Catalytic oxidative dehydrogenation of propane by AMoVNbOx (A = Ni, Co, Pt) synthesised via impregnation method

Propane is a natural gas that is found abundant and low cost material in petroleum industry. In order to upgrade the value of propane, catalytic oxidative dehydrogenation of propane has been carried out to form propylene which is widely used as chemical intermediate in manufacturing process. Thus, Ni, Co and Pt-doped MoVNbOx catalysts were prepared by using impregnation method. These catalysts were used for oxidative dehydrogenation reaction of propane to propylene. The catalysts prepared were characterized by X-ray diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Brunauer-Emmett-Teller (BET) Surface Area Measurement, SBET, Scanning Electron Microscopy (SEM), and Temperature Programmed Reduction in Hydrogen (H2-TPR). From the XRD data, it has been found that all doped catalysts showed the presence of tetragonal Mo5O14-like phases with a much better crystallite formation as compared to the undoped MoVNbOx. The particle crystallinity increases as the amount of dopant loaded increases. ICP-OES analysis displayed that the atomic ratio of Mo/V/Nb was 1/0.24/0.13, agreeing well with the theoretical ones. However, the amount of dopant was a bit less especially for Pt doped catalysts. Doping of Ni, Co and Pt lowered the surface area value as compared to undoped MoVNbOx catalysts (8.8 m2/g). This confirmed the incorporation of dopants occur in the catalytic system. Furthermore SEM images supported this claim by showing the particles developed into c-direction which supported high crystallinity of doped catalysts and the role of dopants as structural promoter. Therefore, the reputed active site (i.e. Mo5O14-like phase) improved when dopants were added, eventually affecting the catalytic performance. H2-TPR showed the reducibility of the catalyst confirming the existence of lattice oxygen of high reaction temperature. Catalytic test of Pt-MoVNbOx catalysts gave the highest activity (13.4 % for aPtMoVNbOx and 23.4 % for bPtMoVNbOx) in propane conversion but 0 % selectivity towards propylene due to the poisoning of Pt site by COx. Meanwhile Ni-MoVNbOx catalysts have relatively lower activity (7.5 % for aNiMoVNbOx) than Pt- MoVNbOx catalysts but higher selectivity for propylene production (44.0 % for aNiMoVNbOx). For Co-MoVNbOx catalysts, the higher activity for propane conversion is found for lower loading of dopants, while high selectivity for propylene is observed for high loading of dopants.

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