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We found that molybdenum carbide (Mo2C) can be applied as a novel and efficient heterogeneous catalyst for hydrogen transfer of anilines and alcohols to synthesize N-alkylamines. The results of experiments and DFT calculations demonstrate that Mo2C surface can reduce the energy barrier of the key step of alcohol dehydrogenation and generate a hydrogen spillover effect, thereby exhibiting outstanding catalytic performance. [ABSTRACT FROM AUTHOR]

In this work, we reported a facile one-pot strategy to construct conjugated vinylene-extended viologen-based ionic radical polyacetylenes (denoted as VIRPs) for visible light-promoted photocatalytic carbon dioxide (CO2) cycloaddition under ambient conditions. As expected, the ionic polymer VIRP-1 was directly prepared in situ by the quaternization-induced spontaneous polymerization (QISP) reaction between 1,2-bis(4-pyridyl)ethylene (BPE) and propargyl bromide (PGB) in CH3CN at 100 °C for 24 h without any catalysts and initiators. To our delight, the radical character of the ionic radical polymer VIRP-2 could be significantly enhanced by using K2CO3 as an alkaline reductant in the QISP reaction process, similar to the synthesis of VIRP-1, which was confirmed by electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the use of K2CO3 not only achieved the in situ one-electron reduction of vinylene-extended viologen cations to stable viologen cationic radicals, but also could remove a large proportion of Br− anions and afford non-halogen anions CO32− within VIRP-2 by anion exchange during the synthetic process. Both ionic radical polyacetylenes VIRP-1 and VIRP-2 exhibit strong and broad visible light-harvesting ability; however, VIRP-2 with much stronger radical intensity possesses better photoinduced charge separation and migration ability. Therefore, the ionic radical polymer VIRP-2 was regarded as a highly efficient and green metal-free heterogeneous photocatalyst in the visible-light-promoted catalytic CO2 conversion with various epoxides into cyclic carbonates at room temperature and atmospheric pressure without using any cocatalysts and solvents. This work affords a new direction to construct task-specific ionic radical polymers towards photocatalytic CO2 cycloaddition under ambient conditions. [ABSTRACT FROM AUTHOR]

In this work, we reported a facile one‐pot route to construct polyhedral oligomeric silsesquioxane (POSS) and phosphonium‐based ionic porous hypercrosslinked polymers (denoted as P‐iPHCPs) with multiple catalytic active sites, which could be regarded as efficient heterogeneous catalysts for the conversion of carbon dioxide (CO2) to highly value‐added cyclic carbonates. The targeted polymers P‐iPHCPs were prepared from a rigid building block octavinylsilsesquioxane (VPOSS) and a low‐cost commercially available organic ionic salt methyltriphenylphosphonium bromide ([Ph3PMe]Br) by the AlCl3‐catalyzed Friedel‐Crafts reaction. The series of polymers P‐iPHCPs that synthesized by different molar ratios of VPOSS to [Ph3PMe]Br possess hierarchical micro/mesoporous structures with high surface areas ranging from 376 to 429 m2 g−1 and behave the flower‐like nano‐morphology. Especially, the desired multiple active sites involved the mixed anions including free Cl−, Br− anions and the in‐situ formed metal‐halogen complex anion [AlCl3Br]− within phosphonium segments, and the enriched POSS‐derived SiOH hydrogen bond donor (HBD) groups that derived from the breakage of POSS cages during the synthetic process. The typical polymer P‐iPHCP‐14 has the aforementioned nucleophilic‐electrophilic multiple catalytic active sites, which was regarded as an efficient recyclable heterogeneous catalyst for synergistic catalytic conversion of CO2 with various epoxides into cyclic carbonates under mild conditions. [ABSTRACT FROM AUTHOR]

The simultaneous achievement of large surface areas and high IL contents in porous materials are highly beneficial for efficient carbon dioxide (CO2) capture and atmospheric fixation. Herein, a series of porous hypercrosslinked poly(ionic liquid)s (HPILs) are successfully developed through a two-step synthetic strategy, including free radical self-polymerization of a specific benzyl bromide-tethered imidazole ionic liquid (IL) to fabricate a linear PIL as a precursor, and a subsequent Friedel–Crafts alkylation between the precursor and the crosslinker for hypercrosslinking. The HPILs featured large surface areas of up to 855 m2 g−1 along with a hierarchically nanoporous structure, high IL contents (2.19–2.91 mmol g−1) and satisfactory CO2-philic properties. By virtue of the combined advantages, HPILs served as metal-free heterogeneous catalysts for solvent-additive-free CO2 cycloaddition with epichlorohydrin at 80 °C and 0.1 MPa CO2 for 24 h, presenting high catalytic activity and stable reusability. A high yield of 99.0% coupled with a turnover frequency (TOF) of 6.0 h−1 was achieved, much higher than most of the reported metal-free heterogeneous catalysts, even superior to homogeneous analogues. Furthermore, various epoxides, including large-sized epoxides, were effectively converted into carbonates with high yields, affording good substrate applicability. This work reports a facile and universal approach for the construction of porous HPILs with both great porosities and high IL contents towards efficient chemical fixation of CO2 under mild conditions. [ABSTRACT FROM AUTHOR]

In this work, we reported a facile catalyst-free and initiator-free strategy to fabricate a new class of viologen-linked ionic polyacetylenes (denoted as VIPAs) that can achieve simultaneous ionization and polymerization in one-pot and one-step. To our surprise, the ionic polymers VIPA-X (X = Br or Cl) were directly synthesized by quaternization-induced in situ polymerization from commercially available 4,4′-bipyridine with propargyl bromide or propargyl chloride. It was found that reaction temperatures have a remarkable influence on the synthesis of VIPAs, achieving the transformation from soluble oligomers to insoluble highly cross-linked polymers by adjusting the temperatures from 30 °C to 100 °C. At a higher temperature of 100 °C, the obtained highly cross-linked ionic polymers VIPA-Br and VIPA-Cl were insoluble in both hot water and even dimethyl sulfoxide (DMSO). By virtue of abundant halogen anions and the absorbed H-bonded water, both VIPA-Br and VIPA-Cl were employed as efficient heterogeneous catalysts for the conversion of CO2 with various epoxides into cyclic carbonates at atmospheric pressure and low temperatures. In particular, the catalytic activities of VIPA-Br for the conversion of various epoxides are much better than those of VIPA-Cl at low temperatures, which should be attributed to the higher nucleophilicity and better leaving ability of the Br− anion than those of the Cl− anion. The present work affords a succinct catalyst-free strategy to construct more task-specific ionic polyacetylenes by quaternization-induced polymerization of multi-N-heterocycle monomers and propargyl halides towards diverse applications. [ABSTRACT FROM AUTHOR]

Pyridinium-based ionic porous organic polymers (Py-iPOPs) were constructed from newly designed acetonitrile-functionalized ionic liquids and multi-carbaldehyde monomers by base-catalyzed Knoevenagel condensation. The obtained Py-iPOPs having in situ formed hydroxide anions and pyridinyl radicals were regarded as efficient metal-free and halogen-free heterogeneous catalysts for atmospheric CO2 fixation under mild conditions. [ABSTRACT FROM AUTHOR]

In this work, we reported a facile one-pot approach to construct polyhedral oligomeric silsesquioxane (POSS) and imidazolium-based ionic porous hypercrosslinked polymers (denoted as iPHCPs) with multiple active sites towards efficient catalytic conversion of carbon dioxide (CO2) to high value-added cyclic carbonates. The targeted iPHCPs were synthesized from a rigid molecular building block octavinylsilsesquioxane (VPOSS) and a newly-designed phenyl-based imidazolium ionic crosslinker through the AlCl3-catalyzed Friedel–Crafts reaction. The desired multiple active sites come from the mixed anions including free Cl− and Br− anions, and in situ formed Lewis acidic metal–halogen complex anions [AlCl3Br]− within imidazolium moieties and POSS-derived Si–OH groups during the synthetic process. The typical polymer iPHCP-12 possesses a hierarchical micro-/mesoporous structure with a high surface area up to 537 m2 g−1 and shows a fluffy nano-morphology. By virtue of the co-existence of free nucleophilic Cl− and Br− anions, the metal complex anion [AlCl3Br]− with both electrophilic and nucleophilic characters and electrophilic hydrogen bond donor (HBD) Si–OH groups, iPHCP-12 is regarded as an efficient recyclable heterogeneous catalyst for synergistic catalytic conversion of CO2 with various epoxides into cyclic carbonates under mild conditions. The present work provides a succinct one-pot strategy to construct task-specific ionic porous hypercrosslinked polymers from easily available modules for the targeted catalytic applications. [ABSTRACT FROM AUTHOR]

Transition metals have been considered as potential catalysts for ammonia decomposition to produce COx-free hydrogen for fuel cells. However, the facile synthesis of transition metal catalysts with small size active species, high porosity and good structural stability is still a challenge in catalytic NH3 decomposition. Herein, mesoporous Co/Al2O3 catalysts with various cobalt contents were synthesized by a facile modified sol–gel method. The catalyst 15CoAl with 15 at% cobalt content realizes the optimal catalytic NH3 decomposition performance. 92% NH3 conversion at 600 °C is achieved with a gaseous hourly space velocity (GHSV) of 24 000 cm3 gcat−1 h−1 and a hydrogen formation rate of 33.9 mmol gcat−1 min−1 at 600 °C is maintained after a 120 h long-duration stability test. Uniform small cobalt particles with high dispersion are well embedded into the skeleton of the mesoporous Al2O3 matrix. The aggregation of active cobalt species during the high temperature reaction can be effectively prevented by the mesoporous Al2O3 matrix due to the strong interaction between them, thus ensuring a good catalytic performance for ammonia decomposition. [ABSTRACT FROM AUTHOR]

Herein, we construct a new series of N-heterocyclic ligand bipyridine-based porous hybrid polymers (denoted Bpy-PHPs) from the Heck reaction of a rigid building unit octavinylsilsesquioxane (VPOSS) and 5,5′-dibromo-2,2′-bipyridine. Surprisingly, the typical sample Bpy-PHP-4 was found to be a metal-/halogen-free heterogeneous catalyst in the cycloaddition reaction of CO2 with a few epoxides under atmospheric pressure. After coordination with ZnBr2, the resultant ZnBr2@Bpy-PHP-4 afforded largely enhanced heterogeneous catalytic activities upon the conversion of carbon dioxide (CO2) and various epoxides into cyclic carbonates without using any co-catalysts under mild conditions. The moderate catalytic activities of Bpy-PHP-4 may be due to the presence of hydrogen bond donors (HBDs), i.e., polyhedral oligomeric silsesquioxane (POSS)-derived Si–OH groups and N active sites from Bpy linkers. In comparison, the high catalytic efficiency of ZnBr2@Bpy-PHP-4 should be attributed to the synergistic catalysis of Si–OH groups, N active atoms, and Bpy-coordinated ZnBr2. Moreover, the catalyst ZnBr2@Bpy-PHP-4 can be easily recovered and reused ten times without any significant loss of catalytic activities. This work affords an efficient metal-based porous hybrid polymer heterogeneous catalyst for the cycloaddition reaction of CO2 and epoxides under mild and co-catalyst-free conditions. [ABSTRACT FROM AUTHOR]