摘要
采用γ－Ａｌ_２Ｏ_３为载体，以硝酸镍、硝酸镁和稀土硝酸盐为原料，按常规浸渍法制备镍负载型催化剂，其中Ｎｉ含量为９．１７％，助剂ＲＥ_２Ｏ_３和Ｍｇ含量分别为５．１８％和１．８０％，该催化剂简称为Ｎ－５－ＲＭ。催化反应评价采用双套管石英反应器，在多功能固定床流动反应装置上进行，以天然气和二氧化碳转化为探针反应，采用连续反应法评价催化剂性能。以反应尾气中合成气摩尔百分数表征催化剂活性。采用理光Ｄ／ｍａｘ－ｒ－Ｂ型Ｘ射线衍射仪测定催化剂晶相。实验发现，催化剂长期使用失活的主要原因是由于活性中心Ｎｉ￣０与载体Ａｌ_２Ｏ_３间形成难还原的ＮｉＡｌ_２Ｏ_４物种，以及活性中心Ｎｉ￣０聚集形成晶相，从而降低了催化剂表面活性中心数。ＴＰＲ结果指出，ＮｉＡｌ_２Ｏ_４物种在高温下通氢气可以得到充分还原。然而，此时催化剂活性仍明显低于新鲜催化剂活性。ＸＲＤ结果表明，此时催化剂存在很强的Ｎｉ￣０衍射峰，说明尽管高温还原已使形成ＮｉＡｌ_２Ｏ_４的Ｎｉ￣（２＋）还原为Ｎｉ￣０，但高温还原又进一步使活性Ｎｉ￣０聚集成晶相，因而降低了催化剂表面活性中心数。这说明，对ＮｉＡｌ_２Ｏ_４的活化仅通过常规高温还原是不够的。２０％过氧化氢水溶液（以下简称?
The cause of deactivation and the regenerating condition of Ni/Al_2O_3 catalyst used in the natural gas(or methane)reforming with carbon dioxide was studied using a fix-bed flow reactor and XRD, TPR techniques.The mechanism for regenerating Ni/Al_2O_3 catalyst was advanced, and an effective agent that can make the deactivated catalyst to restore its activity of the fresh catalyst was found.It is demonstrated that the main reason of the catalyst deactivation is the loss of the Ni￣0 active site due to the formation of NiAl_2O_4 and the aggregation of Ni￣0 to crystallites.When the deactivated catalyst was reduced at 1123K or 1193K in a conventional regeneration process,the activity would increase a little,but were much lower than that of a fresh catalyst.If the deactivated catalyst was first reduced at 1193K,and then treated with an activity-rejuvenating agent A, the activity could be renewed to that of the fresh one.The above process was used to regenerate waste industrial catalyst unloaded from industrial device for steam reforming of natural gas. The activity of reactivated catalyst was almost renewed to that of the fresh catalyst.
出处
《分子催化》
CSCD
1995年第6期445-450,共6页
Journal of Molecular Catalysis(China)
