Construction And Adsorption Desulfurization Performance Of Niobium Based Polyoxometalate Composite Materials

With the increasing global total energy demand,low-carbon alkanes occupy an increasing share in clean energy in the context of energy transformation.However,organic sulfur in light alkane must be properly treated to reduce its impact on the environment,humans,industrial equipment,and so on.This study uses adsorption desulfurization technology to achieve the purpose of removing thiols from low-carbon alkanes.In this study,adsorption desulfurization technology is used to remove thiols from low-carbon alkanes.The focus of the study is to construct an efficient desulfurizer and analyze the adsorption mechanism.The specific research contents are as follows:based on literature experimental data and theoretical results calculated by density functional theory（DFT）,this work investigated the correlation between the band gap structures of polyniobates and polytitanates and Lewis acid/base characteristics.Secondly,with ethanethiol in natural gas as the probe,niobium based polyoxometalate as the precursor,and common desulfurizer Fe₂O₃ as the dispersion phase,niobium based polyoxometalate nanosheets/nanotubes were modified.Then,the contact interface between the niobium based polyoxometalate nanosheet/nanotube and the composite components is regulated and the interaction between the components is explored to achieve the purpose of regulating the properties of the composite materials.The correlation between the band gap structure and Lewis acid-base characteristics was studied,represented by potassium polyniobate(KNb O₃,K₄Nb₆O₁₇ and KNb₃O₈),sodium polyniobate(Na₂Nb₄O₁₁,Na Nb₁₃O₃₃ and Na Nb₁₀O₁₈),sodium polytitanate(Na₂Ti₆O₁₃,Na₂Ti₇O₁₅ and Na₂Ti₉O₁₉),and potassium polytitanate(K₂Ti₂O₅,K₂Ti₄O₉ and K₂Ti₆O₁₃).Examined polymerization degree（PD）and bond angleθ,bond length,the degree of the MO₆（M=Nb or Ti）octahedral distortions,phase structure,electronic band structures and interlayer cation on its band gap energy.Further by correlating conduction band potential,valence band potential,and Sanderson charge fractionδ_i.The qualitative relationship between the bandgap structure and Lewis acid/base properties was determined.In the case of the same phase structure,the deviation of bond length and bond angle of compound leads to different degree distortion of octahedron as the PD changes.The different degree distortion of octahedronoften lead to band gap structure changes that is different valence and conduction band potential.Acid niobium based polyoxometalate nanoflakes/nanotubes were selected as the carrier materials in the experiment,and the interaction between the carrier materials and basic nanoparticles and the effect on ethanethiol were studied.Fe₂O₃ sol was prepared by thermal hydrolysis of Fe Cl₃·6H₂O,and then Fe₂O₃powder was obtained by aging and freeze-drying.The adsorption of ethanethiol by Fe₂O₃was investigated by using ethanethiol in simulated natural gas as a probe.The adsorption performance and ethanethiol adsorption mechanism of Fe₂O₃ were studied using a combination of experimental evaluation and theoretical simulation.Two kinds of two-dimensional niobium based polyoxometalate,HNb₃O₈ nanosheets（HNb₃O₈-NS）and HTi Nb O₅ nanosheets（HTi Nb O₅-NS）,were prepared by liquid phase exfoliation.By calculating the band gap structures of these two nanosheet precursors,it was found that HNb₃O₈ has stronger Lewis acidity.When two kinds of nanosheets are used to adsorb ethanethiol,the adsorption sites of both are hydrogen bonds（Br?nsted acid sites）,but the adsorption performance of HNb₃O₈-NS is better than that of HTi Nb O₅-NS.In addition,Lewis acid sites obtain electrons from the S atom,and the adsorption of sulfides is achieved through acid-base interactions between the two.Two types of niobium based polyoxometalate nanosheets and Fe₂O₃ composite adsorbents were constructed（x Fe₂O₃/HNb₃O₈-NS,y Fe₂O₃/HTi Nb O₅-NS,x and y being the molar ratios of Fe₂O₃ to HNb₃O₈-NS and HTi Nb O₅-NS,respectively）,and the structure and properties of the composite materials were studied using various characterization techniques.With ethanethiol in simulated natural gas as the probe adsorbent,the adsorption performance of the prepared adsorbent was systematically evaluated.The results indicate that the composite materials have better adsorption performance than their precursors HNb₃O₈-NS,HTi Nb O₅-NS,and Fe₂O₃.When x=0.7（y=0.7）,it had the best adsorption performance for ethyl mercaptan,and the adsorption capacity of 0.7Fe₂O₃/HNb₃O₈-NS（0.7Fe₂O₃/HTi Nb O₅-NS）was 48.05 mg?g^-1(68.02 mg?g^-1).After three cycles of regeneration,the regeneration rates of 0.7Fe₂O₃/HNb₃O₈-NS and 0.7Fe₂O₃/HTi Nb O₅-NS were 53.26%and 64.23%,respectively,which were higher than that of Fe₂O₃（51.99%）.Therefore,transition metal oxides nanoparticles and niobium based polyoxometalate are compounded to construct two excellent sulfide adsorbents with stable chemical structure and environmental friendliness,which have good prospects and potential in practical industrial applications.A novel niobium based polyoxometalate nanotube H₂Nb₄O₁₁ nanotube（HNO-NTs）was prepared using a two-step intercalation method as an efficient solid acid adsorbent.The formation mechanism and structural characteristics of the prepared HNO-NTs were studied.Compared with HNb₃O₈-NS and HTi Nb O₅-NS,HNO-NTs have stronger Lewis and Br?nsted acid strengths.The dynamic adsorption experiment showed that the breakthrough adsorption capacity of HNO-NTs for ethanethiol was 52.27 mg?g^-1 at a space velocity of 6000 h^-1.The regenerated HNO-NTs still maintain good performance after 10 adsorption-desorption cycles.Using recombination method to modify nanotubes,a series of Fe₂O₃ and HNO-NTs composites were constructed(z Fe₂O₃/H₂Nb₄O₁₁-NTs,z is the molar ratio of Fe₂O₃ to H₂Nb₄O₁₁-NTs).The adsorption desulfurization experiment showed that the 0.7Fe₂O₃/H₂Nb₄O₁₁-NTs adsorbent had the best adsorption performance,with a breakthrough adsorption sulfur capacity of 86.12 mg?g^-1.In addition,after three adsorption desorption cycles,the regeneration rate of 0.7Fe₂O₃/H₂Nb₄O₁₁-NTs is 54.35%.This study can provide theoretical guidance for the design and preparation of new functional materials by reasonably designing and controlling the relationship between the microstructure and performance of materials,as well as exploring the mechanism of mercaptan adsorption and separation.Figure[93]Table[6]Reference[213]...