Structures and reactivities of the CeO2/Pt(111)reverse catalyst:A DFT+U study

For heterogeneous catalysts,the build-up of interface contacts can influence markedly their activities.Being different from the conventional supported metal/oxide catalysts,the reverse type of oxide/metal structures,e.g.the ceria/Pt composite,have emerged as novel catalytic materials in many fields.However,it remains challenging to determine the optimal interface structure and/or the metal-oxide synergistic effect that can boost catalytic activities.In this work,we conducted density functional theory calculations with on-site Coulomb interaction correction to determine the optimal structures and investigate the physical as well as catalytic properties of various Ce O2/Pt(111)composites containing Ce O2(111)monolayer,bilayer,and trilayer at Pt(111).We found that the interaction strength between Ce O2(111)and Pt(111)substrate first reduces as the ceria slab grows from monolayer to bilayer,and then largely gets converged when the trilayer occurs.Such trend was well rationalized by analyzing the number and distances of O–Pt bonds at the interface.Calculated Bader charges uncovered the significant charge redistribution occurring around the interface,whereas the net electron transfer across the interface is non-significant and decreases as ceria thickness increases.Moreover,comparative calculations on oxygen vacancy formation energies clarified that oxygen removal can be promoted on the Ce O2/Pt(111)composites,especially at the interface.We finally employed CO oxidation as a model reaction to probe the surface reactivity,and determined an intrinsic activity order of monolayer Ce O2(111)>monolayer Ce O2(111)/Pt(111)>regular Ce O2(111).More importantly,we emphasized the significant role of the moderate ceria-Pt interaction at the interface that endows the Ce O2/Pt reverse catalyst both good thermostability and high catalytic activity.The monolayer Ce O2(111)/Pt(111)composite was theoretically predicted highly efficient for catalyzing CO oxidation.

Identification of relevant active sites and a mechanism study for reverse water gas shift reaction over Pt/CeO_2 catalysts

Reverse water gas shift (RWGS) reaction can serve as a pivotal stage in the CO2 conversion processes, which is vital for the utilization of CO2. In this study, RWGS reaction was performed over Pt/CeO2 catalysts at the temperature range of 200-500 degrees C under ambient pressure. Compared with pure CeO2, Pt/CeO2 catalysts exhibited superior RWGS activity at lower reaction temperature. Meanwhile, the calculated TOF and E-a values are approximately the same over these Pt/CeO2 catalysts pretreated under various calcination conditions, indicating that the RWGS reaction is not affected by the morphologies of anchored Pt nanoparticles or the primary crystallinity of CeO2. TPR and XPS results indicated that the incorporation of Pt promoted the reducibility of CeO2 support and remarkably increased the content of Ce 3 + sites on the catalyst surface. Furthermore, the CO TPSR-MS signal under the condition of pure CO2 flow over Pt/CeO 2 catalyst is far lower than that under the condition of adsorbed CO2 with H-2 -assisted flow, revealing that CO2 molecules adsorbed on Ce3+ active sites have difficult in generating CO directly. Meanwhile, the adsorbed CO2 with the assistance of H-2 can form formate species easily over Ce3+ active sites and then decompose into Ce3+-CO species for CO production, which was identified by in-situ FTIR. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.

负载型催化剂Pt-γ-Al_2O_3-CeO_2的合成和活性研究

模拟贫燃机车尾气条件下 ,比较浸渍法和共沉淀法制备的 Pt-γ- Al2 O3- Ce O2 纳米催化剂对 NO的催化还原活性 .结果表明 ,采用浸渍法所得的样品催化活性最高 ,使 NO的转化率达83% ;而共沉淀法所得的样品抗烧结性能好 ,活性温度范围宽 .利用 XRD,BET,TEM等手段对活性好的样品进行了一系列分析和比较 .

Interface-controlled synthesis of CeO_2(111) and CeO_2(100) and their structural transition on Pt(111)

Ceria-based catalytic materials are known for their crystal-face-dependent catalytic properties.To obtain a molecular-level understanding of their surface chemistry,controlled synthesis of ceria with well-defined surface structures is required.We have thus studied the growth of CeOx nanostructures(NSs)and thin films on Pt(111).The strong metal-oxide interaction has often been invoked to explain catalytic processes over the Pt/CeOx catalysts.However,the Pt-CeOx interaction has not been understood at the atomic level.We show here that the interfacial interaction between Pt and ceria could indeed affect the surface structures of ceria,which could subsequently determine their catalytic chemistry.While ceria on Pt(111)typically exposes the CeO2(111)surface,we found that the structures of ceria layers with a thickness of three layers or less are highly dynamic and dependent on the annealing temperatures,owing to the electronic interaction between Pt and CeOx.A two-step kinetically limited growth procedure was used to prepare the ceria film that fully covers the Pt(111)substrate.For a ceria film of^3–4 monolayer(ML)thickness on Pt(111),annealing in ultrahigh vacuum(UHV)at 1000 K results in a surface of CeO2(100),stabilized by a c-Ce2O3(100)buffer layer.Further oxidation at 900 K transforms the surface of the CeO2(100)thin film into a hexagonal CeO2(111)surface.

微量铂与铑对Co/CeO_2催化剂结构与性能的影响

采用等量分步浸渍法先后将Ｃｏ与贵金属组份浸于ＣｅＯ２上，经５００℃焙烧２ｈ，４５０℃氢气还原１ｈ制得Ｃｏ－Ｐｔ／ＣｅＯ２和Ｃｏ－Ｒｈ／ＣｅＯ２催化剂。活性测试结果表明，贵金属与Ｃｏ之间具有催化协同效应。对ＣＯ氧化，Ｐｔ与Ｃｏ的协同效应较显著，而对富氧条件下ＣＨ４选择还原ＮＯ，Ｒｈ与Ｃｏ的协同效应更为明显。ＸＰＳ和ＥＸＡＦＳ结果一致表明，经Ｈ２还原后，样品Ｃｏ／ＣｅＯ２、Ｃｏ－Ｐｔ／ＣｅＯ２和Ｃｏ－Ｒｈ／ＣｅＯ２中Ｃｏ均以高分散的金属钴形式存在，ＸＲＤ已难以检测。此外，样品表面Ｃｏ原子百分数的提高及Ｃｏ－Ｃｏ壳层配位数的下降均表明，微量Ｐｔ或Ｒｈ的加入进一步提高了金属Ｃｏ的分散性。对微量Ｐｔ和Ｒｈ在Ｃｏ／ＣｅＯ２中的作用作了一些探讨。

油包水型微乳液法合成负载Pt催化剂及其评价

以碳酸铵和硝酸铝为原料 ,分别在由十六烷基三甲基溴化铵 (CTAB)、正丁醇、环己烷和水构成的微乳液体系和由十二烷基苯磺酸钠 (DBS)、正丁醇、环己烷和水构成的微乳液体系中合成了一定粒径的γ Al2 O3纳米粒子 .然后在γ Al2 O3纳米粒子上负载Pt和CeO2 形成了Pt/CeO2 /Al2 O3催化剂 .用BET ,TEM ,XRD ,XPS和FT IR对催化剂进行了分析 .结果表明催化剂的粒径随着水与表面活性剂的摩尔比Rw 的增大而减少 .当催化剂粒径为 16nm时 ,催化剂对NO的还原活性最好 .

Effect of active oxygen on the performance of Pt/CeO2 catalysts for CO oxidation

This study was focused on the influence of active oxygen on the performance of Pt/CeO2 catalysts for CO oxidation. A series of CeO2 supports with different contents of active oxygen were obtained by adding surfactant at different synthesis steps. 0.25 wt% Pt was loaded on these CeO2 supports by incipientwetness impregnation methods. The catalysts were characterized by N2 adsorption, X-ray diffraction（XRD）, high-resolution transmission electron microscopy（HRTEM）, H2 temperature-programmed reduction（H2-TPR）, dynamic oxygen storage capacity（DOSC） and in-situ DRIFTS technologies. For S-f supports, the surfactant was added into the solution before spray-drying in the synthesis process, which facilitates more active oxygen formation on the surface of CeO2. After loading Pt, the more active oxygen on CeO2 contributes to dispersing Pt species and enhancing the CO oxidation activity. As for the aged samples,Pt-R-h shows the highest activity above 190 ℃ because of the presence of more partly oxidized Pt^（δ＋） species. Thus the activity is also influenced by the states of Pt and the Pt^（δ＋） species may contribute to the high activity at elevated temperature.

Insight of the stability and activity of platinum single atoms on ceria

Single-atom catalysts (SACs) have recently attracted broad attention in the catalysis field due to their maximized atom efficiency and unique catalytic properties.An atomic-level understanding of the interaction between the metal atoms and support is vital for developing stable and high-performance SACs.In this work,Pt1 single atoms with Ioadings up to 4 wt.% were fabricated on ceria nanorods using the atomic layer deposition technique.To understand the Pt-O-Ce bond interfacial interactions,the stability of Pt1 single atoms in the hydrogen reducing environment was extensively investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy CO chemisorption measurements.It was found that ceria defect sites,metal Ioadings and high-temperature calcination are effective ways to tune the stability of Pt1 single atoms in the hydrogen environment.X-ray photoemission spectroscopy further showed that Pt1 single atoms on ceria are dominantly at a +2 valence state at the defect and step edge sites,while those on terrace sites are at a +4 state.The above tailored stability and electronic properties of Pt1 single atoms are found to be strongly correlated with the catalytic activity in the dry and water-mediated CO oxidation reactions.