Effects of Intimacy between Acid and Metal Sites on the Isomerization of n-C16 at the Large/Minor Nanoscale and Atomic Scale
Junhao Sun, Chao Mu, Dan Guo, Yujun Zhao, Shengping Wang, Xinbin Ma
Abstract
This study designed a series of acid–metal bifunctional catalysts with different degrees of intimacy between acid and metal sites and investigated the effect of the intimacy level on the isomerization of long-chain alkanes. The intimacy at a large nanoscale (∼500–1000 nm) was controlled by the placement of Pt on the HY zeolite, on γ-Al2O3, or on the HY zeolite with mesopores for improved diffusion characteristics. Various Pt/HY@AMS catalysts, featuring a shell of amorphous silica (AMS) and HY as a core, exhibited a uniform distance distribution between metal and acid sites at a minor nanoscale (<100 nm). The intimacy at the minor nanoscale can be precisely controlled by altering the thickness of AMS. Meanwhile, Pt/HY and Pt/Al-MCM-41 prepared via ion exchange exhibited atomic-scale intimacy. The diffusion performance and the accessibility of Pt play a significant role in the effect of intimacy on the isomerization of long-chain alkanes at the large nanoscale. The closer intimacy at the minor nanoscale promoted the isomerization because of the shortened diffusion pathway, while the intimacy at the atomic scale with isolated Pt species surrounded by many acid sites served to facilitate the overcracking of intermediates.