Thermal stability and activity in hydrogen oxidation of palladium catalysts supported on fibrous sulfonic cation exchanger in the hydrogen and magnesium forms

Abstract

The effect of reduced palladium on the thermal stability of the hydrogen and magnesium forms of FIBAN K-1 fibrous sulfonic cation exchanger was studied. The activity of palladium catalyst supported by the H and Mg forms of the cation exchanger in hydrogen oxidation was determined, as influenced by the temperature of treatment of the catalyst with the reaction mixture.As shown previously [135], the thermal stability of sulfonic cation exchangers in the metal forms is higher than that of the H forms. In particular, a mass-spectrometric study (10 37 torr) of the physicochemical properties of FIBAN K-1 sulfonic cation exchanger in the alkali metal and alkaline-earth metal forms showed that the Mg form had the highest thermal stability [4,5]. Hence, the Mg form can be used as a support for metal catalysts of redox reactions.However, the effects exerted by the metal phase on the thermal stability of sulfonic cation exchanger and by the metal cation on the catalytic activity of the supported metal were not understood. In this work we studied the thermal stability of the H and Mg forms of FIBAN K-1 sulfonic cation exchanger containing reduced palladium, the palladium dispersity in these matrices as influenced by the exchangable cation, and the palladium activity in hydrogen reduction as influenced by the temperature of the treatment of the catalysts with the reaction mixture. EXPERIMENTALThe H form of FIBAN K-1 fibrous sulfonic cation exchanger was prepared by bulk radiation grafting of styrene (98%)3divinylbenzene (2%) copolymer to polypropylene staple fiber, followed by sulfonation of the poly(styrene3divinylbenzene) matrix with concentrated H 2 SO 4 [6].Pure Mg form was prepared by washing of a column packed with the H form (exchange capacity 3 mg-equiv g 31 ) with excess 0.5 M MgCl 2 solution until pH of the solution at the outlet became neutral. Then the column was washed with distilled water until the absence of chloride ions in the wash waters and then was dried in air.To prepare catalysts with 2.5 wt % Pd content, the H or Mg form of the cation exchanger was treated under static conditions with a solution of tetramminepalladium(II) chloride [Pd(NH 3 ) 4 )]Cl 2 of a definite concentration at room temperature and pH 838.5. The Pd(II) concentration in the solutions before and after ion exchange was measured spectrophotometrically [7]. Then the samples were washed with distilled water until the absence of chloride anions in the wash waters, and the [Pd(NH 3 ) 4 ] 2+ cations were reduced with an aqueous solution of N 2 H 4 . H 2 O at 40oC for 30 min. After that, the samples were washed again with distilled water to neutral reaction and were dried at room temperature.To determine the degree of Pd(II) reduction, the ion-exchangeable Pd(II) species were completely washed out from the samples with excess 1 M NaCl and then the palladium concentration in the solution was measured. In the course of reduction, the ionexchange sites of the catalyst are converted to the H form after removal of [Pd(NH 3 ) 4 ] 2+ cations. To conv...

Thermal Degradation Studies of Some Strongly Acidic Cation Exchange Resins

“…So, the cationic resins, produced with a high degree of purity, became important as catalysts in various food technologies [18] and for purification in heavy-water moderated nuclear reactors in nuclear industries [19][20][21]. In many cases their use is limited by the relatively low thermal stability [22]. Hence, knowledge of the thermal behavior of cation exchange resins is necessary.…”