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47. Transient microstructural behavior of methanol/n-heptane droplets under supercritical conditions.

Author

Wang, Zhanyuan, Zhao, Wanhui, Wei, Haiqiao, Shu, Gequn, and Zhou, Lei

Subjects
SUPERCRITICAL fluids, ROCKET engines, MOLECULAR dynamics, FLUIDS, LIQUIDS
Abstract

Supercritical fluids exist widely in nature and have enduringly attracted scientific and industrial interest. In power systems like liquid rocket engines, fluids undergo the trans-critical process transferred from the subcritical state to the supercritical state, and the phase change process exhibits different features distinguished from subcritical evaporation. In this work, we conducted a series of molecular dynamics studies on the behavior of methanol (MeOH), n-heptane (C7), and binary C7/MeOH droplets under supercritical nitrogen environments. The emphasis is on clarifying the transient characteristics and physical origins of the trans-critical evolution of droplets. During the trans-critical process, droplets are found to experience an unstable period without a spherical shape, where the droplet diameter no longer decreases, violating the traditional d2-law rule. The occurrence of nonspherical droplets is related to the microstructural behavior of trans-critical droplets. Two types of microscopic structures within the droplet are identified: large-scale thermally induced clusters for long-chain C7 and hydrogen-bond connected network-like structures for MeOH, which contains hydroxyl (–OH) groups. Based on these findings, the mechanism behind the evolution of trans-critical droplets is illustrated. Finally, we determine the boundary of ambient conditions in the form of dimensionless expressions T r − 1 = a (p r − 1) − b , which dictate whether droplets can maintain a spherical shape during the trans-critical process. [ABSTRACT FROM AUTHOR]

Published
2024
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48. H-assisted CO2 dissociation on PdnPt(4−n)/In2O3 catalysts: a density functional theory study.

Author

Wang, Xiaowen, Pan, Jiaying, Wei, Haiqiao, Li, Wenjia, Zhao, Jun, and Hu, Zhen

Abstract

CO2 hydrogenation into valuable chemical compounds can effectively address the issues of greenhouse gas emissions and energy scarcity. The activation and dissociation processes of CO2 are crucial for its reduction reactions, but the effects of *H adatoms on the C–O cleavage are still confusing. This study investigates the H-assisted CO2 dissociation pathways on the PdnPt(4−n)/In2O3 (n = 0–4) catalysts via DFT calculation. Initially, the adsorption properties of *H2, *COOH, and *HCOO species are calculated. Then, two H-assisted CO2 dissociation channels, i.e., *CO2 + *H → *COOH → *CO + *OH and *CO2 + *H → *HCOO → *CHO + *O, are studied. Results show that Pt and Pd promote the CO2 hydrogenation and C–O bond cleavage reactions, respectively. In comparison to CO2 direct dissociation, the COOH-mediated and HCOO-mediated channels facilitate and impede the C–O bond cleavage, respectively. Overall, the Pd3Pt/In2O3 constituent is suggested for the H-assisted CO2 dissociation reaction. The electronic effects of the PdnPt(4−n) bimetals adjust the stabilities of the intermediates and barriers of the elementary steps, and the interactions between PdnPt(4−n) and In2O3 provide extra sites for the adsorbates and reaction steps. This study reveals the effects of *H on the C–O bond dissociation processes and provides useful insight into designing PdPt/In2O3 catalysts for CO2 hydrogenation reactions. [ABSTRACT FROM AUTHOR]

Published
2024
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