Sequential Impregnation Method Research Articles

Performance and Stability of the Ru–Re/γ-Al2O3 Catalyst in the Total Oxidation of Propane: Influence of the Order of Impregnation

Ru–Re/γ-Al2O3 catalysts were prepared by two sequential impregnation methods and their performances for the total oxidation of propane were investigated. TEM, XRD and H2 chemisorption data showed that the metal particle size was about 1.8 nm on both bimetallic catalysts. However, compared to the Ru/γ-Al2O3 catalyst with dispersion of 0.52, the Ru dispersion was improved by the presence of Re going from 0.64 for the catalyst with Re deposited on Ru/γ-Al2O3, to 0.70 for the sample with Ru deposited on Re/γ-Al2O3. The O2 adsorption data indicated that in the Re-modified catalysts the subsurface oxidation of Ru was suppressed, while in the Ru/γ-Al2O3 catalyst ruthenium was oxidized to a larger extent under oxidizing conditions at room temperature. The Ru deposited on Re/γ-Al2O3 exhibited a catalytic performance slightly better than the catalyst with Re impregnated on Ru/γ-Al2O3, but activity of Re-modified catalysts was not improved as compared to the Ru/γ-Al2O3 catalyst. On the other hand, bimetallic Ru–Re/γ-Al2O3 catalysts present better online stability and no deactivation was observed after the on-line tests for 30 h at temperature of 220 °C. TEM and XRD data showed that oxidized rhenium species strongly interacted with γ-alumina prevented large agglomeration of the Ru phase under O2-rich reaction conditions. The used monometallic Ru catalyst contained RuO2 oxide with crystallite size of 26 nm, while in the used bimetallic catalysts with size of 6–7 nm. Thus, in the consecutive catalytic tests Re-promoted Ru/γ-Al2O3 catalysts present higher activity and extended resistance to deactivation.

Sorbitol Hydrogenolysis to Glycols over Baisic Additive Promoted Ni-based Catalysts

A series of Ni based catalysts with different supports and basic additives were prepared by sequential impregnation method. The catalysts were characterized by XRD, BET, H2-TPR and CO2-TPD techniques. It was found that the introduction of basic additives enhanced the basicities of catalyats and promoted the dispersities of Ni particles by strong interaction between Ni2+ and basic additives. Among the Ni based catalysts, 10%Ni/10%La2O3 /ZrO2 showed the superior performance in sorbitol hydrogenolysis. The synergistic effect of Ni and La2O3 was proven to play an essential role in selective synthesis of EG and 1,2-PG. In the optimal reaction condition, the catalyst presented 100% sorbitol conversion and over 48% glycols (EG and 1,2-PG) yield. The kinetics study of polyols (sorbitol, xylitol and glycerol) hydrogenolysis showed that polyols with more hydroxyl number have higher activity and products distribution was final results of kinetic balance, which could give us some inspiration about how to change the products selectivity.

Influence of the support structure and composition of Ni–Cu-based catalysts on hydrogen production by methanol steam reforming

Cu and Ni were supported on ZrO2 by sequential impregnation method, and tested in the steam reforming of methanol (SRM) reaction for H2 production as a function of temperature. Four bimetallic catalysts were investigated, differing in ratio of nickel and copper (Cu: Ni = 1: 4 or 4: 1) and annealing temperature. The synthesized catalysts were characterized by N2 physisorption, DSC/TGA, X-ray diffraction, SEM, TEM. It was shown, that support structure has the main influence on composites activity, while the nature of a dominant metal affected on the selectivity of the resulting catalysts. The activity of catalysts decreases with increasing of materials crystallinity degree. The most active were samples coated with amorphous shell. The selectivity of copper catalysts is higher than nickel-based. Among the tested catalysts, the most active and selective catalyst was the sample Ni0.2-Cu0.8/amorphous ZrO2.

Fischer–Tropsch synthesis over alumina supported bimetallic Co–Ni catalyst: Effect of impregnation sequence and solution

The effect of Ni substitution on the Fischer–Tropsch (FT) synthesis activity and selectivity of alumina supported cobalt (Co/Al2O3) catalyst was investigated with a continuous stirred tank reactor at 230°C and 1MPa. Bimetallic Co–Ni/Al2O3 catalysts were prepared by an impregnation method. Total amount of supported metal was fixed at 20wt%. Influence of the Co/Ni ratio, impregnation sequences and solutions on the structure and activity of Co–Ni/Al2O3 catalyst was systematically studied. Low Ni-loading slightly increased CO conversion rate at nearly constant C5+ selectivity, but excess Ni-loading largely decreased CO conversion rate and C5+ selectivity. The catalytic activity did not depend on impregnation sequence, when Ni-loading amount was low. However, when Co was substituted with large amount of Ni, catalysts prepared by sequential impregnation method (Ni first and then Co) showed higher activity than those prepared by co-impregnation method and reverse sequential impregnation method (Co first and then Ni). These results indicate that catalysts with a Co-rich surface would be better than those with a Ni-rich surface. Impregnation solution also influenced the catalytic activity. Co–Ni/Al2O3 catalysts prepared by co-impregnation method using aqueous NH3 solution (Co+Ni/Al2O3-A) showed higher activity than those prepared using pure water or aqueous HNO3 solution. The best catalyst was Co(19wt%)+Ni(1wt%)/Al2O3-A, which exhibited 1.6 times as high activity as Co(20wt%)/Al2O3 catalyst prepared by a conventional impregnation method. The variation of catalytic activity with the kind of impregnation solution would be attributed to the differences in CO adsorption amount and/or electron density of surface Co metal sites.

Synthesis and physicochemical characterization of ZrO2-doped NiMo/Al2O3 nanocatalyst via precipitation and sequential impregnation methods used in hydrodesulfurization of thiophene

A series of Al2O3-ZrO2 composite with various ZrO2 contents were prepared by precipitation and NiMo was dispersed over them via sequential impregnation. The samples were characterized by XRD, FESEM, EDX, BET, TPR-H2 and FTIR techniques. XRD patterns indicate the homogeneous dispersion of ZrO2 on Al2O3 in small amounts of ZrO2. Comparison of FESEM images implies that with the incorporation of small amounts of ZrO2 (5, 12 and 17 wt%) on Al2O3, the catalyst morphology changed from large ensembles to smaller particles with uniform distribution. According to TPR-H2 profiles, adding ZrO2 increases the reducibility of nanocatalysts. Catalytic activity results showed that the NiMo over Al2O3-ZrO2 composite showed higher hydrodesulfurization activity than that of Al2O3 supported catalyst. The maximum of hydrodesulfurization activity was observed for NiMo/Al2O3-ZrO2 nanocatalyst with 12 wt% of ZrO2 content related to enhanced physicochemical properties.

Fischer–Tropsch synthesis over alumina supported cobalt catalyst: Effect of promoter addition

In order to improve the activity of Co/Al2O3 catalyst for FT synthesis, loading effect of metal promoter on Al2O3 support was examined. In this study, total 13 kinds of metal (Mg, Ca, Sr, Ba, Y, La, Ce, Ti, V, Mn, Zn, Zr and Mo) were employed as promoters and θ-Al2O3 prepared by the calcination of commercial boehmite was used as support. Co/Al2O3 catalysts loaded with various metal promoters were prepared by a sequential impregnation method. Loading of Mn, V and Mo on Al2O3 support decreased Co reducibility and surface area of Co metal, but increased intrinsic activity per active Co metal sties (i.e. TOF). On the other hand, metal additives other than Mn, V and Mo varied Co reducibility and Co surface area, but did not influence TOF. High overall activity was obtained over Co/Al2O3 catalysts loaded with rare earth elements (e.g. La and Ce), which was due to the high surface area of Co metal. We also examined the co-loading of La and V promoters on Al2O3 support. Co/Al2O3 catalysts loaded with both La and V (Co/La+V/Al2O3) showed higher activity than those loaded with either La or V. CO conversion rate over the best Co/La(2)+V(0.5)/Al2O3 catalyst was 1.6 times as high as that over bare Co/Al2O3 catalyst. Over the Co/La+V/Al2O3 catalyst, La and V promoters cooperatively improved Co reducibility, Co surface area and TOF, resulting in an increase of overall catalytic activity.

Hydrogen production by autothermal reforming of methane over NiPd catalysts: Effect of support composition and preparation mode

NiPd/Ce0.5Zr0.5O2/Al2O3 and NiPd/La2O3/Ce0.5Zr0.5O2/Al2O3 catalysts were prepared by incipient wetness co-impregnation method or sequential impregnation method for autothermal reforming of methane (ATR of CH4). The influence of the preparation mode, Ce0.5Zr0.5O2 and La2O3 additives on the physicochemical properties of NiPd supported catalysts and the effect on their activity to produce hydrogen by ATR of CH4 were investigated. Characterization of fresh and spent Ni-based catalysts by X-ray fluorescence spectroscopy, N2 adsorption, X-ray diffraction, H2 temperature-programmed reduction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were performed. It was demonstrated that support composition determines NiO dispersion as well as reducibility of Ni species through different strength of Ni-support interaction. The preparation method modifies the phase composition and catalyst ability for reduction. The catalyst evolution under reaction conditions was studied. The NiO (∼15 nm) and NiPd alloy (∼18 nm) phases were observed in the spent catalysts. It was found that the Nio/NiO ratio can be regulated by support composition and preparation mode of catalysts. It is demonstrated that studied catalysts provide high methane conversion of 90–100%, CO yield of 55–85% and H2 yield of 55–75% in ATR of CH4 at 750–950 °C. The optimal composition and preparation method of catalyst were selected. The best ATR of CH4 performance is provided by 10 Ni0.5Pd/10Ce0.5Zr0.5O2/Al2O3 catalyst prepared by Pd/Ni sequential impregnation method that can be associated with peculiarity of NiPd particles structure and the optimal ratio between NiO species with different ability for reduction.

Co-modified Pd/CeO2-ZrO2 catalysts for methanol decomposition

Pd/Ce0.8Zr0.2O2 catalysts modified by cobalt were prepared by a sequential impregnation method and characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption (Brunauer-Emmet-Teller), oxygen storage capacity (OSC), CO-chemisorption, H2-temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The effect of Co on the performance of methanol decomposition was evaluated at a fixed-bed microreactor. The results showed that the addition of Co can improve the oxygen storage capacity of the catalyst and the dispersion of Pd. XPS results indicated that Pd was in a partly oxidized (Pdδ+, 1<δ<2) state and Co2+ was present in Pd catalysts modified by Co. A 90% conversion of methanol was achieved at around 280 °C over Pd-Co/Ce0.8Zr0.2O2 catalyst which was 20 °C lower than that over Pd/Ce0.8Zr0.2O2, indicating that both Pdδ+and Co2+ play an important role in improving the catalytic activity of methanol decomposition.

Coking-resistant Ni-ZrO2/Al2O3 catalyst for CO methanation

Highly coke-resisting ZrO2-decorated Ni/Al2O3 catalysts for CO methanation were prepared by a two-step process. The support was first loaded with NiO by impregnating method and then modified with ZrO2 by deposition-precipitation method (IM-DP). Nitrogen adsorption-desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, H2 temperature-programmed reduction and desorption, NH3 temperature-programmed desorption, and zeta potential analysis were employed to characterize the samples. The results revealed that, compared with the catalysts with the same composition prepared by co-impregnation (CI) and sequential impregnation (SI) methods, the Ni/Al2O3 catalyst prepared by IM-DP showed much enhanced catalytic performance for syngas methanation under the condition of atmospheric pressure and a high weight hourly space velocity of 120000 mL·g−1 ·h−1. In a 80 h life time test under the condition of 300–600 °C and 3.0 MPa, this catalyst showed high stability and resistance to coking, and the amount of deposited carbon was only 0.4 wt%. On the contrary, the deposited carbon over the catalyst without ZrO2 reached 1.5 wt% after a 60 h life time test. The improved catalytic performance was attributed to the selective deposition of ZrO2 nanoparticles on the surface of NiO rather than Al2O3, which could be well controlled via changing the electrostatic interaction in the DP procedure. This unique structure could enhance the dissociation of CO2 and generate surface oxygen intermediates, thus preventing carbon deposition on the Ni particles in syngas methanation.

Hydrogen production via CO2 reforming of methane over ZrO2-Doped Ni/ZSM-5 nanostructured catalyst prepared by ultrasound assisted sequential impregnation method

In our continuing effort to find the proper catalyst for CO2 reforming of methane, Ni(8%)/ZSM-5-ZrO2 with various zirconium loadings (0–15%) are synthesized via sonochemical method. All samples are characterized by XRD, FESEM, TEM, EDX, BET, FTIR and TPR-H2 techniques. The XRD results confirm existence of NiO, ZrO2 and ZSM-5 as crystalline phase in catalyst structure. FESEM images reveal small particle size of active metals and low numbers of agglomerations for Ni(8%)/ZrO2(5%)-ZSM-5. BET analysis shows that addition of ZrO2 to Ni/ZSM-5 decreases the surface area but Ni/ZrO2(5%)-ZSM-5 has the highest surface area. TEM analysis demonstrates high dispersion of Ni nano particles over the support. EDX depicts the best active metal dispersion for the catalyst with 5% zirconia loading. The TPR results prove that the metal-support interaction is enhanced by zirconia addition, indicating the better Ni dispersion. Apart from characterization, activity tests are performed and parameters such as effect of temperature, CO and H2 yields and H2/CO ratio are investigated. The results show that Ni(8%)/ZrO2(5%)-ZSM-5 has the best structural properties and the highest activity and stability in comparison with the other catalysts.

The effect of impregnation strategy on structural characters and CO2 methanation properties over MgO modified Ni/SiO2 catalysts

Mg-modified Ni/SiO2 catalysts with different MgO contents were prepared by two impregnation methods. The catalysts prepared by co-impregnation method could show better activity and stability than those prepared by sequential impregnation method. The modification of MgO acted as a key factor in enhancing the capacity of CO2 adsorption and accelerating the activation of CO2. Moreover, modified MgO could also increase Ni species dispersion and suppress the metallic Ni sintering and oxidation.

Hydrotreating of Heavy Gas Oil on Mesoporous Mixed Metal Oxides (M–Al2O3, M = TiO2, ZrO2, SnO2) Supported NiMo Catalysts: Influence of Surface Acidity

Mesoporous mixed metal oxides, TiO2–Al2O3, ZrO2–Al2O3, and SnO2–Al2O3, were synthesized using a novel method and were used as a support material for the NiMo hydrotreating catalyst. The catalyst was prepared via the incipient wetness sequential impregnation method. All catalysts were characterized using N2 adsorption–desorption isotherms (BET), X-ray diffraction, FTIR, pyridine-FTIR, acridine-FTIR, CO-chemisorption, ICP-MS, TPD, and TPR. The HDS and HDN activities of the catalysts were determined using Athabasca bitumen derived heavy gas oil at industrial reaction conditions. The catalytic activity of synthesized NiMo/γ-Al2O3 catalyst was also determined for comparative studies. Low angle XRD and BET analysis has confirmed that the method developed for synthesis is suitable for the preparation of a mesoporous mixed oxide based NiMo hydrotreating catalyst. H2-TPR analysis has confirmed that the introduction of metal oxides such as ZrO2, TiO2, and SnO2 in alumina increases the active metal (Mo) and support ...

Catalytic steam reforming of acetic acid as a model compound of bio-oil

The effect of Ni catalysts promoted with Mg on catalytic activity and carbon deposition was investigated in acetic acid steam reforming. Acetic acid was chosen as representative compound for the steam reforming of bio-oil derived from biomass pyrolysis. In this study, nickel catalysts modified with Mg have been prepared by sequential impregnation method with 15wt.% Ni and variable loadings of Mg (1–10wt.%). The samples were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), high resolution transmission electron microscopy (HRTEM), specific surface area (BET) and temperature programmed reduction (TPR-H2). Steam reforming of acetic acid was conducted in a fixed bed reactor at a temperature of 500°C and 600°C. Under reactive conditions, the 15Ni5Mg/Al catalyst proved to be superior to the other catalysts at 600°C at which it presented an effluent gaseous mixture with the highest H2 selectivity and reasonable low coke formation.

Ni–WC/C nanocluster catalysts for urea electrooxidation

A nanocluster Ni–WC/C electrocatalyst is prepared through a sequential impregnation method and is used for the urea electrooxidation in alkaline conditions. The micro-morphology, lattice parameter, composition and surface states of Ni–WC/C particles are determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and X-ray photoelectron spectrometry (XPS) analysis. The electrooxidation activity and stability of the Ni–WC/C catalyst are also investigated by cyclic voltammograms and chronoamperograms. Characterization results indicate that the Ni nanoclusters are uniformly distributed on the WC/C framework, and the Ni–WC/C catalyst shows high electrocatalytic activity and stability for urea electrooxidation. The maximum current density at the Ni–WC/C electrode is almost 700 mA cm−2 mg−1 which is one order of magnitude higher than that at the Ni/C electrode, and the steady current density at the Ni–WC/C electrode is also markedly improved. Furthermore, the ESA values and XPS spectra indicate that the enhanced performance of the Ni–WC/C catalyst could be attributed to the structure effect and electron effect between nickel and tungsten carbide.

Catalytic decomposition of 2,3-dihydrobenzofuran to monomeric cyclic compounds over Pd/XCs2.5H0.5PW12O40/OMC (ordered mesoporous carbon) (X = 10–30 wt.%) catalysts

A series of Pd/XCs2.5H0.5PW12O40/OMC (ordered mesoporous carbon) (X=10, 15, 20, 25, and 30wt.%) catalysts with different Cs2.5H0.5PW12O40 contents (X, wt%) were prepared by a sequential incipient wetness impregnation method for use in the catalytic decomposition of 2,3-dihydrobenzofuran to monomeric cyclic compounds. 2,3-Dihydrobenzofuran was used as a lignin model compound for representing β-5 linkage of lignin. Acidity of Pd/XCs2.5H0.5PW12O40/OMC catalysts served as an important factor determining the catalytic performance in the reaction. Conversion of 2,3-dihydrobenzofuran and total yield for main products (2-ethylphenol and ethylcyclohexane) increased with increasing acidity of Pd/XCs2.5H0.5PW12O40/OMC catalysts.

Direct dehydrogenation of n-butane over Pt/Sn/M/γ-Al2O3 catalysts: Effect of third metal (M) addition

A series of Pt/Sn/M/γ-Al2O3 catalysts with different third metal (M=Zn, In, Y, Bi, and Ga) were prepared by a sequential impregnation method for use in the direct dehydrogenation of n-butane to n-butene and 1,3-butadiene. In the direct dehydrogenation of n-butane, Pt/Sn/Zn/γ-Al2O3 catalyst showed the best catalytic performance. Catalytic performance decreased in the order of Pt/Sn/Zn/γ-Al2O3>Pt/Sn/In/γ-Al2O3>Pt/Sn/γ-Al2O3>Pt/Sn/Y/γ-Al2O3>Pt/Sn/Bi/γ-Al2O3>Pt/Sn/Ga/γ-Al2O3. The catalytic performance increased with increasing metal–support interaction and Pt surface area of the catalyst.

Methane partial oxidation over NiO-MgO/Ce0.75Zr0.25O2 catalysts

Methane partial oxidation (MPO) is considered as an alternative method to produce hydrogen because it is an exothermic reaction to afford a suitable H2/CO ratio of 2. However, carbon deposition on a catalyst is observed as a major cause of catalyst deactivation in MPO. In order to find suitable catalysts that prevent the carbon deposition, NiO-MgO/Ce0.75Zr0.25O2 (CZO) supported catalysts were prepared via the co-impregnation (C) and sequential incipient wetness impregnation (S) methods. The amount of Ni loading was fixed at 15 wt-% whereas the amount of MgO loading was varied from 5 to 15 wt-%. The results revealed that the addition of MgO shifted the light-off temperatures to higher temperatures. This is because the Ni surface was partially covered with MgO, and the strong interaction between NiO and NiMgO2 over CZO support led to the difficulty in reducing NiO to active Ni0 and thus less catalytic activity. However, among the catalysts tested, the 15Ni5Mg/CZO (S) catalyst exhibited the best catalytic stability for MPO after 18 h on stream at 750°C. Moreover, this catalyst had a better resistance to carbon deposition due to its high metallic Ni dispersion at high temperature.

A Comparative Synthesis and Physicochemical Characterizations of Ni/Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt;–MgO Nanocatalyst via Sequential Impregnation and Sol–Gel Methods Used for CO&lt;SUB&gt;2&lt;/SUB&gt; Reforming of Methane

Carbon dioxide reforming of methane is an interesting route for synthesis gas production especially over nano-sized catalysts. The present research deals with catalyst development for dry reforming of methane with the aim of reaching the most stable catalyst. Effect of preparation method, one of the most significant variables, on the properties of the catalysts was taken in to account. The Ni/Al2O3-MgO catalysts were prepared via sol-gel and sequential impregnation methods and characterized with XRD, FESEM, EDAX, BET and FTIR techniques. The reforming reactions were carried out using different feed ratios, gas hourly space velocities (GHSV) and reaction temperatures to identify the influence of operational variables. FESEM images indicate uniform particle size distribution for the sample synthesized with sol-gel method. It has been found that the sol-gel method has the potential to improve catalyst desired properties especially metal surface enrichment resulting in catalytic performance enhancement. The highest yield of products was obtained at 850 degrees C for both of the catalysts. During the 10 h stability test, CH4 and CO2 conversions gained higher values in the case of sol-gel made catalyst compared to impregnated one.

Preparation of Pt-Sn-K/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Catalysts and its Catalytic Performance in Propane Dehydrogenation

Al2O3 supported platinum catalysts prepared by using different impregnation methods have been tested for the dehydrogenation of propane to propylene. The effect of promoter type and amounts of promoters has been investigated in a detail. The results indicated that the best catalytic performance was achieved on the catalyst prepared under the following conditions: sequential impregnation method, Sn and K as promoter, Pt loading 0.5%, Sn loading 1.0%, K loading 2.1%.

Hydrogen production from oxidative steam reforming of methanol: Effect of the Cu and Ni impregnation on ZrO2 and their molecular simulation studies

Cu and Ni were supported on ZrO2 by co-impregnation and sequential impregnation methods, and tested in the oxidative steam reforming of methanol (OSRM) reaction for H2 production as a function of temperature. Surface area of the catalysts showed differences as a function of the order in which the metals were added to zirconia. Among them, the Cu/ZrO2 catalyst had the lowest surface area. XRD patterns of the bimetallic catalysts did not show diffraction peaks of the Cu, Ni or bimetallic Cu–Ni alloys. In addition, TPR profiles of the bimetallic catalysts had the lowest reduction temperature compared with the monometallic samples. The reactivity of the catalysts in the range of 250–350 °C showed that the bimetallic samples prepared by successive impregnation had highest catalytic activity among all the catalysts studied. These results were also confirmed by theoretical calculations. The reactivity of the monometallic and bimetallic structures obtained by molecular simulation followed the next order: NishellCucore/ZrO2 ≅ CushellNicore/ZrO2 > Ni/Cu/ZrO2 > Cu/Ni/ZrO2 > Cu–Ni/ZrO2 > Cu/ZrO2 > Ni/ZrO2. These findings agree with the experimental results, indicating that the bimetallic catalysts prepared by successive impregnation show a higher reactivity than the Cu–Ni system obtained by co-impregnation. In addition, the selectivity for H2 production was higher on these catalysts. This result could be associated also to the presence of the bimetallic Cu–Ni and core–shell Ni/Cu nanoparticles on the catalysts, as was evidenced by TEM–EDX analysis, suggesting that the OSRM reaction may be a structure–sensitive reaction.