Catalytic Activity of Rh–La/HZSM-5 Bimetallic Catalysts in Benzene Methylation Reaction

An HZSM-5 zeolite was modified with lanthanum and rhodium to address the problem of annihilation of a methanol-to-olefin (MTO) side reaction, to increase xylene selectivity (particularly p-xylene), and to enhance the stability of catalysts used in benzene methylation. The catalysts were characterized by X‑ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, temperature-programmed ammonia desorption, and specific surface area and porosity measurements using BET and BJH methods. Benzene was methylated in a plug-flow reactor at 380°C with a benzene-to-methanol molar ratio of 1 : 1 under hydrogen flow. The two-component modification of HZSM-5 decreased the density of strong acid sites to form metal sites, to decrease pore volume, and to increase the catalyst mesoporosity. This led to the annihilation of side reactions, an increase in p-xylene selectivity, and high catalyst stability. The bimetallic Rh–La/HZSM-5 catalyst completely annihilates the MTO side reaction to exhibit high p-xylene selectivity (71.2%), and operational stability (up to 80 h).