Applied Catalysis B, Environmental (v.45, #4)


Low-temperature abatement of CO from mixtures as complicated as smoke was considered. Adsorptive and catalytic properties of some amorphous (Al2O3) and crystalline (zeolites) catalyst supports, Ag- and Pd-containing catalysts were investigated. Zeolites with an aperture size around 5 Å were found capable of adsorbing CO at room temperature. Development of Pd catalysts with Ag as catalyst promoter, supported on zeolite (for a shape-selectivity), proved to be a feasible approach to the smoke application. The mechanisms governing the adsorption and catalysis were studied using non-steady-state oxidation of CO on the Ag catalyst. Distribution and migration of the reaction products in the Pd-containing catalysts and some elements of the mechanism of catalysis are discussed based on the gas-flow and gas-pulse experiments and the literature data.
Keywords: Abatement; CO; Low-temperature catalytic oxidation; Smoke; Ag trap; Pd-Ag catalyst;

A low-temperature abatement of carbon monoxide from mixtures as complicated as smoke was considered. Catalytic oxidation and chemisorption of CO on activated carbon-supported Pd and Cu catalysts were investigated. Heterogenized Wacker-type catalysts and the product of catalyst degradation, a dispersed Pd-Cu catalyst, were prepared and found to be promising for the smoke applications. Deactivation of the catalyst was found to be caused by the catalyst dehydration process, which appeared to be reversible. A heat treatment in a CO+O2 reaction gas flow resulted in the conversion of a Wacker-type transition metal complex catalyst to Pd0 atoms or small clusters. This new system composed a very active chemisorbent of CO and a relatively stable oxidation catalyst at elevated temperatures. This immediately prepared catalyst showed 70% removal of CO from smoke. The elements of the mechanisms of CO oxidation were studied under the gas-flow and gas-pulse conditions.
Keywords: Abatement; CO; Low-temperature catalytic oxidation; Pd-Cu; Wacker catalyst; Smoke;

Effect of V2O5 on the catalytic activity of Pt-based diesel oxidation catalyst by Myoung Rae Kim; Do Heui Kim; Seong Ihl Woo (269-279).
We investigated the suppression of SO2 oxidation activity by vanadium oxide in Pt-based diesel oxidation catalyst using reaction experiments, temperature programmed desorption (TPD), infrared (IR) and X-ray photoelectron spectroscopy (XPS). There was no interaction between Pt and S indicated by the XPS results. SO2 was not adsorbed on Pt at room temperature indicated by the absence of peak arising from SO2 in SO2 TPD spectra. SO2 molecules were adsorbed on the hydroxyl groups of TiO2 and migrated to Pt particles to react with oxygen adsorbed on it. V2O5 decreased the adsorption of SO2 on TiO2 by the blockage of V2O5 on TiO2.
Keywords: Diesel oxidation catalyst; Vanadium oxide; SO2; IR; XPS; TPD;

Catalytic hydrodechlorination of 2,4,4′-trichloro-2′-hydroxydiphenylether under mild conditions by Chuanhai Xia; Jie Xu; Wenzhong Wu; Qian Luo; Jiping Chen; Qing Zhang; Xinmiao Liang (281-292).
More than 99% of 2,4,4′-trichloro-2′-hydroxydiphenylether (TCPE) by the catalytic hydrogenation over palladium/carbon was firstly dechlorinated under mild conditions. Used molecular hydrogen as the reducing agent, TCPE was completely hydrodechorinated to 2-hydroxydiphenylether (PE) at 50 °C and under normal pressure. The solvents affected not only the rate of the dechlorination, but also the selectivity of the hydrogenation. In general, the rate of the dechlorination decreased in the order of alcohols>alkanes>arenes>heterocycles. Addition of the bases (such as sodium hydroxide, sodium carbonate, sodium bicarbonate, triethylamine and pyridine, etc.) to the reaction systems also changed the rate of the reaction and the selectivity of the dechlorination. Except for pyridine, the other bases obviously accelerated the rate of the dechlorination. When the mixture of ethanol–water was used as the reaction solvent instead of ethanol, the rate of the dechlorination was remarkably improved. When a stoichiometric amount of sodium hydroxide was utilized as the proton acceptor in ethanol–water solvent, the catalytic life and the stability of the palladium/carbon were dramatically enhanced and promoted. The dechlorination process worked well in either organic solvents or aqueous solution and thus had potential application in the remediation of contaminated industrial waste water as well.
Keywords: 2,4,4′-Trichloro-2′-hydroxydephenether; Catalytic hydrodechlorination; Base effect; Solvent effect; Palladium/carbon;

The pH influence on photocatalytic decomposition of organic dyes over A11 and P25 titanium dioxide by Beata Zielińska; Joanna Grzechulska; Ryszard J. Kaleńczuk; Antoni W. Morawski (293-300).
The photocatalytic removal (decomposition+adsorption) of four azodyes (Reactive Red 198, Acid Black 1, Acid Blue 7 and Direct Green 99) in water was investigated using Tytanpol A11 (“Police” Chemical Factory, Poland) and Degussa P25 (“Degussa”, Germany) as photocatalysts. The effect of pH of the reaction solution has been examined. The degree of the dye removal in the solution was measured by UV-Vis spectroscopy. Photodecomposition of dye on photocatalyst surface was monitored by FTIR spectroscopy. A11 photocatalyst has lower activity in the reaction of photocatalytic decomposition of organic dyes than Degussa P25. The photocatalytic decomposition of the dyes takes place on the photocatalyst surface at pH=2 while at pH=12 photocatalytic reaction proceeds via photogenerated hydroxyl radicals for both A11 and P25.
Keywords: Photocatalytic decomposition; Titanium dioxide; Azodyes;

A regenerable Fe/AC desulfurizer for SO2 adsorption at low temperatures by Jianrong Ma; Zhenyu Liu; Shoujun Liu; Zhenping Zhu (301-309).
A novel regenerable Fe/activated coke (AC) desulfurizer prepared by impregnation of Fe(NO3)3 on an activated coke was investigated. Experiment results showed that at 200 °C the SO2 adsorption capacity of the Fe/AC was higher than that of AC or Fe2O3. Temperature-programmed desorption (TPD) revealed that H2SO4 and Fe2(SO4)3 were generated on the desulfurizer upon adsorption of SO2. Effect of desulfurization temperature was also investigated which revealed that with increasing temperature from 150 to 250 °C, the SO2 removal ability gradually increases. The used Fe/AC can be regenerated by NH3 at 350 °C to directly form solid ammonium-sulfate salts.
Keywords: Activated coke; Adsorption properties; Desulfurizer; Regeneration;


AUTHOR INDEX (313-314).

SUBJECT INDEX (315-319).