Controlled synthesis of PDDA stabilized Au–Pd bimetallic nanostructures and their activity in hydrogenation of acetylene

Abstract

Pd hydrosol was synthesized by reducing PdCl 2 solution with dissolved H 2 in the presence of PDDA [poly(diallyldimethylammonium chloride)] as ionic stabilizer. O 2 treatment resulted in the reappearance of ligand to metal charge transfer bands of PdCl 4 2). Repeated oxidation and hydrogen treatments caused aggregation/agglomeration of the Pd particles yielding big spherical aggregates of 30-50 nm but still keeping the size of the 5-6 nm primary particles. Aggregation was attributed to the reduction of PdCl 4 2) anion having high local densities around Pd particles surrounded by PDDA polycation. Au-Pd bimetallic hydrosols were synthesized by reduction with 2-propanol and by pulse radiolysis technique in the presence of PDDA. Both reduction modes synthesize Au core-Pd shell structures. The mode of reduction was observed to affect the particle size and the thickness of the Au core and Pd shell. At the Au rich samples the differences in the optical spectra were attributed to different dispersions of the Au-Pd particles. Au-Pd bimetallic hydrosols were adsorbed on Aerosil 200 and the supported samples were tested in gas phase hydrogenation of acetylene.

Radio-frequency H2 plasma treatment of AuPd/TiO2 catalyst for selective hydrogenation of acetylene in excess ethylene

“…One means is to dope the Au catalyst with a second metal. In particular, supported Au-Pd catalysts have been widely studied in selective hydrogenation of acetylene [4][5][6][7][8]. Besides, it is easy for Au and Pd to form alloy, thus the interaction between Au and Pd will not only be beneficial to the activity but also keep a high selectivity of ethylene at the same time during hydrogenation of acetylene to ethylene.…”

Tuning the Behavior of Au and Pt Catalysts for the Chemoselective Hydrogenation of Nitroaromatic Compounds

“…The discovery that gold nanoparticles supported on TiO 2 or Fe 2 O 3 catalyze the selective reduction of a nitro group in substituted nitroaromatics under mild reaction conditions [8] opened a way to substitute these environmentally non sustainable processes by others based on the use of easily recyclable solid catalysts and H 2 as reactant. However, the activity of the original Au/TiO 2 and Au/Fe 2 O 3 materials toward hydrogenation is too low for practical applications [9,10] and attempts to design more efficient catalysts have been done which include the analysis of gold particle size dependence [11], the use of different supports for the gold nanoparticles [12][13][14][15][16][17], alloying gold with traditional hydrogenation metals such as Pd [18][19][20] or Pt [21], or directly preparing nanoparticles of other highly active transition metals such as Pt, Ru or Ni [22,23].…”

Catalytic activities of sonochemically prepared Au-core/Pd-shell-structured bimetallic nanoparticles immobilised on TiO2and its dependence on Pd-shell thickness

“…According to Sarkany et al, Au/Pd molar ratio of 20/80 in core/shell-structured NPs exhibited the highest catalytic activity for the hydrogenation of acetylene. [3] Ishihara et al [11] also reported that bimetallic NPs of Au/Pd ratio of 19/81 immobilised on rutile TiO 2 showed superior performance for hydrogen peroxide synthesis by hydrogen oxidation with O 2 . It is interesting that the optimum ratios are comparable irrespective of the reaction systems.…”

“…Among bimetallic NPs, Au-Pd NPs have attracted much attention mainly in the field of catalysts. [1][2][3] The synergistic effects of the addition of Au to Pd in enhancing the overall catalytic activity, selectivity and stability of the catalyst have been of great interest. Goodman et al [4] investigated the effect of the addition of Au using acetoxylation of ethylene and concluded that the critical reaction site for vinyl acetate synthesis consisted of two non-contiguous Pd monomers suitably spaced by Au.…”