NO Oxidation on Platinum Group Metals Oxides: First Principles Calculations Combined with Microkinetic Analysis

摘要

By combining density functional theory calculation and microkinetic analysis, NO oxidation on the platinum group metal oxides (PtO2, IrO2, OsO2) is investigated, aiming at shedding light on the activities of metal oxides and exploring the activity variations of metal oxides compared to their corresponding metals. A microkinetic model, taking into account the possible low diffusion of surface species on metal oxide surfaces, is proposed for NO oxidation. The resultant turnover frequencies of NO oxidation show that under the typical experimental condition, T= 600 K,p_(O2) = 0.1 atm,p_(NO) = 3×10~(-4) atm, p_(NO2) = 1.7×10~(-4)atm; (i)IrO2(110) exhibits higher activity than PtO2(110) and OsO2(110), and (ii) compared to the corresponding metallic Pt, Ir, and Os, the activity of PtO2 to catalyze NO oxidation is lower, but interestingly IrO2 and OsO2 exhibit higher activities. The reasons for the activity differences between the metals and oxides are addressed. Moreover, other possible reaction pathways of NO oxidation oh PtO2(110), involving O2 molecule (NO + O2-> OONO) and lattice bridge-O_(2c), are also found to give low activities. The origin of the Pt catalyst deactivation is also discussed.