Chemisorption of carbon dioxide

Whereas determination of chemisorption isotherms, e.g., of hydrogen on metals, is a means for calculating the size of the metallic surface area, our results clearly demonstrate that IR studies on the adsorption of nitrogen and carbon monoxide can give valuable information about the structure of the metal surface. The adsorption of nitrogen enables us to determine the number of B5 sites per unit of metal surface area, not only on nickel, but also on palladium, platinum, and iridium. Once the number of B5 sites is known, it is possible to look for other phenomena that require the presence of these sites. One has already been found, viz, the dissociative chemisorption of carbon dioxide on nickel. 

To reduce to the simple rate Equation (2), it is necessary that some of the steps in the general scheme occur at a negligible or an extremely fast rate. It has been observed (37) that carbon monoxide gas is an immediate product of the chemisorption of carbon dioxide on carbon and that the adsorption of carbon dioxide is not reversible to give immediate desorption of carbon dioxide. Therefore, it may be assumed that the lives of CCCOs) and C(CO)x are short. Consequently, the general expressions can be simplified to... 

It seems very probable that the chemisorption of oxygen and carbon monoxide diagnoses the number of surface sites, (Cr3+) (cus), but the degree to which n is 1 or 2 is uncertain. At lower temperatures of activation, chemisorption of carbon dioxide probably diagnoses the number of strongly basic sites, 02-(cus) or OH (cus). The reliability of the second conclusion is less than that of the first. We suggest that the catalytic reactions which we have studied use various eombinations of these sites. 

Chemisorption of carbon dioxide on doped oxides prepared at 250° was also studied calorimetrically. Initial heats of adsorption on NiO(10 Li)(250°) (27 kcal/mole) and on Ni0(10 Ga)(250°) (28 kcal/mole) are similar. The gallium-doped oxide chemisorbs at room temperature the same quantity of carbon dioxide (9.3 cm /gm) as NiO(250°) (9.7 cm3/gm), whereas the quantity of gas adsorbed on Ni0(10 Li)(250°) is larger (13.0 cm /gm). Lithia chemisorbs carbon dioxide at room temperature. However, the difference between the quantities of gas adsorbed on pure and lithiated oxides is not explained by the presence of lithia, as a separate phase, in the doped sample. It seems, therefore, that carbon dioxide, as oxygen, is chemisorbed at room temperature on anionic vacancies whose concentration is particularly large on lithiated oxides. 

Lee, K., Beaver, M., Caram, H. and Sircar, S. (2007) Reversible chemisorption of carbon dioxide- Simultaneous production of fuel-cell grade H2 and compressed CO2 from synthesis gas. Adsorption, 13,385-397. 

Applying the law of mass action to the chemical equation for chemisorption, the equilibrium constant K is found. For example, using sodium carbonate solution (Na2C03) dissolved in water as a solvent for the chemisorption of carbon dioxide (CO2) from a gas mixture, sodium hydrogen carbonate (NaHCOj) is formed according to the chemical equation... 

A reaction mechanism is suggested which involves dissociative chemisorption of hydrogen and water in competition on one type of active sites and chemisorption of carbon dioxide on the other type. Chemisorption of carbon dioxide is so strong that it prevents chemisorption of carbon monoxide. Chemisorbed carbon dioxide and hydrogen are in equilibrium on the surface. Reverse shift takes place by dissociation of the reaction product into carbon monoxide and a chemisorbed hydroxyl-species. The shift reaction is taking place by reaction between carbon monoxide from the gas phase and hydroxyl-species on the surface. Methanol is formed by step-wise hydrogenation of chemisorbed carbon dioxide. 

Adsorption of carbon dioxide or oxygen on the praseodymium samples was carried out in the pressure range of 1-40 Pa to evaluate the number of chemisorption sites on the samples. Praseodymium oxide irreversibly adsorbed 9.5 x 10" mol g of carbon dioxide. The amount of oxygen irreversibly adsorbed on the sample was 15.2 x 10" mol g Carbon dioxide or oxygen was not adsorbed on the samples containing chlorine, i.e., praseodymium chloride and praseodymium oxychloride prepared from the chloride by heating under oxygen flow at 750°C for 1 h. 

Mechanisms A and B both state that carbon monoxide retards the gasification of carbon by carbon dioxide by decreasing the fraction of the surface which is covered by oxygen atoms under steady state conditions. In mechanism A, fli is decreased by the chemisorption of carbon monoxide by a fraction of the active sites. In mechanism B, 61 is decreased by the reaction of a portion of the chemisorbed oxygen with gaseous carbon monoxide to produce gaseous carbon dioxide. Reif (57) shows that only one of these reactions can control retardation at one time. 

Extensive information concerning distribution of the promoters, penetration below the promoters of adsorbed atoms, and chemical behavior of the promoters was obtained by Brunauer and Emmett (25,26). They used chemisorption of carbon monoxide, carbon dioxide, nitrogen, hydrogen, and oxygen, individually and successively measuring the influence of one type of chemisorption upon another type. It was concluded that CO and C02 were chemisorbed as molecules, H2 and N2 as atoms, and 02 probably as ions. C02 is chemisorbed on the alkali molecules located at the surface, whereas H2, N 2, CO, and 02 are chemisorbed on the iron atoms. From the effect of presorbed CO upon the chemisorption of C02 and vice versa it was concluded that the promoters are concentrated on the surface and are distributed so effectively that most surface iron atoms are near to a promoter atom. Strong indication... 

The chemisorption measurements of carbon dioxide and hydrogen were obtained at 298 K using the chemisorption apparatus (Micromeritics ASAP 2000). The samples (1.0-1.2 g) used in the chemisorption studies were reduced for 12 hr at 723 K in a flow of hydrogen, evacuated at the reduction temperature and then cooled to the adsorption temperature. The difference between the adsorption isotherms obtained by the repeated use of gas dosing and degassing system gives the amount of chemisorbed species on the catalysts. 

Carbon dioxide chemisorption is of this type. We have taken chemisorption as that irreversible at 25°, a definition similar to that of Maciver and Tobin (56). That this represents chemisorption is clear but we have not established that our procedures give a saturation value of chemisorption. Doubts as to this are furthered by the observation of Maciver and Tobin that there was a slow loss of carbon dioxide on pumping at 25° and our observation that substantial amounts of carbon dioxide adsorbed at 25° are released in flowing helium at 100°. 

Physical adsorption usually involves a smaller energy change than does chemisorption. The adsorption of nitrogen on carbon evolves about 5000 calories per mole, this heat being somewhat greater than the heat of liquefaction, whereas the initial adsorption of oxygen on some carbons at 0° C liberates over 100,000 calories per mole—an amount that is greater than the heat of formation of carbon dioxide. 

C) but did not return to the initial value (Section A) within 40 min. The addition of 15% water vapor (Section D) further decreased the sulfur dioxide removal efficiency. Curve b in Figure 2 depicts the analyses of carbon dioxide when the bauxite catalyst was subjected to the water treatment. The mirror image resemblance of curves b and a in Figure 2 suggests that the reaction stoichiometry is closely represented by Equation 1 and that the poisoning effect of water is essentially caused by its competition for chemisorption on the alumina Lewis acid sites with the sulfur precursor of the intermediate (9) reductant carbonyl sulfide. 

We also predicted the possibility of chemisorption of carbon and oxygen atoms to the carbon nanotube sidewall. Oxygen atoms were ejected from the substrate after the collision of the argon atom beam with the silicon dioxide substrate. And when a carbon atom was effectively removed from the nanotube sidewall, it ended up doping the substrate or chemisorbed on other sector of the nanotube sidewall. We denoted chemisorption as the adsorption by covalent bonding of an atom to the nanotube sidewall. It could be considered the opposite of a vacancy defect. 

MCM-41 and silica gel as efficient and reusable heterogeneous catalyst for the Knoevenagel Condensation reactions. Burwell and Leal (1974) first reported selective chemisorption of sulfur dioxide on amine-modified silica gel. Leal et al. (1995) studied carbon dioxide adsorption on amine surface-bonded silica gel, although their CO2 adsorption amount (0.3 mmol/g-sorbent at 1 atm CO2) was low. Further work by Huang et al. (2003) produced high-capacity and selective sorbents for both CO2 and H2S. 

The complementary use of nitrogen and carbon dioxide adsorption to charactaj microporous materials as activated carbons has been recommended by various auttmrs [12,13], In the case of pillared clays, little work has been done using carbon dioxide as adsorbate. In a previous work [14], we found that the adsorption of carbon dioxide and that of nitrogen are not sensible to the same type of microporosity. It is also necessary to take into account the possibility of chemisorption when carbon dioxide is used as adsorbate. In this way and from the results presented in this work, there is an effect between the temperature of calcination of the samples (GAmont-Al) and the adsorption of carbon dioxide that cannot be explained from a modification of the texture of the pillarai clays the nature of the surface sites created at 473 K would merit further research. 

Additionally to physisorption, chemisorption can contribute to the solubility of carbon dioxide in ionic liquids. One example is l-alkyl-3-methylimidazolium acetate. The basicity of the anion allows the abstraction of the most acidic proton of the cation, forming a carbene and acetic acid. Subsequently, the former cation is carboxylated. The availability of carbenes in l-alkyl-3-methylimidazolium acetate was used already... 

Jain D, Kuipers JAM, Deen NG Numerical modeling of carbon dioxide chemisorption in sodium hydroxide solution in a micro-structured bubble column, Chem Eng Sci 137 685-696, 2015. 

Carbon dioxide cannot be recommended for routine determinations of specific surface on the other hand, it should be particularly suitable for the study of the polarity of surfaces in systems where chemisorption can be excluded from consideration. 

Many molecules undergo partial oxidation on adsorption and many alkanes and alkenes are believed to yield an adsorbed CHO group on adsorption (Petrii, 1968). These processes usually lead to the complete oxidation of the organic molecule to carbon dioxide and few workers have attempted to halt the reaction at an intermediate stage. Hence, although there are undoubtedly possibilities for using dissociative chemisorption for synthetic reactions, this chapter will not consider these processes further. 

Carbon dioxide chemisorptions were carried out on a pulse-flow microreactor system with on-line gas chromatography using a thermal conductivity detector. The catalyst (0.4 g) was heated in flowing helium (40 cm3min ) to 723 K at 10 Kmin"1. The samples were held at this temperature for 2 hours before being cooled to room temperature and maintained in a helium flow. Pulses of gas (—1.53 x 10"5 moles) were introduced to the carrier gas from the sample loop. After passage through the catalyst bed the total contents of the pulse were analysed by GC and mass spectroscopy (ESS MS). 

---