Shape‐Selective Zeolites Promote Ethylene Formation from Syngas via a Ketene Intermediate

Abstract

Syngas conversion by Fischer-Tropsch synthesis (FTS) is characterized by a wide distribution of hydrocarbon products ranging from one to a few carbon atoms. Reported here is that the product selectivity is effectively steered toward ethylene by employing the oxide-zeolite (OX-ZEO) catalyst concept with ZnCrO -mordenite (MOR). The selectivity of ethylene alone reaches as high as 73 % among other hydrocarbons at a 26 % CO conversion. This selectivity is significantly higher than those obtained in any other direct syngas conversion or the multistep process methanol-to-olefin conversion. This highly selective pathway is realized over the catalytic sites within the 8-membered ring (8MR) side pockets of MOR via a ketene intermediate rather than methanol in the 8MR or 12MR channels. This study provides substantive evidence for a new type of syngas chemistry with ketene as the key reaction intermediate and enables extraordinary ethylene selectivity within the OX-ZEO catalyst framework.

Mordenite Nanorods Prepared by an Inexpensive Pyrrolidine‐based Mesoporogen for Alkane Hydroisomerization

“…MOR zeolite contains various types of Brønsted acid sites (BAS), which can be distinguished on the basis of the IR frequency of the hydroxyl groups . Lukyanov et al.…”

High Ethylene Selectivity in Methanol‐to‐Olefin (MTO) Reaction over MOR‐Zeolite Nanosheets

“…Mordenite (MOR), as a widely used solid‐acid catalyst, is characterized by a pore system composed of 12‐MR main channel (0.65×0.7 nm) and elliptic 8‐MR channel (0.26×0.57 nm) parallelly running along c axis, which are interconnected by 8‐MR windows (0.34×0.48 nm) along the b axis . Recently, it was reported that the 8‐MR pores in MOR exhibited special shape‐selective catalysis in the carbonylation of dimethyl ether to methyl acetate and in the syngas conversion to ethylene . Thus, exposing more 8‐MR windows by reducing the thickness along the b axis of the MOR topology would achieve specific catalytic selectivity.…”

“…[16] Recently, it was reported that the 8-MR pores in MOR exhibited special shape-selective catalysis in the carbonylation of dimethyl ether to methyl acetate [17,18] and in the syngas conversion to ethylene. [19] Thus, exposing more 8-MR windows by reducing the thickness along the b axis of the MOR topology would achieve specific catalytic selectivity. The MOR nanocrystals with 20-50 nm dimensions have been fabricated by using the amphiphilic templates with multiquaternary ammonium heads [13] or the combination of tetraethyl ammonium hydroxide and commercial amphiphilic surfactants, [20] but the crystal orientation and size were uncontrollable.…”

“…The previous researches showed that the acid site distribution within MOR pores has a significant impact on ethylene production. Bao et al [19] provided experimental evidence that the high selectivity of ethylene in the syngas conversion was achieved more likely over the 8-MR sites in MOR framework. Similarly, the C À C coupling to produce light olefins in MTO reaction was controlled by the confined environment of zeolite pores and acid sites.…”

High Ethylene Selectivity in Methanol‐to‐Olefin (MTO) Reaction over MOR‐Zeolite Nanosheets

“…The previous researches showed that the acid site distribution within MOR pores has a significant impact on ethylene production. Bao et al . provided experimental evidence that the high selectivity of ethylene in the syngas conversion was achieved more likely over the 8‐MR sites in MOR framework.…”