Investigation of Ethanol Conversion on H-ZSM-5 Zeolite by in Situ Solid-State NMR

Abstract

The process of ethanol conversion on H-ZSM-5 zeolite with different Si/Al ratios was well-studied with the assistance of in situ solid-state 13C NMR experiments under continuous flow (CF) and batch-like conditions, respectively. Except for the adsorbed ethanol and diethyl ether, the surface ethoxy species, triethyloxonium ion, and even cyclopentadienyl cations were captured on the working catalyst and identified as active intermediates in ethanol conversion. The evolution process of these captured intermediates was exhaustively illustrated subsequently. Especially, two kinds of configuration of the adsorbed ethanol, referred to as side-on and end-on orientations, and diethyl ether (DEE) with an activated state were also revealed in this work. In addition, involved as one of the important active intermediates in MTO reaction, the cyclopentadienyl cations were also speculated to play important roles in the ethanol conversion and have close relation to propene formation.

Dynamic evolution of HZSM-5 zeolite framework under steam treatment

“…This implies that the transformation from Al(IV)-2 to Al(IV)-1 is not achievable through ammonium exchange treatment. This phenomenon differs from the reversible octahedral-tetrahedral coordination transformation observed in the adsorption of water frameworkassociated Al [63] . After treatment at 400 or 500 °C, the same phenomenon is observed [Figure 1A and F], with the extent of dealumination escalating as the hydrothermal conditions become more severe.…”

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

“…25 Many mechanistic and kinetic studies attempted to elucidate their catalytic behavior for ethanol dehydration to ethylene. 28,33–37 At temperatures slightly higher than 260 °C, HZSM-5 usually exhibits ETY selectivity and nearly complete ET conversion. However, such temperatures and narrow micropores (∼0.5 nm) facilitate pore-blocking.…”

Recent advances in solid-state NMR of zeolite catalysts

“…Since the ethylated aromatics are the main HP species in the ETH reaction, the deficiency of the olefins cycle makes the ETH process different from the MTH reaction, which involves both olefins- and aromatics-based cycles [ 138 ]. The active intermediate such as cyclic carbenium species that was proposed to be involved in the formation of aromatics in the ETH process was experimentally identified using 13 C NMR spectroscopy [ 139 ]. Cyclopentenyl cations were observed during the ETH reaction on the ZSM-5 zeolite.…”