Chuanwen Zhao

Low temperature CO catalytic oxidation and kinetic performances of KOH–Hopcalite in the presence of CO2

Catalytic removal of CO from fire smoke is critical to ensure human safety and post-fire atmospheric recovery in typical confined spaces. Copper manganese oxide compounds show promise as highly efficient catalysts for low temperature CO oxidation. However, the CO oxidation activity will be affected when the catalyst is applied in fire smoke containing high-concentration CO2. In this work, a bi-functional catalyst of KOH–Hopcalite is synthesized by impregnation of KOH on Hopcalite (copper manganese oxides mixture) precursor. The catalyst is characterized by N2 adsorption–desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). CO oxidation activity and long-term working stability of the precursor and catalyst in the presence of CO2 are investigated. CO oxidation activity of the precursor would decrease when CO2 is present. KOH modification can mitigate the inhibiting effect of CO2 on CO oxidation activity of the precursor. Reaction mechanisms and kinetic performances of the catalyst in the presence of CO2 are also demonstrated. The catalyst could be potentially utilized as a scavenging agent for post-fire cleanup and atmospheric recovery in confined spaces.

Copper Manganese Oxides Supported on Multi-Walled Carbon Nanotubes as an Efficient Catalyst for Low Temperature CO Oxidation

Multi-walled carbon nanotubes (MWCNTs) with unique properties are finding increasing utility in catalytic applications. In this work, Cu–Mn@MWCNTs (copper manganese oxides supported on MWCNTs) was synthesized as an efficient catalyst for low temperature CO oxidation. The catalyst was characterized by N2 adsorption–desorption, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The CO oxidation activity and long-term working stability of the catalyst were evaluated in 0.1–0.5u2009% CO and balanced air using a modified fixed-bed reactor. The effects of CO concentration and Cu/Mn molar ratio on the CO oxidation performances were also demonstrated. The increasing CO concentration (0.1–0.5u2009%) will impair the CO oxidation performances due to the covering of active sites and formation of carbonates and/or hydroxyl species. The increased CO oxidation activity with the changing Cu/Mn molar ratio (1:8–1:1) is ascribed to the improving oxygen utilization in the redox process by increasing Cu content. The synergistic interaction within the Cu–Mn bimetallic catalytic system and the unique properties of the MWCNTs support are also highlighted for the enhanced CO oxidation activity. The catalyst could be considered as a promising option for removing trace CO from typical confined spaces such as space-crafts, submarines and mine refuge chambers.Graphical Abstract

Typical Gaseous Semi-Volatile Metals Adsorption by Meta-Kaolinite: A DFT Study

Kaolinite can be used as in-furnace adsorbent to capture gaseous semi-volatile metals during combustion, incineration, or gasification processes for the purposes of toxic metals emission control, ash deposition/slagging/corrosion inhibition, ultrafine particulate matter emission control, and so on. In this work, the adsorptions of typical heavy metals (Pb and Cd) and typical alkali metals (Na and K) by meta-kaolinite were investigated by the DFT calculation. The adsorption energies followed the sequence of NaOH-Si surface > KOH-Si surface > PbO-Al surface ≈ CdO-Al surface ≈ NaOH-Al surface > KOH-Al surface > NaCl-Al surface ≈ Na-Si surface > Na-Al surface > KCl-Al surface > Pb-Al surface > PbCl2-Al surface > CdCl2-Al surface ≈ K-Si surface ≈ PbCl-Al surface > K-Al surface > CdCl-Al surface > NaCl-Si surface > KCl-Si surface > Cd-Al surface. Si surface was found available to the adsorptions of Na, K, and their compounds, although it was invalid to the adsorptions of Pb, Cd, and their compounds. The interactions between adsorbates and surfaces were revealed. Furthermore, the discussion of combining with the experimental data was applied to the subject validity of calculation results and the effect of chlorine on adsorption and the effect of reducing atmosphere on adsorption.

Reaction characteristics of KOH-modified copper manganese oxides catalysts for low-temperature CO oxidation in the presence of CO2

Binary copper manganese oxides catalysts supported on different activated carbons were prepared using the co-precipitation and high-pressure impregnation methods. The catalysts were further modified by KOH to mitigate the adverse effect of CO2 on their CO oxidation performances. The as-synthesized catalysts were characterized by N2 adsorption–desorption, X-ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The effects of support and synthesis method, CO concentration, CO2 concentration, gas hourly space velocity (GHSV), and particle size on CO oxidation performances of the catalysts were investigated. The nature of the different activated carbon supports showed no significant effect on their CO oxidation performances. By contrast, the high-pressure impregnation method was conducive to more effective loading and uniform dispersion of the active components on the support and therefore to benefit the catalyst enhanced CO oxidation performances. Under the given experimental conditions, CO oxidation conversion decreased with the increase of CO concentration, CO2 concentration, GHSV, and particle diameter.

Hydrodynamic Study of a Gas–liquid–solid Bubble Column Employing CFD–BPBM Method

Abstract The computational fluid dynamics – bubble population balance model (CFD–BPBM) was employed to predict the hydrodynamic characteristics of a gas–liquid–solid bubble column. A 3D time dependent numerical study was performed and the bubble size distributions at the conditions of different superficial gas velocity (0.089u2006m/s–0.22u2006m/s), solid volume fraction (0.03–0.30) and particle density (2500u2006kg/m3–4800u2006kg/m3) in the three–phase system were investigated, and the simulation results were compared with the experimental results. The bubble diameters ranging from 1u2006mm to 64u2006mm were divided into ten classes. The predicted pressure changing with the bed height had a good agreemeet with the experimental result. The bubble number density predicted decreased when the bubble size increased at each superficial gas velocity, and the bubble coalescence rate became greater than the breakup rate when Ug shifted from 0.089u2006m/s to 0.16u2006m/s. The bubble interaction was similar at 0.16u2006m/s and 0.22u2006m/s both at particle size dp = 75u2006μm and 150u2006μm. The bubble size corresponding to the maximum of the bubble volume fraction increased as Ug increased. The particles can make the bubble break up and coalesce simultaneously when the solid volume fraction was larger than 0.20, and therefore the particles had a contribution to both of the bubble coalescence and breakup in the bubble coalescence regime (Ug = 0.16u2006m/s). The effect of the particle density was similar with that of the solid volume fraction. Increasing the particle density can enhance the breakup rate of the large bubbles.