The mechanism of hydrogen abstraction by high valence transition metal oxo compounds

We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3-H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals (3e, 3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of pi(M-O)* is involved in H abstraction by M = O, resulting in a (4e, 4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M-O pbond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes. (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.

In-Situ FT-IR Investigation Methane to Syngas over of Partial Oxidation of Rh/SiO2 Catalyst

Partial oxidation of methane to syngas （POM） over Rh/SiO2 catalyst was investigated using in-situ FT-IR. When methane interacted with 1.0wt%Rh/SiO2 catalyst, it was dissociated to adsorbed hydrogen and CHx species. The adsorbed hydrogen atoms were transferred to SiO2 surface by ＂spill-over＂ and reacted with lattice oxygen to form surface -OH species. POM mechanism was investigated over Rh/SiO2 catalyst using in-situ FT-IR. It was found that CO2 was formed before CO could be detected when CH4 and O2 were introduced over the preoxidized Rh/SiO2 catalyst, whereas CO was detected before CO2 was formed over the prereduced Rh/SiO2 catalyst.

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-programmed 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 conditions 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.

The origin of the site preference of H adsorption on Pd(100)

Spin-polarized density functional theory(DFT)calculations are carried out to determine the site preference of H adsorption on Pd(100)surface and subsurface.We carefully scrutinize the energy difference between different patterns at=0.50 ML and confirm the LEED observation that surface adsorption can form c(2×2)ordering structure.On the contrary,we disclose that p(2×1)structure become more favorable than c(2×2)for subsurface adsorption.These site preferences are rationalized via an analysis of the layer and orbital resolved density of states.Furthermore,we propose that the interstitial charge as a key factor determining the preferred H adsorbed site.

Preface

Prof.Khi-Rui Tsai was born in Tongan(Xiamen,Fujian),in the December of 1913.After graduted from Xiamen University in 1937,he was appointed as an assistant pro-fessor of Xiamen University.He was selected as a govern-ment-supported oversea student to continue his education in the US in 1947,and obtained his Ph D degree in1950 from the Ohio State University.After the estab-

Active site of praseodymium orthovanadate catalyst in oxidative dehydrogenation of propane

The pure phase of praseodymium orthovanadate (PrVO\-4) has been prepared by the citrate method. The active site of PrVO\-4 was studied by ESR, NO_TPD, O\-2_TPD and 18 O\-2_isotope exchange methods. The results of ESR and NO_TPD confirmed the presence of V 4+ in the catalyst. 18 O\-2_isotope exchange was through a single exchange procedure. From the result of O\-2+TPD and the kinetic study of 18 O\-2_isotope exchange, one can reach a conclusion that the V 4+ species associated with oxygen vacancies are the site for O\-2 activation. The adsorbed O\-2 or O\+- are the active oxygen species in propane oxidative dehydrogenation.