Shifting pathways in the phenol/2-propanol conversion over the tandem Raney Ni + ZSM-5 catalytic system

Abstract

This work investigates the effects of both the zeolite accessibility and the reaction temperature on conversion of phenol assisted by 2-propanol over the tandem system Raney Ni + ZSM-5 zeolite. Two different zeolite samples, containing similar Si/Al ratios, were used: nanocrystalline ZSM-5 (n-ZSM-5) and hierarchical ZSM-5 (h-ZSM-5), operating at temperatures of 125, 150 and 175°C. When working with the Raney Ni + n-ZSM-5 system at low and intermediate temperatures the main products were mostly benzene and cyclohexene formed by phenol deoxygenation. In contrast, when increasing the temperature up to 175°C, a shift in the reaction pathways was observed, leading towards a significant share of valuable alkylphenols (mostly cresols and cyclohexylphenols) in the product distribution, generated by the occurrence of alkylation reactions catalyzed by the zeolite acid sites. This effect was enhanced in the case of the h-ZSM-5 sample, due to its improved accessibility and larger mesopore/external surface area.