Propane transformation over H-ZSM5 zeolite modified with germanium

Abstract

The propane aromatization was studied over H-ZSM5 zeolite modified by Ge, Pt and Pt-Ge. The aromatization was performed in a micro-reactor at 773K and at atmospheric pressure. The addition of germanium on H-ZSM5 increases the activity for propane transformation but decreases the selectivity toward aromatic compounds. The transformation of propane on Pt/H-ZSM5 indicates a significant increase in the activity and a decrease in the selectivity toward aromatics, while on the bimetallic Pt-Ge/H-ZSM5 catalyst both the activity and the selectivity toward aromatics increase. The dehydrogenation of propane over GeO2/SiO2 at 773 K and the n-heptane transformation overH-ZSM5 and Ge/H-ZSM5 at 673 K were performed. Results confirm the dehydrogenation capacity of GeO2 and show similar activity and selectivity for n-heptane conversion on H-ZSM5 and Ge/H-ZSM5. The acidic properties of the catalysts were determined by TPD/NH3 and IR/Pyanalyses. Results show that both the total and strong acidity decrease with the addition of germanium. Therefore, it seems that germanium affects the activity of propane conversion due to the dehydrogenation capacity of GeO2,while the selectivity toward aromatics decreases due to the lower capacity of cyclization, by decreasing the acidity and the number of strong acid sites. In contrast, the Pt-Ge/H-ZSM5 catalyst presents the highest selectivity toward aromatics (53.4%) which is attributed to the decrease in hydrogenolysis capacity of platinum. The TPR results of the Pt-Ge/H-ZSM5 catalyst indicate interaction of Pt-Ge, and from the hydrogen consumption it was seen that Ge4+ is partially reduced to Ge2+, which is attributed to the presence of metallic platinum.