Effect of the oxide support on the propane ammoxidation with Sb–V–O-based catalysts

The role of Nb₂O₅ and γ-Al₂O₃ oxide supports on the ammoxidation of propane on supported mixed Sb–V oxide at different Sb+V surface coverages is studied. Sb and V oxide species on alumina and on niobia support show different structural features that reflect in different performance during the ammoxidation of propane to acrylonitrile. Niobia-supported catalysts are much more selective to acrylonitrile than alumina-supported ones. Alumina interacts weakly with the supported oxides while niobia forms new phases through solid state reactions with the supported oxides during catalytic operation that must account for its higher selectivity values towards acrylonitrile and higher specific rate of acrylonitrile formation per vanadium site.     

Revised Model of Strain in Ceria–Zirconia-Encapsulated Precious-Metal Particles

A previously proposed model of strain in ceria–zirconia-encapsulated precious-metal particles is revised to reflect several new observations: encapsulation of unstrained Pt particles, quantitative relation between partial reduction and the change in ceria–zirconia cell parameters, temperature/time dependence of strain relaxation/imposition in encapsulated Pd and Rh particles, and strained PdO. According to the revised model, the main cause of strain is partial oxidation of the precious metal (rather than the change in oxygen content of ceria–zirconia, as originally suggested).     

Relating catalyst structure and composition to the water–gas shift activity of Cu–Zn-based mixed-oxide catalysts

In order to investigate the effect of cerium oxide on Cu–Zn-based mixed-oxide catalysts four catalyst samples were characterized by means of XRD, in situ XANES and thermogravimetric analysis. The activity of the catalyst samples was tested for the forward water–gas shift reaction. Cerium oxide was found to increase the crystallinity of the ZnO phase indicating a segregation of the Cu and ZnO phases. The TOF of the water–gas shift reaction based on chemisorption data was found to be independent of composition and preparation conditions of the four catalyst samples. In contrast, the catalyst stability depends on composition and preparation conditions. Cerium oxide impregnated before calcination of the hydrotalcite-based Cu–Zn precursors leads to a more stable water–gas shift catalyst.     

Co- and Ni-exchanged ferrierite: The contribution of synchrotron X-ray diffraction data to siting of TMIs

High-silica zeolites exchanged with transition metal ions (TMIs) are the subject of great interest for their unusual catalytic activity and selectivity. Structural information like coordination and accessibility of TMIs in zeolites are important factors for understanding their catalytic activity. Siting of TMIs in zeolites is typically obtained by spectroscopic (EXAFS, EPR, UV–vis and IR) and computational methods, as in the case of Co-ferrierite. However, some controversy exists in the literature concerning the model for incorporation of bare Co ions in ferrierite. We show here that the results of our synchrotron X-ray powder diffraction studies on Co- and Ni-exchanged ferrierite (Si/Al = 8.5) are in a good agreement with the model of Co siting based on an indirect spectroscopic approach and help to validate this model. By direct structural evidences, a possible explanation for the larger catalytic activity of Co sites in the main channels of ferrierite can be inferred. A combination of data from in situ XRD continuous monitoring of the Co ion migration during calcination and crystal-chemical considerations allows to device a strategy for the design of optimised co-cations containing Co-ferrierite catalysts.     

A XRD study of Co/Au multilayers using a laboratory microdiffractometer

In this paper we show that by the analysis of 2D images collected with a laboratory X-ray microdiffractometer it is possible to non-destructively evaluate the structure, the microstructure, and the preferred orientation of films. In particular, the structural analysis of Co/Au multilayers on Si(1 0 0) deposited at different Ar pressures are reported and discussed.     

Selective catalytic reduction of nitric oxide by propane over vanadia-titania aerogels

An investigation has been carried out of the effect of vanadia loading on the activity and selectivity ofV₂O₅TiO₂ aerogel catalysts, prepared by a two-step procedure, for the reduction of NO by propane. The structure of catalysts have been characterized by laser Raman spectroscopy and XRD measurements. At vanadia loading levels below ca. 4.4 wt%, the vanadia is present in the form of coordinated polymeric species, whereas crystallites of V₂O₅ are formed at higher vanadia contents. At this critical level of 4.4 wt% V₂O₅, the kinetic measurements showed also a maximum in the activity per mass of catalyst which very likely indicated that the coordinated polymeric surface species are more active than crystalline V₂O₅. The selectivity towards the formation of dinitrogen decreased as the loading increased, presumably because of the formation of larger polymeric species and V₂O₅ crystallites, below and above the critical loading level, respectively. For the reduction of NO by propane, titania supported vanadia aerogel catalysts are significantly more active, per mass of catalyst, and more selective towards N₂ formation than conventionalV₂O₅TiO₂ and V₂O₅Al₂O₃ aerogel catalysts, at vanadia loading levels below ca. 11 wt%.     

XRD与TEM技术在分析纳米金属晶粒尺寸中的应用

介绍利用（α-石英作为标样来消除X射线衍射过程中仪器因素引起的X射线衍射峰宽化的方法，给出了（α-石英（110）和（223）衍射的仪器因子校正曲线．利用该曲线计算出了纳米不锈钢粉末烧结试样的平均晶粒度．通过和透射电镜观察统计的晶粒度进行比较，发现两者最终得到的晶粒度仅相差5％左右，说明使用这两种方法都能较为准确的计算出纳米材料的晶粒度．     

Facile synthesis of nanocrystalline zinc ferrite via a self-propagating combustion method

Macroporous nanocrystalline zinc ferrite with single spinel-phase was prepared by a facile self-propagating combustion method using zinc nitrate, iron nitrate and glycine. The as-prepared ZnFe₂O₄ were characterized by X-ray diffraction (XRD) analysis, N₂ adsorption, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectrum (EDS). The magnetic properties of the prepared ZnFe₂O₄ were also studied.     

Mid-Temperature Synthesis of CeO2-TiO2 Complex Compound and Its XRD Structure Study

TiO2 andCeO2 aresemiconductormaterials .TiO2hasthepropertiesofphoto catalysis[1] whileCeO2 hastheabilityofoxygenstorageandcanpromotethedispersionofprecionsmetalsonthesupporter[2 ] .CeO2 TiO2 com plexcompoundwasusedascatalystandspecialfunction almaterial[3～ 5] .ThetraditionalsynthesisofCeO2 TiO2complexcompoundisbyceramicmethodthatusesoxidesasrawmaterialsanditiscalcinedabove 130 0℃[6～ 8] .However ,thestructureandmicrostructureofthecomplexcompoundarenotsuitableforcatalystandfunctionalm…     

The flame retardant mechanism of polyolefins modified with chalk and silicone elastomer

This paper presents the current understanding of the flame retardant mechanism of Casico?. The study includes the flame retardant effect of each individual component: ethylene–acrylate copolymer, chalk and silicone elastomer, as well as the formation of an intumescent structure during heating. The flame retardant properties were investigated by cone calorimetry and oxygen index tests. To obtain insight into the flame retardant mechanism, heat treatment under different conditions has also been performed. The results indicate that the flame retardant mechanism of Casico is complex and is related to a number of reactions, e.g. ester pyrolysis of acrylate groups, formation of carbon dioxide by reaction between carboxylic acid and chalk, ionomer formation and formation of an intumescent structure stabilized by a protecting char. Special emphasis is given to the formation of the intumescent structure and its molecular structure as evaluated from ¹³C MAS‐NMR and ²⁹Si MAS‐NMR, ESCA and XRD analysis. After treatment at 500°C the intumescent structure consists mainly of silicon oxides and calcium carbonate and after treatment at 1000°C the intumescent structure consists of calcium silicate, calcium oxide and calcium hydroxide. Copyright © 2003 John Wiley & Sons, Ltd.