Precursor Of Active Component Research Articles

Effects of ultrasound on the desulfurization performance of hot coal gas over Zn-Mn-Cu supported on semi-coke sorbent prepared by high-pressure impregnation method

Zn-Mn-Cu/SC(U) sorbent was hydrothermally synthesized by ultrasound-assisted high-pressure impregnation method with semi-coke (SC) as support and the mixed solution of zinc nitrate, manganese nitrate and copper nitrate as active component precursors. The desulfurization performances of hot coal gas on the prepared sorbent at a mid-temperature of 500 °C were tested in fixed-bed reactor. Morphology and pore structure of the prepared sorbent were also characterized by TEM, N2 adsorption/desorption isotherms and XRD. For comparison, the sorbent of Zn-Mn-Cu/SC prepared by conventional high-pressure impregnation was also evaluated and characterized in order to study the effects of ultrasound treatment. Zn-Mn-Cu/SC(U) sorbent prepared by high-pressure impregnation under ultrasound-assisted condition showed a better desulfurization performance than Zn-Mn-Cu/SC. It could remove H2S from 1000×10−6 m3/m3 to 0.1×10−6 m3/m3 at 500 °C and maintained for 12.5 h with the sulfur capacity of 7.74%, in which both the breakthrough time and sulfur capacity were about 32% and 51% higher than those of Zn-Mn-Cu/SC sorbent. The introduction of ultrasound during high-pressure impregnation process greatly improved the morphology and pore structure of the sorbent. The ultrasonic treatment made particle size of active components smaller and made them more evenly disperse on semi-coke support, which provided more opportunities to contact with H2S in coal-based gases. However, there were no any difference in compositions and existing forms of active components on the Zn-Mn-Cu/SC and Zn-Mn-Cu/SC(U) sorbents.

Effect of High-Pressure Impregnation on Structure Variation and Desulfurization Property of a Zn-Based Sorbent Prepared Using Lignite as a Support

In this study, a series of zinc (Zn)-based sorbents were prepared by high-pressure impregnation under different conditions of time and pressure, followed by fixed-bed pyrolysis using lignite as a precursor of support and zinc nitrate [Zn(NO3)2] as an active component precursor. The desulfurization performances of lignite and sorbents were measured. Moreover, they were characterized by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), N2 adsorption, transmission electron microscopy–energy-dispersive X-ray (TEM–EDX), and scanning electron microscopy–energy-dispersive X-ray (SEM–EDX) techniques. The ambient conditions involved in hydrothermal synthesis are favorable for the efficient uploading of Zn(NO3)2 and the improvement of lignite texture during high-pressure impregnation. The content of Zn in prepared sorbent and the utilization rate of the active component can reach over 20 and 90%, respectively. The impregnation pressure and time are the main factors influencing the desulfurization perfo...

Preparation of Sorbent Loaded with Nano-CuO for Room Temperature to Remove of Hydrogen Sulfide

In this paper, an efficient metal oxide sorbents for the deep removal of H2S were synthesized using equal volume impregnation (EVIM) method. Modified coconut shell charcoal was selected as support to deposite the particles of copper oxide onto the surface. And copper nitrate were selected as the active component precursors in the preparation process of sorbents. Sorption experiments were carried out at room temperature in fixed-bed reactor. The grain size and crystal form of loading metals were characterized by X-ray diffraction (XRD). We investigated the effects of modifier onto coconut shell charcoal, load rate of metal oxide and calcination temperature on the desulfurization activity of the sorbent. Results show that the best modifier for coconut shell charcoal is KOH, which is significantly better than the other modifiers. And the optimum load rate is 20%(wt), the optimum calcination temperature is 300°C. Copper oxide onto the surface of modified coconut shell charcoal proved to be monoclinic nanoparticles with grain size of 18.7nm. Sulfidation test was carried out on the condition of i) the concentration of hydrogen sulfide gas (mixed with nitrogen ) is 1024.2ppm and ii) gas velocity is 20ml/min, iii) 0.1g sample in the middle of the fixed-bed reactor (length: 450 mm, interior diameter: 5 mm) to test. The sample show excellent sulfur removal efficiency and its breakthrough time is up to 287 min on this condition.

Alumina-supported manganese oxide sorbent prepared by sub-critical water impregnation for hot coal gas desulfurization

Manganese oxide was loaded on the surface of γ-Al2O3 by sub-critical water impregnation using manganese acetate and manganese nitrate precursors to synthesize Mn(A) and Mn(N) sorbents for removing H2S from hot coal gas. Active component precursors present very obvious effect on the desulfurization capacity of sorbent. Mn(A, 11) sorbent with 11% Mn content in γ-Al2O3 maintains a desulfurization efficiency of close to 100% over 480min. However, it reduces to below 90% for Mn(N, 11) sorbent when the reaction lasts over 75min. The characterizing results of fresh and used sorbents from different precursors using AAS, SEM, BET, Raman, XAS and XPS techniques show that the acidity and alkalinity of active component precursor solution greatly influences the loading rate, valence state and dispersion of manganese on γ-Al2O3, which are the main properties for improving desulfurization performance of sorbents. The manganese loading rate of Mn(A) sorbent is much higher than Mn(N) sorbent. The better dispersion of manganese on γ-Al2O3 and the higher Mn2+ and Mn3+ contents on the surface of sorbent afford the high desulfurization activity of Mn(A). Moreover, Mn(A, 11) performs well in removing H2S from hot gas at 400°C after three desulfurization -regeneration cycles.

Genesis of the active-component precursor in the synthesis of Pt/Al2O3 catalysts: III. Transformations of adsorbed platinum complexes during drying

The transformations of platinum(IV) complexes subsequent to their sorption on the support are considered. As the Pt(IV)/Al2O3 systems are dried at 25°C in daylight, their dehydration is accompanied by the replacement of inner sphere ligands of Pt(IV) by OH groups and the Coulombic bonding between the adsorbed metal complexes and the support turns into coordination bonding. Drying at a higher temperature of 120°C does not increase the extent of hydrolysis of the bound complexes in the predried samples. The observed increase in the proportion of unreadily reducible platinum species is likely due to the multisite adsorption of platinum complexes taking place.

Preparation and evaluation of hydrotreating catalysts based on activated carbon derived from oil sand petroleum coke

Novel Ni–Mo/activated carbon (AC) hydrotreating catalysts were prepared and evaluated for upgrading heavy vacuum gas oil (HVGO). The AC supports were derived from Alberta oil sand petroleum coke, i.e. fluid coke and/or delayed coke, hereafter referred to as OSP coke, through a chemical process. The BET surface area was as high as 2194m2/g for the fluid coke derived AC and 2357m2/g for the delayed coke derived AC. Both ACs contained a large number of micropores with pore volume as high as 1.2cm3/g. Ni and Mo based active component precursors could be easily loaded on the activated carbon supports by chemical impregnation of nickel nitrate and ammonium molybdate followed by calcination in nitrogen at 773K without further modification or oxidation treatment to the activated carbons. Scanning electron microscopy (SEM) observation showed highly porous surface structure of the bare activated carbon supports and well dispersed metal (oxide) precursor nanoparticles of 30–50nm loaded on the AC supports. For comparison, two reference catalysts were also prepared by the same procedure but using commercial activated carbon and porous alumina as supports. After catalyst activation by sulfiding, the hydrotreating performance of the prepared catalysts was evaluated in a magnetically stirred autoclave with a HVGO feedstock to examine their hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities. Two commercial hydrotreating catalysts were also tested and compared under similar conditions with the same feed. The results showed that the catalysts based on the activated carbon supports prepared from OSP coke had better hydrotreating performance than the other catalysts. Scanning transmission electron microscopy (STEM) characterization of the catalysts after activation showed that small particles of nanostructure (2–5nm in size) were evenly embedded in the carbon matrix except for some bigger particles that were located on the catalyst surface. Energy dispersive X-ray (EDX) spectroscopy revealed that these particles were composed of Ni, Mo and S elements. The dispersed nanoparticles formed the active sites and were responsible for the observed high HDS and HDN activity. Elemental analysis and surface characterization of the spent catalysts showed that the formation of coke precursors was favored on the alumina supported catalyst, which resulted in catalyst deactivation.

Interaction among Metal Components of Zn–Mn–Cu-Based Sorbents Prepared by High-Pressure Impregnation Method and Its Effect on the Removal of H2S from Hot Coal Gas

A series of metal oxide sorbents for the deep removal of H2S from hot coal gas were synthesized using a high-pressure impregnation method. Semicoke was selected as support and the solutions of one or more combination among zinc nitrate, manganese nitrate, and copper nitrate were selected as the active component precursors in the preparation process of sorbents. SEM results show that these metal oxides can be evenly dispersed onto semicoke support with nanometer particle sizes by a high-pressure impregnation method. Simultaneously, the pore structures of the sorbents are significantly improved through the hydrothermal process of high-pressure impregnation. The desulfurization activities of the Zn–Mn–Cu-based sorbents in a fixed-bed reactor under feeding gas of CO (33 vol %), H2 (39 vol %), H2S (500 ppmv), and N2 (balance) are much better than those of single Zn-, Mn-, and Cu-based as well as double Zn–Mn-based sorbents prepared under the same operating conditions. The Z20M4C6SC sorbent can remove H2S from ...

Effect of precursor and preparation method on manganese based activated carbon sorbents for removing H2S from hot coal gas

Activated carbon (AC) supported manganese oxide sorbents were prepared by the supercritical water impregnation (SCWI) using two different precursor of Mn(NO3)2 (SCW(N)) and Mn(Ac)2·4H2O (SCW(A)). Their capacities of removing H2S from coal gas were evaluated and compared to the sorbents prepared by the pore volume impregnation (PVI) method. The structure and composition of different sorbents were characterized by XRD, SEM, TEM, XPS and XANES techniques. It is found that the precursor of active component plays the crucial role and SCW(N) sorbents show much better sulfidation performance than the SCW(A) sorbents. This is because the Mn3O4 active phase of the SCW(N) sorbents are well dispersed on the AC support, while the Mn2SiO4-like species in the SCW(A) sorbent can be formed and seriously aggregated. The SCW(N) sorbents with 2.80% and 5.60% manganese are favorable for the sulfidation reaction, since the Mn species are better dispersed on the SCW(N) sorbents than those on the PV(N) sorbents and results in the better sulfidation performance of the SCW(N) sorbents. As the Mn content increases to 11.20%, the metal oxide particles on AC supports aggregate seriously, which leads to poorer sulfidation performance of the SCW(N)11.20% sorbents than that of the PV(N)11.20% sorbents.

Synthesis of Supported Catalysts by Impregnation and Calcination of Low-Temperature Polymerizable Metal-Complexes

The low-temperature polymerizable metal complex solution has been used as an active component precursor to prepare supported (structured) catalysts by a straight-forward sequence of impregnation, drying and calcination. Two typical samples, 5 wt% Zr x Ce1−x O2/Al2O3 nanocomposite and structured carbon nanofiber supported Cu–CeO2 catalyst, are prepared to explore the potential of this method in the controlled synthesis of catalysts and catalyst supports. The interaction between the active component precursor and the surface of the solid matrices during impregnation and drying is investigated by infrared spectroscopy (IR) and transmission electron microscopy (TEM), demonstrating that the in situ polymerization process is crucial for the deposition of the active component on the surface of solid matrices. The evolution of the phase transformation and the structure of the produced materials during the calcination step is studied by coupling thermal gravimetric analysis–differential thermal analysis–mass spectroscopy (TGA–DTA–MS), TEM and X-ray diffraction (XRD) measurements, indicating that higher thermal stable particles or smaller particles can be obtained with the presence of the Al2O3 or structured carbon nanofibers (SCNF), respectively, after calcination. This method combines the advantages of sol–gel and impregnation, representing a promising route for preparing supported catalysts and catalyst supports. The limitations of the method are also discussed.

Use of High-Pressure Impregnation in Preparing Zn-Based Sorbents for Deep Desulfurization of Hot Coal Gas

A new preparation method of zinc oxide (ZnO) sorbents for removing H2S from hot coal gas was explored. High-pressure impregnation with semi-coke as the support and zinc nitrate as the active component precursor was used to prepare Zn-based sorbents (HZnSC). The desulfurization activity of the sorbents was studied in a fixed-bed reactor under the simulated coal gas mixture of CO (33 vol%), H2 (39 vol %), H2O (5 vol %), H2S (300 ppmv), and N2 (balance) at 300–550 °C. The results show that the desulfurization activity of the HZnSC sorbents is higher than that of the sorbents prepared using atmospheric pressure impregnation. The surface area of the semi-coke expanded from 16.65 to 272.59 m2/g. Nanoscale ZnO was acquired, and the active component was uniformly dispersed on the support with the high-pressure impregnation method, which afforded H2S removal from hot coal gas. HZn20SC (prepared with 20 wt % zinc nitrate solution) reduced H2S from 300 to less than 0.1 ppmv at 300–550 °C, and its sulfur capacity was 4.5 g of S/100 g of sorbent at 500 °C. It also maintained good heat stability during three desulfurization/regeneration cycles. The findings suggest that semi-coke with a low surface area can be used as a support of sorbents to remove H2S from hot coal gas using high-pressure impregnation.

Nanosized Au/C catalyst obtained from a tetraamminegold(III) precursor: Synthesis, characterization, and catalytic activity in low-temperature CO oxidation

A method in which the water-soluble complex [Au(NH3)4](NO3)3 is used as the active-component precursor is suggested for preparing nanosized Au/C catalysts (C = Sibunit, a mesoporous carbon material). The complex is unreadily reducible by the carbon matrix and can be involved in cation exchange with proton-containing groups of the support. This method is referred to as cationic adsorption. It has been demonstrated by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy that the catalyst prepared in this way and treated with H2 at 400°C contains size-uniform gold metal particles with a dominant diameter of <5 nm. The greater part of the gold particles is located on the outer surface of the Sibunit granules; that is, an egg shell type distribution of the active component takes place. The catalyst containing 1.3 wt % Au shows high activity in CO oxidation with excess humid air at 40°C. In this respect, it is far superior to the Au/C catalysts prepared by conventional methods (deposition-precipitation and impregnation), in which the typical gold particle size is several tens of nanometers.

Dimethyl disulfide conversion into dimethyl sulfide in the presence of sulfidized catalysts

The conversion of dimethyl disulfide in the presence of various supported sulfidized metal-containing catalysts at atmospheric pressure and T = 150−350°C was studied. Sulfidized transition metals supported onto aluminum oxide were more active than catalysts based on a carbon support, silicon dioxide, amorphous aluminosilicate, and zeolite ZSM-5. The most active catalyst was 10% Co/Al2O3 prepared with the use of cobalt acetate as an active component precursor and treated with a mixture of hydrogen sulfide with hydrogen at T = 400°C. From kinetic data, it follows that all of the reaction products were formed simultaneously at a temperature of <200°C, whereas a consecutive reaction scheme took place at higher temperatures. In the presence of a sulfidized alumina-cobalt catalyst, the output of dimethyl sulfide was higher than that reached with the use of other well-known catalysts.

Magnetic resonance imaging as an emerging tool for studying the preparation of supported catalysts

Several magnetic resonance imaging (MRI) approaches are presented that can be used to study transport processes when supported catalysts are prepared by impregnating mm-sized porous support bodies. Both diamagnetic and paramagnetic components of an impregnation solution such as the solvent, the metal-containing precursors of an active component, and various organic and inorganic additives can be visualized with MRI. Their spatial distributions within a catalyst support body and the evolution of these distributions in time can be characterized not only qualitatively but also quantitatively, if calibration procedures are used to convert the images into corresponding concentration profiles. In particular, the physicochemical interactions between γ-Al 2O 3 support bodies and the aqueous solutions containing Cu, Co, Mo, citrate and phosphate ions are investigated upon pore volume impregnation as a function of concentration and solution pH. Furthermore, it is shown that multinuclear and solid state MRI can be used to map the solid phase distribution of the active component precursors and additives within the impregnated support bodies after their drying. Based on the case studies discussed, it can be concluded that MRI is an emerging versatile tool for studying the transport processes in support bodies upon their impregnation and the distribution of the key components after drying of the impregnated bodies.

The use of X-ray absorption spectroscopy for developing new-generation Co-Mo catalysts of hydrotreating of diesel fuel

The immediate problem facing the Russian petroleum refining industry is to turn to the production of gasoline complying with European standards [1]. Nowadays, only 12 of the 27 large Russian oil refinery plants have mastered the production of low-sulfur diesel fuel containing less than 0.05% sulfur [2]. Almost all diesel fuel that meets Euro 2, Euro 3, and Euro 4 standards is produced with the use of foreign catalysts since domestic catalysts do not have the required activity level. In this context, Russian industry should proceed as soon as possible to produce new-generation heterogeneous catalysts in which all surface compounds are active centers of hydrorefining reactions. According to the basic principles of the preparation of such catalysts expounded in [3], active center precursors—bimetallic Co‐Mo compounds—should be obtained when preparing an impregnating solution and the structure of these compounds should remain unaltered during the genesis of catalysts. The existence of such a structure in an oxide precursor of hydrorefining catalysts will ensure the formation of highly active disperse sulfide particles during the sulfiding step. To purposefully use this approach, the state and structure of catalyst active component precursors should be thoroughly monitored at all stages of their preparation. The most suitable for this purpose is X-ray absorption spectroscopy, which makes it possible to identify the structure of compounds synthesized in solution and on the support surface during catalyst preparation [4]. In this paper, we report the results of the EXAFS and XANES study of the structure of bimetallic oxide precursors of the active phases of hydrorefining Co‐Mo catalysts. A bimetallic compound and allied catalyst were synthesized from the ammonium salt of the tetranuclear anion [Mo 4 (e 6 c 5 O 7 ) 2 O 11 ] 4– . Solutions and cata

Genesis of the active-component precursor in the synthesis of Pt/Al2O3 catalysts: II. Synthesis of platinum hydroxo complexes on the alumina surface as precursors of the active component of Pt/Al2O3 catalysts

The thermal hydrolysis of chloroplatinate adsorbed on γ-Al2O3 is a possible approach to the synthesis of surface platinum hydroxo complexes as precursors to the active component of supported platinum catalysts. It is demonstrated by EXAFS and diffuse reflectance spectroscopy that the surface chloro complexes undergo deep hydrolysis under hydrothermal conditions at various processing times and temperatures. The average oxygen coordination number of platinum in these complexes is as large as 4.5. According to gradient elution data obtained using both the competitive replacement of adsorbed complex anions and variation of the charged state of the oxide surface, the resulting hydrolyzed precursor differs from the conventional chloride precursor in the nature of binding to the surface and interacts with alumina via a coordination mechanism.

Genesis of the active-component precursor in the synthesis of Pt/Al2O3 catalysts: I. Transformation of the [PtCl6]2− complex in the interaction between chloroplatinic acid and the γ-Al2O3 surface

Gradient elution experiments have revealed the difference between platinum complexes in terms of the strength of their interaction with the alumina surface. A considerable part (30–40%) of the supported platinum is nondesorbable via competitive ion exchange reactions or upon changes in the charge state of the support surface. The surface platinum complexes can be divided into ion-exchangeable and coordinatively fixed species according to the nature of their bonding with aluminum oxide. Combining desorption and spectroscopic methods (EXAFS and diffuse reflectance spectroscopy) has made it possible to characterize the surface complexes. The strongest metal-support interaction takes place in the fixation of hydrolyzed platinum species.

Activity of Rh/TiO2 catalysts in NaBH4 hydrolysis: The effect of the interaction between RhCl3 and the anatase surface during heat treatment

The reaction properties of Rh/TiO2 sodium tetrahydroborate hydrolysis catalysts reduced directly in the reaction medium depend on the temperature at which they were calcined. Raising the calcination temperature to 300°C enhances the activity of the Rh/TiO2 catalysts. Using diffuse reflectance electronic spectroscopy, photoacoustic IR spectroscopy, and chemical and thermal analyses, it is demonstrated that, as RhCl3 is supported on TiO2 (anatase), the active-component precursor interacts strongly with the support surface. The degree of this interaction increases as the calcination temperature is raised. TEM, EXAFS, and XANES data have demonstrated that the composition and structure of the rhodium complexes that form on the titanium dioxide surface during different heat treatments later determine the state of the supported rhodium particles forming in the sodium tetrahydroborate reaction medium.

Molecular mechanism of formation of supported platinum catalysts of the Pt/Al2O3 family

Certain stages of the classical procedure for preparing aluminum-platinum catalysts, whose understanding is important from both the basic and practical viewpoints, are considered on the molecular level. Properties of both participants (active component precursor solution and oxide surface) are shown to be inhomogeneous, which can affect interaction of the components at the fixing stage. Existing views (and their evolution) on the mechanism of adsorption of platinum complexes from aqueous solutions on aluminum oxide surface are discussed. The role of chemical processes on the stage of fixing precursor on the electronic and structural properties of the supported metal is demonstrates. Strong metal-support interaction is shown to endow platinum with specific adsorption and catalytic properties in hydrocarbon transformation reactions.

Characteristics of drying and active component distribution in alumina monoliths using 1H-NMR imaging

The distribution of water in the impregnated monolithic substrates was visualized by 1H-NMR imaging. The two-dimensional water content maps along the axial and radial directions have been collected for different monoliths at variation of the drying conditions. Using the blow-through air for drying of the substrate with coated external walls and with free access of air to external walls leads to the parabolic profile of water concentration along the axial direction of the sample. Drying of the monoliths with open external walls proceeds more uniformly in the radial and axial directions of the substrate. Characteristics of drying of alumina monoliths, calcined at 600, 900 and 1200 °C having differences in the pore structure and pore distribution, are studied. During drying of the impregnated washcoated monolith the certain part of the introduced active component precursor (H 2PtCl 6 or H 2PdCl 4) is transported from the substrate macropores to the mesoporous washcoated layer which leads to enrichment of the washcoat of the final catalyst by active component. The non-destructive character of 1H-NMR microimaging demonstrated its capability to visualize the water content maps in monoliths in the presence of Pt and Pd.

Oxidative dehydrogenation of isobutane on chromium oxide-based catalyst

Isobutane oxidative dehydrogenation offers a prospect of cheaper and environment friendly route to isobutene. The reaction has been studied at 250 °C, 1 atm and feed flow rate of 75 cm 3/min over supported chromium oxide-based catalysts. Effects of various supports (Al 2O 3, MgO, TiO 2 and SiO 2), catalyst precursors (K 2Cr 2O 7, CaCr 2O 7·H 2O, CrO 3, CrK(SO 4) 2·12H 2O and Cr(NO 3) 3·9H 2O) and binary mixed metal oxide catalysts of the form Cr-M-oxide/γ-Al 2O 3 (where M is V, Ni, Co, Mo, W, Ho, La, Li or Bi) were investigated. The supported catalysts are ranked (based on isobutene yields at 250 °C) as; Cr-Mg-O (3.4%) = Cr-Si-O (3.4%) < Cr-Ti-O (4.5%) < Cr-Al-O (6.0%). The performances of the catalysts showed strong dependence on the precursor used. The 10 wt.% Cr-Al-O prepared using K 2Cr 2O 7 and CrK(SO 4) 2·2H 2O exhibited the lowest isobutene yields of 0.14 and 0.3%, respectively. Partial substitution of chromium ions with nickel or tungsten exhibited minor increase in selectivity to isobutene of about 6% at comparable isobutane conversions. Substitution with other metals show similar or inferior performance compared with the base catalyst. Thus, showing that chromium oxide-based catalysts are active for the reaction and their performance could be improved by appropriate choice of active component precursor, support and additives.