Pt-impregnated catalysts on powdery SiC and other commercial supports for the combustion of hydrogen under oxidant conditions

Abstract

We report the study of the catalytic hydrogen combustion over Pt-impregnated powdery silicon carbide (SiC) using H 2 PtCl 6 as precursor. The reaction was conducted in excess of oxygen. -SiC was selected for the study because of its thermal conductivity, mechanical properties, chemical inertness and surface area. The obtained Pt particles over SiC were medium size (average particle diameter of 5 nm for 0.5wt% Pt). The activity of the Pt-impregnated catalyst over SiC was compared to those obtained in oxidized form over TiO 2 and Al 2 O 3 commercial supports (Pt particles very small in size, average particle diameter of 1 nm for 0.5wt% Pt in both cases). The case of a SiO 2 support was also discussed. Those Pt/SiC particles were the most active because of their higher contribution of surface Pt 0 , indicating that partially oxidized surfaces have better activity than those totally oxidized in these conditions. SiC was modified with an acid treatment and thus bigger (average particle diameter of 7 nm for 0.5wt% Pt) and more active Pt particles were obtained. Durability of the SiC and TiO 2 supported catalysts was tested upon 5 cycles and both have shown to be durable and even more active than initially. Exposure to the oxidative reaction mixture activates the *Revised Manuscript Click here to view linked References catalysts and the effect is more pronounced for the completely oxidized particles. This is due to the surface oxygen chemisorption which activates catalysts´ surface.

Nanoporous Pt-based catalysts prepared by chemical dealloying of magnetron-sputtered Pt-Cu thin films for the catalytic combustion of hydrogen

“…The activity of both Ar sputtered samples is negligible at that temperature, but a comparison at 50°C shows that Low Pt-Cu_Ar is more active (1.95 LH2•min -1 •gPt -1 ) than High Pt-Cu_Ar (negligible activity). For both samples with similar crystal size, the trend can be ascribed to the -0.5 eV shift in the Pt 4f level of the Low Pt-Cu_Ar sample with respect to High Pt-Cu_Ar, according to our previous studies [7].…”

“…were calculated (Table 3). The dealloyed Low Pt-Cu_He sample has the lowest AAE of the three (1kJ.mol -1 ), followed by the (as supporting information) show a certain activation upon cycling, demonstrating that the catalyst is durable, as expected for a Pt catalyst under oxidizing conditions [6][7][8].…”

“…Our previous studies on Pt particles over different supports showed that under oxidizing conditions, semi-oxidized Pt-surfaces are more active than the completely oxidized ones [7]. Under this hypothesis, d-High Pt-Cu_Ar should be the most active because of its mostly metallic surface.…”

“…Due to its relative simplicity it can be considered as model catalytic oxidation reaction in the gas phase, and has applications in heaters for domestic or industrial use (for example, cooking, heating spaces, floors and walls, drying and other heating industrial processes) or in safety devices [1][2][3][4][5]. H2 (g) + ½ O2 (g) → H2O (g) (1) Regarding safety applications, the CHC can be employed as a controllable means to eliminate the undesired amounts of hydrogen in installations such as in the nuclear industry or fuel cell-based power generation devices [3][4][5][6][7][8]. The elimination of residual hydrogen from the exhaust gases from fuel cells requires the use of catalysts that are active at room temperature (RT).…”

Porous Silicon Carbide (SiC): A Chance for Improving Catalysts or Just Another Active-Phase Carrier?

“…One main conclusion from these authors was that the Pt/SiC catalyst featured by a larger mean size of metal particles was also the most active in the process because of the higher metallic Pt content in its partially oxidized active phase compared to the smaller and completely oxidized Pt NPs obtained on the more traditional metal oxide carriers. 406 The most attractive raw material for H 2 production remains water whose direct thermal dissociation (thermolysis) is thermodynamically challenging as it requires temperatures above 2200 °C to acquire an appreciable dissociation degree. 408 In order to accomplish the water splitting process under milder conditions, a series of indirect chemical processes whose net result is the evolution of two gases (H 2 and O 2 ) have been setup and named "thermochemical cycles".…”