Modification of Micro- And Nano-Structures of Vanadium Oxide-Based Catalyst for Partial Oxidation of N-Butane
Wong, Yee Ching (2009) Modification of Micro- And Nano-Structures of Vanadium Oxide-Based Catalyst for Partial Oxidation of N-Butane. PhD thesis, Universiti Putra Malaysia.
Sonochemical treatment on V₂O₅ and sonochemical synthesis were employed to produce VOP0₄2H₂O both using ultrasound irradiation. Intercalation-exfoliationreduction using different mixture of solvent as reducing agent to produce VOHPO₄·0.5H₂O and mechanochemical treatment were employed on both VOPO₄·2H₂O and VOHP0₄·0.5H₂O. Besides, the effects of Bi dopant addition also have been studied. The catalysts were synthesised by calcining the precursor, VOHPO₄·0.5H₂O in a flow of n-butane in air (0.75% n-butane in air) for 18 h at 733 K. The physico-chemical properties of the catalysts were characterised by using Xray diffraction (XRD), BET surface area measurement, redox titration, inductively coupled plasma-atomic emission spectroscope (ICP-AES), scanning electron microscope (SEM), transmission electron microscope (TEM) and temperature programmed reduction in H2 flow (H2-TPR). The catalytic properties of the selected catalysts were carried out by using temperature programmed reaction (TPRn) and online microreactor system. The experimental results indicated that V₂O₅ that undergoes ultrasound irradiation for 30 minutes showed an extremely high n-butane conversion (94%) due to its morphology which different from its bulk structures and with the present of kinetically reactive oxygen species. Moreover, nanostructured VPO catalyst produced using sonochemical treated V₂O₅ for 30 min as starting material also shows drastic increment in n-butane conversion (9%) compared to the reference catalyst synthesised via organic route. YOPO₄·2H₂0 produced through sonochemical synthesis technique drastically reduced the synthesis time to only 15 min compared to the conventional reflux method that consumed the synthesis time up to 24 h. The VPO catalyst produced which undergo sonochemical synthesis for 120 min (VPDS 120) shows a drastic increment in n-butane conversion (36%) due to its diameters and thickness of platelets which are smaller thus directly increase the active site of the catalyst for oxidation of n-butane. Furthermore, VPDS 120 catalyst contains more V4+ percentage which directly lead to the increment of the total amount of active and mobile oxygen attached to y4+ phase (0'-V4+ pair). VPO catalyst produced through intercalation-exfoliation-reduction technique using mixture of 2-butanol and ethanol as reducing agent while doping 1% bismuth as promoter, IERC(2Bu-Et)RBil gave the highest maleic anhydride (MA) selectivity due to reactive 02- species released from the additional crystalline V5+ phase formed (02-_V5+ pair) at relative lower temperature. Mechanochemical treated YPO catalyst, YPDM30 shows both reduction peaks occurred at lower temperature compared to the reference catalyst with a suitable oxygen species ratio from V5+N4+ of around 0.25. The lattice oxygen species in the V5+ and V4+ phases which are more reactive, mobile and can be removed easily shown to be the main contribution for YPDM30 to gave high n-butane conversion. A high amount of active oxygen released from V4+ phase (0-_V4+ pair) was shown to be the main contribution for mechanochemi cal treated bismuth doped VPO catalyst, VPDBiMill to be the most active catalyst for n-butane oxidation.
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