Density Functional Theory Study Of The Mechanism Of NO Decomposition Over Rh/SiO₂Catalysts

Nowadays, nitrogen oxides （NOx） has become main atmospheric pollutants whichseriously endanger human’s health. Emissions of nitrogen oxides grow rapidly in recentyears, causing a serious deterioration of our ecological and living environment. Thus,much stress is laid on research to take effective measure of denitration and eliminate thepollution of nitrogen oxides. As the main component of nitrogen oxides, NO is hard toeliminate and considered to be a general concern of the current air pollution problem inthe field of atmospheric pollution control.Studies on the mechanism of NO decomposition are spring up in recent years. Dueto its simple process and non-secondary pollution, direct decomposition process wasconsidered as an ideal procedure to eliminate nitrogen oxides. The transition metalelement, Rh, as previous reported, has better catalytic performance of NOdecomposition than other transition metals （Pt, Pd et al）. But some disadvantage of Rh,such as higher cost and small specific surface area, restrain its development and industryuse. Therefore, we consider that Rh metal atoms are doped into SiO₂, which is acommon metal carrier, to discuss the possibility of NO catalytic decomposition based onthe geometric and electron structure calculations by density functional theory （DFT）.1) In this paper,4-Si eight member ring and3-Si six member ring composed byfour silicon atoms （4-SiO₂） and three silicon atoms （3-SiO₂） are chosen as the carriermodel of catalysts. The results show that4-silicon ring and3-silicon ring clusters havemore excellent stability than six or eight carbon ring system. Thus, such clusters couldsimulate the catalyst carrier SiO₂well and catalyze the decomposition of NO with highreactive Rh atom.2) The electrons in5s and4d orbitals of Rh jump to5p and5d orbitals, or even to6s orbitals, which explain the high reactivity of Rh atom. Therefore,4-silicon ring and3-silicon ring to Rh/SiO₂catalyst clusters are chosen in the mechanism study of NOcatalytic decomposition.3) The mechanism of NO catalytic decomposition are divided into three steps.Firstly, N*or O*terminal is adsorbed to the surface of Rh/SiO₂catalyst. Then, N*terminal of another NO molecule react with the N atom of former molecule, formingN-N bond along with N₂O and O*. Subsequently, either O*react with N₂O and form N₂and O₂, or N₂O is directly absorbed to the surface of the catalyst with the formation of N₂.4) Results show that N₂O is a key intermediate in the process of NO decomposition.The above theoretical research proves that the catalyst cluster of transition metal Rhloaded by SiO₂could be chosen as catalytic material with unique structure, which hasexcellent catalytic and antitoxic properties. Besides, instead of metal surface model orelemental metal cluster model, this material can save cost and improve catalyticproperties by increasing surface area when used in theoretical study of NOdecomposition.