Alicia V. Boix

The nature of cobalt species in Co and PtCoZSM5 used for the SCR of NOx with CH4

Abstract A thorough characterization of CoZSM5 and PtCoZSM5 before and after catalytic use was carried out using a battery of techniques. The bimetallic solid was more selective for N2 production. The TPR profiles showed significant differences. No solid, either fresh or used, exhibited any of the characteristic cobalt oxide X-ray reflections. The XPS data provided information concerning cobalt dispersion. The Raman spectroscopy clearly indicated that Co3O4 species were present only in the monometallic zeolites while a form of highly dispersed CoxOy moieties became dominant in the PtCoZSM5. The diffuse reflectance spectroscopy showed that Co2+ species in the monometallic solids were preferentially located at the main channels while in PtCoZSM5 these cations moved to higher coordination lattice sites. Through the combination of these tools, a much better understanding of the synergetic effect of Pt incorporated to CoZSM5 has been achieved. In view of these findings, related work previously published is revisited.

CoPt clusters in NaMordenites as catalysts for SCR of NOx

A new material based on Pt and Co exchanged in NaMordenite for the selective catalytic reduction (SCR) of nitric oxide with methane in the presence of excess oxygen is studied. The incorporation of 0.5% weight of Pt and 2% weight of Co to the zeolitic matrix after calcination and reduction on H2 flow for 1 h yields a solid converting 100% of NO to N2 and, simultaneously, 100% of CH4 to CO2 with a CH4/NO ratio = 3 and 2% of oxygen in the feed at 450°C. When the oxygen concentration in the feed varies, the NO conversion goes through a maximum for 2% at 450°C. The incorporation of Pt also promotes Co reducibility; 1% is reduced to Coo in the monometallic sample and 13% in the bimetallic sample. XPS results reveal that in the calcined samples Co2+ is at exchange position and, after being reduced, there appear thinly dispersed Coo particles and exchanged Co2+ ions. A greater reducibility and a shift of the maxima in the temperature-programmed reduction profiles suggest a Pt-Co interaction. In order to get an efficient catalysts for nitric oxide abatement it is necessary that the highly dispersed Coo and Pto particles and the Co2+ and H+ ions at exchange positions be in intimate contact inside the mordenite channels.

XPS study of Pt and CoPt clusters in Na Mordenite

The reducibility of CoMordenite and the effect of the addition of different Pt contents were studied by XPS and volumetric reduction with H2. This was related to the activity and selectivity to methane for CO2 hydrogenation. In bimetallic catalysts, Pt2+ and Co2+ ions, and particles of Pt° and Co° were detected by XPS after reductions in situ. The presence of Pt increases the fraction of reduced Co, also increasing the activity and selectivity to methane.