Mingyang Mao

Tuning the K+ concentration in the tunnel of OMS-2 nanorods leads to a significant enhancement of the catalytic activity for benzene oxidation.

OMS-2 nanorods with tunable K(+) concentration were prepared by a facile hydrothermal redox reaction of MnSO4, (NH4)2S2O8, and (NH4)2SO4 at 120 °C by adding KNO3 at different KNO3/MnSO4 molar ratios. The OMS-2 nanorod catalysts are characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption and desorption, inductively coupled plasma, and X-ray photoelectron spectrometry. The effect of K(+) concentration on the lattice oxygen activity of OMS-2 is theoretically and experimentally studied by density functional theory calculations and CO temperature-programmed reduction. The results show that increasing the K(+) concentration leads to a considerable enhancement of the lattice oxygen activity in OMS-2 nanorods. An enormous decrease (ΔT50 = 89 °C; ΔT90 > 160 °C) in reaction temperatures T50 and T90 (corresponding to 50 and 90% benzene conversion, respectively) for benzene oxidation has been achieved by increasing the K(+) concentration in the K(+)-doped OMS-2 nanorods due to the considerable enhancement of the lattice oxygen activity.

Tremendous Effect of the Morphology of Birnessite-Type Manganese Oxide Nanostructures on Catalytic Activity

The octahedral layered birnessite-type manganese oxide (OL-1) with the morphologies of nanoflowers, nanowires, and nanosheets were prepared and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric/differential scanning calorimetry (TG/DSC), Brunnauer-Emmett-Teller (BET), inductively coupled plasma (ICP), and X-ray photoelectron spectroscopy (XPS). The OL-1 nanoflowers possess the highest concentration of oxygen vacancies or Mn(3+), followed by the OL-1 nanowires and nanosheets. The result of catalytic tests shows that the OL-1 nanoflowers exhibit a tremendous enhancement in the catalytic activity for benzene oxidation as compared to the OL-1 nanowires and nanosheets. Compared to the OL-1 nanosheets, the OL-1 nanoflowers demonstrate an enormous decrease (ΔT(50) = 274 °C; ΔT(90) > 248 °C) in reaction temperatures T50 and T90 (corresponding to 50 and 90% benzene conversion, respectively) for benzene oxidation. The origin of the tremendous effect of morphology on the catalytic activity for the nanostructured OL-1 catalysts is experimentally and theoretically studied via CO temperature-programmed reduction (CO-TPR) and density functional theory (DFT) calculation. The tremendous catalytic enhancement of the OL-1 nanoflowers compared to the OL-1 nanowires and nanosheets is attributed to their highest surface area as well as their highest lattice oxygen reactivity due to their higher concentration of oxygen vacancies or Mn(3+), thus tremendously improving the catalytic activity for the benzene oxidation.

Synergetic effect between photocatalysis on TiO2 and solar light-driven thermocatalysis on MnOx for benzene purification on MnOx/TiO2 nanocomposites

MnOx/TiO2 nanocomposites are prepared by the hydrothermal redox reaction of Mn(NO3)2 and KMnO4 with KMnO4/Mn(NO3)2 molar ratio of 2 : 1 in the presence of TiO2(P25). The MnOx/TiO2 nanocomposites are characterized by XRD, TEM, EDX, XPS, and BET. Manganese oxide supported on TiO2 nanoparticles is amorphous. The MnOx/TiO2 nanocomposites can efficiently transform absorbed solar energy into thermal energy, resulting in a considerable increase of temperature. The MnOx/TiO2 nanocomposites exhibit excellent catalytic activity and durability for the gas-phase oxidation of carcinogenic and recalcitrant benzene under the irradiation of full solar spectrum light and visible-infrared light. For the first time, we find a synergetic effect between photocatalysis on TiO2 and solar light-driven thermocatalysis on supported manganese oxide, which significantly improves the catalytic activity of the MnOx/TiO2 nanocomposites.

UV-Visible-Infrared Light Driven Thermocatalysis for Environmental Purification on Ramsdellite MnO2 Hollow Spheres Considerably Promoted by a Novel Photoactivation

Novel ramsdellite MnO2 hollow spheres consisting of closely stacked nanosheets (R-MnO2-HS) were synthesized by a facile method. The R-MnO2-HS sample was characterized with SEM, XRD, TEM, BET, XPS, diffusive reflectance UV-vis-IR absorption, etc. Remarkably, R-MnO2-HS exhibits highly efficient catalytic activity for the purification of benzene (a carcinogenic air pollutant) under the full solar spectrum or visible-infrared irradiation, even under the infrared irradiation. Its catalytic activity (initial CO2 production rate) under the full solar spectrum irradiation is as high as 210.5 times higher than TiO2(P25), a well-known benchmark photocatalyst for environmental cleanup. The excellent catalytic activity of R-MnO2-HS is ascribed to its efficient thermocatalytic activity and its efficient photothermal conversion in the whole solar spectrum region, resulting in high efficient solar light driven thermocatalysis. Very interestingly, a novel photoactivation, which is completely different from the well-known photoactivation induced by photoexcited electrons and holes on TiO2, considerably enhances the solar light driven thermocatalysis. By use of CO temperature-programmed reduction (CO-TPR) under solar light irradiation and in the dark together with density function theory (DFT) calculations, the origin of the novel photoactivation was revealed: The lattice oxygen activity plays a crucial role in the thermocatalysis on MnO2. The solar light irradiation significantly promotes the lattice oxygen activity of R-MnO2-HS, consequently resulting in a considerable enhancement in the thermocatalytic activity.

Highly efficient UV-Vis-infrared catalytic purification of benzene on CeMnxOy/TiO2 nanocomposite, caused by its high thermocatalytic activity and strong absorption in the full solar spectrum region

The nanocomposite of amorphous cerium manganese oxide supported on nano TiO2 (CeMnxOy/TiO2) was prepared by the facile hydrothermal redox reaction of Ce(NO3)3 and KMnO4 in the presence of nano TiO2. The CeMnxOy/TiO2 nanocomposite was characterized by XRD, TEM, SEM, EDX, XPS, BET, CO-TPR, and diffusive reflectance UV-Vis-IR absorption. It exhibits efficient thermocatalytic activity for the oxidation of the carcinogenic and recalcitrant benzene, which is comparable to that of the expensive noble metal catalyst (0.5% Pt/Al2O3), and is much higher than the CeO2/TiO2 and MnOx/TiO2 nanocomposites with the same metal/Ti molar ratio. Its specific CO2 production rate (rCO2) at 220 °C (88.6 μmol g−1 min−1) is 6.3 and 7.5 times higher than the nanocomposites of CeO2/TiO2 and MnOx/TiO2, respectively. The highly efficient thermocatalytic activity of the CeMnxOy/TiO2 nanocomposite is attributed to its higher oxygen activity, compared to the nanocomposites of CeO2/TiO2 and MnOx/TiO2. Remarkably, the CeMnxOy/TiO2 nanocomposite can be driven by simulated solar light for benzene oxidation. It exhibits highly efficient catalytic activity with the irradiation of the full solar spectrum, visible-infrared, and infrared light. Its initial CO2 production rate is 117.0, 94.8 and 37.9 μmol g−1catalyst min−1, under the irradiation of the full solar spectrum, visible-infrared light with wavelength above 420 nm, and infrared light with wavelength above 830 nm, respectively. This is attributed to the fact that the CeMnxOy/TiO2 nanocomposite efficiently transforms the absorbed solar energy into thermal energy, due to its strong absorption in the full solar spectrum region, resulting in a significant increase in its temperature above its light-off temperature, for the thermocatalytic oxidation of benzene.

Preparation of the Monolith of Hierarchical Macro-/Mesoporous Calcium Silicate Ultrathin Nanosheets with Low Thermal Conductivity by Means of Ambient-Pressure Drying

Calcium silicate monolith was prepared by the hydrothermal reaction of a slurry of SiO2 , calcium hydroxide, and surfactant (OP-10) obtained by high-energy ball milling, followed by drying at ambient pressure. By using this strategy, the shrinkage due to the collapse of pores during the drying of porous materials, which is a commonly observed phenomena, was successfully avoided. It has a unique microstructure of hierarchical macro-/mesoporous ultrathin calcium silicate nanosheets with a layered gyrolite crystalline structure. Very interestingly, the calcium silicate nanosheets can be peeled off to give a single-layer nanosheet (1.23 nm) of gyrolite by ultrasonication. The monolith has a low apparent density (0.073 g cm(-3) ) and low thermal conductivity (0.0399 W K(-1)  m(-1) ). The reasons behind why the formation of the unique hierarchical macro-/mesoporous ultrathin nanosheets avoids shrinkage during the hydrothermal reaction and drying, and considerably decreases the thermal conductivity, is discussed.

Efficient UV-vis-IR light-driven thermocatalytic purification of benzene on a Pt/CeO2 nanocomposite significantly promoted by hot electron-induced photoactivation

Complete oxidation of volatile organic compounds (VOCs) as major air pollutants on supported noble metal catalysts is a very important industrial reaction for environmental purification. It is highly desirable but greatly challenging to find a green process with low energy consumption and high catalytic efficiency for VOC abatement by using renewable solar energy. Here, we achieve highly efficient catalytic oxidation of benzene (one of the typical VOCs) on a nanocomposite of Pt nanoparticles partially confined in the mesopores of microsized mesoporous CeO2 (Pt/CeO2-MM) with the irradiation of full solar spectrum or visible-infrared light, even with infrared light irradiation. The highly efficient catalytic activity arises from the solar light-driven thermocatalysis on Pt/CeO2-MM due to the excellent thermocatalytic activity and the local heating effect induced by strong surface plasmonic absorption of the Pt nanoparticles in the entire solar spectrum region from 200 to 2500 nm. Remarkably, it is found that a novel hot electron-induced photoactivation process significantly enhances the solar light-driven thermocatalytic activity. In situ FTIR in the dark and with solar light irradiation reveals that the hot electron-induced photoactivation of benzene adsorbed on the Pt nanoparticles in Pt/CeO2-MM plays a decisive role in the catalytic enhancement.

Solar-light-driven CO2 reduction by methane on Pt nanocrystals partially embedded in mesoporous CeO2 nanorods with high light-to-fuel efficiency

A unique nanocomposite of Pt nanocrystals partially embedded in mesoporous CeO2 nanorods was prepared by a facile method. The nanocomposite exhibits highly efficient catalytic activity and very good durability for CO2 reduction by methane (CRM) under focused solar light. It produces very high fuel production rates of H2 and CO (5.7, 6.0 mmol min−1 g−1) with a very high light-to-fuel efficiency (η, 10.3%). Remarkably, even under the visible-infrared irradiation with wavelengths above 690 nm, it still exhibits efficient catalytic activity with a very high η (10.6%). Based on experimental evidence we demonstrate that the highly efficient catalytic activity arises from a novel efficient solar-light-driven thermocatalytic process of CRM on the nanocomposite. We find a synergetic effect between Pt nanoparticles as catalytically active sites and CeO2 in Pt/CeO2-MNR that significantly improves the catalytic activity and durability. We provide an insight into the synergetic effect based on the evidence of in situ FTIR and isotope labeling: the partial confinement of Pt nanocrystals in mesoporous CeO2 in Pt/CeO2-MNR makes the oxygen of CeO2 at the Pt/CeO2 interface more active due to the metal–support interaction. The active oxygen of CeO2 at the Pt/CeO2 interface not only directly participates in the dissociation of CH4 and the oxidation of the formed CHx species on CeO2, but also migrates through the reverse oxygen spillover to the surface of Pt nanoparticles and participates in the dissociation of CH4 and the oxidation of the formed CHx species on Pt nanoparticles. On the other hand, both the oxygen vacancies in ceria at the Pt/CeO2 interface formed by the oxidation of the CHx species and the Pt sites on the surface of Pt nanoparticles participate in the dissociation of CO2. Meanwhile, the chemisorbed oxygen on the surface of Pt nanoparticles formed by the dissociation of CO2 migrates through the oxygen spillover to ceria, where it replenishes the formed oxygen vacancies and participates in the oxidation of the CHx species on CeO2. The synergetic effect significantly improves the catalytic activity of Pt/CeO2 and inhibits the carbon deposition, thus considerably improving the durability.