Methusalem advisory board meeting, LCT, Ghent, 19/6/2014

Pt-Ga catalyst formation studied with in situ XAS using Fourier and wavelet transformed analysis.

M. Fileza, H. Poelmana,*, E. Redekopa, V.V. Galvitaa, C. Detavernierb and G.B. Marina

http://www.lct.UGent.be *E-mail: Hilde.Poelman@UGent.be

a Laboratory for Chemical Technology, Ghent University, Technologiepark 914, B-9052 Zwijnaarde, Belgiumb Department of Solid State Sciences, COCOON, Ghent University, Krijgslaan 281/S1, B-9000 Ghent, Belgium

M. Filez acknowledges financial support from theFund for Scientific Research Flanders (FWOG.0209.11). H. Poelman and V. Galvita acknowledgefinancial support from the ‘Long Term StructuralMethusalem Funding by the Flemish Government’. E.Redekop acknowledges financial support from MarieCurie project (ICKARUS FP7-People-2011-IIF-301703). This work was supported by the Fund forScientific Research Flanders (FWO-Vlaanderen) insupplying financing of beam time and travel costs.We are grateful to S. Nikitenko and D. Banerjee atDUBBLE, ESRF, France, for assistance and to theESRF staff for smoothly running the facility and to V.Bliznuk for TEM measurements.

European Research Institute of Catalysis

Motivation & Introduction Experimental Wavelet transformation

Wet impregnation of Pt(acac)2 on Mg(Ga)(Al)Ox results in physisorption of theprecursor molecules. Oxidative heating of Pt(acac)2/Mg(Ga)(Al)Ox up to 350°°°°C leads tothe decomposition and full oxidation of Pt(acac)2 molecules, yielding dispersed Pt-species with 5-fold oxygen coordination. Further calcination up to 650°°°°C results insintering of the dispersed Pt species causing the formation of Pt clusters with metalliccore and oxidized cluster surface. Subsequent low temperature reduction (< 450°°°°C)gradually reduces the Pt clusters. Between 450°°°°C and 650°°°°C, Ga atoms migrate fromthe support towards the Pt phase, leading to bimetallic Pt-Ga alloying.

Conclusions

25°C

350°C

650°C

250°C

350°C

450°C

25°C

H2/He

O2/He

O2/He

H2/He

After 650 °C calcination and cool down to 250 °C:

• XANES: WLI decrease: +II• FT EXAFS: Pt-O shell + metallic Pt bulk• WT EXAFS: O shell + Pt contribution

During reduction to 450 °C:

• XANES: WLI gradual decrease• FT EXAFS: = structure but Pt-O/Pt-Pt decreases• WT EXAFS: O intensity decreases relative to Pt

After reduction to 650 °C:

• XANES: Edge shift + WL amplitude decrease• FT EXAFS: Ga-shell fits experimental signal• WT EXAFS: k-space maximum intermediate to

O and Pt � Ga

[1,2]

[3]

[4]

[5]

[6,7]

[8]

References

[1] V.V. Galvita et al., J. Catal. 271 (2010) 209[2] G. Siddiqi et al., J. Catal. 274 (2010) 200[3] P. Sun et al., J. Catal. 274 (2010) 192[4] C. Antoniak, Beilstein J. Nanotechnol. 2 (2011) 237[5] M. Womes et al., Cat. Lett. 85 (2003) 1-2[6] M. Muñoz et al., American Mineralogist 88 (2003) 694[7] B. Ravel et al., J. Synch. Rad. 12 (2005) 537[8] R. Giedigkeit et al., http://hasyweb.desy.de/science/annual_reports/2002_report/part1/contrib/41/6974.pdf

As prepared state:

• XANES: WLI = +II = Pt+2(acac)2

• FT EXAFS: Pt(acac)2 structure• WT EXAFS: O shell + C contribution

� Pt(acac)2 physisorption

After 350 °C calcination:

• XANES: WLI = +IV = PtO2-like• FT EXAFS: PtO2 profile but modelling impossible• WT EXAFS: O shell + O/Mg/Al contributions

� Pt(acac)2 decomposition and oxidation� Dispersed Pt with 5-fold O coordination in contact with Mg(Ga)(Al)O support

� Dispersed Pt species sintered� Cluster formation: metal core + oxidizedsurface

� Gradual reduction of the Pt clusters

�Ga migration from Mg(Ga)(Al)Ox to Pt phase�Bimetallic Pt-Ga alloy formation

Ga

Mg/Al/O

650°C

25°C