Tuning the Acid Nature of the ZSM-5 Surface for Selective Production of Ethylene from Ethanol at Low Temperatures

Abstract

Solid-acid ZSM-5 catalysts stand out as highly reactive for ethanol dehydration, but the selective production of ethylene at low temperatures, however, is still a challenge. Herein, two ZSM-5 zeolites with a distinct Si/Al ratio have been modified with Ce, La, or P species or treated with H 2 O or NH 3 to get a better understanding on the contribution of acid sites to the ethanol-to-ethylene catalysis. The doping of ZSM-5 affects both the number and strength of acid sites, of which the Ce content inversely increases the population of weak acid sites (WAS). Atomically dispersed oxygen vacancy-rich CeO x synergistically contribute to the dissociation of H 2 O during the synthesis of Alrich ZSM-5 to modify the local Al environment by forming new Al−OH bonds, acting as WAS. This significantly enhances the conversion of ethanol into intermediates and ultimately into ethylene (selectivity up to 92%). Further poisoning of strong acid sites (SAS) by in situ NH 3 -titration confirms that ethanol-to-ethylene catalysis at low temperatures occurs mostly over WAS, while the contribution of SAS is minor. The underpinning insights can serve as a basis for further developments in the combination of other multivalence species with ex situ water treatments or in situ cofeeding to design robust catalysts that are able to efficiently dehydrate bioethanol into ethylene at low temperatures.

From CO2 to Sustainable Aviation Fuel: Navigating the Technology Landscape

“…Ethanol dehydration is a mildly endothermic reaction (Δ H 0 = 45.6 kJ/mol) that can be catalyzed by acid-based catalysts such as silica and alumina . The current industrial reactor for C 2 H 4 production via ethanol dehydration uses alumina-supported catalysts with an ethanol feed purity of 95 wt %, operating at 300–500 °C and 1–2 bar, achieving a C 2 H 4 selectivity of 94–99%. , Although the ethanol dehydration to C 2 H 4 production process is mature, ongoing research focuses on intensifying the process and lowering the operating temperature with further advancements in catalyst design, reactor design, and process optimization. ,, Furthermore, the dehydration reactor is followed by a two-phase separator, where the gas stream consists of primary crude C 2 H 4 and the liquid stream consists of water and ethanol. After this, the crude C 2 H 4 must be purified through various stages, including water washing, alkaline washing, drying, and separation in a light-ends tower and a heavy-ends tower to remove light and heavy byproducts .…”

Perspectives on Recent Advances in Hierarchical Zeolites for Bioethanol Conversion to Chemicals, Jet Fuels, and Carbon Nanotubes

“…Most recent studies on bioethanol dehydration processes employ acid catalysts, particularly alumina or zeolite materials . While alumina-based catalysts are widely utilized in the current industrial ethylene production processes at the temperature range of 400 to 450 °C, zeolite catalysts offer a promising alternative due to the significantly lower operating temperature conditions ranging from 200 to 350 °C. , This review also focuses on the development of hierarchical zeolite catalysts utilized in ethanol dehydration, aiming to provide insights into their reaction mechanisms in the presence of hierarchical structures and the catalyst modification to enhance catalytic activity and stability.…”