Acid-modified clinoptilolite as a support for palladium–copper complexes catalyzing carbon monoxide oxidation with air oxygen
Samples of natural clinoptilolite were modified by an acid–thermal method at nitric acid concentrations of 0.25, 0.5, 1.0, and 3.0 M and a contact time of 30 min. A series of catalysts, K2PdCl4–Cu(NO3)2–KBr/S (S = 0.25H-CLI, 0.5H-CLI, 1H-CLI, and 3H-CLI) was obtained. All samples were investigated by X-ray phase and thermogravimetric analysis, FT-IR spectroscopy, water vapor ad/desorption and pH metric method. Besides, K2PdCl4–Cu(NO3)2–KBr/S samples were tested in the reaction of low-temperature carbon monoxide oxidation. It have been found that, owing to special physicochemical and structural-adsorption properties of 3H-CLI, it promotes formation of the palladium–copper catalyst providing carbon monoxide oxidation at the steady-state mode down to CO concentrations lower than its maximum permissible concentration at air relative humidity varied within a wide range.
Ozone decomposition on Ag/SiO2 and Ag/clinoptilolite catalysts at ambient temperature.
Silver modified zeolite (Bulgarian natural clinoptilolite) and Ag/silica catalysts were synthesized by ion exchange and incipient wet impregnation method respectively and characterized by different techniques. DC arc-AES was used for Ag detection. XRD spectra show that Ag is loaded over the surface of the SiO(2) sample and that after the ion-exchange process the HEU type structure of clinoptilolite is retained. UV-VIS (specific reflection at 310 nm) and IR (band at 695 cm(-1)) spectroscopy analysis proved that silver is loaded as a T-atom into zeolite channels as Ag(+), instead of Na(+), Ca(2+), or K(+) ions, existing in the natural clinoptilolite form. The samples Ag/SiO(2) and Ag-clinoptilolite were tested as catalysts for decomposition of gas phase ozone. Very high catalytic activity (up to 99%) was observed and at the same time the catalysts remained active over time at room temperature.
Change of pore-opening structure of mordenite upon dealumination by hydrochloric acid
Abstract The structure of dealuminated mordenites prepared at 340–358 K of hydrochloric acid was studied. 27Al MAS n.m.r. and XPS were measured to determine the species and depth profile of alumina, and these were corroborated with adsorption experiments using adsorbates of different sizes. Adsorption capacity of nitrogen was unaltered so that the structure of mordenite was retained, while that of 2,2,4-trimethylpentane with a larger kinetic diameter increased below 358 K of dealumination temperature, but then decreased above that. The H-mordenite (HM, Norton 100-H) contained a large amount of octahedral aluminum species (ca. 28%), and the nonframework aluminum was removed preferentially by the dealumination. Aluminum depth profile showed the homogeneous distribution on the inherent HM, but the enrichment on the samples prepared above 350 K. Based upon these findings, the following conclusions were drawn: (1) On the inherent HM, a small portion of nonframework aluminum near the pore opening disturbs the adsorption of large molecules: (2) The pore-opening size of the sample dealuminated at 358 K was large enough to adsorb 2,2,4-trimethylpentane: (3) However, upon the dealumination above 358 K, the pore opening was partly destroyed or blocked by nonframework alumina again to inhibit the adsorption of large molecules. Most of the aluminum impurity species seemed to be occluded as blocks or clusters in the mordenite. These variations of structure of the pore opening can be well related to those of the catalyst activity.