| Noble-metal catalysts are widely used in catalytic hydrogenation.Capping agent can bind on the particle surface to regulate their catalytic activity for hydrogenation.Biomolecules with variable sequence and complex structures were used as capping agents to prepare noble-metal nanocatalysts with specific morphology and function.In this study,various noble-metal nanocatalysts regulated by different biomolecules were prepared and applied to catalyze hydrogenation reactions.Nucleosides and their derivatives were employed as capping agents of Pd nanoparticles（NPs）,and their effect on Pd activity was evaluated.The relationship between the catalytic hydrogenation activity of Pd NPs and the structure of capping agents was systematically studied.All four kinds of nucleosides exhibited obvious promoting effect on the activity of Pd NPs in comparison to that without any capping agent.Pd NPs regulated by pyrimidine-based nucleosides exhibited higher catalytic activity than those regulated by purine-based nucleosides on account of the absence of the five-membered N-heterocyclic ring.The general promoting effect sequence of nucleosides and their derivatives on the activity of Pd NPs was nucleoside≥nucleotide>deoxynucleoside>base>deoxynucleotide.The quantitative correlation between the activity promoting effect and the structure of nucleosides and their derivatives were studied using the method based on poly-parameter linear free energy relationships.The effect of different groups on the Gibbs free energy of activation was also verified.Moreover,the kinetic behaviors of 4-NIP hydrogenation over Pd NPs regulated by different nucleosides（adenosine,guanosine,cytidine,andβ-thymidine）were studied systematically and different kinetic models were developed to fit the data.The obtained kinetic data fitted well to the Langmuir-Hinshelwood（L-H）model,where the surface reaction is the rate-controlling step.The apparent activation energy,adsorption enthalpy of 4-NIP,and dissociated adsorption enthalpy of hydrogen（H2）were calculated and compared for a better understanding of the mechanism.Pd NPs regulated by cytidine（Cs）showed the lowest apparent activation energy of 43.66 k J mol–1.Pd and Pt nanoparticles regulated by Cs were loaded on various carbon carriers for the hydrogenation of CAL by H2.Synergistic effect of Cs and polyvinylpyrrolidone（PVP）together with the influences of,carbon carrier type,reaction pressure,and Pt precursor type on the activity was investigated.On Pd/MWCNTs,the synergistic effect of Cs and PVP mainly enhanced the hydrogenation activity,by which high CAL conversion（100%）and selectivity（97.35%）of hydrocinnamaldehyde（HCAL）were achieved.Pt/SWCNTs regulated by Cs and PVP exhibited high selectivity（76.74%）of cinnamyl alcohol（COL）.The results indicate that metal-support interaction has great influence on the selectivity of hydrogenation.Pd supported on MWCNTs had high selectivity for C=C hydrogenation,and Pt supported on SWCNTs was apt to undergo C=O hydrogenation.Various Pd/Al2O3 catalysts were prepared by an impregnation method and used to catalyze the hydrogenation of naphthalene.Polydopamine（PDA）was employed as surface coating to regulate the interface of Pd/Al2O3 catalyst.The effects of PDA carbonization temperature,calcination temperature,metal content,and the ratio of PDA and support on catalytic activity and product selectivity were investigated.Then,direct coal liquefaction product was hydrogenated using commercial Pd/Al2O3 catalyst.The aromatic content of direct coal liquefaction product was reduced from 39.89%to 6.35%under 210°C,4 MPa of H2,and 2.0 h-1 of space velocity. |
