Studies on influence of hydrogen and carbon monoxide concentration on reduction progression behavior of molybdenum oxide catalyst Alinda Samsuri a,* , Mohd Nor Latif b,e , Mohd Razali Shamsuddin c , Fairous Salleh d , Maratun Najiha Abu Tahari d , Tengku Shafazila Tengku Saharuddin f , Norliza Dzakaria g , Mohd Ambar Yarmo d a Department of Chemistry and Biology, Centre for Defence Foundation Studies, Universiti Pertahanan Nasional Malaysia, Kem Sungai Besi, Kuala Lumpur, 57000, Malaysia b GENIUS@Pintar National Gifted Centre, Universiti Kebangsaan Malaysia, Bangi, Selangor, 43600, Malaysia c Catalysis Science and Technology Research Centre (PutraCAT), Chemistry Department, Faculty of Science, Universiti Putra Malaysia, UPM Serdang, Selangor, 43400, Malaysia d Centre for Advanced Materials and Renewable Resources, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, 43600, Malaysia e Department of Chemical & Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi, Selangor, 43600, Malaysia f Faculty of Science and Technology, Universiti Sains Islam Malaysia, Bandar Baru Nilai, Nilai, Negeri Sembilan, 71800, Malaysia g School of Chemistry and Environment, Faculty of Applied Sciences, Universiti Teknologi MARA, Cawangan Negeri Sembilan, Kampus Kuala Pilah, Pekan Parit Tinggi, Kuala Pilah, Negeri Sembilan, 72000, Malaysia highlights  Reduction of MoO 3 proceed in three-step reduction: Mo 6þ / Mo 5þ / Mo 4þ / Mo 0 .  Hydrogen is a stronger reducing agent than carbon monoxide in reduction of MoO 3 .  Reduction of MoO 3 in carbon monoxide atmosphere promotes to the formation of Mo 2 C. article info Article history: Received 30 December 2019 Received in revised form 23 August 2020 Accepted 25 August 2020 Available online xxx Keywords: Reduction Molybdenum oxide abstract Temperature programmed reduction (TPR) analysis was applied to investigate the chemical reduction progression behavior of molybdenum oxide (MoO 3 ) catalyst. The composition and morphology of the reduced phases were characterized by X-ray diffraction spectros- copy (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). The reduction progression of MoO 3 catalyst was attained with different reductant types and concentration (10% H 2 /N 2 , 10% and 20% CO/N 2 (%, v/v)). Two different modes of reduction process were applied. The first approach of reduction involved non-isothermal mode reduction up to 700  C, while the second approach of reduction involved the isothermal mode reduction for 60 min at 700  C. Hydrogen tem- perature programmed reduction (H 2 -TPR) results showed the reduction progression of three-stage reduction of MoO 3 (Mo 6þ / Mo 5þ / Mo 4þ / Mo 0 ) with Mo 5þ and Mo 4þ . XRD * Corresponding author. E-mail address: alinda@upnm.edu.my (A. Samsuri). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (xxxx) xxx https://doi.org/10.1016/j.ijhydene.2020.08.214 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Samsuri A et al., Studies on influence of hydrogen and carbon monoxide concentration on reduction pro- gression behavior of molybdenum oxide catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2020.08.214