C H Activation of Methane to Syngas on Mn x Ce 1xy Zr y O 2 : A Molecular Beam Study Anjani Dubey, [a] Sadhu K. Kolekar, [a] and Chinnakonda S. Gopinath* [a, b] Introduction Methane is a principal constituent of natural gas, and accord- ing to the international energy agency (IEA) its consumption is expected to increase by 30–40 % every 25 years. [1] It is antici- pated that there will be a gradual deficit in the oil production in the not so distant future, and there will be an increasing demand for energy resources. [2] Therefore, there is a need to convert natural gas to large petroleum resources to compen- sate the deficit in the oil production. Production of syngas (CO+H 2 ) is the first step in the conversion of methane gas to liquid fuels. Catalytic partial oxidation of methane [Eq. (1)] is one of the better methods compared to other processes, such as steam reforming [Eq. (2)] and autothermal reforming for generation of H 2 and CO, which require high temperature and high pressure. Catalytic partial oxidation is exothermic in com- parison to steam reforming of CH 4 . CH 4 þ 1 = 2 O 2 ! CO þ 2H 2 DH ¼36 kJ mol 1 ð1Þ CH 4 þ H 2 O ! CO þ 3H 2 DH ¼þ206 kJ mol 1 ð2Þ Nonetheless, the main hindrance is the C H activation of CH 4 , which requires 439 kJ mol 1 for its bond dissociation. [3] The adsorption of CH 4 molecule on the catalyst surface decides the activation energy for C H activation. [4, 5] The characteristics of partial oxidation of methane are high temperature and short contact time. [6] Generally, metal surfaces are used to oxi- dize alkanes either to olefins or syngas at high temperatures of approximately 1000 K. [7, 8] It has been suggested that partial ox- idation of methane to syngas happens through two types of mechanisms, namely, a) direct partial oxidation, and b) com- bustion–reformation pathway. Wilson and Zaera studied partial oxidation of CH 4 on Rh (111) surfaces at 1165 K and found that it occurs through the direct partial oxidation pathway. [9] Sasaki et al. studied the energetics of activation of methane and ethane on Pt and Rh foils and found that partial oxidation occurs at  900 K. [10] Horn et al. evaluated Rh-coated a-Al 2 O 3 for methane to syngas between 1083 and 1313 K and found that the reaction proceeds through the combustion–reforma- tion pathway. [11] The combustion–reformation pathway is highly preferred, as it involves two of the most stable mole- cules as reactants to produce the desired syngas. CH 4 þ CO 2 ! 2 CO þ 2H 2 DH ¼þ247 kJ mol 1 ð3Þ Larimi employed Ni/CeZrO 2 mixed oxides and found that methane-to-syngas reaction occurs between 723 and 1173 K. [12] Owing to the endothermic nature of C H activation, it general- ly occurs at approximately 1000 K and there are not many cat- alysts that show activity below 1000 K. Further, mechanism of partial oxidation of CH 4 is yet to be addressed in detail, be- cause of the complex nature of the reaction itself and the mac- roscopic nature of kinetic data. Little information on elementa- Mn-doped ceria zirconia thin films (Mn x Ce 1xy Zr y O 2 , MCZ) were employed as flat model catalyst surfaces for CH 4 activation. MCZ films exhibit characteristics of single crystal and powder materials, such as smooth surfaces and porosity. From molecu- lar-beam studies, it has been identified that the oxygen stor- age capacity increases with Mn content. Mutually exclusive ob- servation of H 2 O or a mixture of products (CO 2 + CO + H 2 ) occurs, when the reactants was allowed to react directly on MCZ, underscoring their formation or prevention (and con- sumption), respectively. The results suggest that there is com- petition and cooperation among different elementary reactions under complementary conditions. From a significant partial ox- idation of CH 4 through C H activation, it is found that forma- tion of syngas begins at 700 K and the reaction rate increases with increasing temperature. Kinetic evidences indicate that the reaction proceeds through a combustion–reformation pathway. [a] A. Dubey, Dr. S. K. Kolekar, Prof. C. S. Gopinath Catalysis Division National Chemical Laboratory Dr. Homi Bhabha Road, Pune 411 008 (India) E-mail : cs.gopinath@ncl.res.in Homepage: http://academic.ncl.res.in/cs.gopinath [b] Prof. C. S. Gopinath Center of Excellence on Surface Science National Chemical Laboratory Dr. Homi Bhabha Road, Pune 411 008 (India) Supporting information for this article can be found under http:// dx.doi.org/10.1002/cctc.201600365. They contain the materials synthesis and characterization and X-ray diffraction data of MCZ films (SI–1), TEM (SI–2), SEM (SI–3), XPS of the O 1s and Ce 3d core level and deconvolu- tion (SI–4), oxygen adsorption on few MCZ films (SI–5), typical mass spectrum recorded during oxygen adsorption (SI–6), s and OSC calcula- tion method (SI–7), first signature of methane activation (SI–8), methane oxidation performed on ceria–zirconia at 850 K (SI–9), and XPS of Zr 3d and Mn 2p core levels of spent MCZ films (SI–10). ChemCatChem 2016, 8, 1 – 12  2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 These are not the final page numbers! ÞÞ These are not the final page numbers! ÞÞ Full Papers DOI: 10.1002/cctc.201600365