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 Ce_1?x O₂/Al₂O₃ nanocomposite and structured carbon nanofiber supported Cu?CCeO₂ 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?Cdifferential thermal analysis?Cmass spectroscopy (TGA?CDTA?CMS), 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?Cgel and impregnation, representing a promising route for preparing supported catalysts and catalyst supports. The limitations of the method are also discussed.     

Effect of the nature of silicon oxide structures on the activity of an alumina-chromium catalyst in the reaction of iso-butane dehydrogenation

The formation of silicon oxide structures in the composition of an alumina-chromium catalyst for the dehydrogenation of iso-butane is studied by means of nitrogen adsorption, XRD analysis, solid-state ²⁹Si NMR spectroscopy, temperature-programmed desorption of ammonia, and UV-Vis and Raman spectroscopy. It is established that 0.5–1.2 wt % silicon was distributed on the catalyst surface in the form of Si(OSi)₄ structures. As the silicon content was increased to 2.2–3.6 wt %, Si(OSi)₃(O-) structural elements were present on the surface in addition to Si(OSi)₄. The formation of silicon oxide structures on the catalyst surface was responsible for an increase in the concentration of Cr(III) ions and a decrease in the surface acidity; the activity and selectivity of the catalysts in the reaction of iso-butane dehydrogenation increased.     

Preparation of a Novel Copper Catalyst in Terms of the Immiscible Interaction Between Copper and Chromium

Based on the metallurgical point of view, we aimed to design a new form of copper catalysts with high thermal stability and activity. Delafossite CuCrO₂ has been studied as a precursor for copper catalyst. The CuCrO₂ was reduced to fine dispersion of Cu and Cr₂O₃ particles with porous structure by the treatment in H₂ at 600 °C, which exhibited much higher activity and thermal stability for steam reforming of methanol (SRM) than those of the CuO and/or Cr₂O₃ catalysts. Sintering of Cu particles was significantly suppressed even after H₂ reduction at 600 °C. Moreover, the CuCrO₂ can be regenerated by calcination in air at 1,000 °C where the activity is also restored completely even after sintering at high temperatures. Fine porous structure generated by the reduction of CuCrO₂ and immiscible interaction between Cu and Cr₂O₃ are important in stabilizing of copper nanoparticles. Based on these findings, we propose that the CuCrO₂ is an effective precursor for a high performance copper catalyst.     

Effects of the preparation methods on the performance of the Cu–Cr–Fe/γ-Al2O3 catalysts for the synthesis of 2-methylpiperazine

Co-precipitation, impregnation and ultrasonic sol–gel (USG) methods have been used to prepare Cu–Cr–Fe/γ-Al₂O₃ catalysts, which were further used to synthesize 2-methylpiperazine. The catalysts were characterized by XRD, XPS, TG/DSC, BET, TPR, AAS and TEM. It is found that preparation method can greatly impact the catalytic performance of the catalysts, the Cu–Cr–Fe/γ-Al₂O₃ catalyst prepared by the ultrasonic sol–gel method proved to be the most active and stable for this reaction. The dispersion and stabilization of Cu⁰ in the reduced catalysts are attributed to the existence of CuCr₂O₄ and Fe₂O₃. A surprising copper migration was detected by XPS analysis for the Cu–Cr–Fe/γ-Al₂O₃-USG catalyst after the calcination process, which may be crucial to the high activity and stability of this catalyst.     

n-Butane Isomerization Catalyzed by Sulfated Zirconia Nanocrystals Supported on Silica or γ-Alumina

Supported sulfated zirconia catalysts with zirconia contents of 10, 20 and 50 wt% were prepared by impregnation of SiO₂ and γ-Al₂O₃ supports with H₂SO₄/ Zr(SO₄)₂ solutions followed by calcination at 923 K. The catalysts were characterized by X-ray diffraction, extended X-ray absorption fine structure measurements, thermal analysis, UV–vis spectroscopy, and electron microscopy. Tetragonal zirconia was detected in all silica-supported samples but only in the 50 wt% zirconia-containing alumina-supported sample, indicating high dispersion of zirconia on alumina. Alumina-supported samples retained additional sulfate, at least in part as Al₂(SO₄)₃. All samples were active in n-butane isomerization (1 kPa n-butane, 378 K). There was no relation between the presence of tetragonal zirconia in these samples and the catalytic performance.     

Effect of chemical composition and method of preparation on the physicochemical properties of the NiO/B2O3-Al2O3 system and its catalytic activity in ethylene oligomerization

The effect the chemical composition of a support, the content of nickel, and the method of its binding has on the physicochemical and catalytic properties of the NiO/B₂O₃-Al₂O₃ system is studied. The boron oxide content in the support is varied from 2 to 30 wt %, while the nickel concentration is 0.59–3.18 wt %. The catalyst samples are studied via X-ray diffraction analysis, temperature-programmed desorption of ammonia, IR spectroscopy (including that of adsorbed CO), and UV-VIS diffuse reflectance spectroscopy. Tests of the catalysts in ethylene oligomerization are conducted in a fixed-bed flow reactor at a temperature of 200°C, a pressure of 1 MPa, and a space velocity of ethylene of 0.5 h^?1. The feedstock is an ethylene-methane gas mixture containing 30 wt % of ethylene. It is suggested that the activity of the NiO/B₂O₃-Al₂O₃ system in ethylene oligomerization can be attributed to the formation of octahedral Ni²⁺ cations environed by borate anions on the surface of the system. The most active catalysts contain 2–3 wt % Ni and 10–20 wt % B₂O₃ in the supports. The method of preparation (adsorption binding or impregnation) has little effect on the state of nickel in the NiO/B₂O₃-Al₂O₃ system samples and their catalytic properties. The prepared catalysts are characterized by the ease of preparation, availability, and a low cost of the initial materials, as compared to known catalysts.     

Dependence of n-Butane Activation on Active Site of Vanadium Phosphate Catalysts

The nature and the role of oxygen species and vanadium oxidation states on the activation of n-butane for selective oxidation to maleic anhydride were investigated. Bi–Fe doped and undoped vanadium phosphate catalysts were used a model catalyst. XRD revealed that Bi–Fe mixture dopants led to formation of α_II-VOPO₄ phase together with (VO)₂P₂O₇ as a dominant phase when the materials were heated in n-butane/air to form the final catalysts. TPR analysis showed that the reduction behaviour of Bi–Fe doped catalysts was dominated by the reduction peak assigned to the reduction of V⁵⁺ species as compared to the undoped catalyst, which gave the reduction of V⁴⁺ as the major feature. An excess of the oxygen species (O^2?) associated with V⁵⁺ in Bi–Fe doped catalysts improved the maleic anhydride selectivity but significantly lowering the rate of n-butane conversion. The reactive pairing of V⁴⁺-O^? was shown to be the centre for n-butane activation. It is proposed that the availability and appearance of active oxygen species (O^?) on the surface of vanadium phosphate catalyst is the rate determining step of the overall reaction.     

Influence of Rare-Earth and Bimetallic Promoters on Various VPO Catalysts for Partial Oxidation of n-Butane

Vanadium phosphorous oxide (VPO) catalyst was prepared using dihydrate method and tested for the potential use in selective oxidation of n-butane to maleic anhydride. The catalysts were doped by La, Ce and combined components Ce + Co and Ce + Bi through impregnation. The effect of promoters on catalyst morphology and the development of acid and redox sites were studied through XRD, BET, SEM, H₂-TPR and TPRn reaction of n-butane/He. Addition of rare-earth element to VPO formulation and drying of catalyst precursor by microwave irradiation increased the fall width at half maximum (FWHM) and reduced the crystallite size of the Vanadyl hydrogen phosphate hemihydrate (VOHPO₄ · 1/2 H₂O, VHP) precursor phase and thus led to the production of final catalysts with larger surface area. The Ce doped VPO catalyst which, assisted by the microwave heating method, exhibited the highest surface area. Moreover, the addition of promoters significantly increased catalyst activity and selectivity as compared to undoped VPO catalyst in the oxidation reaction of n-butane. The H₂-TPR and TPRn reaction profiles showed that the highest amount of active oxygen species, i.e., the V⁴⁺–O^? pair, was removed from the bimetallic (Ce + Bi) promoted catalyst. This pair is responsible for n-butane activation. Furthermore, based on catalytic test results, it was demonstrated that the catalyst promoted with Ce and Bi (VPOD1) was the most active and selective catalyst among the produced catalysts with 52% reaction yield. This suggests that the rare earth metal promoted vanadium phosphate catalyst is a promising method to improve the catalytic properties of VPO for the partial oxidation of n-butane to maleic anhydride.     

Catalytic removal of methane over thermal-proof nanostructured catalysts for CNG engines

Five spinel-type catalysts AB₂O₄ (Co_0.8Cr₂O₄, CoCr₂O₄, MnCr₂O₄, MgFe₂O₄ and CoFe₂O₄) were prepared and characterized by XRD, BET and FESEM techniques. The activity of these catalysts towards the combustion of methane was evaluated in a Temperature Programmed Combustion (TPC) apparatus. The half conversion temperature of methane over the Co_0.8Cr₂O₄ catalyst was 369 °C with a W/F = 0.12 g s/cm³. On the basis of Temperature Programmed Desorption (TPD) of oxygen as well as of catalytic combustion runs, the prevalent activity of the Co_0.8Cr₂O₄ catalyst could be explained by its higher capability to deliver suprafacial chemisorbed oxygen species. This catalyst, promoted by the presence of 1 wt% of Pd, deposited by wet impregnation, was lined on cordierite monoliths and then tested in a lab-scale test rig. The combination of Pd and Co_0.8Cr₂O₄ catalysts enables half methane conversion at 340 °C (GHSV = 10,000 h⁻¹), a performance similar to that of conventional 4 wt% Pd-γ Al₂O₃ catalysts but guaranteed with just a four-fold lower amount of noble metal. Both the catalysts in powder and the monolith hosting the Co_0.8Cr₂O₄ + 1 wt% Pd catalyst, submitted to a thermal ageing treatment in air at 700 °C for 12 h, displayed a negligible deactivation.     

Chromia-alumina catalysts for the dehydrogenation of propane prepared by a modified method of codeposition

A method for preparing chromia-alumina catalysts for the dehydrogenation of propane, enabling us to increase the activity and thermal stability of a catalyst relative to currently known catalysts, is proposed. Chromia-alumina catalysts were prepared for the first time using a modified method of codeposition, in which a suspension of chromium and aluminum hydroxides was subjected to a high-temperature treatment (550°C). The proposed method is simple and allows us to reduce the number of stages in the preparation of the catalyst. The phase composition and texture of the catalyst, and the formation and properties of surface-active forms in dependence on the conditions of catalyst preparation, were studied using a set of physicochemical methods. The selected conditions of catalyst preparation ensured high specific surface area and a stable bond between the surface forms of chromium and the support, hindering the formation of the catalytically low-activity form α-Cr₂O₃ during calcination. In this work, we synthesized and studied laboratory samples of a chromia-alumina catalyst with different contents of chromium (2.8–11.3 wt %). With respect to the main parameters (conversion of propane, selectivity to propylene, and resistance to coke formation), the catalyst was as good as more active samples known from the literature and exhibited high activity at low chromium contents (2.8–5.5 wt %). This method of catalyst preparation is protected by a patent of the Russian Federation and recommended for improving industrial technology.     

Effects of the preparation methods on the performance of the Cu–Cr–Fe/γ-Al2O3 catalysts for the synthesis of 2-methylpiperazine

Co-precipitation, impregnation and ultrasonic sol–gel (USG) methods have been used to prepare Cu–Cr–Fe/γ-Al₂O₃ catalysts, which were further used to synthesize 2-methylpiperazine. The catalysts were characterized by XRD, XPS, TG/DSC, BET, TPR, AAS and TEM. It is found that preparation method can greatly impact the catalytic performance of the catalysts, the Cu–Cr–Fe/γ-Al₂O₃ catalyst prepared by the ultrasonic sol–gel method proved to be the most active and stable for this reaction. The dispersion and stabilization of Cu⁰ in the reduced catalysts are attributed to the existence of CuCr₂O₄ and Fe₂O₃. A surprising copper migration was detected by XPS analysis for the Cu–Cr–Fe/γ-Al₂O₃-USG catalyst after the calcination process, which may be crucial to the high activity and stability of this catalyst.     

Effect of support structure on the activity of Cr/nanosilica catalysts and the morphology of prepared polyethylene

Phillips‐type catalysts are responsible for the commercial production of more than one‐third of all polyethylene sold worldwide. Many types of chromium‐based catalysts are used in the Phillips polymerization process. Ordered mesoporous silica structures were synthesized using various surfactant species. Chromium nitrate nonahydrate (Cr(NO₃)₃·9H₂O) complex was grafted onto the surface of pure silica and was used for ethylene polymerization. The materials were characterized using X‐ray diffraction, nitrogen adsorption‐desorption, inductively coupled plasma optical emission spectroscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. In the as‐synthesized materials, Cr³⁺ is present as a surface species in pseudo‐octahedral coordination. After calcination, Cr³⁺ is almost completely oxidized to Cr⁶⁺, which is anchored onto the surface in various oxidative states. The catalyst polymerization activity is dependent on the chromium loading, the pre‐calcination temperature and the support properties. In particular, the chromium catalyst prepared using spherical SBA‐15 is more active than the other catalysts investigated. Porous and nano‐fibrous polyethylene samples were prepared using various silica‐supported chromium catalytic systems. Differential scanning calorimetry results show that the melting point of samples produced with the SBA‐15‐supported catalyst is higher than that of samples produced with Cr/SiO₂ under the same conditions, which could be related to the existence of an extended‐chain structure. Copyright © 2010 Society of Chemical Industry     

Catalytic dehydrogenation of propane on chromia,palladium and platinum supported catalysts

The dehydrogenation of propane to propylene over Cr₂O₃/Al₂O₃, Pd/Al₂O₃ and Pt/SiO₂ has been investigated in the temperature range 580–618°C. Runs were performed on propane, alone or in the presence of nitrogen (as a diluent), with complete analysis of the reaction products. The reaction was carried out in a fixed bed reactor at space velocities from 450–800 h^?1 which are close to industrial values and at pressures from 0.3 to 1 atm. A set of runs was made over a commercial chromia-alumina catalyst (10% Cr₂O₃) and over a promoted catalyst prepared in the laboratory by impregnation (16.8% Cr₂O₃ + 2% K₂O). The latter catalyst showed high selectivity and stability even when subjected to continuous cycles of dehydrogenation, regeneration and purging. Of the two noble metal supported catalysts used, reduced Pd/Al₂O₃ showed higher activity than Pt/SiO₂ at 618°C. The former catalyst gave a propylene yield of around 98% at 20% conversion level.     

Effect of Ce addition on Cr/γ-Al2O3 catalysts for methane catalytic combustion

Cerium modified and chromium-based catalysts using nano-γ-Al₂O₃ as the carrier were prepared via incipient wetness impregnation method and investigated for the catalytic combustion of methane (CH₄). The Cr-based catalysts promoted with 3 wt.% Ce displayed the most effective catalytic activity among all catalysts investigated. In addition, Ce significantly improved the catalytic performance of CH₄ combustion by increasing the amount of reaction site [CrO₄]_ads species on the surface of Cr-based catalysts. Introduction of Ce content also restrained the deactivation of catalysts at high calcination temperature. Cr-based catalysts modified with cerium seem to be a promising cheap and low-temperature catalyst for CH₄ combustion.     

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.     

CO removal from reformed fuel over Cu/ZnO/Al2O3 catalysts prepared by impregnation and coprecipitation methods

A composition of Cu/ZnO/Al₂O₃ catalysts prepared by the impregnation method was optimized for water gas shift reaction (WGSR) coupled with CO oxidation in the reformed gas. The optimum composition of the impregnated catalyst for high WGSR activity was 5 wt.% Cu/5 wt.% ZnO/Al₂O₃. The optimum loading amounts of Cu and ZnO in the impregnated catalyst were smaller than those in the coprecipitated catalyst. Its catalytic activity above 200 °C was comparable to that of the conventional coprecipitated Cu/ZnO/Al₂O₃ catalyst. However, the activity of the impregnated Cu/ZnO/Al₂O₃ catalysts was significantly lowered at 150 °C, whereas no deactivation was observed for the coprecipitated catalyst at the same temperature. It was found that deactivation occurred over impregnated catalysts with H₂O and/or O₂ in the reaction gas; it prevented CO adsorption on the surface.     

Fabrication of supported Pd–Ir/Al2O3 bimetallic catalysts for 2‐ethylanthraquinone hydrogenation

A series of χ wt % Pd‐(1‐χ) wt % Ir (χ = 0.75, 0.50, and 0.25) catalysts supported on γ‐Al₂O₃ have been prepared by co‐impregnation and calcination‐reduction, and subsequently employed in the hydrogenation of 2‐ethylanthraquinone—a key step in the manufacture of hydrogen peroxide. Detailed studies showed that the size and structure of the bimetallic Pd–Ir particles vary as a function of Pd/Ir ratio. By virtue of its small metal particle size and the strong interaction between Pd and Ir, the 0.75 wt % Pd–0.25 wt % Ir/Al₂O₃ catalyst afforded the highest yield of H₂O₂, some 25.4% higher than that obtained with the monometallic 1 wt % Pd catalyst. Moreover, the concentration of the undesired byproduct 2‐ethyl‐5,6,7,8‐tetrahydroanthraquinone (H₄eAQ) formed using the Pd–Ir bimetallic catalysts was much lower than that observed with the pure Pd catalyst, which can be assigned to the geometric and electronic effects caused by the introduction of Ir. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3955–3965, 2017     

Catalytic oxidation of methane on CuO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/FeAlO/FeAl cermet catalysts

The activity of plates of CuO/Al₂O₃/FeAlO/FeAl structured cermet catalysts is compared by varying their alumina content. The catalysts were prepared by impregnation of cermet supports obtained by mechanochemical activation of powder mixtures of an alumina precursor [20–50% (wt.)], iron, and aluminum, followed by hydrothermal treatment and calcination. It is shown that increasing the content of the alumina precursor (product of thermal activation of gibbsite) increases the specific surface area of the support and the mesopore and macropore volumes and reduces its mechanical strength. The content of the active component (CuO) also increases, resulting in an increase in the specific activity of catalyst despite a reduction in the effectiveness of using the active component. The activity of catalysts with a moderate concentration of alumina is sufficient to initiate methane oxidation.     

Steam reforming of kerosene over a metal-monolithic alumina-supported Ru catalyst: Effect of preparation conditions and electrical-heating test

A plate-type anodic alumina support (γ-Al₂O₃/Fe–Cr–Ni alloy/γ-Al₂O₃) was used to prepare a series of Ru catalysts. The performance of these catalysts was investigated in the steam reforming of kerosene (SRK). Ethanol solution impregnation was used to enhance metal dispersion on the catalyst surface. The catalyst prepared by ethanol solution impregnation and dried at 120 °C (Ru/Al₂O₃-ED) gave a higher metal dispersion and more favorable activity and durability than that prepared in aqueous solution. However, owing to shrinking caused by the oxidation of ruthenium species, high temperature calcination in air after impregnation greatly decreased the metal dispersion on the catalyst surface, regardless of the impregnation solution type. In contrast to calcination in air, high temperature N₂ treatment could decompose the reducible ruthenium species on the Ru/Al₂O₃-ED completely. This indicates that H₂ pre-reduction is not an essential procedure for the SRK reactions over this catalyst. The experimental results also confirm this hypothesis. The effect of Ce addition was also investigated and was found to enhance significantly the catalyst tolerance to carbon deposition thereby improving the SRK durability of Ru/Al₂O₃-ED under a high space velocity. In addition, owing to the high electrical resistance of the Fe–Cr–Ni alloy, the anodic alumina catalyst itself can be used as a heater, when an electrical current is applied along the alloy layer. Under an electrical-heating pattern, the SRK reaction system reached stability within 15 min, offering a strong possibility for shortening the start-up time of conventional reformers from 1 to 2 h to a few minutes.     

Catalytic dehydrogenation of isobutane over ordered mesoporous Cr2O3–Al2O3 composite oxides

A series of ordered mesoporous Cr₂O₃–Al₂O₃ composite oxides synthesized via improved one-pot evaporation induced self-assembly strategy were investigated as the catalysts for catalytic dehydrogenation of isobutane. These mesoporous catalysts with good structural properties and thermal stability performed excellent catalytic properties. Besides, the effect of the ordered mesopore structure on improving catalytic properties was also studied. Compared with non-mesoporous catalyst, the current mesoporous catalyst could accommodate the gaseous reactant with more “accessible” active sites. Therefore, the present materials were considered as promising catalyst candidates for catalytic dehydrogenation of isobutane.