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Journal ArticleDOI

FT-IR study of the adsorption and transformation of formaldehyde on oxide surfaces

19 Aug 1987-Journal of the American Chemical Society (American Chemical Society)-Vol. 109, Iss: 17, pp 5197-5202
TL;DR: The adsorption of formaldehyde on different oxides (silica, pure and fluorided alumina, magnesia, titania, thoria, zirconia, and iron oxide) has been studied by FT-IR spectroscopy in the temperature range 170-570 K as mentioned in this paper.
Abstract: The adsorption of formaldehyde on different oxides (silica, pure and fluorided alumina, magnesia, titania, thoria, zirconia, and iron oxide) has been studied by FT-IR spectroscopy in the temperature range 170-570 K. The following adsorbed species have been identified and characterized spectroscopically: (i) physisorbed HCHO, (ii) coordinated HCHO, (iii) dioxymethylene, (iv) polyoxymethylene, (v) formate ions, and (vi) methoxy groups. On silica at 170 K formaldehyde physisorbs on surface OH groups and, by warming, polymerizes producing linear polyoxymethylene. On ionic oxides at about 250 K dioxymethylene is always observed, generally together with variable amounts of the linear polymer that has been isolated on magnesia at 170 K. Heating up to or above room temperature results in the disproportionation of dioxymethylene into formate and methoxide groups, probably via a Cannizzaro-type mechanism. Such a route probably parallels an oxidative route, involving direct oxidation of dioxymethylene into formates, as observed on iron oxide.
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Journal ArticleDOI
Jianghao Zhang1, Yaobin Li1, Lian Wang1, Changbin Zhang1, Hong He1 
TL;DR: In this article, the catalytic performance of MnO2 catalysts with different crystal structures was investigated and it was shown that the tunnel structure and active lattice oxygen species are the main factors that contribute to the excellent performance of δ-MnO2.

431 citations

Journal ArticleDOI
TL;DR: In this article, the selectivity pattern and the formation rates of the reaction products are used to characterize both structural (dispersion) as well as chemical properties (acid base and redox) on supported oxide catalysts, especially for molybdenum-based systems supported on silica and vanadia on titanium oxide.
Abstract: The goal of this review is to present some aspects of the use of a test reaction, i.e., methanol oxidation, as a tool to characterize oxidation catalysts. The selectivity pattern and the formation rates of the reaction products are used to characterize both structural (dispersion) as well as chemical properties (acid-base and redox) on supported oxide catalysts, especially for molybdenum-based systems supported on silica and vanadia on titanium oxide. This highly sensitive technique which gives information on the catalytically active sites at the molecular level characterizes a catalyst at work and is particularly well-adapted to the study of supported catalysts.

428 citations

Journal ArticleDOI
TL;DR: In this article, the results obtained from the oxidation of the aminoazobenzene dye AO52 by the UV/H2O2, UV/TiO2 and VIS/Ti2 systems are presented.
Abstract: This paper presents the results obtained from the oxidation of the aminoazobenzene dye AO52 by the UV/H2O2, UV/TiO2 and VIS/TiO2 systems. In the former case, we investigated the formation of first by-products by means of GC/MS, HPLC and 1H NMR. spectroscopy. We conclude that hydroxyl radicals are added to aromatic rings in the ipso position with respect to the sulfonate group or to the azo-linkage-bearing carbon. The reaction of the inorganic radical with the N,N-dimethylamino substituent, leading to demethylation, adds to the multiplicity of the possible pathways. Degradation by the UV/TiO2 system is pH dependent. Whereas hydroxyl radicals are the main oxidative agent in neutral and alkaline solutions, positive hole-induced oxidation competes with the reduction of the protonated dye molecules in acid media. Moreover, FTIR spectroscopy of AO52/TiO2 wafers provided an insight to the nature of the photoproducts. This process is very efficient since only ultimate breakdown products, i.e. aliphatic acids and inorganic salts, are detected. Similar results were obtained using visible light as the irradiation source in the case of wafers whereas in heterogeneous solutions, the dye seems to be resistant to degradation.

428 citations

Journal ArticleDOI
TL;DR: In this paper, the selective catalytic reduction of NO with C3H6 in the presence of a large excess of O2 was studied over γ-Al2O3 and the lowloading silver material exhibited high conversions to N2 whereas the highloading sample predominantly yielded N2O.

346 citations

Journal ArticleDOI
TL;DR: In this article, the authors report on the mechanism of the PROX reaction on Pt/CeO2 catalyst, using catalytic tests, in situ DRIFTS, high-pressure XPS, HRTEM, and TDS techniques.

333 citations