CO2 Hydrogenation Studies on Co and CoPt Bimetallic Nanoparticles Under Reaction Conditions Using TEM, XPS and NEXAFS

Abstract

. (2011) 'CO2 hydrogenation studies on Co and CoPt imetallic nanoparticles under reaction conditions using TEM, XPS and NEXAFS.', Topics in catalysis., 54 (13-15). pp. 778-785. Further information on publisher's website:http://dx.doi.org/10.1007/s11244-011-9695-9Publisher's copyright statement:The nal publication is available at Springer via http://dx.doi.org/10.1007/s11244-011-9695-9.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract:Cobalt and platinum-cobalt bimetallic alloy nanoparticles of uniform size distribution where prepared and supported on MCF-17 to produce a controlled and wellcharacterized model catalyst which was studied under reaction conditions during CO 2 hydrogenation. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to elucidate the oxidation state of the catalyst under reaction conditions while the 2 | P a g e effect of reducing H 2 gas on the composition and structure of the bimetallic PtCo nanoparticles was measured using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and environmental transmission electron microscopy (ETEM). NEXAFS indicates that Pt aids the reduction of Co to its metallic state under relevant reaction conditions, while AP-XPS and ETEM indicate that Pt is enriched at the surface by exchange with subsurface layers which become Pt deficient -in agreement with the "Ptlike" selectivity seen during catalytic testing of these materials.

Combining in Situ NEXAFS Spectroscopy and CO2 Methanation Kinetics To Study Pt and Co Nanoparticle Catalysts Reveals Key Insights into the Role of Platinum in Promoted Cobalt Catalysis

“…We identified this was attributable to platinum segregating to the surface in reducing conditions as demonstrated by ambient pressure X-ray photoelectron spectroscopy and environmental transmission electron microscopy in H 2 . 3 Here, we identify a different, more realistic model for the catalyst structure involved in the Pt promotional effect. Instead of the two metals being present within a single nanoparticle, we have instead taken discrete monometallic nanoparticles of both Pt and Co and deposited them in close proximity within the pores of a mesoporous silica, MCF-17.…”

“…This is slightly more than the often < 1:100 molar ratio found in commercial type catalysts to allow us to characterize the Pt nanoparticles present with a range of techniques. We have previously demonstrated that the pure Pt nanoparticles are inactive for this reaction, 3 therefore we assume that all CH 4 production is derived from the pure Co particles. The dramatic increase in rate is therefore the result of platinum nanoparticles enhancing the activity of the cobalt.…”

Recent developments in the application of nanomaterials to understanding molecular level processes in cobalt catalysed Fischer–Tropsch synthesis

“…The Pt then covers the particle surface as shown in Figure 4. 82 These Pt encapsulated particles were found to be completely inactive for CO 2 hydrogenation. 82 It was reported that preparing nanoparticles of consistently low Pt concentration is synthetically very difficult owing to their segregation into particles with and without Pt.…”

The use of preformed nanoparticles in the production of heterogeneous catalysts

“…[1][2][3] This has largely arisen out of their size dependent properties, ease of preparation for FT active metals and large number of atoms at their surface. Despite the development in a number of chemical approaches 4 that give control over particle size and composition, and the subsequent assemblage of these preformed particles onto supports, 5 very few literature examples involving the addition of preformed nanoparticles to support materials exist.…”

“…Despite the development in a number of chemical approaches 4 that give control over particle size and composition, and the subsequent assemblage of these preformed particles onto supports, 5 very few literature examples involving the addition of preformed nanoparticles to support materials exist. 3,6,7 This method is highly advantageous as it allows greater control over what species are assembled onto a support material and it removes the dispersion problems seen with metal clusters in traditional FT catalysts. 8 Further research is required to develop new systems based on the assemblage of preformed particles onto supports so that an assessment of the benefits of these materials can be made.…”