the spatial confinement due to their tunable pore dimensions, well-defined metal nodes, tunable chemical composition and surface functionality. [14,15,16] Nevertheless, it has also confirmed challenging that the active metal is in the state of oxidation due to the coordination with supports although it is geometrically homogeneously isolated, but cause the loss of the metal properties, resulting in the decreased activity relative to the metal nanoparticles in some certain reactions. [17,18] Recently, exploring the dynamic change of the local coordination and electronic states over active sites under reactive environments has long been of interest, [19,20,21] with our recent experimental work discovering the restructuring of noble metal species under reaction conditions to control the reactivity of heterogeneous catalysts, but merely regulate and control the localized electronic states while maintaining the metal atoms in the form of single atoms is still difficult.Selective hydrogenation of acetylene is one of the important reactions in chemical process to remove a small amount of acetylene, which could poison the downstream polymerization catalysts. For many decades, this has been achieved over palladium containing catalysts, since Pd is highly active. However, the challenge here lies in controlling selectivity and stability at high conversion since the ethylene is prone to further hydrogenation to form the ethane or polymerization to generate green oil. A significant amount of research has focused on the development of alternative catalysts including the change of particle sizes, alloy with a second metals, surface or subsurface modifications and oxide catalysts. Also, the restructuring of the active metal species can be found in the reaction process. However, less has been exploited this aspect to positively affect catalyst behavior.Herein, in this study, Zr-based MOFs (UIO-66-NH 2 ) was employed as the support to fabricate the single Pd atom catalysts via the uniform spatial confinement at a well-defined location, which are further activated in reactive C 2 H 2 /C 2 H 4 / H 2 mixtures with different ratio at a programmed temperature. How the charge state and coordination structure of isolated Pd species can be transformed under the environmental conditions of acetylene hydrogenation and the principal reason were first explored by in situ XRD and XAFS. Next, the as-activated Pd single atom catalysts were employed in the selective hydrogenation of acetylene to investigate the influence of the change of active metal species on the catalytic reactivity, taking Pd nanoparticles and the nontreated Pd single atoms as contrast. More importantly, the catalytic mechanism of the as-activated Aiming at regulating and controlling the localized electronic states while maintaining the metal atoms in the isolation form, an in situ adsorbate induced strategy is proposed at a programmed temperature to activate Zrbased metal-organic framework (MOF) supported single Pd atom catalyst. It is discovered that in situ treatment envir...
Bin Liu 2 ( ), and Xiaoming Sun 1 ( ) Porous monolithic catalysts with high specific surface areas, which can not only facilitate heat/mass transfer, but also help to expose active sites, are highly desired in strongly exothermic or endothermic gas-solid phase reactions. In this work, hierarchical spinel monolithic catalysts with a porous woodpile architecture were fabricated via extrusion-based three-dimensional (3D) printing (direct ink writing, DIW in brief) of aluminate-intercalated layered double hydroxide (AI-LDH) followed by low temperature calcination. The intercalation of aluminate in LDH is found crucial to tailor the M 2+ /Al 3+ ratio, integrate LDH nanosheets into monolithic catalyst, and enable the conversion of LDH to spinel at the temperature as low as 500 °C with high specific surface areas (> 350 m 2 /g). The rapid mass/heat transfer resulted from the versatile 3D network at macroscale and the highly dispersed and fully exposed active sites benefited from the porous structure at microscale endow the 3D-printed Pd loaded spinel MgAlmixed metal oxide (3D-AI-Pd/MMO) catalyst with excellent catalytic performance in semi-hydrogenation of acetylene, achieving 100% conversion at 60 °C with more than 84% ethylene selectivity.
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