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Gallium Nitride Catalyzed Oxidative Dehydrogenation Of N-butane To Olefins

Posted on:2018-04-06Degree:MasterType:Thesis
Country:ChinaCandidate:T XingFull Text:PDF
GTID:2351330542477652Subject:Chemical processes
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Currently,the conversion and effective utilization of light alkanes has drawn much attention of researchers around the world.It is important for theoretical studies and applications for the effective utilization of light alkanes and environmental protection.n-Butane is one of the most important light alkanes.The oxidative dehydrogenation?ODH?of butane is used for producing ethylene,propylene and C4 olefin?including 1-butene,t-butene,c-butene,butadiene?,which are useful intermediates for producing synthetic rubbers,plastics,and a number of industrial important chemicals.Thus,the ODH of n-butane is taken as a probe reaction so as to investigate both the activation of C-H bond and the selective conversion of light alkanes,which is significant to the conversion and effective utilization of light alkanes and the understanding of structure-function relationship of the GaN catalysts.In the present thesis,the supported catalysts were intentionally prepared using GaN as the active phase and titanosilicates as the support,and applied in the ODH of n-butane.The effects of GaN species and GaN particle size on catalytic activity were discussed based on the physicochemical properties of the catalysts obtained by N2 adsorption-desorption,transmission electron microscopy?TEM?,hydrogen temperature-programmed desorption?H2-TPD?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,dynamic light scattering?DLS?,and Fourier-transform infrared spectroscopy?FT-IR?.The results of ODH performances were correlated with the characterization results to explore the structure-function relationship of the GaN catalysts for the ODH,especially the key role of GaN in the activation of O species and C-H.The main results are summarized as follows:?1?Investigation of GaN/titanosilicates supported catalyst for the ODH of n-butane.GaN was supported onto titanosilicates via physical grinding method in which the vanadium oxide was introduced as the promoter for ODH n-butane.The prepared catalysts were evaluated and characterized to reveal the mechanism of activation of C-H and O species on GaN,and the relationship between the catalystic performances and the structure of the catalyst was also discussed.Finally,the expected supported GaN catalyst was obtained with high activity and high selectivity of light olefins.It is found that the supported GaN catalyst shows a high catalytic activity for the ODH of n-butane at lower temperature?460 ??.The activity as well as the selectivity of GaN catalyst increases with the decrease of the particle size of GaN.It is indicated that the presence of GaN obviously increases the catalytic activity and GaN can be used as a new active phase for ODH of n-butane.?2?Exploration of the interaction between titanosilicates and GaN.The interaction between GaN and titanosilicates was discussed based on the catalytic performances and characterization results.It is shown that GaN particles can interact with the TiO2?anatase type?on the surface Ti-SBA-15 support,resulting in an increase in the physical absorption capability of oxygen on Ti02 and an increase of the activated O species?O2-?ad?,O22-?ad?,O-?ad??on the surface of GaN catalysts.Based on the results of various characterization,it is concluded that the catalyst with different particle size of GaN possess different capability for activation of O species.Moreover,lower particle size of GaN shows higher ODH activity for n-butane,indicating that the lower GaN nanoparticle can highly activate O species and C-H bond of light alkane.?3?Investigation of Ga-based catalyst for the ODH reaction at high temperature.A series of Ga-based catalysts were prepared via different methods for the ODH of n-butane at high temperature?700 ??.The difference of performances between GaN and Ga2O3 catalyst was investigated to explore the cracking mechanism of ODH on Ga-based catalysts.It is shown that the Ga-based catalysts show both superior activity and selectivity for ODH of n-butane at higher temperature.The total olefin?C2-4?selectivity at 700 ? is much higher than that at 460 ?,while the selectivity of C4 olefin greatly decreased.This may be derived from the thermal cracking of n-butane over the GaN supported catalysts,resulting in higher yields of C2-3 alkenes.Compared with Ga2O3 catalysts,GaN catalysts show higher performances for ODH of n-butane.Furthermore,the results of catalytic tests indicate that the GaN catalysts showed better stability than V-containing and Ga2O3 catalysts.According to the results of TGA,there is no obvious coke on the surface of GaN catalysts and the activity of GaN catalysts in ODH reaction could keep stable for 50 h.
Keywords/Search Tags:Oxidative dehydrogenation, n-butane, GaN catalyst, titanosilicates
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