K. Krishna

Selective catalytic reduction of NO with NH3 over Fe-ZSM-5 catalysts prepared by sublimation of FeCl3 at different temperatures

Fe-ZSM-5 catalysts were prepared by subliming FeCl3 into H-ZSM-5. The method used allowed Fe-ZSM-5 catalyst preparation by FeCl3 exchange at a desired sublimation temperature and was found to be more precise. The sublimation of FeCl3 into H-ZSM-5 was carried out at 320 and 700 °C. Fe-ZSM-5 prepared by sublimation of FeCl3 at 320 °C followed by rapid heating to 700 °C and the catalyst prepared by subliming FeCl3 at 700 °C were found to be more active for NO reduction with NH3 in the presence of simulated exhaust gases containing water vapor than catalysts prepared by subliming FeCl3 at 320 °C. To determine the active sites, the catalysts were characterized by H2-TPR, in situ DRIFTS of NO adsorption, NH3-TPD, XRD and chemical analysis methods. The observed NO conversion differences in selective catalytic reduction using NH3 could be correlated to the iron cation species present at different locations determined from diffuse reflectance infrared spectroscopy. Enhanced NO reduction activity was obtained when γ positions in Fe-ZSM-5, corresponding to Fe2+(NO) band at 1877 cm-1 in DRIFTS, were preferentially occupied.

Preparation of a monolith-supported Au/TiO2 catalyst active for CO oxidation

The development of a method for making an adherent coating of Au/TiO2 on a cordierite monolith is described. The optimum method entails first forming a wash-coat of TiO2 by combining a colloidal dispersion of TiO2 with Degussa P-25 TiO2 that has been washed, dried and crushed. Subsequent deposition of gold from HAuCl4 solution at pH 9 resulted in a catalyst that was less active for the oxidation of carbon monoxide than a similar preparation using only P-25, but reproducible values of T50 of about 250 K were obtained.

In situ preparation of ferrierite coatings on structured metal supports

Abstract In situ synthesis of binderless ferrierite (ZSM-35) coatings on 110–140 csi monoliths prepared of metal foil, metal microfiber and metal gauze was studied. The influence of the silica-to-alumina ratio, dilution ratio, synthesis time and pretreatment procedure on the coating characteristics was investigated. Uniform and continuous ferrierite coatings were obtained with surface loadings of up to 27 g FER /m 2 sup (75 kg FER /m 3 packing ) on the foil monoliths, 5 g FER /m 2 sup (104 kg FER /m 3 packing ) on the microfiber monoliths and 24 g FER /m 2 sup (82.7 kg FER /m 3 packing ) on the gauze monoliths. The formation of ferrierite was confirmed by X-ray diffraction. Scanning electron microscopy images showed ferrierite crystals with shapes varying from multilayered cubes to thin spines. The prepared ferrierite coatings were firmly bonded to the support and were stable under ultrasonic treatment.