王艷芹

摘要：運(yùn)用基于密度泛函理論的第一性原理計(jì)算研究單個(gè)CO分子與含有氧空穴的二氧化鈰的（110）及（111）表面晶格氧的反應(yīng)，深入探討了氧空穴對CeO2（110）及（111）表面晶格氧催化氧化CO活性的影響，提出了CO分子在二氧化鈰表面存在缺陷時(shí)與晶格氧的反應(yīng)機(jī)理。 通過計(jì)算CO分子在缺陷CeO2 （110）與（111）表面吸附的吸附能發(fā)現(xiàn)，CO分子在缺陷二氧化鈰（110）與（111）的吸附與干凈表面的結(jié)果大致相同，但是與CO分子在干凈二氧化鈰（110）表面反應(yīng)的能壘相比，一部分的氧原子由于氧空穴的存在，與CO反應(yīng)的能壘降低，對CO反應(yīng)的活性增強(qiáng)；在缺陷CeO2 （111）表面，晶格氧與 CO的反應(yīng)能力也有所增強(qiáng)。CO與缺陷CeO2 （110）與（111）表面的晶格氧原子反應(yīng)后，會(huì)生成一個(gè)較穩(wěn)定吸附CO2物種的中間態(tài)，該物種的繼續(xù)反應(yīng)途徑有兩種：（1）與其它晶格氧反應(yīng)生成碳酸鹽；（2）直接脫附變?yōu)闅庀嗟腃O2分子。通過比較反應(yīng)能壘發(fā)現(xiàn)，CO在缺陷CeO2的（110）及（111）表面生成碳酸鹽比其在干凈表面生成碳酸鹽的難度增加。另外形成中間態(tài)CO2后，由于周圍氧原子的缺少，缺陷CeO2 （110）與（111）表面上的中間態(tài)脫附形成氣相CO2分子的趨勢也比相應(yīng)的干凈表面上要強(qiáng)。綜上可以得出，當(dāng)氧空穴存在時(shí)，二氧化鈰表面晶格氧與CO的反應(yīng)更容易，但生成碳酸鹽更難。同時(shí)計(jì)算結(jié)果也表明，稀土元素特有的局域化的Ce的4f軌道/電子在通過抑制局域電子的進(jìn)一步發(fā)生來調(diào)控表面反應(yīng)的難易程度中仍然發(fā)揮了關(guān)鍵作用。

關(guān)鍵詞：二氧化鈰；氧空穴；CO催化氧化；局域電子

Abstract：Density functional theory calculations corrected by on-site Coulomb interaction have been conducted to illuminate the effect of O vacancies on the surface reactivities toward direct CO oxidation at CeO2（110） and （111）. CO adsorption at and further reaction with various surface O at the vacancy were systematically calculated， and extensive geometric and electronic analyses were also performed to understand the calculation results. It has been shown that though the existence of O vacancy can reduce the activities of neighboring O as the barriers of elementary steps are generally higher than those at stoichiometric surfaces， the relative preference for CO2 desorption is also increased due to the missing of nearby O for carbonate formation. Moreover， our calculation results also showed that the characteristic localized 4f orbitals/electrons of Ce still play the key role in determining the surface reactivities as the vacancy induced localized electrons can hinder their further occurrence and the corresponding reactions.

Keywords：Cerium dioxide； Oxygen vacancy； CO oxidation； Electron localization