Preferential CO Oxidation in a H₂-Rich Stream on Pt−ReO_x/SiO₂: Catalyst Structure and Reaction Mechanism

Abstract

Modification of Pt/SiO 2 with ReO x species enhanced the catalytic activity of the CO oxidation with O 2 in the presence of H 2 . The amount of Re modifier on Pt-ReO x /SiO 2 was optimized to be Re/Pt ) 0.5 on the molar basis. The promoting effect of Re species appeared after the reduction above 673 K. Characterization of the reduced Pt-ReO x /SiO 2 catalyst by means of EXAFS, XANES, temperature-programmed reduction, and CO adsorption measurements suggested the formation of the ReO x clusters on the surface of Pt metal particles with the average valence of Re of +2.7. The CO adsorption on Pt-ReO x /SiO 2 gave a higher wavenumber then that on Pt/SiO 2 at the same CO coverage, showing the weakened interaction between CO and the Pt surface, which is also supported by the desorption profile of the adsorbed CO. The CO coverage on Pt-ReO x / SiO 2 during the preferential CO oxidation was much smaller than that in the absence of H 2 , suggesting that an oxygen-containing species was coadsorbed on the reduced catalyst. The pulse reaction showed that the reduced Pt-ReO x /SiO 2 can activate O 2 even when the catalyst surface is saturated with CO. These tendencies can be explained by the mechanism where the reduced ReO x species activates O 2 and the oxidizing species is spilled over from the ReO x species to the Pt surface.

Bimetallic Ru-Re/γ-Al2O3 catalysts for the catalytic combustion of propane: Effect of the Re addition

“…Only for the Ru 50 -Re 50 catalyst, the O 2 adsorption at RT is 16% lower than that of the Ru catalyst which suggests a smaller extent of the subsurface ruthenium oxidation probably because of the larger covering of the RuRe nanoparticles with ReO x species. Literature data also show that in the Pt-Re/SiO 2 [27], Rh-Re/SiO 2 [28] and Ir-Re/SiO 2 [29] catalysts Pt, Rh or Ir metal surface was partially covered by the two-dimensional Re oxide clusters. At adsorption temperature of 150 • C, the complete oxidation of the metal phase in the Ru 90 -Re 10 and Ru 75 -Re 25 catalysts occurs, while in the Ru 50 -Re 50 sample full oxidation is not attained even at 250 • C. Since in this catalyst some fraction of Re is segregated [20], thus at 250 • C spreading of the rhenium oxide species from the Re metal particles both on the Ru phase and the ␥-alumina surface occurs causing additional covering of the Ru surface with ReO x species, thus hindering O 2 adsorption.…”

Role of Re Species and Acid Cocatalyst on Ir-ReOx/SiO2in the C-O Hydrogenolysis of Biomass-Derived Substrates

“…The formation of ReOx clusters on the surface of metal particles has also been reported in other metal-Re bimetallic systems such as Pt-ReOx. [29,30] Catalytic Performance in the Hydrogenolysis of Various Substrates Using Ir-ReO x /SiO 2 Catalyst in Water and Alkane Solvents Activity tests as well as reduction of the catalysts were performed in a 190 mL stainless steel autoclave with an inserted glass vessel. The catalyst (25-100 mg), a spinner and the reaction solvent (n-heptane or water; typically 10 mL) were placed into the autoclave and heated at 473 K under 8 MPa H2 for 1 h for the reduction pretreatment.…”

Hydrodeoxygenation of Vicinal OH Groups over Heterogeneous Rhenium Catalyst Promoted by Palladium and Ceria Support

“…The Pd À Re bond was also observed, suggesting that a part of the Re species are attached on the Pd particles like it is the case for ReO x -modified Ir, Pt, and Rh metal catalysts. [5,11,36] The reaction mechanism of the hydrodeoxygenation of 1,4-AHERY on ReO x -Pd/CeO 2 is discussed here. Toste et al have reported CH 3 ReO 3 -catalyzed deoxydehydration of 1,4-AHERY to 2,5-dihydrofuran.…”