Preparation Of Pt Nanocrystals By Biomimetic Regulation For Catalytic Hydrogenation

Due to green,efficient and economical characteristics,catalytic hydrogenation technology is widely used in petrochemical and fine chemical industry.The precious metal nanoparticles,with high specific surface area and the excellent adsorption and dissociation properties for hydrogen,is the most commonly used active components for hydrogenation catalyst.In this work,the controllable biomimetic synthesis of nano precious metal hydrogenation catalyst was studied.The catalytic hydrogenation properties of the synthesized nano precious metal via molecular regulation under mild condition was inverstigated and the mechanism of catalytic hydrogenation was preliminary exploration.Varous Pt nanocrystals were synthesized by reduction method using small biomolecules（adenine,adenosine,adenine nucleotides,etc.）as a regulating reagent at room temperature.The influence of Pt precursor and reducing agents,the kind and amount of regulating reagent on the catalytic hydrogenation of Pt nanocrystalline was studied.The optimumized condition for the preparation of the catalyst was obtained:K₂PtCl₄ as metal precursor,Na BH₄ as reductant;deoxyadenosine with a concentration of 0.15 mg/mL as capping agent.It was found that when the biomolecular with-OH radicals was used as regulator,Pt nanocrystals showed higher catalytic activity.While Pt nanocrystals synthesizd via the regulator with-H₂PO₄ radicals was lower.Based on those results,Pt nanocrystals with special morphology and excellent hydrogenation activity were prepared by using biological macromolecules which contains large number of-OH,such as dextran and lignin.But Pt nanocrystals prepared in this way showed low stability,and the hydrogenation activity reduced significantly after 22 h,.In order to inhibit agglomeration and instability of nanocrystals,we selected different carbon materials（carbon powder,graphene,carbon nanotubes）as supports where dextran and lignin were regulating reagents.Loading Pt on the reduced graphene oxide（RGO）resultied into an excellent catalyst with high activity and stability.The catalytic activity still remained over 90%after 17 days from preparation.Fur further improving the dispersion of Pt on carbon material,the supports were doped by nitrogen and the performance of catalytic hydrogenation was investigated.When carbon nanotubes were doped by N,the activity of Pt nanocrystals increased obviously compared to that without N-doped,meanwhile,the degree of dispersion of Pt was also improved.Finally,the interfacial regulation mechanism of metal-substrate for supported hydrogenation catalyst and the commonality of the activity between different metals were deeply discussed in this paper.It indicated that the activity of precious metal nanocrystal modifed by PDA has been improved when polydopamine（PDA）was introduced to the SBA-15.For reducing 4-NP by borohydride ions,the average rate constant k of Pt/DA-SBA-15 as catalyst was 19.6 times larger than that of Pt/SBA-15catalyst.Combining the reaction kinetics experiment data with the reaction energy density functional theory（DFT）calculation results,the interaction between PDA and noble metal NPs can selectively adjust the binding energy of reactant closer to the optimal value for higher catalytic activity.A volcano plot according with the Br?nsted–Evans–Polanyi relation has been obtained.The optimum catalyst should be one with a 4-NP binding energy of-0.78 eV（-75 kJ/mol）.The interface control mechanism of PDA has universality and can be suitable for different kinds of metals and substrates,which provides theoretical basis and experimental guidance for the preparation of high efficiency supported hydrogenation catalyst.