利用密度泛函理論計算探討甲醇氧化反應在白金、鈀與其合金上的反應機構
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2017
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在本篇論文中，藉由密度泛函理論(DFT)研究Pt(100)、Pd(100)以及其合金上的甲醇氧化反應(MOR)的機理。我們研究了甲醇氧化化反應在Pt、Pd與以3:1、1:1、1:3比例混成的合金上的催化活性和穩定性。首先我們計算甲醇與其裂解產物和氧化反應在(100)催化表面上吸附能，然後在計算反應能與反應的活化能障以及能勢面(PES)。Pt(100)上的可行路徑遵循CH₃OH￫CH₃O￫CH₂O￫CHO￫CO。分解反應有較低的能量，意謂著更好的活性，但也導致CO毒化Pt催化劑。另一方面，甲醇在Pd(100)最初優先斷裂C-H鍵並遵循CH₃OH￫CH₂OH￫CHOH￫CHO，CHO的中間體利於氧化反應形成CHOOH，而非利於解離反應在Pd(100)上形成毒化的CO，因此有效提升CO耐受性。在合金的計算中，相對於單金屬，Pt加入Pd能夠改善MOR的活性使反應有更低的能障。此外，加入Pd能夠改變催化路徑從甲醇分解變成氧化。而Pt/Pd為1比1的合金顯示出最佳的催化活性及穩定性。
In this thesis, the mechanism of methanol oxidation reaction (MOR) on Pt(100), Pd(100) and their alloys were investigated by density functional theory (DFT). We examined the catalytic activity and stability of MOR on Pt, Pd and the alloys with the ratio of 3:1, 1:1, 1:3. Our work started with the calculation of the adsorption energy of methanol and its fragments in the decomposition and oxidation reactions on the (100) surface of catalysts; then the reaction energy and activity barrier of the reactions and potential energy surface (PES). The energetically feasible pathway on Pt(100) follows CH₃OH￫CH₃O￫CH₂O￫CHO￫CO. The decomposition reaction has lower energetics, implying the better activity, but results the detrimental CO poisoning Pt catalyst. Methanol on Pd(100), on the other hand, preferentially breaks C-H bond initially and follows CH₃OH￫CH₂OH￫CHOH￫CHO. The intermediate of CHO favors the oxidation reaction forming CHOOH than the dissociation reaction forming the poisoning CO on Pd(100); thus efficiently enhance the CO tolerance. In the calculations of alloys, the reactions have lower barriers than those on Pt with Pd to improve MOR activity. Also, the addition of Pd can change the catalytic pathway from methanol decomposition to oxidation As a result, the alloy with Pt/Pd = 1/1 shows the best catalytic activity and stability.
In this thesis, the mechanism of methanol oxidation reaction (MOR) on Pt(100), Pd(100) and their alloys were investigated by density functional theory (DFT). We examined the catalytic activity and stability of MOR on Pt, Pd and the alloys with the ratio of 3:1, 1:1, 1:3. Our work started with the calculation of the adsorption energy of methanol and its fragments in the decomposition and oxidation reactions on the (100) surface of catalysts; then the reaction energy and activity barrier of the reactions and potential energy surface (PES). The energetically feasible pathway on Pt(100) follows CH₃OH￫CH₃O￫CH₂O￫CHO￫CO. The decomposition reaction has lower energetics, implying the better activity, but results the detrimental CO poisoning Pt catalyst. Methanol on Pd(100), on the other hand, preferentially breaks C-H bond initially and follows CH₃OH￫CH₂OH￫CHOH￫CHO. The intermediate of CHO favors the oxidation reaction forming CHOOH than the dissociation reaction forming the poisoning CO on Pd(100); thus efficiently enhance the CO tolerance. In the calculations of alloys, the reactions have lower barriers than those on Pt with Pd to improve MOR activity. Also, the addition of Pd can change the catalytic pathway from methanol decomposition to oxidation As a result, the alloy with Pt/Pd = 1/1 shows the best catalytic activity and stability.
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密度泛函理論, 甲醇氧化反應, Pt(100), Pd(100), PtPd合金, density functional theory, methanol oxidation reaction, Pt(100), Pd(100), PtPd alloys