E2C 2013 – 10/29/2013 Fritz-Haber-Institut der Max-Planck-Gesellschaft Katharina Mette 1, Stefanie Kühl 1, Andrey Tarasov 1, Robert Schlögl 1, Malte Behrens 1, Hendrik Düdder 2, Kevin Kähler 2, Martin Muhler 2 1 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin, Germany 2 Ruhr-University Bochum, Laboratory of Industrial Chemistry, Bochum, Germany Synthesis and characterization of long- term sintering-stable Ni catalysts for dry reforming of CH 4

anthropogenic emission of CO 2 : ≈ 28 Gt/a CO 2 utilized in industry: 20 Mt/a as industrial gas, 110 Mt/a as chemical feedstock CO 2 = attractive option for sustainable utilization of global carbon sources for the conversion to chemical intermediates dry reforming of methane (DRM):CO 2 + CH 4 ⇌ 2 CO + 2 H 2 ΔH 0 = 247 kJ/mol Motivation 2 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin [1] A. van der Drift, H. Boerrigter, ECN Biomass, Coal and Environmental Research, 2006, 1-31.

CO 2 conversion to syngas 3 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin [2] J. Zhang, H. Wang, A. K. Dalai, Journal of Catalysis 249 (2007), Equilibrium constants of reactions as a function of temperatures: [2]

Goal: Development of a heterogeneous, noble-metal free catalyst for CO 2 reforming of CH 4 catalyst requirements:  high mechanical and thermal resistance  transition metal for CH 4 activation  high resistance against coking [3] CO 2 conversion to syngas 4 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin [3] M. C. J. Bradford, M. A. Vannice, Catal. Rev. - Sci. Eng. 41 (1999) 1.  catalytically active: Ni-based catalysts as well as noble metal-based catalysts (Rh, Ru, Pd, Pt, Ir)  Ni-based catalysts economical more suitable for commercial applications

5 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin  Synthetic Approach Ni based catalysts in MgAlO x matrix – basic matrix with high surface area as well as high temperature stability obtained from hydrotalcite-like precursor – joint cation lattice of Ni* with Mg** and Al** in homogeneous compound *active component** supporting component Experimental Strategy Catalyst Atomic ratio Ni:Mg:Al Ni loading [a] (wt%) Ni5050:17: Ni2525:42: Ni505:62:336.6 Ni101:66:331.3 Ni000:67:330.0 Series of Ni-based catalysts [a] in final catalyst (after reduction)  controlled co-precipitation of hydrotalcite-like precursors  Ni x Mg 0.67-x Al 0.33 (OH) 2 (CO 3 ) 0.17 ∙ m H 2 O with 0 ≤ x ≤ 0.5 (0-50 mol% Ni)

Catalyst Structure 6 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin XRD: phase pure hydrotalcites NiMgAl co-precipitated precursor NiMgAl co-precipitated precursor Calcined Reduced TG, TPO, TPR Definition of the thermal treatment conditions: T calc, T red. TG TG-TPR XRD, XAS, TEM XRD, SEM XRD, SEM, XAS Precursor Calcined (600°) XRD: nearly amourphous mixed oxides

Catalyst Structure 7 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin Reduced at 800°C Calcined at 600°C TPR: increasing reduction temperature with decreasing Ni content SEM: platelet-like morphology still dominant after reduction

Catalyst Structure 8 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin Variation of Ni content:  small Ni particles at 1000°C  well dispersed in Mg-Al oxide matrix Ni5Ni25 900°C1000°C Ni50-red: Stable microstructure up to 900°C.* 50mol% Ni after reduction :  SEM: platelet-like morphology still dominant  TEM: small Ni nanoparticles dispersed in oxide matrix – sintering at 1000°C Ni50-red NiX after reduction at 1000°C *recently published: K. Mette, S. Kühl, H. Düdder, K. Kähler, A. Tarasov, M. Muhler, M. Behrens, ChemCatChem 2013 in press: DOI: /cctc

Catalyst Structure 9 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin Catalyst Ni loading [a] (wt%) Ni particle size (TEM) / nm Ni surface area / m 2 /g cat Ni dispersion / % Ni ± Ni ± Ni ± Ni Ni00.0-  decreasing specific Ni surface area (SA) with decreasing Ni content – high embedment of Ni particles  Ni5: highest Ni dispersion Strong support effect on Ni embedment. [a] in final catalyst (after reduction) Activity in DRM Coke formation spent catalyst Catalytic tests, TG of carbon deposition TPO of spent catalyst TEM

10 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin DRM:CO 2 + CH 4 ⇌ 2 CO + 2 H 2 ΔH 0 = 247 kJ/mol Activation: 4%H 2 in Ar, 5Kpm, 1000°C (Ni0: 900°C) DRM: 240 Nml/min 40% CO 2 / 32% CH 4 / Ar, T= 900°C, 10 h 50mol% Ni catalyst highly active in DRM almost stable performance for 100h time on stream deactivation: Activity in Dry Reforming of Methane X(CH 4 ) ≈ 75%

accessible Ni-SA responsible for activity coke formation - no direct correlation to Ni content lowest coking for Ni5 (sample with highest Ni dispersion) Ni 0  high activity at 900 °C 11 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin Higher activity with increasing Ni content. Linear correlation between activity and available Ni metal surface area.  Variation of Ni content Activity in Dry Reforming of Methane

12 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin Activity in Dry Reforming of Methane High Ni dispersion is mitigating coke deposition. O 2 consumption (TPO)

TEM spent samples Ni50 Ni 0 Ni25 Ni5 amorphousgraphitic Graphitic + filamenteous C type of carbon species changed with Ni content:  only high Ni contents produce filaments  Ni5 forms only graphtic C Carbon amount and species are influenced by catalyst composition. Coking Investigations Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Anorganische Chemie, Berlin13

Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Anorganische Chemie, Berlin 14 Strong dependence of coking rate on temperature and Ni content. Coking Investigations THERMOBALANCE (in situ DRM): 40% CO 2, 32% CH 4, 28% Ar, 120ml/min in situ TG: carbon formation during DRM monitored higher coking rate at 800°C and for Ni50 DRM – showing continuous carbon formation despite stable performance

Conclusion 15 noble metal free Ni/MgAlOx catalysts developed from phase pure NiMgAl hydrotalcite-like precursor small Ni particles embedded in MgAl oxide matrix with stable microstructure at high temperatures highly active in DRM with linear correlation to specific Ni metal surface area coking rate strongly depends on reaction temperature and Ni content direct correlation of carbon amount to Ni dispersion Ni5 most attractive catalyst: showing a compromise of activity and carbon formation – interplay of dispersion and embedment Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin

Acknowledgement 16 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Anorganische Chemie, Berlin Hendrik Düdder Kevin Kähler Martin Muhler Thank you for your attention ! Frank Girgsdies Michael Hävecker Jasmin Allan Gisela Weinberg Robert Schlögl Malte Behrens Katharina Mette Andrey Tarasov in the framework of CO 2 RRECT Project (FKZ 01RC1006)

Reduced catalysts 17 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin XRD: metallic Ni, poorly crystalline oxidic matrix

DRM calculations 18 Stefanie Kühl, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin Comparison to thermodynamic equilibrium