Oxidative decomposition of dichlorodifluoromethane (CFC-12) in the presence of butane over Tungsten(VI) oxide catalysts supported on alumina–zirconia

The oxidative decomposition of dichlorodifluoromethane (CFC-12) in the presence of butane was investigated with tungsten(VI) oxide catalyst supported on alumina–zirconia. In this reaction, it is considered that CFC-12 might react with water formed by the combustion of butane at high temperatures above 773 K, and that most of CFC-12 might react directly with oxygen at low temperatures below 723 K. The CFC-12 conversion over the tungsten(VI) oxide catalyst decreased with the passage of time on stream at low temperatures below 673 K. This deactivation of the catalyst was attributed to the coke deposition on the acid sites of the catalyst as well as to the fluorination of the acid sites. The CFC-12 conversion at 4 h on stream became higher when the catalyst was loaded with platinum or palladium, but the butane conversion was not changed by loading. The amount of the coke deposited on platinum- or palladium-loaded tungsten(VI) oxide catalysts, which exhibited a high CFC-12 conversion at 4 h on stream, was very small. Accordingly, the depression of the catalyst deactivation might be caused by the combustion of the coke deposited on the acid sites due to the catalysis of platinum and palladium.     

Catalytic hydrolysis of chlorofluorocarbon (CFC-12) over WO3/ZrO2

The catalytic decomposition of CFC-12 (CCl₂F₂) in the presence of water vapor was investigated over a series of solid acids WO₃/ZrO₂. Compared with tungstic acid, ammonium metatungstate is a better source of tungsten oxide for the preparation of WO₃/ZrO₂ catalysts. CFC-12 decomposition activities of WO₃/ZrO₂ catalysts are in good agreement with their acidities. Enhancing the acidities of catalysts is favorable to increase their CFC-12 decomposition activities. WO₃/ZrO₂ catalysts calcined at higher temperature exhibit good catalytic activity and stability for the hydrolysis of CFC-12, and show better structural stability during the reaction.     

Iron–ceria–zirconia fluorite catalysts for methane selective oxidation to formaldehyde

Ceria–zirconia catalysts modified by partial substitution of zirconium by iron were investigated for the reaction of the selective oxidation of methane to formaldehyde. The insertion of iron was ensured by the preparation method, based on decomposition of the mixed precursors. The crystalline structure was studied by XRD and the iron state was determined by Mössbauer spectroscopy. The insertion of Fe³⁺ into the lattice of the mixed oxide and the partial substitution of zirconium ions with iron cations up to 25% have not resulted in any phase rejection of the formed iron oxide. The reducibility of Ce⁴⁺ in the modified ternary oxide is enhanced by doping with iron. Despite their low specific surface area, the catalysts are efficient at activating the methane independently of the iron content. The selectivity to formaldehyde strongly depends on the amount of the iron inserted in the mixed oxide.     

Catalytic hydrolysis of dichlorodifluoromethane (CFC-12) on unpromoted and sulfate promoted TiO2–ZrO2 mixed oxide catalysts

The mixed oxide of zirconium and titanium was investigated for the catalytic hydrolysis of dichlorodifluoromethane. The mixed oxide was further promoted by doping with sulfate ions. It was found by both powder X-ray diffraction and Raman spectroscopy that addition of hydrogen peroxide to the methanol solution of ZrOCl₂ and TiCl₄ before gelation was induced by ammonia addition promoted the formation of the mixed oxide phase with the anatase structure in addition to the expected phase of columbite structure. This increased the surface area and activity of the mixed oxide. Promotion with sulfate enhanced the acidity and activity of the catalysts. When sulfate was added by treatment with sulfuric acid, phase transformation, depending on the concentration of the acid used, in addition to sulfate deposition on the oxide surface, occurred. The treatment with 96% sulfuric acid resulted in a catalyst with nearly entirely the anatase structure. This catalyst was found to be the most active, capable of complete conversion of CFC-12 and 100% selectivity to carbon dioxide at 280°C. Prolonged reaction of this catalyst at 280°C for 211 h resulted neither in reduction of activity nor reduction in CO₂ selectivity. The performance of this catalyst is among the highest reported in the literature.     

Solvent effect on synthesis of zirconia support for tungstated zirconia catalysts

Solvothermal reaction of zirconium n-butoxide (ZNB) in different solvent media, such as 1,3-pentanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol resulted in the formation of zirconium dioxide (ZrO₂) nanostructure. Then, the 15%W/ZrO₂ (WZ) catalysts using different zirconia supports were prepared by impregnation method. The effects of solvent on preparation of zirconia on the catalytic performance of WZ catalysts in esterification of acetic acid and methanol at 60 °C were investigated. The experimental results showed that ZrO₂ particles prepared in 1,4-butanediol (ZrO₂-BG) have a spherical shape, while in other glycols the samples were irregularly-shaped particles. The reaction results of esterification illustrated that the W/ZrO₂-BG catalysts had high surface acidity and showed high acetic acid conversion. The W/ZrO₂-PeG catalysts (ZrO₂ particles prepared in 1,5-pentanediol, PeG) exhibited the lowest surface acidity among other samples due to strong interaction of proton species and the zirconia supports as proven by TGA. One of the possible reasons can be attributed to different amounts of carbon residue on the surface of catalysts.     

CFC-12催化加氢制备HFC-32的研究

探索了二氟二氯甲烷(CFC-12)催化加氢制备HFC-32的方法.比较了不同贵金属催化剂及催化剂载体对加氢反应的影响,结果表明Pd/C催化剂对CFC-12的转化率和HFC-32的选择性都要优于其它的催化剂.研究了助剂Th对Pd/C催化剂性能的影响,发现添加一定量的Th可有效改善HFC-32的选择性,但过多的Th将导致CFC-12转化率的下降.该法为实现CFC-12无害化处理提供了一条可行的途径.     

锆/铪基催化剂催化转移加氢反应的研究进展

催化转化是可再生生物质资源利用的重要途径,高效催化剂的构建是生物质及其衍生物催化转化的关键环节.生物质衍生羰基类化合物加氢转化为醇或酯类化合物是生物质催化转化利用过程中重要的反应步骤.由于氢转移加氢反应过程具有反应条件温和的优点,因此非均相氢转移加氢催化剂在羰基类生物质平台分子转化中得到广泛应用.过渡金属锆、铪是常用的...     

Ni/ZrO2催化剂的制备及甲烷分步水蒸气重整反应性能

采用沉淀法制备了ZrO₂载体,进一步采用浸渍法制备了不同Ni负载量的Ni/ZrO₂催化剂。通过XRD、N₂物理吸附、H₂-TPR和H₂-TPD等表征手段对Ni/ZrO₂催化剂的物理结构和化学特性进行了研究,探讨了活性金属Ni物种的状态,并计算了Ni粒子的大小。随着Ni负载量的增加,Ni/ZrO₂催化剂的比表面积逐渐减小,金属Ni的分散度逐渐减小,Ni粒子尺寸逐渐增大,低温H₂脱附峰所占比例逐渐增大。当Ni负载量为10.2%（质量分数）时,Ni/ZrO₂催化剂上ZrO₂晶粒的平均尺寸和Ni粒子的尺寸大小均接近30nm。进一步考察了Ni/ZrO₂催化剂在甲烷分步水蒸气重整反应中的催化性能。结果表明,Ni负载量在一定范围内的Ni/ZrO₂催化剂对于甲烷分步水蒸气重整反应具有良好的催化性能,Ni负载量过高或过低均不利于甲烷的转化。当Ni负载量为10.2%时,载体ZrO₂粒子和金属Ni粒子尺寸匹配,Ni/ZrO₂催化剂表现出最佳的甲烷转化活性和稳定性。     

Hydrodechlorination of CFC-12 over Novel Supported Palladium Catalysts

Novel supported palladium catalysts were prepared through organometallic Pd compounds including dichlorobistriphenylphosphine palladium (DCTPPP) and dithiocyanatobistriphenylphosphine palladium (DTTPPP) for the hydrodechlorination of CFC-12. These catalysts exhibited excellent catalytic activities in hydrodechlorination of CFC-12. Particularly, high selectivities of CH₂F₂ formation were achieved over the catalysts, DCTPPP/MgF₂ with 88.1% and DTTPPP/MgF₂ with 85.8%, at a limited conversion level (<5%). No obvious deactivation was observed for DCTPPP/MgF₂ and DTTPPP/MgF₂ catalysts within 60 h. The higher catalytic activity, CH₂F₂ selectivity and catalyst stability may be mainly attributed to high dispersions of palladium.     

Hydrodechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) over supported ruthenium and other noble metal catalysts

The hydrodechlorination of CCl₂F–CClF₂ (CFC-113) was studied using silica- and activated carbon-supported Ru, Rh, Pd, and Pt catalysts. The activity of the catalysts changed with time-on-stream. Ru was most stable among the four noble metals and gave a simple product distribution yielding CClF=CF₂ (CFC-1113) and CHClF–CClF₂ (HCFC-123a) as main products. Over silica-supported Ru, CFC-1113 yield decreased gradually with time-on-stream but HCFC-123a yield did not change throughout the reaction, suggesting that these products were formed on different sites of Ru. XRD studies and temperature-programmed reduction of the spent catalyst revealed that the deactivation was caused by halogen-containing carbonaceous species accumulated on the Ru surface during the reaction. The carbonaceous species seemed to be formed on the active site for CFC-1113 formation. Because CFC-1113 selectivity was higher over the catalyst having higher Ru dispersion, it was assumed that the hydrodechlorination of CFC-113 is structure-sensitive and CFC-1113 formation is promoted by Ru having highly unsaturated coordination sphere.     

Nanocrystalline Oxalate/Carbonate Precursors of Ce and Zr and Their Decompositions to CeO2 and ZrO2 Nanoparticles

The oxalate and carbonate precursors of cerium and zirconium have been prepared using reverse micelles as nanoreactors. Cerium oxalate precursor on thermal decomposition leads to a mixture of nanorods and nanoparticles of cerium oxide (nanoparticles of 10 nm and nanorods with 7 nm diameter and 30 nm length). Cerium oxide with crystallite size of 10 nm was obtained from cerium carbonate precursor. Monodispersed nanoparticles of zirconia with an average size of 3–5 and 12 nm were obtained from the oxalate and carbonate precursor, respectively. Detailed dielectric properties of sintered discs of nanocrystalline ceria and zirconia have been studied with variation of frequency and temperature.     

球形四方相氧化锆的水热法合成与表征

以氧氯化锆为原料，尿素为矿化剂，氧化钇为稳定剂，水和乙醇为反应溶剂，结合一步水热的方法，在不添加表面活性剂以及不经过煅烧的前提下，通过改变水热温度、水热时间、醇水比以及氧化钇添加量等条件探究了球形四方相氧化锆的形成机理，制备了结晶性好、粒度分布均匀以及球形度高的四方相氧化锆粉体。     

Pd/C催化剂上CFC-12加氢脱氯生成HFC-32的研究

通过浸渍法制备了Pd/C催化剂,研究了其CFC-12加氢脱氯生成HFC-32性能,考察并优了载体种类及负载量等因素对催化剂性能的影响。在最优催化剂的基础上,得出最佳反应条件为:CFC-12∶H2=1∶4(摩尔比)、总空速为600 mL·g-1(catal.)h-1、反应温度为523 K时。在此反应条件下,CFC-12转化率可达53.4%,对HFC-32选择性为61.5%。并研究了催化剂的稳定性,发现720 h后,催化剂活性方开始下降。     

Electrochemical conversion of CFC-12 to tetrafluoroethylene: electrochemical formation of difluorocarbene

A large amount of chlorofluorocarbons (CFCs) is still in use in the world, although they are known to cause depletion of the ozone layer in the stratosphere. It is desirable that CFCs are converted to compounds that are recyclable as industrial materials. In this paper, we attempted the efficient conversion of CFC-12 to tetrafluoroethylene under high pressure. Under the high-pressure condition, the constant supply of CFC-12 to the electrode is expected to enhance the dimerization of the reaction intermediates. At a Pb electrode, it is known that the C-Cl bond of CFC-12 is selectively broken in aqueous solution, TFE was produced with a current efficiency of 43.2%, whereas TFE was hardly produced at Ag and Cu electrodes that are known to break both the C-Cl bond and C-F bond of CFC-12. The current efficiency for the TFE formation was largely dependent on the potential imposed on the electrode. The current efficiency for the TFE formation was improved to 70.7% at −1.5 V versus Ag. By trapping the reaction intermediate, the reaction mechanism under high pressure CFC-12 at a Pb electrode was presumed to proceed via dimerization of difluorocarbene.     

Preparation and properties of sulfated zirconia for hydrolysis of ethyl lactate

Sulfated zirconia catalysts are proposed for the reversible hydrolysis of ethyl lactate instead of liquid acids. Sulfated zirconia catalysts were prepared by precipitation-impregnation method. The zirconium hydroxide was produced from zirconium oxychloride by adding aqueous ammonia and then impregnated in sulfuric acid. The solid samples were obtained by filtration and evaporation of the mixtures, respectively. After the samples were calcined, the sulfated zirconia catalysts were prepared. The results showed that the catalyst prepared by evaporation has higher catalytic activity. The physicochemical characteristics of the sulfated zirconia catalysts were studied by thermal analysis, X-ray powder diffraction (XRD), temperature programmed desorption of ammonia (NH₃-TPD) and N₂ adsorption-desorption, respectively. By the precipitation-impregnation-evaporation method, the optimal sulfated zirconia catalyst of tetragonal phase was prepared under liquid-solid ratio of 5ml/g, 1 mol/L of H₂SO₄ and calcination at 650 °C for 3 h. The conversion of the ethyl lactate was 87.8% in 3 h at 85 °C with the catalyst loading 2 wt% and initial molar ratio of water to ethyl lactate 20: 1.     

Oxidation of o-Xylene to Phthalic Anhydride on Sb-V/ZrO2 Catalysts

Zirconia-supported and bulk-mixed vanadiumantimonium oxide catalysts were used for the oxidation of o-xylene to phthalic anhydride. X-ray diffraction, Raman spectroscopy and photoelectron spectroscopy were used for characterization. It was found that vanadium promotes the transition of tetragonal to monoclinic zirconia. The simultaneous presence of Sb and V on zirconia at low coverage led to a preferential interaction of individual V and Sb oxides with the zirconia surface rather than the formation of a binary Sb-V oxide, while at higher Sb-V contents the formation of SbVO₄ took place. Sb-V/ZrO₂ catalysts showed high activity for o-xylene conversion and better selectivity to phthalic anhydride as compared to V/ZrO₂ catalysts. However, their selectivity to phthalic anhydride was poor in comparison to a V/TiO₂ commercial catalyst. The improved selectivity of the Sb-containing catalysts is attributed to the blocking of non-effective surface sites of ZrO₂, the decrease of the total amount of acid sites and the formation of surface V-O-Sb-O-V structures.     

Characterization and reductive amination of cyclohexanol and cyclohexanone over Cu/ZrO2 catalysts

Reductive amination of cyclohexanol/cyclohexanone was studied over copper catalysts supported on zirconia. The effect of copper loading and dispersion was studied on the activity and selectivity of the reaction. A series of zirconia supported copper catalysts with varying copper loadings (1–15 wt%) were prepared by incipient wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD) and temperature-programmed reduction (TPR). Copper dispersion and metal area were determined by N₂O decomposition by passivation method. X-ray diffraction patterns indicate the presence of crystalline CuO phase from 4.0 wt% Cu on zirconia. TPR patterns reveal the presence of highly dispersed copper oxide at lower temperatures and bulk CuO at higher temperatures. The acid–base properties of catalysts were investigated by means of a model reaction cyclohexanol dehydrogenation to cyclohexanone and compare with the results of TPD of ammonia, which allows to measure the acid–base properties of the support and to investigate the changes in surface acidity or basicity, resulting from the metal impregnation.     

Molten salt preparation of stabilized zirconia catalysts : characterization and catalytic properties

Supports of Mo and NiMo catalysts were prepared and tested in hydrotreatment model reactions. These supports, composed of zirconia and various amounts of yttria, were obtained by synthesis in molten salts.

It was found that the distribution of yttrium in zirconium oxide was homogeneous. Moreover, it was shown that the crystalline structure as well as the textural properties (especially the porosity) were stabilized.

These solids were then used as supports of Mo and NiMo sulphides and their activities were compared to those of a commercial NiMo alumina catalyst.

In biphenyl hydrogenation, with the same coverage of Mo (2.8 at/nm²), the activities per gram of both catalysts (supported on zirconia and alumina) were similar, while the activity per atom of Mo of the catalyst supported on ZrO₂---Y₂O₃ was twice the activity of the catalyst supported on alumina.

For NiMo catalysts, a ratio R= Ni/(Ni+Mo)=0.4 with Mo = 2.8 at/nm² and a co-impregnation of the Mo and Ni were required to have a good synergetic effect. The activity per atom of Mo in biphenyl hydrogenation was then enhanced more than twofold when compared to the NiMo/alumina catalyst. In an HDN model reaction (conversion of diethylanyline in the presence of quinoline) the results obtained with zirconia were much better than with alumina.     

Oxidative Dehydrogenation of Ethane Over Zirconia‐Supported Lithium Chloride Catalysts

A series of Li‐doped catalysts on zirconia or sulfated zirconia were prepared and investigated in the catalytic reaction of ethane oxidative dehydrogenation into ethylene. It is found that zirconia and sulfated zirconia supports prepared by different methods show varying nature and thus influence the catalytic performance of their supported Li catalysts in this reaction. Li catalysts doped on the sulfated zirconia prepared by a two‐step method can exhibit high ethane conversion, selectivity towards ethylene and ethylene yield as well as a stable catalytic performance. The Li precursors also affect the catalytic behavior. LiCl doped on sulfated zirconia can give high ethane conversion and ethylene selectivity. Addition of transitional and lanthanide metal oxides to the LiCl/SZ system significantly improves the activity and yield of ethylene in the oxidative dehydrogenation of ethane. Among the oxides studied, NiO and Nd₂O₃ demonstrate the best promoting effect in terms of catalytic conversion and ethylene yield.     

Influence of zirconia raw materials on the development of DeNOx monolithic catalysts

Pd-zirconia-based monolithic catalysts were prepared with various commercial zirconia raw materials and a natural magnesium silicate binder, sepiolite, for the selective catalytic reduction (SCR) of NO with CH₄ in oxygen excess. The different textural properties, metastable tetragonal zirconia phase stability, surface acidity, Pd dispersion and catalytic properties of these monoliths were compared to select the most suitable structured catalyst for NO_x control in natural gas-fired power plants. The influence of operating temperature in the two reactions, NO reduction and CH₄ combustion, with the monolithic catalysts was determined. A 0.4 wt.% Pd-zirconia catalyst, manufactured from a sulphated zirconium hydroxide raw material, was selected as the most appropriate in the reaction under study, reaching a maximum NO conversion at 400 °C.