Shifting Pathways in the Phenol/2-Propanol Conversion over the Tandem Raney Ni + ZSM-5 Catalytic System

This work investigates the effects of both zeolite accessibility and reaction temperature on the conversion of phenol assisted by 2-propanol over the tandem system Raney Ni + ZSM-5 zeolite. Two different zeolite samples, containing similar SiAI ratios, were used: nanocrystalline ZSM-5 (n-ZSM-5) and hierarchical ZSM-5 (h-ZSM-5), operating at temperatures of 125, 150, and 175 degrees 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, on increasing the temperature up to 175 degrees C, a shift in the reaction pathways was observed, leading toward 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.