Pt−Co/SiO₂ Bimetallic Planar Model Catalysts for Selective Hydrogenation of Crotonaldehyde

Abstract

Surface science models of silica-supported Pt−Co bimetallic catalysts with various Pt/Co ratios have been successfully prepared using the spin-coating technique. Platinum and cobalt loadings on a series of silica-supported model catalysts were quantified by Rutherford backscattering spectrometry. Atomic force microscopy images indicate that flattish layerlike structures were obtained in all cases. The electronic state of Co and Pt was investigated using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). NEXAFS shows that cobalt is mainly forming octahedrally coordinated Co2+ species in the unreduced catalysts. The formation of the active phase has been investigated by XPS and “in situ” soft X-ray absorption spectroscopy (XAS). The NEXAFS measurements performed under 1−2 mbar of H2 reveal that cobalt is fully reduced to Co0 at relatively low temperature in bimetallic catalysts and reveal a decrease of the electron density of Co as the Pt/(Pt + Co) ratio increases, indicating the formation of alloyed bimetallic particles. This is also supported by XPS measurements. The crotonaldehyde hydrogenation has been studied on planar surface science model catalyst under diffusion-limitation-free conditions in gas phase at atmospheric pressure and temperatures between 100 and 150 °C. The addition of Co significantly improved the selectivity toward crotyl alcohol. This improvement is correlated with the electronic properties of the active phase.

Chemoselective hydrogenation of carbonyl compounds over heterogeneous catalysts

“…Bimetallic catalysts with group 10 metals, Ni, Pd, Pt. Several bimetallic catalysts having metal from group 10 have been investigated in chemoselective hydrogenations, like Pd-Cu/SiO 2 [81,104], Pd-Sn/SiO 2 [105,106], Ni-Cu/ SiO 2 [102], Ni-Co-B [125], Ni-Pt/Y [24], Pt-Sn/Al 2 O 3 [43,64,127], Pt-Sn/SiO 2 [29], Pt-W/Al 2 O 3 [116], Pt-Ge/ Al 2 O 3 [43,127], Pt-Sn/C [43,126], Pt-Co/SiO 2 [128], Pt/ ZnO [36,67], Pt-Sn-B [108], Pt/SnO 2 [68,69], Pt-Sn/SiO 2 [29,[129][130][131][132], Pt-Sn/MgO [15], Sn/Pt(1 1 1) model catalyst [107] and Pd-Au/C [133].…”

“…Several Pt catalysts modified with tin [15,29,43,64,76,107,126,127,[129][130][131][132], Pt-Co [128] and Pt-Zn catalysts [36,67,114] have been recently tested. The high chemoselectivities in carbonyl bond hydrogenation over PtSn can originate from the alloy formation, presence of ionic tin [29,130], surface enrichment of tin on Pt, changing the geometry of Pt particles [43] as well as from the lowered hydrogen adsorption capacity caused by tin addition [64].…”

Promotion effect in Pt–ZnO catalysts for selective hydrogenation of crotonaldehyde to crotyl alcohol: A structural investigation

“…For the platinum-based bimetallic catalysts, some electropositive metals, such as Fe, Sn, Zn, Ni and Co, etc., have prominent promotion effects [6][7][8][9][10][11][12][13]. For example, Pt 80 Fe 20 alloy was reported to enhance the activity and the selectivity of carbonyl bond hydrogenation on its (111) surface.…”

Combining Solid State Physics Concepts and X-Ray Absorption Spectroscopy to Understand DeNOx Catalysis

“…Bimetallic clusters are increasingly the subject of experimental measurement [94][95][96]. Renouprez et al [97] described the catalytic activity of a series of silica-supported Pd-Ni catalysts in the hydrogenation of 1,3-butadiene, for which pure palladium is an order of magnitude more active than pure nickel.…”