In the early studies, a lot of work was done on the surface structure, adsorption properties and reaction mechanism of Ru catalysts, but the effect of residual Cl- content in highly dispersed catalysts was often overlooked. With the deepening of research, the negative impact of Cl on the performance of catalysts has gradually attracted the attention of researchers. The residual chloride ion on the catalyst will poison the ammonia synthesis reaction. Especially when the oxide is used as the carrier, the chloride ion will bond with oxygen. Even at a higher reduction temperature, the residual chloride ion is not easily removed. . Aika et al. used a different Ru precursor as the precursor, and used A1, O as the carrier, without a promoter, to obtain a series of Ru/A1:O, catalysts in a similar manner. The activity of the catalyst and the amount of chemical adsorption of hydrogen were measured under the same conditions, and it was found that Cl strongly inhibited the activity. When the reduction temperature is lower than 900K, the reaction of Cl with a pair of synthetic ammonia is a non-negligible poison, and the HC1 released during the reduction process has a corrosive effect on the reaction equipment. There are currently two widely accepted mechanisms for the poisoning of Cr.
One view is that the strong electronegativity of chlorine allows chlorine to attract electrons from helium atoms or other electron donating aids, and the electron cloud density on the surface of helium atoms is weakened to inhibit the dissociation of N-N bonds. Early Bond_4 pointed out that the residual cl in the highly dispersed catalyst can cause the charge density of Ru loaded on A1 O to decrease, which needs to be studied carefully. The study by Charcosset et al. suggests that the presence of Cl-I is not completely reduced to Ru by Ru. Proof of the. A similar result was obtained by Bossi et al., who found that even after the same conditions of reduction, Cl—has a much larger residual tendency on Ru/Al, O than on Ru/SiO. The presence of Cl-I indicates that Ru ̈ is not completely reduced to Ru. . Shiflett believes that the presence of cl-I reduces the electron density of Ru on the rhodium catalyst, thereby inhibiting the synthesis rate, increasing the performance activation energy, and increasing the inhibitory effect of NH on the reaction rate. Dalla Betta_4 mentions that residual cl may have an effect on CO adsorption and reaction performance, and that residual cl may cause a decrease in the charge density of Ru supported on A1, O, thereby inhibiting the rate of synthesis, increasing apparent activation energy, and increasing The inhibitory effect of NH on the reaction rate. Reference [42] mentions that Si 02 does not significantly adsorb chloride ions, while A1 O contains a large amount of chloride ions in its structure, and residual cl changes the surrounding environment of Ru, thereby weakening the adsorption of H. Similarly, the dissociative adsorption of N as a control step is also weakened, so that the rate of ammonia synthesis decreases. Hard work and so on.åŽŸä½ In-situ infrared spectroscopy was used to investigate the CO adsorption state of Ru/A1 O samples with different Cl content. It was found that when RuC1 /A1 O was reduced at 300 °C, Ru was reduced and part of Cl was transferred to A1:O near Ru, on the carrier, and forming a strong L acid center with A1, O, can interact with the reduced Ru to form an electron-deficient Ru center. After evacuation at 400 °C, a small part of Cl is in the form of HC1. In addition to desorption, part of Cl interacts with the nearby electron-deficient Ru center to form a [Ru cl-[] complex, which results in a significant decrease in CO adsorption.
Another argument is that the presence of chloride ions promotes the adsorption of hydrogen (a chloride ion can generate approximately 6 hydrogen adsorption sites), thus inhibiting the activation of nitrogen. We know that there is a competitive adsorption of H and N2 on the surface of the ruthenium catalyst. Since the adsorption heat of H2 is greater than the adsorption heat of N2, the strong adsorption of H, occupies the active center of the ruthenium catalyst surface, and it is possible to generate a sub-layer hydrogen bridge compound, which strongly adsorbs. Hydrogen is a common feature of lanthanide ammonia synthesis catalysts. It has been suggested that the presence of chloride ions in the catalyst further promotes the adsorption of hydrogen on its surface. Lu et al. showed that the presence of electronegative chloride ions in the catalyst can deepen the chemical adsorption of H. In the experiment, they used RuC1, and Ru, (CO): as the active precursor to prepare Ru/A1:O, a catalyst to study the adsorption of H on the two samples. From the research results, it is found that the chemisorption phenomenon of H on the sample with RuC1 as precursor is very active, while the chemisorption phenomenon of H on the chlorine-free sample is not very significant, which proves that the presence of Cl-1 promotes the catalyst to hydrogen. Adsorption. In subsequent reports, they proposed that electronegative chlorine-adsorbed ions preferentially adsorb on the surface Ru of the high-valence state and hinder the adjacent low-valent Ru from supplying electrons to the hydrogen molecules. At the end of the zui, they concluded that the addition of one chloride ion to the catalyst produced six activated hydrogen adsorption sites.
One view is that the strong electronegativity of chlorine allows chlorine to attract electrons from helium atoms or other electron donating aids, and the electron cloud density on the surface of helium atoms is weakened to inhibit the dissociation of N-N bonds. Early Bond_4 pointed out that the residual cl in the highly dispersed catalyst can cause the charge density of Ru loaded on A1 O to decrease, which needs to be studied carefully. The study by Charcosset et al. suggests that the presence of Cl-I is not completely reduced to Ru by Ru. Proof of the. A similar result was obtained by Bossi et al., who found that even after the same conditions of reduction, Cl—has a much larger residual tendency on Ru/Al, O than on Ru/SiO. The presence of Cl-I indicates that Ru ̈ is not completely reduced to Ru. . Shiflett believes that the presence of cl-I reduces the electron density of Ru on the rhodium catalyst, thereby inhibiting the synthesis rate, increasing the performance activation energy, and increasing the inhibitory effect of NH on the reaction rate. Dalla Betta_4 mentions that residual cl may have an effect on CO adsorption and reaction performance, and that residual cl may cause a decrease in the charge density of Ru supported on A1, O, thereby inhibiting the rate of synthesis, increasing apparent activation energy, and increasing The inhibitory effect of NH on the reaction rate. Reference [42] mentions that Si 02 does not significantly adsorb chloride ions, while A1 O contains a large amount of chloride ions in its structure, and residual cl changes the surrounding environment of Ru, thereby weakening the adsorption of H. Similarly, the dissociative adsorption of N as a control step is also weakened, so that the rate of ammonia synthesis decreases. Hard work and so on.åŽŸä½ In-situ infrared spectroscopy was used to investigate the CO adsorption state of Ru/A1 O samples with different Cl content. It was found that when RuC1 /A1 O was reduced at 300 °C, Ru was reduced and part of Cl was transferred to A1:O near Ru, on the carrier, and forming a strong L acid center with A1, O, can interact with the reduced Ru to form an electron-deficient Ru center. After evacuation at 400 °C, a small part of Cl is in the form of HC1. In addition to desorption, part of Cl interacts with the nearby electron-deficient Ru center to form a [Ru cl-[] complex, which results in a significant decrease in CO adsorption.
Another argument is that the presence of chloride ions promotes the adsorption of hydrogen (a chloride ion can generate approximately 6 hydrogen adsorption sites), thus inhibiting the activation of nitrogen. We know that there is a competitive adsorption of H and N2 on the surface of the ruthenium catalyst. Since the adsorption heat of H2 is greater than the adsorption heat of N2, the strong adsorption of H, occupies the active center of the ruthenium catalyst surface, and it is possible to generate a sub-layer hydrogen bridge compound, which strongly adsorbs. Hydrogen is a common feature of lanthanide ammonia synthesis catalysts. It has been suggested that the presence of chloride ions in the catalyst further promotes the adsorption of hydrogen on its surface. Lu et al. showed that the presence of electronegative chloride ions in the catalyst can deepen the chemical adsorption of H. In the experiment, they used RuC1, and Ru, (CO): as the active precursor to prepare Ru/A1:O, a catalyst to study the adsorption of H on the two samples. From the research results, it is found that the chemisorption phenomenon of H on the sample with RuC1 as precursor is very active, while the chemisorption phenomenon of H on the chlorine-free sample is not very significant, which proves that the presence of Cl-1 promotes the catalyst to hydrogen. Adsorption. In subsequent reports, they proposed that electronegative chlorine-adsorbed ions preferentially adsorb on the surface Ru of the high-valence state and hinder the adjacent low-valent Ru from supplying electrons to the hydrogen molecules. At the end of the zui, they concluded that the addition of one chloride ion to the catalyst produced six activated hydrogen adsorption sites.
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