Selective Conversion of Syngas into Higher Alcohols via a Reaction-Coupling Strategy on Multifunctional Relay Catalysts

Abstract

Direct conversion of syngas (CO/H 2 ) into higher alcohols is highly desirable but remains challenging due to the low C 2+ OH selectivity. Herein, an effective strategy was developed through the combination of partially reduced Zn-Cr-Al trinary oxides (ZnCrAlO x ) and Mo-based sulfides to significantly raise the alcohol selectivity. The introduction of K on Mo-based sulfides suppresses the acid sites and stabilizes alkoxy species (CH x O*), which greatly enhances the selectivity of alcohols. The close proximity of the two components on the multifunctional relay catalyst ZnCrAlO x |KNiMoS-MMO-5 can effectively promote the migration of reaction intermediates by shifting the DME formation equilibrium on ZnCrAlO x , achieving an alcohol selectivity of 60.4% with more than ∼72.7% of C 2+ OH selectivity in alcohols under a CO conversion of 9.8%, and significantly improves the turnover frequency (TOF) of C 2+ OH (71.9 h −1 ). A plausible reaction mechanism is also proposed on the multifunctional relay catalyst ZnCrAlO x |KNiMoS-MMO-5. This work provides a promising avenue to improve the selectivity of higher alcohols through a multifunctional relay catalyst affording multiple types of active sites.

Direct Conversion of Syngas to Higher Alcohols over a CuCoAl|t‐ZrO2 Multifunctional Catalyst

“…Generally, the typical enol mechanism and CO insertion mechanism and the corresponding different monomers (CH x O* and CO*, where the asterisk means chemisorbed) for the chain propagation were used to explain the synthesis of higher alcohols. [65] The methoxy (CH 3 O*) and formate (b-HCOO) species were considered to be critical to the formation of higher alcohols. [60,66] Sun et al [21] proposed that formate (b-HCOO) species underwent hydrogenation to produce methoxy (CH 3 O*) species, subsequently reacted with CH x to form CH x CO species, and finally hydrogenated to form ethanol.…”

“…Generally, the typical enol mechanism and CO insertion mechanism and the corresponding different monomers (CH x O* and CO*, where the asterisk means chemisorbed) for the chain propagation were used to explain the synthesis of higher alcohols [65] . The methoxy (CH 3 O*) and formate (b‐HCOO) species were considered to be critical to the formation of higher alcohols [60,66] .…”

Selective C2+ alcohol synthesis by CO2 hydrogenation via a reaction-coupling strategy

“…The prominently enhanced HA productivity over the multifunctional catalyst implies a strong synergistic effect between CuZnAlZr and 4.7KCFZ. 25,28,32,33…”

“…25 Therefore, the rational introduction of a promoting component for CO/CH x O synthesis into the C–C coupling network is an effective strategy for HAS. 25,28,32,33,36 Given the above analysis, a plausible reaction mechanism for the tandem catalysis of HAS is proposed, as shown in Scheme 1. Over the sole primary KCFZ catalyst, HA follows a tandem mechanism of rWGSR and coupling of CH x and CO* via an aldehyde intermediate ( e.g.…”

“…Recently, great breakthroughs have been made in CO 2 hydrogenation to liquid fuels and HAS from syngas due to the proposal of the reaction-coupling strategy or tandem catalysis. 26–32 Typically, CO 2 hydrogenation to HAs goes through the reverse water gas shift reaction (rWGSR) to CO and the insertion of CO*/CH x O* to which are produced from the dissociation and non-dissociation adsorption activation of CO. Therefore, this reaction-coupling strategy or tandem catalysis holds great potential for improving HA selectivity by CO 2 hydrogenation by facilitating the formation or transfer/migration of key intermediates (CH x O* or CO*) via introducing CH 3 OH/CO synthesis components.…”