Effect of boron incorporation on the structure, products selectivities and lifetime of H-ZSM-5 nanocatalyst designed for application in methanol-to-olefins (MTO) reaction

The effect of boron incorporation into H-ZSM-5 nanocatalyst on the stability, product distribution and hydrocarbons selectivity in methanol to olefins (MTO) reaction was investigated. The reference and boron-modified ZSM-5 nanocatalysts were prepared by hydrothermal method. The fresh and used nanocatalysts were characterized using TG-DTA, XRD, FE-SEM, BET, FT-IR, TPH, TPO and NH3-TPD techniques. The performance test runs of the two H-ZSM-5 and [B]-H-ZSM-5 samples were conducted in a fixed-bed reactor at T = 480 degrees C, P = 1 atm, methanol WHSV = 0.9 h(-1) with methanol to water weight ratio of unity in the feed. The results revealed that propylene selectivity does not change significantly with the isomorphous substitution of B in H-ZSM-5 zeolite. However, the lifetime of the modified zeolite (1300 h) showed a significant increase compared to that of the reference sample (340 h). The considerable enhancement of the lifetime and catalytic stability could be attributed to reduction of strong/mild acid sites ratio as well as small crystal size of the [B]-H-ZSM-5 nanocatalyst. The characterization of the deactivated nanocatalysts showed that incorporation of boron decreased both rates of coke formation and coke-susceptibility of the ZSM-5 nanocatalyst. (C) 2014 Elsevier Inc. All rights reserved.