Prediction of experimental methanol decomposition rates on platinum from first principles

摘要

A microkinetic model for methanol decomposition on platinum is presented.The model incorporates competitive decomposition pathways,beginning with both O- H and C-H bond scission in methanol,and uses results from density functional theory(DFT)calculations [Greeley and Mavrikakis.J.Am.Chem.Soc.124(2002)7193.Greeley and Mavrikakis.J.Am.Chem.Soc.126(2004)3910].Results from reaction kinetics experiments show that the rate of H_2 production increases with increasing temperature and methanol concentration in the feed and is only nominally affected by the presence of CO or H_2 with methanol.The model,based on the values of binding energies,pre-exponential factors and activation energy barriers derived from first principles calculations,accurately predicts experimental reaction rates and orders.The model also gives insight into the most favorable reaction pathway,the rate-limiting step,the apparent activation energy,coverages,and the effects of pressure.It is found that the pathway beginning with the C-H bond scission(CH_3OH -> H_2COH -> HCOH -> CO)is dominant compared with the path beginning with O-H bond scission.The cleavage of the first C- H bond in methanol is the rate-controlling step.The surface is highly poisoned by CO,whereas COH appears to be a spectator species.