CH_3O和CO在Pd(111)表面偶联反应机理的理论研究

Theoretical Studies on the Reaction Mechanisms of Methoxy Group and Carbon Monoxide over the Surfaces of Pd( 111)

采用DMol3程序包中的GGA-PW91方法,结合周期平板模型,对CH3O和CO在Pd(111)表面的反应进行了系统研究.计算结果表明,吸附在Pd(111)表面顶位上的CO分子中C原子所带正电荷最多,容易与亲核试剂反应,化学吸附能稍低,有利于在表面上移动发生亲电插入反应;CH3O在Pd(111)表面fcc穴位吸附稳定,O原子上所带的负电荷较多,易被亲电试剂进攻.过渡态搜索表明,Pd(111)表面顶位上的CO与fcc穴位上CH3O反应生成CH3OOC的为放热反应,反应能垒较低,有利于偶联反应的进行.

The possible reaction mechanisms of CH3O and CO on Pd（111） surface were studied with GGA-PW91 in the DMol3 software package based on density functional theory（ DFT） . The relative calculated results indicate that the equilibrium state of CH3 O adsorbed at fcc position is the most stable configuration with more negative charges on O atom, be apt to be attacked by electrophilic reagents. While, CO adsorbed on top site perpendicularly by the interaction between C atom and Pd surface has lower adsorption energy, and its carbon atoms will possess more positive charges, which avail the migration for electrophilic insert reaction. Compared with CO on the bridge and hollow sites, CO adsorbed on the top sites is the optimistical configuration for the coupled reaction yielding CH3 OOC, which may be attributed to the mobility and electrophilcity of CO.