CO oxidation at low temperature over Pd/CeO 2 -TiO 2 catalyst was carried out in the feed containing different contents of water vapor (H 2 O). A positive effect of H 2 O was observed on the catalytic performance of Pd/CeO 2 -TiO 2 in CO oxidation at low temperature. The extent of this effect depends on the content of H 2 O in the feed; with a H 2 O content being 2.5 vol%, the catalyst Pd/ CeO 2 -TiO 2 exhibits the highest stability (longest life time for CO oxidation at 80°C). The results of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction (TPReaction) reaction illustrated that H 2 O in the feed supplies sufficient OH groups in the presence of O 2 , which can react with adsorbed CO on Pd species to produce CO 2 . Moreover, H 2 O may also enhance the adsorption of CO and suppress the formation of some carbonate species.
The effects of carbon addition on CoMo catalyst performance for sulfidation and hydrodesulfurization (HDS) were investigated. The carbon-containing catalyst was prepared by impregnation of γ-Al 2 O 3 support with NH 3 aqueous solution containing Co(NO 3 ) 2 ·6H 2 O, (NH 4 ) 6 Mo 7 O 24 ·4H 2 O and ethylenediamine. The results indicated that the incorporation of proper carbon on CoMo catalyst can improve its HDS performance. The carbon species on the catalyst were characterized by temperature-programmed oxidation and reduction, temperature-programmed desorption of ammonia and ultraviolet-visible diffuse reflectance spectra. Two forms of carbon species were differentiated: one is spread over the catalyst surface, similar to coke formed from reaction; the other interacts with active phase as an intermediate support. The carbon species acting as intermediate support may decrease the interaction of active metals with support, which enhances the sulfidation and HDS activities of CoMo catalyst.
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