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Along with the fast development of economy and growth of world’s population, the demand for energy is significantly enhanced. The conventional petroleum and coal resources are unrenewable and bring about severe pollution to the environment. In the past decade, the technological advances in drilling and exploitation lead to a significant increase in the production capacity of shale gas worldwide. The U.S. Energy Information Administration projects that the annual shale gas output would rise by 104% from 2012 to 2040, which could ignite “shale gas revolution” and change the energy landscape [1]. As we know, the main component in natural and shale gas is methane which contributes to 83%–99%. Consequently, technologies utilizing methane efficiently are more and more recognized and predicted as leading actor in the coming century of natural/shale gas chemical engineering. Up to now, the industrial approach of catalytic valorization of CH4 mainly comes through the routes of steam reforming to syngas, which can then be converted into methanol and other value added chemicals by FischerTropsch synthesis at a large scale [2]. Comparatively, the direct, one-step transformation of CH4 to liquid oxygenates, which is more energy-effective and economic for the avoidance of expensive syngas intermediates, has been proven difficult due to low conversion, selectivity and yield of target product. Particularly, the selective oxidation of methane to methanol, which is famous as a “holy grail” reaction in catalysis science, has long time been studied but bloomed again only recently. The scientific challenge lies in the inertness of methane molecules with low electron affinity and high C–H bond energy of 439 kJ mol, causing the cleavage of first C–H bond as the rate-determining step [3]. Various formulations of catalysts have been developed, particularly in mimic enzymatic systems of methane monooxygenases, among which the zeolites containing Cu or Fe species were reported as star catalysts to produce methanol from methane [4]. On these catalysts, the production of methanol originates from multi-steps of methane activation, conversion to methoxyl, then being extracted by H2O [5,6]. These processes can lead to satisfactory selectivity of nearly 100%, however, the rate of CH4 conversion and the yield of methanol are too low due to the stoichiometric production of methoxyl from the activation of methane on Cu or Fe sites in either stepwise or chemical looping modes. The supported noble metal catalysts give another alternative but suffer from no serious consideration previously due to facile deep dissociation of C–H bond and over-oxidation to CO2 on the metal sites. Nevertheless, the one-step conversion of CH4 to CH3OH or CH3COOH was feasible on homogeneous Pt or Pd based catalysts despite of using corrosive oxidants or media [7,8]. Moreover, the theoretical studies found that the metal sites with lower coordination number can stabilize CH3 species to avoid the successive dehydrogenation of CH4 [9]. Recently, corresponding author Prof. Maria FlytzaniStephanopoulos of Tufts University and her coworkers made a big breakthrough in the mild oxidation of methane not only to methanol but also to acetic acid by heterogeneous catalysis [10]. They prepared ZSM-5 supported Rh single atom catalyst by a simple wet chemistry method with Rh loading amount of around 0.5 wt%. The typical image of high-angle annual dark-filed scanning transmission electron microscopy in Fig. 1a indicate that there are isolated Rh atoms on ZSM-5. The CO adsorption infrared spectroscopy result in Fig. 1b further proves the presence of Rh single atoms from the peaks at 2,116 and 2,049 cm that are attributed to the symmetrical and asymmetrical stretching of CO from the isolated mononuclear Rh(CO)2 species. Of great significance, this cat-

Rh single atom catalyst for direct conversion of methane to oxygenates