TY - JOUR
T1 - High-Pressure oxidative coupling of methane on alkali metal catalyst – Microkinetic analysis and operando thermal visualization
AU - Yu, Yuhang
AU - Obata, Keisuke
AU - Movick, William J.
AU - Yoshida, Shintaro
AU - Palomo, Jose
AU - Lundin, Sean Thomas B.
AU - Urakawa, Atsushi
AU - Sarathy, S. Mani
AU - Takanabe, Kazuhiro
PY - 2024
Y1 - 2024
N2 - To introduce promotional H2O effects for both CH4 rate and C2 selectivity, the OH radical formation, catalyzed through H2O activation with O2 surface species, was critical for modeling selective Mn-K2WO4/SiO2 catalysts. Based on our reported experimental evidence, which demonstrates the formation of H2O2 through surface alkali peroxide intermediate, the elementary reactions that account for the OH-mediated pathway were added into the microkinetic model. The advanced model adeptly replicated the promotional H2O effects on both OCM rate and selectivity. The data from a low-pressure microkinetic study were treated isothermally, and extended for near-industrially relevant pressures up to 901 kPa. Thermal visualization using an infrared camera found substantial temperature increases at undiluted high-pressure conditions which caused C2 selectivity to drop significantly. When the furnace temperatures were decreased after ignition, side reactions after O2 depletion (e.g., hydrocarbon reforming) were suppressed, obtaining 13.7 (11.8) % yields at 19.9 % CH4 conversion with 68.6 (59.1) % selectivities for C2-4 (C2) at 901 kPa. The temperature was found to be the determining factor of C2 yield which was perturbed by varying space velocity or CH4/O2 ratios. The optimum temperature for high-pressure conditions was predicted as 885 °C at 901 kPa. The study provides mechanistic and industrially relevant understandings for further OCM catalyst design and system application.
AB - To introduce promotional H2O effects for both CH4 rate and C2 selectivity, the OH radical formation, catalyzed through H2O activation with O2 surface species, was critical for modeling selective Mn-K2WO4/SiO2 catalysts. Based on our reported experimental evidence, which demonstrates the formation of H2O2 through surface alkali peroxide intermediate, the elementary reactions that account for the OH-mediated pathway were added into the microkinetic model. The advanced model adeptly replicated the promotional H2O effects on both OCM rate and selectivity. The data from a low-pressure microkinetic study were treated isothermally, and extended for near-industrially relevant pressures up to 901 kPa. Thermal visualization using an infrared camera found substantial temperature increases at undiluted high-pressure conditions which caused C2 selectivity to drop significantly. When the furnace temperatures were decreased after ignition, side reactions after O2 depletion (e.g., hydrocarbon reforming) were suppressed, obtaining 13.7 (11.8) % yields at 19.9 % CH4 conversion with 68.6 (59.1) % selectivities for C2-4 (C2) at 901 kPa. The temperature was found to be the determining factor of C2 yield which was perturbed by varying space velocity or CH4/O2 ratios. The optimum temperature for high-pressure conditions was predicted as 885 °C at 901 kPa. The study provides mechanistic and industrially relevant understandings for further OCM catalyst design and system application.
KW - High pressure
KW - Microkinetic analysis
KW - OCM mechanisms
KW - OH-mediated pathway
KW - Operando thermal visualization
UR - http://www.scopus.com/inward/record.url?scp=85187797764&partnerID=8YFLogxK
U2 - 10.1016/j.jcat.2024.115414
DO - 10.1016/j.jcat.2024.115414
M3 - Article
AN - SCOPUS:85187797764
SN - 0021-9517
VL - 432
JO - Journal of Catalysis
JF - Journal of Catalysis
M1 - 115414
ER -