Synthesis And Catalytic Performance Of Supported Catalysts Based On Ultrathin Titanate Nanosheets

Since single layer graphene was obtained from graphite by mechanical stripping in 2004,ultrathin two-dimensional(2D)materials with single or a few atomic layers thicknesses have received extensive attention.Owing to their unique geometric structures,electronic band structures and large specific surface area,2D materials are widely used in many research yield,such as optoelectronic deviceultrathin,energy storage,sensing,and catalysis.The liquid exfoliation method is usually utilized to prepare nanosheets due to its low cost and high field.However,nanosheets prepared by exfoliation method tend to stack during the drying process to obtain solids as catalyst supports,thus losing the large specific surface area.Therefore,their applications in traditional catalysis have been far less investigated up to now.In this paper,single layer titanate nanosheets(TiONS)obtained by exfoliation method were used as supports to prepare a series of supported catalysts by in-situ reduction in liquid,successfully avoiding the stacking of exfoliated nanosheets.And the as-prepared catalysts have been further used in various liquid phase reactions to explore their catalytic performance.The main research contents and conclusions of the thesis are summarized as follows:(1)A novel liquid-partnered high-efficiency catalyst Pd/TiONS based on exfoliated titanate nanosheets(TiONS)has been successfully developed for the first time.Single-layer TiONS with thickness of about 1 nm were successfully obtained by liquid exfoliation method and Pd/TiONS was prepared by loading Pd on TiONS supports in situ.The catalyst exhibited excellent performance in the selective hydrogenation of phenol to cyclohexanone(selectivity>99.9%and conversion rate>99.9%).Compared to Pd/TiO2,Pd/TiONS showed superior performance,which can be attributed to the negative charge of ultrathin TiONS supports and their high specific surface area that can expose a large number of Pd active sites.In sharp contrst,the dried Pd/TiONS showed stacked structure,which largely reduced surface area,resulting in a decrease of exposed active sites and catalytic activity.(2)Using TiONS in liquid as supports,a series of Pt/TiONS catalysts have been successfully prepared and exhibited excellent performance in the hydrogenation of phenylacetylene.The conversion after 5 hours of reaction at 50? reached 98.0%,and the selectivity was 82.0%.Compared with Pt/TiONS,the activity of Pd/TiO2 was much higher(conversion 95.0%after 30 minutes),but the excessive hydrogenation on Pd/TiO2 led to alow selectivity of 70.0%as a result of the sluggish desorption of styrene on TiO2 supports.The introduction of metallic Cu improved the selectivity of Pt/TiONS while the selectivity decreased.When added different amounts of Pt into Pd,the catalytic acitiviy was greatly enhanced,and the optimal catalyst with a Pd/Pt ratio of 1/50 demonstrated a high activity of 90.0%and selectivity of 81.6%under room temperature(25?)with the inhibition of excessive hydrogenation.(3)The Pt-s/TiONS loaded nanosheet Pt has been successfully synthesized for hydrogenation of nitrobenzene to aniline.At room temperature(25?),Pt-s/TiONS showed high catalytic performance with>99.9%conversion and>99.9%selectivity just in one hour.Pt-s/TiONS mainly exposed Pt(110),thus revealed superior catalytic performance to nanoparticle Pt supported Pt/TiONS.With TiO2 as supports,the conversion of Pt-s/TiO2 was only 1.5%and the selectivity was 69.2%.After repeated use of Pt-s/TiONS for five times,its high catalytic performance was still maintained,indicating its excellent stability.In summary,this thesis mainly foucuses on the study of using the TiONS obtained by the liquid exfoliation method as supports for the preparation of a series of catalysts via in-situ liquid reduction and their catalytic performance for liquid phase reaction.The proposed preparation method successfully avoids the stacking of exfoliated 2D nanosheet supports,and presents a new idea and strategy for the application of the ultrathin materials prepared from liquid exfoliation method in the traditional catalytic reactions.