Supplementary data for the paper in Topics in Catalysis

Potassium-doped Ni-MgO-ZrO2 catalysts for dry reforming of methane to synthesis gas

Bhari Mallanna NagarajaDmitri A. Bulushev Sergey BeloshapkinSarayuteChansaiJulianR.H. Ross*

Chemical & Environmental Science Department,University of Limerick, Limerick, Ireland.

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The supported nickel catalysts were prepared by impregnation of the various supports using solutions of nickel nitrate; the final content of reduced nickelwas about 10 wt.%.

Powder X-ray diffraction (XRD) patterns were measured on a Philips X’Pert PRO MPD system equipped with a rotating anode and using Ni-filtered Cu Kα radiation (λ = 1.5418 Å).

Table S1Phase composition of the dried and calcined supports from X-ray diffraction studies.

Supports / XRD Phases
Dried / Calcined
K-Zr / Amorphous / ZrO2 (Monoclinic & Tetragonal)
K-Mg / Hydromagnesite / MgO
K-Mg5Zr2 / Hydromagnesite / MgO, Mg-Zr-Oand/or ZrO2-Tetragonal
K-Mg2Zr5 / Amorphous / MgO, Mg-Zr-Oand/or ZrO2-Tetragonal

The XRD patterns obtained for the samples containing approximately 10%Ni on the different supports and reduced at 1023 K for 2 h are shown in Fig. S1.

Fig. S1 X-ray difractograms of the reduced 10%Ni catalysts on different supports.

The TEM images of the reduced (Ni/K-Mg and Ni/K-Mg5Zr2, 1023K for 2h) catalysts were taken with aJEOL JEM-2100F (200 kV) microscope are shown in Fig. S2.

Fig. S2 TEM images of the reduced 10% Ni catalysts on different supports. (a) Ni/K-Mg and

(b) Ni/K-Mg5Zr2.

The X-ray photoelectron spectroscopy (XPS) studies were performed with a Kratos Axis 165 spectrometer using monochromatic Al Kα radiation (λν =1486.58 eV) and a fixed analyzer pass energy of 20 eV.

Table S2X-ray Photo-electron Spectroscopy Results for the reduced Ni/K-Mg5Zr2 catalyst.

Binding energy region / Position,
eV / Atomic surface ratio relative to Mg2+
Mg 2s / 88.0 / 1
Ni 2p3/2, Ni 2p1/2 / 855.2, 861.1 / 0.01
Zr 3d5/2, Zr 3d3/2 / 181.8, 184.1 / 0.03
K 2p3/2 / 292.6 / 0.004
O 1s / 529.5-533.0 / -

The reduced Ni/K-Mg5Zr2 catalystwas examined using X-ray photoelectron spectroscopy with the aim of obtaining information about the electronic state of the Ni and the chemical composition of the sample surface. The data obtained from analysis of the spectra (Ni 2p, Mg 2s, Zr 3d, O 1s and K 2s species) are shown in Table S2. The XPS pattern of the Ni in the catalyst contains two maxima, one at 855.2 and the other at 861.1 eV, both being characteristic of Ni2+ compounds; no other peaks were observed. Hence, there was no evidence of the presence of metallic Ni; however, as discussed in the main text, this was most likely due to the sample being oxidized by oxygen of the air during the transfer to the XPS chamber [1]. The two peaks of Zr 3d observed correspond to the Zr 3d5/2 (181.8 eV) and Zr 3d3/2 (184.1 eV) transitions, these being assigned to the Zr4+ state [2]. The peak for Mg 2s occurred at 88.0 eV, this being characteristic of Mg2+. The O 1s spectrum of the Ni-Mg5Zr2 sample had three components, at 529.5, 531.3 and 533.0 eV; these may arise from either lattice oxygen or from hydroxyl/carbonate groups.

An important feature of the XPS results was that the atomic ratios of the surface concentrations of Zr to Mg were very low - 0.03 (Table S2). This indicates that magnesia covers a phase either composed of tetragonal zirconia or a MgO/ZrO2 solid solution. Thus, we can conclude that the surface of the support in this sample is quite similar to that of pure MgO. Similar results were obtained for other samples [3]. Cationic potassium was also found on the sample surface and this is in accord with the AAS data (Table 1, main text). The atomic surface ratio of the K relative to Mg was 0.004 (Table S2).

1. Guczi L, Stefler G, Geszti O, Sajo I, Paszti Z, Tompos A, Schay Z (2010) Applied Catalysis a-General 375:236-246

2. Tsunekawa S, Asami K, Ito S, Yashima M, Sugimoto T (2005) Applied Surface Science 252:1651-1656

3. Nagaraja BM, Bulushev DA, Beloshapkin S, Ross JRH (2011) Catalysis Today 178:132-136

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