Mechanistic studies of methane partial oxidation to syngas over SiO{sub 2}-supported rhodium catalysts
- Hong Kong Baptist Univ., Kowloon Tong (Hong Kong)
The reaction behaviors of CH{sub 4} and CH{sub 4}/O{sub 2} (2/1) with reduced (Rh/SiO{sub 2}) and oxidized (Rh(O)/SiO{sub 2}) SiO{sub 2}-supported rhodium catalysts were investigated at temperatures ranging from 600 to 800{degrees}C over a pulse microreactor. The interaction of methane with Rh/SiO{sub 2} led to CO, H{sub 2} and surface carbon formation. The conversion of methane increased with the increase in rhodium loading. During the interaction of methane with Rh(O)/SiO{sub 2} catalysts having rhodium, loading >0.5%, besides CO, H{sub 2}, and surface carbon, CO{sub 2} and H{sub 2}O were formed. Total oxidation of methane occurred over rhodium oxide together with the simultaneous reduction of Rh{sup 3+} to Rh{sup 0}. The partial oxidation of methane as well as the decomposition of methane took place over the resulting metallic rhodium. Within the first pulse of CH{sub 4}/O{sub 2} (2/1), rhodium oxide in the oxidized catalysts was reduced to metallic rhodium. From the second pulse onward, both methane conversion and CO selectivity were similar to those observed over the reduced catalysts. The results indicate that metallic rhodium is the active site for methane partial oxidation and chemisorbed oxygen species have participated in the methane oxidation reaction. The results indicate that methane dissociation is a key step and that CO and CO{sub 2} are formed via some common intermediates, viz. surface CH{sub x} (x = 0-3) species. The activation energies for methane dissociation with or without the involvement of chemisorbed oxygen on a Rh(111) surface were calculated by means of the bond-order conservation Morse-potential approach. 30 refs., 5 figs., 3 tabs.
- OSTI ID:
- 563473
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 167; ISSN JCTLA5; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
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