Effect of ceria and zirconia supports on NO reduction over platinum-group metal catalysts: A DFT study with comparative experiments
Effect of ceria and zirconia supports on NO reduction over platinum-group metal catalysts: A DFT study with comparative experiments
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DOI：
10.1016/j.cattod.2018.07.023
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发表时间：
2019-07-15
期刊：
影响因子：
5.3
通讯作者：
Okumura, Mitsutaka
中科院分区：
文献类型：
--
作者：
Koga, Hiroaki;Hayashi, Akihide;Okumura, Mitsutaka
在分子水平上理解支撑效应对于改进铂族金属（PGM）三元催化剂（TWC）的设计至关重要。作为第一步，我们对CeO2（111）和ZrO2（111）负载的四面体M-4簇（M = Pt， Pd或Rh）进行了密度泛函理论（DFT）计算，并研究了它们对NO的吸附和还原活性。我们发现M-4簇在氧化铈上带正电，而在氧化锆上则接近中性。用氧化锆代替氧化铈对NO吸附的位置偏好影响不大。NO倾向于从M-4/ZrO2中比从M-4/CeO2中获得更多的负电荷。CO与吸附的NO的反应不表现出很强的载体依赖性。相比之下，NO在金属/氧化物界面的解离表现出强烈的载体依赖性，通过将氧化铈换成氧化锆，过渡态（TS）降低了0.7-1.1 eV。这种降低是因为ZrO2中的Zr比CeO2中的Ce携带更多的正电荷，与NO的O端相互作用更强，促进了解离。计算得到的NO解离TS能（以及解离吸附能）与我们比较TWC实验中得到的NO还原活性密切相关。因此，在氧化物载体的帮助下，催化剂结合N和O的能力是PGM催化剂还原no活性的关键。
Understanding support effects at the molecular level is vital for improving the design of the platinum-group metal (PGM) three-way catalyst (TWC). As a first step, we performed density functional theory (DFT) calculations for tetrahedral M-4 clusters (M = Pt, Pd, or Rh) supported on CeO2(111) and ZrO2(111) and examined their activity toward NO adsorption and reduction. We found that the M-4 clusters are positively charged on ceria but close to neutral on zirconia. The site preference of NO adsorption is not affected much by changing ceria for zirconia. NO tends to gain slightly more negative charge from M-4/ZrO2 than from M-4/CeO2. The reaction of CO with adsorbed NO does not exhibit strong support dependence. In contrast, NO dissociation at the metal/oxide interface exhibits strong support dependence, with the transition state (TS) lowered by 0.7-1.1 eV by changing ceria for zirconia. This lowering occurs because Zr in ZrO2, carrying more positive charge than Ce in CeO2, interacts more strongly with the O end of NO to promote dissociation. The calculated TS energy for NO dissociation (as well as the dissociative adsorption energy) is strongly correlated with the NO-reduction activity obtained in our comparative TWC experiments. Thus, the ability of a catalyst to bind N and O, with the help of the oxide support, is key for the NO-reduction activity of PGM catalysts.