ADSORPTION-DESORPTION PROPERTIES OF NATURAL AND MODIFIED TRIPOLI TOWARDS Cu(II) AND Pd(II) AS COMPONENTS OF CATALYSTS FOR CARBON MONOXIDE OXIDATION

Abstract

Adsorption of copper(II) ions by natural tripoli and its modified forms obtained as a result of using different treatment methods for natural tripoli modification, i.e. thermal treatment in air, boiling in water, and boiling in diluted nitric acid, was investigated. It has been found that the process of is accompanied by a decrease in pH at equilibrium copper(II) concentrations close to those required for monolayer formation In this case, the copper(II) anchoring occurs by ionexchange reactions resulted in the formation of inner-sphere complexes. Different strength of bonds formed by metal ions with tripoli adsorption sites is caused by multiplicity and inhomogeneity of functional groups ((≡AlOH, ≡SiOH, Si(OH)Al) on the tripoli surface and the fact that there is a competition between Cu(II) and Pd(II) for the active adsorption sites. The presence of weakly and strongly bound Pd(II) and Cu(II)) forms and contents of these forms can be determined by the combination of two methods of testing: by desorption of metal ions and by the kinetic method, i.e. the measurement of catalytic activity of Pd(II)-Cu(II)/tripoli compositions in the reaction of carbon monoxide oxidation. Kinetic investigations confirmed that the simultaneous presence and certain ratio of palladium(II) and copper(II) in the tripoli anchored compositions is required for steady-state CO oxidation over them It has been found that copper(II), as distinct from palladium(II), forms strong bonds with all Tripoli forms. These bonds do not break even after boiling in nitric acid for 1 h. An extent of Cu(II) and Pd(II) removal and a strength of their bonding with the tripoli surface were evaluated by the kinetic method. The results obtained show that the most active anchored Pd(II)-Cu(II) composition is that based on tripoli modified by boiling in water. This composition contains 68 % of copper(II) that cannot be extracted even by nitric acid and 66 % of weakly bound palladium(II).

Keywords

• природний і модифікований трепел, слабко- і міцнозв’язаніформи паладію(ІІ) і купруму(ІІ), каталізатори окиснення монооксиду вуглецю