Exploring the promoting effect of Fe, Nb, Mo, and Ag on HZSM-5 for n-propanol dehydration

Abstract

Bioderived n-propanol has multiple applications, including its use as a solvent and in the production of higher-value products. This study evaluates the production of di-n-propyl ether (DPE) and propylene from the dehydration of n-propanol, analyzing the effects of transition metals — iron, molybdenum, silver, and niobium — on ZSM-5 zeolite with silica/alumina ratio of 28. Catalysts were synthesized with a 5 wt% metal loading using incipient wetness impregnation. Characterization of catalysts included XRD, NH₃-TPD, N₂ physisorption, XPS, DRIFTS, TEM, SEM-EDS and TGA. Metal impregnation reduced both surface area and pore volume. Fe^3 + /Fe²⁺, Nb⁵⁺, Ag⁰ and Mo⁵⁺/Mo⁴⁺ species were identified, agglomeration of Fe particles was clearly observed, but no significant structural differences in other catalysts. Results showed that metal impregnation alters strong/weak ratio of acid sites, which is detrimental to catalytic activity. Catalytic tests conducted in a U-shaped quartz reactor were performed, and Mo/HZSM-5 showed superior yield for DPE production due to a higher proportion of weak acid sites. At 473 K, the Nb/HZSM-5 catalyst showed increased stability over HZSM-5, reaching an initial yield of 86 % for propylene, and an average yield of 50 % after 200 min. TGA of spent catalysts showed a coke concentration of 29 % for spent HZSM-5 and 20 % for Nb/HZSM-5. This study demonstrates the potential of transition metal-promoted ZSM-5 catalysts for efficient DPE and propylene production from n-propanol, advancing the application of renewable feedstocks in catalysis.