Song-Hai Chai

A Superacid-Catalyzed Synthesis of Porous Membranes Based on Triazine Frameworks for CO2 Separation

A general strategy for the synthesis of porous, fluorescent, triazine-framework-based membranes with intrinsic porosity through an aromatic nitrile trimerization reaction is presented. The essence of this strategy lies in the use of a superacid to catalyze the cross-linking reaction efficiently at a low temperature, allowing porous polymer membrane architectures to be facilely derived. With functionalized triazine units, the membrane exhibits an increased selectivity for membrane separation of CO(2) over N(2). The good ideal CO(2)/N(2) selectivity of 29 ± 2 was achieved with a CO(2) permeability of 518 ± 25 barrer. Through this general synthesis protocol, a new class of porous polymer membranes with tunable functionalities and porosities can be derived, significantly expanding the currently limited library of polymers with intrinsic microporosity for synthesizing functional membranes in separation, catalysis, and energy storage/conversion.

Lab-in-a-Shell: Encapsulating Metal Clusters for Size Sieving Catalysis

Here we describe a lab-in-a-shell strategy for the preparation of multifunctional core-shell nanospheres consisting of a core of metal clusters and an outer microporous silica shell. Various metal clusters (e.g., Pd and Pt) were encapsulated and confined in the void space mediated by the entrapped polymer dots inside hollow silica nanospheres acting first as complexing agent for metal ions and additionally as encapsulator for clusters, limiting growth and suppressing the sintering. The Pd clusters encapsulated in hybrid core-shell structures exhibit exceptional size-selective catalysis in allylic oxidations of substrates with the same reactive site but different molecular size (cyclohexene ∼0.5 nm, cholesteryl acetate ∼1.91 nm). The solvent-free aerobic oxidation of diverse hydrocarbons and alcohols was further carried out to illustrate the benefits of such an architecture in catalysis. High activity, outstanding thermal stability and good recyclability were observed over the core-shell nanocatalyst.

Constructing Hierarchical Interfaces: TiO2-Supported PtFe–FeOx Nanowires for Room Temperature CO Oxidation

In this communication, we report a facile approach to constructing catalytic active hierarchical interfaces in one-dimensional (1D) nanostructure, exemplified by the synthesis of TiO2-supported PtFe-FeO(x) nanowires (NWs). The hierarchical interface, constituting atomic level interactions between PtFe and FeO(x) within each NW and the interactions between NWs and support (TiO2), enables CO oxidation with 100% conversion at room temperature. We identify the role of the two interfaces by probing the CO oxidation reaction with isotopic labeling experiments. Both the oxygen atoms (Os) in FeO(x) and TiO2 participate in the initial CO oxidation, facilitating the reaction through a redox pathway. Moreover, the intact 1D structure leads to the high stability of the catalyst. After 30 h in the reaction stream, the PtFe-FeO(x)/TiO2 catalyst exhibits no activity decay. Our results provide a general approach and new insights into the construction of hierarchical interfaces for advanced catalysis.

Synthesis of Porous, Nitrogen‐Doped Adsorption/Diffusion Carbonaceous Membranes for Efficient CO2 Separation

A porous, nitrogen-doped carbonaceous free-standing membrane (TFMT-550) is prepared by a facile template-free method using letrozole as an intermediate to a triazole-functionalized-triazine framework, followed by carbonization. Such adsorption/diffusion membranes exhibit good separation performance of CO2 over N2 and surpassing the most recent Robeson upper bound. An exceptional ideal CO2 /N2 permselectivity of 47.5 was achieved with a good CO2 permeability of 2.40 × 10(-13) mol m m(-2) s(-1) Pa(-1) . The latter results arise from the presence of micropores, narrow distribution of small mesopores and from the strong dipole-quadrupole interactions between the large quadrupole moment of CO2 molecules and the polar sites associated with N groups (e.g., triazine units) within the framework.

Three-Phase Catalytic System of H2O, Ionic Liquid, and VOPO4–SiO2 Solid Acid for Conversion of Fructose to 5-Hydroxymethylfurfural

Efficient transformation of biomass-derived feedstocks to chemicals and fuels remains a daunting challenge in utilizing biomass as alternatives to fossil resources. A three-phase catalytic system, consisting of an aqueous phase, a hydrophobic ionic-liquid phase, and a solid-acid catalyst phase of nanostructured vanadium phosphate and mesostructured cellular foam (VPO-MCF), is developed for efficient conversion of biomass-derived fructose to 5-hydroxymethylfurfural (HMF). HMF is a promising, versatile building block for production of value-added chemicals and transportation fuels. The essence of this three-phase system lies in enabling the isolation of the solid-acid catalyst from the aqueous phase and regulation of its local environment by using a hydrophobic ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]). This system significantly inhibits the side reactions of HMF with H2O and leads to 91 mol % selectivity to HMF at 89 % of fructose conversion. The unique three-phase catalytic system opens up an alternative avenue for making solid-acid catalyst systems with controlled and locally regulated microenvironment near catalytically active sites by using a hydrophobic ionic liquid.

In situ growth synthesis of heterostructured LnPO4–SiO2 (Ln = La, Ce, and Eu) mesoporous materials as supports for small gold particles used in catalytic CO oxidation

A general in situ growth method was successfully employed to prepare lanthanide phosphate–SiO2 mesostructured cellular foams (MCFs) (LnPO4–MCFs; Ln = La, Ce, and Eu; MCFs = SiO2). These heterostructured MCFs (LnPO4–MCFs) feature binary interpenetrating LnPO4 and silica frameworks, large surface areas, and uniform mesopore diameters. They were characterized by small-angle X-ray scattering, X-ray diffraction, nitrogen sorption, and transmission electron microscopy. The essence of this in situ growth synthesis lies in the controlled heterogeneous reaction of highly dispersed lanthanide oxides embedded in MCFs with phosphate ions in solution, leading to the formation of highly dispersed crystalline phosphate nanorods (nanocrystalline LnPO4) on the walls of MCFs. The resultant heterostructured LnPO4–MCFs were used as a novel support system for gold catalysts in CO oxidation at low temperatures. Gold precursor species can be readily introduced on LnPO4 nanophases of LnPO4–MCFs via a simple deposition–precipitation method. The resulting Au–LnPO4–MCF (2 wt% Au) catalysts exhibited high catalytic activities even below room temperatures. Because of the alteration of surface properties engineered by the in situ growth methodology and the strong interaction of metallic gold species with LnPO4, these catalysts are highly sinter-resistant. Although some cationic Au species are also present on the LnPO4–MCF surfaces, the metallic gold species are shown to be the key catalytic active sites for CO oxidation via in situ infrared spectroscopy.

A renewable HSO3/H2PO3-grafted polyethylene fiber catalyst: an efficient heterogeneous catalyst for the synthesis of 5-hydroxymethylfurfural from fructose in water

Irradiation-induced co-grafting of acrylonitrile and vinylsulfonic acid (or vinylphosphonic acid) monomers on polyethylene fiber was studied for the heterogeneous catalysis of fructose dehydration into 5-hydroxymethylfurfural (HMF) solely in water. The acidic co-polymer exhibited excellent catalytic activity and maintained a high yield after being regenerated. We attribute these catalytic properties to a branched environment created by grafted chains, hydrophilic enough to interact with fructose in water but collectively dense enough to form a unique local phase mimicking organic solvents.

Heterostructured BaSO4–SiO2 mesoporous materials as new supports for gold nanoparticles in low-temperature CO oxidation

Nanosized BaSO4-based mesoporous hybrid materials have been developed and identified as new efficient inorganic salt-based support systems for ultrastable gold nanoparticles in low-temperature CO oxidation.

Electrochemical Control of Ion Transport through a Mesoporous Carbon Membrane

We report a carbon-based, three-dimensional nanofluidic transport membrane that enables gated, or on/off, control of the transport of organic molecular species and metal ions using an applied electrical potential. In the absence of an applied potential, both cationic and anionic molecules freely diffuse across the membrane via a concentration gradient. However, when an electrochemical potential is applied, the transport of ions through the membrane is inhibited.

Synthesis of MCF-supported AuCo nanoparticle catalysts and the catalytic performance for the CO oxidation reaction

The oxidation of carbon monoxide under low temperature is increasingly becoming an important process, and supported gold nanoparticles have generated an immense interest in this field due to their extremely high reactivity. In this paper, we have synthesized MCF-supported AuCo nanoparticles, and through heating the AuCo/MCF in an O2 atmosphere, we have developed Au–CoOx heterostructured catalysts for CO oxidation. The structure of the Au–CoOx/MCF hybrid catalysts was investigated by using a combination of XRD, TEM, HR-TEM, EDX, SEM, XPS and in situ FTIR experiments. Various pretreatment conditions were required to form a highly active and stable Au–CoOx/MCF catalyst to achieve 100% CO conversion under low temperature. The AuCo/MCF catalyst calcined at 500 °C for 1 h was found to produce the most active and stable catalyst for CO oxidation with the highest activity at a reaction temperature of 30 °C for 15 h on-stream. Furthermore, XRD results of the used Au–CoOx/MCF catalyst showed its good resistance to sintering during catalytic process. However, by heating the Au–CoOx/MCF catalyst in H2 at 400 °C for 1 h to reduce the CoOx back to Co to reform the AuCo catalyst, it was found that the AuCo/MCF catalyst was much less active for CO oxidation. This was explained by the in situ FTIR results, which showed that CO molecules could be chemisorbed and activated on the Au–CoOx/MCF catalyst more than on the AuCo/MCF catalyst. It was likely that the increased interfacial contact between the Au and CoOx formed the most active site on the catalyst and was responsible for the enhanced catalytic properties when compared with pure Au/MCF.