Selective methane oxidation to formaldehyde using polymorphic T-, M-, and H-forms of niobium(V) oxide as catalysts

The investigations of selective methane oxidation to formaldehyde over T-Nb(2)O(5), the mixture of M-Nb(2)O(5) and H-Nb(2)O(5) as well as H-Nb(2)O(5) were carried out. The tests were conducted under atmospheric pressure, in the temperature range 420-750 degrees C, using oxygen as the oxidizing agent. T-Nb(2)O(5) 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 Nb(2)O(5) displayed various formaldehyde and carbon dioxide yield. Using H-Nb(2)O(5) and M-Nb(2)O(5) phases with a block type structure, made it possible to obtain higher formaldehyde selectivity (78 % at 0.9 s) as compared to T-Nb(2)O(5) (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-Nb(2)O(5) supported on SiO(2). (c) 2008 Institute of Chemistry, Slovak Academy of Sciences.