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For the dehydrogenation of C 2 H 6 with CO 2 to C 2 H 4 , a silicalite-2 zeolite supported Fe–Mn catalyst has been developed, with an achievement of 93% of C 2 H 4 selectivity and 66% of C 2 H 6 conversion. The promotion of Mn to the Fe/Si-2 catalyst lies not only in increasing C 2 H 4 selectivity but also in improving the catalytic stability greatly. A thermo-balance was employed to investigate the behavior of coke deposition on Fe/silicalite-2 and Fe–Mn/silicalite-2 catalysts during C 2 H 6 dehydrogenation. By studying the effects of reaction temperature and partial pressures of C 2 H 6 and CO 2 on coke deposition, the kinetic parameters of the coking reaction were satisfied and the corresponding coking reaction kinetics equations were thus established. The rate of coke deposition on Fe–Mn/silicalite-2 is much less than that on Fe/silicalite-2, due to the modification of Mn to the Fe/silicalite-2 catalyst. The promotion of Mn to the improvement of the catalytic stability of the Fe/silicalite-2 catalyst results from the great prohibition of coke formation on Fe–Mn/silicalite-2 catalyst surfaces.

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. (C) 1997 Elsevier Science B.V.

By using high-resolution solid state Nuclear Magnetic Resonance spectrometer with Al-27 and Si-29 probes, the interaction between Mo species and HZSM-5 of Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminium in the zeolite can be easily extracted by the introduction of Mo species. The extract ability of framework aluminium by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al-2(MoO4)(3). The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The MAS NMR results give us an evidence that Al-2(MoO4)(3) crystallites are much less active for the reaction.

The addition of K2O and MnO promoters enhances catalyst activity and selectivity to light alkenes during CO hydrogenation over silicate-2 (Si-2) supported Fe catalysts. The results of CO hydrogenation and CO-TPD, CO/H2-TPSR, C2H4/H2-TPSR and C2H4/H2 pulse reaction over Fe/Si-2 catalysts with and without promoters clearly show that the MnO promoter mainly prohibits the hydrogenation of C2H4 and C3H6. Therefore, it enhances the selectivity to C2H4 and C3H4 products. Meanwhile further incorporating the K2O additive into the FeMn/ Si-2 catalyst leads to a remarkable increase in both the capacity and strength of the strong CO adspecies. These produce much more [Cad] via their dissociation and disproportionation at higher temperatures. This results in an increase in the CO conversion and the selectivity to light olefins. Moreover, the K2O additive modifies the hydrogenating reactivity of [Cad] and suppresses the disproportionation of C2H4 that occurs as a side-reaction. Both K2O and MnO promoters play key roles for enhancing the selective production of light alkenes from CO hydrogenation over Fe/Si-2 catalyst.

Sro-la2o3/cao(slc) catalysts have been found to be active for the oxidative coupling of methane (ocm), but the lattice oxygen of them is only active for total oxidation as revealed by the studies of in - situ ft-ir on the interaction between ch4 and the oxide surface concerned.

CO-TPD and H2-TPD and CO/H2-TPSR were used to study the effect of the support on the performance of Fe-MnO catalysts in CO hydrogenation for the production of light olefins. It was found that a Fe-MnO/MgO catalyst (based on a basic support) is capable of strongly adsorbing CO and H2 favorable for the production of light olefins and CO conversion. A Fe-MnO/ Al2O3 catalyst (based on an acidic support) only showed strong adsorption of H2, but weaker adsorption of CO, and so, it was a poor catalyst for light olefins from syngas.

The TPSR technique was used to investigate the effect of the support on the secondary reactions of ethylene formed during CO hydrogenation. Based on the results of CO hydrogenation and CO/H2-TPSR characterization, it was found that different supports induced different secondary reactions, and thus affected the selectivity to light olefins directly. The Fe-MnO/MgO catalyst (based on basic support) causes disproportionation of C2H4, and thus, leads to the formation of C3H6. The Fe-MnO/Al2O3 catalyst (based on acidic support) showed obvious hydrogenation of C3H6. The disproportionation of C2H4 was also promoted by the Fe-MnO/Al2O3 catalyst, but because of its activity for C3H6 hydrogenation, a large amount of C3H8 was produced. The different C2H4 secondary reactions are relevant to different CO/H2 reaction pathways over the catalyst surface, so the Fe-MnO/MgO catalyst is a desirable catalyst for the production of light olefins from CO/H2 while the Fe-MnO / Al2O3 catalyst was not so.

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.

MnO and K 2 O are two kinds of promoters to Fe/Silicalite-2 (denoted as Fe/Si-2) catalyst for light olefin formation from CO 2 hydrogenation. It has been revealed that CO 2 adsorption capacity was enhanced by the addition of MnO, and that K 2 O could further increase both the adsorption capacity and bonding strength of the Fe-Mn/Si-2 catalyst to CO 2 and CO species. Based on a two step reaction mechanism in which a reversible water gas shift reaction and a Fischer-Tropsch reaction are involved, the promotional effects of these two kinds of promoters for the formation of C 2 H 4 and C 3 H 6 can be explained.

Catalysts containing 1 wt.% ruthenium and variable amounts of copper, corresponding to Ru100 Ru91Cu9, Ru66Cu33 and Ru50Cu50, have been prepared from ruthenium chloride and copper nitrate with silica as support. Their activities for n-butane hydrogenolysis have been measured between 413 and 533 K after various reduction and oxidation treatments. The structural effects of these treatments were analysed by the use of TPR, TEM and XPS. The principal conclusions are as follows: Reduction of the impregnated salts at 623 K affords very small metal particles (d ⋍ 1 nm) which are incompletely covered by copper atoms: the activity decreases only slowly with increasing copper content. Oxidation at 623 K destroys the clusters, and subsequent low-temperature reduction (~433 K) forms separate ruthenium and copper particles: the activity does not then decrease markedly with rising copper content. Further reduction at 623 K forms somewhat larger clusters, since a small amount of copper greatly diminishes the activity. The implications of these findings for other bimetallic catalysts are briefly considered.

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.

The hydrogenolysis of n-butane has been studied on 1 and 5% ruthenium/titania catalysts pretreated in hydrogen at various temperatures and in air at 623 K. Increasing the temperature of reduction of impregnated ruthenium trichloride from 623 to 758 K gives an increase in activity attributed to removal of chloride, but the low activities associated with a strong metal–support interaction (SMSI) are not found until a reduction temperature of 893 K is used. Subsequent oxidation followed by low-temperature reduction gives much higher activities: this is ascribed to spreading of ruthenium oxide over the support, reduction of which affords more highly dispersed metal which easily succumbs to SMSI on a further high-temperature reduction. This interpretation receives some support from temperature-programmed-reduction results.Product distributions are interpreted according to the scheme devised by Kempling and Anderson. The oxidation treatment and low-temperature reduction creates a new type of active site which appears to favour terminal bond splitting in adsorbed n-butane and has greater reactivity for bond splitting in adsorbed C2 and C3 species. This analysis also leads to the conclusions that a second reduction at 623 K does not wholly convert the well dispersed metal to the SMSI state and that not quite all of the oxide formed at 623 K spreads over the support. The strange behaviour of this system is contrasted with that of ruthenium and of platinum supported on silica.

The activity of Ru/TiO2 catalysts for n-butane hydrogenolysis is greatly increased by oxidation at 433 K after reduction at 758 or 893 K; strong metal–support interaction is then easily effected by a second reduction at these temperatures.