Preparation Of Tantalum-based Catalysts And Study On The Performance Of Selective Catalytic Hydrogenation Of Nitroaromatics And Cinnamaldehyde

Catalytic selective reduction of nitrobenzene derivatives and aldehyde derivatives carried multifunctional group,is generally used chemical method for the preparation of drugs,dyes,herbicides.However,the regional selectivity and stability have been the important issues to hinder its industrialization process.For instance,when the substrate contains multiple easily reducing groups（such as alkene,alkynes,alcohol,aldehyde,etc.）,the selective reduction of nitro moiety or aldehyde group while the olefin group being retained,is very important and challenging work.The catalytic transfer hydrogenation method to reduce the target functional groups of the nitro or aldehyde groups under the reactive conditions such as the absent of high-pressure gas,the green solvent,the better controllability of the reduction degree,is an efficient,safe,low cost,green approach for the hydrogenation reduction reaction of the aromatic derivatives with the multiple groups hydrocarbon.The tantalum-based catalysts as the main research materials in this thesis,the physical and chemical properties of the materials are modified by their catalytic characteristics to design the efficient,excellent active,high selective and cycle stable heterogeneous catalytic materials for selective catalytic hydrogenation.The prepared materials have been applied in the hydrogenation reation of the p-nitrophenol to the corresponding aniline,3-nitrostyrene to 3-vinylaniline,3-nitrophenylacetylene to 3-aminophenylacetylene,and cinnamaldehyde to cinnamyl alcohol.The research contents are as follows:1.Focusing on the catalytic transfer hydrogenation of p-nitrophenols to the corresponding anilines,a series of tantalate-supported silver catalysts Ag/M_xH₂–_xTa₂O₆（M=H,Li,Na,K,Sr）were prepared and their catalytic activity and reusability were evaluated.The results show that the Ag/H₂Ta₂O₆ catalyst can completely convert p-nitrophenol to p-aminophenol within 2 minutes,and still maintain constant catalytic activity after 30 cycles of testing.As a comparison,abundant non-tantalate solid acid catalysts(Ag/Al₂O₃,Ag/Si O₂-Al₂O₃,Ag/Zr O₂-SO₄^2-,and Ag/heteropolyacid)were also prepared.It is proved that the H species inside the H₂Ta₂O₆ support plays a promoting role in the catalytic transfer process of p-nitrophenol.Mechanistic studies demonstrate that the intrinsic proton H species of the Br?nsted solid acid support can directly participate in the formation of products.Meanwhile,Ag nanoparticles can form an embedded distribution by exchanging with structural H species,responsible for the stabilization of catalytic active sites.2.Focusing on the selective hydrogenation of nitroarenes with multiple competitive reducible groups,Cu₂O/M₂Ta₂O₆（M=H,Li,Na,K,Ag,Bi）catalysts were prepared to evaluate their catalytic performance by using 3-nitrostyrene as a model reaction.The results confirm pristine Cu₂O has a highly activity to hydrogenate 3-nitrostyrene but low selectivity due to the coexisted with various by-products.Whereas,the independent tantalate can converse 3-nitrostyrene to sole product via absolutely preferential reduction of-NO₂ moiety with a low conversion rate.Further,if combining Cu₂O and tantalate,the activity and selectivity of 3-vinylaniline are obviously increased.In addition,mechanistic studies confirm tantalate played a decisive role in the formation of the appointed product,and the hydrogenation activity is closely related with the catalysts’intrinsic basicity and preferential adsorption of target group.This work presents an eco-friendly and low-cost route to tailor precisely selectivity for hydrogenation reaction of nitroaromatics3.Focusing on the catalytic transfer hydrogenation of 3-nitrophenylacetylene to3-aminophenylacetylene,a series of novel ternary nanocomposite of Pt-Fe/Ta₂O₅ was successfully assembled via a simple one-step calcination method.By varying the molar ratios of platinum to iron,and using ammonia borane as the hydrogen source,the Pt₁-Fe₃/Ta₂O₅ catalyst is found to exhibit an optimum catalytic performance:the selectivity to 3-aminophenylacetylene reaches 100%when the conversion of 3-nitrophenylacetylene is 90%,and the catalyst does not deactivate through five rounds cyclic experiments with excellent stability.Mechanistic studies demonstrate the improved catalytic selectivity can be attributed to the fact that the introduction of Fe element change the electron density of the catalyst and the adsorption behavior of the reactants.4.Focusing on the selective hydrogenation of multifunctional aldehyde compounds to prepare the corresponding alcohol compounds,Cu-Ag bimetallic nanoparticles supported on ultrathin KTa O₃ nanosheets were developed for the selective catalytic transfer hydrogenation reduction of cinnamaldehyde under room temperature and atmospheric pressure conditions and exhibited optimum cinnamaldehyde conversion and selectivity of cinnamyl alcohol.Mechanistic studies reveal that ultrathin KTa O₃ nanosheets structure offers surface defects and rich lewis acid sites,which can selectively chemisorb and activate reaction molecules.Therefore,the ultrathin nanosheet-structured KTa O₃ plays a crucial role in the selectivity of target products.The superior catalytic performance for hydrogenation is attributed to a synergistic effect of Cu,Ag and KTa O₃ nanosheets.This work provides a reference to guide the design of ultrathin nanosheet catalysts with functional metal sites for precise control of the formation of target products in chemoselective catalytic transfer hydrogenation under environmentally friendly reaction conditions.