SnxOy/SAPO-34 as catalysts for catalytic dehydration of bio-ethanol: impacts of oxidation state, interaction, and loading amount

Abstract

Light olefins are primarily used for the production of petrochemicals and polymers. The increases in the price of naphtha feedstock and light olefins are often observed with the shortage of petroleum. Together with the green concept, the production of light olefins from renewable resources has received wide attention. SAPO-34 is a potential catalyst for the catalytic dehydration of ethanol to light olefins, especially propylene due to its mild acidity and suitable pore size. Tin oxide-doped SAPO-34 was found to enhance the production of propylene, and its oxidation state can also alter the product distribution. Besides propylene, light aromatic hydrocarbons and oxygenates were also co-produced. Therefore, in this work, further studies were made on tin oxide-doped SAPO-34 catalysts in order to observe the changes of product distribution upon the changes of oxidation state, interaction with the support, and the amount of Sn loading. All supported catalysts were prepared by solid–solid interaction method, and characterized by using SAA, XPS, and XRD. The reaction was carried out in an isothermal fixed bed reactor at 400 °C and 1 atm. The gaseous and liquid products were analyzed by an online-GC, SIMDIST-GC and GC × GC-TOFMS. As a result, unsupported Sn0 catalyst was found responsible for the formation of cooking gas (hereby defined as the mixture of propane and butane), whereas SnO2 enhanced hexane, cyclohexane and benzene formation. SnO gave the high selectivity of oxygenate compounds. Owing to the Sn-support interaction, metallic Sn-doped SAPO-34 exhibited significantly higher selectivity of cooking gas that of using the unsupported metallic Sn, possibly due to the higher dispersion of metal oxide on the support and the interaction between the metal and the support. Furthermore, the impacts of tin oxides and their interaction with the SAPO-34 support were more pronounced at a high loading percentage. Propylene and cooking gas were more highly produced at a higher Sn loading.