Investigating the Influence of Au Nanoparticles on Porous SiO₂–WO₃ and WO₃ Methanol Transformation Catalysts

Abstract

American Chemical SocietyDepuccio, DP.; Ruiz-Rodríguez, L.; Rodriguez-Castellon, E.; Botella Asuncion, P.; López Nieto, JM.; Landry, CC. (2016) AbstractAnalyzing the structural and chemical properties of materials at the interface of metal nanoparticles and metal oxide supports is important for catalytic applications. Tungsten oxide (WO 3 ) is a widely studied catalyst, but changing the catalytic reactivity at the surface of this oxide with metal nanoparticles is of interest. In this work, we sought to modify the redox properties of porous WO 3 and SiO 2 -WO 3 catalysts with sonochemically deposited gold nanoparticles (Au NPs) in order to access and study this reaction pathway. Characterization using powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and inductively-coupled plasma optical emission spectroscopy (ICP-OES) confirmed that crystalline Au NPs with diameters of 5 -12 nm were distributed throughout the catalysts. Temperature-programmed desorption (TPD) was used to probe the surface acidity of the catalysts. The physic-chemical characteristics of catalysts have been also discussed by considering the catalytic performance of these materials in the aerobic transformation of methanol. Catalysts containing nanocrystalline WO 3 but no Au NPs displayed very high selectivity to DME (> 60%) at all conversions with minor oxidation reactivity, which highlighted the acidic nature of these catalysts. No effect on the acidity of the catalysts was observed by TPD when Au NPs were loaded in the catalysts. The reducibility of the crystalline WO 3 species, however, increased significantly due to the interaction with Au NPs, as observed by temperature-programmed reduction (TPR). In the gas-phase transformation of MeOH under aerobic conditions, catalysts modified with Au NPs showed greater activity compared to non-modified catalysts. In addition, oxidation selectivity to products such as methyl formate as well as formaldehyde, dimethoxymethane, and carbon oxides became heavily favored with only minor dehydration selectivity. The redox properties of these WO 3 catalysts could be tuned by changing the Au loading. More labile lattice oxygen and enhanced redox properties at the surface of WO 3 modified with Au NPs clearly altered these traditional dehydration catalysts to potential oxidation catalysts. Thus, modification of WO 3 with Au is an effective way to expand the MeOH transformation product distribution beyond DME to other useful, oxidized products not typically observed over pure WO 3 .

Amidoxime functionalization of a poly(acrylonitrile)/silica composite for the sorption of Ga(III) – Application to the treatment of Bayer liquor

“…FTIR spectra of PAN/SiO 2 , and PAO/ SiO 2 for identifying the chemical modifications of the support; for amidoxime sorbent: spectra after Ga(III) sorption and after metal desorption (scaled to the wavenumber range: 400-2400 cm −1 ). [68,69], is not affected by metal binding. A new peak, assigned to O-Ga, is also appearing at 530.3 eV; this may be attributed to either Ga precipitate or interaction of amidoxime with Ga(III).…”

Tungsten-Based Catalysts for Environmental Applications

“…Attempts to modify the activity of WO 3 /SiO 2 catalysts by means of gold nanoclusters revealed that the acidity of tungsten oxide is not modified by Au (methanol transformation tests) [94]. WO 3 /SiO 2 is highly selective for dimethyl ether, while the presence of gold is necessary for the formation of methyl formate and dimethoxymethane.…”

Nd(III) and Gd(III) Sorption on Mesoporous Amine-Functionalized Polymer/SiO2 Composite

“…Other O 1 s peaks are shift to higher BEs level after Nd(III) binding, i.e., 532.47 eV, 534.25 eV, and 535.75 eV for O(C, H,=C) SiO 2 , and C–O–C, respectively. For Gd(III) sorption, O(C, H,=C) and SiO 2 are identified at BE 532.43 eV [ 56 ], while the signal at BE 534.3 eV which assigned to O–S of sulfate groups [ 57 ] and to C–O–C. This means that metal binding is partly occurring through oxygen sharing.…”