Catalytic oxidation of hydrogen sulphide by air over an activated carbon fibre

Activated carbon fiber (ACF), FN-200CF-15, made from coal tar, oxidized hydrogen sulphide effectively to sulphuric acid at an inlet concentration of 200 ppm and space velocity (SV = flow rate/packing volume) of 100 h⁻¹ (sulphur load 11 g-S/day kg-fiber) for one and a half months only by keeping the moisture content of ACF more than 50%. This phenomenon is different from granular activated carbon (GAC) reported previously.     

Catalytic oxidation of hydrogen sulphide on activated carbons

Activated carbon is a suitable adsorbent for removal of hydrogen sulphide from natural, synthesis or other product gases. The process depends predominantly on physical adsorption, though catalytic oxidation is also involved. During catalytic oxidation the H₂S is converted in the presence of oxygen to elemental sulphur, which is adsorbed onto the internal surface of the activated carbon, thus leading to a sulphur load of up to 120% by weight. The oxidation rate depends on the partial pressure of both reactants, H₂S and O₂ and is largely controlled by the characteristics of the activated carbon. The activity of the catalyst can be improved by impregnating the activated carbon with promoters such as iron and iodine. The regeneration of spent carbon is currently carried out using hot gas desorption methods at temperatures around 450 °C.     

Influences of surface functional groups on catalytic activity over activated carbon catalysts for sulfur dioxide removal from flue gases

The catalytic oxidation of sulfur dioxide in flue gases over activated carbon catalysts was studied. Catalysts made from different materials or by different methods were markedly different. The catalysts were characterized by BET isotherms and X-ray power diffraction. The acidic and basic sites and/or strength on the catalysts were determined by temperature-programmed desorption, while surface functional groups were determined by X-ray photoelectron spectroscopy. The catalytic activity depended on oxygen-containing surface functional groups with Brønsted basicity properties. These groups on a furfural residue activated carbon could be increased by a suitable treatment to enhance the catalytic activity but other catalysts in this study showed no activity enhancement with a similar treatment.     

活性炭载体对TiO2/AC光催化降解苯酚影响研究

分别以典型煤基活性炭和椰壳活性炭为载体,采用溶胶-凝胶法制备了TiO2/AC复合光催化剂,采用低温氮气吸附、X射线衍射、扫描电镜等对其性能进行了表征,分析了活性炭载体对复合光催化剂性能的影响.结果表明:TiO2在椰壳活性炭载体上的负载率高于煤基活性炭,TiO2负载使椰壳活性炭的比表面积和微孔容明显减小,TiO2溶胶对微...     

活性炭负载催化剂臭氧催化氧化处理印染废水研究

以堇青石蜂窝陶瓷、硅藻土、活性氧化铝和活性炭作为载体、金属氧化物(FexOy、CuO、NiO、MnxOy、BaO)作为催化活性组分,对臭氧催化氧化印染废水进行了试验对比,并对影响载铁型活性炭催化剂臭氧催化氧化印染废水的因素进行了研究。结果表明,载铁型的催化剂活性相对较高,当焙烧温度为750℃时,催化性能最好。利用载铁型活性炭催化剂,在臭氧质量浓度为10mg/L、pH值为6、反应时间为60min的条件下,催化氧化具有最佳的效果,COD去除率达86%;催化剂的重复利用性好,连续使用12次,COD的去除率仍可达64%。     

Application of alumina supported gold-based catalysts in total oxidation of CO and light hydrocarbons mixture

Gold nanoparticles supported on alumina have been produced using the anionic exchange method and ammonia washing procedure. The catalysts are tested in the reaction of total oxidation of a mixture of light hydrocarbons and carbon monoxide in order to study the possibility of application in the reduction of cold start emissions. The obtained results are promising according to the temperature range observed for the oxidation of unsaturated hydrocarbons. The results obtained for acetylene confirms the difference of oxidation of this hydrocarbon over gold catalysts. An ageing procedure has been employed. This procedure does not affect the comportment of the catalysts versus hydrocarbon oxidation.     

The influence of sulfur dioxide on propane oxidation activity over supported platinum and palladium

Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated -alumina or zirconia compared to -alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/-alumina, Pt/zirconia, Pd/-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/-alumina, and Pd/zirconia is less active than Pd/-alumina.     

Effect of carbon dioxide on the selectivities obtained during the partial oxidation of methane and ethane over Li+/MgO catalysts

AtT 650 °C carbon dioxide either formed during reaction or added to the system increases the selectivity for the desired hydrocarbon products during the oxidative coupling of methane and the oxidative dehydrogenation of ethane reaction over Li⁺/MgO catalysts. Similarly, CO₂ inhibits secondary reactions of CH₃-radicals with the surface of the Li⁺/MgO. The improved selectivities are attributed to the poisoning effect that CO₂ has on the secondary reactions of alkyl radicals with the surface.     

类水滑石负载的二氧化钛制备及对苯酚羟基化反应的活性

利用微波晶化法合成了四元类水滑石前体,以此为载体制备了负载TiO2的水滑石催化剂,考察了其对苯酚羟基化反应的活性,结果表明:负载TiO2类水滑石催化剂表现出了较好的羟化反应活性,研究了苯酚羟化的反应工艺条件对催化剂活性的影响,确定了适宜的羟基化反应条件为:温度为70℃、反应时间为60min、催化剂用量为0.53g、30%的H2O2用量为24mL、苯酚加入量为5.0g。在此条件下,苯酚的转化率为89%。     

Selective catalytic reduction of sulfur dioxide with hydrogen to elemental sulfur over Co---Mo/Al2O3

The selective reduction of sulfur dioxide with hydrogen to elemental sulfur was studied over Co---Mo/Al₂O₃. When the feed conditions were properly optimized (SO₂/H₂ mole RATIO = 1:3), a sulfur yield of about 80% was achieved at temperatures around 300°C. The temperature is the lowest that has been reported so far for any catalyst for this reaction. The catalytic activity remained high and stable after presulfiding with 10% H₂S in hydrogen. Little influence on the catalytic activity was observed if the water content in the feed was kept below 11 vol.-%. The overall reaction consisted of two individual steps occurring on two different sites; sulfur dioxide was first hydrogenated to hydrogen sulfide on the metal sulfide phase, then followed by the Claus reaction of hydrogen sulfide with sulfur dioxide to produce elemental sulfur on the acidic sites of the alumina support.     

Catalyst modification and process design considerations for the oxidation of low concentrations of hydrogen sulfide in natural gas

Low concentrations of hydrogen sulfide (H₂S) in natural gas can be selectively oxidized over an activated carbon catalyst to elemental sulfur, water and a small fraction of sulfur dioxide (SO₂). Efforts to improve catalyst performance and product sulfur quality have been made by a) modification of the catalyst composition b) removal of the heavy hydrocarbons from the feed and c) choice of reaction conditions. The use of a guard bed to absorb heavy hydrocarbons and operation at elevated pressures show positive results. A preliminary flow diagram incorporating these findings has been prepared for a small commercial unit capable of processing sour natural gas containing 1.0% H₂S.     

SWA/TiO_2微球的制备及催化α-蒎烯异构化性能

采用溶胶-凝胶法和浸渍法,制备了纳米负载型H4SiW12O40（SWA）催化剂,考察了载体种类、SWA浸渍浓度对催化剂性能的影响。结果表明,用TiO2固载、8%SWA浸渍所得催化剂SWA/TiO2的催化性能较佳。利用XRD、TEM和BET比表面测定技术对其结构进行了表征。结果显示,该催化剂颗粒为圆球形,粒径为40～50 nm,具有较好的分散性。载体TiO2的引入明显增大了SWA的比表面积。将纳米SWA/TiO2用于催化α-蒎烯异构化反应,实验结果表明,该催化剂具有较好的催化活性和选择性,异构化反应的主产物是莰烯。在适宜的实验条件下,α-蒎烯的转化率达98%,莰烯的产率达58%。与其它负载型催化剂比较,SWA/TiO2具有用量少、活性高、反应时间短等特点。     

Nitric oxide reduction and carbon monoxide oxidation over carbon-supported copper-chromium catalysts

Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed.     

Silver catalysts supported over activated carbons for the selective oxidation of CO in excess hydrogen: effects of different treatments on the supports

Commercial activated carbon (AC) was used as a support either in its original form or after various modifications, giving diverse textural and surface chemical characteristics. The changes of these properties were monitored by N₂ adsorption–desorption isotherms, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ag catalysts were prepared over the AC supports by a conventional wet impregnation method. The catalytic performances of supported Ag/AC catalysts in the selective oxidation of CO in excess H₂ were tested. The results indicate the textural and surface chemical characteristics are responsible for the different catalytic performances.     

Ring hydrogenation of naphthalene and 1-naphthol over supported metal catalysts in supercritical carbon dioxide solvent

Catalytic ring hydrogenations of naphthalene and 1-naphthol were studied over several supported metal catalysts in supercritical carbon dioxide solvent at low temperature. Higher concentration of hydrogen in supercritical carbon dioxide and lower reaction temperature were responsible for higher catalyst activity and selectivities to the desired partial ring hydrogenated products as compared with those observed in organic solvent for the same catalyst.     

Chaos and synchronisation in heterogeneous catalytic systems: CO oxidation over Pd zeolite catalysts

The influence of experimental parameters on the structure of global reaction rate oscillations and the coupling of local oscillators on a catalyst bed in a continuous stirred tank reactor is studied for the oxidation of CO on zeolite supported palladium catalysts. Global coupling can be achieved via mass transfer through the gas phase or via heat transfer in the case of a support of high heat conductivity. Characteristic differences in the activity of catalysts as well as in the period and the amplitude of the oscillations are related to the size of the palladium clusters and can be simulated by adding the state of the oxidation of the metal surface as a parameter to a common kinetic model. The analysis of observed chaotic behaviour leads to the conclusion that diffusional chaos characteristic of a distributed system is observed on the level of the zeolite crystallite that supports the palladium clusters.     

低温法制备二氧化钛薄膜及其光催化氧化处理电镀含铬废水

以钛酸四丁酯为原料,采用微波辅助低温法在玻璃表面制备锐钛矿结构的二氧化钛薄膜.分别用X射线衍射法(XRD)和扫描电子显微镜(SEM)表征其相结构和表面形貌;通过光催化降解实际电镀含铬废水实验,探讨了光源、废水pH、废水初始浓度、光照时间及涂膜层数对总铬去除率的影响.光催化氧化的最优条件为:废水初始浓度3 000～9 000 mg/L,pH=8.3,负载4层薄膜,254 nm紫外光照射3h.在最优条件下,废水的总铬去除率高达99.8％.     

Promotional effect of hydroxyl on the aqueous phase oxidation of carbon monoxide and glycerol over supported Au catalysts

Gold particles supported on carbon and titania were explored as catalysts for oxidation of CO or glycerol by O₂ at room temperature in liquid-phase water. Although Au/carbon catalysts were not active for vapor phase CO oxidation at room temperature, a turnover frequency of 5 s⁻¹ could be achieved with comparable CO concentration in aqueous solution containing 1 M NaOH. The turnover frequency on Au/carbon was a strong function of pH, decreasing by about a factor of 50 when the pH decreased from 14 to 0.3. Evidently, a catalytic oxidation route that was not available in the vapor phase is enabled by operation in the liquid water at high pH. Since Au/titania is active for vapor phase CO oxidation, the role of water, and therefore hydroxyl concentration, is not as significant as that for Au/carbon. Hydrogen peroxide is also produced during CO oxidation over Au in liquid water and increasing the hydroxyl concentration enhances its formation rate. For glycerol oxidation to glyceric acid (C₃) and glycolic acid (C₂) with O₂ (1–10 atm) at 308–333 K over supported Au particles, high pH is required for catalysis to occur. Similar to CO oxidation in liquid water, H₂O₂ is also produced during glycerol oxidation at high pH. The formation of the C-C cleavage product glycolic acid is attributed to peroxide in the reaction.     

Partial oxidation of methane to synthesis gas via the direct reaction scheme over Ru/TiO2 catalyst

The partial oxidation of methane to synthesis gas has been investigated over various supported metal catalysts. The effects of operational variables on mass and heat transport resistances were investigated for defining the kinetic regime. It is observed that, in the absence of significant mass and heat transfer resistances, high selectivity (up to 65%) to synthesis gas is obtained over Ru/TiO₂ catalysts in the low methane conversion range ( ) whereas only negligibly small selectivity to synthesis gas is observed over all other catalysts investigated under similar conditions. This indicates that the Ru/TiO₂ catalyst possesses unique properties, offering high selectivity to synthesis gas formation via the direct reaction scheme, whereas the other catalysts promote the sequence of total oxidation of methane to CO₂ and H₂O, followed by reforming reactions to synthesis gas. An increase of selectivity to synthesis gas, in the presence of oxygen, is achieved over the Ru/TiO₂ catalyst by multi-feeding oxygen, which is attributed to suppression of deep oxidation of H₂ and CO.     

Combined catalytic partial oxidation and CO2 reforming of methane over supported cobalt catalysts

The combined partial oxidation and CO₂ reforming of methane to synthesis gas was investigated over the reduced Co/MgO, Co/CaO, and Co/SiO₂ catalysts. Only Co/MgO has proved to be a highly efficient and stable catalyst. It provided about 94–95% yields to H₂ and CO at the high space velocity of 105000 mlg^–1h^–1 and for feed ratios CH₄/CO₂/O₂=4/2/1, without any deactivation for a period of study of 110 h. In contrast, the reduced Co/CaO and Co/SiO₂ provided no activity for the formation of H₂ and CO. The structure and reducibility of the calcined catalysts were examined using X-ray diffraction and temperature-programmed reduction, respectively. A solid solution of CoO and MgO, which was difficult to reduce, was identified in the 800°C calcined MgO-supported catalyst. The strong interactions induced by the formation of the solid solution are responsible for its superior activity in the combined reaction. The effects of reaction temperature, space velocity, and O₂/CO₂ ratio in the feed gases (while keeping the C/O ratio constant at 1/1) were investigated over the Co/MgO catalyst. The H₂/CO ratio in the product of the combined reaction increased with increasing O₂/CO₂ ratio in the feed.