Zn-loaded HY zeolite as active catalyst for iso-propylation of biomass-derived phenolic compounds: A comparative study on the effect of acidity and porosity of zeolites

• Published in: Molecular catalysis 2017-11, Vol.441, p.122-133
• Main Authors: Afreen, Gul, Patra, Tanmoy, Upadhyayula, Sreedevi
• Format: Article
• Language: English
• Subjects: Alkylation; Biomass; m-Cresol iso-propylation; Solid acid catalysts; Thymol; Zeolites
• ISSN: 2468-8231; 2468-8231
• DOI: 10.1016/j.mcat.2017.08.010

[Display omitted] •Catalytic activity comparison of different zeolites in iso-propylation of m-cresol.•Zn-loaded HY zeolite with high Lewis acidity exhibited 91.6% m-cresol conversion.•Maximum catalytic efficiency was obtained at 250°C and WHSV value of 2.8h−1.•ZnY selectively produced C-alkylated product thymol (C/O alkylation ratio:32.3).•ZnY catalyst showed maximum stability with least coking percentage (6.7%). Liquid bio-oil formed from pyrolysis of lignocellulosic biomass needs further upgradation by CC bond formation reaction between the phenolic compounds and small oxygenates to retain the maximum amount of carbon in the fuel range (C10C13), prior to hydrodeoxygenation step. In this contribution, we have explored the gas-phase alkylation of m-cresol with iso-propanol over zeolites like HZSM5, HBEA, HMCM22, HY, and ZnY solid acid catalysts. The fresh and spent catalysts were characterized by XRD, N2 sorption, ICP-MS, Py-FTIR, NH3-TPD, SEM, and TEM techniques. The time-on-stream and temperature studies were carried out over these catalysts at a WHSV value of 2.8h−1 to analyze the role of different active acidic sites as well as their pore dimensions on the catalytic activity and product distribution. Among all the catalysts, formation of thymol by C-alkylation was highly dominant over ZnY which has strong Lewis acid sites. Coke analysis revealed that HBEA was found to rapidly deactivate by coking (16.4% coke) and pore blocking. Time-on-stream study at 250°C showed that maximum conversion of m-cresol (92%) was obtained on fresh ZnY catalyst having strong Lewis acidity and moderate Bronsted acidity, confirming the fact that strong Lewis acidity in combination with Bronsted acidity improved the stability of iso-propyl cation and consequently, enhanced the conversion of m-cresol. Moreover, the presence of Zn2+ content in FAU zeolite framework was found to alter its acid site distribution and pore volume as compared to HY zeolite and resulted in predominant mono-alkylated product formation, especially thymol.