Hydrogen Chemisorption on Al₂O₃-Supported Gold Catalysts

Abstract

Hydrogen is dissociatively adsorbed on the gold particles in Au/Al(2)O(3) catalysts, as demonstrated by a combination of in-situ X-ray absorption spectroscopy, chemisorption, and H/D exchange experiments. This chemisorption of hydrogen induces changes in the Au L(3) and L(2) X-ray absorption near-edge structures. The gold atoms on corner and edge positions dissociate the hydrogen, which does not spill over to the face sites. Therefore, the average number of adsorbed hydrogen atoms per surface gold atom increases with decreasing particle size. With temperature, the hydrogen uptake by supported gold increases or remains constant, whereas it decreases for platinum. Furthermore, in H/D exchange experiments, the activity of Au/Al(2)O(3) increases strongly with temperature. Thus, the dissociation and adsorption of hydrogen on gold is activated.

Hydrogenation over gold catalysts: The interaction of gold with hydrogen

“…The chemisorption of hydrogen on Al 2 O 3 supported gold particles with a mean cluster size of about 4 nm was examined by Jia and coworkers (21). They observed that about 14% of the surface atoms adsorbed hydrogen almost irreversible at 273 K. The hydrogen chemisorption properties of Au/Al 2 O 3 and Au/SiO 2 catalysts were investigated by Bus et al (64) in a temperature range of 298 to 523 K. For the 1 to 1.5 nm supported gold clusters, H/M values (number of adsorbed hydrogen atoms per total number of metal atoms) of at least 0.1 and as high as 0.73 were determined. However only 10-30% of the total adsorbed hydrogen did not desorb while evacuating for 2 h at the analysis temperature.…”

“…Thus it was proposed that hydrogen atoms only adsorb at edges and corners of the gold particles. The Au/H interaction was made visible by X-ray absorption spectroscopy (XAS) (64).…”

Overcoming the limitations of gold catalysts in hydrogenation: enhanced activity with full hydrogen utilization

“…1cI) with an associated surface area weighted mean of 2.8 nm. It has been noted elsewhere [23] that Au particle size \ 10 nm is critical for significant hydrogenation activity. Hydrogen chemisorption on Au/CeO 2 was appreciably lower than that measured under reaction conditions for the benchmark Pd/CeO 2 and Ni/CeO 2 ( Table 1).…”

The water‐gas shift reaction: from conventional catalytic systems to Pd‐based membrane reactors—a review

“…For a realistic reformate feed, a higher apparent reaction order for CO is expected due to the co-adsorption of hydrogen on Au. [91] For Pt catalysts, the forward reaction order with respect to CO 2 is slightly negative and close to zero, which can be explained by the weak interaction of CO 2 with Pt. A more significant inhibition effect by CO 2 over Au-based catalysts is observed.…”