Au In Catalyst Research Articles

Catalytic performance of non-alloyed bimetallic PtAu electrocatalysts for methanol oxidation reaction

Reduced graphene oxide (RGO) supported PtmAu electrocatalysts with different atomic Pt/Au ratios (m = 0.5–2.0) are prepared via co-reduction of H2PtCl6 and HAuCl4. The catalysts are comprehensively characterized through TEM, XRD and XPS. The catalytic behaviors of the PtmAu catalysts toward methanol oxidation reaction (MOR) in alkaline electrolyte are investigated via cyclic voltammetry (CV) and chronoamperometry (CA) techniques. Results show that methanol oxidation currents on the PtmAu catalysts are higher than that on pure Pt catalyst, suggesting that the introduction of Au in Pt catalyst can significantly promote the catalytic properties of Pt. Among the PtmAu catalysts, Pt1.0Au/RGO shows the highest mass-specific activity (MSA) and intrinsic activity (IA). The MSA and IA of Pt1.0Au/RGO is 0.72 A mg−1Pt+Au and 105.4 A m−2Pt, which are ca. 2.40 and 3.56 times those of Pt/RGO (0.30 A mg−1Pt+Au and 29.6 A m−2Pt), respectively. CO stripping voltammograms and CV curves suggest that the improved electrocatalytic properties of the PtmAu/RGO catalysts are especially attributed to the decreased CO formation rather than the facile removal of CO on the surface of Pt. The findings of this work have potential applications in understanding the mechanism of MOR and designing highly effective Pt-based anodic catalysts of direct methanol fuel cells.

A new recoverable Au(III) catalyst supported on magnetic polymer nanocomposite for aromatic bromination

This Letter presents a facile alternative synthesis of a recoverable Au(III) catalyst supported on Fe3O4@SiO2∼MPS grafted by poly(N-vinyl-2-pyrrolidone) (PVP). The solid magnetic support was prepared by anchoring 3-methacryloxypropyltrimethoxysilane (MPS) onto the Fe3O4@SiO2 surfaces followed by free radical polymerization with N-vinyl-2-pyrrolidone. Au(III) was immobilized onto the magnetic support in aqueous media to afford Au(III)/Fe3O4@SiO2∼PVP (catalyst 1). Catalyst 1 was characterized by FT-IR, TEM, VSM, TGA, XRD, and ICP-AES. The amount of Au in catalyst 1 was measured to be 0.64wt% by ICP-AES. This newly prepared catalyst can catalyze the aromatic bromination reaction with comparable activity as homogeneous AuCl3. Moreover, the supported catalyst is easy to recover and can be used in four cycles without apparent loss of activity.

Effective Au-Au+-Clx/Fe(OH)y catalysts containing Cl− for selective CO oxidations at lower temperatures

Supported Au catalysts Au-Au+-Clx/Fe(OH)y (x<4, y≤3) and Au-Clx/Fe2O3 prepared with co-precipitation without any washing to remove Cl− and without calcining or calcined at 400°C were studied. It was found that the presence of Cl− had little impact on the activity over the unwashed and uncalcined catalysts; however, the activity for CO oxidation would be greatly reduced only after Au-Au+-Clx/Fe(OH)y was further calcined at elevated temperatures, such as 400°C. XPS investigation showed that Au in catalyst without calcining was composed of Au and Au+, while after calcined at 400°C it reduced to Au0 completely. It also showed that catalysts precipitated at 70°C could form more Au+ species than that precipitated at room temperatures. Results of XRD and TEM characterizations indicated that without calcining not only the Au nano-particles but also the supports were highly dispersed, while calcined at 400°C, the Au nano-particles aggregated and the supports changed to lump sinter. Results of UV–vis observation showed that the Fe(NO3)3 and HAuCl4 hydrolyzed partially to form Fe(OH)3 and [AuClx(OH)4−x]− (x=1–3), respectively, at 70°C, and such pre-partially hydrolyzed iron and gold species and the possible interaction between them during the hydrolysis may be favorable for the formation of more active precursor and to avoid the formation of Au–Cl bonds. Results of computer simulation showed that the reaction molecular of CO or O2 were more easily adsorbed on Au+ and Au0, but was very difficultly absorbed on Au−. It also indicated that when Cl− was adsorbed on Au0, the Au atom would mostly take a negative electric charge, which would restrain the adsorption of the reaction molecular severely and restrain the subsequent reactions while when Cl− was adsorbed on Au+ there only a little of the Au atom take negative electric charge, which resulting a little impact on the activity.