Acid Activated Vermiculites As Catalysts

Published Date: 02 Nov 2017

Vermiculite was treated with 0.8 M solutions of hydrochloric and sulphuric acids for 2, 8, and 24 h. The obtained materials were characterized with respect to their composition (XRF), structure (XRD, FTIR, UV–vis-DRS), texture (BET), surface acidity (NH3-TPD) and catalytic properties. Modification of vermiculite with acids significantly increased its surface area and pore volume and led to partial leaching of iron, aluminium and magnesium ions from its octahedral sheets. Efficiency of the leaching process depended on its duration and the nature of acid used. Acid treatment strongly modified the vermiculite structure leading to a distinct increase of its catalytic activity in the selective catalytic reduction of nitric oxide (SCR NO) process. In a series of the studied samples the best catalytic performance was found for vermiculite treated with sulphuric acid for 8 h.

Abstract

The effect of Cs and Cu contents in Cs–Cu/ZrO2 catalysts has been studied in the simultaneous abatement of NOx and carbon black (CB), used as a model of soot. Cu/ZrO2 and Cs–Cu/ZrO2 catalysts with a low Cs content are moderately active but show a beneficial role of NOx in CB elimination. Cs–Cu/ZrO2 catalysts with high amount of cesium are the more active systems towards both CB oxidation and NOx reduction. The increase in the amount of Cs leads to the formation of a higher proportion of CuO crystallites which are active for CB oxidation. Cesium in Cs–Cu/ZrO2 also acts as a promoter favouring the contact between reactants: on the first hand it increases the exchange surface between CB and the catalyst surface and on the other hand, it enhances the NOx adsorption capacity of Cs–Cu/ZrO2 and the further NOx reduction.

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The development of an alternative oxygen reduction electrocatalyst to platinum based electrocatalysts is critical for practical use of the polymer electrolyte membrane fuel cell (PEMFC). Transition metal sulfide chalcogenides have recently been reported as a possible candidate for Pt replacement. Our work focused on chalcogenides composed of ruthenium, molybdenum, and sulfur (RuMoS). We elucidate the factors affecting electrocatalytic activity of carbon supported RuXMoYSZ catalyst. This was demonstrated through a correlation of oxygen reduction reaction (ORR) activity of the catalysts with structural changes resulting from designed changes in sulfur composition in the catalysts.

Abstract

The feasibility of processing less-expensive alternative coatings to platinum aluminide was examined. Three approaches were followed: (1) enhancement of nickel-aluminide coatings by application of sol-gel derived two-phase-glass (TPG) overlayers, (2) evaluation of TPG coatings on bare IN 738LC, and (3) substitution of Pt with a less expensive platinum group metal (palladium). Accordingly, IN 738LC coupons were tested with several coatings including TPG, aluminide coatings (platinum aluminide, palladium aluminide, and conventional nickel aluminide), and TPG overlayers on the aluminide coatings. Isothermal-oxidation, cyclic-oxidation, and hot-corrosion tests were conducted at 900°C for 500 h to evaluate the coatings. The results showed that the TPG by itself provided superior protection compared to the platinum-aluminide coatings under both oxidation and hot-corrosion conditions. The TPG coating also showed promise as an overcoat on aluminide coatings.

Abstract

Selective catalytic reduction of nitrogen monoxide by methane on zeolite catalysts in an oxygen-rich atmosphere

Selective reduction of NO by CH4 on zeolite catalysts has been studied. After an investigation of the catalytic features of various cation-exchanged zeolites, we found that Ga-ZSM-5 and In-ZSM-5 were highly active and selective for NO reduction by CH4. We also showed that this reaction was moderately promoted even by H-form ZSM-5, mordenite, and ferrierite. From the catalytic performance of Ga-and In-ZSM-5 in NO-CH4-O2, NO2-CH4-O2, and NO-O2 reactions, it is concluded that the selective reduction of NO on these catalysts proceeds in two stages: (1) NO is oxidized to NO2 on zeolite acid sites, (2) NO2 and CH4 react on gallium or indium sites. The highly selective features of Ga and In in the zeolite for the NO2-CH4 reaction seem to be attributed to the coordinatively unsaturated nature of these sites which adsorb both of these reactants on the same site. Effect of water vapor on NO conversion was also investigated. It was found that Ga-ZSM-5 was strongly inhibited by steam, while In-ZSM-5 was fairly active even in the presence of 10% steam.

Improved NOx reduction over the staged Ag/Al2O3 catalyst system

Abstract

The reaction mechanism of reducing NOx with hydrocarbons over Ag/Al2O3 has been examined to improve its NOx reduction performance at lower temperatures, using ethanol and n-octane as representative hydrocarbon reductants. Based on the results obtained at the early stages of the hydrocarbon oxidation and NO reduction, it is proposed that the partial oxidation of hydrocarbons and the oxidation of NO are the first reaction steps over Ag/Al2O3. n-Octane is broken up into smaller hydrocarbon molecules, which are then subsequently oxidized to form various aldehydes, while ethanol is also rapidly converted to acetaldehyde. At the same time, NO is oxidized effectively to NO2 in the presence of reductants.

These observations and additional experiments with variable amounts of Al2O3 placed downstream of the Ag/Al2O3 catalyst suggest that the NO reduction by hydrocarbons over Ag/Al2O3 may occur via a bifunctional reaction mechanism; NO and hydrocarbons are converted into NO2 and more reactive hydrocarbon species (i.e., smaller alkenes, oxygenated hydrocarbons), respectively, over the Ag sites, while N2 is produced from the subsequent reactions between these intermediate species over different sites including Al2O3.

The proposed bifunctional reaction mechanism offers an opportunity to improve the overall NOx reduction performance of Ag/Al2O3 by optimizing individual reaction steps separately. Thus, the concept of a staged catalyst system has been examined using Ag/Al2O3 for the formation of reaction intermediates, and a secondary catalyst (e.g., Al2O3 or BaY) for the subsequent N2 production reaction. Significant improvement in NOx reduction to N2 was obtained at lower temperatures, when BaY was used as the second catalyst and ethanol was used as reductant.

Graphical abstract

Based on the proposed bifunctional reaction mechanism, the concept of a staged catalyst system has been examined using Ag/Al2O3 for oxidizing NO and hydrocarbons, and a secondary catalyst for reducing NOx with partially oxidized hydrocarbons. Significant improvement in NOx reduction to N2 was obtained at lower temperatures, when BaY was used in the second layer and ethanol was used as the reductant.