Zhengping Dong

Cobalt nanoparticles supported on N-doped mesoporous carbon as a highly efficient catalyst for the synthesis of aromatic amines

Inexpensive and reusable transition metal heterogeneous catalysts exhibiting excellent catalytic performance represent an attractive alternative to noble metal and homogeneous catalysts. In this work, we fabricated a novel nanocatalyst comprised of Co nanoparticles (NPs) supported on a N-doped mesoporous carbon (Co/mCN-900) by simple one-pot pyrolysis of a homogeneous mixture of melamine, polyacrylonitrile, and Co(NO3)2·6H2O under a N2 atmosphere at 900°C. The as-obtained Co/mCN-900 catalyst displayed a fluffy mesoporous structure with highly dispersed and accessible Co NPs acting as catalytic active sites. The Co/mCN-900 catalyst was effective in hydrogenating nitroarenes at milder conditions (i.e., 1MPa H2 and 120°C) as compared to previously reported Co- and Ni-based catalysts. The Co/mCN-900 catalyst also catalyzed the reductive N-alkylation of nitroarenes with carbonyl compounds to form the corresponding aromatic secondary amines under very mild reaction conditions. In addition, the Co/mCN-900 catalyst showed good reusability since its morphology and activity were maintained after several reaction cycles. Therefore, this work provides a facile and promising method for fabricating non-precious transition metal-based catalysts with excellent performance and great potential for sustainable chemistry applications.

PdCo nanoparticles supported on carbon fibers derived from cotton: Maximum utilization of Pd atoms for efficient reduction of nitroarenes

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 CoCl2, 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, Pd2+ 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 NaBH4, NH2NH2 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.

Facile preparation of fluffy N-doped carbon modified with Ag nanoparticles as a highly active and reusable catalyst for catalytic reduction of nitroarenes

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.

Immobilization of Pt nanoparticles in hollow mesoporous silica nanocapsules: An aggregation- and leaching-resistant catalyst

In this study, hollow mesoporous silica nanocapsules (h-mNSiO2) with uniformly dispersed Pt nanoparticles (Pt NPs) in their hollow core (Pt@h-mNSiO2) were successfully fabricated. The as-synthesized Pt@h-mNSiO2 was core@shell like structure with silica shells and Pt-rich cores. The catalyst was synthesised in an oil-water biphasic stratification system, then the self-assembly of reactants occurred in the oil-water interface for one-pot sustaining interfacial growth. The as-prepared Pt@h-mNSiO2 catalyst exhibited superior activity for hydrogen generation from the hydrolysis of ammonia borane, with a turnover frequency of 371.7 molH2 mol-1Pt min-1 at ambient temperature, probably owing to the abundant mesopores and high surface area, leading to a considerable increase in the accessible active sites. Besides, almost no Pt NP aggregation was observed during reusability tests. Notably, Pt leaching was not observed during the reaction, possibly related to the protective effect of the mesoporous silica shell. Thus, this study provides a facile route to synthesise aggregation- and leaching-resistant catalysts with superior activity, accessibility, and recyclability for the environment and energy chemistry.

Facile fabrication of γ-Fe2O3-nanoparticle modified N-doped porous carbon materials for the efficient hydrogenation of nitroaromatic compounds

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.

Biowaste soybean curd residue-derived Pd/nitrogen-doped porous carbon with excellent catalytic performance for phenol hydrogenation

Use of renewable raw materials for fabrication catalysts with excellent catalytic performance is of considerable importance for sustainable chemistry. Here, biowaste soybean curd residue (SCR) was used to prepare porous N-doped carbon materials (PNCM) via the carbonization method, and subsequently modified with small Pd nanoparticles (NPs) to generate the Pd/PNCM catalyst. Pd/PNCM was used for catalytic hydrogenation of phenol to cyclohexanone, as the latter is an important chemical intermediate that is usually produced under harsh reaction conditions. The Pd/PNCM catalyst can hydrogenate phenol to cyclohexanone in aqueous solution under mild reaction conditions with excellent catalytic performance. In addition, compared to commercial Pd/C, Pd/PNCM exhibits excellent catalytic performance and stability, which is attributed to the synergetic effects of N-doping of porous carbon supports and stabilization of ultra-small Pd NPs. Thus, this study highlights a new pathway for preparing N-doped porous carbon materials using biomass waste as the precursor material, and subsequently fabricating precious metal-modified catalysts with excellent catalytic performance for sustainable and green catalysis.

Ultrafine and Highly Dispersed Platinum Nanoparticles Confined in a Triazinyl-Containing Porous Organic Polymer for Catalytic Applications

The fabrication of stable porous organic polymers (POPs) with heteroatoms that can firmly anchor noble metal nanoparticles (NPs) is a challenging and significant task for heterogeneous catalysis. In the current work, we used piperazine and cyanuric chloride as precursors and successfully fabricated a PC-POP material. Then, through the impregnation method and subsequently the reduction method, ultrafine Pt NPs were confined in the PC-POP with a high dispersion. The Pt NP active sites are accessible due to the uniform mesopores of the PC-POP that facilitate diffusion and mass transfer. The organic cages and nitrogen atoms in the PC-POP frameworks can make the Pt NPs stably anchored in the PC-POP during the catalytic process. The obtained Pt@PC-POP nanocatalyst showed excellent catalytic activity and good recyclability in the selective hydrogenation of halogenated nitrobenzenes and catalytic hydrolysis of ammonia borane as compared with many other reported noble metal catalysts.

Highly dispersed ultrafine palladium nanoparticles encapsulated in a triazinyl functionalized porous organic polymer as a highly efficient catalyst for transfer hydrogenation of aldehydes

Fabrication of highly dispersed ultrafine noble metal nanoparticle (NMNP) based catalysts with high stability and excellent catalytic performance is a challenging issue for heterogeneous catalysis. As an alternative complement to existing solutions, herein, we designed and synthesized a stable triazinyl-pentaerythritol porous organic polymer (TP-POP) through a facile polycondensation between cyanuric chloride and pentaerythritol. The obtained TP-POP material has a three-dimensional folded structure, rich triazinyl groups, abundant hydrophobic pores and high thermal stability. Ultrafine Pd NPs with a narrow size distribution (1.4–2.8 nm) are then successfully confined in the organic pores of the TP-POP, through a reversed double solvent approach (RDSA). It is worth noting that the current strategy can effectively confine Pd NPs in the inner space of the TP-POP, and successfully avoids the agglomeration of Pd NPs as compared with the common impregnation-reduction method. The as-prepared Pd@TP-POP catalyst shows excellent catalytic activity in the reduction of 4-nitrophenol and transfer hydrogenation of aromatic aldehydes under very mild conditions. The excellent performance of the Pd@TP-POP catalyst is attributed to the abundant mesopores of the TP-POP which can enhance the accessibility of the highly dispersed ultrafine Pd NP active sites that are confined in the organic pores. More importantly, the Pd@TP-POP catalyst is easily recycled and highly stable without loss of its catalytic activity even after ten reaction cycles. Therefore, this study provides a new platform for designing and fabricating stable POP materials to confine size-controlled NMNPs with superior catalytic performance for various potential catalysis applications.

Aminal-based Hypercrosslinked Polymer Modified with Small Palladium Nanoparticles for Efficiently Catalytic Reduction of Nitroarenes

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.