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Highly active Pt–Fe bicomponent catalysts for CO oxidation in the presence and absence of H2

“…Since H 2 PtCl 6 can be reduced at lower temperature than Fe(NO 3 ) 3 , Pt NPs form first, which then favor the reduction of iron ions via spillover of H atoms from the Pt NPs. 14,48,49 Therefore, in the initial stage of the reduction the Pt-Fe catalyst should consist of Pt NPs decorated with surface Fe ensembles. Reduction of the bimetallic catalysts at elevated temperatures results in inward diffusion of the surface Fe into the core regions of the NPs.…”

Hydrogen Spillover. Facts and Fiction

“…of Fe 2 O 3 to Fe 3 O 4 in the temperature-programmed reduction (TPR) of a mixture of Pt/zeolite and Fe 2 O 3 was enhanced by the presence of the Pt-containing catalyst, but only when the catalyst had been oxidized (Figure7).34 TEM and X-ray energy dispersive spectrometry indicated that neither H nor Pt atoms migrated, but rather that Pt oxide (probably PtO 2 ) migrated from a nonacidic Pt/NaMOR catalyst, while Pt 2+ cations migrated from acidic Pt/HMOR 35. During the subsequent TPR run, these Pt species reduced to Pt metal particles on the Fe 2 O 3 .…”

A Nanoscale Demonstration of Hydrogen Atom Spillover and Surface Diffusion Across Silica Using the Kinetics of CO2 Methanation Catalyzed on Spatially Separate Pt and Co Nanoparticles.

“…5,6 Many examples of alleged hydrogen spillover on these materials have been reported, but it is argued there are simpler explanations such as migration of other reactants to the metal site, 7 contamination of the catalysts, 8 or migration of the metal itself across the support. 9 In many cases, H−D exchange has been claimed to indicate H atom spillover, but it is important to note that the minimum necessary criterion for H−D exchange on the support is only that H + and D + ions can interchange (with no net H atom transfer). For hydrogenation reactions, the distinction between net hydrogen atom transfer (leading to the possibility of increased hydrogenation rates) and proton exchange is, however, an important one.…”

“…This is because, while reducible oxides can transfer protons and electrons independently by reduction of the support (and thus allow a net migration of hydrogen atoms as proton plus electron), there is no low energy pathway thought to exist for H atoms to interact with irreducible supports. Molecular orbital energy calculations have been conducted on materials such as low index surfaces of Al 2 O 3 and SiO 2 showing H atom spillover to be unfavorable. , Many examples of alleged hydrogen spillover on these materials have been reported, but it is argued there are simpler explanations such as migration of other reactants to the metal site, contamination of the catalysts, or migration of the metal itself across the support . In many cases, H–D exchange has been claimed to indicate H atom spillover, but it is important to note that the minimum necessary criterion for H–D exchange on the support is only that H + and D + ions can interchange (with no net H atom transfer).…”