Methane partial oxidation by unsupported and silica supported iron phosphate catalysts. Influence of reaction conditions and co-feeding of water on activity and selectivity
- Colorado School of Mines, Golden, CO (United States)
The partial oxidation of methane to methanol and formaldehyde by molecular oxygen has been investigated over crystalline and silica supported FePO{sub 4} at a pressure of 1 atm and i n the temperature range of 723--973 K. The quartz phase of FePO{sub 4}, as well as silica supported FePO{sub 4} prepared by impregnation (5 wt%), were examined in a continuous flow reactor. Experiments carried out over FePO{sub 4} show high selectivity to formaldehyde at low conversion and suggest that formaldehyde is the primary reaction product, but selectivity decreased rapidly as conversion was increased. The highest space-time yield of formaldehyde observed for this catalyst was 59 g/kg{sub cat}-h. Above 5% methane conversion, carbon oxides were the only products. For silica-supported FePO{sub 4}, formaldehyde selectivity did not fall off rapidly, exhibiting a formaldehyde selectivity of 12% at about 10% conversion (STY = 285 g/kg{sub cat}-h). Quantifiable yields of methanol were observed at very low conversion levels, i.e., below 3% (STY = 11 g/kg{sub cat}-h). Addition of steam (up to 0.1 atm partial pressure) into the feed stream increased the selectivity to methanol ({approximately}25 g/kg cat/h with up to 3% selectivity) and formaldehyde ({approximately}487 g/kg cat/h with up to 94% selectivity) for the silica-supported FePO{sub 4} catalyst. Steam addition had little effect on catalyst activity. Characterization results indicate the presence of FePO{sub 4}, as well as fivefold coordinate Fe{sup 3+} in silica supported catalyst samples, and this species is proposed to be responsible for methane activation. After catalysis in the presence of steam, the fivefold coordinate iron is present, but a significant fraction of the FePO{sub 4} has been reduced to Fe{sub 2}P{sub 2}O{sub 7}. Enhanced selectivity in the presence of steam is attributed in part to the ease of the reversible formation of surface hydroxyl groups (P-OH) from pyrophosphate (P-O-P) groups.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC22-92PC92110
- OSTI ID:
- 316317
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 181; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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