and resulted in the increase of acetic acid selectivity from 20% to 30%.For the 2 and 5 min anodized CF,after introducing N-（β-aminoethyl）-γ-ammonia propyl methyl dimethoxy silane（CF-Si）which have coordinating groups by the surface hydroxyl condensation respectively,the loading amount of Ir increased to 4.49% and 6.43% respectively,while the ratio of monodentated iridium/bidentate iridium increased.The grafted silane molecular provids CF surface with a soluble soft chain of coordination sites,which contributed to the increase of Ir loading amount and improving the chemical environment for coordinated iridium.Consequently,acetic acid selectivity increased to 72.5% and 77.8%.