Promoting mechanism of sulfur addition in catalytic dehydrogenation of isobutane over Mo/MgAl2O4 catalysts
•Mo/MgAl2O4 catalysts with sulfur addition are efficient in dehydrogenation.•MoS2 formed during the induction period probably constitutes the active phase.•MoS2 formation requires treatment of appropriate reducing gases.•Mo/MgAl2O4 catalysts sulfided by H2S/N2 exhibit a high initial activity.•Loss of sulfur is the main reason for irreversible deactivation of the catalysts.
Mo/MgAl2O4 catalysts with sulfur addition were verified to exhibit excellent performance in catalytic dehydrogenation of isobutane, which could yield up to 56.3 wt% isobutene at 560 °C. Catalyst characterization and activity test results jointly revealed that MoS2 formed during the induction period probably constituted the active phase for dehydrogenation. As to the formation of MoS2, treatment with appropriate reducing gases (e.g., CO) was required. However, in the atmosphere of H2, molybdate species were partially reduced to MoO2, which inhibited the formation of MoS2. Furthermore, Mo/MgAl2O4 catalysts sulfided by H2S/N2 exhibited a high initial activity, further confirming that MoS2 species were indispensable to dehydrogenation reaction. Stability evaluation of the Mo/MgAl2O4-S catalyst indicated that the catalytic activity decreased slightly within six reaction-regeneration cycles. The irreversible deactivation probably resulted from the obvious sulfur loss. Therefore, appropriate measures to replenish sulfur should be carried out in future commercial application.
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Journal: Applied Catalysis A: General - Volume 478, 20 May 2014, Pages 71–80