Understanding the Catalytic Stability of Cs₂O–P₂O₅ over Acid-Activated Montmorillonite for the Gas-Phase Dehydration of Monoethanolamine to Ethylenimine

This is the authors' abstract. We don't add key points for this paper.

In this work, the gas-phase selective dehydration of monoethanolamine (MEA) to ethylenimine (EI) was studied by using cesium and phosphorus oxides (Cs2O–P2O5) over acid-activated montmorillonite (Acid-MMT) as a catalyst, and key factors affecting the catalytic stability are focused by operating the reaction for a time on stream (TOS) of 100 h. By keeping a fixed content of Cs2O over the catalyst, the change of the P2O5/Cs2O molar ratio from 0.16 to 0.58 leads to significantly varied MEA conversion and EI selectivity. Importantly, a stable EI yield of about 60% for a TOS of 100 h is achieved over the optimal catalyst, with a P2O5/Cs2O molar ratio of 0.51. Physicochemical properties of fresh/spent catalysts were characterized by powder X-ray diffraction, X-ray fluorescence, N2 adsorption–desorption isotherms, and temperature-programmed desorption of NH3 and CO2. Moreover, properties of the coke deposited over the spent catalysts were explored by thermal analysis and X-ray photoelectron spectroscopy. Results disclose that the acidic/basic sites play a key role for catalyzing the conversion of MEA to different products, and the catalyst with a higher amount of acidic/basic sites exhibits a lower deactivation rate. Although stronger acidic/basic sites are not directly involved in producing the targeted EI product, they promote the side reactions related to the coke deposition. The heteroatom-containing coke is beneficial to improving the EI selectivity via preferentially poisoning the stronger acidic/basic sites, which inhibits the unwanted side reactions. Considering the abundance of the precursors and the simple procedure of catalyst preparation, Cs2O–P2O5/Acid-MMT is a promising catalyst for the large-scale production of EI via gas-phase MEA dehydration.