Effects of zeolite frameworks and hierarchical structures on catalytic bioethanol dehydration: In-situ DRIFTS and DFT studies

New mechanistic insights into the role of water in the dehydration of ethanol into ethylene over ZSM-5 catalysts at low temperature

“…To unveil the consequences of H 2 O-treated Al-species in ET dehydration, solid-state 27 Al MAS-NMR analyses were performed for HZ(23)_H 2 O and HZ(80)_ H 2 O zeolites and their parent counterparts. The 27 Al MAS-NMR spectra (Fig.…”

“…The coordination Al species in the framework of chosen HZSM-5 samples were analyzed by 27 Al MAS-NMR using an Avance III 400 MHz NMR spectrometer (Bruker). 27 Al nuclei were studied at resonance frequencies of 104.3 MHz by using a single-pulse π/2 excitation and a repetition every 0.5 s. Before the measurements, the samples were exposed in a desiccator to saturated vapors of Ca(NO 3 ) 2 solution at room temperature overnight. Hydrated powder of Al(NO 3 ) 3 was used as an external reference for the 27 Al-NMR spectra.…”

“…27 Al nuclei were studied at resonance frequencies of 104.3 MHz by using a single-pulse π/2 excitation and a repetition every 0.5 s. Before the measurements, the samples were exposed in a desiccator to saturated vapors of Ca(NO 3 ) 2 solution at room temperature overnight. Hydrated powder of Al(NO 3 ) 3 was used as an external reference for the 27 Al-NMR spectra. The 2D multiplequantum MAS-NMR analyses were also performed over samples loaded with tri-methylphosphine oxide (TMPO) that was used as the probe molecule.…”

“…In turn, zeolites such as Beta, Y, Mordenite, and Mobil Five (MFI) show promising ET-to-ETY yields. 10,24–28 The modification of MFI-type zeolites with noble metals (Ru, Rh, Pd, Pt, etc . 10 ), transition metals (Co, Ni, Cu, Fe, etc .…”

“…32 In an attempt to understand the effect of water during the alkali treatment, we also have water-treated parent HZSM-5 in the ex situ liquid-or in situ vapor-phase. Systematic analyses by NH 3 -TPD (temperature-programmed de-sorption), N 2 sorption and 27 Al-NMR (nuclear magnetic resonance) spectroscopy correlate ETY with the appearance of new extra-framework (EF) penta-coordinated Al(V) species emerging from water treatment. The obtained insights would help propose new catalytic pathways to ETY that explain the role of water in ethanol dehydration or as a co-feed, as it occurs in industrial bioethanol streams containing nearly 5% water.…”