No abstract

No abstract

Phase relations in the ternary oxide system Al 2 O 3 -V 2 O 5 -MoO 3 in the solid state in air have been investigated by using the x-ray diffraction (XRD) and differential thermal analysis/thermogravimetric (DTA/TG) methods. It was confirmed that in the subsolidus area of the Al 2 O 3 -V 2 O 5 -MoO 3 system, there exist seven phases, that is Al 2 O 3 , V 2 O 5(s.s.) , MoO 3 , AlVO 4 , Al 2 (MoO 4 ) 3 , AlVMoO 7 , and V 9 Mo 6 O 40 . Seven fields, in which particular phases coexist at equilibrium, were isolated. The crystal structure of AlVO 4 has been refined from x-ray powder diffraction data. Its space group is triclinic, P " 1, Z = 6, with a = 0.65323 (1) nm, b = 0.77498(2) nm, c = 0.91233(3) nm, a = 96.175(2)°, b = 107.234(3)°, c = 101.404(3)°, V = 0.42555 nm 3 . The crystal structure of the compound is isotypic with FeVO 4 . Infrared (IR) spectra of AlVO 4 and FeVO 4 are compared.

The presented work encompasses the subject of the studies and the results obtained over the last years by the research workers of the Department of Inorganic Chemistry. They include mainly the studies on the reactivity of metal oxides, searching for new phases in binary and ternary systems of metal oxides as well as describing phase relations establishing in such systems. They also encompass works on the extensive characteristics of physico-chemical properties of the newly obtained compounds

The investigations of selective methane oxidation to formaldehyde over T-Nb2O5, the mixture of M-Nb2O5 and H-Nb2O5 as well as H-Nb2O5 were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420–750°C, using oxygen as the oxidizing agent. T-Nb2O5 samples were examined at the contact time 0.7–1.8 s (GHSV 2000–5143 h−1). Other polymorphic forms of niobium(V) oxide were examined at the contact time 0.9 s. Various polymorphic forms of Nb2O5 displayed various formaldehyde and carbon dioxide yield. Using H-Nb2O5 and M-Nb2O5 phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared to T-Nb2O5 (47 % at 0.9 s), a polymorphic form which does not have a block type structure. However, the highest space time yield of formaldehyde (46 g per kg of catalyst per h) was obtained over T-Nb2O5 supported on SiO2.