Shengpeng Mo

Excellent low temperature performance for total benzene oxidation over mesoporous CoMnAl composited oxides from hydrotalcites

Mesoporous CoMnAl mixed metal oxide catalysts with various Co/Mn atomic ratios have been obtained by calcination at 450 °C of layered double hydroxide (LDH) precursors prepared by the NH4OH co-precipitation–hydrothermal method without distinct MnCO3 peaks. The catalysts exhibited high efficiency for total oxidation of volatile organic compounds (VOCs). The physicochemical properties of the catalysts were characterized using several analytical techniques. Among them, CoMn2AlO shows the optimal activity and the temperature required to achieve a benzene conversion of 90% (T90) was about 238 °C, with a reaction rate and activity energy (Ea) of 0.24 mmol gcat−1 h−1 and 65.77 kJ mol−1 respectively. This temperature was 47 °C lower than that on the Co3AlO sample with a lower reaction rate of 0.19 mmol gcat−1 h−1 and a higher Ea 130.31 kJ mol−1 at a high space velocity (SV = 60 000 mL g−1 h−1). The effects of calcination temperature on the textural properties and catalytic activity of the CoMn2AlO catalyst were further investigated. The as-prepared CoMn2AlO-550 sample displayed superior catalytic activity, with T90 at 208 °C, compared CoMn2AlO-450. The formation of a solid solution with high surface area, rich oxygen vacancies, high Mn4+/Mn3+ and Co3+/Co2+ ratios and low-temperature reducibility made a great contribution to the significant improvement of the catalytic activity.

Determination of time- and size-dependent fine particle emission with varied oil heating in an experimental kitchen

Particulate matter (PM) from cooking has caused seriously indoor air pollutant and aroused risk to human health. It is urged to get deep knowledge of their spatial-temporal distribution of source emission characteristics, especially ultrafine particles (UFP<100nm) and accumulation mode particles (AMP 100-665nm). Four commercial cooking oils are auto dipped water to simulate cooking fume under heating to 265°C to investigate PM emission and decay features between 0.03 and 10μm size dimension by electrical low pressure impactor (ELPI) without ventilation. Rapeseed and sunflower produced high PM2.5 around 6.1mg/m3, in comparison with those of soybean and corn (5.87 and 4.65mg/m3, respectively) at peak emission time between 340 and 460sec since heating oil, but with the same level of particle numbers 6-9×105/cm3. Mean values of PM1.0/PM2.5 and PM2.5/PM10 at peak emission time are around 0.51-0.66 and 0.23-0.29. After 15min naturally deposition, decay rates of PM1.0, PM2.5 and PM10 are 13.3%-29.8%, 20.1%-33.9% and 41.2%-54.7%, which manifest that PM1.0 is quite hard to decay than larger particles, PM2.5 and PM10. The majority of the particle emission locates at 43nm with the largest decay rate at 75%, and shifts to a larger size between 137 and 655nm after 15min decay. The decay rates of the particles are sensitive to the oil type.

General Synthesis of Transition‐Metal Oxide Hollow Nanospheres/Nitrogen‐Doped Graphene Hybrids by Metal–Ammine Complex Chemistry for High‐Performance Lithium‐Ion Batteries

We present a general and facile synthesis strategy, on the basis of metal-ammine complex chemistry, for synthesizing hollow transition-metal oxides (Co3 O4 , NiO, CuO-Cu2 O, and ZnO)/nitrogen-doped graphene hybrids, potentially applied in high-performance lithium-ion batteries. The oxygen-containing functional groups of graphene oxide play a prerequisite role in the formation of hollow transition-metal oxides on graphene nanosheets, and a significant hollowing process occurs only when forming metal (Co2+ , Ni2+ , Cu2+ , or Zn2+ )-ammine complex ions. Moreover, the hollowing process is well correlated with the complexing capacity between metal ions and NH3 molecules. The significant hollowing process occurs for strong metal-ammine complex ions including Co2+ , Ni2+ , Cu2+ , and Zn2+ ions, and no hollow structures formed for weak and/or noncomplex Mn2+ and Fe3+ ions. Simultaneously, this novel strategy can also achieve the direct doping of nitrogen atoms into the graphene framework. The electrochemical performance of two typical hollow Co3 O4 or NiO/nitrogen-doped graphene hybrids was evaluated by their use as anodic materials. It was demonstrated that these unique nanostructured hybrids, in contrast with the bare counterparts, solid transition-metal oxides/nitrogen-doped graphene hybrids, perform with significantly improved specific capacity, superior rate capability, and excellent capacity retention.

Promoted VOC oxidation over homogeneous porous CoxNiAlO composite oxides derived from hydrotalcites: effect of preparation method and doping

Homogeneous porous and curve plated CoxNiAlO composite metal oxide catalysts are obtained from the thermal decomposition of CoxNiAl-layered double hydroxide (LDH) precursors, which are prepared by urea co-precipitation with surfactant, followed by a hydrothermal treatment. The as-prepared samples were characterized by XRD, BET, SEM, TEM, H2-TPR and XPS. The Co3AlO sample shows 90% benzene conversion (T90) at 236 °C at a high space velocity (SV = 60000 mL g−1 h−1), and possesses much higher activity than Co3AlO prepared with NaOH co-precipitation without surfactant, with T90 = 288 °C. This is mainly correlated with the narrower pore size (2.9 vs. 17.2 nm) and lower temperature reducibility (319 vs. 360 °C). The Co2NiAlO sample exhibits enhanced activity at T90 = 227 °C with the low activation energy of 39.0 kJ mol−1, and its lower temperature reducibility is ascribed to the larger amount of surface accessible Co3+. The Co2NiAlO sample owns good reproducibility and superior reversibility and long stability with prolonged time on benzene stream in the presence of 3.5% water vapor. Moreover, a monolithic Co2NiAlO film catalyst is fabricated by the thermal decomposition of an LDH film precursor through an in situ growth methodology, with a high reaction rate of 1.21 mmol g−1 h−1 under T90 = 275 °C.

Low-temperature CO oxidation over integrated penthorum chinense-like MnCo2O4 arrays anchored on three-dimensional Ni foam with enhanced moisture resistance

Advanced integrated nanoarray (NA) catalysts have been designed by growing metal-doped Co3O4 arrays on nickel foam with robust adhesion. Ternary MCo2O4 NA catalysts were prepared by doping urchin-like Co3O4 with different transition metals (Cu2+, Mn2+, Fe2+, Ni2+, Zn2+, Fe3+ and Al3+). These catalysts exhibited novel morphologies and can be directly applied as monolithic materials for CO oxidation. Among the MCo2O4 NA catalysts, CuCo2O4 nanoneedles manifested the highest catalytic activity in dry air, achieving an efficient 100% CO oxidation conversion of 20 000 h−1 at 146 °C, due to its reducibility at lower temperature, lattice distortion of the spinel structure, and abundant surface-adsorbed oxygen (Oads). The doped catalytic systems were further optimized by controlling the volume ratio of reactive components in the mixed solvent, the Cu or Mn contents to determine excellent catalysts for direct application to CO oxidation at 1.0 vol% moisture. Penthorum chinense-like MnCo2O4 NAs showed optimal catalytic performance at 1 vol% moisture (T100 = 175 °C), with activity higher than that of the CuCo2O4 NA catalyst, indicating that the synergistic effect between MnOx and Co3O4 improved the moisture resistance and stability. It was concluded that the moisture resistance provided by introducing active sites on Co-based catalysts decreased as follows: Mn sites > Co sites > Cu sites > Ni sites. MCo2O4 NAs, with predominantly exposed {110} surfaces, showed higher catalytic activity than catalysts with exposed {111} surfaces. This study suggests that the as-prepared MnCo2O4 NAs anchored on 3D Ni foam with remarkable moisture resistance have potential applications in CO oxidation.

Vertically-aligned Co3O4 arrays on Ni foam as monolithic structured catalysts for CO oxidation: effects of morphological transformation

A generic hydrothermal synthesis route has been successfully designed and utilized to in situ grow highly ordered Co3O4 nanoarray (NA) precursors on Ni substrates, forming a series of Co3O4 nanoarray-based monolithic catalysts with subsequent calcination. The morphology evolution of Co3O4 nanostructures which depends upon the reaction time, with and without CTAB or NH4F is investigated in detail, which is used to further demonstrate the growth mechanism of Co3O4 nanoarrays with different morphologies. CO is chosen as a probe molecule to evaluate the catalytic performance over the synthesized Co-based oxide catalysts, and the effect of morphological transformation on the catalytic activity is further confirmed via using TEM, H2-TPR, XPS, Raman spectroscopy and in situ Raman spectroscopy. As a proof of concept application, core-shell Co3O4 NAs-8 presenting hierarchical nanosheets@nanoneedle arrays with a low density of nanoneedles exhibits the highest catalytic activity and long-term stability due to its low-temperature reducibility, the lattice distortion of the spinel structure and the abundance of surface-adsorbed oxygen (Oads). It is confirmed that CO oxidation on the surface of Co3O4 can proceed through the Langmuir-Hinshelwood mechanism via using in situ Raman spectroscopy. It is expected that the in situ synthesis of well-defined Co3O4 monolithic catalysts can be extended to the development of environmentally-friendly and highly active integral materials for practical industrial catalysis.

Integrated Cobalt Oxide Based Nanoarray Catalysts with Hierarchical Architectures: In Situ Raman Spectroscopy Investigation on the Carbon Monoxide Reaction Mechanism

Herein, a facile strategy for the in situ growth of a Co3O4‐based precursor with unique hierarchical architectures oriented diagonal or perpendicular to Ni surfaces is reported. This strategy to prepare grafted ZIF‐67@Co3O4 and MOF‐199@Co3O4 precursor structures is based on a simple hydrothermal synthesis method to obtain the Co3O4 precursor and the subsequent in situ growth of ZIF‐67 and MOF‐199, respectively. The morphologies of the Co3O4 products can be tailored by controlling the solvent polarity and concentration of precipitants. CO is chosen as a probe molecule to evaluate the catalytic performance of the as‐synthesized Co3O4‐based oxide catalysts, and the structure–activity relationships are confirmed by using TEM, H2 temperature‐programmed reduction, X‐ray photoelectron spectroscopy, Raman spectroscopy and in situ Raman spectroscopy, and extended X‐ray absorption fine structure analysis. These analysis results demonstrate that irislike Co3O4 exhibits a high catalytic activity for CO oxidation and contains an abundance of surface defect sites (Co3+ species) to result in an excellent low‐temperature reducibility, oxygen vacancies and unsaturated chemical bonds on the surface. Moreover, we used in situ Raman spectroscopy to record the structural transformation of Co3O4 directly during the reaction, which confirmed that CO oxidation on the surface of Co3O4 can proceed through the Langmuir–Hinshelwood mechanism (<200 °C) and the Mars–van Krevelen mechanism (>200 °C).