Low-temperature catalytic CO2 hydrogenation with geological quantities of
ruthenium: a possible abiotic CH4 source in chromitite-rich serpentinized rocks
Giuseppe Etiope1,2*, Artur Ionescu 2
1
2
Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 2, Italy
Faculty of Environmental Science and Engineering, Babes-Bolyai University Cluj-Napoca, Romania.
* Corresponding author: giuseppe.etiope@ingv.it
Supporting Information
Figure S1. A schematic plot of temperature and time scales considered in FTT experiments in geology
and industrial catalysis. All geological experiments were conducted at temperatures above 100°C. Our
study is the first to report methane generation and its isotopic composition below 100°C, which is the
temperature field of land-based serpentinization. 1. Thampi et al. (1987); Jacquemin et al. (2010);
2 .Lancet et al. (1970); 3. Medina et al. (2000); 4. Horita and Berndt (1999); 5. Taran et al. (2010); 6.
Ni and Yin (2011); 7. Taran et al. (2007); 8. Foustoukos and Seyfried (2004); 9. Fu et al. (2007); 10.
Zhang et al. (2013). The “industrial catalysis” field is based on Wang et al. (2011) and references
therein.
1
(a)
(b)
Figure S2. Ru-based abiotic methane in genetic diagrams, compared with natural gas. (a) 13C vs.
C1/(C2+C3) diagram; (b) Isotopic diagram (Schoell’s plot). The abiotic fields of methane in
Precambrian rocks (boreholes in Canadian, Fennoascandian and South African shields), continental
(i.e. land-based) serpentinization (seeps in the Philippines, Turkey, Greece, Portugal, New Zealand),
igneous inclusions (Lovozero, Khibiny, Ilimaussaq) and volcanic-hydrothermal systems are from
Etiope and Sherwood Lollar, (2013), McCollom and Seewald (2007), Tassi et al. (2012), Potter and
Konnerup-Madsen (2003). The biotic field is from Etiope and Sherwood Lollar (2013; and references
therein). The 13C range for abiotic methane generated with Ru catalyst (red lines), is the theoretical
range based on the lowest isotopic separations observed in the experiments from 20 to 90°C, assuming
initial CO2 of magmatic or limestone origin. Since the isotopic composition of pristine molecular H2
produced by serpentinization, not residual after CO2 hydrogenation, is unknown, the theoretical 2HCH4
range cannot be evaluated.
2
Figure S3. Field Emission Scanning Electron Microscopy (FESEM) images of Ru/alumina catalyst. a.
Support particle (alumina); b and c Ru particle aggregates; d individual Ru particle. Smaller Ru
particles can only be observed by Transition Electron Microscopy (TEM).
Table S1. Comparative tests with Fe and Ni catalysts
Catalyst
T (°C)
N. bottles
Fe
200
90
50
25
blank 90°C
200
90
50
25
blank 90°C
90
25
4
15
3
7
2
2
4
2
3
3
5
2
Ni
Fe+Ni
Time
(days)
1 to 5
1 to 120
76
50 to 108
10 and 50
2 and 5
6 to 120
76
50 to 108
30
6 to 30
CH4 (ppmv)
98 to 11200
1.2 to 13
0.1, 0.5 and 13.4
<0.5
14 and 8
1290 and 12000
<0.1 to 0.5
<0.1
<0.1
0.7
<1
<0.1
3
Fig. S4. CH4 concentrations observed with Ni and Fe catalyst at 90°C.
Supplementary references
Foustoukos DI, Seyfried WEJ (2004). Hydrocarbons in hydrothermal vent fluids: the role of
chromium-bearing catalysts. Science 304, 1002–1005.
Medina JC, Butala SJ, Batholomew CH, Milton LL (2000). Low temperature iron and nickelcatalyzed reactions leading to coalbed gas formation. Geochim. Cosmoch. Acta, 64, 643-649.
Ni Y, Jin Y (2011). Carbon isotopic fractionations during Fischer-Tropsch synthesis. Petrol. Expl.
Dev. Online 38, 249-256.
Potter J, Konnerup-Madsen J (2003). A review of the occurrence and origin of biogenic hydrocarbons
in igneous rocks, in Petford, N., McCaffrey, K.J.W. (Eds), Hydrocarbons in Crystalline Rocks,
Geological Society Special Publication 214, The Geological Society of London, London. pp. 151–173.
Tassi F, Fiebig J, Vaselli O, Nocentini M (2012). Origins of methane discharging from volcanichydrothermal, geothermal and cold emissions in Italy. Chem. Geol., 310-311, 36-48.
4