Disentangling the activity-selectivity trade-off in catalytic conversion of syngas to light olefins

Abstract

Breaking the trade-off between activity and selectivity has been a long-standing challenge in the field of catalysis. We demonstrate the importance of disentangling the target reaction from the secondary reactions for the case of direct syngas conversion to light olefins by incorporating germanium-substituted AlPO-18 within the framework of the metal oxide–zeolite (OXZEO) catalyst concept. The attenuated strength of the catalytically active Brønsted acid sites allows enhancing the targeted carbon-carbon coupling of ketene intermediates to form olefins by increasing the active site density while inhibiting secondary reactions that consume the olefins. Thus, a light-olefins selectivity of 83% among hydrocarbons and carbon monoxide conversion of 85% were obtained simultaneously, leading to an unprecedented light-olefins yield of 48% versus current reported light-olefins yields of ≤27%.

Spatially Separated Active Sites Enable Selective CO Oxidation Reaction on Oxide Catalyst

“…In a syngas conversion process over an oxide-zeolite (OX-ZEO) catalyst, dissociated O species from CO are expected to react with CO producing CO 2 while avoiding the consumption of H 2 in the feed gas and thus reducing the formation of wastewater due to reaction of the O species with H 2 . 5,6 Selective CO oxidation in H 2 -rich streams on platinum group metal (PGM) catalysts, e.g., Pt, Ir, Rh, and Ru, has been reported previously. 7,8 The selectivity toward CO oxidation on PGM catalysts has been explained by the stronger adsorption of CO on the metal surface than H 2 .…”

“…For example, preferential oxidation of CO in H 2 -rich streams (PROX) is a simple and efficient method in the on-board H 2 purification step in ammonia production plants and proton exchange membrane fuel cells, in which O 2 selectively reacts with CO but not H 2 . In a syngas conversion process over an oxide-zeolite (OX-ZEO) catalyst, dissociated O species from CO are expected to react with CO producing CO 2 while avoiding the consumption of H 2 in the feed gas and thus reducing the formation of wastewater due to reaction of the O species with H 2 . , …”

Atomic-Scale Visualization of Heterolytic H2 Dissociation and COx Hydrogenation on ZnO under Ambient Conditions

“…6,7 ZnO-based oxides, when integrated into bifunctional oxide-zeolite (OXZEO) composite catalysts, demonstrated a most promising catalytic performance for syngas conversion. 3,4,8 ZnO-supported metal nanoparticles are also widely employed as major catalysts for methanol synthesis 9 and the reverse water gas shift reaction (RWGS). 10,11 As such, research interest in the role of ZnO in catalytic hydrogenation reactions has surged, making it a central focus within the catalysis field in recent years.…”

“…Oxide catalysts for hydrogenation reactions − have increasingly caught attention due to their high selectivity. In this regard, ZnO is particularly crucial for the catalytic hydrogenation of CO , and CO 2 . , ZnO-based oxides, when integrated into bifunctional oxide-zeolite (OXZEO) composite catalysts, demonstrated a most promising catalytic performance for syngas conversion. ,, ZnO-supported metal nanoparticles are also widely employed as major catalysts for methanol synthesis and the reverse water gas shift reaction (RWGS). , As such, research interest in the role of ZnO in catalytic hydrogenation reactions has surged, making it a central focus within the catalysis field in recent years. Although industrial catalysts typically used the combination with supported metal catalysts or zeolites, the importance of ZnO in H 2 dissociation and H spillover has been highlighted by Mehar et al on hydrogenation reactions at the ZnO-Cu interface.…”

“…Hydrogen adsorption and dissociation on metal oxides are central to diverse applications, including hydrogen sensing and hydrogenation catalysis. ,− Two primary mechanisms underpin H 2 dissociation on oxide surfaces: homolytic and heterolytic cleavage. Homolytic cleavage leads to the formation of two hydrogen atoms at oxygen sites, resulting in the generation of OH groups and the simultaneous reduction of surface metal ions.…”