In situ FTIR and ex situ XPS/HS-LEIS study of supported Cu/Al_(2)O_(3)and Cu/ZnO catalysts for CO_(2)hydrogenation

Cu-based catalysts are commonly used in industry for methanol synthesis.In this study,supported catalysts of 5 wt%Cu/Al_(2)O_(3)and 5 wt%Cu/ZnO were prepared,and their surface characteristics during H_(2) reduction and CO_(2)hydrogenation were investigated using in situ Fourier transform infrared spectroscopy(FTIR),ex situ X-ray photoelectron spectroscopy,and high sensitivity low energy ion scattering spectroscopy.During the H2 reduction and CO_(2)hydrogenation processes,it was found that Al_(2)O_(3)can stabilize Cu^(+).In situ FTIR spectra indicated that the 5 wt%Cu/Al_(2)O_(3)can adsorb large amounts of bicarbonate and carbonate species,which then convert into formate during CO_(2)hydrogenation.For the 5 wt%Cu/ZnO,it was found that Cu nanoparticles were gradually covered by a highly defective ZnOx overlayer during H2 reduction,which can effectively dissociate H2.During CO_(2)hydrogenation,the adsorbed bicarbonate or carbonate species can convert into formate and then into a methoxy species.Using these surface sensitive methods,a more in-depth understanding of the synergistic effect among the Cu,Al_(2)O_(3),and ZnO components of Cu-based catalysts was achieved.

Site-specific deposition creates electron-rich Pd atoms for unprecedented C-H activation in aerobic alcohol oxidation

Here,we demonstrate a photochemical strategy to site-specifically deposit Pd atoms on Au nanoparticles.The high-sensitivity low-energy ion scattering spectra combined with the X-ray photoelectron spectra reveal that the surface electronic structure of Pd can be continuously regulated by tailoring the Pd-to-Au molar ratio and the location of Pd atoms in Au Pd nanoparticles.It is revealed that electron-rich Pd atoms are considerably more active than the net Pd atoms in aerobic alcohol oxidation.Remarkably,the catalyst with the most electron-rich Pd sites(binding energy downshift:1.0 e V)exhibits an extremely high turnover frequency(~500000 h-1 vs 12000 h-1 for that with net Pd atoms)for solvent-free selective oxidation of benzyl alcohol,which is,to the best of our knowledge,the highest value ever reported.Kinetic studies reveal that electron-rich Pd atoms can accelerate the oxidation of benzyl alcohol by facilitating C-H cleavage,as indicated by the significant reduction in the activation energy as compared to net Pd atoms.

Applications of in-situ wide spectral range infrared absorption spectroscopy for CO oxidation over Pd/SiO_(2) and Cu/SiO_(2) catalysts

Infrared(IR)absorption spectroscopy has been widely used for dynamic characterization of catalysts and mechanism of catalytic reactions.However,due to the strong infrared absorption of heterogeneous catalysts(mainly oxides,or supported metal and metal oxides,etc.)below 1200 cm^(-1),and the intensity of regular infrared light source rapidly decays at low-wavenumber range,most in-situ infrared spectroscopy studies are limited to the detection of surface adsorbates in the range of 4000-900 cm^(-1).The change of catalytically active component itself(M-O,M-M bond,etc.,1200-50 cm^(-1))during the reaction is hard to be tracked under reaction conditions by in-situ IR.In this work,a home-made in-situ IR reactor was designed and a sample preparing method was developed.With such progresses,the changes of reactants,products,surface adsorbates,and catalysts themselves can be measured under the same reaction conditions with a spectral range of 4000-400 cm^(-1),providing a new opportunity for in-situ characterization of heterogeneous catalysis.CO oxidation on Pd/SiO_(2) and Cu/SiO_(2) catalysts were taken as examples,since both the two catalytic systems were extensively used commercially,and moreover reduction and oxidation of palladium and copper occur during the examined reaction conditions.The characteristic bands of Pd^(2+)-O(670,608 cm^(-1)),Cu^(+)-O(635 cm^(-1))and Cu^(2+)-O(595,535 cm^(-1))were observed by IR,and the changes during CO oxidation reaction were successfully monitored by IR.The oxidation/reduction of palladium and copper were also confirmed by ex-situ XPS.Moreover,Pd^(0) in Pd/SiO_(2) and Cu^(+)in Cu/SiO_(2) were found as the thermal dynamically stable phases under the examined conditions for CO oxidation.

非计量Zn-Cr尖晶石中离子占位对催化合成气合成异丁醇中的关键作用

异丁醇是一种基本有机化工原料和燃料添加剂。从煤基或生物质合成气制异丁醇符合我国"贫油富煤"的能源结构,对于保障我国能源安全具有重要的现实意义。Zn-Cr基催化剂合成异丁醇具有寿命长、积碳少,产物分布简单的优点,被广泛应用于合成异丁醇研究。本文总结了近年来合成气合成异丁醇的进展,重点介绍本课题组近几年在异丁醇合成过程中发现的非计量Zn-Cr尖晶石中离子占位对催化合成气合成异丁醇中的关键作用。首先概述了异丁醇的催化剂体系、合成工艺以及生成机理,然后介绍了促进阳离子在尖晶石结构中混乱分布的策略,包括调节Zn/Cr比例、煅烧温度、制备方法以及负载碱金属等,同时介绍了两种常用的定量检测尖晶石结构离子占位的方法。本课题组首次发现异丁醇产率与离子分布混乱程度呈近似直线关系,是因为离子占位强烈影响催化剂的物化性质。最后展望了异丁醇合成过程中的机遇和挑战,期望此文对能源化工、材料科学等相关学科的学者有一定的参考和启示作用。

Catalysis under shell： Improved CO oxidation reaction confined in Pt@h-BN core-shell nanoreactors

Core-shell nanostructures consisting of active metal cores and protective shells often exhibit enhanced catalytic performance, in which reactants can access a small part of the core surfaces through the pores in the shells. In this study, we show that Pt nanoparticles （NPs） can be embedded into few-layer hexagonal boron nitride （h-BN） overlayers, forming Pt@h-BN core-shell nanocatalysts. The h-BN shells not only protect the Pt NPs under harsh conditions but also allow gaseous molecules such as CO and 02 to access a large part of the Pt surfaces through a facile intercalation process. As a result, the Pt@h-BN nanostructures act as nanoreactors, and CO oxidation reactions with improved activity, selectivity, and stability occur at the core-shell interfaces. The confinement effect exerted by the h-BN shells promotes the Pt-catalyzed reactions. Our work suggests that two-dimensional shells can function as robust but flexible covers on nanocatalyst surfaces and tune the surface reactivity.

The study of the active surface for CO oxidation over supported Pd catalysts

CO oxidation was investigated on various powder oxide supported Pd catalysts by temperature-programined reaction. The pre-reduced catalysts show significantly higher activities than the pre-oxidized ones. Model studies were performed to better understand the oxidation state, reactivities and stabilities of partially oxidized Pd surfaces under CO oxidation reaction condi tions using an in situ infrared reflection absorption spectrometer （IRAS）. Three O/Pd（100） model surfaces, chemisorbed oxygen covered surface, surface oxide and bulk-like surface oxide, were prepared and characterized by low-energy electron diffraction （LEED） and Auger electron spectroscopy （AES）. The present work demonstrates that the oxidized palladium surface is less active for CO oxidation than the metallic surface, and is unstable under the reaction conditions with sufficient CO.

NO Reduction on Cu-Based Model Catalysts Studied by in-situ IRAS

Cu-based catalyst has been widely used for catalytic reduction of NO.Well-defined TiO_(x)/Cu(110)films were prepared and investi-gated by in situ reflection absorption infrared spectroscopy(IRAS),Auger electron spectroscopy(AES)and low energy electron dif-fraction(LEED).A complex surface structure of Cu^(+)(-O-Ti-)-O-Cu^(δ+)/Cu(110)was proposed,in which the topmost surface Cu+is highly dispersed,isolated and fixed by the TiO_(x) layer.Such a'single atom'-like surface site appears a very narrow vco peak at 2130 cm^(-1),and is more stable upon both CO reduction and vacuum annealing than the Cu_(2)O/Cu(110).Such isolated Cu^(+)(-O-Ti-)site on TiO_(x)/Cu(110)is also fairly stable in NO+CO reaction,but the overall catalytic activity is slightly lower than that on the Cu(110)surface,indicating that the single-atom Cu^(+)(-O-Ti-)site is less efficient for NO+CO reaction at the examined conditions.The study provides useful infor-mation for the design and application of single-atom catalysts and understanding the nature of catalytically active centers.