Effects Of Coordination Cations Over Zeolite On Hydrogenation Performance Of The Prepared Pd/H-ZSM-5

Zeolite-supported noble metal catalysts have been widely used in important industrial reactions such as hydrogenation,hydrocracking and hydrodeoxygenation.The catalytic performance is not only dependent on the properties of the metal component,the particle size of the metal,the pore structure and acid property of the zeolite support and the metal-support interaction,but also on the method of catalyst preparation.Zeolite-supported noble metal catalysts can be prepared by a variety of methods including impregnation,ion exchange,chemical deposition and in situ encapsulation,which has paid a lot of attention in recent years.Among of these,impregnation and ion exchange methods are commonly used in industry due to their simplicity and high availability of active components.In the preparation of zeolite-supported noble metal bifunctional catalysts by ion exchange and impregnation,H⁺or NH₄⁺zeolites are usually used as support and metal salts are introduced,followed by calcination and reduction to obtain bifunctional catalysts with both metal and acid functions.However,differences in zeolite coordination cations can lead to different interactions between the support and the metal precursors,not only affect the dispersion of the loaded metal on the support,but also have an effect on the acidic properties of the support,and lead to the preparation of zeolite-supported noble metal catalysts show different catalytic performance.The performance of zeolite coordination cations in the preparation of zeolite-supported noble metal catalysts has not been studied in more detail.Therefore,this work investigates the effects of zeolite coordination cations（H⁺and NH₄⁺）on the metal dispersion,acidity and catalytic hydrogenation performance of noble metal-loaded catalysts prepared by ion exchange and impregnation methods,with a view to providing a practical basis for optimising the preparation conditions of zeolite-supported noble metal catalysts through the above findings..The main studies are as follows:（1）The Pd/H-ZSM-5 catalysts were prepared by ion exchange method with industrial hierarchical NH₄-ZSM-5（Alpha）and H-ZSM-5（NH₄-ZSM-5 calcined at 550°C for 6 h in air atmosphere）zeolite as the supports,and Pd（NO₃）as the metal precursor.The physicochemical properties and catalytic performance of the prepared catalysts were characterized by X-ray diffraction,SEM,N₂ adsorption-desorption,NH₃-TPD,and applied to the naphthalene hydrogenation reaction.The results show that the Pd/H-ZSM-5-（NH₄）-IX catalyst has a higher metal dispersion and more acid sites compared to the Pd/H-ZSM-5-（H）-IX catalyst,the prepared Pd/H-ZSM-5-（NH₄）-IX catalyst has better catalytic performance than Pd/H-ZSM-5-（H）-IX in naphthalene hydrogenation reaction.（2）A series of Pd/H-ZSM-5 catalysts were prepared by impregnation method with industrial hierarchical zeolites NH₄-ZSM-5 and H-ZSM-5 as the support,H₂Pd Cl₄ as the metal precursor,and the catalytic performance of Pd/H-ZSM-5 in naphthalene hydrogenation reaction was investigated.The results showed that the coordination cations over zeolites greatly influence the dispersion of the supported metal species,catalyst acidity and the catalytic performance of the catalysts in hydrogenation reaction.The NH₄⁺over ZSM-5 support is conducive to the dispersion of the supported Pd species,and the prepared Pd/H-ZSM-5（NH₄）has more acid sites than Pd/H-ZSM-5（H）.In naphthalene hydrogenation reaction,the catalytic performance of Pd/H-ZSM-5 catalysts depend on the integrated effect of the Pd dispersion and the acidity.Among the Pd/H-ZSM-5（NH₄）and Pd/H-ZSM-5（H）catalysts,Pd/H-ZSM-5（NH₄）catalysts with a higher metal dispersion and more acid sites exhibited higher hydrogenation activity,where the presence of metal Pd species was important for the hydrogenation function and the acidic energy had a much greater effect on the hydrogenation performance than the metal dispersion,with the acid sites of the support The acid sites,especially the strong acid sites,are the main active centres for overflow hydrogenation,and overflow hydrogenation is the main part of the catalyst hydrogenation function.（3）The catalytic performance of the Pd/H-ZSM-5 catalysts prepared by impregnation method was investigated in toluene hydrogenation and anisole hydrodeoxygenation reactions.The Pd/H-ZSM-5（NH₄）catalysts with higher metal dispersion and more acid sites still showed excellent catalytic activity in the toluene hydrogenation reaction,while the catalytic activities of the Pd/H-ZSM-5（NH₄）and Pd/H-ZSM-5（H）catalysts were 18.4%and 14.3%,respectively,in the anisole hydrodeoxygenation reaction.The Pd/H-ZSM-5（NH₄）catalyst was more selective for the reaction products（benzene,toluene and xylene）than the Pd/H-ZSM-5（H）catalyst.