Selective reduction of NOx by propylene over silver catalyst under oxidative conditions

Abstract

Neste trabalho foram estudados catalisadores Ag/Al 2 O 3 e Ag/Al 2 O 3 /Corderita, preparados por um método de impregnação convencional, na reação de redução de NO utilizando propeno como agente redutor. Os catalisadores foram caracterizados por redução a temperatura programada (RTP), quimissorção de oxigênio e área superficial, pelo método BET. A atividade catalítica foi determinada utilizando uma mistura reacional contendo 100 ppm de NO, 250 ppm de C 3 H 6 e 2% de oxigênio e uma velocidade espacial de 100000 h -1 . Os produtos da reação foram estudados por FTIR. Os resultados dos testes catalíticos mostraram 56% de conversão de NO para o catalisador 2,22%Ag/ Al 2 O 3 a 723 K. Os catalisadores de cordierita apresentaram um comportamento semelhante, mas a temperatura de máxima conversão de NO deslocou-se para temperaturas menores.In this study, a Ag/Al 2 O 3 and Ag/Al 2 O 3 /Cordierite catalyst was prepared by a conventional impregnation method and NOx reduction investigated using propylene as a reducing agent. The catalysts were characterized by Temperature Programmed Reduction (TPR), oxygen chemisorption and surface area, using the standard BET method. The catalytic activities were measured under the same reaction conditions, i.e., 100 ppm NO, 250 ppm C 3 H 6 , 2% of oxygen and 100000 h -1 space velocity. The reaction products were analyzed by FTIR. The results of the catalytic activity obtained for the 2.22%Ag/Al 2 O 3 catalyst showed 56% NO conversion at 723 K. The catalysts based on Cordierite presented an analogous behavior, but the temperature of maximum NO conversion was lower (620 K).Keywords: NOx reduction, silver/alumina catalyst, propylene, Cordierite IntroductionThe generation of NOx effluents from stationary and mobile sources poses an important environmental problem. [1][2][3][4] Gas effluent control in internal combustion engines, whose air/gasoline ratio is stoichiometric, can be achieved by using the so-called "three way catalysts" (TWC) typically containing Pt and Rh as the active metals. On the other hand, lean-burn engines, such as diesel engines and stationary sources for industrial use, operate with excess oxygen to ensure complete combustion. In these cases, TWCs are ineffective for NO elimination, for which reason selective catalytic reduction (SCR) is used. A typical commercial SCR catalyst uses V 2 O 5 -WO 3 -TiO 2 as the metal system and NH 3 as the reducing agent. This catalyst involves problems relating to the transport and storage of NH 3 and to vanadium toxicity. 5 In their studies of several catalysts prepared from zeolites substituted with H + , Na + , K + , Mg 2+ , Ca 2+ , Cr 3+ , Fe 3+ , Co 3+ , Ni 2+ , Cu 2+ , Zn 2+ and Ag, Iwamoto et al. 6,7 found that Cu-ZSM5 provided better NO reduction activity when hydrocarbons were used as reductants. However, this catalyst has a low thermal stability 6 and deactivates in the presence of water vapor and SO 2 . Moreover, large amounts of water vapor inhibit the catalyst's action, promoting the migration of Al +3 out of the zeolite struct...

Temperature‐programmed reduction of silver(I) oxide using a titania‐supported silver catalyst under a H2 atmosphere

“…As for the additional Ag 2 O reduction at higher temperature, there are two plausible reasons to this phenomenon: (a) Variation in particle size of TiO 2 or Ag 2 O species; (b) Reduction variation between surface and bulk lattice oxygen species. The first explanation accounts for the possibility of having a portion of Ag 2 O aggregates existing in smaller particle sizes and better dispersion, which in turn experienced a stronger metal‐support interaction with the TiO 2 support . However, the result in this study (Figure b) showed that the slight increase in TiO 2 particle size had negligible effects on the reduction phenomenon while the Ag particle size was noted to be consistent across the samples as mentioned in Section 3.1.…”

Effect of the Synthesis Method on Alumina Supported Silver Based Catalyst for NO x Selective Reduction by Ethanol

“…For Ag/Al 2 O 3 (ESI) , two peaks for H 2 uptake are shown, the first peak at 170°C (Fig. 2B (a)) is attributed to the reduction of Ag 2 O clusters interacting weakly with the support, which typically are easier to reduce than small metal oxide particles (peak at 220°C) [10]. In the case of Ag/Al 2 O 3 (IWI) ( Fig.…”