Scale-up analysis of the oxidative dehydrogenation of ethane over MoVTeNbOx catalysts in an autothermal reactor

Chen, Jiakang; Sun, Zhe; Bollini, Praveen; Balakotaiah, Vemuri

doi:10.1016/j.ces.2023.118649

Cited by 2 publications

(1 citation statement)

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“…Ethylene is a valuable commodity chemical that is currently produced through the highly endothermic, non-catalytic steam cracking of naphtha and ethane. − The oxidative dehydrogenation (ODH) of ethane to ethylene on metal oxide catalysts is an attractive exothermic alternative that is energy self-sufficient, and may even be carried out autothermally. ,− On the other hand, non-selective reactions such as the production of CO, CO 2 , or C 2 + oxygenates limit ODH adoption despite advances in catalyst formulations and reactor designs that mitigate formation of these side products. ,− Several studies show how the electrophilic nature of gas phase O 2 or chemisorbed oxygen drives non-selective reaction pathways, whereas nucleophilic oxygen stored in the oxide lattice drives selective ODH. ,,, Electrophilic chemisorbed oxygen has been proposed to favor the scission of electron-dense C–C and CC bonds that result in CO x formation, whereas nucleophilic lattice oxygen has been ascribed the role of cleaving C–H bonds while preserving the C–C bond, thereby resulting in C 2 H 4 formation. ,,− …”

Section: Introductionmentioning

confidence: 99%

Kinetic Requirements for Selectivity Enhancement During Forced Dynamic Operation of the Oxidative Dehydrogenation of Ethane

Morales,

Harold,

Bollini

2024

ACS Catal.

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The viability of alkane oxidative dehydrogenation (ODH) processes specifically, and catalytic partial oxidation reactions more generally, are oftentimes limited by the formation of undesired deep oxidation products such as CO and CO 2 . The forced dynamic operation (FDO) of catalytic reactors has been proposed as a means for enhancing desired olefin or oxygenate selectivity and yield over those of CO and CO 2 , but an elucidation of the precise mechanistic bases for the dynamic enhancement observed continues to remain evasive. In this work, we provide an explanation of the extent of dynamic enhancement noted during ethane ODH over supported MoO x catalysts but not VO x ones� an explanation grounded in a quantitative analysis of the density and reactivity of chemisorbed and lattice oxygen species on these two classes of catalysts. Supported vanadia catalysts, unlike molybdena ones, carry oxygen species with similar reducibilities, resulting in highly contrasting trends in dynamic and steady state ODH properties for the two catalysts. Whereas in the case of VO x /Al 2 O 3 , oxygen speciation affects the nature of the hydrocarbon activated (ethane or ethylene), in the case of MoO x /Al 2 O 3 , it affects the type of product formed (ethylene or CO x ). Metal oxide loading is shown to be a key parameter impacting dynamic enhancement, with the FDO enhancement of higher loading molybdena samples converging toward that of the vanadia catalyst. The preferential depletion of chemisorbed oxygens is revealed to be a key determinant of the extent of dynamic enhancement, with an asymmetry in modeled O * /O L ratios under dynamic conditions relative to SS ones helping rationalize the effect that modulation frequency has on FDO enhancement. Collectively, the results presented here establish a quantitative, molecular-level basis for dynamic enhancement noted during the ODH of ethane, and point to considerations relating to the reactivity of chemisorbed and lattice oxygens as well as their dynamic and steady state ratios as levers for mitigating side-product formation through FDO.

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