In this work, we report a hydrothermal route to synthesize hierarchical TS-1 zeolites with abundant mesopores (5–40 nm) inside the zeolite crystals by using polydiallyldimethylammonium chloride (PDADMAC) as a mesopore-directing template. The textural parameters of the hierarchical TS-1 zeolites can be adjusted by changing the amount of PDADMAC in the synthesis system; in particular, a hierarchical TS-1C sample with abundant and uniform mesopores (around 10 nm) can be obtained by optimizing the amount of PDADMAC. The resultant hierarchical TS-1 zeolite exhibits excellent catalytic activity in the oxidation of bulky organosulfur compounds. Moreover, the hierarchical TS-1 catalysts possess high structural stability and can be easily recycled without any post treatment. This work demonstrates a facile route to synthesize hierarchical TS-1 zeolites with abundant intracrystalline mesopores by using a cheap and easily available mesoporous template, which will open new perspectives for the potential application of hierarchical TS-1 zeolites in catalytic oxidation of bulky organic compounds.

A series of amine-modified ZrSBA-15 supported PdAu bimetallic nanoparticle (NP) catalysts were prepared, and their catalytic properties were studied for the dehydrogenation of formic acid in aqueous solution without any additives. The catalytic activities of the supported PdAu catalysts varied with the change of amines and Pd/Au ratios. The optimized catalyst achieves a very high efficiency under ambient conditions, and even works well at a temperature near the freezing point of the solution. During the preparation process of the catalysts, different organic amines could coordinate with the cations of Au and Pd to produce metal complexes with different structure stabilities and redox properties, and finally result in the formation of PdAu NPs with different particle sizes and dispersion states. The co-existence of small PdAu alloy NPs and the suitable amino groups within the single solid support could provide highly efficient bifunctional sites for synergistically activating FA molecules to produce H2 and CO2.

•Acid-treated TiO2 nanoblet is used to prepare supported Pt catalyst (Pt/TiNB-ac).•Pt/TiNB-ac shows very high activity for low-temperature oxidation of HCHO.•TiNB-ac has rough surface, abundant chemisorbed oxygen and hydroxyl species.•More metal-support interface active sites are present in Pt/TiNB-ac catalyst.In this work, two kinds of novel Pt/TiO2 catalysts were prepared by impregnation method using hydrothermally synthesized TiO2 nanobelt (TiNB) and sulfuric acid-treated TiO2 nanoblet (TiNB-ac) as supports, and their catalytic properties were investigated in the oxidation of formaldehyde. It was found that Pt/TiNB-ac exhibits much higher catalytic activity, which can efficiently convert formaldehyde to CO2 and H2O at ambient temperature. The addition of water vapor into the feed stream can further promote the catalytic activity of Pt/TiNB-ac catalyst. A variety of characterization results showed that TiNB-ac possesses much rougher surface, and more defect sites (including abundant chemisorbed oxygen and surface hydroxyl species) due to the treatment by sulfuric acid. These features should be beneficial to achieve high dispersion of Pt nanoparticles on the rough-surface of TiNB-ac, to produce more interface active sites like Pt-O(OH)x-Ti species through the interaction between the Pt naoparticles and the surface hydroxyl species of TiNB-ac support, thus resulting in the formation of highly efficient Pt/TiNB-ac catalyst for the oxidation of formaldehyde under mild conditions.Download high-res image (179KB)Download full-size image

Hierarchical TS-1 zeolites with uniform intracrystalline mesopores have been successfully synthesized through the hydrothermal method by using the green and cheap surfactant Triton X-100 as the mesoporous template. The resultant materials exhibit remarkably enhanced catalytic activity in oxidative desulfurization reactions compared to the conventional TS-1 zeolite.

•PMA/KAP was obtained by supporting phosphomolybdic acid on PPh3 functionalized KAP.•PMA/KAP is active and stable catalyst for olefin oxidation with H2O2/ethyl acetate.•Multi-weak interaction exits between PMA unit and PPh3 ligands knitted in the KAP.•Degradation of PMA to small species can be inhibited by the multi-weak interaction.A phosphomolybdic acid (PMA)-based heterogeneous catalyst, denoted as PMA/KAP, was prepared by immobilizing PMA onto a knitting aryl network polymer (KAP) based on triphenylphosphine (PPh3). The catalytic property of PMA/KAP was investigated for the selective oxidation of olefins with aqueous hydrogen peroxide (H2O2) as oxidant. When using ethyl acetate (EAC) as reaction medium, PMA/KAP performs higher activity and selectivity to epoxide for a variety of olefins, and it can be reused for several times without obvious loss of activity. When the reaction was carried out in acetonitrile (AN) medium, deactivation of PMA/KAP catalyst can be observed immediately. A variety of characterization results suggest that the degradation of PMA unit to (PO4[MoO(O2)2]4)3− occurs easily when the PMA/KAP catalyst is operated in H2O2/AN system, while such degradation behavior could be significantly inhibited when the catalyst is used in the system of H2O2/EAC. We proposed that the neighbouring P-containing ligands dispersed in the framework of KAP can produce a steric pocket with low electron density, which can promote the formation of multi-weak coordination interaction between PMA unit and several P ligands. Such multi-weak interaction can inhibit the degradation of PMA to (PO4[MoO(O2)2]4)3−, thus avoiding the leaching of active species from the KAP support, and resulting in the formation of relatively stable heterogeneous PMA supported catalyst for olefin epoxidation with H2O2 in the media of EAC.

A series of γ-Al2O3 supported Pt–FeOx catalysts (Pt–FeOx/Al2O3) with different Fe/Pt atom ratios were prepared, and their catalytic properties were investigated in the oxidation of formaldehyde. It was found that the catalytic activities of Pt–FeOx/Al2O3 catalysts are varied with the change of Fe/Pt ratios. Among them, the sample with a Fe/Pt ratio of 1.0 exhibits the highest activity, which can efficiently convert formaldehyde to CO2 at ambient temperature. The catalytic activity of the Pt–FeOx/Al2O3 catalyst can be further improved by the addition of water vapor into the feed stream. A variety of characterization results showed that both Pt nanoparticles and FeOx species are highly dispersed on the surface of the γ-Al2O3 support. Changing Fe/Pt ratios could influence the chemical states and the redox properties of Pt and Fe species. The catalysts with appropriate Fe/Pt ratios have more accessible active sites, i.e., the Pt–O–Fe species, which are located at the boundaries between FeOx and Pt nanoparticles, thus showing high activity for the oxidation of formaldehyde under ambient conditions.

•PMA@COF-300 was prepared by immobilizing 12-phosphomolybdic acid onto COF-300.•The PMA units are uniformly dispersed on the surface/cavities of COF-300.•Electrostatic interaction is present between the PMA units and COF-300 framework.•PMA@COF-300 is efficient heterogeneous catalyst for the epoxidation of olefins.Novel heteropolyacid-based hybrid composites (denoted as PMA@COF-300) have been obtained by immobilizing 12-phosphomolybdic acid (PMA) onto a covalent organic framework material (COF-300). Structural and spectroscopic studies show that the PMA units are uniformly dispersed on the surface/cavities of COF-300, and relatively stable linkages can be built between the PMA units and the matrix of COF-300 when suitable preparation conditions are adopted. The catalytic properties of the PMA@COF-300 are investigated in the epoxidation of olefins with t-BuOOH as oxidant. The experimental results show that the PMA@COF-300 composites can act as efficient heterogeneous catalysts for the epoxidation of cyclooctene, and can even convert the relatively inert terminal alkene of 1-octene into 1,2-epoxyoctane rapidly at mild conditions. The existence of unique interpenetrated 3-D structure, suitable porous characteristics, and the abundant protonated imine groups in COF-300 play critical role in dispersing and stabilizing the anions of PMA, which is beneficial to the fabrication of highly active and stable heterogeneous PMA functionalized COF-300 catalysts for olefin epoxidation.

A series of boron phosphate (BPO4) modified ion-exchanged CsX zeolites, prepared by impregnation method, were characterized by a variety of means and utilized as catalysts for the side-chain alkylation of toluene with methanol. Both BPO4 and Cs species are highly dispersed on the surface/channel of the BPO4/CsX zeolites. The addition of a small amount of BPO4 has no obvious effect on the basic strength of catalysts, but decreases the number of basic sites slightly. Meanwhile, more weak Lewis acidic sites appear with the increasing BPO4 loading. Compared with CsX, the BPO4 modified CsX catalysts exhibit lower ability for the adsorption/activation of methanol to produce surface intermediates like formaldehyde, unidentate formate and bidentate formate. Catalytic reaction results showed that modification of CsX with boron phosphate can improve both the conversion of toluene and the selectivity of styrene. The inhibition role in producing the unfavorable bidentate formate might be a key factor for finally resulting in the improvement of the catalytic properties of BPO4/CsX catalysts for the side-chain alkylation of toluene with methanol.

A novel polyoxometalate-based compound, [H(atrz)]4[(atrz)2(Mo8O26)]·2H2O (1) (atrz = 3-amino-1,2,4-triazole), has been synthesized by traditional hydrothermal method, and characterized by means of elemental analysis, FT-IR spectroscopy, Powder X-ray diffraction and single-crystal X-ray. The compound 1 contains a 2D supramolecualr layer which is constructed from [(atrz)2(γ-Mo8O26)]4− units via intermolecular hydrogen-bonding interactions. Furthermore, the adjacent 2D layers are packed together through the aromatic π⋯π stacking interactions and exhibits a 3D supramolecular structure. The catalytic properties of 1 were investigated in olefin epoxidation with tert-butylhydroperoxide (t-BuOOH) as the oxidant. It was found that compound 1 could serve as active and stable heterogeneous catalyst for the epoxidation of cyclooctene and 1-octence. Besides, introducing copper ions into compound 1 could further improve the catalytic activity for olefin epoxidation.

Three supported Pt/Fe2O3 catalysts were prepared by depositing platinum colloids with discrete particle sizes onto the surface of Fe(OH)3 powders, which were then calcined at an elevated temperature. Pt nanoparticle colloids with mean diameters of 1.1, 1.9, or 2.7 nm were synthesized in order to investigate the effects of particle size on the structure and CO oxidation properties of these Pt/Fe2O3 catalysts. All Pt/Fe2O3 catalysts demonstrated activity in low-temperature CO oxidation, with the sample containing Pt nanoparticles with a mean diameter of 1.9 nm (designated Pt/Fe2O3-b) exhibiting relatively higher catalytic activity. Compared with the other two catalysts, Pt/Fe2O3-b exhibited an increased ability to activate oxygen and maintain the stability of Pt species, correlating with its higher catalytic activity. The results of various characterization techniques revealed that the mean particle size of the Pt nanoparticles could influence the chemical states of Pt species and the strength of metal–support interactions of the Pt/Fe2O3 catalysts. It was observed that the metal–support interactions in Pt/Fe2O3 catalysts were able to adjust the redox properties and the O2-activation abilities of the catalysts. Finally, it is proposed that the interacting Pt and Fe species located at the Pt–FeOx interface are the primary active sites for the activation of CO and O2, respectively.

A manganese-based hybrid mesoporous material (denoted as 5) was synthesized by covalent grafting of [MnII(1)2](OAc)2 (3) (1 = [3-(2-pyridyl)pyrazol-1-yl]acetic acid amide) onto the surface of SBA-15, and characterized by means of XRD, N2 adsorption–desorption, FT-IR, Raman, EPR and UV–vis spectroscopic techniques. Catalytic tests showed that 5 could act as an efficient heterogeneous catalyst for the epoxidation of a wide range of alkenes (including terminal ones) under mild reaction conditions when peracids (e.g., meta-chloroperbenzoic acid) are used as oxidants. Moreover, the catalytic performance of 5 is solvent-dependent, it exhibits higher catalytic activity and selectivity to epoxides when the reaction is carried out in aprotic solvent like CH3CN. UV–vis and electrochemical measurements revealed that high-valent Mn species are easily formed during the reaction course, when meta-chloroperbenzoic acid is used as oxidant and CH3CN is used as solvent, being probably the main reason for the high activity of 5 and its selectivity toward epoxide formation.Graphical abstractMesoporous SBA-15 materials modified with manganese pyrazolylpyridine complexes is an efficient heterogeneous catalyst for the epoxidation of alkenes (including terminal alkenes) with m-CPBA as oxidant under mild conditions. UV–vis measurements results revealed that high-valent Mn species are easily formed when CH3CN is used as solvent, should be the main active intermediates for the epoxidation reaction.Highlights► Manganese pyrazolylpyridine complexes modified SBA-15 (5) is prepared. ► 5 is active and stable heterogeneous catalyst for the epoxidation of terminal alkenes. ► OMnIV-species should be the main active intermediates for the epoxidation reaction.

A series of carbon-supported CaO materials, prepared using different porous carbon materials as supports, were tested as basic catalysts for the transesterification of triacetin with methanol and characterized by means of X-ray diffraction (XRD), N2 adsorption, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). It was found that all of the carbon-supported CaO catalysts are active for the transesterification reaction, and their catalytic performance can be influenced by a variety of factors, such as the types of carbon supports, the concentration of impregnated CaO, the heat-treated temperatures of the catalysts, and the reaction temperatures. Particularly, the supported CaO catalyst, which is prepared using a kind of porous carbon (NC-2) as a support, exhibits very high activity, stability, and recyclability. We suppose that the main characteristics of this porous carbon, such as the presence of relatively abundant surface oxygen-containing functional groups and well-developed porosity, may be beneficial to build a suitable interaction between CaO particles and the carbon support, thus resulting in the formation of an active and stable catalyst system.

The synthesis, characterization and catalytic properties of COK-5 with different Si/Al ratios are described. Various key parameters (including the ratios of Si/Al and/or Na/Si, the type/concentration of alkali cations, and the structure of dialkylammonium) are investigated in detail for the successful synthesis of COK-5. Under our synthesis conditions, it is found that COK-5 zeolites could be synthesized only in a narrow range of Si/Al ratios and Na/Si ratios. The concentration of Na+ in the initial gel should be carefully controlled for the successful synthesis of COK-5 with lower Si/Al ratios. Rising the crystallization temperature (<453 K) or adding seed (including heterogeneous seeds ZSM-57 and ZSM-22) can shorten the crystallization time of COK-5. N2 adsorption–desorption results suggest that the COK-5 samples synthesized from gels with different Si/Al ratios show different texture properties. NH3-TPD characterization demonstrates the presence of some relatively strong acid sites on the surface of H-form COK-5 zeolites. The resultant COK-5 zeolites with different Si/Al ratios are catalytic active in the liquid-phase tert-butylation of phenol. The acid sites located on the external surface and near the entrance of pore channels of COK-5 zeolites are the main active centers for the reaction. Compared with other 10-ring and/or 12-ring zeolites, different product selectivities are observed on COK-5. We speculate that the nature of less stronger acids and the unusual pore systems of COK-5 zeolites, especially with distorted 12-ring pore structures, should be highly correlated with their catalytic properties.

Mg–Al mixed oxides with different Mg/Al molar ratios were prepared by using a citric acid route and tested as catalysts for the gas phase self-aldol condensation of acetone to isophorone. The sample with Mg/Al ratio of 1.0 exhibits relatively high activity and stability, and its catalytic performance could be further improved by adding alkali promoter.

Titania−silica mixed oxides (denoted as TiO2−SiO2) with different Ti contents are prepared by a sol−gel route in the presence of citric acid (CA). Various characterization techniques, including XRD, FT-IR, N2-adsorption, TEM, solid-state CP-MAS NMR spectroscopy, UV−vis, and NH3-TPD, have been carried out to investigate the physical−chemical properties, states of Ti species, and the formation process of TiO2−SiO2 materials. The characterization results show that the TiO2−SiO2 materials possess a mesoporous silicate framework with high specific surface area and thermal stability. Titanium species in the TiO2−SiO2 materials are mainly present in the form of two-dimensional low polymeric TiOx species, which are uniformly dispersed on the surface of mesoporous silica. Additionally, the titanium species have a strong resistence to high-temperature sintering, even for the sample with high Ti contents (25 wt %). Weak acid sites are observed over TiO2−SiO2 materials, and the amount of acidic sites increases with the increment of Ti contents. The acid catalytic performance of TiO2−SiO2 materials is investigated in the transesterification of dimethyl oxalate (DMO) with phenol. All the materials are active for the reaction, and the total selectivity to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) is very high (>99%). The formation mechanism of such materials is discussed concerning the interaction between citric acid and precursors of silicon and titanium. We propose that a portion of CA can act as a ligand to coordinate with titanium species to form the titanium−CA complexes. Both CA and the titanium−CA complexes may act as a template for the formation of a silica framework. After calcination, titanium species release from the titanium−CA complex and reach a position on the surface of silica, forming the resultant TiO2−SiO2 materials.

A simple and efficient route is reported for the synthesis of porous carbon materials via carbonizing a kind of composite containing citric acid (CA) and aluminum phosphate (AlPO). The resulting carbon materials, bearing mesoporous and/or microporous characteristics, possess uniform pore size distribution and certain degree graphitic phase characteristic. The structural parameters of these materials, including mean pore sizes, pore volumes and specific surface areas, can be further tuned within a certain range by addition of suitable amount of sucrose (SU) into the CA/AlPO composite. The mesostructured AlPO, which is formed insitu during the carbonization, can be regarded as a hard-template for the formation of porous carbon material. We propose that the uniform distribution of CA, and the presence of suitable interaction between CA and aluminum phosphate are critical factors for the formation of mesoporous carbon network.

•Two kinds of triphenylamine-based porous organic polymers (POP-I and POP-II) were synthesized.•Phosphomolybdic acid and cobalt phosphomolybdate (PMA) were immobilized onto the POPs.•CoPMA/POP-II is active and stable heterogeneous catalyst for olefin oxidation with H2O2.•Multiple electronic/coordination interactions are present between PMA and POP-II support.•Co2+ may strengthen the interactions between PMA and POPs by coordinating with TPA ligands.Two kinds of triphenylamine-based porous organic polymers (POPs) were synthesized by FeCl3-triggered Friedel-Crafts polymerization of triphenylamine (TPA) and formaldehyde dimethylacetal (FDA) in the absence or presence of benzene (Ph), which are denoted as POP-I (without additional Ph) and POP-II (with additional Ph as linker), respectively. Various characterization results confirm the successful synthesis of TPA-based polymers with different bridged linkers and hierarchical pore structure. Phosphomolybdic acid (HPMA) and cobalt phosphomolybdate (CoPMA) were immobilized onto the POPs, to form phosphomolybdate (PMA) functionalized POPs catalysts, and their catalytic properties were investigated for the selective oxidation of olefins with H2O2. All the PMA functionalized POPs materials are catalytically active for the epoxidation/oxidation of olefins, while CoPMA/POP-II shows the highest activity, stability and recyclability. TPA-based POPs have distinctive electron-donating and transferring ability, which can be further tuned by introducing more bridged linkers of -Ph and -CH2 groups. Multi-interactions between PMA and POPs supports could be built through the electronic and geometric effects exerted by the 3-D POPs supports on the PMA clusters. Moreover, the existence of Co cations may further strengthen the interactions between PMA and POPs supports by forming electrostatic or coordination interactions with the TPA ligands, thus resulting in the high stability of the CoPMA/POP-II against leaching of active species during the H2O2 mediated catalytic oxidation process.

The catalytic performance of an amorphous mesoporous aluminophosphate (AlPO) was investigated for the transesterification of diethyl carbonate (DEC) with dimethyl carbonate (DMC) to synthesize ethyl methyl carbonate (EMC). Compared with other solid acid and/or base catalysts, the mesoporous AlPO showed remarkably high activity, stability and recoverability for the reaction. We proposed that the presence of suitable weak acid–base pairs on the surface of the mesoporous AlPO material should play a critical role in the activation of reactants to produce EMC.Download full-size imageResearch Highlights► Mesoporous AlPO is an active heterogeneous catalyst for EMC production. ► AlPO showed good stability and recoverability for the transesterification reaction. ► Weak acid–base pairs are the main active sites for the reaction.

A series of amine-modified ZrSBA-15 supported PdAu bimetallic nanoparticle (NP) catalysts were prepared, and their catalytic properties were studied for the dehydrogenation of formic acid in aqueous solution without any additives. The catalytic activities of the supported PdAu catalysts varied with the change of amines and Pd/Au ratios. The optimized catalyst achieves a very high efficiency under ambient conditions, and even works well at a temperature near the freezing point of the solution. During the preparation process of the catalysts, different organic amines could coordinate with the cations of Au and Pd to produce metal complexes with different structure stabilities and redox properties, and finally result in the formation of PdAu NPs with different particle sizes and dispersion states. The co-existence of small PdAu alloy NPs and the suitable amino groups within the single solid support could provide highly efficient bifunctional sites for synergistically activating FA molecules to produce H2 and CO2.

Hierarchical TS-1 zeolites with uniform intracrystalline mesopores have been successfully synthesized through the hydrothermal method by using the green and cheap surfactant Triton X-100 as the mesoporous template. The resultant materials exhibit remarkably enhanced catalytic activity in oxidative desulfurization reactions compared to the conventional TS-1 zeolite.

In this work, we report a hydrothermal route to synthesize hierarchical TS-1 zeolites with abundant mesopores (5–40 nm) inside the zeolite crystals by using polydiallyldimethylammonium chloride (PDADMAC) as a mesopore-directing template. The textural parameters of the hierarchical TS-1 zeolites can be adjusted by changing the amount of PDADMAC in the synthesis system; in particular, a hierarchical TS-1C sample with abundant and uniform mesopores (around 10 nm) can be obtained by optimizing the amount of PDADMAC. The resultant hierarchical TS-1 zeolite exhibits excellent catalytic activity in the oxidation of bulky organosulfur compounds. Moreover, the hierarchical TS-1 catalysts possess high structural stability and can be easily recycled without any post treatment. This work demonstrates a facile route to synthesize hierarchical TS-1 zeolites with abundant intracrystalline mesopores by using a cheap and easily available mesoporous template, which will open new perspectives for the potential application of hierarchical TS-1 zeolites in catalytic oxidation of bulky organic compounds.