Preparation And Application Of Coated Palladium-based And Nickel-based Catalysts Based On Selective ALD

The design and fabrication of catalysts with atomic level control over active sites and composite structures is of great importance for advanced catalysis.This paper focuses on the design and modification of composite catalysts by area selective atomic layer deposition（ALD）method.By optimizing the area selective ALD processes,the MnO_x/Pd/Al₂O₃and FeO_x/Ni/Al₂O₃composite catalytic structures with discontinuous coating are developed based on the difference of facet selectivity and binding energy.The two designed catalysts are applied to the areas of the selective oxidation of benzyl alcohol and the dry reforming of methane.In addition,the catalytic performance of the two catalysts,including activity,selectivity and stability,are also characterized.Finally,the summary and outlook of area selective ALD for catalysts design and application are given.Based on that,and the details in our work are listed as below:（1）Two kinds of composite catalysts with discontinuous coating,denoted as MnO_x/Pd/Al₂O₃ and FeO_x/Ni/Al₂O₃,are designed and synthesized via area selective ALD method.The selective deposition process of metal oxides on metal-based nanoparticles is explored,and the selective growth behavior of MnO_x and FeO_x on the surface of metal-based catalysts during the ALD process is studied.（2）The MnO_x/Pd/Al₂O₃ catalysts fabricated by ALD show enhanced conversion and selectivity simultaneously,thus a high yield of benzaldehyde is obtained.The Pd（111）facets are selectively passivated by MnO_x deposition,which completely suppresses the formation of byproduct toluene.At the same time,the proposed structure is also beneficial for inhibiting the decarbonylation reaction of benzaldehyde.On the other hand,the introduction of MnO_x via ALD realizes modulating the electronic structure of Pd,and large amount of highly active Pd-MnO_x interface perimeters are formed,resulting in boosting the catalytic activity and reaction rate.The TOF of MnO_x-decorated Pd catalyst reaches 31561 h^-1, which is 8.7 times larger than that of the unmodified Pd catalyst.Meanwhile,the maximum conversion of benzyl alcohol and the yield of benzaldehyde are improved to 84.72%and 76.54%,respectively.（3）The FeO_x-Ni composite nano-catalytic structure with discontinuous coating is fabricated by atomic layer deposition（ALD）,which can improve the catalytic activity and eliminate carbon deposition in the DRM reaction effectively.The optimal catalytic performance can be achieved by tuning the density of the FeO_x coating on the Ni nanoparticles precisely.At 650℃,the conversion of CH₄ increases from 52.21%to 64.27%.On the one hand,the discontinuous coating structure separates the Ni surface to prevent the formation of continuous carbon nanotube networks.On the other hand,FeO_x provides active sites for methane decomposition,and the interaction between FeO_x-Ni helps to stabilize the metal phase of Ni in the DRM reaction,which is conducive to the improvement of catalyst activity.More importantly,the addition of FeO_x enhances the adsorption and activation of CO₂,which is beneficial for the reduced formation of the carbon intermediates.As for the FeO_x/Ni/Al₂O₃ catalysts with Fe content of 0.1wt%,the conversion of CH₄ reduces only 7%after 72 hours aging at 650℃,which implies the excellent durability.