Bauer, Matthias

Boubnov, Alexey

Chiarello, Gian Luca

Christensen, Jakob Munkholt

Grunwaldt, Jan-Dierk

Jensen, Anker Degn

Temel, Burcin

Wu, Qiongxiao

Online Research Database In Technology

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Downloaded from orbit.dtu.dk on: Dec 19, 2017In situ XAS study of supported CuNi-catalyst for CO hydrogenationChiarello, Gian Luca; Wu, Qiongxiao; Christensen, Jakob Munkholt; Temel, Burcin; Boubnov, Alexey;Bauer, Matthias; Jensen, Anker Degn; Grunwaldt, Jan-DierkPublication date:2011Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Chiarello, G. L., Wu, Q., Christensen, J. M., Temel, B., Boubnov, A., Bauer, M., ... Grunwaldt, J-D. (2011). In situXAS study of supported CuNi-catalyst for CO hydrogenation. Abstract from 10th EuropaCat Congress ,Glasgow, United Kingdom.In situ XAS study of supported CuNi-catalyst for CO hydrogenation  Gian Luca Chiarello1Institute of Chemical Technology and Polymer Chemistry, 1, Qiongxiao Wu2, Jakob M. Christensen2, Burcin Temel3,  Alexey Boubnov1, Matthias Bauer1, Anker D. Jensen2 and Jan-Dierk Grunwaldt1* Karlsruhe Institute of Technology, Engesserstr. 20, 76131 Karlsruhe (Germany) 2Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads, Building 229, 2800 Kgs. Lyngby (Denmark) 3Haldor Topsøe A/S, Nymoellevej 55, 2800 Kgs. Lyngby (Denmark) * E-mail address: grunwaldt@kit.edu  Introduction  The synthesis of higher alcohols (C2+ alcohols) from synthesis gas has received a renewed attention in the last years for its application in the field of biofuel and bioadditive production [1-2]. Indeed, synthesis gas can be successfully produced by gasification of biomass waste. Among other transition metals, Ni/Cu based catalysts are promising candidates for the title reaction. This work provides a comparison of catalytic activity results and in-situ X-ray absorption spectroscopic (XAS) investigations of CuNi/Al2O3 and CuNi/CNTs (Carbon Nanotubes) to elucidate: i) the Cu/Ni structure after reduction and ii) the effect of the support.  Experimental  10wt%Cu/10wt%Ni deposited on CNTs (Sigma-Aldrich) or Al2O3 catalysts were prepared by impregnation of Cu and Ni nitrates, followed by overnight drying at 120°C and annealing in air or N2 (CNTs based cats.) at 400°C for 4 h. The so obtained catalysts have been characterized by BET, HRTEM, in-situ XRD, QMS-TPR and in-situ XAS at the Ni K- and Cu K-edges both during reduction and exposure in syngas. The XAS experiments were performed with a recently installed in-situ setup at the synchrotron of Karlsruhe ANKA-XAS beamline [3]. Catalytic tests were performed in a fixed-bed continuous-flow reactor [2]. Prior to the reaction, the catalysts were pre-reduced under flowing 10% H2/N2 mixture for 12 h at 300 °C. Typical operating conditions are: P = 60-100 bar; T = 250-325 °C; GHSV = 2000 h-1; Feed: H2/CO=1 (v/v).   Results/Discussion  The two samples display different QMS-TPR profiles: a single-broad peak centred at 200 ºC for the CNT supported catalyst (Fig.1) and a doubled peak at 212 and 230ºC for the Al2O3 supported sample. In-situ XANES (Fig.1) show that both Ni and Cu start to reduce almost simultaneously at ca.180 ºC on the former catalyst, whereas Ni on Al2O3 starts to reduce at higher T than Cu. However, on both samples Cu rapidly fully reduces, whereas Ni displays a slower reduction profiles along T and at 300ºC a significant fraction of Ni still retains the oxidised state. These results suggest that Ni is present in different forms i.e. partially alloyed with Cu, which reduces at lower T, together with NiO and very likely NiAl2O4 in the case of the alumina supported sample [4], which are reduced at higher temperature. In-situ EXAFS spectra recorded under flowing syngas at 300ºC revealed no changes in the copper particles but some variation in the structure of nickel.      Figure 1.  in-situ XANES spectra at the Cu K-edge during reduction up to 300 ºC (left panel) and fraction of oxidised Cu and Ni obtained by linear combination of the in-situ XANES spectra together with QMS-TPR profile (right panel) over the CuNi/CNTs sample.  Table 1 shows that Cu-Ni catalysts supported on Al2O3 and CNTs exhibited different catalytic behaviors for CO hydrogenation [5]. The CNTs supported catalyst showed higher activity than the Al2O3 supported one. These results are interpreted on the basis of Lewis acidic sites of γ-Al2O3 and strong interaction between Ni and Al2O3 which hinders the formation of the active Cu/Ni alloy. The current work is focused on changing the catalytic selectivity towards higher alcohols by modifying the basicity of the catalysts with alkali and other promoters.  Table 1.  Catalytic results of CuNi-based catalysts in CO hydrogenation at 300°C and 100 bar Catalyst CO conv. / mol% Carbon based selectivity / mol% Alcohols Oxygenates Hydrocarbons CO2 CuNi/Al2O3 27.9 4.4 34.4 12.7 48.5 CuNi/CNTs 37.6 77.6 3.4 6.7 12.3 References  1.  V. Subramani , S.K. Gangwal, Energy Fuels, 22, 814 (2008).  2.  J.M. Christensen, P.M. Mortensen, R. Trane, P.A. Jensen, A.D. Jensen, Appl. Catal. A  366, 29 (2009).  3.  J.-D. Grunwaldt, M. Caravati, S. Hannemann, A.Baiker, Phys. Chem. Chem. Phys. 6, 3037 (2004). 4.  L. De Rogatis, et al. Catal. Today, 145, 176 (2009). 5.  Q. Wu, J.M. Christensen, B. Temel, J.-D. Grunwaldt, A.D. Jensen, in preparation. 

In situ XAS study of supported CuNi-catalyst for CO hydrogenation

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In situ XAS study of supported CuNi-catalyst for CO hydrogenation

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