Properties of the surface layer and catalytic activity of Ta2O5 with Pt or Pd additives in the oxidation of hydrogen

Abstract

The catalytic activity in the oxidation of hydrogen (in the gaseous state in the presence of excess oxygen) has been studied for samples of Pt(Pd)/Ta 2 O 5-x , formed by reduction with hydrogen. The samples obtained had greater activity than the traditional catalysts Pt(Pd)/Al 2 O 3 . According to X-ray diffraction analysis and electron microscopic studies, Ta 2 O 5-x becomes amorphous with the formation of more reduced non-stoichiometric oxygen-deficient tantalum oxides with a surface layer of catalyst.It is known [1-3] that higher oxides of transition metals of groups V and VI, modified by small amounts of precious metals, particularly platinum or palladium, on partial reduction with hydrogen or light hydrocarbons, are capable of forming surface compounds which are highly active in various heterogeneous catalytic processes.We have shown previously [4, 5] that formation of tungsten (molybdenum) oxide bronzes and/or oxygen deficient phases by the reduction of tungsten or molybdenum trioxides with hydrogen in the presence of metallic Pt or Pd leads to a considerable increase in both the specific surface of the composite catalysts and in its catalytic activity in the oxidation of small molecules (H 2 , CO, and CH 4 ).At the present time there is no information on the state of the surface layer of oxides of transition metals of group Vvanadium, niobium and tantalum obtained on reduction with hydrogen in the presence of platinum metals, nor data on their catalytic activity in the oxidation of small molecules in gaseous mixtures with an excess of oxygen.The objective of the present work was to investigate the properties of the surface layer and the catalytic activity of Ta 2 O 5 with a layer of Pt or Pd, reduced with hydrogen, on the oxidation of H 2 .Samples were obtained by impregnating tantalum pentaoxide (Alfa-Aesar 99.995 mass %) with solutions of H 2 PtCl 6 or PdCl 2 to 0.5 mass % of platinum metal in the composition of the sample. The samples calcined at 393 K (1 h) and reduced with hydrogen (10 vol.% H 2 in Ar) for 1 h at 673 K. The specific surface of the samples was determine by low temperature adsorption of argon. To compare the activity of the catalysts prepared with traditional catalysts, samples with 0.5 mass % Pt(Pd)/Al 2 O 3 (S sp Al 2 O 3 = 3.6 m 2 /g) were prepared by the same method. Treatment of these catalysts with hydrogen was carried out by the same regime as for the Pt(Pd)/Ta 2 O 5 samples.Catalytic activity of the samples was investigated with a flow-type apparatus at atmospheric pressure with a reaction mixture with the composition 1 vol.% H 2 + 20 vol.% O 2 and 79 vol.% Ar. The rate of flow of the reaction mixture was 0.1 L/min and the mass of catalysts was 0.5 g. Analysis of the reaction components (H 2 and O 2 ) was by chromatography (LKhM-8MD chromatograph with a thermal conductivity detector). The temperature required to achieve a particular extent of conversion of H 2 into H 2 O served as the characteristic of catalytic activity.

Improved Fuel Cell Oxidation Catalysis in Pt1−xTax

“…Surface Ru serves as a source of active oxygen and thus enhances CO oxidation, 10 but TaO y diminishes the adsorption of CO, possibly through a decrease in the Pt-CO bond strength. The Ta oxidation state was not characterized in the materials of Ueda et al, 9 but Lesnyak et al 11 found that the use of a similar material as a gas phase H 2 oxidation catalyst resulted in partial reduction of the Ta 2 O 5 support. The electrode, consisting of Pt nanoparticles on a Ta 2 O 5 support, was characterized by XRD, electron diffraction and X-ray spectral microanalysis both before and after use as a catalyst for oxidation of H 2 in a fuel stream with 20:1 O 2 :H 2 .…”

1.1.4 SiC-based MIS gas sensor for CO detection in very high water vapor environments

“…However, both theories fail to explain the lack of response to CO molecules in dense-gate devices or the reversibility of the CO effects on the devices in pure nitrogen atmospheres. The CO spillover phenomenon (interphase diffusion of adsorbed atoms or molecules), which is common metal-assisted catalysis on mixed oxides [15][16][17], could provide a more consistent explanation. According to this, the sensor's response to CO could be attributed to CO molecules that, after being adsorbed at the Pt near the bare patches of TaO x , migrate to this oxide via spillover [3,18].…”

Platinum/Tantalum Carbide Core–Shell Nanoparticles with Sub‐Monolayer Shells for Methanol and Oxygen Electrocatalysis

“…Prior work had reported TaO x carburization temperatures above 1200 °C; [13,14] however, we hypothesize that Pt facilitates the TaO x reduction via H 2 spillover and decomposition of CH 4 , which serves as the carbon source, thereby substantially decreasing the carburization temperature. [15][16][17][18] Pt/TaC nanoparticles supported on carbon were subsequently obtained by dissolving the silica shell using ethanol-diluted hydrofluoric acid solution and then dispersing the particles onto a carbon black support. Pt/TaC nanoparticles with four different shell thicknesses were prepared by using different amounts of Pt precursors.…”