Vapor-phase selective hydrogenation of maleic anhydride to succinic anhydride over Ni/TiO2 catalysts

A series of supported Ni/TiO₂ catalysts were prepared by incipient wetness impregnation method under different calcination temperatures, and the as-prepared catalysts were characterized by X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic properties of these Ni/TiO₂ catalysts were investigated in the vapor phase hydrogenation of maleic anhydride (MA) to succinic anhydride (SA). The results showed that the catalytic activity and the selectivity of the Ni/TiO₂ catalysts were strongly affected by the calcination temperature. The catalyst calcined at 1023 K showed a relatively higher SA selectivity of 96% at high MA conversion (96%) under the tested conditions (493 K and 0.2 MPa). The improvement of SA selectivity could be mainly assigned to the presence of suitable metal–support interaction, which can play a role in catalytic property of active nickel species as electron promoter. Besides, the change of surface properties of TiO₂ support with the increasing calcination temperatures, e.g., the decrease of Lewis acid sites, might also have some positive role in reducing the side-products like γ-butyrolacetone (GBL).     

Hydrothermal stability of HZSM-5 catalysts modified with Ni for the transformation of bioethanol into hydrocarbons

The hydrothermal stability of catalysts prepared from HZSM-5 zeolites doped with Ni (by impregnation) has been studied in the transformation of bioethanol into hydrocarbons, in order to remove the main barrier for the use of HZSM-5 zeolite catalysts in this process, which is the irreversible deactivation by dealumination of the zeolite above 400 °C with water in the reaction medium. The main effect of doping is the attenuation of the zeolite acid strength from 135 to 125 kJ (mol of NH₃)⁻¹ for a Ni content of 1 wt.%. The catalysts maintain a high level of activity and a high selectivity of propene and butenes, and Ni doping significantly attenuates irreversible deactivation of the catalyst by dealumination of the zeolite. The zeolite catalyst doped with 1 wt.% of Ni maintains its kinetic behaviour in reaction-regeneration cycles when the reaction step is carried out at 500 °C and with 5 wt.% of water in the feed. This catalyst allows operating at 400 °C without irreversible deactivation with bioethanol containing 75 wt.% of water.     

Synthesis of 2-Methylpyrazine Over Highly Dispersed Copper Catalysts

Abstract  

A series of CuCoAl catalysts were synthesized by co-precipitation and impregnation methods, tested in synthesis of 2-methylpyrazine (2-MP) and characterized by X-ray diffraction, N₂ adsorption, thermo-gravimetry analysis, H₂-temperature-programmed reduction, dissociative N₂O adsorption and temperature-programmed oxidation. The precursors prepared by co-precipitation method shows a well-crystallized hydrotalcite. The study proves that the calcination temperature of hydrotalcite has a significant effect on the catalyst surface area, crystallite size and copper dispersion. In comparison with catalyst prepared by impregnation, the catalyst prepared by co-precipitation method calcined at 500 °C exhibits higher specific surface area, higher copper dispersion and the better reducibility. Consequently, CuCoAl catalyst derived from hydrotalcite is more active and selective for synthesis of 2-MP. Moreover, it shows the better stability due to the good resistance to coke formation.     

Influence of binder on catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone

The influences of binders (alumina, silica sol, kaolin) on the performance of Ni/H-ZSM-5 for hydrodeoxygenation of cyclohexanone were investigated in a fixed-bed reactor. N₂ sorption, X-ray diffractions, H₂-temperature-programmed reduction, transmission electron microscopy, ²⁷Al MAS NMR, and temperature-programmed desorption of ammonia were used to characterize the catalysts. The obtained results exhibited that porosity and acidity of the catalysts were strongly influenced by the binders. The most outstanding catalytic performance was observed on catalyst with alumina binder, which bears a well-developed pore structure and more acid sites than the others. Thus, alumina was chosen as the optimum binder to Ni/HZSM-5.     

Transformation of olefin over Ni/HZSM-5 catalyst

Olefins in the cracked naphtha can be transformed into aromatics and isoparaffin to reduce the olefin content as well as to improve the octane number. In this work, Ni/HZSM-5 bifunctional catalyst was prepared and was characterized by nitrogen adsorption, FT-IR analysis with adsorbed pyridine as well as by X-ray powder diffraction analysis. The activity of the catalyst was investigated with the transformation of 1-hexene. The experimental results show that the main reactions occurring over Ni/HZSM-5 at relatively low temperature are cracking and isomerization of 1-hexene, which results in the high concentration of olefin in the hydrotreated product. The double-bond isomerization of 1-hexene is dominant at low temperature (<220 °C) while the skeletal isomerization is elevated at high temperature, and the aromatization activity of the Ni/HZSM-5 catalyst is promoted by high temperature. The sulfided Ni/HZSM-5 catalyst shows higher aromatization activity than the reduced one and the zeolite supported Ni catalysts show comparatively better stability than that without metal components.     

Microwave discharge-assisted NO reduction by CH4 over Co/HZSM-5 and Ni/HZSM-5 under O2 excess

Microwave discharge-assisted reduction of NO by CH₄ in the presence of excess O₂ over Co/HZSM-5 and Ni/HZSM-5 catalysts was studied. By comparing the activities of the catalysts in the microwave discharge mode with that in the conventional reaction mode, it is demonstrated that microwave discharge enhanced greatly the conversion of NO to N₂, and expanded the reaction temperature range of the catalysts. For the Co/HZSM-5 catalyst, the conversion of NO to N₂ increased by 30%, and the optimum temperature decreased by 200°C. With the Ni/HZSM-5 catalyst, the highest activity was close to 100%, and the optimum temperature decreased by 325°C. The conversion of CH₄ also increased in the microwave discharge mode over both of the catalysts.     

Interaction between ammonium heptamolybdate and NH4ZSM-5 zeolite: the location of Mo species and the acidity of Mo/HZSM-5

Mo/HZSM-5 catalysts show high reactivity and selectivity in the activation of methane without using oxidants. Mo/HZSM-5 catalysts with Mo loading ranging from 0 to 10% were prepared by impregnation with an aqueous solution of ammonium heptamolybdate (AHM). The samples were dried at 393 K, and then calcined at different temperatures for 4 h. The interaction between Mo species and NH₄ZSM-5 zeolite was characterized by FT-IR spectroscopy, differential thermal analysis (DTA) and temperature programmed decomposition (TPDE) and NH₃-TPD at different stages of catalyst preparation. The results showed that if Mo/HZSM-5 catalysts were calcined at a proper temperature, the Mo species will interact with acid sites (mainly with BrØnsted acid sites) and part of the Mo species will move into the channel. The Mo species in the form of small MoO₃ crystallites residing on the external surface and/or in the channel, and interacting with BrØnsted acid sites may be responsible for the methane activation. Strong interaction between Mo species and the skeleton of HZSM-5 will occur if the catalyst is calcined at 973 K. This may lead to the formation of MoO ₄ ^2– species, which is detrimental to methane activation.     

Characterization and testing of sol-gel catalysts prepared as thin layers in a plate reactor

Catalytic plate reactors offer many advantages over conventional reactors, including a major reduction in size and much better temperature control. This study examines the characteristics of thin catalyst coats prepared by the sol-gel method and calcined at different conditions. Employing the catalyst as a thin layer (< 100 μm) on the surface of plate reactors reduces mass and heat transfer limitations compared with pellet catalysts and can improve the effectiveness factor. A sol-gel of Ni/Al₂O₃ catalyst, with good rheological properties and good adherence onto stainless steel substrate, was prepared and characterized. The effects of calcination temperature, nickel content and calcination environment on the catalyst properties were investigated. The results revealed that the highest catalyst surface area was obtained at 400 °C for all calcined coatings. The presence of nitrogen gas during drying and calcining seemed to increase the catalyst surface areas and improve its adherence properties. Rheological evaluation of the prepared coats proved to be an effective tool in characterizing the thin coatings. The Ni/Al₂O₃ catalyst exhibited high activity and achieved more than 80% conversion for steam reforming of methane. The reactions were not diffusion limited based on the values of activation energy.     

Synthetic natural gas from CO hydrogenation over silicon carbide supported nickel catalysts

Silicon carbide supported nickel catalysts for CO methanation were prepared by impregnation method. The activity of the catalysts was tested in a fixed-bed reactor with a stream of H₂/CO = 3 without diluent gas. The results show that 15 wt.% Ni/SiC catalyst calcined at 550 °C exhibits excellent catalytic activity. As compared with 15 wt.% Ni/TiO₂ catalyst, the Ni/SiC catalyst shows higher activity and stability in the methanation reaction. The characterization results from X-ray diffraction and transmission electron microscopy suggest that no obvious catalyst sintering has occurred in the Ni/SiC catalyst due to the excellent thermal stability and high heat conductivity of SiC.     

High-temperature close coupled catalysts Pd/Ce-Zr-M/Al2O3 (M = Y, Ca or Ba) used for the total oxidation of propane

A series of high-temperature close coupled catalysts Pd/Ce-Zr-M/Al₂O₃ (M = Y, Ca or Ba) were prepared by ultrasonic-assisted successive impregnation. The catalysts were subjected to a series of characterization measurements. The results of activity evaluation show that Y is the best promoter for propane total oxidation, especially at the calcination temperature of 1100 °C. It is interesting that although the BET specific surface areas and the dispersion of Pd species decrease, the Y-promoted catalyst calcined at 1100 °C shows higher catalytic activity than the corresponding one calcined at 900 °C and better sulfur-resisting performance. The results of TEM, TPHD and CO chemisorption indicate that Y can remarkably increase the dispersion of Pd species. However, the dispersion is hard to be connected with the activity increase as the calcination temperature is elevated from 900 to 1100 °C. The change of active phases and the interaction between Pd species and the supports may account for the activity enhancement. Combined with XRD, H₂-TPR and O₂-TPD results, it is deduced that the coexistence of metallic Pd and PdO species in the catalysts calcined at 1100 °C may be also favorable to C₃H₈ oxidation. In a word, Pd/Ce-Zr-Y/Al₂O₃ is indeed a promising high-temperature close coupled catalyst applicable to high temperature.     

Transformation of methanol to gasoline range hydrocarbons using HZSM-5 catalysts impregnated with copper oxide

Various CuO/HZSM-5 catalysts were studied in a fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. The catalysts were prepared by wet impregnation technique. Copper oxide loading over HZSM-5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, BET surface area, metal oxide content, scanning electron microscopy (SEM) and thermogravimetric (TGA) techniques were used to characterize the catalysts. Higher yield of gasoline range hydrocarbons (C₅-C₁₂) was obtained with increased weight % of CuO over HZSM. Effect of run time on the hydrocarbon yields and methanol conversion was also investigated. The activity of the catalyst decreased progressively with time on-stream. Hydrocarbon products’ yield also decreased with the increase in wt% of CuO. Relatively lower coke deposition over HZSM-5 catalysts was observed compared to CuO impregnated HZSM-5 catalyst.     

焙烧温度对HZSM-5分子筛催化1-丁烯齐聚性能的影响

考察焙烧温度对HZSM-5分子筛催化剂结构及1-丁烯齐聚性能的影响,采用XRD、SEM和NH3-TPD对催化剂进行表征。结果表明,升高焙烧温度,对HZSM-5分子筛催化剂的晶相和晶粒尺寸没有影响,催化剂中弱酸与强酸的酸强度和酸量均随焙烧温度的升高逐渐减弱。在催化剂晶粒尺寸一定条件下,催化剂酸性对催化剂的齐聚性能有较大影响,焙烧温度500℃时,C5+收率和C10+选择性最佳。     

Hydrogenation of Levulinic Acid Using Formic Acid as a Hydrogen Source over Ni/SiO2 Catalysts

Several Ni/SiO₂ catalysts were developed for the hydrogenation of levulinic acid using formic acid as the hydrogen source. The catalysts were prepared by a variety of methods including impregnation, co‐precipitation, deposition‐precipitation, and citric acid assisted impregnation combustion. The morphological properties were investigated by XRD, N₂ sorption, HRTEM, and H₂ pulse chemisorption measurements. XRD patterns of the calcined material revealed the presence of NiO particles, while calcination in an inert atmosphere produced Ni particles through in situ reduction of NiO. The reaction proceeded without external H₂ flow using formic acid as hydrogen source. The Ni/SiO₂ catalyst prepared by the citric acid assisted method and calcined in inert gas flow was the most efficient for the hydrogenation of levulinic acid without external H₂ flow. The high catalytic performance was attributed to the high dispersion of cheap and earth‐abundant Ni nanoparticles and optimal porosity.     

Studies of a Supported Titanium Catalyst System Using Magnesium Dichloride–Alcohol Adduct

Magnesium dichloride reacts with aliphatic alcohols [ROH; R = n-C₂H₅, n-C₃H₇, i-C₃H₇, n-C₄H₉, i-C₄H₉, t-C₄H₉, n-C₅H₁₁, n-C₆H₁₃, C₆H₁₂(C₂H₅)] to form well-defined solid adducts. Compositional analysis of adducts indicates that the stoichiometric ratio of magnesium dichloride to alcohol depends on length of alkyl group and nature of isomeric alcohol. Magnesium dichloride-2-ethyl-l-hexanol adduct was treated with diphenyldichlorosilane in the presence of dibutylphthalate to obtain active magnesium dichloride support. The titanation process of active magnesium dichloride gives supported magnesium–titanium catalyst (Mg–Ti). The catalyst was characterized by compositional analysis and specific surface area measurements. Performance of the catalyst for polymerization of propene was evaluated with triethylaluminum (TEAL) and phenyltriethoxysilane (PES) as cocatalyst. The yield and isotacticity of the polymer is governed by polymerization parameters such as Si/A1 ratio and polymerization time.     

用于环戊烯氧化合成戊二醛反应的钨基催化剂的表征

Tungsten-containing hexagonal mesoporous silica （W-HMS） supported tungsten oxide catalysts （WOx/W-HMS） was prepared for the selective oxidation of cyclopentene with aqueous hydrogen peroxide to glutaraldehyde. X-ray diffraction （XRD） results indicated that the crystal form of the active phase （tungsten oxide） of the WOx/W-HMS catalysts was dependent on the W loading and calcination temperature. X-ray photoelectron spec- troscopy （XPS） analysis revealed that the dispersed tungsten oxides on the surface of W-HMS support consisted of a mixture of W（V） and W（VI）. It was found that a high content of amorphous W species in （5＋） oxidation state resuited in the high catalytic activity. When the W loading was up to 12% （by mass） or the catalyst precursor was treated at temperature of 623 K, the catalytic activity decreased due to the presence of WO3 crystallites and the oxidation of W（V） to W（VI） on the catalyst surface. Furthermore, NH3-temperature-programmed-desorption （NH3-TPD） analysis showed that the effects of W loading and calcination temperature on the acidity of the catalysts were related to the catalytic activity. A high selectivity of 80.2% for glutaraldehyde with a complete conversion of cyclopentene was obtained over 8%WOx/W-HMS catalyst calcined at 573 K after 14 h of reaction.     

Formation of the rhodium oxides Rh2O3 and RhO2 in Rh/NaY

The oxidation states of Rh in NaY supported catalysts have been studied by temperature programmed reduction (TPR). After calcination of the exchanged catalyst to 380°C, both RhO₂ and Rh₂O₃ are identified, besides small amounts of RhO⁺ and Rh³⁺. Quantitative reduction is possible for samples calcined at temperatures not exceeding 500°C. Re-oxidation of the reduced samples leads to formation of RhO₂ and Rh₂O₃, with negligible protonolysis to Rh³⁺. The dioxide prevails after re-oxidation at 320°C, but the sesquioxide after oxidation at 500°C. In the temperature regime where both oxides coexist the reduction of NO with propane is catalyzed even at an O₂/C₃H₈ ratio of 10. Total oxidation of propane reaches 80% at 350°C.     

Reduction of NO by CH4 with Microwave Heating

The reduction of NO by CH₄ in the presence of excess O₂ over Co/HZSM-5, Ni/HZSM-5 and Mn/HZSM-5 catalysts with microwave heating was studied. By comparing the activities of the catalysts in the microwave heating mode with that in the conventional reaction mode, it was demonstrated that microwave heating could greatly reduce the reaction temperature, and could clearly expand the temperature window of the catalysts. Especially for the Co/HZSM-5 catalyst, the maximum conversion of NO to N₂ in the conventional reaction mode was consistent with that in the microwave heating mode. However, the temperature window for the maximum conversion in the microwave heating mode was from 260 to 360 °C instead of a temperature of 420 °C in the conventional reaction mode. The results suggest that microwave heating has a novel effect in the reduction of NO.     

Calcination of Co-Based Fischer–Tropsch Synthesis Catalysts

The calcination of Co-based slurry-phase Fischer–Tropsch synthesis catalysts was investigated. Fischer–Tropsch synthesis is part of the gas-to-liquids (GTL) process that produces gas oil and naphtha from natural gas. For the GTL process, the preparation of highly active Co-based catalysts is of utmost importance. This paper shows that the conditions during the calcination of impregnated cobalt precursors have a significant influence on the performance of the final catalyst. The options of calcination in rotary kilns, furnaces and fluidized-bed reactors were considered. It was found that the catalyst performance is strongly dependent on the heating rate and the air-space velocity during the preferred option of fluidized bed calcination. The postulation that Co₃O₄ is not the preferred oxide phase of the calcined intermediate catalyst is supported by a temperature-programmed reduction (TPR) study.     

Effect of calcination behaviors on precipitated iron–manganese Fischer–Tropsch synthesis catalyst

Calcination behaviors play an important role in Fischer–Tropsch (FT) performance over a slurry iron–manganese catalyst. The present study was undertaken to investigate the effects of calcination behaviors (calcination temperature, heating rate and calcination atmosphere) on the textural properties, reduction/carburization behavior, bulk phase structure and FT synthesis performances over precipitated Fe–Mn catalysts. N₂ physisorption, X-ray photoelectron spectroscopy (XPS), H₂ thermal gravimetric analysis (TGA) and M?ssbauer effect spectroscopy (MES) were used to characterize the catalyst. It is found that increasing calcination temperature and heating rate lead to low surface area and high enrichment of Mn on the catalyst surface. High calcination temperature also increased the crystallite size of α-Fe₂O₃ and suppressed the reduction/carburization of the catalysts in H₂ and syngas. Low calcination temperature and low heating rate promoted the further carburization of the catalyst and increased the activity during FT process. High calcination temperature and low heating rate restrained the formation of CH₄, increases C₅⁺ selectivity and improved the selectivity to light olefins. In addition, calcination in argon could improve the carburization and increase FT activity of the catalyst. The present iron–manganese catalyst with lower calcination temperature, lower heating rate and calcined in argon is optimized for its FT performances.     

The effect of catalyst calcination temperature on the diameter of carbon nanotubes synthesized by the decomposition of methane

The effect of catalyst calcination temperature on the uniformity of carbon nanotubes (CNTs) diameter synthesized by the decomposition of methane was studied. The catalysts used were CoO-MoO/Al₂O₃ without prior reduction in hydrogen. The results show that the catalyst calcination temperature greatly affects the uniformity of the diameter. The CNTs obtained from CoO-MoO/Al₂O₃ catalysts, calcined at 300 °C, 450 °C, 600 °C, and 700 °C had diameters of 13.4 ± 8.4, 12.6 ± 5.1, 10.7 ± 3.2, and 9.0 ± 1.4 nm, respectively, showing that an increase in catalyst calcination temperature produces a smaller diameter and narrower diameter distribution. The catalyst calcined at 750 °C was inactive in methane decomposition. Transmission electron microscopy (TEM) studies showed that CNTs grown on the catalyst calcined at 700 °C were of uniform diameter and formed a dense interwoven covering. High-resolution TEM shows that these CNTs had walls of highly graphitized parallel graphenes.