Oxidative Conversion of PFC via Plasma Processing with Dielectric Barrier Discharges

Perfluorocompounds (PFCs) have been extensively used as plasma etching andchemical vapor deposition (CVD) gases for semiconductor manufacturingprocesses. PFCs have significant effects on the global warming and havevery long atmospheric lifetimes. Laboratory-scale experiments were performedto evaluate the effectiveness of CF4 conversion by using dielectric barrierdischarges (DBD). The results of this study revealed that the removalefficiency of CF₄ increased with application of higher voltage, gas residence time, oxygen content, and frequency. Combined plasma catalysis(CPC) is an innovative way for abatement of PFC and experimental results indicated that combining plasma with catalysts could effectively remove CF4. Products were analyzed by Fourier transform–infrared spectroscopy (FT–IR) and the major products of the CF4 processing with DBD were CO2, COF2, and CO, when O was included in the discharge process. Preliminary results indicated that as high as 65.9% of CF4 was decomposed with CPC operated at 15 kV, 240 Hz for the gas stream containing 300 ppmv CF₄,20% by volume O₂, and 40% by volume Ar, with N₂ as thecarrier gas.     

Spectroscopic Characterization of CH4 + CO2 Plasmas Excited by a Dielectric Barrier Discharge at Atmospheric Pressure

Plasma processing of a (CH ₄ +CO ₂ ) mixture can lead to the formation of synthesis gas (CO+H ₂ ). The use of a nonthermal plasma for this type of process seems very promising. We report here an electric and spectroscopic characteristic of plasma created in a (CH ₄ +CO ₂ ) mixture by a high-voltage, steep front-voltage (>10 ¹² V/s), very-short-pulse triggered dielectric barrier discharge in a tubular cell. Particular attention was payed to the determination of the rotational temperature for C ₂ . Time resolved investigation of the Swan band leads to an estimated value around 3000 K.     

A parametric study of CO2/N2 gas separation membrane processes for post-combustion capture

Capture of CO₂ from flue gases produced by the combustion of fossil fuels and biomass in air is referred to as post-combustion capture. Chemisorbent processes are considered to be the most feasible method and are already at an advanced stage of development, but gas separation membranes are attracting more and more attention as a possible alternative. This paper describes a detailed parametric study of mass and energy balances for a simulated single membrane process. Typical operating conditions (CO₂ concentration in the flue gas, pressure and temperature, etc.) together with the influence of the membrane quality (permeability, selectivity) and membrane area on membrane performance (CO₂ separation degree and CO₂ purity) are simulated over a wide range of parameters.     

Synthesis and Characterization of TiO2/YFeO3 and Its Photocatalytic Oxidation of Gaseous Benzene

YFeO₃ was prepared by coprecipitation method and citric acid method, and TiO₂/YFeO₃ heterosystem photocatalysts were synthesized by loading TiO₂ sol on the surface of YFeO₃via sol-gel method. Their photocatalytic activities were evaluated by the decomposition of gaseous benzene under UV light illumination. The prepared photocatalysts were characterized by nitrogen adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy. Results revealed that the heterosystem photocatalysts prepared by coprecipitation method showed higher activity, and the maximum conversion of benzene could reach 44.7% within 180 min. The YFeO₃ samples prepared from coprecipitation method and citric acid method were absolutely in orthorhombic phase. The deposited titania was dispersed on the surface of carrier and a certain interaction existed between TiO₂ and YFeO₃. The two heterosystems photocatalysts had narrow band-gap energies.     

CuO-CeO_2的固相反应法制备及其催化CO低温氧化性能

采用固相化学反应法制备了一系列CuO-CeO_2催化剂,并用X-射线衍射(XRD)、程序升温还原(H_2-TPR)和氮吸附等技术对样品进行了表征,利用微反-色谱装置考察了其催化CO低温氧化反应的活性,研究了CuO含量和催化剂焙烧温度对CuO-CeO_2催化活性的影响。结果表明,随着CuO含量的增加,CuO-CeO_2的催化活性提高,至不小于15%时达到稳定;随焙烧温度的升高,CuO-CeO_2的催化活性先提高,至650℃时达到最大,之后又降低。CuO-CeO_2的催化活性与其CuO的还原性之间有较好的对应关系。     

制备方法对CuO/CeO_2-ZrO_2催化CO低温氧化活性的影响

采用微波加热分解法(一步法)和微波加热处理共沉淀+浸渍法(两步法)制备了CuO/CeO2-ZrO2催化剂,并对其进行了X射线衍射、低温氮气吸附/脱附和程序升温还原等表征,采用色谱流动法考察了催化剂的催化CO低温氧化性能.结果表明,一步法比两步法更有利于使催化剂表面CuO高度分散,CuO与CeO2-ZrO2间的相互作用更强,CuO更容易被还原,从而具有更高的催化CO氧化活性.与CeO2-ZrO2有相互作用的高分散和小颗粒CuO有利于催化剂活性的提高,与CeO2-ZrO2无相互作用的大颗粒CuO对催化剂的活性有抑制作用.     

Oxidation of Dilute Benzene in an Alumina Hybrid Plasma Reactor at Atmospheric Pressure

The combination of plasma discharge and adsorption was examined for oxidation of dilute benzene in air in a plasma reactor packed with a mixture of BaTiO ₃ pellets and porous Al ₂ O ₃ pellets (i.e., an alumina hybrid reactor). The oxidative decomposition of benzene was enhanced by the benzene concentrating on the Al ₂ O ₃ pellets. Furthermore, there was a higher selectivity to CO ₂ in the products from the hybrid than from a plasma reactor packed with BaTiO ₃ pellets alone. The presence of the Al ₂ O ₃ pellets suppressed the formation of N ₂ O.     

Gas-phase and On-surface Chemical Reduction of CO2 to HCHO and CO under Dielectric Barrier Discharge

Selective chemical reduction of CO_2(g) (with carrier Ar) in presence of organic compounds, either mixed in the gas-phase or present as a contact surface, under Dielectric Barrier Discharge is presented in this study. Along with gas-phase CO generation, added hydrocarbons (C _n H _2n+x ; n = 6–12; x = 0 or 2) resulted in HCHO production with the maximum H-atom utilization efficiency being ∼15% of the total present. Product CO and HCHO were estimated separately by pre-concentration in specific absorber solutions followed by their discrete colorimetric measurements. On the other hand, in presence of various types of organic surfaces (e.g. wax, plastics and polymers, also acting simultaneously as a dielectric barrier), it was found that while CO could be estimated as above, in the ensuing chemical conversion, product HCHO was retained on these surfaces. On leaching the HCHO into the absorber solution, its production efficiency was estimated to be ∼5% of CO₂.     

CO Oxidation on Cu/MgO-SiO2 Sol-Gel Derived Catalysts

Sol-gel Cu//MgOSiO₂ catalysts were prepared gelling tetraethoxysilane (TEOS), magnesium ethoxide and copper acetylacetonate at pH 3 and pH 9. The catalysts shown specific surface areas ca. 500 m²/g and 140 m²/g for pH 9 and pH 3 preparations respectively. Si(OH) and Si(OH)₂ hydroxy groups were observed by MAS-RMN spectroscopy in both preparations. CO₂-TPD and NH₃-TPD desorption thermograms showed that acid and basic sites were formed on the catalysts surface. It has been found that the catalysts having the highest density of basic sites were the catalysts showing the highest activity for the CO oxidation. It is proposed that the catalytic activity depends of the relative Cu⁼¹/Cu⁼² stability given by the support acidity.     

CARS Diagnostic and Modeling of a Dielectric Barrier Discharge

Dielectric barrier discharges (DBD) with planar- and knife-shaped electrodes are operated in N₂O₂NO mixtures under a pressure of 20 and 98 kPa. They are excited by means of consecutive unipolar or bipolar high-voltage pulse packages of 10 kV at a pulse repetition rate of 1 and 2 kHz. The rotational and vibrational excitation of N ₂ molecules and the reduction of nitric oxide (NO) in the discharge have been investigated using coherent anti-Stokes Raman scattering (CARS) technique. Rotational (gas) temperatures near the room temperature and vibrational temperatures of about 800 K at atmospheric pressure and 1400 K at a pressure of 20 kPa are observed. Therefore, chemical reactions of NO with vibrationally excited N ₂ are probably insignificant. One-dimensional kinetic models are developed that balance 35 chemical reactions between 10 species and deliver equations for the population density of excited vibrational levels of N ₂ together with a solution of the Boltzmann equation for the electrons. A good agreement between measured vibrational temperatures of N ₂ , the concentration of NO, and calculated data is achieved. Modeling of the plasma discharge verifies that a DBD operated with a N₂NO mixture reduces the NO content, the simultaneous presence of O ₂ , already 1%, is enough to prevent the NO reduction.     

Roles of Oxygen Vacancies of CeO2 and Mn-Doped CeO2 with the Same Morphology in Benzene Catalytic Oxidation

Mn-doped CeO₂ and CeO₂ with the same morphology (nanofiber and nanocube) have been synthesized through hydrothermal method. When applied to benzene oxidation, the catalytic performance of Mn-doped CeO₂ is better than that of CeO₂, due to the difference of the concentration of O vacancy. Compared to CeO₂ with the same morphology, more oxygen vacancies were generated on the surface of Mn-doped CeO₂, due to the replacement of Ce ion with Mn ion. The lattice replacement has been analyzed through XRD, Raman, electron energy loss spectroscopy and electron paramagnetic resonance technology. The formation energies of oxygen vacancy on the different exposed crystal planes such as (110) and (100) for Mn-doped CeO₂ were calculated by the density functional theory (DFT). The results show that the oxygen vacancy is easier to be formed on the (110) plane. Other factors influencing catalytic behavior have also been investigated, indicating that the surface oxygen vacancy plays a crucial role in catalytic reaction.     

Ni Oxidation State and Ligand Saturation Impact on the Capability of Octaazamacrocyclic Complexes to Bind and Reduce CO2

Two 15-membered octaazamacrocyclic nickel(II) complexes are investigated by theoretical methods to shed light on their affinity forwards binding and reducing CO₂. In the first complex ¹[Ni^IIL]⁰, the octaazamacrocyclic ligand is grossly unsaturated (π-conjugated), while in the second ¹[Ni^IILH]²⁺ one, the macrocycle is saturated with hydrogens. One and two-electron reductions are described using Mulliken population analysis, quantum theory of atoms in molecules, localized orbitals, and domain averaged fermi holes, including the characterization of the Ni-C_CO2 bond and the oxidation state of the central Ni atom. It was found that in the [NiLH] complex, the central atom is reduced to Ni⁰ and/or Ni^I and is thus able to bind CO₂ via a single σ bond. In addition, the two-electron reduced ³[NiL]²⁻ species also shows an affinity forwards CO₂.     

铝掺杂对铜铈复合氧化物催化一氧化碳氧化性能的影响

以金属硝酸盐为原料、碳酸钠为沉淀剂,采用共沉淀法制备了一系列Cu0.1Ce0.9-xAlxOy复合氧化物催化剂,并用低温氮气吸附/脱附、X-射线衍射(XRD)和氢-程序升温还原(H2-TPR)等对样品进行了表征,利用微反-色谱评价装置考察了催化剂对CO低温氧化反应的活性,研究了Al含量(x=0～0.3)和催化剂焙烧温度(350、500和650℃)对Cu0.1Ce0.9-xAxOy催化活性的影响。结果表明,随着催化剂中Al含量(x)的增加,Cu0.1Ce0.9-xAlxOy的催化活性先提高,至x=0.1时达到最大,之后又逐渐降低;当催化剂的焙烧温度为500℃时,Cu0.1Ce0.8Al0.1Oy的催化活性最大。Cu0.1Ce0.9-xAlxOy的催化活性与其CuO的还原性之间有较好的对应关系。     

xAu/α-MnO2催化剂的结构及催化氧化VOCs气体性能

以NaOH为沉淀剂,采用沉积-沉淀法制备了α-MnO2负载Au催化剂xAu/α-MnO2(x=1.0%～7.0%,质量分数),利用X射线衍射(XRD)、N2吸附-脱附、H2程序升温还原(H2-TPR)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等技术对所得样品进行了表征,并对其催化氧化挥发性有机化合物(VOCs,苯和甲苯)的性能进行了研究.XRD结果表明,负载Au对α-MnO2载体结构影响不大,但对其晶粒大小和比表面积略有影响.随着Au含量的增加,α-MnO2结晶度增强,颗粒增大,Au粒径明显增大.XPS结果表明,随着Au负载量的增加,xAu/α-MnO2的晶格氧(O2-),Mn4+和Au3+的浓度增加.H2-TPR结果表明,由于贵金属的溢氢作用,Au明显提升了xAu/α-MnO2的还原能力,其中3%Au/α-MnO2的还原能力最强.负载Au明显影响xAu/α-MnO2的催化性能,xAu/α-MnO2的催化性能与Au的颗粒分散性、低温还原性能及表面氧物种密切相关,其中3%Au/α-MnO2显示出最佳活性,其催化氧化苯和甲苯的T100分别为280和250℃.     

Influence of ZrO2 on Carbon Monoxide Oxidation Over Pd/Al2O3

The influence of ZrO₂ on the properties of Al₂O₃ and performances of Pd/Al₂O₃ catalyst in CO oxidation have been investigated. TPD results show that the activity enhanced is due to the increase of the adsorptive capacity of CO and the activation of C=O bond after the introduction of ZrO₂.     

陈化温度和pH值对氨基功能化介孔氧化硅吸附CO_2性能的影响

本研究采用溶胶-凝胶法,分别以十二烷基肌氨酸钠、氨丙基三甲氧基硅烷(APTMS)和正硅酸乙酯(TEOS)为结构导向剂(SDA)、共结构导向剂(CSDA)和硅源合成了氨基功能化的介孔氧化硅预产物。利用乙醇和乙醇胺混合液对预产物进行萃取后获得氨基功能化介孔氧化硅。利用红外光谱、元素分析、N2吸-脱附、透射电镜等手段对材料进行了表征。红外光谱结果证明通过萃取方法可较好地去除表面活性剂;N2吸附结果表明所有样品都具有介孔结构;元素分析和透射电镜结果说明反应陈化温度、pH值等合成条件对材料孔道内表面的氨基含量和材料结构有较大的影响。CO2吸附实验证明在低陈化温度、相对较低的pH值下合成的材料具有较高的CO2吸附量。     

焙烧温度对Mn/Al2O3-TiO2催化剂结构及氧化NO性能的影响

采用溶胶凝胶法和浸渍法制备10% Mn/Al₂O₃-TiO₂催化剂,借助TPO、XRD、O₂-TPD、Raman、XPS等手段,考察焙烧温度(450~650 ℃)对催化剂结构以及氧化NO性能的影响。TPO结果表明催化剂活性随焙烧温度的升高先增后减,其中焙烧温度为550 ℃时催化剂活性最好。XPS结果显示随着焙烧温度的升高(450~550 ℃),催化剂表面Mn³⁺的含量逐渐升高,与催化剂活性的强弱成对应关系,并且催化剂晶格氧含量下降,而表面化学吸附氧从40.9%增加到64.8%。Raman分析显示550 ℃焙烧时,催化剂表面存在丰富的Mn₂O₃活性物种,并且O₂-TPD分析也表明随着焙烧温度的升高,晶格氧向表面化学吸附氧流动,提高了化学吸附态氧物种的含量。这些结果表明Mn₂O₃可能是NO氧化起主要作用的活性Mn物种,释放更多的表面化学吸附氧物种,将有助于促进NO的催化氧化。     

焙烧温度对Mn/Al2O3-TiO2催化剂结构及氧化NO性能的影响

采用溶胶凝胶法和浸渍法制备10%Mn/Al_2O_3-TiO_2催化剂,借助TPO、XRD、O_2-TPD、Raman、XPS等手段,考察焙烧温度(450~650℃)对催化剂结构以及氧化NO性能的影响。TPO结果表明催化剂活性随焙烧温度的升高先增后减,其中焙烧温度为550℃时催化剂活性最好。XPS结果显示随着焙烧温度的升高(450~550℃),催化剂表面Mn~(3+)的含量逐渐升高,与催化剂活性的强弱成对应关系,并且催化剂晶格氧含量下降,而表面化学吸附氧从40.9%增加到64.8%。Raman分析显示550℃焙烧时,催化剂表面存在丰富的Mn_2O_3活性物种,并且O_2-TPD分析也表明随着焙烧温度的升高,晶格氧向表面化学吸附氧流动,提高了化学吸附态氧物种的含量。这些结果表明Mn_2O_3可能是NO氧化起主要作用的活性Mn物种,释放更多的表面化学吸附氧物种,将有助于促进NO的催化氧化。     

Selectivity of the cyclic carbonate formation by fixation of carbon dioxide into epoxides catalyzed by Lewis bases

Cyclic carbonate and polycarbonate have been selectively obtained with good conversion by coupling carbon dioxide with diglycidylether of bisphenol A. The ruthenium trichloride supported on tetraethylammonium bromide and polyphosphotungstic acid has been found active and selective to produce the corresponding monomeric and polymeric carbonates. These catalysts can be recycled keeping their high product conversion and selectivity. The heteropolyacid itself showed high activity also under supercritical CO₂ conditions to yield polycarbonate.     

Pt/MOx(M=Ni,Fe,Co,Ce)催化剂上CO氧化反应中抗H2O与CO2的性能研究

我们研究了4种负载型Pt催化剂（1Pt/NiO、1Pt/FeO_x、1Pt/Co₃O₄和Pt/CeO₂）上不同反应条件下CO氧化活性及抗H₂O和CO₂性能.发现反应气氛中CO₂的加入与CO形成了竞争吸附,并在催化剂表面形成了碳酸盐物种堵塞了活性位,从而导致催化剂失活.反应气氛中H₂O的加入对1Pt/CeO₂催化剂的活性有所抑制,但对1Pt/FeO_x、1Pt/NiO和1Pt/Co₃O₄催化剂的活性却有促进作用.在1Pt/FeO_x和1Pt/CeO₂催化剂上的分步反应实验和动力学研究表明,尽管H₂O的加入在两种催化剂上均与CO形成了竞争吸附,但在1Pt/FeO_x催化剂上H₂O在载体表面解离形成的羟基更易与CO反应,开辟了新的反应途径,从而提高了反应性能.此外,H₂O的加入能有效分解该催化剂上的碳酸盐物种,从而保持了其稳定性.