1 The carburization of transition metal molybdates (M x MoO 4 , M= Cu, Ni or Co) and the generation of highly active metal/carbide catalysts for CO 2 hydrogenation Wenqian Xu a , Pedro J. Ramírez a, b , Dario Stacchiola a , Joaquín L. Brito c , and José A. Rodriguez a,* a Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA b Facultad de Ciencias, Universidad Central de Venezuela, Apartado 20513, Caracas 1020-A, Venezuela. c Centro de Química, Instituto Venezolano de Investigaciones Científicas (IVIC), Apartado 21827, Caracas 1020-A, Venezuela. *email: Rodriguez, Jose [rodrigez@bnl.gov] ABSTRACT: A new approach has been tested for the preparation of metal/Mo 2 C catalysts using mixed-metal oxide molybdates as precursors. Synchrotron-based in situ time-resolved X-ray diffraction was used to study the reduction and carburization processes of Cu 3 (MoO 4 ) 2 (OH) 2 , ɑ- NiMoO 4 and CoMoO 4 nH 2 O by thermal treatment under mixtures of hydrogen and methane. In all cases, the final product was β-Mo 2 C and a metal phase (Cu, Ni, or Co), but the transition sequence varied with the different metals, and it could be related to the reduction potential of the Cu 2+ , Ni 2+ and Co 2+ cations inside each molybdate.The synthesized Cu/Mo 2 C, Ni/Mo 2 C and Co/Mo 2 C catalysts were highly active for the hydrogenation of CO 2 . The metal/Mo 2 C systems exhibited large variations in the selectivity towards methanol, methane and C n H 2n+2 (n > 2) hydrocarbons depending on the nature of the supported metal and its ability to cleave C-O bonds. Cu/Mo 2 C displayed a high selectivity for CO and methanol production. Ni/Mo 2 C and Co/Mo 2 C BNL-107990-2015-JA