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The encapsulation of metal nanoparticles (NPs)‐based active sites and homogeneous catalysts in nanoporous materials has been of highly research focus for tuning their catalytic activity, selectivity and stability. Although the catalysts with strong metal‐support interaction (SMSI) hold the reversible encapsulation feature in a certain atmosphere, there is still a lack of systematic research on them in a real confined environment. Herein, we present a highly selective and stable Pt/TiO2@S‐1 catalyst, which is prepared by in‐situ growth of classical silicalite‐1 on the external surface of Pt/TiO2‐450H pre‐catalyst with SMSI effect. Encouragingly, the encapsulated 20Pt/TiO2@S‐1 catalyst demonstrates unprecedented catalytic performance for various nitroaromatics and without any degradation in selectivity after 7 cycles (>99%) for the hydrogenation of 1‐chloro‐4‐nitrobenzene. Such situation is attributed to the high surface area, SMSI effect in confined space as well as the pore structure of silicalite‐1 with selective adsorption of substrates. [ABSTRACT FROM AUTHOR]

N‐doped carbon nanotubes (NCNTs) based composites have shown great prospect in catalysis relevant communities, which are often evolved from commercial CNTs and nitrogenous hybrid precursors. However, the direct fabrication of high‐performance and non‐noble metal uniformly embedded NCNTs from a single molecule level without foreign ions remains a thorny issue. Herein, we firstly report a high surface area and large diameter NCNTs (215.7 m2 g−1, 150 nm) embedded with Co NPs and atomically dispersed CoNx active sites via a facile and self‐template pyrolysis of a novel synthesized cobalt dicyanamide molecule. The resulting Co@NCNTs‐800 catalyst exhibits superior catalytic activity toward nitrobenzene hydrogenation compared to the catalyst prepared from a mixture of dicyandiamide and CoCl2 under mild conditions (>99 % vs. 1.3 % conversion). Furthermore, it also presents a prominent activity and selectivity for the hydrogenation of various nitroaromatics, and possesses the best catalytic performance compared to the existing non‐noble metal‐based heterogeneous catalytic systems. [ABSTRACT FROM AUTHOR]

Metal-free carbon catalysts with excellent catalytic performance have drawn much research attention recently. Herein, polymer-derived N,S co-doped carbon catalysts (PDNSC-X) with a hierarchically porous structure were facilely prepared by a cost-effective and convenient strategy via carbonization of a N- and S atom-containing polymer precursor and were subsequently used as efficient metal-free catalysts. The catalytic activity of the as-fabricated PDNSC-800 was greater than those of other reported heteroatom-doped carbon catalysts in catalytic reduction of various nitroarenes. The high catalytic activity of PDNSC-800 was related to the synergistic effects of a high surface area, a hierarchically porous structure, abundant N- and S-containing active sites, and defect formation. In addition, the close relationship between the N species (especially pyrrolic N) and high selectivity in metal-free catalytic synthesis was investigated in the reduction of nitroarenes and selective oxidation of ethylbenzene. This study may provide a new strategy to fabricate specific heteroatom-doped metal-free carbon catalysts for environmentally friendly efficient organic transformation. [ABSTRACT FROM AUTHOR]

Porous nanoreactors demonstrate immense potential for applications in heterogeneous catalysis due to their excellent mass‐transfer performance and stability. The design of a simple, universal strategy for fabricating nanoreactor catalysts is of significance for organic transformation. In this study, a nanoreactor with a hierarchical mesoporous yolk‐shell structure was successfully prepared by the high‐temperature carbonization of a ZIF‐67@polymer composite. The core of the resultant Co@ZDC@mC material comprised Co NPs anchored in the ZIF‐67‐derived carbon framework, while the shell comprised resin‐polymer‐derived mesoporous carbon. The as‐obtained Co@ZDC@mC‐700 catalyst enriched reactants, efficiently catalyzed the reaction in the core, and permitted the desorption of the product from the nanoreactor. In the catalytic reduction of nitrobenzene with N2H4⋅H2O, Co@ZDC@mC‐700 exhibited superior catalytic efficiency (TOF=1136.3 h−1). In addition, Co@ZDC@mC‐700 exhibited excellent performance for the catalytic reduction of various functionalized nitroarenes, as well as good reusability and recyclability. Hence, a simple, useful approach for fabricating a metal‐organic‐framework‐derived non‐noble metal‐based yolk‐shell nanoreactor for effective catalytic transformation is proposed. [ABSTRACT FROM AUTHOR]

Fabrication of non‐noble metal‐based heterogeneous catalysts by a facile and cost‐effective strategy for ecofriendly catalytic transfer hydrogenation (CTH) is of great significance for organic transformations. A cobalt@nitrogen‐doped carbon (Co@NC) catalyst was prepared from renewable biomass‐derived sucrose, harmless melamine, and earth‐abundant Co(AcO)2 as the precursor materials by hydrothermal treatment and carbonization. Co nanoparticles (NPs) were coated with NC shells and uniformly embedded in the NC framework. The as‐obtained Co@NC‐600 (carbonized at 600 °C) catalyst exhibited excellent catalytic efficiency for CTH of various functionalized nitroarenes with formic acid (FA) as hydrogen donor in aqueous solution. The uniformly incorporated N atoms in the C matrix and the encapsulated Co NPs showed synergistic effects in the CTH reactions. A mechanistic analysis indicated that the protons from FA were activated by Co sites after being captured by N atoms, and then reacted with nitroarenes adsorbed on the surface of the catalysts to generate the corresponding aromatic amines. Moreover, the catalyst showed excellent durability and reusability without obvious decrease in activity even after five reaction cycles. Thus, the study reported herein provides a cost‐effective, sustainable strategy for fabrication of biomass‐derived non‐noble metal‐based catalysts for green and efficient catalytic transformations. Give it some sugar: A cobalt nanoparticles@nitrogen‐doped carbon (Co@NC) catalyst is prepared from biomass‐derived sucrose, ecofriendly melamine, and earth‐abundant Co(AcO)2. The Co@NC catalyst exhibits excellent catalytic efficiency for catalytic transfer hydrogenation (CTH) of various functionalized nitroarenes with formic acid as hydrogen donor in aqueous solution [ABSTRACT FROM AUTHOR]

Fabrication of heterogeneous catalysts with excellent activity, selectivity and stability is significant for various catalytic applications. Here, we prepared a hypercrosslinked polymer (HCP) via a facile and cost‐effective strategy using ferrocenecarboxaldehyde and melamine as building blocks. Then, the HCP was modified with highly dispersed ultrafine Pd nanoparticles (Pd/HCP). The obtained Pd/HCP shows excellent catalytic activity in the catalytic reduction of nitroarenes under mild reaction conditions. It′s worth mentioning that the N atoms in the HCP can efficiently coordinate Pd ions to form small Pd nanoparticles (NPs) and subsequently prevent the aggregation and leaching of Pd NPs during the reaction, so the Pd/HCP catalyst is highly stable and can be reused at least eight cycles without loss of catalytic activity. Therefore, this work may provide possibilities for using HCPs as ideal supporting materials for fabricating highly stable and efficient heterogeneous catalysts. Aminal kingdom! A highly active Pd/HCP catalyst was prepared via a facile and low‐cost strategy. Ultrafine Pd NPs were stably anchored on the HCP surface with high dispersity. The Pd/HCP catalyst shows excellent catalytic performance for catalytic reduction of nitroarenes. [ABSTRACT FROM AUTHOR]

Palladium (Pd)-based catalysts with maximum utilization of the Pd atoms are attractive for hydrogenation reactions and conserving Pd resources. Herein, the highly dispersed Ni nanoparticle (NP)-modified mesoporous N-doped carbon (Ni/mCN) was successfully prepared by pyrolyzing a mixture of polyacrylonitrile, melamine and Ni(NO3)2·6H2O. Then, the resulting Ni/mCN material with highly dispersed metallic Ni NPs was treated with Pd(AcO)2, and Pd2+ was spontaneously reduced to metallic Pd by the Ni NPs, affording the PdNi NP-based catalyst (PdNi/mCN). The spontaneous reduction process deposits most of the Pd atoms on the surface of the Ni NPs, thus allowing for the maximum utilization of the noble metal Pd. The prepared mesoporous N-doped carbon support can not only provide more surface area to adsorb reaction substrates, but also enhances the accessibility of the active sites of PdNi NPs. The prepared PdNi/mCN nanocatalyst shows a very high catalytic activity for the transfer hydrogenation of nitroarenes using formic acid as the reductant under ambient conditions in aqueous solution, as compared to other Pd-based catalysts, probably because of the highly dispersed PdNi NPs and the maximum utilization of the Pd atoms, as well as the superior structure of mCN. Moreover, the PdNi/mCN nanocatalyst exhibits excellent recyclability and reusability, and the catalytic activity does not obviously decrease after ten reaction cycles. Therefore, we believe that this study should open a new frontier in the preparation of porous N-doped carbon-supported catalysts with maximum utilization of the noble metals for green and sustainable catalysis. [ABSTRACT FROM AUTHOR]

Novel γ-Fe2O3-nanoparticle (NP) modified N-doped porous carbon materials (γ-Fe2O3/mCN) were prepared by one-pot pyrolysis of a mixture of melamine, polyacrylonitrile, and FeCl3·6H2O at different temperatures. At a pyrolysis temperature of 900 °C, γ-Fe2O3/mCN-900-20 exhibited a high surface area and a N content of 8.47%, caused by the complete pyrolysis of melamine and polyacrylonitrile at 900 °C. The obtained material γ-Fe2O3/mCN-900-20 was used as a cost-effective catalyst for the hydrogenation of nitrobenzene using N2H4·H2O as the reductant under mild reaction conditions. As compared to other catalysts (e.g., noble metal catalysts), γ-Fe2O3/mCN-900-20 exhibited high catalytic performance (TOF of 311.83 h−1, selectivity of 100%). During the catalytic hydrogenation of nitroaromatic compounds with reducible groups, e.g., alcoholic hydroxyl, halogen, and amino groups, an excellent selectivity close to 100% was achieved. Moreover, because the active sites of γ-Fe2O3 has magnetic performance, the catalyst can be easily recovered using a magnet, and reused at least four runs without an obvious activity decrease. Hence, the easily prepared, cost-effective and reusable γ-Fe2O3/mCN catalyst fabricated in this study demonstrates potential for applications in selective reduction of aromatic nitro compounds. [ABSTRACT FROM AUTHOR]

Highlights: [•] The synthesized HMMS-NH2-Pd shows excellent catalytic activity in amination reaction with over 97% yield in 6h. [•] The catalyst can be recycled 6 times without loss activity. [•] The catalysts can be easily recovered by using an external magnet. [Copyright &y& Elsevier]

Abstract: A high-performance palladium-based catalyst has been prepared by the co-precipitation method. The catalyst was characterized by TEM, XRD, VSM and ICP. It was found that the catalyst showed a high activity for the one-pot direct reductive amination of aldehydes with nitroarenes in the presence of molecular hydrogen in ethanol, even at room temperature. Furthermore, the catalyst was easily recovered by applying an external magnet and reused for eight cycles without significant loss of activity. [Copyright &y& Elsevier]

In the present work, a facile and environment-friendly route is illustrated for the efficient fabrication of highly dispersed PdCo nanoparticles (NPs) by modified cotton-derived carbon fibers (PdCo/CCF). Firstly, commercial cotton was impregnated with CoCl 2 , followed by pyrolysis under high calcination temperature to obtain the Co NPs modified CCF sample (Co/CCF). Secondly, Co/CCF was treated with Pd(AcO) 2 aqueous solution, wherein, through a spontaneous replacement reaction process, Pd 2+ is reduced to metallic Pd and mostly covered on the surface of the Co NPs. Thus, the PdCo/CCF catalyst was obtained avoiding the use of toxic reductants like NaBH 4 , NH 2 NH 2 and HCHO. The PdCo/CCF catalyst exhibits excellent catalytic activity and recyclability for the reduction of 4-nitrophenol and other nitroarenes compared with Pd/CCF, PdCo NPs and many other noble metals based catalysts. The reasons could be attributed to the uniformly dispersed and accessible PdCo NPs on the surface of the CCF, and the Pd atoms deposited on the Co NPs surface that makes the Pd active sites available for optimum use. The PdCo/CCF catalyst also exhibits potential application for catalytic reduction of nitroarenes in a fixed bed reactor under mild reaction conditions. Furthermore, the PdCo/CCF catalyst can be magnetically recycled and reused for at least ten cycles without either losing catalytic activity or leaching of Pd active sites, thereby confirming its superior stability. [ABSTRACT FROM AUTHOR]

Ultrathin γ-Fe 2 O 3 nanosheets (γ-Fe 2 O 3 -UNSs) were successfully prepared through a simple strategy. The as-prepared γ-Fe 2 O 3 -UNSs were used for the chemoselective hydrogenation of nitroaromatic compounds to corresponding aniline compounds using N 2 H 4 ·H 2 O as a hydrogen donor. An excellent catalytic activity and 100% selectivity for the aniline products were obtained. Moreover, γ-Fe 2 O 3 -UNSs can be easily separated from the reaction solution by an external magnet due to its superparamagnetic property, and recycled at least six cycles without any obvious decrease in its catalytic activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfur-doped ordered mesoporous carbon (SMC) with ordered channels was prepared. • Ultrafine Pt clusters were firmly anchored on the SMC by the interactions with sulfur atoms. • The hydrogenation of p -CNB by electron-rich Pt clusters exhibited excellent selectivity. • Pt/SMC catalyst can be easily recovered and reused without loss of activity. Chemoselective hydrogenation of unsaturated organic compounds is a significant research topic in the catalysis field. Herein, a sulfur-doped ordered mesoporous carbon (SMC) material was prepared to anchor ultrafine platinum (Pt) clusters for the chemoselective hydrogenation of halogenated nitroarenes. The confinement effect of the ordered pores and the strong metal-support interaction caused by Pt clusters and sulfur atoms, efficiently suppress the aggregation and regulate the electronic states of the ultrafine Pt clusters. Thus, the hydrogenation of parachloronitrobenzene (p -CNB) shows high selectivity catalyzed by the ultrafine Pt clusters with electron-rich states. Meanwhile, the catalytic performance of the hydrogenation reaction catalyzed by Pt/SMC is capable of being maintained after at least 5 cycles, and the catalytic universality can also be applied to different halogenated nitroarenes hydrogenation. Therefore, this study may promote the research into the construction of noble metal-based catalysts for chemoselective hydrogenation reactions in green and sustainable chemical processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • γ-Fe 2 O 3 /NPC catalyst was derived from a ferrocene-functionalized POP material. • γ-Fe 2 O 3 /NPC shows excellent catalytic activity in the reduction of nitroarenes. • γ-Fe 2 O 3 /NPC catalyst could be easily recycled and reused. Fabrication of cost-effective non-noble metal-based catalysts is significant for heterogeneous catalysis. Here, we prepared a porous organic polymer (POP) through the facile condensation of p-phenylenediamine with ferrocene carboxaldehyde, and then the ferrocene-functionalized POP material was carbonized under inert atmosphere, obtaining the γ-Fe 2 O 3 nanoparticles (NPs) modified N-doped porous carbon catalyst (γ-Fe 2 O 3 /NPC). Various characterizations (such as XRD, BET, TEM and XPS etc.) indicated that the obtained γ-Fe 2 O 3 /NPC catalyst exhibits unique structural properties with uniformly dispersed γ-Fe 2 O 3 species, porous morphology, and N-doped defective amorphous carbon. The γ-Fe 2 O 3 /NPC catalyst shows excellent activity in the catalytic reduction of nitroarenes with hydrazine hydrate as reductant. The synergistic effect between γ-Fe 2 O 3 NPs and N-doped porous carbon improve the hydrazine hydrate adsorption and activation for active hydrogen atoms production, which is beneficial for nitroarenes reduction. Moreover, the γ-Fe 2 O 3 /NPC catalyst could be easily recycled by using a magnet and reused without obviously loss of catalytic activity. Therefore, this work should provide a useful platform for designing and fabricating stable non-noble metal NPs based catalysts derived from POP materials that have potential for various catalytic applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Cost-effective triazinyl-containing 2D COFs were prepared via a facile method. • 2D-COFs were self-templated carbonization to fabricate NC materials. • NC materials serve as metal-free catalysts for hydrogenation of nitroarenes. • Graphitic N and its related defects in NC material serve as the active site. • NC-700 displayed excellent recyclability and stability. Abstract Heteroatom-doped carbon materials with superior physico-chemical properties and high stability are potential candidates for environmentally friendly metal-free catalysis. In this study, mesoporous carbon materials with high N content and lattice defects were successfully fabricated via self-templated carbonization of a two-dimensional covalent organic framework (2D COF). The ordered structure and clear composition of intrinsic COF precursors aid the understanding of the specific role of dopants in the as-prepared N-doped mesoporous carbon materials. Based on the obtained experimental results and characterizations, graphitic N and its related defects were found to be closely associated with catalytic activity, indicating they are probably the main active sites. In addition, the obtained catalyst showed remarkable catalytic performance in both hydrogenation of nitroarenes and Knoevenagel condensation of aromatic aldehyde derivatives in aqueous solution. This study is expected to provide a new inspiration for the synthesis of heteroatom-doped carbon materials from cost-effective COFs via self-templated carbonization for eco-friendly metal-free catalysis. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Porous organic polymers (POPs) containing nitrogenous substituents have potential practical applications as heterogeneous catalysts based upon controlled porous structure and surface-anchored noble metal nanoparticles (NMNPs). In this work we prepared a POP material from piperazine and cyanuric chloride starting materials (PC-POP). The PC-POP material contains numerous triazinyl moieties, thus rendering the pores hydrophobic. Subsequently, by means of a novel reverse double-solvent approach (RDSA), microdroplets of Pd(AcO) 2 /CH 2 Cl 2 were introduced into the hydrophobic pores of PC-POP in an aqueous environment; Pd(II) was rapidly reduced by NaBH 4 to form ultra-fine Pd NPs and confined within the pores of PC-POP at high dispersity. The extensive porosity and dispersity of the Pd NPs made the active sites readily accessible, and led to efficient mass transfer. Thus, Pd@PC-POP exhibits superior catalytic performance in catalytic reduction of various nitroarenes. Furthermore, Pd@PC-POP has excellent recyclability, without significant loss of activity nor leaching of Pd active sites during 10 successive reaction cycles. This work points to a practical and cost-effective approach to preparation of POP materials, and also for confining ultra-fine NMNPs in POPs for use as catalysts. [ABSTRACT FROM AUTHOR]

Novel fluffy smoke like mesoporous N-doped carbon (mNC) was prepared through a facile one-pot carbonization method using the low-cost melamine and polyacrylonitrile as the precursor materials. The obtained mNC material exhibits a high surface area, rich nitrogen content and can be used as an ideal catalyst support to fabricate noble metal modified nanocatalysts. Here, small Ag nanoparticles were supported on the mNC material with high dispersion to give the Ag/mNC nanocatalyst. The obtained Ag/mNC nanocatalyst was used in the catalytic reduction of nitroarenes and showed excellent catalytic activity, probably due to the small Ag NPs which highly dispersed on the fluffy mNC material that can enhance the accessibility and mass transfer, and subsequently enhance the catalytic activity. It is worth mentioning that, in the catalytic reduction of nitroarenes with halogenated groups, almost no dehalogenation phenomenon can be observed, which implies the superior catalytic chemoselectivity of the Ag/mNC nanocatalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] In this paper, we successfully prepared magnetic SiO 2 @Fe 3 O 4 @m-MnO 2 microspheres with uniform morphology and mesoporous MnO 2 shell. The prepared material was used as a catalyst support for fabricating the Pd(6%)/SiO 2 @Fe 3 O 4 @m-MnO 2 nanocatalyst which exhibited excellent catalytic activity and easy recyclability in the environmental catalysis. • Uniform magnetic SiO 2 @Fe 3 O 4 @m-MnO 2 microspheres with mesoporous MnO 2 shell were prepared. • The Pd(6%)/SiO 2 @Fe 3 O 4 @m-MnO 2 nanocatalyst exhibited excellent catalytic activity. • The Pd(6%)/SiO 2 @Fe 3 O 4 @m-MnO 2 nanocatalyst also can be easily recovered and reused. In this study, magnetic SiO 2 @Fe 3 O 4 @m-MnO 2 microspheres with uniform morphology and mesoporous MnO 2 shell were successfully prepared. The MnO 2 sheets structured mesoporous shell could provide a large specific surface area, thereby increasing the catalytically active sites. Thus, magnetic SiO 2 @Fe 3 O 4 @m-MnO 2 microspheres were used as a catalyst support. Palladium nanoparticles (Pd NPs) were successfully anchored with high dispersion on SiO 2 @Fe 3 O 4 @m-MnO 2 surface, successfully obtained Pd(6%)/SiO 2 @Fe 3 O 4 @m-MnO 2 nanocatalyst with a Pd weight percentage of 6%. The obtained nanocatalyst was employed in the hydrodechlorination of highly toxic 2,4-dichlorophenol and catalytic reduction of the widely used nitroaromatics and organic dyes under ambient conditions. In these catalytic reactions, the Pd(6%)/SiO 2 @Fe 3 O 4 @m-MnO 2 nanocatalyst with large and accessible pore surface area exhibited excellent catalytic activity as compared to other noble metal supported catalysts. The Pd(6%)/SiO 2 @Fe 3 O 4 @m-MnO 2 nanocatalyst could also be easily and conveniently recovered from the reaction mixture by using an external magnet, attributed to its magnetism, thus preventing the catalyst loss. Moreover, it could also be reused for at least six times without significant decrease in the catalytic activity, indicating its excellent reusability and stability. This study provides a useful platform and a new perspective for fabricating mesoporous MnO 2 microspheres based noble metals modified catalysts for environmental catalysis. [ABSTRACT FROM AUTHOR]

In this study, a novel catalyst has been prepared through supporting Pd nanoparticles (NPs) on the surface of boehmite (γ-AlOOH) based hollow aluminosilicate microspheres (HAM@γ-AlOOH). The prepared Pd/HAM@γ-AlOOH catalyst has high catalytic activity for the hydrogenation of nitroarenes to their corresponding amino derivatives with high yields at ambient conditions. The high catalytic efficiency is attributed to the large pore size of the flower-like hierarchical flakes structure of HAM@γ-AlOOH, that gives Pd NPs on the support surface easy accessibility. Moreover, the Pd/HAM@γ-AlOOH catalyst can also be easily recycled at least five times without obvious decrease of catalytic activity. This work may provide a useful method for the fabrication of supported noble metal NP-based catalysts on the surface of mesoporous hierarchical structure materials with easy accessibility and superior activity. [ABSTRACT FROM AUTHOR]

Transfer hydrogenation reactions using non-noble metal-based nanocatalysts are extensively attractive due to their low-cost and green reaction conditions. But construction of such catalysts with maximum metal atom efficiency and high catalytic activity is still a challenging research goal. Here, atomically dispersed Co catalysts with Co-N 4 active sites were fabricated, which builds a bridge for transfer hydrogenation between nitroarenes and saturated N-heterocycles in aqueous solution. The TOF value of the transfer hydrogenation reaction is much higher than nanoparticle catalyst for this reaction. Density functional theory (DFT) calculations and control experiments reveal that the excellent performance origins from the Co-N 4 sites, which combines the dehydrogenation of 1,2,3,4-tetrahydroquinoline with hydrogenation of nitrobenzene in one-pot. This work not only has an in-depth understanding of active sites but also shows a unique activity to the challenging, highly efficient, and green transfer hydrogenation reaction. [Display omitted] • Atomically dispersed Co catalysts were prepared by a direct pyrolysis procedure. • The Co-N 4 catalysts show high performance for transfer hydrogenation reaction. • The hydrophobicity of the Co-N 4 catalysts avoids the influence of by-product H 2 O. • DFT calculations confirm the mechanism of the transfer hydrogenation reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two 3D hydrophobic porous organic polymers (3D-HPOPs) were fabricated. • 3D-HPOPs exhibit N atoms containing cages to confine ultrafine Pd nanoclusters. • Pd@3D-HPOPs can catalyze phase transfer hydrogenation of nitroarenes in water. • Pd@3D-HPOPs catalysts can be easily recovered and reused without loss of activity. Fabrication of catalysts based on metal nanoclusters has attracted intensive research attention due to their superior catalytic activity. Herein, two three-dimensional hydrophobic porous organic polymers (3D-HPOPs-1 and 3D-HPOPs-2, respectively) that exhibited high specific surface areas and unique microporous-mesoporous structures were fabricated. Ultrafine Pd nanoclusters were successfully confined into the N atoms containing cages of 3D-HPOPs via impregnation and subsequent reduction. Besides, the 3D-HPOPs exhibited excellent hydrophobicity, thus can preferentially adsorb and enrich organic reactants in the pores of the catalyst, this in turn leads to the catalytic reaction as only in the organic phase. High conversion and selectivity were observed for the catalytic hydrogenation of nitroarenes over as-obtained Pd(0.7%)@3D-HPOPs-1 in water under mild reaction conditions. Moreover, the prepared catalyst can be easily recovered and reused without loss of activity. This study may provide a feasible strategy for fabricating noble-metal-nanocluster-based catalysts for various reactions under mild and environmentally friendly conditions. [ABSTRACT FROM AUTHOR]

• Two Triazinyl-COFs with different pore diameters were successfully synthesized. • Pd clusters with size of ˜0.8 nm were confined in the pores of Triazinyl-COFs with high dispersion. • The Pd@COF-Ph and Pd@COF-BPh have high utilization of Pd active sites. • Pd@COF-BPh catalyst exhibits superior catalytic activity as compared with other catalysts. • Pd@COF-Ph and Pd@COF-BPh catalysts display excellent recyclability and stability. Noble-metal-cluster-based catalysts have attracted immense research attention due to their high atom utilization ratio and superior catalytic activity. However, it is still challenging to control the size growth of noble-metal clusters. Here, triazinyl-functionalized covalent organic frameworks (Triazinyl-COFs) with different pore diameters were synthesized by the condensation of cyanuric chloride with each of p-phenylenediamine and 4,4′-diaminobiphenyl, referred to as COF-Ph and COF-BPh, respectively. A simple synthetic strategy was employed for controlling the Pd clusters growth and anchoring Pd clusters based on the confinement effect of Triazinyl-COFs pores. The as-obtained Pd@COF-Ph and Pd@COF-BPh catalysts with a Pd cluster size of ˜0.8 nm exhibited superior activity and excellent stability for the reduction of 4-nitrophenol, attributing to the high utilization of Pd active sites and the confinement effect of Triazinyl-COFs. Besides, the influence of the different pore sizes of COF-Ph and COF-BPh on the catalytic performance of the obtained catalysts was also investigated. [ABSTRACT FROM AUTHOR]