Synergistic effect of Zn with Ni on ZSM-5 as propane aromatization catalyst: effect of temperature and feed flowrate

Abstract

This work shows how propane was catalytically converted to aromatic compounds over Zn-Ni/HZSM-5 to investigate the synergistic role of nickel as a zinc stabilizer and promoter in propane aromatization. Co-impregnation method was employed for Zn-Ni/ZSM-5 synthesis fixed 2 wt% of zinc and 1, 2 and 3 wt% of nickel. Modified catalysts’ were fully characterized. Catalysts crystallinity, structure and microporosity were retained from the analysis results. The propane aromatization process was conducted at 540 °C, 1200 ml/g-h gas hourly space velocity and atmospheric pressure. The presence of Ni with Zn improved catalytic performance for all Ni loading. Aromatic selectivity and propane conversion were improved, with the best performance to be Zn-Ni/ZSM-5 with 2 wt% Zn, 2 wt% Ni on ZSM-5 averaging 88 and 60% for twelve hours’ time on stream. Aromatic selectivity on Zn-Ni/ZSM-5 is eight times better than the parent HZSM-5 and one and half times better than the Zn/ZSM-5 catalyst. The electronic interaction of zinc and nickel resulting from equality of oxidation state of +1 and +2 and metal-binding energy change synergistically improved the catalytic performance of the bimetallic Zn-Ni/ZSM-5 over the HZSM-5 and Zn/ZSM-5. Flowrate increase from 6 to 35 ml min−1 decreased propane conversion from 80–40% with increased aromatic selectivity from 55–80%. Temperature increase from 500–580 °C favours both propane conversion and aromatic selectivity increase from 50–68 and 55–92% respectively. The metallic interactions from H2-TPR and XPS analysis revealed a big improvement in propane conversion, aromatic selectivity and product distribution.