DFT Study Of Adsorption System On MoO3(010)Surface

In the recent year, the elimination of nitrogen oxides from automobile exhaust emissions is becoming important research subject in the field of environmental catalysis, as the harm of automobile exhaust emissions is an increasing problem. Based on first principle, in this work the adsorption of NH3、 NO、 H2O、 O2on MoO3(010) surface and the influences of different OT vacancies have been investigated by quantum chemistry calculations, the results are listed as follow:(1) NH3can adsorb on the OT vacancy of MoO3(010) surface as N-down not H-down. After adsorption NH3loses electrons and is activated slightly, Mo atom receives electrons and is reduced. The second OT vacancy around seems nothing to the optimized configurations, but affects adsorption energy, quantity of electron transfer and the reduction degree of Mo atom:the diagonal OT vacancies around strengthen the NH3adsorption stabilization but the adjacent OT vacancies around weaken the adsorption stabilization; both of the diagonal OT vacancies and the adjacent OT vacancies reduce the quantity of electron transfer; both of the diagonal OT vacancies and the adjacent OT vacancies weaken the reduction degree of Mo atom, but the effect of adjacent OT vacancies is stronger than that of diagonal OT vacancies. In addition, NH3adsorption on Lewis acid site is more stable than that on bronsted acid site.(2) NO can adsorb on the OT vacancy of MoO3(010) surface both as O-down and N-down, but the adsorption stabilization as O-down is weaker than that as N-down, which is owing to the stronger ability to receive electron and lose give electron of N atom than that of O atom for NO molecule. NO adsorption as N-down on the OT vacancy is spontaneous chemical adsorption, NO receives electrons and is activated while Mo atom receives electrons and is reduced. The second OT vacancy around strengthen the adsorption stabilization, increase the reduction degree of Mo atom, greater the quantity of electron transfer, here the effect of diagonal OT vacancies is greater than that of adjacent OT vacancies. In the same time the NO is activated further and the effect for both diagonal Ot vacancies and adjacent OT vacancies is equal. The more quantity of electron transfer is, the stronger adsorption stabilization is, which suggests that electron contribution is key factor for NO adsorption on the OT vacancy of MoO3(010) surface as N-down.(3) H2O can adsorb on the OT vacancy of MoO3(010) surface as O-down not H-down. H2O adsorption as O-down on the OT vacancy is spontaneous chemical adsorption, H2O loses electrons and is activated while Mo atom lose electrons and is oxidated. The second OT vacancy around reduce the adsorption stabilization and the quantity of electron transfer, in the same time H2O is activated further. A linear correlation is obvious between adsorption stabilization, quantity of electron transfer and the activation degree of H2O. The stronger adsorption stabilization is, the less quantity of electron transfer is and the higher activation degree is, which suggests that electron contribution is important for H2O adsorption on the OT vacancy of MoO3(010) surface.(4) O2adsorption on the OT vacancy vertically is spontaneous chemical adsorption, O2receives electrons and is activated while Mo atom lose electrons and is oxidated. The second OT vacancy around seems nothing to adsorption stabilization, but affects charge distribution: adding quantity of electron transfer, increasing the oxidation degree of Mo atom and activating O2further, here the effect of adjacent OT vacancies is greater than that of diagonal OT vacancies.(5) All adsorbates of NH3) NO, H2O, O2can adsorb on the OT vacancy of MoO3(010) surface stably, which shows that Mo atom is coordinated unsaturated and have great reactive activation owing to the presence of OT vacancy. NO adsorption as N-down is the most stable. There is competition between NH3adsorption and O2adsorption but O2 adsorption is more stable slightly. H2O adsorption is the least stable.(6) When NH3, NO, H2O, O2adsorb on the OT vacancy of MoO3(010) surface stably, the different adsorbate leads to different charge type and charge quantity. Refering to NO and O2adsorption the adsorbate takes with negative charges, which is caused by the great electronegativity of adsorbate atoms and the strong ability to receive electron of adsorbate. For NH3and H2O adsorption, the adsorbate takes with positive charges. The charge change of Mo atom depends on the atom type bonding to Mo atom. Refering to NH3and NO adsorption as N-down Mo-N bond is formed, Mo atom receives electron and is reduced. For H2O, O2and NO adsorption as O-down Mo-O bond is formed, Mo atom loses electron and is oxidated.