Guo Xiexian

Preparation and characterization of hydroxyl-FeAl pillared clays

Solutions containing hydroxy-FeAl oligocations (HFA) were prepared by two procedures: (1) treatment of a mixture of FeCl3 and AlCl3 with aqueous Na2CO3, followed by aging of the product and (2) preliminary preparation and aging of hydroxy-Al13 oligocations followed by reaction of the latter with aqueous FeCl3. Ion-exchange of Na-montmorillonite with HFA yield pillared clay (designated as FeAl-PILC) with d(001) values of 1.98–1.56 nm and a surface area of 230 m2/g. The pillar structure, thermal stability, surface acidity, and reduction behavior of the pillared clays were determined by 27Al-NMR, XRD, DTA, Mössbauer spectroscopy, Py-IR, TPD, TPR. Fe/Al ratios greatly affect the pillar structure, surface area and thermal stability of FeAl-PILC. The pillar in FeAl-PILC with Fe/Al ratio <0.5 has a Keggin structure, similar to that of Al-PILC, but the pillar structures of FeAl-PILC with Fe/Al ≥0.5 are the ferric tripolymer species similar to those of Fe-PILC. The basal spacings, surface area, and thermal stability are decreased with increasing Fe/Al ratio. There is relatively strong interaction between Fe and Al in the pillars. The interaction is enhanced with decreasing Fe/Al ratio. Reduction of the Fe phase in FeAl-PILC was reduced by the interaction of Fe with Al.

Chlorine on Ag(111): the intermediate coverage case

Previous works on Cl adsorption on Ag(111) showed that there are different stages of adsorption. We have supposed three main stages before the growth of a thick AgCl layer. These are labelled stages (a)-(c). We report on a characterization of the stage (c) structure with AES, HREELS, LEED, UPS, ISS and work-function changes. AES, HREELS, UPS and LEED show that the main feature of the stage (c) structure is the coexistence of Ag and AgCl crystallites on the surface. Additional details for the stage (c) structure revealed by HREELS and ISS are presented. The additional features are the presence of Ag defect sites and that the concentration of Cl on the Ag crystallites is less than full coverage.

Effect of various pretreatments on rhenium oxide-alumina catalysts: the structure and activity of active sites for propene metathesis

Abstract A series of Re 2 O 7 -Al 2 O 3 catalysts containing 3.0 – 15.3 wt.% Re 2 O 7 has been studied in a microcatalytic pulse reactor for propene metathesis. The effect of various pretreatments has been examined by catalyst evaluation as well as by the change in surface properties observed in TPR, O 2 -adsorption, ESR and XPS measurements. After N 2 pretreatment a linear relationship is obtained between the intensities of the ESR signal, assigned to partially reduced Re-O-Re dimeric species, and the activities of Re 2 O 7 -Al 2 O 3 catalysts. The concentration of the dimeric species strongly depends on the Re 2 O 7 loading. H 2 reduction at 450 °C followed by O 2 uptake at reaction temperature (80 °C) is effective in enhancing the activity of low loading catalysts, and the amount of reversibly adsorbed O 2 is shown to be closely connected with the catalytic activity. In this case, it is easy to detect the formation of O 2 − ions on the surface by ESR observation. Surface species of is very plausibly responsible for the enhanced activity of the low loading catalyst. By pretreatment with propene at 450 °C, the activity of the low loading catalyst is greatly increased. A significant partial reduction of Re 2 O 7 and simultaneous carbonaceous deposit on the catalyst surface are observed by ESR and XPS examination. It seems probable that monomeric species of Re +6 (or Re +5 -O-Al +3 are highly active and that the formation of such species on the surface is facilitated by treating the low loading catalyst with propene at 400 – 450 °C. It is apparent that the presence of appropriate unsaturated coordinated species of high-valence Re ions on dehydrated alumina is essential for active metathesis catalysts.

Re2O7/γ-Al2O3 catalyst for propene metathesis: a further study on the effect of pretreatments

Abstract The temperature dependence of propene metathesis over Re 2 O 7 /Al 2 O 3 catalysts pretreated with He and/or propene and of the spectra of these samples were studied to obtain further information on the nature and the structure of the active sites. It is demonstrated that after He pretreatment, catalysts with high Re ion density show higher activity if the reaction is carried out at a higher temperature. In contrast, after propene pretreatment, the catalyst with low Re ion density displays higher activity at lower temperature. XPS spectra of Re 4f for the catalyst after reaction imply that the surface species are composed of Re ions in different valence states - more reduced when pretreated with propene, less reduced when pretreated with helium. Unfortunately it is still not possible to confirm what species are responsible for propene metathesis over Re 2 O 7 / Al 2 O 3 catalysts pretreated with He and/or propene.

Effect of basicity and adding CO2 in the feed on the oxidative coupling of methane over K2O and SrO promoted La2O3/ZnO catalysts

LZ and SLZ catalysts are fairly active for oxidative coupling of methane. Their catalytic performance can be further improved by adding K+ cations (supposedly in the form of K2O) as promoters. Under conventional reaction conditions such as a reaction temperature of 1073 K, methane conversion is 18.2% and C-2-selectivity is 68.3%. The effect of adding CO2 into the feed has also been examined in order to understand the promotional effect of K2O on the reaction. XRD, CO2-TPD and XPS techniques were used to characterize the basicity and possible active oxygen species of KSLZ catalysts. The functions of K2O in KSLZ catalyst can be attributed to its high dispersion, enrichment of surface basic sites and the ability to create active oxygen adspecies on the catalyst surface. Unfortunately, at the moment it is difficult to definitely identify the nature of the active oxygen adspecies. Meanwhile, it is found that with decreasing concentrations of SrO species on the catalyst surface, the catalyst will be less sensitive to the addition of CO2 in the feed

The Characterization of Modified ZSM-5 Catalysts Prepared Via a Solid State Reaction for Propane Aromatization

Abstract This paper describes a simple method of solid state reaction for preparation of Zn-, Mo-, and Cr-ZSM-5 catalysts instead of ion exchange. NH 3 -TPD, IR, TPR, ESR and XPS techniques were used to characterize the interaction of HZSM-5 with ZnO, MoCl xxx , and CrO xxx which leads to introduction of cations into the channels of zeolites. Zn-ZSM-5 is more active for propane conversion and gives the better BTX selectivity. Over Mo-ZSM-5, propane mainly undergoes cracking into methane and ethane, and the loading of Cr 5+ of ZSM-5 enhances the propane dehydrogenation to propene.

Interaction between metal and support: Effects of support acidity on adspecies of co over Ru

Supported Ru/X catalysts (X: SiO2, Al2O3, SiO2·Al2O3, HY) have been investigated by IR and TPR (temperature programmed reduction). Due to interaction between Ru and Lewis or Brönsted sites of the support, the Ru sites become electron-deficient. Stronger acidity of the support makes the Ru sites more electron-deficient, and as a result, adspecies of Ru+δ (CO)4 or Ru+δ(CO)2 can occur more easily.AbstractНанесенные катализаторы Ru/X (X:SiO2, Al2O3, SiO2·Al2O3, HY) исследованы с помощью ИК-спектроскопии и ТПВ. Вследствие взаимодействия Ru с льюисными и брёнстэдными центрами рутениевые центры приобретают электронную дефицитность. Повышенная кислотность носителя увеличивает электронную дефицитность рутениевых центров, в рузультате чего легче образуются аддитивы Ru+δ(CO)4 или Ru+δ(CO)2.

EHMO calculations for the chain growth process in fischer-tropsch synthesis on supported group VIII metals

Abstract EHMO calculations and orbital analysis of fragments were performed for the chain growth reaction in Fischer-Tropsch synthesis using a butterfly model for the Al2O3-supported metals. Theoretical speculation consistent with experimental facts has been given for the activity sequence of various metals and the product distribution in accordance with the carbidic mechanism of CH2 insertion for the chain growth reaction on the reduced metals.

Metathesis of hexene-1 over supported rheniamolybdena-alumina catalysts

The metathesis of hexene-1 was investigated on Re-, Mo- and Re-Mo-Al2O3 catalysts. Surface properties of the different catalysts were examined by chemisorption measurements and through the use of various physical methods. Isomerization of hexene-1 took place in parallel with metathesis, and the resulting internal olefins (hexene-2 and -3) participated actively in the total reaction of hexenes. Consequently, in addition to C2= and C10=, olefins ranging from C3= to C9= were obtained as products, which can be illustrated by the following overall reaction scheme : Catalyst characterization data from H2 TPR, O2 uptake, NH3 TPD, XRD, ESR and ESCA measurements have indicated that all of the properties related to the surface state of the Mo oxide, such as the oxidation state and binding energies of Mo cations, the dispersion state, surface acidity etc., are scarcely influenced by the presence of Re cations. There is therefore no obvious interaction between the Re and Mo oxides on the surface. Based on the catalytic behaviour and surface properties of Re-Mo-Al2O3 observed in this work, a dual site mechanism was suggested in which the Re and Mo surface species exist independently. The main function of the Re species is to create more metathesis sites, which operate independently, while the isomerization reaction takes place on the acidic sites of the Mo-Al2O3 surface.

The mechanistic relation between isomerization and hydrogenolysis of alkane on molybdena-lnteracted supported Pt catalysts

Anchored Pt-Mo-SiO/sub 2/ catalysts prepared with Mo(..pi..-allyl)/sub 4/ and Pt(..pi..-allyl)/sub 2/ compounds are examined by comparing the activity and selectivity for conversion of alkanes with that of monometallic Pt catalysts in a pulse reactor under hydrogen pressure of 1.5 atm and in the temperature range of 300-340/sup 0/C. The rule of Pt/Mo ratio dependent product distribution for Pt-Mo-SiO/sub 2/ catalysts is interpreted by the preferential formation of 1,3 dehydrogenated species on molybdena-interacted Pt sites leading to a high contribution of the reaction pathway via the bond-shift mechanism. Additional evidence further demonstrating the mutual coupling between bond cleavage and C-skeleton rearrangement on supported platinum catalysts cited in a previous work is described. 14 references.