are studied in a plug‐flow reactor at temp. of 550‐700 K and CO and N2O partial pressures in the ... more are studied in a plug‐flow reactor at temp. of 550‐700 K and CO and N2O partial pressures in the range 0.6‐7 torr.
Abstract The effect of high-temperature oxygen aging on the local structure of Rh oxide particles... more Abstract The effect of high-temperature oxygen aging on the local structure of Rh oxide particles in a Rh/Al 2 O 3 catalyst has been characterized using X-ray absorption fine structure (XAFS) measurements. Thermal aging of the catalyst was performed at various temperatures and for different lengths of time at selected temperatures. Following treatment in 5% oxygen at or above 500°C, the supported Rh is completely oxidized to orthorhombic Rh 2 O 3 . The coordination of the dominant shells in the radial distribution function increases with treatment temperature, reaching a maximum at 800°C. Above this treatment temperature, the coordination in these shells decreases dramatically with increasing treatment temperature. Treatment in 5% oxygen at temperatures near 800°C for an extended period results in an increase in coordination of the first three dominant shells. Most of this increase takes place during the initial 1-2 h of treatment, but proceeds more slowly thereafter. Extended treatment at lower temperatures (600°C) results in slow and gradually increasing coordination in these shells, while at much higher temperatures (1000°C) the coordination initially increases but then decreases over extended treatment periods. The latter behavior is coincident with an apparent change in the structure as well. Since XAFS provides insight about single crystallite domains, the results suggest that at 800°C, Rh 2 O 3 crystallite growth or consolidation is more favored than at lower or higher temperatures. The behavior of the supported Rh 2 O 3 at high temperatures indicates a strong interaction with the support; however, this interaction does not appear to involve formation of a spinel or dissolution of Rh cations into the alumina lattice. Alternative explanations for these observations are discussed.
Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) w... more Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) were measured in a laboratory plug-flow reactor at temperatures between 550 and 700 K, space times between 0.06 and 0.26 s, and CO and NâO partial pressures between 0.6 and 7 Torr. A brief comparison was also made between the CO-NâO kinetics and kinetics of the CO-NO and CO-Oâ reactions. The comparison showed that the CO-NâO reaction is an important subreaction of the CO-NO reaction (i.e., CO reacts initially with NO to produce NâO, which undergoes further reaction with CO to yield Nâ and COâ). The comparison also showed that the rate of the CO-NâO reaction is much lower than rates of the CO-NO and CO-Oâ reactions (ratio of turnover frequencies at 475 K estimated as 1 (CO-NâO) vs 7.1 à 10² (CO-NO) vs 4.4 à 10âµ (CO-Oâ)). CO-NâO rate measurements under differential conversion conditions at temperatures of 564 and 583 K yielded reactions orders of -1.0 {plus minus} 0.15 in CO pressure, 0....
Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) w... more Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) were measured in a laboratory plug-flow reactor at temperatures between 550 and 700 K, space times between 0.06 and 0.26 s, and CO and NâO partial pressures between 0.6 and 7 Torr. A brief comparison was also made between the CO-NâO kinetics and kinetics of the CO-NO and CO-Oâ reactions. The comparison showed that the CO-NâO reaction is an important subreaction of the CO-NO reaction (i.e., CO reacts initially with NO to produce NâO, which undergoes further reaction with CO to yield Nâ and COâ). The comparison also showed that the rate of the CO-NâO reaction is much lower than rates of the CO-NO and CO-Oâ reactions (ratio of turnover frequencies at 475 K estimated as 1 (CO-NâO) vs 7.1 à 10² (CO-NO) vs 4.4 à 10âµ (CO-Oâ)). CO-NâO rate measurements under differential conversion conditions at temperatures of 564 and 583 K yielded reactions orders of -1.0 {plus minus} 0.15 in CO pressure, 0....
are studied in a plug‐flow reactor at temp. of 550‐700 K and CO and N2O partial pressures in the ... more are studied in a plug‐flow reactor at temp. of 550‐700 K and CO and N2O partial pressures in the range 0.6‐7 torr.
Abstract The effect of high-temperature oxygen aging on the local structure of Rh oxide particles... more Abstract The effect of high-temperature oxygen aging on the local structure of Rh oxide particles in a Rh/Al 2 O 3 catalyst has been characterized using X-ray absorption fine structure (XAFS) measurements. Thermal aging of the catalyst was performed at various temperatures and for different lengths of time at selected temperatures. Following treatment in 5% oxygen at or above 500°C, the supported Rh is completely oxidized to orthorhombic Rh 2 O 3 . The coordination of the dominant shells in the radial distribution function increases with treatment temperature, reaching a maximum at 800°C. Above this treatment temperature, the coordination in these shells decreases dramatically with increasing treatment temperature. Treatment in 5% oxygen at temperatures near 800°C for an extended period results in an increase in coordination of the first three dominant shells. Most of this increase takes place during the initial 1-2 h of treatment, but proceeds more slowly thereafter. Extended treatment at lower temperatures (600°C) results in slow and gradually increasing coordination in these shells, while at much higher temperatures (1000°C) the coordination initially increases but then decreases over extended treatment periods. The latter behavior is coincident with an apparent change in the structure as well. Since XAFS provides insight about single crystallite domains, the results suggest that at 800°C, Rh 2 O 3 crystallite growth or consolidation is more favored than at lower or higher temperatures. The behavior of the supported Rh 2 O 3 at high temperatures indicates a strong interaction with the support; however, this interaction does not appear to involve formation of a spinel or dissolution of Rh cations into the alumina lattice. Alternative explanations for these observations are discussed.
Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) w... more Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) were measured in a laboratory plug-flow reactor at temperatures between 550 and 700 K, space times between 0.06 and 0.26 s, and CO and NâO partial pressures between 0.6 and 7 Torr. A brief comparison was also made between the CO-NâO kinetics and kinetics of the CO-NO and CO-Oâ reactions. The comparison showed that the CO-NâO reaction is an important subreaction of the CO-NO reaction (i.e., CO reacts initially with NO to produce NâO, which undergoes further reaction with CO to yield Nâ and COâ). The comparison also showed that the rate of the CO-NâO reaction is much lower than rates of the CO-NO and CO-Oâ reactions (ratio of turnover frequencies at 475 K estimated as 1 (CO-NâO) vs 7.1 à 10² (CO-NO) vs 4.4 à 10âµ (CO-Oâ)). CO-NâO rate measurements under differential conversion conditions at temperatures of 564 and 583 K yielded reactions orders of -1.0 {plus minus} 0.15 in CO pressure, 0....
Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) w... more Kinetics of the rhodium-catalyzed reaction between carbon monoxide (CO) and nitrous oxide (NâO) were measured in a laboratory plug-flow reactor at temperatures between 550 and 700 K, space times between 0.06 and 0.26 s, and CO and NâO partial pressures between 0.6 and 7 Torr. A brief comparison was also made between the CO-NâO kinetics and kinetics of the CO-NO and CO-Oâ reactions. The comparison showed that the CO-NâO reaction is an important subreaction of the CO-NO reaction (i.e., CO reacts initially with NO to produce NâO, which undergoes further reaction with CO to yield Nâ and COâ). The comparison also showed that the rate of the CO-NâO reaction is much lower than rates of the CO-NO and CO-Oâ reactions (ratio of turnover frequencies at 475 K estimated as 1 (CO-NâO) vs 7.1 à 10² (CO-NO) vs 4.4 à 10âµ (CO-Oâ)). CO-NâO rate measurements under differential conversion conditions at temperatures of 564 and 583 K yielded reactions orders of -1.0 {plus minus} 0.15 in CO pressure, 0....
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