Successive Impregnation Method Research Articles

Metal–support interactions over Ni/CeO2–ZrO2 catalysts for ethanol steam reforming and their effects on the coke gasification

In this study, we investigated the metal–support interactions over Ni/CeO2–ZrO2 (Ni/CZ) catalysts for ethanol steam reforming. Different Ni contents (5, 10, and 15 wt%) were loaded onto the CZ support using two catalyst preparation methods, namely one-pot, and successive impregnation methods. Using the one-pot method, the Ni species over the Ni/CZ catalysts strongly interacted with the CZ support, resulting in smaller Ni nanoparticles with abundant oxygen vacancies. In contrast, the successive impregnation method mainly generated an isolated Ni phase at a high Ni content, resulting in large Ni clusters with limited oxygen vacancies. The poor Ni dispersion over the Ni/CZ catalysts prepared by the successive impregnation method induced low ethanol conversions and hydrogen production rates. In addition, the large Ni clusters over the Ni/CZ catalysts prepared by the successive impregnation method achieved a fast-coking behavior, thereby increasing the coke amount. Further, coke gasification was demonstrated to dominate the Ni surface with the Ni/CZ catalysts prepared by the one-pot method because of the high Ni dispersion and abundant oxygen vacancies.

Performance of Modified Alumina-Supported Ruthenium Catalysts in the Reforming of Methane with CO2

Ruthenium (1 wt%) catalysts supported on alumina doped with alkaline (Na and K) and alkaline earth metals (Ba, Ca, and Mg) of different concentrations (1, 5, and 10 wt%) were tested in the dry reforming of methane. All catalysts were prepared by the successive impregnation method. Supports were characterized by X-ray diffraction, BET surface area, temperature-programmed desorption of CO2, and 2-propanol dehydration. Additionally, catalysts were characterized by temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Stability tests to study coke deposition were performed using long-time dry reforming reactions. All the catalysts showed good catalytic activity, and activity falls were never detected. Ru metallic phase seemed to be resistant to coke formation even though its particles are sintered during a long-term reaction.

Titanium-modified MCM-41 molecular sieves as efficient supports to increase the hydrogenation abilities of NiMoS and CoMoS catalysts

Ti modified MCM-41-supported NiMo and CoMo catalysts and their respective Ti free reference catalysts were prepared, characterized, and tested for the hydrodesulfurization reactions. The samples were synthesized by well-known procedures, such as liquid crystal templating and successive impregnation method for the supports and catalysts, respectively. Ti precursor was directly incorporated into the micellar solution before adding the silica precursor at different molar Si/Ti ratios (x=75 and 50). Fourier transform infrared spectroscopy, solid-state 29Si-nuclear magnetic resonance, small- and wide-angle X-ray diffraction, and nitrogen physisorption were used as characterization techniques. Four sulfided catalysts were also characterized by high-resolution transmission electron microscopy. The catalysts showed important increases in the reaction rates during both thiophene and dibenzothiophene hydrodesulfurization when the support was structurally modified with Ti-atoms. The samples supported on Ti-MCM-41(75) presented a higher activity than those supported on Ti-MCM-41(50), and they were superior to their respective Si-MCM-41-supported NiMoS and CoMoS catalysts, even NiMoTiM75 and CoMoTiM75 catalysts presented better performance compared to the conventional NiMo/Al2O3 and CoMo/Al2O3 catalysts in the DBT hydrodesulfurization. Ti incorporation also enhanced the selectivities to the hydrogenated products, which could be beneficial to destabilize refractory S-containing molecules.

Simultaneous Desulfurization and Denitrification Using La-Ce-V-Cu-ZSM-5 Catalysts in an Electrostatic Precipitator.

Different catalysts were loaded onto the collecting plate of an electrostatic precipitator to achieve the simultaneous removal of multiple pollutants from coal-fired gas. The synergistic desulfurization and denitrification effect of the catalyst and the effect of corona discharge on the activity of the catalyst were studied. The La(6%)–Ce(8%)–V(7%)–Cu(8%)–ZSM-5 catalyst prepared by successive impregnation methods had the optimum simultaneous desulfurization and denitrification efficiency at a roasting temperature of 600 °C. The desulfurization and denitrification rates reached 97.09 and 83.30%, respectively. BET and SEM characterization results showed that the loading of active components and additives improved the pore structure of the molecular sieve, which contributed to the high stability of the catalyst’s internal structure and large surface area, as well as better desulfurization and denitrification efficiency. Corona discharge can significantly improve the catalytic effect.

Extraction-Induced Fabrication of Yolk–Shell-Structured Nanoparticles with Deformable Micellar Cores and Mesoporous Silica Shells for Multidrug Delivery

Yolk-shell-structured nanoparticles (YSNs) provide useful carriers for applications in biomedicine and catalysis due to the excellent loading capability and versatile functionality of the flexible core and porous shell. Unfortunately, the reported YSNs always require complex multistep synthesis processes and a harsh hard-template etching strategy. Herein, a facile "selective extraction" strategy is developed to synthesize yolk-shell-structured polymer@void@mSiO2 nanoparticles (designated as YSPNs) comprising deformable and soft polystyrene-b-poly(acrylic acid) (PS-b-PAA) micellar cores and mesoporous silica shells. The YSPNs are formed by a morphological change and volume shrinkage of the PS-b-PAA aggregates from large compound vesicles to large compound micelles during the extraction process. As a multidrug vehicle, both hydrophobic curcumin (Cur, 6.4 wt %) and hydrophilic doxorubicin hydrochloride (Dox, 19.4 wt %) can be coloaded onto YSPNs through a successive impregnation method. Moreover, the resulting Cur/Dox@YSPNs possess intelligent pH-responsive capability, time-sequenced release behavior, and high in vivo antitumor efficiency, demonstrating excellent potential as safe and efficient multidrug nanocarriers for tumor chemotherapy. We envision that such a facile "selective extraction" strategy will enable pathways to construct organic-inorganic hybrid nanoparticles with yolk-shell structures for various applications.

Effect of preparation method on the Pt-In modified Mg(Al)O catalysts over dehydrogenation of propane

The Pt-In modified Mg(Al)O catalysts were prepared by co-precipitation, co-impregnation, and successive impregnation methods with Pt and In loading at 0.3 and 0.6 wt.%, respectively. The catalysts were tested in the propane dehydrogenation at 550 °C and atmospheric pressure. Pt loading on In-modified Mg(Al)O support prepared by co-precipitation (Pt/Mg(In)(Al)O) exhibited the highest catalytic performances with initial propane conversion and propylene selectivity of 24.2%.and 98.2%, respectively. As revealed by the H2-TPR and XPS results, the Pt/Mg(In)(Al)O exhibited a stronger metal-support interaction and favorable led to more PtIn alloy formation compared to those obtained by the other methods, which greatly enhanced the catalytic performance and stability. Coke formation was significant reduced on all the prepared bimetallic PtIn catalysts, especially coke on the active metal, which diminished the catalytic deactivation. The catalysts were also characterized by CO chemisorption, transmission electron microscopy (TEM), NH3-temperature program desorption (NH3-TPD).

Influence of Method of Introduction of Cu- and Zn-Based Modifiers on the Properties of Chromia–Alumina Catalysts

Three methods of introduction of modifiers based on Cu and Zn compounds into the CrOx/Al2O3 catalysts for dehydrogenation of light paraffin hydrocarbons are considered: Introduction from sol, introduction using successive impregnation technique and introduction of modifiers by impregnation along with precursor of chromium oxide. The obtained samples are studied by a complex of physical-chemical methods (XRD, UV-Vis spectroscopy, temperature-programmed reduction with hydrogen (TPR-H2), X-ray fluorescent (XRF) spectrometry, low-temperature N2 sorption). The catalytic properties of the samples are studied in kinetic mode in isobutane dehydrogenation. Cu- and Zn-modifiers are shown to influence on the peculiarities of reduction of Cr6+ and, hence, specify the state of active surface of CrOx/Al2O3 catalysts formed in the reductive reaction medium. Not only do the states of modifiers influence on the initial activity of the catalyst, but also on its activity after oxidative regeneration. Introduction of modifiers by successive impregnation method results in formation of copper and zinc aluminates or defective spinels on the Al2O3 surface. When the active component is introduced, the modified surface of the support promotes formation and stabilization of Cr6+ sites that can undergo reversible reduction–oxidation and provide high activity and selectivity towards formation of isobutylene (>98%).

Enhanced activity and stability of copper oxide/γ-alumina catalyst in catalytic wet-air oxidation: Critical roles of cerium incorporation

By successive impregnation method, the Ce-modified Cu-O/γ-Al2O3 catalyst was prepared and characterized using nitrogen adsorption-desorption, scanning electron microscopy energy dispersive X-ray analysis (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, and H2-Temperature programming reduction (H2-TPR). In catalytic wet-air oxidation (CWAO) process for the printing and dyeing wastewater (PDW), the effects of Ce addition on performance, mechanism and kinetics of the catalyst were investigated. The Ce addition increases the Brunauer-Emmett-Teller (BET) surface area and pore volume of the catalyst and makes the active components uniformly distributed on the catalyst surface. Formation of a stable CuAl2O4 solid solution by anchoring Cu onto the γ-Al2O3 crystal lattice leads to a significant decrease in metal leaching of the Ce-modified catalyst. The proportion of lattice oxygen in the catalyst substantially increases and the apparent activation energy of Cu-O/γ-Al2O3 catalyst decreases owing to Ce addition. Therefore, the catalytic activity and stability of the Ce-modified catalyst are considerably improved. The scavengers experiments identify the active species existed in the CWAO reaction system, with the order of reactivity: h+ > O2•− > H2O2 > HO•. This novel Cu-Ce-O/γ-Al2O3 catalyst has great potential in applications for treatment of concentrated organic wastewater due to its superior catalytic activity and improved stability.

Activation by pretreatment of Ag–Au/Al2O3 bimetallic catalyst to improve low temperature HC-SCR of NOx for lean burn engine exhaust

Bimetallic Ag–Au/Al2O3 catalyst was synthesised by successive impregnation of 1% Au and 1% Ag on in-house prepared high surface area alumina (450m2/g). The corresponding monometallic catalysts were also prepared by loading 1% Ag or 1% Au on the same high surface area alumina for comparison. The catalysts were characterised by various physico-chemical techniques and tested for SCR activity under lean burn engine exhaust conditions. Ag–Au/Al2O3 catalyst prepared by successive impregnation method showed considerably higher NO reduction (100%) to N2 compared to 1% Au/Al2O3 (70%) whereas the activity was comparable with that of 1% Ag/Al2O3 (96%). The effect of various pretreatments on SCR activity of Ag–Au/Al2O3 was studied and pretreatment at 250°C in flow of hydrogen was found to give the best results with 100% NO conversion to N2 at 353°C. Further ageing of the catalyst under reaction feed at 500°C resulted in considerable increase in low temperature activity of bimetallic catalyst with ∼40% NO conversion at 222°C. Even though the SCR activity of pretreated Ag–Au/Al2O3 and Ag/Al2O3 were comparable, after ageing the Ag–Au/Al2O3 showed significantly higher NO conversion (95%) compared to Ag/Al2O3 (83%) and Au/Al2O3 (70%). The formation of H2 and CO due to steam reforming of higher hydrocarbon (decane) was evidenced at the temperature of highest deNOx activity. Detailed investigation of the textural properties of the pretreated and aged catalysts showed presence of well dispersed metallic Au and Agnδ+ clusters after pretreatment in hydrogen at 250°C.

A study on the catalytic synergism between K and Pd in Co3Al(O) hydrotalcite-derived oxide catalysts used for soot combustion

The K/Co3−xPdxAl(O) (x=0 or 0.02) and K/Pd/Co3Al(O) catalysts promoted by K and Pd were synthesized by using pH-constant co-precipitation and successive impregnation methods through the precursors of hydrotalcites. The physicochemical properties of these catalysts were systematically characterized by XRD, EXAFS, XANES, XPS, HRTEM, H2-TPR, soot-TPR and in-situ FT-IR. It is found that the catalyst K/Pd/Co3Al(O) prepared by successive impregnation displays the lowest characteristic temperatures including the initial and final combustion temperatures (Ti and Tf). The coexistence of K and Pd in K/Pd/Co3Al(O) or K/Co3−xPdxAl(O) can improve both the reducibility and the oxidizability of the catalysts, generating a prominent catalytic synergism on soot oxidation. K–Co–O and K–Pd–O have been identified as the main active phases in the catalysts simultaneously promoted by K and Pd. Based on the results of in-situ FT-IR three potential reaction pathways for soot combustion have been revealed, namely the direct soot oxidation, nitrate-enhanced soot oxidation and NO2-assisted soot oxidation. As compared with the conventional Pd/Al2O3 catalyst, the as-prepared K/Pd/Co3Al(O) catalyst possesses much higher thermal stability.

The relationship between the structural properties of bimetallic Pd–Sn/SiO 2 catalysts and their performance for selective citral hydrogenation

The effect of Sn addition to Pd on the selective liquid-phase hydrogenation of citral to α,β-unsaturated alcohols (UA: nerol and geraniol) was examined. Pd–Sn/SiO 2 bimetallic catalysts were prepared by successive impregnation method and were characterized by transmission electronic microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDX), temperature-programmed reduction (TPR), Fourier transform infrared (FTIR) spectroscopy of adsorbed CO, and X-ray photoelectron spectroscopy (XPS). Sn addition to Pd/SiO 2 catalysts significantly modifies their properties for citral hydrogenation performed at 130 °C, under 7 MPa and in isopropanol solvent, inducing a promoting effect on the UA selectivity. This promoting effect is related to the existence of a Pd–Sn interaction highlighted by EDX analysis, TPR under hydrogen and FTIR of adsorbed CO. The latter technique suggested the presence of a geometric effect on catalytic activity. Maximum UA selectivities (>75% at 30% citral conversion) were obtained when an alloy of the Pd 3Sn type is formed in the bimetallic particles, as confirmed by TPR and XPS. Moreover, FTIR measurements of the adsorbed CO singleton frequency as well as XPS binding energy shifts strongly imply an electron transfer from Sn to Pd, which is proposed to be responsible for enhanced adsorption of citral C O bond on the surface of Pd–Sn/SiO 2 bimetallic catalysts. To our knowledge, it is the first time that modified Pd catalysts lead to such important UA selectivity values during α,β-unsaturated aldehyde hydrogenation.

K and Sr promoted Co alumina supported catalysts for the CO 2 reforming of methane

K and Sr promoted Co alumina supported catalysts for the CO 2 reforming of methane (973 K, CH 4:CO 2 (1:1)) have been prepared by the coimpregnation and successive impregnation methods. The catalysts (fresh and used (after reaction)) have been characterized using the following techniques: Atomic Absorption Spectroscopy (ICP-OES), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray (EDX) and Temperature Programmed Oxidation (TPO). The obtained results indicate that K is a more effective promoter than Sr and that the preparation method does not affect the catalyst performance. Because of that, the coimpregnation method (the simplest one) has been selected to prepare a series of K promoted catalysts with variable amount of potassium. It has been found that the amount of potassium influences both, the methane conversion and the amount of deposited carbon. The optimum amount of potassium seems to be around 0.6 wt.%, as the catalyst with this K loading presents a relatively high methane conversion (60%) and a quite low amount of deposited carbon (0.08% molar of the converted carbon) after 6 h reaction.

Impact of preparation method and support modification on the activity of mesoporous hydrotreating CoMo catalysts

Abstract This work seeks to optimize CoMo/HMS-Ti catalysts for the hydrodesulphurization (HDS) of dibenzothiophene (DBT) by support modification with phosphorous, as well as select a suitable catalyst preparation method. The Ti-loaded hexagonal mesoporous silica ((HMS)-Ti material prepared with Si/Ti molar ratio of 40) was modified varying the phosphorus amount (0.2–1.0 wt%) and used as support to deposit oxide Co and Mo precursors by simultaneous and successive impregnation methods. Structural features of the pure supports and oxide CoMo-loaded materials have been revealed by different techniques including specific surface area ( S BET ), X-ray diffraction, temperature-programmed reduction (TPR), UV–vis diffuse reflectance spectroscopy (DRS UV–vis) and micro-Raman spectroscopy. Activity–structure correlations showed that the number of irregular oxide Mo 6+ particles, as determined by Raman spectroscopy, influenced the final catalytic response of sulphided systems. All catalysts prepared by simultaneous impregnation showed larger HDS activity than their counterparts prepared by successive impregnation, and this was linked, in part, to a higher specific surface area of the former systems. All P-containing catalysts recorded greater activity than their P-free counterparts because the presence of phosphorus on the support surface forced the formation of octahedral Co 2+ species and irregular oxide Mo 6+ particles. From the activity–structure correlation, the optimum P-loading was archived at 0.64% of P 2 O 5 .

Synthesis of CoMo-based carbon hydrodesulfurization catalysts: Influence of the order of metal impregnations on the activity

Series of CoMo-based carbon catalysts were synthesized via the successive impregnation method, in which the carbon material was impregnated first with cobalt. The activity of the catalysts in the hydrodesulfurization of dibenzothiophene using a high pressure batch reactor operating at 340°C under 3MPa of hydrogen was investigated. In general, the carbon-supported CoMo catalysts synthesized by the successive impregnation method (in this case cobalt was the first to be introduced) showed higher hydrodesulfurization activities for dibenzothiophene than the reference CoMo-based carbon catalyst prepared by the conventional successive impregnation. The remarkable hydrodesulfurization activities of these CoMo-based carbon catalysts are suggested to be a consequence of forming a new synergy between molybdenum and cobalt. The data provide evidence that the CoMo-bimetallic synergy is affected by the nature of the support and by the order of metal impregnation. The results support the view of the electronic origin of such synergy.

Influence of the preparation method on the catalytic behaviour of PtSn/TiO2 catalysts

PtSn/TiO2 catalysts containing 2wt% Pt and a Pt:Sn atomic ratio of 2:1 and 1:1 were prepared by coimpregnation or successive impregnation method with aqueous solutions of SnCl2·2H2O and H2PtCl6·6H2O of a commercial TiO2 (P25, from Degussa). Both catalyst series, independent of the preparation method, were reduced at 473 and 773K. XPS results show that tin was in an oxidized state after reduction at 473K, and that a fraction was in the metallic state after reduction at 773K. By use of in situ FTIR spectroscopy of adsorbed CO, the presence of bimetallic Pt–Sn phases was assessed after reduction at 773K. Microcalorimetric analysis of CO adsorption enthalpy indicates that reduction at 773K causes the appearance of a more heterogeneous distribution of active sites, as well as a loss in the amount of sites. The catalytic activity for the gas phase hydrogenation of crotonaldehyde was greatly improved when the catalysts were prepared by coimpregnation, at both reduction temperatures. The selectivity toward crotyl alcohol was higher after reduction at 773K and independent of the preparation method, although it increased with the amount of tin, suggesting a promoting effect of tin on this reaction.

Effect of Co addition for carburizing process of Ti-oxide/SiO2 into TiC/SiO2

Lowering the carburization temperature of Ti-oxide into TiC down to 1173 K could be achieved by the addition of Co. Co-promoted TiC/SiO 2 catalysts were prepared by the temperature programmed reaction (TPR) method. Co–Ti/SiO 2 precursors were prepared by use of the successive impregnation method (sc) and the co-impregnation method (co). Samples were characterized by X-ray absorption fine structure (XAFS) measurements and X-ray diffraction (XRD) results. The carburization degree of TiC was affected by the method of Co addition. The carburization degree of sc Co–TiC/SiO 2 was better than that of co Co–TiC/SiO 2 . The activity of thiophene hydrodesulfurization reaction at 693 K on sc Co–TiC/SiO 2 was higher than that on co Co–TiC/SiO 2 . The HDS activity was related to the carburization degree of TiC. Lowering the carburization temperature of Ti-oxide into TiC down to 1173 K could be achieved by the addition of Co. Co-promoted TiC/SiO 2 catalysts were prepared by the temperature programmed reaction (TPR) method. Co–Ti/SiO 2 precursors were prepared by use of the successive impregnation method (sc) and the co-impregnation method (co). Samples were characterized by X-ray absorption fine structure (XAFS) measurements and X-ray diffraction (XRD) results. The carburization degree of TiC was affected by the method of Co addition. The carburization degree of sc Co–TiC/SiO 2 was better than that of co Co–TiC/SiO 2 . The activity of thiophene hydrodesulfurization reaction at 693 K on sc Co–TiC/SiO 2 was higher than that on co Co–TiC/SiO 2 . The HDS activity was related to the carburization degree of TiC.

Comparative study of the activity of cobalt and nickel as promoters of HDS catalysts

AbstractA series of trimetallic (NiCoMo) hydrodesulphurisation supported catalysts were prepared using a successive impregnation method, varying the ratio of promoters Ni/(Ni + Co) and maintaining the ratio (Ni + Co)/Mo constant. Optima for higher thiophene hydrodesulphurisation activity were found for ratios Ni/(Ni + Co) of 0.7 and 0.8. It is suggested that the optima may be strongly dependent on method of catalyst preparation, and/or type of support employed. Presulphidation was found to increase the activity in NiMo more than in CoMo. Testing of commercial catalysts confirmed various differences between CoMo and NiMo catalysts.