Effect of Pt on the water resistance of Co-zeolites upon the SCR of NOx with CH4

The objective of this work was to study the promotional effect of Pt on Go- zeolite (viz. mordenite, ferrierite, ZSM-5 and Y-zeolite) and Co/Al2O3 on t he selective catalytic reduction (SCR) of NOx with CH4 under dry and wet re action stream. After being reduced in H-2 at 350 degrees C, the PtCo bimeta llic zeolites showed higher NO to N-2 conversion and selectivity than the m onometallic samples, as well as a combination of the latter samples such as mechanical mixtures or two-stage catalysts. After the same pretreatment, u nder wet reaction stream, the bimetallic samples were also more active. Amo ng the other catalysts studied with 5% of water in the feed, (NO=CH4=1000 p pm, O-2=2%), the NO conversion dropped to zero over Co(2.0)Mor at 500 degre es C and GHSV = 30,000 h(-1), whereas it is 20% in Pt(0.5)Co(2.0)Mor. In Pt /Co/Al2O3 the NO, conversion dropped below 5% with only 2% of water under t he same reaction conditions. The specific activity given as molecules of NO converted per total metal atom per second were 16.5 x 10(-4) s(-1) for Pt( 0.5)Co(2.0)Fer, 13 x 10(-4) s(-1) for Pt(0.5)Co(2.0)Mor, 4.33 x 10(-4) s(-1 ) for Pt(0.5)Co(2.0)ZSM-5 and 0.5 x 10(-4) s(-1) for Pt/Co/Al2O3. The Y-zeo lite-based samples were inactive in both mono and bimetallic samples. The s pecies initially present in the solid were Pt degrees and Co degrees, toget her with Co2+ and Pt2+ at exchange positions. Co degrees seems not to parti cipate as an active site in the SCR of NOx. Those species remained after th e reaction but some reorganization occurred. A synergetic effect among the different species that enhances both the NO to NO2 reaction, the activation of CH4 and also the ability of the catalyst to adsorb NO, could be respons ible for the high activity and selectivity of the bimetallic zeolites. (C)1 999 Elsevier Science B.V. All rights reserved.