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The partial oxidation of propane and the mechanism of selective catalytic reduction (SCR) of NO by propane over Ga2O3/Al2O3 in excess of O2 have been investigated using in situ Fourier transform infrared spectroscopy. An optimized Ga2O3/Al2O3 catalyst shows high activity and efficiency of the reducing agent propane (100% conversion of NO at 623 K, GHSV: 10,000 h(-1)). One molecule of propane converts more than 4 NO molecules to N2. The reaction starts with the partial oxidation of C3H8 by O2 and carboxylates (acetate, formate) are formed on the catalyst surface above 573 K. This oxidation represents the rate-determining step of the SCR reaction. These surface carboxylates represent a dominating intermediate and (easily) react with (adsorbed) NO forming nitrogen-containing organic species. The latter are proposed to react with NO to form N2. Total oxidation of propane was enhanced at temperatures above 773 K leading to decreased reductant efficiency. Surface nitrite and nitrate species can also be observed, but they were found to be spectators only. This could be concluded from the electron balance (conversion of propane relative to NO) and from the relative rates of the single reaction steps. On the basis of these investigations and stoichiometric calculations, a conclusive reaction mechanism is proposed.

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Antimony-modified vanadia-on-titania catalysts were prepared for the selective oxidation of o-xylene to phthalic anhydride by ball milling of powder mixtures followed by calcination. A binary Sb 2 O 3 -V 2 O 5 system was also prepared for comparison purposes. The resulting materials were physically characterized by surface area measurements, X-ray diffraction analysis (XRD), laser Raman spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, electron spin resonance (ESR), magnetic susceptibility determination, and 15 V solidstate NMR. The catalytic performance of the TiO 2 -supported materials was tested for o-xylene oxidation. After calcination of the Sb 2 O 3 -V 2 O 5 binary mixture at 673 K, Sb 3+ is almost quantitatively oxidized to Sb 5+ , while both V 3+ and V 4+ are detected. V 3+ and some V 4+ are most likely located in a nonstoichiometric VSbO 4 -like structure, while the majority of V 4+ preferentially concentrates within shear domains in oxygendeficient V 2 O 5-x particles. In the titania-supported catalyst system, both Sb 2 O 3 and V 2 O 5 spread on the anatase surface. Sb 3+ is oxidized to Sb 5+ , and V 3+ , V 4+ , and V 5+ are detected. VSbO 4 -like structures are not observed. The presence of antimony leads to the formation of presumably V 3+ -O-V 5+ redox couples. The paramagnetic centerssin contrast to the binary mixturesare largely isolated. Antimony preferentially migrates to the surface and appears to exhibit a dual function catalytically. It is inferred from the experimental data that the addition of antimony leads to site isolation and to a reduction of surface acidity. We suggest that V-O-V-O-V domains or clusters are interrupted by incorporation of Sb to form V-O-Sb-O-V species. As a consequence of this site isolation and a reduction of surface acidity, overoxidation of o-xylene is reduced. These two effects are therefore most probably responsible for the improved selectivity of the ternary catalyst system over the binary one toward phthalic anhydride.

Vor kurzem berichteten wir ilber einen neuen Zugang zu Metallacycloalkanen aus Metallkomplexen mit zwei nucleophilen Zenfren und a,wdisubstituierten Kohlenwasserstoffen I -5 ) . Von besonderer Bedeutung filr den Ablauf der Reakfionen ist die Natur der Abgangsgruppe in den Alkanen. Sie muD so beschaffen sein. daD die a,wstgndigen C-Aiome eine moglichst hohe 5( 2 ) Chem. Ber. 114(1981)