Selective Catalytic Reduction of NO by Methane over Pd Loaded on Heteropolyacids/SiO2 at Low Temperature

Abstract

Pd was loaded on heteropolyacids/SiO2, and used for the selective reduction of NO with methane in the presence of oxygen and moisture. The catalyst exhibited activity in the selective reduction of NO in the temperature range between 473 and 573 K. The temperature was significantly lower than that in the conventional catalysts, such as Pd-loaded zeolites or monolayer-type oxides. Among tested heteropolyacids, H3PW12O40 gave rise to the highest activity in the reaction. The catalytic performance was improved by the addition of water vapor. The generation of highly dispersed PdO species was observed in the Pd K-edge EXAFS spectra, whose structure was similar to those found in the conventional Pd-loaded zeolites catalyst. The reason for the evolution of NO reduction activity over Pd/H3PW12O40/SiO2 was attributed to the formation of NOH+, as measured by IR, in addition to the generation of highly dispersed PdO species at low temperature on the Brønsted acid sites of heteropolyacid.

Evolution of the Structure and Chemical State of Pd Nanoparticles during the in Situ Catalytic Reduction of NO with H2

“…The present work focuses on the reduction of NO with H 2 (H 2 -SCR). − This reaction is not as selective for N 2 as, for instance, ammonia, but it has potential technological applications due to its lower onset temperature and the fact that H 2 is readily available in exhaust streams (from the water-gas-shift reaction or from hydrocarbons) . Noble-metal-based catalysts are generally preferred for the H 2 -SCR of NO because of their high selectivity and reduced operation temperatures. ,− Although Rh is overall catalytically better than Pd for NO-SCRs, the lower cost, higher abundance, and low-temperature activity of Pd have made it a material of choice in industrial applications. ,− A vast amount of literature is available describing the conversion and selectivity of various combinations of metal catalyst, support, and reducing agent. ,,− However, much less attention has been paid to the optimization of the structure and oxidation state of the active catalysts, its evolution under reaction conditions, and its influence on catalytic performance. , Nevertheless, previous work has revealed the important role of the oxidation state of metal catalysts in their activity, selectivity, and stability for NO-SCRs. For example, oxidized Rh catalysts are more active for H 2 -SCR than metallic Rh, and NO adsorption on Cu catalysts is faster on the oxidized surface, contrary to the faster adsorption reported on the reduced surfaces of other materials such as chromia or manganese oxides .…”

“…4,26,29À31 However, much less attention has been paid to the optimization of the structure and oxidation state of the active catalysts, its evolution under reaction conditions, and its influence on catalytic performance. 70,71 Nevertheless, previous work has revealed the important role of the oxidation state of metal catalysts in their activity, selectivity, and stability for NO-SCRs. For example, oxidized Rh catalysts are more active for H 2 -SCR than metallic Rh, 72 and NO adsorption on Cu catalysts is faster on the oxidized surface, contrary to the faster adsorption reported on the reduced surfaces of other materials such as chromia or manganese oxides.…”

Heteropoly acid promoted V2O5/TiO2 catalysts for NO abatement with ammonia in alkali containing flue gases

“…The catalyst exhibited high activity for NO reduction when branched aromatic hydrocarbons, such as toluene and xylene, were used as reductants. 13,14 Several authors have reported the deactivation of V 2 O 5 -WO 3 /TiO 2 catalysts by alkaline metals in biomass fired power plants. [15][16][17] Most conclude that poisonous elements (e.g.…”