Comparison of steaming stability of Cu-ZSM-5 with those of Ag-ZSM-5, P/H-ZSM-5, and H-ZSM-5 zeolites as naphtha cracking catalysts to produce light olefin at high temperatures

We performed n-heptane cracking over Cu-ZSM-5, Ag-ZSM-5, and P/H-ZSM-5 before and after steaming under various conditions. The reduced Cu-ZSM-5 and Ag-ZSM-5 exhibited similar n-heptane cracking activities to H-ZSM-5 due to generation of Bronsted acid sites by reduction of metal cations. The order of steaming stabilities in the presence of 02 was Cu-ZSM-5 > Ag-ZSM-5 >> P/H-ZSM-5, which was the reverse order of cumene cracking activities in the presence of O-2. Cumene cracking activity is a function of Bronsted acidity. Therefore, these findings indicate that the steaming stability of a catalyst is strongly related to its Bronsted acidity. Cu2+ and Cu+ cations in the 194%Cu-ZSM-5 were not reduced to Cu-0 at a high temperature of 1023 K in the presence of 02 and, therefore, 194%Cu-ZSM-5 exhibited an ultra-high steaming stability in the presence of O-2. The Bronsted acidity of 95%Ag-ZSM-5 was extremely low, almost equal to 194%Cu-ZSM-5. However, the thermal reduction of Ag+ took place during steaming even in the presence of O-2 at a high temperature of 1023 K and, therefore, the steaming stability of 95%Ag-ZSM-5 in the presence of O-2 was much lower than that of 194%Cu-ZSM-5. (C) 2014 Elsevier B.V. All rights reserved.