CO2 and NH3 interaction with ZnO surface: An AM1 study

摘要

The ZnO surfaces have important catalytic activities. The H-2/CO/CO2 mixture plays an important role in the synthesis of methanol. However, CO2 interaction is known to inhibit the CO interaction for methanol synthesis, protecting the surface against complete reduction or formate formation, but may also be used to promote the methanol synthesis on the Cu/ZnO catalyst. The NH3 adsorption is important to connect the surface acidic activity. The CO interaction is complex, and the NH3 interaction could help to understand the CO adsorption, since the Lewis basis NH3 is known to adsorb physically and chemically on the ZnO surfaces bonding nitrogen to the unsaturated zinc cation. The semi-empirical AM1 method, as well as the (ZnO)(22) and (ZnO)(60) large cluster models were used to study the interaction of CO2 and NH3 molecules with ZnO surfaces. The adsorbed molecules were fully optimized. We have found three different configurations for the CO2 interaction. The binding energy calculated for the CO2 adsorption is greater than the calculated value for the CO and NH3 interaction using the AM1 method. The C-O bond length increases upon adsorption. The NH3 molecule adsorbs dissociatively on ZnO surfaces, forming the amide and hydroxyl species. The charge-transfer process, density of states, and self-consistent field orbital energies are also investigated. (C) 1998 John Wiley & Sons, Inc. [References: 44]