Volatile organic compounds (VOCs) removal over dual functional adsorbent/catalyst system

This study is focused on the elimination of tetrachloroethylene (PCE) and methylethylketone (MEK) by adsorption/catalytic oxidation in humid conditions using zeolites as adsorbent and catalyst. Adsorption experiments have led to the conclusion that HFAU(17) zeolite was a very efficient adsorbent for the removal of PCE and MEK. Furthermore, complete transformation of PCE into CO₂ and HCl was achieved at 500 °C over 1.2%Pt/HFAU(5). MEK was completely converted into CO₂ at 220 °C over 1%Pt/NaX, without formation of CO. Formation of coke occurs during MEK oxidation reaction, especially over acid catalyst, and at low reaction temperature. Furthermore, it was pointed out that water has a negative effect on MEK conversion. Lastly, adsorption/catalytic oxidation of PCE and MEK was performed over a dual functional HFAU(17)-Pt/FAU adsorbent/catalyst system. The adsorption step was performed at 30 °C with an HFAU(17) adsorbent, and the oxidation step was carried out at 450 °C for PCE with 1.2%PtHFAU(5), and at 250 °C for MEK transformation with 1%PtNaX. It appeared that the adsorbent-catalyst couple remains efficient for MEK transformation during successive adsorption/oxidation cycles.     

Low-temperature catalytic combustion of trichloroethylene over cerium oxide and catalyst deactivation

Cerium oxide catalysts prepared by a thermal decomposition method using the salt nitrate as precursor were tested for the catalytic combustion of trichloroethlyene (TCE), as a model of chlorinated volatile organic compounds (CVOCs). CeO₂ catalysts calcined at different temperature were found to possess high catalytic activity for catalytic combustion of TCE, and CeO₂ calcined at 550 °C was the most active catalyst and the complete combustion temperature (T_90%) of TCE was 205 °C. Effects of systematic variation of reaction conditions, including space velocity, inlet TCE concentration and water concentration on TCE catalytic combustion were investigated. Additionally, the stability and deactivation of CeO₂ catalysts were studied by various characterization methods (such as TG/DTA, EDS, XRD, Raman and XPS) and other assistant experiments.     

Dehydrodimerization of Isobutene to 2,5‐Dimethyl‐1,5‐Hexadiene over Bismuth‐(III)‐Oxide and Various Additives

Bi₂O₃ and mixtures with different additives (Cr₂O₃, MoO₃, NH₄VO₃, SnO₂, and V₂O₅) have been chosen to study the oxidative dehydrodimerization of isobutene. The catalytic performances were investigated by variation of the residence time, isobutene to oxygen molar ratio, and pressure. The best results for 2,5‐dimethyl‐1,5‐hexadiene (DMH) yield (13 %) were achieved with Bi₂O₃ as the catalyst. The selectivity of DMH reaches values of over 90 %.     

改性镧系钙钛矿催化剂强化挥发性有机物催化氧化的研究进展

钙钛矿因其结构稳定并具有优异的物化性质,近年来在催化剂方面的应用受到了广泛关注。本文综述了采用不同方法对镧系钙钛矿进行改性来增强催化剂的活性、抗毒性、稳定性和选择性的研究进展;分析了镧系钙钛矿的结构、表面参数、活性氧和低温还原性对于挥发性有机物转化效率的影响,重点阐述了通过优选钙钛矿的制备方法、制备负载型钙钛矿和掺杂型钙钛矿等改性方法来提高镧系钙钛矿催化剂的性能,由此展望了未来改性镧系钙钛矿催化剂的研究方向：采用非金属元素掺杂或多种强化方法结合制备高效催化剂、利用催化燃烧协同光催化氧化转化挥发性有机物、进一步通过实验和仿真模拟制备理想钙钛矿催化剂催化氧化多种挥发性有机物混合物以满足工业化需求。     

Catalytic oxidation of volatile organic compounds (VOCs) mixture (isopropanol/o-xylene) on zeolite catalysts

The catalytic oxidation of isopropanol and o-xylene alone and in mixture was investigated over basic zeolites (CsX and NaX) and an acidic zeolite (HY). For a given temperature, the conversion of VOCs mixture into CO₂ increases with the basicity of the zeolite. Results show that VOCs are oxidized through a basic mechanism over NaX, and through an acidic mechanism over HY. Over HY, the presence of isopropanol increases the oxidation of o-xylene, probably because of the formation of isopropyldimethylbenzenes obtained via an acidic mechanism. The addition of platinum over zeolites increases the rate of the VOCs oxidation, this behavior being more pronounced over PtHY maybe because of a higher Pt dispersion.     

Aerobic degradation by white‐rot fungi of trichloroethylene (TCE) and mixtures of TCE and perchloroethylene (PCE)

BACKGROUND: Trichloroethylene (TCE) and perchloroethylene (PCE) are considered among the most important groundwater pollutants around the world. These compounds are usually found together in polluted environments but little is known about the ability of microorganisms to simultaneously degrade TCE and PCE. RESULTS: Data showed that several species of white‐rot fungi, including Trametes versicolor, Ganoderma lucidum, and Irpex lacteus, degrade substantial levels of TCE in pure culture. T. versicolor was chosen for further study since it degraded higher levels of TCE than the other organisms. Initial glucose concentration and reoxygenation of samples increased the amount of TCE dechlorination, but no significant difference in percentage TCE degradation was observed. T. versicolor was able to degrade 34.1 and 47.7% of PCE and TCE added as mixtures (containing 5 and 10 mg L⁻¹, respectively). CONCLUSIONS: The degradation ability of TCE was extended to other species of white‐rot fungi. Percentage degradation as well as chloride release from mixtures of TCE and PCE showed that T. versicolor degrades mixtures of TCE and PCE almost as well as its ability to degrade individually added TCE or PCE. The results suggest the potential promise of T. versicolor for bioremediation of TCE and PCE in the environment. Copyright © 2008 Society of Chemical Industry     

Effect of the pressure on the catalytic oxidation of volatile organic compounds over Ag/Al2O3 catalyst

The catalytic oxidation of volatile organic compounds (VOCs: ethanol, 1-propanol and 2-propanol) over Ag/Al₂O₃ catalyst under low and normal atmospheric pressure conditions has been studied with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (PIMS). The partial oxidation intermediates of the VOCs under different pressures were identified by PIMS and their photoionization efficiency (PIE) spectra. Alkene is preferentially formed under the low pressure conditions, while aldehyde and acid are favored under the normal atmospheric pressure conditions. In addition, the low pressure conditions are more suitable for observing the active intermediates, such as ethenol, ketene and propenal. The results indicate that the pressure has a significant effect on the oxidation pathway of VOCs over Ag/Al₂O₃ catalyst.     

Photo-degradation characteristics of TCE (trichloroethylene) in an annulus fluidized bed photoreactor

The effects of gas velocity, annulus gap on solid (ε_s) and gas phase holdups (ε_g), UV light transmittance and photocatalytic reduction of TCE (trichloroethylene) over TiO₂/silica gel photocatalyst have been determined in an annulus fluidized bed photoreactor. The optimum TCE reduction efficiency exhibits at ε_s/ε_g of 0.48, annulus gap of 8 mm and UV light transmittance around 0.20. The most pronounced effects on TCE conversion are found to be gas velocity (U_g) and annular gap in the photoreactor.     

Bis(pyridine-2-carboxaldehyde oxime)copper(II) sulphate as catalyst precursor in the oxidation of veratryl alcohol by dioxygen

In situ generated [Cu^II(pyridine-2-carboxaldehyde oxime)₂] complex catalyses selective oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) to aldehyde by molecular oxygen in aqueous solution. Under alkaline conditions, the catalyst has both oxime groups deprotonated and the solid state structure of the complex reveals a square pyramidal geometry established by two pyridine-2-carboxaldehyde oxime ligands and sulphate as a counter anion.     

Activated carbon as catalyst in wet oxidation of phenol: Effect of the oxidation reaction on the catalyst properties and stability

Catalytic wet oxidation (CWO) of phenol has been carried out in a continuous three-phase reactor by using a commercial activated carbon (AC) as catalyst, feeding oxygen as gas phase and an aqueous solution 1000 ppm in phenol to the reactor. A stable catalyst under operation conditions is one of the main difficulties to pass up in the catalytic wet oxidation process, so the stability of the activated carbon with the time on stream (TOS) was investigated. To do this the phenol conversion change was analyzed with TOS and results were contrasted to the change of the physicochemical properties of the AC with the TOS. Gas adsorption/desorption, TPD, XPS and SEM measurements were applied to the AC taken from the reactor after several TOS values. A significant reduction of the micro-pore volume and BET surface area of the catalyst was observed with TOS. However, as reaction proceeded the external surface area and the total amount of oxygen surface group increased. Moreover, regeneration of the initial catalyst properties was done by washing with water saturated in oxygen, at the reaction conditions or by heating in N₂ atmosphere at 450, 700 and 900 °C. The total micro-pore volume and internal surface area of the catalyst were not recovered by the regeneration process, probably due to blockage of the narrow micropores by pyrolytic carbon produced during the first step of the wet oxidation process.     

Destruction of carbon tetrachloride in the presence of hydrogen-supplying compounds with ionisation and catalytic oxidation: Part 2. Methane as hydrogen font

The performance of methane (CH₄) as hydrogen donor molecule for the deep and clean oxidation of tetracloromethane (CCl₄) has been experimented. The oxidation of CCl₄–CH₄ admixtures were performed by catalytic combustion with and without pre-catalytic actions (i.e. ionisation/ozonisation) over manganese oxide based catalyst. The extent of CCl₄ and CH₄ combustion was controlled by quantitative determinations of both CO₂ and HCl formed and of CCl₄ and CH₄ converted. Experiments were performed in the 100–500 °C reaction interval in a continuous reaction line at laboratory scale. Fixed CCl₄ concentration (2000 ppmv) with/without CH₄ addition to air constituted the feed. Methane was added to the feedstream in variable concentration (1000–3000 ppmv), the obtained organic mixtures had H/Cl atomic ratios (R_H/Cl) from 0.5 to 1.5. Comparing the tests of ionisation/ozonisation (I/O) of pure CCl₄ streams and CCl₄–CH₄ admixtures, the efficiency of the hydrogen donor role of CH₄ was evidenced. The residue CH₄ concentration was not affected by the residence time (14–42 s) in the ionisation reactor while the residue concentration of CCl₄ decreased by increasing it. A first-order rate equation in CCl₄ concentration was found to represent the ionisation process both in the absence and in the presence of hydrocarbon. On the manganese oxide catalyst, CCl₄ catalytic combustion (CC) was not remarkably influenced by CH₄ presence. CCl₄ destruction by catalytic combustion assisted with ionisation (IOCC) gave rise to higher HCl yield in comparison with conventional combustion. The HCl formation increased with increasing the R_H/Cl value both in the I/O and IOCC experiments, while the CO₂ formation lightly decreased for high R_H/Cl in the CC and IOCC experiments due to incomplete oxidation of CH₄.     

燃煤有机污染物排放及其控制技术研究展望

有机污染物排放是导致大气复合型污染、诱发雾霾、产生光化学烟雾的重要诱因,是当前研究的热点问题。燃煤是有机污染物的来源之一。本文综述了燃煤有机污染物的排放特性,包括燃煤有机物的排放浓度及主要组分,影响燃煤有机物生成的因素,指出燃煤有机污染物浓度较低,苯系物是其重要组成之一。分析了烟气系统中有机物的迁移转化以及烟气处理设施（选择性催化还原脱硝、湿法脱硫、电除尘、湿式电除尘、低低温电除尘）的协同去除作用。最后基于吸附技术和催化技术的研究现状,展望了未来燃煤有机污染物控制的研究方向为：结合现有设备的协同去除作用,优化工艺条件,开发适合燃煤有机物的高效吸附剂和催化剂,开发集高效吸附/氧化/烟气协同净化技术于一体的燃煤有机物高效控制技术。     

The catalytic oxidation of organic air pollutants. Part 3. Catalysts from manganese and copper sulphates

Manganese sulphate and copper sulphate were evaluated as the basis of catalysts for the control of organic air pollutants responsible for malodorous process emissions. Tests were made with low concentrations, 100 volumes × 10^?6 in air, (i.e. 100 parts × 10^?6 by volume), of methyl mercaptan or mercaptan + n-butanal as a function of temperature and time to determine efficiencies for destructive oxidation. The complex pattern of odorant removal and product formation observed using manganese sulphate is discussed in terms of active sites which convert mercaptan to SO₂ but are inhibited by the onset of dimethyl disulphide formation at higher temperatures; reactions between the odorants may also occur. Copper sulphate formed dimethyl disulphide at the lower temperatures but only SO₂, SO₃, CO and CO₂ were detected above 300°C; after a 100 h durability test at 400°C, the odour removal efficiency determined by dynamic dilution olfactometry was 99.9%. Hence copper sulphate is preferable to manganese sulphate and is equal in performance to the copper oxide tested previously (Part 1) but with the advantage of a stable performance from the outset under sulphating conditions.     

Comparative study of the oxidative decomposition of trichloroethylene over H-type zeolites under dry and humid conditions

H-type zeolites (H-Y, H-ZSM-5, and H-MOR) have been investigated for the catalytic oxidative decomposition of trichloroethylene under dry and humid (1000, 7500 and 15,000 ppmv of water) conditions, between 200 and 550°C. The activity order was found to be: H-MOR>H-ZSM-5>H-Y. Temperature-programmed desorption of ammonia and diffuse reflectance FT-IR measurements of adsorbed pyridine revealed that strong Brønsted acidity plays an important role in controlling the oxidative activity of the H-type zeolites. The main oxidation products were CO, CO₂, HCl and Cl₂. Small amounts of tetrachloroethylene were also detected.

The addition of water to the feed stream did not alter the activity order of the zeolites observed in dry conditions. Better conversions were anticipated over H-MOR and H-ZSM-5 at low temperatures and excess of water concluding that both oxygen and water accounted for the TCE destruction. In contrast, H-Y showed a low activity in humid air due to its strong hydrophilic character. It was found that water promoted the formation of CO₂ and limited the generation of undesired chlorinated by-products (Cl₂ and C₂Cl₄). XRD analysis indicated that H-ZSM-5 was the most resistant zeolite to dealumination by chlorination.     

HPWA/HY-SBA-15催化氧化脱除FCC汽油中含硫化合物

采用浸渍合成法,将磷钨酸负载到微孔-介孔复合分子筛上制备HPWA/HY-SBA-15催化剂。以四丁基溴化铵为相转移催化剂,二甲基亚砜为萃取剂,H2O2为氧化剂,考察HPWA/HY-SBA-15催化氧化脱除FCC汽油含硫化合物的工艺条件。结果表明,反应温度40℃,反应时间90min,HY分子筛占复合分子筛的质量分数为40%,脱硫率可达86.3%。在相同条件下,对比考察了HY、HPWA/HY、HPWA/HY-SBA-15和HPWA/SBA-15催化氧化脱硫的效果,实验证明HPWA/HY-SBA-15催化氧化脱硫的效果最好。     

Low temperature oxidation of methane over Pd/SnO2 catalyst

Catalytic activities of supported Pd were investigated for low temperature oxidation of methane. Pd/SnO₂ catalysts demonstrated excellent activity for methane oxidation in spite of their low surface area. The catalytic activity of Pd/SnO₂ was strongly affected by the preparation procedure. Impregnation of Pd on SnO₂ using aqueous solution of Pd(CH₃COO)₂ was most effective in enhancing the catalytic activity. The catalytic activity was also improved when well-crystallized SnO₂ was employed as a support material. TEM observations revealed that catalytic activity is strongly influenced by the dispersion state of Pd. For the active catalysts, strong interaction between Pd and SnO₂ support was observed in the adsorption of oxygen.     

Stability of protonic zeolites in the catalytic oxidation of chlorinated VOCs (1,2-dichloroethane)

The deactivation of protonic zeolites in the catalytic oxidation of 1,2-dichloroethane (DCA) was evaluated. DCA oxidation reactions were carried out in a conventional fixed-bed reactor at atmospheric pressure under conditions of lean DCA concentration in air (1000 ppm). The outlet composition was analysed by a gas chromatograph, an IR spectroscopy-based analyser and another UV analyser. The effect of the zeolite crystalline structure was examined in order to track the catalytic stability of H-ZSM-5, H-MOR and H-BEA under typical reaction environment and conditions (1000 ppm DCA, 300 °C, 13,500 h⁻¹). With the aim of a better understanding of the deactivation pathway, the influence of the space velocity and temperature on the durability of protonic zeolites was analysed. Since some products formed during reaction could also cause deactivation, H₂O and HCl were introduced in the feed stream along with the DCA itself, so as to evaluate their effect. In general terms, coke formation was concluded to be the main reason for zeolite catalyst deactivation. Coke was formed from the intermediate vinyl chloride (VC), which resulted from a first dehydrochlorination step of DCA.     

Negative activation energies in CO oxidation over an icosahedral Au/Mg(OH)2 catalyst

In the course of our studies on CO oxidation over Au/Mg(OH)₂ we have discovered a catalyst which exhibits an apparent negative activation energy when studied under ultra‐dry conditions (80 ppb moisture content). A review of current literature suggests that the oxidation of CO may occur by a reaction between CO and OH radicals and not by oxygen as previously thought. Substantial differences in catalytic behaviour between low and high temperature suggest that the reaction is complex and that more than one reaction pathway is present. This revised version was published online in July 2006 with corrections to the Cover Date.     

MoOx/SBA-15丙烷选择氧化催化剂的研究

采用浸渍法制备了一系列不同Mo含量的MoOx/SBA-15催化剂,并考察了丙烷选择氧化生成醛类含氧化合物（甲醛、乙醛和丙烯醛）的催化剂性能,利用FT-IR和XRD等技术对催化剂及载体的物化性能进行了表征。结果表明,催化剂的活性主要取决于Mo的负载量,当x(Mo)=1.75%［n(Mo)∶n(Si)=1.75∶100］时,醛类选择性约30%,总醛收率为10.4%,高分散催化剂尤其有利于醛类含氧化合物的定向生成。