REACTION ENGINEERING, KINETICS AND CATALYSIS Co-Doped ZnO Thin Films Grown by Pulsed Electron Beam Ablation as Model Nano-Catalysts in Fischer-Tropsch Synthesis Asghar Ali and Redhouane Henda School of Engineering, Laurentian University, Sudbury, ON P3E 2C6, Canada James Aluha and Nicolas Abatzoglou Dept. of Chemical & Biotechnological Engineering, Universite de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada DOI 10.1002/aic.16177 Published online in Wiley Online Library (wileyonlinelibrary.com) A single-step deposition of cobalt-doped zinc oxide (Co-ZnO) thin film nano-composites on three different crystalline substrates, viz., Al 2 O 3 (c-sapphire), silicon (100) (Si), and SiO 2 (quartz) is reported, using pulsed electron beam ablation (PEBA). The results indicate that the type of substrate has no effect on Co-ZnO films stoichiometry, morphology, micro- structure, and film thickness. The findings show the presence of hexagonal close-packed metallic Co whose content increases in the films deposited on Al 2 O 3 and Si substrates relatively to SiO 2 substrate. The potential of the films as model nano-catalysts has been evaluated in the context of the Fischer-Tropsch (FT) process. Fuel fractions, which have been observed in FT liquid products, are rich in diesel and waxes. Specifically, Co-ZnO/Al 2 O 3 nano-catalyst shows a selectivity of 4%, 31%, and 65% towards gasoline, diesel, and waxes, respectively, while Co-ZnO/SiO 2 nano-catalyst shows a selectivity of 12%, 51%, and 37%, for gasoline, diesel, and waxes, respectively. VC 2018 American Institute of Chemical Engineers AIChE J, 00: 000–000, 2018 Keywords: Co-ZnO nano-composites, nano-catalysts, pulsed electron beam ablation, Fischer-Tropsch synthesis, substrate Introduction Doping with transition metals, such as Mg, Al, Ag, and Co, is a powerful tool used to modify, tune, or improve the perfor- mance of nano-materials. 1–4 Cobalt is considered a potential material for incorporation in ZnO because of its abundant electron states and large solubility into ZnO matrix. 5,6 While ZnO has a wide band gap and a large free exciton binding energy, is low cost, nontoxic, and stable over a wide range of temperatures, 5–7 Co-doped ZnO, in particular, is a promising candidate for use as a dilute magnetic semiconductor and as a model nano-catalyst. On the one hand, doping with Co has attracted much interest as it is attributed to narrowing the band gap, 4 increasing the links between nanoparticles with ensuing increase in carrier concentration, 8 improving the performance of gas sensors, 6 and enhancing antibacterial as well as photo- catalytic activities of Co-ZnO films. 7 On the other hand, Co- ZnO nano-composites hold promise as model nano-catalysts in many energy-intensive processes such as H 2 production, 9 steam reforming, 10 and Fischer-Tropsch synthesis (FTS). 11 The properties of nano-catalysts depend on size, structure, and the presence of the metal in elemental form, so that it is criti- cal to control these aspects during film growth to achieve desirable catalytic performance. 12 The microstructure of Co-ZnO films, while temperature dependent, is affected by the level of Co doping in ZnO. A threshold limit (10–12 wt % Co) has been reported in the liter- ature beyond which secondary phases, such as metallic Co and Co oxides, appear in Co-ZnO films. 13,14 Below this threshold limit, the properties of Co-ZnO are similar to those of ZnO. 13 The morphological and structural changes in thin films are also dependent on the precursor sources and deposition tech- nique. Pulsed electron beam ablation (PEBA) has recently emerged as a potential technique for the fabrication of superior quality thin films. The production of well controlled nano- sized particulates is a characteristic feature of PEBA, which has a strong bearing on the surface morphology of the depos- ited films. 15 These nano-sized particulates can find many industrial applications including the production of nano- catalysts. Further, single-step processes are made possible using PEBA, whereas many steps (including impregnation, drying, decomposition/calcination, activation/reduction) are involved in the preparation of FTS-based catalysts by conven- tional wet chemical methods. The nature of substrate used is very important for the growth of high quality films in terms of lattice and thermal mismatch between the film and the underlying substrate, which, in turn, may result in the development of undesired stresses in the films. The substrate, being one of the significant parameters in catalyst synthesis, could affect the characteris- tics of deposited films by affecting their structural properties, 16 Correspondence concerning this article should be addressed to A. Ali at aali2@ laurentian.ca. VC 2018 American Institute of Chemical Engineers AIChE Journal 1 2018 Vol. 00, No. 00