Molecular/electronic structure–surface acidity relationships of model-supported tungsten oxide catalysts

Kim, Tae Jin; Burrows, Andrew; Kiely, Christopher J.; Wachs, Israel E.

doi:10.1016/j.jcat.2006.12.018

Cited by 184 publications

(173 citation statements)

References 35 publications

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“…These results clearly indicate the formation of a great number of acid sites in the CuZr nanocomposites. This is probably due to the effect of fine dispersion of CuO on the surface of ZrO 2 [52]. C H2 6 Scheme 1.…”

Section: Resultsmentioning

confidence: 99%

Physico-Chemical and Catalytic Properties of Mesoporous CuO-ZrO2 Catalysts

et al. 2016

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Mesoporous CuO-ZrO 2 catalysts were prepared and calcined at 500˝C. The performance of the synthesized catalysts for benzylation of benzene using benzyl chloride was studied. The bare support (macroporous ZrO 2 ) offered 45% benzyl chloride conversion after reaction time of 10 h at 75˝C. Significant increase in benzyl chloride conversion (98%) was observed after CuO loading (10 wt. %) on porous ZrO 2 support. The conversion was decreased to 80% with increase of CuO loading to 20 wt. %. Different characterization techniques (XRD, Raman, diffuse reflectance UV-vis, N 2 -physisorption, H 2 -TPR, XPS and acidity measurements) were used to evaluate physico-chemical properties of CuO-ZrO 2 catalysts; the results showed that the surface and structural characteristics of the ZrO 2 phase as well as the interaction between CuO-ZrO 2 species depend strongly on the CuO content. The results also indicated that ZrO 2 support was comprised of monoclinic and tetragonal phases with macropores. An increase of the volume of monoclinic ZrO 2 phase was observed after impregnation of 10 wt. % of CuO; however, stabilization of tetragonal ZrO 2 phase was noticed after loading of 20 wt. % CuO. The presence of low-angle XRD peaks indicates that mesoscopic order is preserved in the calcined CuO-ZrO 2 catalysts. XRD reflections due to CuO phase were not observed in case of 10 wt. % CuO supported ZrO 2 sample; in contrast, the presence of crystalline CuO phase was observed in 20 wt. % CuO supported ZrO 2 sample. The mesoporous 10 wt. % CuO supported ZrO 2 catalyst showed stable catalytic activity for several reaction cycles. The observed high catalytic activity of this catalyst could be attributed to the presence of a higher number of dispersed interactive CuO (Cu 2+ -O-Zr 4+ ) species, easy reducibility, and greater degree of accessible surface Lewis acid sites.

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Section: Resultsmentioning

confidence: 99%

Physico-Chemical and Catalytic Properties of Mesoporous CuO-ZrO2 Catalysts

et al. 2016

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“…[1][2][3][4][5][6][7][8][9][10][11] These previous studies have established a good understanding of the performance of these catalysts as a function of WO 3 domain size and support effects. The acid site reactivity of WO 3 catalysts is commonly probed using the selective transformation of methanol (MeOH) to dimethyl ether (DME).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2016

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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 .

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“…[9] For catalytic applications, the use of polyoxometalates (POMs) can provide a "molecular scale" model for a better understanding of the interaction between the substrates and the oxide surface. [10][11][12] For several decades, polyoxometallic species have attracted much interest because of their great versatility, with applications from biology to materials science and catalysis. [13] Numerous research groups worldwide are specialized in the synthesis of these molecules with fine control of shape, size and elemental composition.…”

Section: Introductionmentioning

confidence: 99%

“…This strategy also allows the selective assembly of mixed-metal clusters under mild conditions, often using aqueous solvents. Specifically, the reaction of Na 2 3 ] 4 [LM = Cp*Rh [32] and (p-MeC 4 H 4 iPr)Ru [33] ] and their tungsten analogues [({η 6 -arene}Ru) 4 (WO) 4 (µ-O) 12 ] (arene = C 6 Me 6 , pMeC 6 H 4 -iPr). [38] We have worked extensively on the aqueous chemistry of the air-stable organometallic complexes Cp* 2 M 2 O 5 (M = Mo, W) [39][40][41][42][43][44][45][46][47][48][49][50] and have recently reported the synthesis and structure of Cp* 2 Mo 6 O 17 (1).…”

Section: Introductionmentioning

confidence: 99%

Rational, Facile Synthesis and Characterization of the Neutral Mixed‐Metal Organometallic Oxides Cp₂Mo_xW_6–xO₁₇ (Cp = C₅Me₅, x = 0, 2, 4, 6)

et al. 2009

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The reaction of the bis(pentamethylcyclopentadienyl)pentaoxidodimetal complexes Cp*2M2O5 with four equivalents of Na2M′O4 (M, M′ = Mo, W) in acidic aqueous medium constitutes a soft and selective entry into neutral Lindqvist‐type organometallic mixed‐metal oxides Cp*2MoxW6–xO17 [x = 6 (1), 4 (2), 2 (3), 0 (4)]. The identity of the complexes is demonstrated by elemental analyses, thermogravimetric analyses and infrared spectroscopy. Thermal degradation of 1–4 up to above 500 °C leads to Mox/6W1–x/6O3. The molecular identity and geometry of compound 2 is further confirmed by a fit of the powder X‐ray diffraction pattern with a model obtained from previously reported single‐crystal X‐ray structures of 1 and 4, with which 2 is isomorphous. DFT calculations on models obtained by replacing Cp* with Cp (I–IV) validate the structural assignments and assist in the assignment of the M,M′–O vibrations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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Molecular/electronic structure–surface acidity relationships of model-supported tungsten oxide catalysts

Cited by 184 publications

References 35 publications

Physico-Chemical and Catalytic Properties of Mesoporous CuO-ZrO2 Catalysts

Physico-Chemical and Catalytic Properties of Mesoporous CuO-ZrO2 Catalysts

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

Rational, Facile Synthesis and Characterization of the Neutral Mixed‐Metal Organometallic Oxides Cp₂Mo_xW_6–xO₁₇ (Cp = C₅Me₅, x = 0, 2, 4, 6)

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Molecular/electronic structure–surface acidity relationships of model-supported tungsten oxide catalysts

Cited by 184 publications

References 35 publications

Physico-Chemical and Catalytic Properties of Mesoporous CuO-ZrO2 Catalysts

Physico-Chemical and Catalytic Properties of Mesoporous CuO-ZrO2 Catalysts

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

Rational, Facile Synthesis and Characterization of the Neutral Mixed‐Metal Organometallic Oxides Cp*2MoxW6–xO17 (Cp* = C5Me5, x = 0, 2, 4, 6)

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

Rational, Facile Synthesis and Characterization of the Neutral Mixed‐Metal Organometallic Oxides Cp₂Mo_xW_6–xO₁₇ (Cp = C₅Me₅, x = 0, 2, 4, 6)