An Operando Nuclear Magnetic Resonance Spectroscopy Study On Heterogeneous Benzene Hydrogenation Reaction With The Parahydrogen-Induced Polarization

In recent years,heterogeneous catalytic systems have been used more and more widely due to the great advantages of hydrogenation heterogeneous catalysts in product separation and catalyst reuse.Therefore,it is particularly important for the application of heterogeneous catalysts to understand the mechanism of hydrogenation and find the appropriate catalyst structure to achieve efficient and highly selective catalytic hydrogenation.In situ nuclear magnetic resonance?NMR?method was used to study the hydrogenation mechanism in solid-liquid heterogeneous catalytic environment.The effect of Pd cocatalyst with different crystal plane morphology on the hydrogenation products of benzene was studied systematically.The results showed that the?111?exposed surface of Pd octa nanocrystalline had catalytic effect on the hydrogenation of benzene,and the product was cyclohexene.However,Pd cube nanocrystalline particles with?100?faces have no catalytic hydrogenation effect of benzene.Controlling the exposed surface of nanoparticles provides a good opportunity to study the mechanism of structure sensitive reactions and to optimize catalytic performance in terms of activity and selectivity.Through the parahydrogen-induced polarization?PHIP?tool,the researchers can realize the super sensitive detection of intermediates in catalytic hydrogenation reaction.However,PHIP is usually observed during homogeneous hydrogenation.In order to evaluate the potential of PHIP to combine with heterogeneous catalytic hydrogenation,the heterogeneous hydrogenation of benzene was studied using Pd nanocrystalline catalyst with different surface states.Through the research,we found the polarization enhancement of the product signal.It also shows that two hydrogen atoms in the presence of pH₂ molecules are transferred to the same product molecule in pairs.