Methylation of 2-Methylnaphthalene with Methanol to 2,6-Dimethylnaphthalene over ZSM-5 Modified by Zr and Si

ZSM-5 samples modified by isomorphic substitution of Si, Zr, or a combination thereof were characterized by FT-IR and UV spectroscopies, XRD, XRF spectroscopy, and NH3-TPD and used in the methylation of 2-methylnaphthalene (MN) to produce 2,6dimethylnaphthalene (2,6-DMN). The results indicated that Si or Zr is inserted in the framework of ZSM-5 after modification and Zr is unstable and preferentially substituted by Si in the simultaneous presence of Zr and Al. Siliconization of ZSM-5 mainly improves its stability and is slightly preferable to enhancement of selectivity to DMNs, 2,6-DMN, and (beta), (beta)-DMNs. A Zr-substituted sample can obviously improve the 2,6-DMN selectivity, yield, and ratio of 2,6- to 2,7-DMN. Co-modified ZSM-5 embodies the advantages of stable activity on Si-modified ZSM-5 and high selectivity on Zr-modified ZSM-5. The preferable catalyst was prepared by incorporation of Zr in silicated ZSM-5. About 52% 2,6-DMN and 85% (beta), (beta)-DMNs selectivity, over a 2.0 ratio of 2,6- to 2,7-DMN, and a 9% 2,6-DMN yield can be obtained. The superior methylation performance can be ascribed to the weakening of the acid strength and change in pore dimensions for different modifications.