An ESCA study of metal deposition on cracking catalysts

Andersson, S. Lars T.; Lundin, Sten T.; Järås, Sven; Ottersedt, Jan-Eric

doi:10.1016/0166-9834(84)80003-2

Cited by 35 publications

(18 citation statements)

References 7 publications

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“…Similar conclusion has been reported from XPS measurements (56). Owing to the polar nature of vanadium porphyrin complexes, vanadium is initially deposited on the catalyst outer surface, where during regeneration in air, forms V 2 O s .…”

Section: (65)supporting

confidence: 73%

“…Initially, Ni was found to be homogeneously distributed on the catalyst surface; then as Ni levels increased above 2%, surface enrichment of Ni occurred (56). Ni migration can be correlated with the luminescence quenching of the rare-earths (RE) containing Y-zeolite (REY) present in the FCC matrix (16).…”

Section: Transmission Electron Micrographs and Xps Results Have Been mentioning

confidence: 98%

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Metal-Resistant Fluid Cracking Catalysts

Occelli¹

1991

ACS Symposium Series

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Section: (65)supporting

confidence: 73%

Section: Transmission Electron Micrographs and Xps Results Have Been mentioning

confidence: 98%

Metal-Resistant Fluid Cracking Catalysts

Occelli¹

1991

ACS Symposium Series

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“…, and V 3? , respectively [5,17,[36][37][38]. The spectra for the freshly prepared catalysts VFe-f, VFe150-f and VFe250-f catalysts are rather similar showing contributions from all three oxidation states (for quantitative data see Table 4).…”

Section: Surface Composition Of Fe 28 V 02 O Xmentioning

confidence: 97%

Cation Vacant Fe3−x−y V x □ y O4 Spinel-Type Catalysts for the Oxidation of Methanol to Formaldehyde

2011

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The potential of Fe-V-oxide catalysts for use in methanol oxidation is explored. Our results show that although FeVO 4 is active and selective for formaldehyde (FA) formation, it is not completely stable towards volatilization under reaction conditions. Attempts to stabilize Fe-V-oxide were made using titania, alumina and silica supports. However, we observe that although some stabilization is achieved using titania and alumina, the supported catalysts are sensitive to volatilization considering the relatively low content of active oxide. Compared with supported V-oxide, the results show that iron causes stabilization of vanadium decreasing its volatility. Considering the observation that the neat FeVO 4 restructures to form a spinel-type phase under influence of the catalysis, we prepared a series of cation vacant spinel-type Fe 3-x-y V x h y O 4 catalysts with various V/Fe ratio and consequent number of cation vacancies h. Opposed to the activity, which is rather constant irrespectively of the vanadium content, the selectivity to FA passes through a maximum of about 90% for Fe/V = 14. A spinel-type phase with the composition Fe 2.62 V 0.19 h 0.20 O 4 was prepared and subsequently preoxidized to different degree. It is observed that the spinel-type structure is stable and that the oxidation of vanadium and iron is balanced by an increasing number of cation vacancies. Moreover, irrespectively of the original degree of preoxidation, it is found that in methanol oxidation a steady state is reached where all samples are equally active and selective and have the same composition both in the bulk and at the surface. The results clearly demonstrate that the spinel-type catalysts are phase-stable, nonvolatile and flexible in that the cations can change oxidation state retaining the same basic structure type and Fe/V ratio.

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“…Considering that the width of the 2p 3/2 peaks at half maximum was in all cases *1.6 eV, it can be concluded that it is a single peak. By comparison with the binding energies reported in the literature for vanadia and reduced vanadia [25,26], the binding energy measured here for the 2p 3/2 peak suggests that the V at the surface is pentavalent. The Ti 2p spectrum in Fig.…”

Section: Xps Characterizationmentioning

confidence: 66%

Substituted Mo–V(Ti)–Te(Ce)-oxide M2 Catalysts for Propene Ammoxidation

et al. 2008

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One of the most effective propane to acrylonitrile ammoxidation catalyst is comprised of the two phases M1 (orthorhombic) Mo 7.5 V 1.5 NbTeO 29 and M2 (pseudo-hexagonal) Mo 4 V 2 Te 2 O 20 . Under reaction conditions, the two phases work in symbiosis with each other where M1 is the paraffin activating component and M2 is the olefin activating component. Since the catalytic improvement of either phase should result in an enhancement of the overall acrylonitrile yield, controlled substitution of certain elements in either or both phases might result in the desired improvement. Our current study concentrates on the partial substitutions of V with Ti and Te with Ce in the M2 phase. Ti substitution results in a considerable propene activity improvement, whereas the selectivity to acrylonitrile is unaffected. Substitution with Ce, on the contrary, substantially improves the selectivity to acrylonitrile. Also, a minor improvement of the activity is notable. The acrylonitrile selectivity improvement is a result of better NH 3 utilization and comes at the expense of reduced acrolein make. XRD reveals that all of the substituted compositions retain the M2 structure and essentially are monophasic. XANES recordings show for the bulk that the Mo is 6?, the V is 4?, or 4? and 5? when Ce is present, the Ti is 4?, the Ce is 3?, and the Te 4? with some 6? also present. According to the ESR data, in the M2 with Ce (7Te/3Ce) only 21% of the V is 4?, the remainder being 5?, which tentatively can be explained by the existence of some cation vacancies in the hexagonal channels. HRTEM imaging reveals little if any differences between the materials, all have the typical pseudo-hexagonal habit of the M2 phase and expose a 1-2 nm thick surface layer without any apparent long-range ordering. XPS data show that all catalysts, including the base, are highly enriched at the surface with Te at the expense of other metals. The 7Te/3Ce composition exhibits also substantial Ce surface enrichment. Moreover, the valences of the cations at the surface differ from the bulk in that for all fresh catalysts V is 5? and Te is 6? on the surface. Characterization by XPS of catalysts used in propene ammoxidation, reveals reduction of Te and, except when Ce is present, also Mo. Therefore, it might be inferred that the surfaces of the catalysts studied here are comprised essentially of one or a few monolayers of TeMoO or TeCeMoO on an interacting M2 crystalline base.

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An ESCA study of metal deposition on cracking catalysts

Cited by 35 publications

References 7 publications

Metal-Resistant Fluid Cracking Catalysts

Metal-Resistant Fluid Cracking Catalysts

Cation Vacant Fe3−x−y V x □ y O4 Spinel-Type Catalysts for the Oxidation of Methanol to Formaldehyde

Substituted Mo–V(Ti)–Te(Ce)-oxide M2 Catalysts for Propene Ammoxidation

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