Hydrodechlorination of tetrachloroethylene over sulfided catalysts: kinetic study

In this work, a commercial sulfided hydrotreatment catalyst (2.8% NiO, 13.5% MoO₃, supported on γ-alumina, supplied by Shell) is compared with different iron sulfide based catalysts. These catalysts were prepared from a by-product (called red mud (RM)) of the bauxite leaching in the Bayer process. Two different activation procedures were tested, both based in dissolving the RM in an acid solution (HCl or HCl+H₃PO₄) followed by a precipitation with ammonia at pH=8 and calcining at 500 °C. All the catalysts were sulfided at 400 °C.

The commercial catalyst was more active than the iron sulfide catalysts in all the range of space times tested. However, considering the low prize of the RM based catalysts, they could be an interesting alternative to the hydrotreatment catalysts. The selectivity for ethane was near 100% for all the catalysts tested.

Kinetics results were successfully modeled with a Langmuir–Hinshelwood model, assuming that the chemisorption of hydrogen (considered as associative) and TTCE occurs over analogous active sites.     

Characterisation and deactivation studies of sulfided red mud used as catalyst for the hydrodechlorination of tetrachloroethylene

Sulfided red mud (a by-product in the production of alumina by the Bayer process) has been shown to be active as a catalyst in hydrodechlorination reactions. In order to evaluate the feasibility of red mud in industrial processes, which would be most interesting as the cost of this material is much lower than that of commercial catalysts, its deactivation must be characterised.

In this study, the deactivation of sulfided red mud as a catalyst for the hydrodechlorination of tetrachloroethylene at 100 bar and 350°C was studied. The variation of conversion with reaction time was determined in the presence and absence of carbon sulfide in the feed, a notorious increase in the catalyst life being observed in the presence of carbon sulfide.

Fresh and used catalysts were characterised by nitrogen adsorption, X-ray diffraction, scanning electron microscopy and X-ray dispersion spectrometry. An increase in the specific surface and chlorine surface concentration of the catalyst and a decrease in sulphur surface concentration were observed, as well as crystallographic changes in iron species.     

Comparison of the dynamics of the high-temperature water-gas shift reaction on oxide catalysts

The dynamics of the high-temperature water-gas shift reaction on iron oxide and Co-Mo-oxide catalysts was studied with transient response experiments performed at 563–673 K at atmospheric pressure in a gradientless spinning basket reactor. At the reaction start-up the step response of CO₂ on the iron oxide catalyst was always faster than the response of H₂, whereas the response of H₂ on the Co-Mo catalyst was faster than the response of CO₂. Water pretreatment retarded the response of H₂ on the iron oxide catalyst, whereas a similar pretreatment accelerated the response of H₂ on the Co-Mo catalyst. Based on the results of the transient response experiments reaction mechanisms were proposed for the water-gas shift reaction on both catalysts. The rate determining steps on the iron oxide catalyst were assumed to be the CO₂ desorption and surface hydroxyl decomposition steps. The rate determining steps on the Co-Mo catalyst were assumed to be the surface reaction and CO₂ desorption steps. The transient responses were modelled with non-steady-state rate equations based on the mechanisms, and the kinetic constants were determined by regression analysis. The kinetic models were able to describe the transient behaviours of the oxide catalysts.     

Fischer–Tropsch synthesis. Conversion of alcohols over iron oxide and iron carbide catalysts

Both iron oxide (Fe₂O₃) and iron carbide catalysts are active for the dehydration of tertiary alcohols; the oxide catalyst is not reduced nor is the bulk carbide oxidized by the steam generated during the dehydration reaction. Secondary alcohols are selectively converted to ketones plus hydrogen by both the iron oxide and carbide catalyst. Fe₂O₃ is reduced to Fe₃O₄ during the conversion of secondary alcohols. Both iron carbide and oxide catalysts dehydrogenate a primary alcohol (C_n) to an aldehyde which undergoes a secondary ketonization reaction to produce a symmetrical ketone with 2n−1 carbons. These results plus those of our earlier ¹⁴C-tracer studies suggest that dehydration of alcohols to produce olefins makes a minor, if any, contribution during Fischer–Tropsch synthesis with an iron catalyst at low and intermediate pressure conditions.     

Modified iron-molybdate catalysts with various metal oxides by a mechanochemical method: enhanced formaldehyde yield in methanol partial oxidation

A mechanochemical method was employed to prepare modified iron molybdate catalysts with various metal salts as precursors. The physicochemical properties of the iron molybdate catalysts were characterized, and their performances in catalyzing the reaction from methanol to formaldehyde (HCHO) were evaluated. Iron molybdate catalysts doped with Co(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O resulted in high HCHO yields. Compared with a commercial catalyst, the HCHO yields in the reaction with the modified catalyst at an optimal Co/Mo molar ratio reached 97.37%. According to chemical state analysis, the formation of CoO and the efficient decrease in the MoO₃ sublimation rate could be important factors enhancing the HCHO yield in reactions catalyzed with iron molybdate doped with different Co/Mo mole ratios.     

Development of a dispersed iron catalyst for first stage coal liquefication

A procedure yielding a very small particle size iron catalyst for coal liquefaction has been developed at the Pittsburgh Energy Technology Center. This procedure has two important components. The first is incipient wetness impregnation of coal with an aqueous solution of ferric nitrate (subsequently converted to hydrated iron oxide by contact with ammonium hydroxide). The second is proper time/temperature activation of the iron under a gaseous atmosphere of H₂/H₂S to produce pyrrhotite. In continuous operations, an optimum preliquefaction temperature of 275° C was observed for the activation of hydrated iron oxide in the presence of Illinois No. 6 coal. The net effect of proper implementation of this procedure was the development of a finely divided iron catalyst that exhibited high levels of activity in comparisons with molybdenum catalysts.     

Synthesis and characterization of P-modified mesoporous CoMo/HMS–Ti catalysts

A hexagonal mesoporous siliceous material with a wormhole framework structure incorporating Ti (HMS-Ti; Si/Ti atomic ratio of 40) was modified with variable amounts of phosphorous and used as support for CoMo phases. The catalysts were prepared by successive impregnation, with Mo being introduced first. The supports and catalysts were characterized by N₂ adsorption–desorption, High-resolution transmission electron microscopy, X-ray diffraction, FT-IR study of the framework vibrations, DRIFT spectra in the OH region, ¹H NMR, FT-IR spectra of adsorbed NO, micro-Raman spectroscopy and X-ray photoelectron spectroscopy. The catalysts were tested in the reaction of hydrodesulfurization (HDS) of dibenzothiophene (DBT) and their activity compared with that of a commercial P-containing CoMo/γ-Al₂O₃ catalyst. The physical and chemical characterization of the P-modified HMS–Ti substrates shows that the presence of P₂O₅ on the support surface does not change its mesoporous character, but modifies its surface properties. In addition, characterization data of the oxide catalysts show that phosphate favors the dispersion of the active phases and increases the population of octahedral Co²⁺ ions associated to Mo species. As a result, HDS activity was strongly enhanced upon P-loading, which reached a maximum of 0.64 wt%. This catalyst is 3.7 times more active than the commercial one and 2.4 times more active than its P-free counterpart. The highest activity of this catalyst was explained in terms of the specific electronic properties of its active phases and the largest Mo surface exposure on the support.     

Fe2O3/AC催化剂上对甲基苯硫酚的水相催化氧化偶联

以对甲基苯硫酚为模型底物，空气为氧化剂，来研究硫醇水相催化氧化偶联制备二硫醚。以活性炭为载体，采用等体积浸渍法制备了一系列负载型氧化物催化剂，并考察了其在对甲基苯硫酚氧化偶联制备对甲苯二硫醚反应中的催化性能。反应结果表明，活性炭负载的铁氧化物具有最佳催化性能。采用N₂物理吸附、X射线衍射、X射线光电子能谱和透射电镜等表征手段对活性炭负载的铁氧化物催化剂进行了表征。表征结果表明，铁氧化物为高度分散在活性炭上的Fe₂O₃物种。以Fe₂O₃/AC为催化剂，当催化剂焙烧温度为400℃，Fe负载量为5%，在50℃下反应30min时，对甲苯二硫醚的收率高达97.4%；该催化剂循环使用5次后活性无明显下降。     

煅烧温度对磁性铁钛复合氧化物微观结构及脱硝活性的影响

利用共沉淀微波法构筑新型磁性铁钛复合氧化物催化剂,研究了煅烧温度对其物性结构及NH₃-SCR脱硝性能的影响,揭示了钛掺杂对磁性γ-Fe₂O₃晶体高温热转化及其脱硝性能的优化机制。结果表明：当煅烧温度由300℃升至500℃时,磁性铁氧化物的比表面积、孔容先增大后减小,且较高的煅烧温度促使其γ-Fe₂O₃晶体逐步转变为α-Fe₂O₃晶体,导致磁性铁氧化物表面Fe²⁺和活性氧浓度增大,促使其NH₃-SCR脱硝性能降低;掺杂钛可提高磁性铁氧化物的热稳定性,抑制了高温煅烧下γ-Fe₂O₃晶体向α-Fe₂O₃晶体的不可逆转变和其孔隙结构的坍塌,增大了高温煅烧时磁性铁氧化物催化剂的比表面积和比孔容,合适的煅烧温度为400℃;该煅烧温度下,催化剂低温活性最佳,反应温度高于220℃、空速比60000h^-1时可获得80%以上的NO_x转化效率。     

Si含量对CO_2加氢制烃铁基催化剂的影响

以湿固相研磨法制备不同硅含量的铁基催化剂,采用X射线衍射、H2程序升温还原和傅里叶红外光谱对催化剂进行表征,在V(H_2)∶V(CO_2)∶V(N_2)=16∶8∶1、反应压力1.6 MPa、反应温度230℃、反应时间48 h和空速6 000 m L·(h·g-cat)-1条件下,在固定床反应器中考察催化剂的CO_2加氢制烃反应活性和烃类选择性。结果表明,随着Si O_2掺入量增加,催化剂的还原性能降低,结晶度呈下降趋势,CO_2转化率下降,但C5+烃类产物选择性在硅含量为10%时达到最大,为38.6%。     

NH3-SCR脱硝催化剂现状及中毒失活现象研究进展

随着国家能源深度调峰的推进并降低锅炉负荷运行,发现锅炉出口烟温难以驱动选择性催化还原脱硝反应的问题,通过综述氨选择性催化还原反应（NH₃-SCR）催化剂在国内外的研究进展,发现单一贵金属催化剂温度窗口窄、易中毒和比表面积较小等问题影响了其催化活性,而复合的金属氧化物催化剂、新兴的生物炭催化剂和沸石催化剂具有多孔性和良好的稳定性等优点。催化剂脱硝机理可以简单表示为其表面的酸性位点吸附氨气和氧气并与之反应,催化剂的中毒原因可总结为其内部空隙被碱金属堵塞、金属氧化物被二氧化硫抢先反应和酸性位点被羟基覆盖,具体表现为催化剂的活性降低、吸附NH₃的效率下降。对比了商用催化剂和新兴催化剂的脱硝性能得出结论,未来的研究方向是研发耐硫、耐水、耐碱的低温高效脱硝催化剂。     

固体碱K_2CO_3/Al-Ni及K_2CO_3/Al-Ni-O催化制备生物柴油

分别采用合成的铝镍类水滑石和其焙烧后复合氧化物为载体,负载K_2CO_3制得负载型固体碱催化剂,并用于催化食用菜籽油制生物柴油的反应。考察甲醇与菜籽油物质的量比、反应时间和反应温度对催化性能的影响,结果表明,在甲醇与菜籽油物质的量比10∶1、反应温度60℃、反应时间6 h和催化剂用量为油质量的5%条件下,生物柴油产率最高,为82.4%,且催化剂可重复使用,具有稳定的催化作用。     

The structures of VOx/MOx and alkali-VOx/MOx catalysts and their catalytic performances for soot combustion

Vanadium oxides supported on γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ were studied on their molecular structures and reactive performances for soot combustion. To investigate the effect of different alkali metals on the structures and reactivities of supported-vanadium oxide catalysts, they were doped into the V₄/TiO₂ catalyst which had the best intrinsic activity for soot combustion in the selected supported vanadium oxide catalysts. The experimental results demonstrated that the catalytic properties of these catalysts depended on the vanadium loading amount, support nature, and the presence or the absence of alkali metals. The spectroscopic analysis (FT-IR and UV–vis) and H₂-TPR results revealed that the higher activity of alkali-promoted vanadium oxide catalysts could be related to the ability of alkali metal promoting the redox cycle of the active vanadyl species. TG results showed that adding alkali to V_m/TiO₂ catalyst was beneficial to lowering their melting points. Low melting points could ensure the good surface atom migration ability, which would improve the contact between the catalyst and soot. Due to the alkali metal components promoting the redox ability and the mobility of the catalysts, alkali-modified vanadium oxide catalysts could remarkably improve their catalytic activities for soot combustion. The catalytic activity order for soot combustion followed Li > Na > K > Rb > Cs in the catalyst system of alkali-V₄/TiO₂, and the reason why it followed this sequence was discussed.     

聚合硫酸铁铝的制备及除磷性能研究

介绍了利用硫酸法生产钛白粉的副产硫酸和赤泥提铁渣资源化制备聚合硫酸铁铝（PAFS）的工艺,实验得到优化后的最佳工艺条件参数：液固质量比为6∶1、溶出温度为105 ℃、溶出时间为80 min,在此工艺条件下赤泥提铁渣的溶出率达到65.2%,且优化合成的聚合硫酸铝铁中全铁的质量分数为8.23%、氧化铝的质量分数为1.12%、盐基度为12.88%。利用以上工艺条件制备得到的聚合硫酸铁铝与市售净水剂（聚合硫酸铁、聚合氯化铝）做除磷对比实验,实验结果表明,在同一加药量的情况下本研究制备的聚合硫酸铁铝除磷效果较好,去除率最高可达95.45%（加药量为300 mg/L）。     

The nature of metal oxide on adsorptive and catalytic properties of Pd/MeOx/Al2O3 catalysts

The role of ceria, niobium and molybdenum oxides on the promotion of the NO reduction by CO was studied. A bifunctional mechanism was discussed as a function of both the nature of interaction between metal oxide and palladium and the redox properties of each metal oxide.

The NO dissociation was better on the Pd/MoO₃/Al₂O₃ catalyst than on the Pd/CeO₂/Al₂O₃ and Pd/Nb₂O₅/Al₂O₃ catalysts. The explanation for the very high N₂ production on Pd–Mo catalyst during the TPD analysis may be attributed to the NO+Me^δ+ stoichiometric reaction.

The promoting effect of a reducible oxide for the NO+CO reaction at low temperature can be ascribed mainly to its easiness for a redox interchange and its interaction with the noble metal particles. This would increase the surface redox ability and favor the dynamic equilibrium needed for high N₂ selectivity.     

Toluene removal by a DBD-type plasma combined with metal oxides catalysts supported by nickel foam

The performance on toluene removal in a dielectric barrier discharge (DBD) type plasma system under different background gases, including N₂, Ar, N₂/Ar, and N₂/O₂ was studied at room temperature and atmospheric pressure. For comparison, another laboratory-scale plasma-catalysis system was set up and four kinds of metal oxides, i.e., copper oxide, iron oxide, cobalt oxide, and manganese oxide supported on alumina/nickel foam (NF), were used as catalysts. The reaction mechanism and dynamics analysis on toluene removal were suggested. In addition, the characterization of the catalysts was performed by BET, XRD, SEM, FT-IR, and EDS. It has been found that adding argon in the background gas could improve the toluene removal efficiency significantly in the plasma system. Combining plasma with catalyst in situ could improve the toluene removal efficiency, increase the carbon dioxide selectivity and suppress byproducts formation. In addition, manganese oxide/alumina/NF was confirmed as the most effective catalyst for toluene removal. The XRD and SEM results showed that the proportion of metal oxide increased while aluminate decreased after plasma application. The granularity of the grain on the catalyst surface became smaller and the distribution became more uniform after discharge. The results of FT-IR and EDS suggested that some organic compounds deposited on the catalysts after plasma reaction.     

复合氧化物催化剂催化氧化甲苯性能

以γ-Al2O3为催化剂载体,铜、锰为活性组分,稀土元素铈为助催化剂,采用浸渍法制备复合氧化物催化剂5%Cu/γ-Al2O3、5%Mn/γ-Al2O3、5%Cu-5%Mn/γ-Al2O3和5%Cu-5%Mn-1.6%Ce/γ-Al2O3,并考察其催化氧化甲苯性能。研究表明,复合氧化物催化剂催化氧化甲苯具有显著的效果,5%Cu-5%Mn/γ-Al2O3催化剂和5%Cu-5%Mn-1.6%Ce/γ-Al2O3催化剂表现出良好的低温活性和催化性能,对甲苯的完全燃烧温度分别为340℃和285℃。采用SEM和BET对催化剂进行表征,结果表明,催化剂的催化活性与活性组分在催化剂表面的分散度和催化剂的孔结构相关。     

修饰的CuO/Fe2O3水煤气变换催化剂的性能测试与表征

ZrO₂是一种高熔点金属氧化物,同时具有弱酸性和弱碱性以及氧化性与还原性,具有p型半导体性质,易产生氧空穴,是理想的催化材料。通过添加不同质量分数的ZrO₂(0~5%) 作为助剂,采用分步沉淀法制备系列CuO/Fe₂O₃-ZrO₂催化剂,通过XRD、N₂物理吸附-脱附、H₂-TPR和CO₂-TPD等表征技术,考察ZrO₂助剂对CuO/Fe₂O₃水煤气变换催化剂催化性能的影响。结果表明,适量ZrO₂（质量分数1%）的添加,削弱了CuFe₂O₄中铜铁物种之间的协同作用,增加了催化剂中可被还原的铜物种的数量,形成较多的弱碱性位点,有利于增加活性中心铜的数量,具有较好的水煤气变换反应活性和热稳定性。     

Oxidation of benzene to phenol on supported Pt-VOx and Pd-VOx catalysts

Gas-phase oxidation of benzene using a mixture of oxygen and hydrogen has been carried out on silica-supported vanadium oxide catalysts modified with platinum or palladium. Catalyst activity and phenol selectivity were studied as a function of the precious metal used, the vanadium oxide loading as well as of temperature. The binary catalysts have been characterized by TPR and TEM. Pt-VO_x/SiO₂ catalysts were more active than Pd-VO_x/SiO₂ catalysts. By using platinum catalysts benzene conversion amounted to 1.0% (S_phenol=97%) at 413 K, whereas palladium catalysts reached a conversion of only 0.2% (S_phenol=86%) for the same contact time and temperature. The most active catalyst for the oxidation of benzene to phenol was a low vanadium loaded 0.5 wt.% Pt–3 wt.% V on silica catalyst. At temperatures above 413 K phenol selectivity decreased strongly because of enhanced total oxidation. Active catalysts need both components: a dispersed transition metal oxide such as VO_x as well as small precious metal particles such as platinum. The activity of the catalysts arises from a close interaction between the redox-active compound VO_x and the electron mediator and hydrogen activator platinum as was confirmed by correlation of catalytic results and catalyst properties. Highly dispersed platinum particles are exclusively located on the vanadium oxide covered surface as demonstrated by TEM investigations. TPR studies showed and enhanced reducibility of a part of vanadium(V) oxide indication a close neighborhood of VO_x and platinum.     

Characterization of Ni---W/A12O3-SiO2 aromatics saturation catalysts used in a one-year commercial HDS run

A series of Ni---W/A1₂O₃-SiO₂ catalysts with different A1₂O₃/SiO₂ ratios were prepared and loaded in a commercial HDS unit for a year. The catalytic properties of the freshly sulfided and spent catalysts were investigated by performing structural analyses and model test reactions. The aggregation of the WS₂ slabs in the lateral direction, which was observed by EXAFS and TEM, was a major cause of the catalyst deactivation. The addition of SiO₂ into the catalyst support was found to suppress the structural changes of the catalyst.