Ni/Pt(111) Bimetallic Surfaces:  Unique Chemistry at Monolayer Ni Coverage

Abstract

We have utilized the dehydrogenation and hydrogenation of cyclohexene as probe reactions to compare the chemical reactivity of Ni overlayers that are grown epitaxially on a Pt(111) surface. The reaction pathways of cyclohexene were investigated using temperature-programmed desorption, high-resolution electron energy loss (HREELS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our results provide conclusive spectroscopic evidence that the adsorption and subsequent reactions of cyclohexene are unique on the monolayer Ni surface as compared to those on the clean Pt(111) surface or the thick Ni(111) film. HREELS and NEXAFS studies show that cyclohexene is weakly pi-bonded on monolayer Ni/Pt(111) but di-sigma-bonded to Pt(111) and Ni(111). In addition, a new hydrogenation pathway is detected on the monolayer Ni surface at temperatures as low as 245 K. By exposing the monolayer Ni/Pt(111) surface to D2 prior to the adsorption of cyclohexene, the total yield of the normal and deuterated cyclohexanes increases by approximately 5-fold. Furthermore, the reaction pathway for the complete decomposition of cyclohexene to atomic carbon and hydrogen, which has a selectivity of 69% on the thick Ni(111) film, is nearly negligible (<2%) on the monolayer Ni surface. Overall, the unique chemistry of the monolayer Ni/Pt(111) surface can be explained by the weaker interaction between adsorbates and the monolayer Ni film. These results also point out the possibility of manipulating the chemical properties of metals by controlling the overlayer thickness.

Enhancing H2 and CO Production from Glycerol Using Bimetallic Surfaces

“…The Ni/PtA C H T U N G T R E N N U N G (111) bimetallic surfaces were prepared by thermal evaporation of Ni onto PtA C H T U N G T R E N N U N G (111) as described previously. [10,11] The NiA C H T U N G T R E N N U N G (849 eV)/PtA C H T U N G T R E N N U N G (241 eV) Auger ratios were used to determine Ni coverages based on previous calibrations. [10,11] …”

“…[10,11] CO desorption occurred from a desorption-limited peak at 367 K. Overall, PtNi-PtA C H T U N G T R E N N U N G (111) displayed decreased H 2 and CO peak areas as compared to PtA C H T U N G T R E N N U N G (111). In contrast, increased H 2 and CO peak areas were observed on Ni-Pt-PtA C H T U N G T R E N N U N G (111) as compared to PtA C H T U N G T R E N N U N G (111).…”

“…[9][10][11][12] Increasing the deposition temperature to 600 K allows the Ni atoms to diffuse to the subsurface, producing a sandwich structure, Pt-Ni-PtA C H T U N G T R E N N U N G (111). Both experiments and DFT calculations have shown that the different locations of the Ni atoms lead to very different chemical properties of Ni-Pt-PtA C H T U N G T R E N N U N G (111) and Pt-Ni-PtA C H T U N G T R E N N U N G (111) surfaces.…”

Correlating Low-temperature Hydrogenation Activity of Co/Pt(111) Bimetallic Surfaces to Supported Co/Pt/γ-Al2O3 Catalysts

“…We have previously conducted surface science studies of the novel low-temperature reaction pathways of cyclohexene on both Ni/Pt(111) and Co/Pt(111) surfaces [9,[19][20][21][22]. Our surface science and DFT modeling results led to the prediction that materials such as Ni-Pt and Co-Pt would exhibit novel low-temperature activity for the hydrogenation of cyclohexene [10,20,22].…”

Pd-based bimetallic catalysts prepared by replacement reactions

“…Bimetallic catalysts have been widely used in many industrial processes [1][2][3][4], and many of the corresponding model catalysts have been investigated extensively in surface science studies [5][6][7][8][9][10][11][12][13][14][15][16][17]. It has been found that depositing one metal onto the single crystal surface of another metal can often introduce unique physical and chemical properties that are not seen in either pure metal alone due to the electronic and structural interactions at the metal-metal interface.…”