Nanosize metal oxides generally possess high catalytic activity, but they tend to agglomerate into larger particles during a reaction. Therefore, the preparation of nanosize metal oxides with high stability is a crucial challenge. A novel and facile approach involving impregnation followed by a double solvent method was developed to directly encapsulate ultrafine Mn3O4 nanoparticles (NPs) into the nanocages of metal–organic frameworks (MOFs). A series of MIL-101 encapsulated Mn3O4 NPs were prepared, in which the contents of Mn3O4 ranged from 3.2% to 33%. Ultrafine Mn3O4 NPs with a particle size of about 3 nm have been successfully embedded in the nanocages of MIL-101 with a uniform distribution. The MIL-101 encapsulated Mn3O4 NPs with a Mn3O4 content of 15% exhibits the highest conversion of benzyl alcohol (38.7%) and a >99% selectivity to benzaldehyde. Furthermore, after being repeatedly used 10 times, its catalytic activity is hardly changed. When the content of Mn3O4 NPs was further increased, the catalytic activity of the catalyst decreases, due to aggregated Mn3O4 particles with a large size which formed outside the MIL-101 matrix.

Selective oxidation of saturated hydrocarbons with molecular oxygen has been of great interest in catalysis, and the development of highly efficient catalysts for this process is a crucial challenge. A new kind of heterogeneous catalyst, cobalt-doped carbon nitride polymer (g-C3N4), was harnessed for the selective oxidation of cyclohexane. X-ray diffraction, Fourier transform infrared spectra and high resolution transmission electron microscope revealed that Co species were highly dispersed in g-C3N4 matrix and the characteristic structure of polymeric g-C3N4 can be retained after Co-doping, although Co-doping caused the incomplete polymerization to some extent. Ultraviolet–visible, Raman and X-ray photoelectron spectroscopy further proved the successful Co doping in g-C3N4 matrix as the form of Co(II)N bonds. For the selective oxidation of cyclohexane, Co-doping can markedly promote the catalytic performance of g-C3N4 catalyst due to the synergistic effect of Co species and g-C3N4 hybrid. Furthermore, the content of Co largely affected the activity of Co-doped g-C3N4 catalysts, among which the catalyst with 9.0 wt% Co content exhibited the highest yield (9.0%) of cyclohexanone and cyclohexanol, as well as a high stability. Meanwhile, the reaction mechanism over Co-doped g-C3N4 catalysts was elaborated.A new kind of heterogeneous catalyst, cobalt-doped carbon nitride polymer (g-C3N4), was demonstrated to be highly efficient and recyclable for selective oxidation of cyclohexane with molecular oxygen.Download high-res image (177KB)Download full-size image

Sm-Mn mixed oxide catalysts prepared by the coprecipitation method were developed, and their catalytic activities were tested for the selective catalytic reduction (SCR) of NO with ammonia at low temperature. The results showed that the amount of Sm markedly influenced the activity of the MnOx catalyst for SCR, that the activity of the Sm-Mn mixed oxide catalyst exhibited a volcano-type tendency with an increase in the Sm content, and that the appropriate mole ratio of Sm to Mn in the catalyst was 0.1. In addition, the presence of Sm in the MnOx catalyst can obviously enhance both water and sulfur dioxide resistances. The effect of Sm on the physiochemical properties of the Sm-MnOx catalyst were investigated by XRD, low-temperature N2 adsorption, XPS, and FE-SEM techniques. The results showed that the presence of Sm in the Sm-MnOx catalyst can restrain the crystallization of MnOx and increase its surface area and the relative content of both Mn4+ and surface oxygen (OS) on the surface of the Sm-MnOx catalyst. NH3-TPD, NO-TPD, and in situ DRIFT techniques were used to investigate the absorption of NH3 and NO on the Sm-MnOx catalyst and their surface reactions. The results revealed that the presence of Sm in the Sm0.1-MnOx catalyst can increase the absorption amount of NH3 and NO on the catalyst and does not vary the SCR reaction mechanism over the MnOx catalyst: that is, the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms (bidentate nitrate is the active intermediate), in which the Eley–Rideal mechanism is predominant.Keywords: ammonia reducing agent; nitrogen oxide; role of Sm; selective catalytic reduction; Sm-Mn oxide catalyst

•V-MCFs were synthesized by co-condensation of TEOS and VTMS.•A-MCFs were prepared by copolymerization of V-MCFs with methacrolein.•A-MCFs retain the ultra-large and continuous 3D mesoporous structure.•PGA is immobilized covalently on the surface of A-MCFs.•PGA/A-MCFs shows high initial enzymatic activity and operational stability.Aldehyde-functionalized mesostructured cellular foams (A-MCFs) were successfully prepared by copolymerization of vinyl groups on the surface of vinyl-functionalized mesostructured cellular foams (V-MCFs) with methacrolein, and used for covalent immobilization of penicillin G acylase (PGA). Effects of functionalization with the organo-functional groups on the physicochemical properties of V-MCFs and A-MCFs, and the enzymatic activity and the operational stability of the immobilized PGA were investigated. A-MCFs-15% sample retains the characteristic ultra-large and continuous 3D mesoporous structure of MCFs with high surface area and large pore volume, which is beneficial for immobilization of PGA and diffusion of substrates and products, and thus results in high enzymatic activity of the immobilized PGA. PGA is immobilized covalently on A-MCFs sample via the reaction to produce Schiff’s base between the free amino groups of lysine residues of PGA and the aldehyde groups on the surface of A-MCFs, which greatly increases the operational stability of the immobilized PGA. PGA/A-MCFs-15% sample shows the initial enzymatic activity of 9531 U g−1 and retains 87% of its initial activity after recycled for ten times.

Cu/ZSM-5 and Ce doped Cu/ZSM-5 catalysts were prepared by the incipient-wetness-impregnation method, and the effect of Ce doping on the structure and the catalytic performance of the Cu/ZSM-5 catalyst was investigated in detail for the selective catalytic reduction (SCR) of NO with NH3. The results showed that the addition of Ce can markedly broaden the operation temperature window of the Cu/ZSM-5 catalyst for NH3-SCR and enhance its H2O and SO2 resistance. The presence of Ce promoted an enrichment of copper species (isolated Cu2+ ions and CuO nanoparticles) on the catalyst surface and the increase in the Lewis acid sites on the surface of the Cu/ZSM-5 catalyst, and strengthened the redox property of the Cu/ZSM-5 catalyst. As a result, Ce-doped Cu/ZSM-5 catalyst possessed the high adsorption ability of NH3 and nitrite/nitrate, which is propitious to the increase in the reactivity of the Ce-doped Cu/ZSM-5 catalyst. In situ DRIFTS results indicated that the NH3-SCR reaction on the Cu/ZSM-5 catalyst and Ce1–Cu4/ZSM-5 catalysts definitely followed Langmuir–Hinshelwood mechanisms, and bridged nitrates and bidentate nitrates were the active intermediate. However, Eley–Rideal mechanism can't be confirmed over the Cu/ZSM-5 and Ce1–Cu4/ZSM-5 catalysts.

•The surface properties of Ce-MCM-48 affect its reactivity for cyclohexane oxidation.•F-modified Ce-MCM-48 exhibits 8.9% conversion with 91.2% selectivity to KA oil.•The catalysts prepared exhibit the excellent reusability.Ce-doped MCM-48 (Ce-MCM-48) mesoporous molecular sieve was prepared hydrothermally and its surface was modified with organic groups or fluorine, and their physicochemical properties were characterized by XRD, low-temperature N2 adsorption, TEM, UV–visible and FT-IR spectroscopies, XPS and contact angle measurement. The results indicated that Ce species were highly dispersed on the MCM-48 materials as Ce3+ and Ce4+. After post-functionalization of Ce-MCM-48, the organic groups or fluorine species have been immobilized on the surface of Ce-MCM-48, but the chemical status of Ce species were hardly changed, and the post-functionalization improved the surface hydrophobicity of the Ce-MCM-48 sample. The catalytic activity testing for the oxidation of cyclohexane with molecular oxygen showed that, Ce-MCM-48 after post-functionalization exhibited the higher cyclohexane conversion and selectivity to cyclohexanol and cyclohexanone, 8.9% cyclohexane conversion with 91.2% selectivity to cyclohexanone and cyclohexanol could be achieved over the Ce-MCM-48 with F-modified catalyst, which was attributed to the proper modification of their surface properties including hydrophobicity and polarity. The F-modified catalyst also showed excellent reusability, and its catalytic performance has no obvious deterioration after being repeatedly used five times.

•Cu-CeO2-Al2O3 catalyst has better catalytic performance.•Removal of residual sodium and water improves catalytic performance and stability.•Higher Cu dispersion and Cu surface area are advantageous.Cu-CeO2-Al2O3 catalysts were prepared by the co-precipitation method with different washing operations during the preparation process for the purpose of controlling the contents of the residual sodium and water in the catalyst precursors. Cu-CeO2-Al2O3 catalysts were characterized by ICP-AES, XRD, SEM, nitrogen sorption, N2O chemisorption, Raman spectroscopy and H2-TPR. Effects of the residual sodium and water in the catalyst precursor on the catalytic performance of Cu-CeO2-Al2O3 catalyst for gas-phase hydrogenation of maleic anhydride to γ-butyrolactone at atmospheric pressure, and the structure–activity relationships were investigated. The results show that the residual water and sodium in the form of Na2CO3 in the catalyst precursor lead to a decrease in Cu dispersion and Cu surface area, which is disadvantageous to the catalytic performance and stability. Washing step of the residual sodium in the catalyst precursor with the deionized water and then removing step of the residual water using azeotropy distillation shows a great improvement in the stability of Cu-CeO2-Al2O3 catalyst, in which 100% of conversion of maleic anhydride and 100% of selectivity to γ-butyrolactone were maintained for 12 h.

The Pd–Fe–Ox/Al2O3 catalysts were prepared by co-impregnation (co-Pd–Fe–Ox/Al2O3) and sol–gel method (sol–gel–Pd–Fe–Ox/Al2O3) and characterized by N2 adsorption–desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The CO catalytic oxidation was investigated over Pd–Fe–Ox/Al2O3 catalysts prepared by different methods. The 100% conversion temperature (T100) over pre-reduced co-Pd–Fe–Ox/Al2O3 (co-Pd–Fe–Ox/Al2O3–R) and pre-reduced sol–gel–Pd–Fe–Ox/Al2O3 (sol–gel–Pd–Fe–Ox/Al2O3–R) is 90 and 25 °C when fed with the reaction mixture containing 1 vol.% CO and a balance of air, respectively. XRD results indicate that the sol–gel method is favorable for the high dispersion of PdO particles compared with co-impregnation method. H2-TPR results suggest that the interaction between Pd and Fe is existent over both sol–gel–Pd–Fe–Ox/Al2O3 and co-Pd–Fe–Ox/Al2O3 catalysts, while the interaction in former catalyst is stronger than that in the latter. The XPS results show that the Pd species on the surface of both sol–gel–Pd–Fe–Ox/Al2O3–R and co-Pd–Fe–Ox/Al2O3–R catalysts are the mixture of oxide and metal state, leading to the high activity for CO oxidation. Furthermore, the different Pd2+/Pd0 ratio may be the reason for the different activity between sol–gel–Pd–Fe–Ox/Al2O3–R and reduced co-Pd–Fe–Ox/Al2O3–R catalysts.