Mechanism of catalytic hydropyrolysis of sedimentary organic matter with MoS_2

MoS2 was used as an efficient catalyst for hydropyrolysis （Hypy） of three samples of sedimentary organic matter with different maturities. Through comparison with Soxhlet extraction （SE）, it was found that MoS2 catalytic Hypy can remarkably promote the yields of total chloroform extracts, saturates, aromatics, hopanes and steranes. In addition, the difference of biomarker parameters indicated that isomerization of covalently-bound biomarkers is much more difficult than their free counterparts. Meanwhile, the high conversion of total organic carbon （TOC） in MoS2 catalytic Hypy of organic matter proved that the presence of dispersed molybdenum sulfide accelerated the breaking of C-C bonds and the release of hydrocarbons. To address the catalytic mechanism, a series of control experiments based on free Hypy and catalytic Hypy were conducted. The results showed that the calculated atomic ratio of carbon conversion/hydrogen conversion for catalytic Hypy was much larger than the presumed value of 1/2, indicating that intensive hydrogenation took place and significantly influenced the distribution of liquid products. Analysis of stable hydrogen isotope data, infrared spectra and m/z 83 ion chromatograph of the saturate fraction further confirmed this hypothesis. The difference of S content changing （AS） between catalyst-free Hypy and catalytic Hypy, and the thermal characteristics of the catalyst, indicated that active H2S was definitely generated and it probably initiated free radical reactions in the early stage of hydropyrolysis of organic matter.

Assessing Possibilities and Limitations for Biomarker Analyses on Outcrop Samples:A Case Study on Carbonates of the Shibantan Member (Ediacaran Period, Dengying Formation, South China)

The Shibantan Member（Dengying Formation, South China） represents one of only two carbonate settings with Ediacara-type organisms and offers a rare opportunity to study the biogeochemistry of these ecosystems. To evaluate possibilities and limitations for future biomarker studies on fossil-bearing outcrop samples of the Shibantan Member, we analysed the spatial distribution of hydrocarbons in extractable organic matter（i.e. bitumen） on a millimetre scale. Our study demonstrates that the sample and most likely also other rocks from the same setting are contaminated with petroleum-derived compounds that bear the potential for erroneous interpretations in palaeo-reconstructions. The contamination was revealed by distribution patterns and amounts of extractable n-alkanes and acyclic isoprenoids. The contamination is linked to the external weathering surfaces but also to cracks within the rock, and the extent most likely depends on concentration gradients between these contamination sources. Here we show that contamination can successfully be distinguished from syngenetic signals obtained from non-extractable organic matter（i.e. kerogen） using catalytic hydropyrolysis（Hy Py）. However, we observed that decalcification is necessary to achieve sufficient yields of kerogen-bound hydrocarbons and to avoid artificial alteration of the biomarker signals due to matrix effects.