Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H_2

Activated carbon （AC） supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation （PROX） in excess H2 was evaluated. Ag/AC catalysts, after reduction in H2 at low temperatures （≤200 ℃） following heat treatment in He at 200 ℃ （He200H200）, exhibited the best catalytic properties. Temperature-programmed desorption （TPD）, X-ray diffraction （XRD） and temperature-programmed reduction （TPR） results indicated that silver oxides were produced during heat treatment in He at 200 ℃ which were reduced to metal silver nanoparticles in H2 at low temperatures （≤200 ℃）, simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 ℃. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H200 treatment displayed similar PROX of CO reaction properties to Ag/SiO2. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.

Selective and stable Au-Cu bimetallic catalyst for CO-PROX

Gold-based catalysts are promising in CO preferential oxidation(CO-PROX)reaction in H_(2)-rich stream on account of their high intrinsic activity for CO elimination even at ambient temperature.However,the decrease of CO conversion at elevated temperature due to the competition of H_(2)oxidation,together with the low stability of gold nanoparticles,has posed a dear challenge.Herein,we report that Au-Cu bimetallic catalyst prepared by galvanic replacement method shows a wide temperature window for CO total conversion(30-100℃)and very good catalyst stability without deactivation in a 200-h test.Detailed characterizations combined with density functional theory(DFT)calculation reveal that the synergistic effect of Au-Cu,the electron transfer from Au to Cu,leads to not only strengthened chemisorption of CO but also weakened dissociation of H_(2),both of which are helpful in inhibiting the competition of H_(2)oxidation thus widening the temperature window for CO total conversion.