ADSORPTION and desorption are basic steps in catalytic reaction. The desorbing rate under a gas phase is faster than that in vacuum. This phenomenon has been studied extensively since its discovery. Study of this phenomenon will help understand the “pressure gap” in the field of catalytic research. ADSORPTION and desorption are basic steps in catalytic reaction. The desorbing rate under a gas phase is faster than that in vacuum. This phenomenon has been studied extensively since its discovery. Study of this phenomenon will help understand the “pressure gap” in the field of catalytic research.