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  • 1
    ISSN: 1572-879X
    Keywords: Dimethylether amination ; methylamines ; zeolite T ; acidic properties ; TPDA ; IR spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Freshly prepared and used H/Na, K-T-zeolite catalysts for the conversion of dimethyl ether and ammonia to the three methylamines have been characterized by temperature-programmed desorption of ammonia and IR spectroscopy. Activity and selectivity depend on the nature and number of the acid sites. With time on-stream, deep alterations in the catalyst behaviour have been observed. The activity of the catalyst is decreased by blocking of active sites ≈ 5–10 h: furthermore, during an initial period hydrocarbons were formed almost exclusively on strong-acid sites. A second period is characterized by an increased “shape selectivity” observed in the distribution of the methylamines. The amination will proceed probably on left weak-acid sites and on the outer surface in a third period, however, without “shape selectivity” due to the progressive blocking of the inner catalyst surface.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9028
    Keywords: ammoxidation ; vanadium phosphate catalysts ; catalyst/feed interaction ; reaction mechanism ; FTIR spectroscopy ; TAP technique ; isotope experiments ; TPD ; TPRS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction pathway of the ammoxidation of toluene on (VO)2P2O7 used as catalyst and the interaction of potential intermediates with the pyrophosphate were studied by spectroscopic techniques (FTIR, EPR), temperature-programmed chemisorptions/ reactions (TPD, TPRS) and transient studies such as the temporal analysis of products (TAP) technique. NH3 is chemisorbed on the catalyst surface, forming three different species, i.e., NH 4 + ions located on BrØnsted sites, coordinatively bound NH3 on Lewis sites and NH 2 − groups, presumably P-NH2. Toluene that is probably adsorbed on Lewis sites reacts in a first step to a benzyl radical. A subsequent partial oxidation by interaction of VIV=O groups generates a V...O=CH-C6H5 surface structure. This benzaldehyde-like surface species reacts with adsorbed NH3 according to a Langmuir-Hinshelwood mechanism. TAP experiments on ammonium-containing vanadium phosphates revealed that NH 4 + ions could act as potential N-insertion species. No formation of benzylamine as well as the generation of V=NH surface groups as possible intermediates or N-insertion sites were observed.
    Type of Medium: Electronic Resource
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