Reactions at the gas-phase-porous-solid interface: Mechanisms and effects of surface geometry around room temperature

The luminescence quenching of Ru(bpy)²⁺₃ by molecular oxygen on a porous silica and controlled porous glass was studied at the 253-353 K temperature range. The reaction was observed to take place by a mixture of an Eley-Rideal (ER) and a Langmuir-Hinshelwood mechanism. The relative contribution of the two mechanisms was calculated and the ER component was found to dominate at higher temperatures. The lack of effect of the average pore diameter (apd) on the rate of the quenching reaction supports our contention that the Knudsen diffusion controlled reaction theory developed elsewhere is incorrect. In addition we show that, for porous solids, diffusion controlled reaction theory is not applicable in principle below the Knudsen regime.