HZSM-5分子筛催化剂表面酸性质对异丁烯直接胺化反应的影响

研究了以不同离子改性的HZSM-5分子筛催化剂对异丁烯直接胺化反应的催化活性,发现以铈改性的HZSM-5分子筛催化剂的催化活性最佳。在氨烯摩尔比2∶1、反应温度230℃、压力0.5M Pa、空速450h-1的条件下,异丁烯转化率可达平衡转化率的67.53%。以吡啶为探针分子的原位红外光谱(In-situ IR)研究表明,稀土元素铈的加入增加了表面B酸中心浓度。由In-situ IR及过渡应答吸附研究结果可推断,异丁烯胺化反应过程是经由化学吸附的氨与气相的异丁烯作用形成反应中间物种叔丁基正离子,叔丁基正离子进一步与气相或化学吸附的氨作用生成叔丁胺。

Effect of Surface Acidity of HZSM -5 Molecular Sieve Catalyst on Direct Amination of Isobutene

Effect of modification with different metallic ions on activity of HZSM-5 molecular sieve catalyst in direct amination of isobutente was investigated.Catalyst modified with cerium had excellent activity.Under optimal conditions:reaction temperature 230℃,total pressure 0.5MPa,mole ratio of ammonia to isobutene(2 ∶1),and space velocity of isobutene 450h~(-1),conversion of isobutene was 3.1%,which was 67.53% of equilibrium conversion.According to In-situ IR spectra with pyridine as probe molecule,strength and concentsation of B acid sites increased due to adding cerium to catalyst.By means of In-situ IR spectra and transient response technique,amination mechanism could be inferred as follows: chemisorbed ammonia first reacted with gaseous isobutene and tert-butyl cation,an intermediate formed.It successively reacted with ammonia to produce tert-butylamine.