Sequential Impregnation Method Research Articles

Effect of preparation method on the bimetallic NiCu/SAPO-11 catalysts for the hydroisomerization of n-octane

Abstract The bimetallic NiCu/SAPO-11 catalysts were prepared by co-impregnation, sequential impregnation, co-precipitation, and mechanical mixing methods. Powder X-ray diffraction, nitrogen adsorption-desorption, temperature-programmed desorption of ammonia, transmission electron microscopy, temperature-programmed reduction of hydrogen, and X-ray photoelectron spectroscopy were used to characterize the physicochemical properties of the catalysts. The catalytic performance of the catalysts was assessed by the hydroisomerization of n -octane. Results indicated that the conversion of n -octane and selectivity to n -octane isomers were related to the preparation methods of the catalysts. The catalysts with Ni-Cu alloy effectively restrained the hydrogenolysis reaction that decreases the selectivity of isomerization. The catalyst prepared by the mechanical mixing of NiO and CuO hardly formed Ni-Cu alloy, showing obvious hydrogenolysis and low selectivity to n -octane isomers. The unbalance between the metal and acid sites resulted in the low conversion of n -octane and selectivity to n -octane isomers. Among all the catalysts, the catalyst prepared by the co-impregnation method exhibited high catalytic activity and selectivity to n -octane isomers.

A study of the synergy between support surface properties and catalyst deactivation for CO2 reforming over supported Ni nanoparticles

The correlation between surface acidity-basicity and catalyst deactivation have been investigated in the CO2 reforming of methane by adjusting the surface properties of the catalyst. Silica and alumina based support with different acidity-basicity have been prepared by two methods, (i) a solvothermal method and (ii) a sequential impregnation method. Then each of the supports has been decorated with Ni nanoparticles followed by variation of their activity towards CO2 reforming of methane (DRM). The catalytic materials have been analyzed before and after reaction by a variety of analytical techniques including BET, XRD, H2-TPR, XPS, CO2-TPD, NH3-TPD, O2-TPD, TG, O2-TPO, H2-TPH, SEM, and TEM. Catalysts with higher acidity were found to promote methane-cracking reactions, while the Boudouard and deactivation owing to metal oxidation were dominant at high basicity. Catalysts with more acidic or basic surfaces were found to be more prone to deactivation and metal sintering. The turnover frequency (TOF) and activation energy (Ea) of both the reactants showed a Gaussian curve with acidity-basicity of the catalyst surfaces. Among the tested catalysts, the best performing was those with homogeneous dispersion of surface acidic and basic sites, prepared by a single step synthesis. In contrast, under the same conditions, two-step synthesized supports with the significantly imbalanced distribution of acidic and basic sites favoured the Reverse water gas shift (RWGS) reaction, active metal oxidation by surface adsorbed oxygen and hence deactivated rapidly.

Sequential impregnation vs. sol-gel synthesized Ni/Al2O3-CeO2 nanocatalyst for dry reforming of methane: Effect of synthesis method and support promotion

The effects of CeO2 addition (10wt.%) as a support promoter on the catalytic performances of Ni catalysts supported over Al2O3 were studied in the dry reforming of methane (DRM). Ni/Al2O3-CeO2 nanocatalyst was prepared with sequential impregnation and sol-gel methods using low cost metal nitrate precursors to explore the effect of preparation method. The obtained materials were characterized by XRD, FESEM, BET and FTIR techniques. Catalytic activity and time-on-stream catalytic performance have been explored at different feed ratios, gas hourly space velocities and reaction temperatures. The results showed that CeO2 addition as a support modifier to the Ni/Al2O3 catalysts improved catalytic activity and stability. High dispersion of active phase in sol-gel synthesized catalyst was achieved in comparison with the impregnation synthesized one. FESEM images display smaller particle size (100% below 100nm) and a narrow particle size distribution for sol-gel synthesized sample, also this sample showed higher activity in the reforming reactions.

Aerobic oxidative esterification of primary alcohols over Pd-Au bimetallic catalysts supported on mesoporous silica nanoparticles

We have prepared a series of mesoporous silica nanoparticle (MSN) supported Pd-Au bimetallic catalysts using a newly developed sequential impregnation method. These catalysts were fully characterized by various techniques including nitrogen sorption, powder X-ray diffraction, inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM) and high angle annular dark-field scanning transmission electron microscopy (HADDF-STEM). By using this synthetic approach, we observed metal nanoparticles (NP) with diameters of 1–2nm homogeneously supported on the MSN. The catalytic performance of these MSN supported metal NPs was tested by aerobic oxidative esterification in a tandem reaction where primary alcohols are oxidized to their corresponding aldehydes and to esters in a subsequent reaction. We determined that Pd NPs are very efficient in the first step of oxidation; however, stagnant in the subsequent oxidation. On the contrary, Au NPs show slow reactivity in converting alcohols to aldehydes, but extraordinarily efficient in the oxidation of aldehydes to esters. By fine tuning the metal ratio, the bimetallic catalyst exhibits better reactivity and selectivity toward a variety of primary alcohols than the corresponding monometallic catalysts. In addition, we also found that the bimetallic Pd-Au@MSN catalysts can be recycled three times without a significant loss in activity.

Synthesis of the supported catalysts by co-impregnation and sequential impregnation methods

The non-sulfide catalysts Co-Mo/USY were prepared with three different methods, i.e. co-impregnation and two sequential impregnation procedures. The phases of the synthesized materials and their composition were characterized with X-ray diffraction. Furthermore, the X-ray diffraction patterns were analyzed using Le Bail methods with Rietica software. Finally, an overview of the substitution effect of cobalt and molybdenum on the metal content and acidity of the catalyst were also investigated.

Hydrogen production from biomass woodchips using Ni/CaO\u2013ZrO2 catalysts

This work aimed at the determination of the influence of various types of lignocellulosic biomass on the performance of Ni/ZrO2 catalyst modified by CaO in the production of hydrogen rich gas from lignocellulosic feedstock. The catalysts were prepared by co-impregnation and sequential impregnation methods. The catalytic activity of the synthesized materials was examined in the high temperature conversion of cellulose (model compound) and real biomass samples—woodchips from pine, beech, birch and poplar. The surface properties of Ni/CaO–ZrO2 catalysts were characterized by X-ray diffraction (XRD), time-of-flight secondary ion mass spectrometry (ToF–SIMS), thermogravimetric analysis (TG–DTA–MS) and BET methods. The obtained results revealed that an incorporation of calcium into the structure of the catalyst led to a decrease in the coke formation rate on its surface. Moreover, the influence of the preparation method on the material composition and related properties was demonstrated.

Effect of incorporation manner of Zr on the Co/SBA-15 catalyst for the Fischer–Tropsch synthesis

The effect of incorporation manner of Zr on the textural properties, surface physicochemical properties, reduction degree and catalytic performance of Co/SBA-15 catalyst for the Fischer–Tropsch synthesis (FTS) was investigated. The catalysts were prepared by sequential impregnation, co-impregnation and in-situ synthesis method, respectively. The loading amount of Co and Zr remained constant in all catalysts with 15wt.% and 5wt.%, respectively. The catalysts were characterized by N2 adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), temperature-programmed reduction (H2-TPR) and evaluated for the FTS. It was revealed that the Co3O4 was considered as the main surface cobalt phase, and the BET surface area and pore size were decreased regardless of the incorporation manner. The reduction degree of cobalt species increased from 80% (Co/SBA-15) to 90% (Co/Zr/SBA-15) and 85% (CoZr/SBA-15) with the addition of Zr, except for the Co/Zr-SBA-15 catalyst (74%). The catalyst prepared by sequential impregnation method (Co/Zr/SBA-15) showed the highest selectivity of long-chain hydrocarbons (C12–C22, 53%) with the chain growth probability α up to 0.84, which could be attributed to the highest reducibility of cobalt species.

PtSnNa@SUZ-4-catalyzed propane dehydrogenation

SUZ-4-based Pt-Sn catalysts with different sodium ion contents were prepared through sequential impregnation method. The structural and catalytic properties of the catalysts were studied by using various techniques combined with micro-reactor tests. The experimental results showed that PtSnNa/SUZ-4 catalysts exhibited high durability, high propylene selectivity and high stability with adequate sodium ion content. Sodium ion additives neutralized the strong acid sites and prevented the formation of coke. However, excess sodium ion not only reduced tin species to metallic tin, which reduced the catalyst activity by forming PtSn alloys, but also led to more Pt particles inside the pore of zeolite, which were easily deactivated by coke. It was found that catalysts with the sodium ion content at 0.5–1.5wt% led to the highest propane conversion and propylene selectivity.

Effect of Cu–Mo Activities on the Ni–Cu–Mo/Al2O3 Catalyst for CO2 Reforming of Methane

A series of Ni–Cu–Mo/Al2O3 catalysts with different metal contents were prepared by sequential impregnation method. The performance of the catalysts for carbon dioxide reforming of methane was investigated in a quartz tubular reactor at CH4/CO2 ratio of 4/6, feed gas flux of 100 mL/min, catalysts 460 mg, temperature range of 600–900 °C and atmospheric pressure. The catalysts were characterized by XRD, XPS, BET, CO2-TPD, TG, EDS and SEM. The performance and characterization results showed that the addition of Cu and Mo was beneficial for the reaction. The formation of spinel (NiMoO4, NiAl2O4, Cu6Mo4O15) and alloy (Ni3Mo, Cu3.8Ni) structures could significantly improve the catalytic activity and prevent the generation of carbon deposition. XRD patterns of the catalyst with the mass ratio of Ni:Mo = 0.75 after reaction suggested Mo2C formation which could eliminate the coke and extend the stability. The catalyst with the mass ratio of Ni:Mo = 0.75 showed better activity and still remained highly active under the condition of 800 °C for 60 h. Therefore, the highly effective Ni–Cu–Mo/Al2O3 catalyst could be a potential catalyst for carbon dioxide reforming of methane.

Effects of Ga doping on Pt/CeO2‐Al2O3 catalysts for propane dehydrogenation

This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO2‐Al2O3 catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO2‐Al2O3 catalysts were prepared by a sequential impregnation method. The as‐prepared catalysts were characterized employing N2 adsorption‐desorption, X‐ray diffrtaction, temperature programmed reduction, O2 volumetric chemisorption, H2‐O2 titration, and transmission electron microscopy. We have shown that Ga3+ cations are incorporated into the cubic fluorite structure of CeO2, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO2 is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016

Formation of Ru Shell on Co/Al2O3 by Galvanic Deposition Method and Its High Catalytic Performance for Three-Way Conversion

Abstract A supported Ru catalyst was prepared by a galvanic deposition (GD) of Ru on Co particles supported on Al2O3 (Ru/Co-GD). The structure and chemical state of Ru/Co-GD was characterized by using a pulsed CO chemisorption technique, STEM-EDS, XAFS, XPS, CO adsorption FT-IR spectroscopy, and temperature-programed reduction (TPR) method. It is indicated that Ru/Co-GD forms Ru shell on Co nanoparticles. Such a unique structure was not formed on Ru/Co/Al2O3 prepared by a conventional sequential impregnation method (Ru/Co-seq). The Ru shell of Ru/Co-GD showed higher reducibility than Ru species of Ru/Co-seq as well as higher than Ru/Al2O3. Owing to the Ru shell having high reducibility, Ru/Co-GD showed enhanced catalytic activity for NO–C3H6 reaction. In addition, Co oxide on Ru/Co-GD exhibited high catalytic activity for CO and C3H6 oxidation. As a result, Ru/Co-GD showed superior performance for NO–C3H6–CO–O2 reaction compared to the conventional catalysts. The Ru shell structure also contributed to the suppression of Ru vaporization.

Influence of Support Structural Characteristics on Long-term Performance of Pd-Ag/α-Al2O3 Catalyst for Tail-end Acetylene Selective Hydrogenation

Abstract The selective hydrogenation of acetylene to ethylene in acetylene/ethylene mixture over Pd-Ag/α-Al2O3 catalysts prepared by sequential impregnation method was studied. The α-Al2O3 support was prepared by thermal treatment of γ-Al2O3 in temperature range of 1,090–1,100 °C. The samples were characterized for their structural properties and coke deposition. They showed egg-shell structure with penetration depth increasing with sintering temperature of the support. A kinetic model based on 1st order in acetylene and 0.5th order in hydrogen for the main reaction and 2nd order independent decay law for catalyst deactivation was used to fit the conversion-time data and to obtain quantitative assessment of catalyst performances. Fair fits were observed from which the reaction and deactivation rate constants were evaluated. The highest selectivity to ethylene, and therefore best performance, was obtained for the highest calcination temperature which was attributed to its lower acidity and larger pore diameters.

Direct Dehydrogenation of n-Butane Over Pt/Sn/Zn-K/Al2O3 Catalyst: Effect of Hydrogen in the Feed.

Al2O3 was prepared by a sol-gel method for use as a support. Pt/Sn/Zn-K/Al2O3 catalyst was then prepared by a sequential impregnation method, and it was applied to the direct dehydrogenation of n-butane to n-butenes and 1,3-butadiene. Physicochemical properties of Pt/Sn/Zn-K/Al2O3 catalyst were examined by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherm, inductively coupled plasma atomic emission spectroscopy (ICP-AES), temperature-programmed reduction (TPR), CO chemisorption, and temperature-programmed oxidation (TPO) measurements. In order to improve the catalyst stability, the effect of hydrogen in the feed on the catalytic performance in the direct dehydrogenation of n-butane was studied. The catalyst stability and reusability in the direct dehydrogenation of n-butane was also investigated. Experimental results revealed that the addition of hydrogen in the feed decreased conversion of n-butane and yield for total dehydrogenation products but improved the stability of the catalyst. The catalytic activity and stability of regenerated Pt/Sn/Zn-K/Al2O3 catalyst in the presence of hydrogen slightly decreased compared to those of fresh Pt/Sn/Zn-K/Al2O3 catalyst due to the slight sintering of platinum particles.

High purity hydrogen production via sorption enhanced chemical looping reforming: Application of 22Fe2O3/MgAl2O4 and 22Fe2O3/Al2O3 as oxygen carriers and cerium promoted CaO as CO2 sorbent

High purity hydrogen can be produced using sorption enhanced chemical looping reforming (SE–CLR) in which an oxygen carrier and an in situ CO2 sorbent are involved. In this study, the effectiveness of alumina modification with Mg as the support of Fe2O3 based oxygen carriers is investigated in CLR and SE–CLR processes for clean hydrogen production. The 22Fe2O3/Al2O3 and 22Fe2O3/MgAl2O4 oxygen carriers are synthesized with impregnation and sequential impregnation methods, respectively. Prior to SE–CLR process, the performance of three different calcium based sorbents including industrial CaO, synthesized CaO and cerium promoted CaO are investigated for CO2 sorption in calcium loop. The characterization of the oxygen carriers and sorbent samples is performed by XRD, BET, FESEM and TEM. It is found that the addition of cerium to the calcium-based sorbent effectively improves its structural properties and CO2 sorption performance. The obtained results reveal that the sorbent surface area is a significant parameter affecting its CO2 removal efficiency at high temperatures. In addition, the presence of Mg in oxygen carrier structure successfully prevents the formation of Fe–Al spinel by MgAl2O4 formation. An excessive H2/CO molar ratio of 16.7 is also achieved using Fe2O3/MgAl2O4 oxygen carrier and synthesized Ce/Ca=0.2 sorbent at 600°C in SE–CLR process.

Hydrogen production by chemical looping steam reforming of methane over Mg promoted iron oxygen carrier: Optimization using design of experiments

In the chemical looping reforming (CLR) process, methane is converted to hydrogen and carbon monoxide through cyclic reduction–oxidation reactions of fuel with active lattice oxygen (O2−) of an oxygen carrier. In this research, Mg promoted iron based oxygen carrier was used in the process. The response surface method (RSM) based on Box–Behnken design was applied to examine the operating conditions of chemical looping steam methane reforming process. Independent variables including reaction temperature (550–750°C), Mg loading (0–10%) and oxygen carrier preparation method (co-impregnation and sequential impregnation methods) were selected for investigation and optimization of methane conversion, hydrogen production yield and CO/CO2 molar ratio using RSM. The characterization of samples was accomplished by means of X-ray diffraction (XRD), N2 adsorption–desorption (BET test) and transmission electron microscope (TEM). The Design expert software suggested several optimized solutions; among them, the best choice was 15Fe/5Mg/Al2O3 oxygen carrier synthesized with sequential impregnation method at reaction temperature of 650°C. However, 15Fe/5Mg/Al2O3 oxygen carrier is consistently stable in chemical looping reforming with high hydrogen producing capacity over redox cycles.

V-promoted Ni/Al2O3 catalyst for synthetic natural gas (SNG) production: Catalyst preparation methodologies

The effect of preparation method on the catalytic performance of V-promoted Ni/Al2O3 catalysts for synthetic natural gas (SNG) production via CO methanation has been investigated. The Ni-V/Al2O3 catalysts were prepared by co-impregnation (CI) method, deposition precipitation (DP) method as well as two sequential impregnation (SI) methods with different impregnation sequence. Among the prepared catalysts, the one prepared by CI method exhibited the best catalytic performance due to its largest H2 uptake and highest metallic Ni dispersion. In a 91h-lifetime test, this catalyst showed high stability at high temperature and weight hourly space velocity. This work demonstrates that the catalytic performance of the V-promoted Ni/Al2O3 catalysts can be improved by carefully controlling the preparation method/conditions.

Effect of impregnation sequence of Ce promoter on the microstructure and performance of Ce-promoted Rh-Fe/SiO2 for the ethanol synthesis

Ce-promoted Rh-Fe/SiO2 catalysts were prepared using different impregnation methods and evaluated in syngas conversion to ethanol. The catalyst prepared by co-impregnation method (Rh-Fe-Ce/SiO2) showed higher ethanol selectivity than those prepared by sequential impregnation methods (Ce/Rh-Fe/SiO2 and Rh-Fe/Ce/SiO2). Characterization results indicated that when Ce was co-impregnated with Rh and Fe, it had higher dispersion and inhibited the reduction of Rh oxides. Additionally, the reduction of CeO2 was promoted. The Rh-Fe-Ce/SiO2 catalyst exhibited the highest spatial association between Rh and Ce, which was responsible for the highest ethanol selectivity.

Platinum-Tin Nano-Catalysts Supported on Alumina for Direct Dehydrogenation of n-Butane.

Al2O3 supports were prepared by a precipitation method using various basic solutions (NaOH, KOH, NH4OH, and Na2CO3) as precipitation agents, and Pt/Sn/Al2O3 nano-catalysts were then prepared by a sequential impregnation method. The prepared catalysts were applied to the direct dehydrogenation of n-butane to n-butenes and 1,3-butadiene. The effect of precipitation agents on the physicochemical properties and catalytic activities of Pt/Sn/Al2O3 nano-catalysts in the direct dehydrogenation of n-butane was investigated. Catalytic performance of Pt/Sn/Al2O3 nano-catalysts decreased in order of Pt/Sn/Al2O3 (NaOH) > Pt/Sn/Al2O3 (KOH) > Pt/Sn/Al2O3 (NH4OH) > Pt/Sn/Al2O3 (Na2CO3). Among the catalysts tested, Pt/Sn/Al2O3 (NaOH) nano-catalyst showed the best catalytic performance in terms of yield for total dehydrogenation products (TDP, n-butenes and 1,3-butadiene). Hydrogen chemisorption experiments revealed that platinum surface area of the catalyst was closely related to the catalytic performance. Yield for TDP increased with increasing platinum surface area of the catalyst.

Direct Dehydrogenation of n-Butane Over Pt/Sn/Zn/γ-Al2O3 Nano-Catalyst: Effect of Zn Content.

A series of Pt/Sn/XZn/γ-Al2O3 nano-catalysts with different Zn content (X = 0, 0.25, 0.5, 0.75, and 1.0 wt%) were prepared by a sequential impregnation method. They were applied to the direct dehydrogenation of n-butane to n-butene and 1,3-butadiene. The effect of zinc content of Pt/Sn/XZn/γ-Al2O3 nano-catalysts on their physicochemical properties and catalytic activities in the direct dehydrogenation of n-butane was investigated. The catalytic performance of Pt/Sn/XZn/γ-Al2O3 nano-catalysts strongly depended on zinc content. Among the catalysts tested, Pt/Sn/0.5Zn/γ-Al2O3 nano-catalyst showed the best catalytic performance in terms of yield for total dehydrogenation products (TDP, n-butene and 1,3-butadiene). TPR (temperature-programmed reduction) and H2-chemisorption experiments were carried out to measure metal-support interaction and Pt surface area of the catalysts. Experimental results revealed that metal-support interaction and Pt surface area of the catalysts were closely related to the catalytic performance. Yield for TDP increased with increasing metal-support interaction and Pt surface area of the catalysts.

High Efficiency Conversion of Glycerol to 1,3-Propanediol Using a Novel Platinum–Tungsten Catalyst Supported on SBA-15

The hydrogenolysis of glycerol to 1,3-propanediol was conducted over a series of Pt-WO3/SBA-15 catalysts with Pt content ranging from 0.5 to 3 wt % and W content of 10 wt % in vapor phase under atmospheric pressure for the first time. The catalysts prepared via sequential impregnation method were systematically characterized using XRD, NH3-TPD, Py-IR, CO chemisorption, TPR, TEM, and surface area measurements. The catalysts exhibited unprecedented activity for selective formation of 1,3-propanediol via hydrogenolysis of glycerol. The effect of various reaction parameters such as catalyst loading, reaction temperature, hydrogen flow rate, glycerol concentration and reaction time were studied. The optimized reaction conditions showed that a high glycerol conversion (86%) and 1,3-propanediol selectivity (42%) was obtained over 2Pt-10WO3/SBA-15 catalyst illustrating the potential of SBA-15 supported platinum–tungsten catalyst to be highly active and efficient. The Bronsted acid sites of the catalyst formed due...