Pyridinic Nitrogen Sites Dominated Coordinative Engineering of Subnanometric Pd Clusters for Efficient Alkynes’ Semihydrogenation

Abstract

Among them, one of the most important but challenging reactions is the alkynes' semihydrogenation to corresponding alkenes because of their poor alkene selectivity due to excessive hydrogenation and desorption barriers of alkenes, especially when the conversion is high. [7][8][9][10] The current problem-solving technique mainly relies on the development of diverse supported metal catalysts, [11][12][13][14] while the precondition is to exploit available support material that can stabilize and promote the active metal sites to own outstanding catalytic activity and selectivity for the semihydrogenation of alkynes.In this respect, nitrogen-doped carbons, as a type of promising support materials, have attracted tremendous attention due to their unique electron effects, tailorable surface characteristics, and excellent chemical and thermal stability. [15][16][17][18][19][20][21][22] In the regime of strong metal-support interactions, there are electron interactions in the form of charge redistribution and structural interactions in the form of mass redistribution between nitrogen-doped carbon and the anchored active metals. [23][24][25] Consequently, accurately adjusting the composition and spatial structure of nitrogen-doped carbon is a key point. High nitrogen contents can effectively limit the size of the metal, and more importantly, abundant coordination sites formed with metal can greatly lower the reaction energy barrier, resulting in high catalytic activity. And the electron effect generated by the nitrogen species in the supports can alter the electron density of the active metal sites, [26][27][28] which favors desorption of the monoene to obtain high catalytic selectivity. Following these principles, plentiful nitrogen-doped carbon-supported metals have been proven to be appealing catalysts. However, due to the proximity of nitrogen dopants' generation energy, the incorporation of nitrogen atoms into the carbon skeleton leads to the simultaneous doping of various nitrogen configurations including pyridinic N, pyrrolic N, graphitic N, and oxidized N. [29][30][31] Under this circumstance, most of the previous works simply manifest that active metal centers (M) are coordinated with nitrogen atoms (N) embedded in the matrix of carbon to form M-N x as active sites, [32][33][34] but it is still controversial for researchers to sufficiently understand which nitrogen configuration can dominant strong metal-support interactions to Supported metal catalysts have played an important role in optimizing selective semihydrogenation of alkynes for fine chemicals. There into, nitrogendoped carbons, as a type of promising support materials, have attracted extensive attentions. However, due to the general phenomenon of random doping for nitrogen species in the support, it is still atremendous challenge to finely identify which nitrogen configuration dominates the catalytic property of alkynes' semihydrogenation. Herein, it is reported that uniform mesoporous N-doped carbon spheres derived from mesoporous polypyrrole spheres ...

Rational Fabrication of Well-Defined Mesoporous Carbon-Supported TiO2 Nanostructures for Anode Material of Lithium-Ion Batteries

“…Moreover, the doped nitrogen is easily tunable by varying the used carbonization temperatures. The XPS analysis (Figure d, S27 and Table S5) indicates that with the increase of temperature from 600 to 800 °C, the nitrogen content varies from 5.2 to 4.8 atom %; meanwhile, the graphitic N gradually dominates with the consumption of the less stable pyrrolic N and pyridinic N …”

“…Moreover, the doped nitrogen is easily tunable by varying the used carbonization temperatures. The XPS analysis (Figure 6d, S27 and Table S5) indicates that with the increase of temperature from 600 to 800 °C, the nitrogen content varies from 5.2 to 4.8 atom %; meanwhile, the graphitic N gradually dominates with the consumption of the less stable pyrrolic N and pyridinic N. 45 Besides direct carbonization, the polymerization of pyrrole moieties followed by carbonization is another way for deposition of carbon coating to create the desired carbon/ TiO 2 heterostructures. This preparation procedure provides a unique possibility for the flexible incorporation of functional moieties into the formed carbon coating by using different oxidative agents for pyrrole chemical transformation.…”

Metal and Metal Oxide Supported on Ordered Mesoporous Carbon as Heterogeneous Catalysts

“…Doping p -block atoms in carbon materials can change their work function, , but the degree of the electron transfer at the interface is still low. And it remains elusive how heteroatom-doped carbon tailors the charge state of metals and thereby affects the catalytic performance. , …”

“…And it remains elusive how heteroatom-doped carbon tailors the charge state of metals and thereby affects the catalytic performance. 175,199 3.2.1.6. Reactivity Descriptor.…”

Metal-Free Light-Driven 1,4-NADH Regeneration System from Nitrogen and Sulfur Codoped Carbon Dots

“…18−20 As was reported, the N element in N-doped carbon materials usually serves as the active site, whereas the product selectivity is closely related to the N species. 21,22 Particularly, pyrrolic N is, in theory, capable of catalyzing proton-coupled-electron transfer reactions, a major process in NAD(P)H regener- ation. 23−26 However, pyrrolic N usually occupies a small proportion of N-doped carbon materials.…”