This work describes the transformation of Pd species under reaction condition to control the reactivity of heterogeneous catalysts, in which the real active sites for hydrogenation differ from simple Pd sites on a carbon nanofiber. Specifically, in the presence of C2H2/C2H4/H2 reaction mixtures, a permeable amorphous hydrocarbon overlayer is formed with simultaneous insertion of carbon atoms into Pd lattice that drives the formation of low coordinated Pd-carbide, thus providing more reactive Pd-Csub@Clayer sites (Csub: subsurface carbon; Clayer: carbon layer on the surface). The combination of these surface and subsurface effects hinders Pd-hydride, weakens ethylene adsorption confirmed by density functional theory (DFT) calculation, and thus improve catalytic behaviour for selective hydrogenation of acetylene (93% ethylene selectivity @ 100% conversion) with long-term stability. In the absence of hydrogen, a denser more crystalline overlayer is formed with severely restricted permeability, resulting in significantly lower activity. Moreover, by X-ray absorption 2 spectroscopy (XAS) and in-situ X-ray diffraction (XRD), it is demonstrated that different active sites dominate this catalytic reaction depending on choice of adsorbate and exposure temperature. This work represents an alternative and arguably simpler manner to design more reactive catalytic sites with the characteristics of long-term stability and facile preparation which would enable promising industrial application.

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...

Non-noble metal-based catalysts are gradually employed for the conversion of the unsaturated carbon−carbon bond, which exhibits improved selectivity but at the expense of catalytic activity. Herein, in this work, an Fe y MgO x -modified Cu interfacial structure with different Cu/Fe ratios was constructed by a structural topotactic transformation of layered double hydroxides, in which Cu-Fe 0.16 MgO x displayed an enhanced catalytic behavior (95% of selectivity at 100% of conversion and turnover frequency (TOF) of 0.048 s −1 ) in selective hydrogenation of acetylene. By virtue of X-ray absorption spectroscopy, reaction kinetic models, and the calculation based on density functional theory on analyzing the Cu-Fe y MgO x interfacial structure, we demonstrated the formation of the low coordinated Cu δ− -Fe 0.16 δ+ MgO x interfacial sites and further unraveled their dual functions. Specifically, the interfacial Cu δ− sites played a role in the activation of acetylene and hydrogen, while the formed intermediate bounded with the interfacial Cu atom and the interfacial Fe atom, respectively, which was favorable for the desorption to produce ethylene instead of over hydrogenation. This study offers a basic understanding on bifunctional interfacial catalysis for the conversion of the unsaturated carbon−carbon bond, which is of constructive significance for the rational design and preparation of supported non-noble metal materials with high efficiency.