酸碱性和氧化还原性对负载型钒基催化剂丙烷氧化脱氢性能的影响

用ＸＲＤ、Ｒａｍａｎ、ＴＰＲ和Ｐｙ－ＩＲ表征乙酰丙酮络钒法制备的不同氧化物和磷酸盐负载的钒氧化物催化剂，结果表明，钒氧化物在载体ＭｇＯ、Ａｌ２Ｏ３、Ｍｇ３（ＰＯ４）２、ＡｌＰＯ４和Ｚｒ３（ＰＯ４）４上是高分散的，没有生成明显的Ｖ２Ｏ５晶相；催化剂的可还原性与相应载体氧化物或磷酸盐的金属还原电位序有较好的对应关系，同时与其丙烷氧化脱氢活性也存在较好的平行关系，表明钒氧化物与载体的阳离子形成Ｖ－Ｏ－Ｍ桥键，该桥键氧较易移去，可能是丙烷氧化脱氢的活性氧物种；催化剂表面酸性位有利于丙烷Ｃ－Ｈ键的活化，但导致深度氧化产物增多。     

SCANNING ELECTRON MICROSCOPY STUDY OF CO-PRECIPITATED IRON OXIDE CATALYSTS

ABSTRACT

Iron oxide Fischer-Tropsch catalysts were prepared using a sol-gel method to incorporate varying amounts of silica (SiO₂) and a constant amount of potassium oxide (K₂O) promoters. The sol-gel slurries containing different Fe/Si ratios were dried using a spray dryer. The spray-dried materials were calcined at 300°C prior to the use as catalysts for the Fischer-Tropsch reaction. Scanning electron microscopy (SEM), combined with energy dispersive X-ray spectroscopy (EDS) and elemental dot mapping (EDM) techniques, was utilized to characterize the structural morphology for these promoted iron oxide catalysts. The results indicate that the promoters (SiO₂, k₂O) are evenly distributed throughout the catalysts, and no agglomerated regions of iron, silica or potassium could be observed. Thus, the sol-gel preparation, followed by spray drying produces industrial catalysts of fine particle morphology and a uniform distribution of the promoters.     

Synthesis of Vanadium Catalysts Supported on Cerium Containing TiO<Subscript>2</Subscript> Nanotubes for the Oxidative Dehydrogenation of Propane

Cerium containing TiO₂ nanotubes (CeTNTs) were successfully synthesized through the hydrothermal method and applied as support for vanadium catalyst in the oxidative dehydrogenation of propane. The impregnation method was employed to load 2, 5 and 8 wt % vanadium on the CeTNT surface. The catalysts were labeled as xV/CeTNT which x refers to the amount of vanadium loading. For a comparison, pure TNT was also synthesized and impregnated with 5 wt % vanadium. Based on TGA, XRD and TEM analyses, it was concluded that the addition of Ce increased the thermal stability of TNT. The Raman results showed that the 5V/CeTNT sample with a higher surface area hosted a higher number of monomeric VO_x species compared to 5V/TNT. On the other hand, it was shown that the population of monomeric VO_x species decreased as the vanadium loading increased. Catalytic results showed that propane conversion increased while propylene selectivity decreased as the vanadium loading increased. The best catalytic performance belonged to the 5V/CeTNT sample with propylene yield of about 10.6 wt % at the reaction temperature of 500°C.     

n-Pentane Hydroconversion Using Pt-loaded Zeolite Catalysts

Abstract

Pt/H-ZSM-5 and Pt/H-MOR catalysts with different Pt contents were prepared via impregnation using H₂PtCl₆ · 6H₂O or via exchange using Pt(NH₃)₄Cl₂, calcination in air at 530°C and reduction in H₂ at 500°C. The prepared catalysts were tested for n-pentane hydroisomerization and hydrocracking via bifunctionality at 250–500°C using a micro-catalytic pulse reactor. It is found that the dispersion of Pt-exchanged zeolites is higher than the corresponding Pt-impregnated zeolites at all Pt contents. It is also found that the dispersion of Pt/H-ZSM-5 catalysts either exchanged or impregnated are higher than the corresponding Pt/H-MOR catalysts. Temperature-programmed desorption (TPD) data showed that the impregnated catalysts possess a higher acid sites number than the exchanged catalysts; and that the Pt/H-ZSM-5 catalysts have a higher number of acid sites than do the Pt/H-MOR catalysts, whereas the latter catalysts possess higher strength of acid sites at all Pt contents. The hydroisomerization activities using Pt exchanged catalysts, supported either on H-ZSM-5 or H-MOR, are higher than the impregnated catalysts at almost all Pt contents. It is also concluded that the H-ZSM-5-supported catalysts, either exchanged or impregnated, are more active than the H-MOR supported ones. Hydrocracking is higher using all loaded H-MOR catalysts.     

Selective nano alumina supported vanadium oxide catalysts for oxidative dehydrogenation of ethylbenzene to styrene using CO2 as soft oxidant

Nano alumina-supported V₂O₅ catalysts with different loadings have been tested for the dehydrogenation of ethylbenzene with CO₂ as an oxidant. High surface area nano-alumina was prepared and used as support for V₂O₅ as the catalyst. The catalysts were synthesized by impregnation techniques followed by calcinations and microwave treatment, denoted as V₂O₅/γ-Al₂O₃-C and V₂O₅/γ-Al₂O₃-MW, respectively. The V₂O₅ loading was varied on nano-alumina from 5 to 30 wt%. The support and catalysts were characterized by X-ray diffraction (XRD), Barett–Joyner–Halenda (BJH) pore-size distribution, N₂-adsorption isotherms, Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and temperature programed desorption (TPD-NH₃). The characterization results indicated that V₂O₅ is highly dispersed on alumina up to 30%-V₂O₅/γ-Al₂O₃-MW prepared by MW method. The TPD studies indicated that there are significant differences in acid amount and strength for V₂O₅/γ-Al₂O₃-C and V₂O₅/γ-Al₂O₃-MW-catalysts. The catalytic activity of the prepared catalysts was evaluated in the temperature range 450–600 °C in relation to the physicochemical properties and surface acidity. The results revealed that optimum catalytic activity and selectivity (～100%) toward styrene production were obtained using 10% V₂O₅/γ-Al₂O₃-MW catalyst treated with microwave.     

Effects of Modified Co-Mo Catalysts for FCC Gasoline HDS on Catalytic Activity

Abstract

In this article, a series of catalysts with HZSM-5/γ-Al₂O₃, HZSM-5/TiO₂-γ-Al₂O₃ as supports, bearing Co-Mo as active components, were prepared, and the catalysts were modified with alkaline earth and VIII, IB metal oxide. The catalysts were evaluated by hydrodesulfurization for QILU FCC gasoline. The experiment results showed that: (1) the RON (research octane number) of effluents rose with the increase of ZSM-5 mass percent in the support, but the HDS ratio reduced; (2) the catalysts with ZSM-5/TiO₂-Al₂O₃ as support had higher HDS ratio but lower RON of effluent; and (3) the catalysts modified with metal oxide had higher RON of effluent, but lower HDS ratio, compared with the stuff, and as to RON of effluent and hydrodesulfurization ratio for the modified catalysts, it had the following order: Ba-modified > Fe-modified > Cu-modified.     

Efficacy ofapplication of zinc oxide on the surface of the NiO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalytic system

The surface and catalytic properties of the NiO/Al₂O₃ system after deposition of 3 to 7% zinc oxide on its surface and heat treatment at 400, 600, and 800°C were investigated by X-ray diffraction analysis, nitrogen adsorption at −196°C, and catalytic oxidation of carbon monoxide by oxygen at 150-250°C. It was shown that calcination of the catalyst at 400°C decreases the specific surface area, while it increases it at 600 and 800°C. The decrease in the specific surface area is accompanied by an increase in the size of the NiO/Al₂O₃ crystallites. The activity of the catalysts calcined at 400°C in oxidation of carbon monoxide by oxygen, manifested by a constant reaction rate, increases with an increase in the zinc oxide content on the surface. After deposition of the zinc oxide, the mechanism of the oxidation reaction remains as before, but the concentration of active centers in the catalyst changes.     

Hydrotreating of Maya Crude Oil: I. Effect of Support Composition and Its Pore-diameter on Asphaltene Conversion

Abstract

A systematic study for a concept governing support effect in heavy oil hydrotreating (HDT) catalysts is performed. Different Al₂O₃ and its mixed oxides supports were prepared and CoMo supported catalysts were tested for Maya heavy crude oil hydrotreating. Fresh and spent catalysts are characterized with N₂ adsorption-desorption, element analysis, and scanning electron microscopy-energy dispersion analysis by x-ray (SEM-EDAX), which confirms that coke and metals deposition on the surface of catalyst is most probably near the pore mouth. It is also demonstrated from these results that asphaltene conversion depends on the pore diameter of the catalyst, while other hydrotreating conversions (hydrodesulfurization (HDS), hydrodenitogenation (HDN), and in some extent hydrodemetallization (HDM)) are more likely affected by the nature of active metal distribution. The evaluation of alumina mixed oxide (TiO₂, ZrO₂, B₂O₃, and MgO) supported catalysts indicates that supports with basic nature have better stability than the acid ones.     

Atomic and nanocluster Ce species on graphene oxides for selective catalytic reduction of NO with NH3

In this work, a catalyst of graphene oxide supported CeO₂ (referred to as CeO₂/GO) is prepared and characterized by TEM, H₂-TPR, NH₃-TPD and XPS. The catalytic tests show a NO conversion of 97% at a range of 225?°C to 325?°C with a good stability and water resistance. The microscopic studies display atomic and nanocluster scale distributions of Ce species on large specific surface areas of GO. The structural and surface analyses demonstrate high ratio of Ce³⁺ and chemisorbed oxygen on surface due to the strong interaction between ceria and GO are beneficial to NH₃-SCR.     

KINETIC AND STRUCTURAL STUDIES OF CALCIUM-BASED SORBENTS FOR HIGH-TEMPERATURE COAL-GAS DESULFURIZATION

ABSTRACT

The absorption of H₂S by large particles of limestone, dolomitic limestone and dolomite (average mass-radius of 0·40 mm) was tested under simulated coal gases. Below the calcination temperature of CaCO₃ (about 900^°C under 1 bar of CO₂), complete conversion of the calcium carbonate to calcium sulfide can only be achieved with dolomite. Above the calcination temperature of CaCO₃, the conversion to CaS is complete for all three sorbents in about one hour when 10,000 ppm H₂S is present in the gas phase. Large particles of limestone thus appear to be a suitable sorbent for high-temperature coal-gas desulfurization (above about 900 ^°C). A mathematical model based on the kinetic information collected in this work predicts the desulfurization performance of a packed or moving bed of limestone particles. Finally, a low-temperature regeneration scheme for the spent sorbent (CaS) in which sulfur can be subsequently recovered as the element is suggested.     

Novel high-energy ionic molecules deriving from new monovalent and divalent 4-oxyl-3,5-dinitropyrazolate moieties

ABSTRACT

In recent years, the exploration of a practical strategy for novel energetic molecules with high energy and low sensitivity is very desirable but highly challenging. Novel ionic energetic molecules have attracted much attention in this area due to their prominent advantages including low sensitivities, high thermal stability, and excellent energy performances. Herein, five different ionic energetic molecules based on new monovalent and divalent 4-oxyl-3,5-dinitropyrazolate moieties with enhanced oxygen balance have been synthesized, characterized and evaluated as potential high-energy materials. Thermal stability, sensitivities and energy output test were measured and studied in detail. The heats of formation and energetic parameters were calculated by using Gaussian 09 suite of programs and EXPLO 5 code. The results suggest that all as-prepared new molecules exhibit good thermal stability with high decomposition temperature (3, 231°C; 5, 160°C; 6, 185°C; 7, 180°C; 8, 213°C), and relative low sensitivity (IS > 20 J, FS = 324 N). Inheriting the significant oxygen content of monovalent and divalent 4-oxyl-3,5-dinitropyrazolate moieties, they also possess good energy properties (v _D = 8238 ~ 9208 m s^?1, P = 26.8 ~ 36.7 GPa, V _o = 481.8 ~ 959.4 L kg^?1), which make them competitive high-energy materials.     

The Support Effect on Hydrogenolysis of Thiophene and Gas–Oil

Abstract

Results are reported on the support effect on the catalytic activity in thiophene hydrodesulfurization (HDS) of sulfided Ni-Mo catalysts supported on pure niobia, mixed oxides of Nb₂O₅-TiO₂ prepared by sol-gel method, and Nb₂O₅/TiO₂ and Nb₂O₅/Al₂O₃ prepared by surface deposition. The prepared samples were characterized using N₂ adsorption at ?196°C, X-ray diffraction (XRD), and temperature-programmed reduction (TPR) techniques. This study showed activity variation as a function of support composition. The activity of niobia-rich catalysts was no longer promoted by the synergy between Ni and Mo. The absence of synergy between molybdenum and nickel on niobia can be explained by the strong interaction of each metal with niobia at the expense of interaction with each other. It was found that 5 wt% Nb₂O₅/TiO₂-supported catalyst was the better catalyst for thiophene HDS. It was shown that by means of an adequate support design it is possible to significantly increase the functionalities of HDS catalysts. Semiconducting supports like TiO₂ can improve the HDS activity by exerting electronic effects on the active phase, helping in this way the formation of sulfur vacancies. The 5 wt% Nb₂O₅/TiO₂ was also tested at high pressure with gas oil feedstock. It is observed with the hydrogeolysis of sulfur compounds against time-on-stream that the activity of this catalyst decreases fast with time.     

COMPOSITE ZEOLITES SYNTHESIZED FROM (TEA)2O-Na2O- Al2O3-SiO2-H2O SYSTEM : STRUCTURAL CHARACTERISTICS AND HYDRATION ACTIVITY

ABSTRACT

Several catalysts of composite zeolites were synthesized from (TEA) ₂O-Na₂O-Al₂O₃-SiO₂-H₂O system adopting different conditions of the preparation. The prepared zeolites, in the hydrogen-exchanged form were characterized by EDS and XRD. The obtained catalysts consisted of ß-zeolite composited with different amounts of other zeolites such as morderute and/or analcime. Acidic properties of these composite zeolites were measured potentiometrically in an aqueous medium. The hydration of butene-1 over the H-exchanged composite zeolites was carried out at 250°C and 180 atm, and with a water/olefin ratio of 3.86. The hydration activity was discussed in terms of structural characteristics and acidic properties of the prepared catalysts.     

Hydrogen treatment of vacuum gas oil on sulfide catalysts: Influence of composition and porous structure

Three samples of γ-Al₂O₃ with different textural characteristics have been synthesized from AlOOH powders (Sasol). Ni(Co)Mo/Al₂O₃ catalysts have been prepared by single impregnation of the γ-Al₂O₃ samples with solutions of active ingredients. The morphology of the active phase of the sulfided samples has been studied by high-resolution transmission electron microscopy. The catalytic activity has been measured with the use of vacuum gas oil (VGO) as a feedstock at temperatures of 360, 390 and 420°C. After catalytic activity measurements, the catalysts have been investigated by means of differential thermal and thermographic analysis (DTA-TGA). Textural characteristics of the catalysts in the oxide and sulfide forms have been determined, including those after the measurement of activity in VGO hydrotreating. The textural characteristics of the samples have been shown to correlate with the extent of the hydrogenation reactions of aromatic hydrocarbons and hydrodesulfurization. The highest hydrogenating and hydrodesulfurizing activity has been displayed by the sample on the support with the largest specific surface area and the smallest effective pore radius.     

Promoted catalysts for hydrogenation of bicyclic aromatic hydrocarbons obtained in situ from molybdenum and tungsten carbonyls

Promoted Мo and W catalysts have been prepared in situ via thermal decomposition of precursors, oil-soluble salts Mo(CO)₆, W(CO)₆, С°C₁₆H₃₀O₄, and NiC₁₆H₃₀O₄. TiO₂, Al₂O₃, and ZrO(NO₃)₂ · 6H₂O have been used as the acidic additives. Also, Mo and W unsupported sulfide catalysts have been prepared in the presence of elemental sulfur as the sulfiding agent. The catalysts have been characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The activity of the catalysts prepared in situ has been evaluated in the hydrogenation reaction of bicyclic aromatic hydrocarbons by the example of model mixtures of 10% solutions of naphthalenes (unsubstituted naphthalene, 1- and 2-methylnaphthalenes, and 1,5- and 2,3-dimethylnaphthalenes) in n-hexadecane. The effect of the precursor/acidic oxide ratio on the activity of the formed catalyst has been found. Hydrogenation of bicyclic aromatic hydrocarbons has been conducted at a hydrogen pressure of 2 and 5 MPa and a temperature of 380 and 400°C for 2 h. Hydrogenation of the unsubstituted aromatic ring has been preferable due to the absence of steric hindrances. The degree of conversion of n-hexadecane under the reaction conditions has been 1.5–7.5% depending on the reaction temperature. It has been found that the activity of the sulfided catalyst in the conversion of 1- and 2-methylnaphthalenes is inferior to the activity of the unsulfided analogue, while partial replacement of TiO₂ by Al₂O₃ results in a decrease in the conversion of the substrates as opposed to the unsulfided catalysts, in which the use of nanocrystalline Al₂O₃ promotes an increase in the conversion.     

Different outlet for preparing nano-TiO2 catalysts for the photodegradation of Black B dye in water

Two nano-titania catalysts were prepared using two economically varying titanium precursors: titanium tetrachloride (A) and titanium isopropoxide (B). The catalysts were calcined at temperatures of 500 °C, 600 °C and 700 °C and characterized using X-ray diffraction (XRD), electron diffraction (ED), BET surface properties and high resolution transmission microscopy (HRTEM). The calcined catalysts were found to differ markedly in their physical characters and TiO₂ phases produced as well as their photocatalytic activities. The anatase titania phase diminished from 100% to 83% in TiO₂A but from 64% to zero in TiO₂B via temperature increase from 500 °C to 700 °C, due to transforming anatase to rutile. The brookite TiO₂ phase only appeared (17%) in catalyst B500. In general, the catalyst of choice is A600 by virtue of many compositional, economical and catalytic advantages.     

Dibenzothiophene Hydrodesulfurization Activity of MoS2 Supported in Sol–Gel ZrO2–TiO2 Mixed Oxides

Abstract

In this work, we report the effect of support composition on the properties of MoS₂ impregnated in sol–gel ZrO₂–TiO₂ mixed oxides as dibenzothiophene hydrodesulfurization catalyst. The supports calcined at 500°C were characterized by N₂ physisorption and X-ray diffraction (electronic radial distribution function). The oxidic impregnated materials (2.8 Mo atoms/nm²) were sulfided at 400°C under a H₂S/H₂ stream. The sample impregnated on the equimolar support showed the highest activity per mass of catalysts whereas the one with TiO₂ carrier was superior in a per mass of Mo basis. Marked differences in products selectivity were observed by TiO₂ addition in the supports. The hydrodesulfurization route to partially hydrogenated compounds was favored over the mixed oxides-supported catalysts meanwhile the direct desulfurization (to biphenyl) was promoted on the ZrO₂-supported solid. It is suggested that among other properties the dispersion and morphology of the MoS₂ phase could influence that behavior.     

A Study on Modified HZSM-5 Aromatization for FCC Light Gasoline

Abstract

In this article, the HZSM-5 type zeolite catalysts modified with zinc nitrate and calcium nitrate are prepared by impregnation method. The FCC gasoline (<75°C fraction) is observed and studied on the modified HZSM-5 type zeolite catalysts. The results are that the Z _x -HZSM-5 type zeolite catalysts have a high initial aromatic yield but a rapid deactivation. The C _y -HZSM-5 type zeolite catalysts have a lower aromatic yield and a familiar deactivation comparing to Z _x -HZSM-5. The HZSM-5 type zeolite catalysts modified with bimetal zinc nitrate and calcium nitrate have a rather low initial aromatic yield but a long catalyst life; among them, the C_3.5Z_2.0HZSM-5 has the best performance. And also, the C_3.5Z_2.0HZSM-5 type zeolite catalyst has demonstrated good regenerated performance. After regenerated three times, the catalyst still has a good stability. The reaction operational conditions are also observed and studied. The results are that the optimal reaction temperature is 450–490°C, the liquid hours space velocity (LHSV) is 1 h^?1 and the reaction pressure is 0.1 MPa.     

Comparative Evaluation of Catalysts Containing 0.35% Pt Supported on H-BEA Zeolite Dealuminated via EDTA,HCl Leaching,or Hydrothermally With Steam

Abstract

H-BEA was steamed at 500°C for 2 hr and then loaded with Pt to produce 0.35% Pt/St-H-BEA catalyst. Also, H-BEA was dealuminated with ethylenediamine tetraacetic acid (EDTA) and then loaded with Pt to produce 0.35% Pt/EDTA-H-BEA catalyst. Finally, H-BEA was dealuminated via HCl leaching followed by Pt loading to produce 0.35%Pt/HCl-H-BEA catalyst. These catalysts were reduced under H₂ flow at 500°C to give Pt metal. All catalysts were tested at 250°C–450°C for n-hexane hydroconversion. Maximum hydroisomerization of n-hexane was attained (75.1%) on 0.35% Pt/EDTA-H-BEA and 0.35% Pt/HCl-H-BEA catalysts but at 275°C on the former catalyst and at 300°C on the latter. At this temperature, n-hexane hydrocracking is only 1.2%. The hexane isomers selectivity on both catalysts was >99%. For the 0.35% Pt/St H-BEA catalyst, isohexanes yield and selectivity were lower than the above-mentioned catalysts. The catalyst of choice is 0.35% Pt/EDTA-H-BEA for its economic application at 275°C.     

Iron catalyst for decomposition of methane: Influence of Al/Si ratio support

20% iron catalysts supported on combined alumina and silica through different proportions (Al₂O₃:SiO₂: 100:0.00, 90.0:10.0, 80.0:20.0 and 0.0:100.0) were tested for the catalytic decomposition of methane to produce H₂ and carbon. The catalysts were prepared via impregnation technique. The physicochemical properties of the catalysts were characterized with TGA, XRD, H2-TPR, and TEM techniques. The results specified no reaction for all temperatures when the catalysts were supported with bare silica. Indeed, the 20%Fe/(Si-80)-800 catalyst with 20% silica support operated at 800?°C produced CH₄ conversion profile that rapidly descended from 64% to 5% due to the high content of silica. Plain alumina supported catalyst demonstrated the best conversion and stability operated at 800?°C. The CH₄ conversion started from 83.4% and lasts at 82.2% after 300?min on stream.