Various unpromoted and alkali (earth) promoted gold catalysts were characterized by means of XRD, HRTEM, DR/UV-Vis and TPR. Based on the results we conclude that metallic Au is the active species in CO oxidation and that the reduction of Au 3+ to Au 0 proceeds below 200°C. Pretreatment at mild temperatures, viz. 200°C, results in the highest catalytic performance of Au/Al 2 O 3 in low-temperature CO oxidation. Alkali (earth) metal oxide additives are most probably structural promoters. The best promoting effect is found for BaO.
The effect of Ag (1 wt%) and Au (1 wt%) on the catalytic properties of Ni/Al 2 O 3 (7 wt% Ni) for methane steam reforming (MSR) was studied in parallel with the effect of CeO 2 (6 wt%) and La 2 O 3 (6 wt%) addition. The addition of 1 wt% Ag to the alumina supported nickel catalyst drastically decreased its catalytic properties at temperatures lower than 600°C, due to the blockage of metal catalytic centers by silver deposition. The addition of Au and CeO 2 (La 2 O 3 ) to the nickel catalyst improved the methane conversion, CO 2 selectivity and hydrogen production at low reaction temperatures (t \ 600°C). At 700°C under our working conditions, the additives have no important effect in hydrogen production by MSR. The best hydrogen production at low temperatures was obtained for Ni-Au/Al 2 O 3 , due to the higher CO 2 selectivity, cumulated with slightly higher methane conversion in comparison with Ni/CeO 2 -Al 2 O 3 . At high temperature, Ni/CeO 2 -Al 2 O 3 is stable for 48 h on stream. are mainly deactivated due to the temperature effect on Au and Ag nanoparticles and less through coke formation. On , crystalline, graphitic carbon was deposited after 48 h of reaction leading to catalyst partial deactivation. On the Ni/CeO 2 -Al 2 O 3 surface, a porous amorphous form of deposited carbon was found, which does not decrease its catalytic activity after 48 h of reaction.Electronic supplementary material The online version of this article (
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