Mechanism of Activation of Water in Steam Dealkylation of Alkylbenzene over Rh/MgWO₄ C atalyst

Abstract

The mechanism of activation of water in the steam dealkylation of in-xylene was investigated by the use of a pulse reactor. In the activation of H₂O over Rh/Al₂O₈ catalyst the formation of active surface OH groups occurs. It was demonstrated that the mechanism of activation of H₂O over Rh/MWO ₄ (M=M g, Ca and Sr) differs from that over Rh/Al₂O₃ catalyst. Namely, the activation over Rh/MgWO₄ brings about the cleavage of H₂O molecule into gaseous H₂ and surface oxygen ato m. The high reactivity of this surface oxygen on Rh/MgWO₄ catalyst seemed to be responsible for the high steam-dealkylating activity of this catalyst. Thus, the mechanism of activation of H₂O in the steam dealkylation of alkylbenzene over Rh/MWO₄ catalyst is well expressed by the following two equations:
1/dx MWO₄+ R → 1/dx MO + 1/dx W O_3-dx RO (a)
1/dx MO + 1/dx WO_3-dx + H₂O → 1/dx MWO₄ + H₂ (b)
R: Intermediate species for demethylattion on rhodium.