High Catalytic Performance of Fine Particles of Metallic Iron Formed from Limonite in the Decomposition of a Low Concentration of Ammonia

Abstract

Catalytic NH 3 decomposition with limonite rich in a-FeOOH has been studied as a hot gas cleanup method to remove a low concentration of NH 3 from fuel gas produced in coal gasification. Fine particles of metallic Fe formed from a-FeOOH achieve the almost complete decomposition of 2000 ppm NH 3 to N 2 at 500°C under a high space velocity of 45,000 h )1 and show the stable catalytic performance for 50 h. The predominant catalytic mechanism involving the formation and subsequent decomposition of Fe nitrides may be proposed on the basis of the XRD and TPD results.

Removal of Hydrogen Sulfide and Ammonia by Goethite-Rich Limonite in the Coexistence of Coke Oven Gas Components

“…To avoid rapid oxidation of the α-Fe particles upon exposure to laboratory air, the limonite after H 2 reduction, H 2 S removal or NH 3 decomposition was passivated using 1% O 2 /He at room temperature and then recovered from the reactor. 10) Temperature-programmed oxidation (TPO) was carried to quantitate the formation amounts of Fe 3 C and C deposition during H 2 S removal or NH 3 decomposition runs. In a TPO run, the limonite in the reactor after H 2 S removal or NH 3 decomposition was first quenched to room temperature in a stream of high purity He and then heated at 10°C/min to 950°C in 10% O 2 /He.…”

“…Therefore, preventing C deposition and retransformation of Fe 3 C into metallic Fe, as shown in Eqs. (10), (12) and (13) and Eqs. (11), (15) and (16), respectively, may be the driving force for the high NH 3 decomposition performance with 5% CO 2 , 5% H 2 O or 5% CO 2 /5% H 2 O coexisted to 50% H 2 /30% CH 4 /5% CO.…”

“…(17) and (18). [8][9][10][11][12][13][14]16) On the other hand, crystallized carbon (CC) was detected at around 32° in the samples recovered after reaction in 50% H 2 /30% CH 4 /He, along with peaks corresponding to α-Fe and Fe 3 C. The peaks attributable to crystallized C and Fe 3 C were also observed for the in catalyst after the decomposition run in 50% H 2 /30% CH 4 /5% CO/He. The formation In 50% H2/30% CH4/He, (c) In 50% H2/30% CH4/5% CO/ He, (d) In 50% H2/30% CH4/5% CO/5% CO2/He, (e) In 50% H2/30% CH4/5% CO/5% H2O/He, (f) In 50% H2/30% CH4/5% CO/5% CO2/5% H2O/He.…”

“…[8][9][10][11][12][13][14][15][16][17][18] We have found that fine particles of metallic iron (α-Fe) formed from low-value iron ore (limonite) give high activity in the decomposition of NH 3 and model tar-N compounds. Limonite can achieve almost complete decomposition of 2 000 ppmv NH 3 in inert or simulated fuel gas from coal gasification at 500-850°C.…”

“…Limonite can achieve almost complete decomposition of 2 000 ppmv NH 3 in inert or simulated fuel gas from coal gasification at 500-850°C. 10) In addition, we have recently…”