Co-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.

Synthesis of NiMo Catalysts Supported on Gallium-Containing Mesoporous Y Zeolites with Different Gallium Contents and Their High Activities in the Hydrodesulfurization of 4,6-Dimethyldibenzothiophene

Mesoporous MY-xGa zeolites exhibiting both crystallized pore walls and narrowly dispersed mesopores with different Ga content were successfully synthesized. The synthesized samples were characterized by XRD, N2 adsorption desorption isotherms, SEM, TEM, XPS, FTIR, 29Si MAS NMR, 71Ga MAS NMR, and Py-FTIR methods. The results show that the synthesized samples exhibit unique open channel like mesopore systems and outstanding crystallite natures; no nonframework Ga species were observed over the MY-xGa series samples, and their acidic properties can be modulated by varying the Ga/Al ratio in the initial synthesis gel. The corresponding NiMo/HMY-xGa catalysts were prepared via the incipient wetness coimpregnation method; the morphologies of the sulfide catalysts were characterized by HRTEM, and the covalent states of the active metals were characterized by XPS. The catalytic activities of the investigated catalysts for the 4,6-DMDBT HDS reaction were assessed, and the collected products were analyzed by GC and...

Selective hydrogenation of furfural over Pt based and Pd based bimetallic catalysts supported on modified multiwalled carbon nanotubes (MWNT)

Nano-Pt and Nano-Pd particles were introduced to modified multiwalled carbon nanotubes via co-impregnation method for hydrogenation of furfural in liquid phase using ethanol as a solvent. Different transition metal (Cr, Mn, Fe, Co, Ni) was used as promoters using Pt/MWNT and Pd/MWNT catalysts and various supports were also compared to further investigate the hydrogenation process of furfural. Among the catalysts investigated, Pt–Fe/MWNT (Pt: 0.5wt%) showed highest conversion and selectivity to furfuryl alcohol (yield of 87.4%), while Pd–Ni/MWNT (Pd: 0.5wt%) catalysts exhibited the best catalytic performance (83.3% yield of tetrahydrofurfuryl alcohol) under the optimized conditions of 30bar hydrogen and 5h, at 100 and 130°C, respectively. Synergistic effect of bimetallic catalysts has been utilized to improve catalytic activity and stability. The extremely active for the selective hydrogenation of furfural over Pt–Fe/MWNT and Pd–Ni/MWNT catalyst might be attributed to active crystal planes exposed over Pt and Pd promoted by Fe and Ni. Catalysts have shown stable activity and selectivity after 5 cycles using Pt–Fe/MWNT and Pd–Ni/MWNT catalysts. Moreover, we suggest that acid sites of conventional supports might have an impact on furfural conversion.

Hydrogen Production from Cyclic Chemical Looping Steam Methane Reforming over Yttrium Promoted Ni/SBA-16 Oxygen Carrier

In this work, the modification of Ni/SBA-16 oxygen carrier (OC) with yttrium promoter is investigated. The yttrium promoted Ni-based oxygen carrier was synthesized via co-impregnation method and applied in chemical looping steam methane reforming (CL-SMR) process, which is used for the production of clean energy carrier. The reaction temperature (500–750 °C), Y loading (2.5–7.4 wt. %), steam/carbon molar ratio (1–5), Ni loading (10–30 wt. %) and life time of OCs over 16 cycles at 650 °C were studied to investigate and optimize the structure of OC and process temperature with maximizing average methane conversion and hydrogen production yield. The synthesized OCs were characterized by multiples techniques. The results of X-ray powder diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) of reacted OCs showed that the presence of Y particles on the surface of OCs reduces the coke formation. The smaller NiO species were found for the yttrium promoted OC and therefore the distribution of Ni particles was improved. The reduction-oxidation (redox) results revealed that 25Ni-2.5Y/SBA-16 OC has the highest catalytic activity of about 99.83% average CH4 conversion and 85.34% H2 production yield at reduction temperature of 650 °C with the steam to carbon molar ratio of 2.

Up-gradation of α-tetralone to jet-fuel range hydrocarbons by vapour phase hydrodeoxygenation over Pd[sbnd]Ni/SBA-16 catalysts

Mesoporous molecular sieve SBA-16 supported PdNi bimetallic catalysts were synthesized by the co-impregnation method. PdNi/SBA-16 bimetallic Im3m mesoporous catalyst showed superior catalytic performance in the production of jet-fuel range hydrocarbons. Vapour phase hydrodeoxygenation of α-tetralone was carried out under ambient pressure and the highest selectivity (88.21%) for the isomerized product trans-decalin was obtained. PdNi impregnated on different mesoporous (MCM-41, SBA-15, KIT-6) and metal oxides (γ-Al2O3, CeO2, TiO2, ZrO2, SiO2) supports and the catalytic activity was compared with PdNi/SBA-16. Synergetic interaction between the Pd(111) and Ni(111) with increased total acidity enhanced the catalytic activity of PdNi/SBA-16. Among the bimetal, Nickel was found to be the most active metal for the complete reduction of aromatic ring, while Pd favoured the deoxygenation. The major products obtained from hydrodeoxygenation of α-tetralone were cis/trans-decalin, tetralin and α-tetralol.

Isolation of Pd atoms by Cu for semi-hydrogenation of acetylene: Effects of Cu loading

Cu-alloyed Pd single-atom catalysts exhibit excellent catalytic performance for the semi-hydrogenation of acetylene; however, the limit of the Cu/Pd atomic ratio for forming the alloyed Pd single-atom catalyst is ambiguous. Herein, silica-supported Cu–Pd bimetallic catalysts with fixed Pd content and varied Cu loadings were synthesized using an incipient wetness co-impregnation method. The X-ray absorption spectroscopy results indicated that Pd formed an alloy with Cu after reduction at 250 °C and that the Pd atoms were completely isolated by Cu for Cu/Pd atomic ratios ≥ 40/1. Notably, increasing the reduction temperature from 250 to 400 °C hardly affected the catalytic performances of the Cu–Pd/SiO2 catalysts. This finding can be attributed to the similar chemical environments of Pd demonstrated by the X-ray absorption spectroscopy results.

Low-temperature catalytic oxidation of toluene over Mn–Co–O/Ce0.65Zr0.35O2 mixed oxide catalysts

Ce0.65Zr0.35O2 was prepared by co-precipitation method and a series of Mn1-yCoy/Ce0.65Zr0.35O2 catalysts with different Mn/Co molar ratio were synthesized via the co-impregnation method. These catalysts were applied for gaseous toluene oxidation, which showed that the catalytic activity was significantly improved by the addition of Mn and Co. In particular, Mn–Co(1:1)/Ce0.65Zr0.35O2 with Mn/Co molar ratio of 1:1 displayed the best result with the lowest complete conversion temperature of 242 °C under a GHSV of 12,000 h−1. The as-prepared catalysts were characterized by X-ray diffraction, H2 temperature-programmed reduction, N2 adsorption–desorption, X-ray photoelectron spectroscopy and O2 temperature-programmed desorption. These characteristics revealed that the coexistence of Mn and Co could enhance the redox property and generate more surface adsorbed oxygen, thereby improving the performance of the catalysts for toluene low-temperature oxidation. The Mn–Co(1:1)/Ce0.65Zr0.35O2 exhibited the best catalytic activity and high stability. The excellent catalytic activity of the Mn–Co(1:1)/Ce0.65Zr0.35O2 could be ascribed to a greater amount of surface adsorbed oxygen species and Mn4+ on the catalyst surface.

Aerobic oxidation of primary amines into corresponding nitriles over MnxCe1-xOs catalysts prepared by co-impregnation method

Mn-Ce mixed oxides, synthesized by co-impregnation method, have been used in the catalytic oxidation of primary amines to corresponding nitriles. The effects of Mn/Ce molar ratio on the structure and catalytic properties were investigated, and the results showed the MnxCe1-xOs mixed oxides exhibited higher catalytic activity than MnOx or CeO2. It was found that favorable selectivity and the best conversions for benzylic, heterocyclic, and aliphatic primary amines were obtained when the Mn/Ce atomic mole ratio was 2:1 (denoted as Mn0.67Ce0.33Os). These materials have been investigated using XRD, FT-IR, SEM, HRTEM, XPS, DR-UV–vis, H2-TPR, and EPR techniques. XRD results showed that the samples did not appear any diffraction of manganese oxides. SEM images showed that the nanoparticles of the mixed oxides can be uniformly distributed than MnOx or CeO2. HRTEM micrographs exhibited that Mn-Ce mixed oxides were all exposed (111) and (220) planes corresponding to CeO2, and Mn0.67Ce0.33Os catalyst had the highest mutual solubility, thus this catalyst could have the stronger interaction than other Mn-Ce mixed oxides, which was in accordance with XPS, H2-TPR, and EPR analysis. XPS studies confirmed that the highest concentration of Ce3+ was obtained at the surface of Mn0.67Ce0.33Os sample, this situation provides a basis for the formation and stabilization of oxygen vacancies, and it is beneficial for oxidation reaction, which is in consistent with DR-UV–vis results. In addition, XPS data also showed that Mn0.67Ce0.33Os sample provided the most adsorbed oxygen species, this suggested that the mobility and availability of the active oxygen species were enhanced. This conclusion also can be drawn from H2-TPR analysis. EPR studies further supported the formation of Mn0.67Ce0.33Os solid solution. Based on the above analysis, the excellent catalytic performance should be attributed to the formation of a solid solution with the incorporation of Mnx+ into the CeO2 cubic fluorite lattice, this reduces the formation energy of oxygen vacancies and enhances the mobility of active oxygen species from the bulk to the catalyst surface.

Comparison of transesterification and thermal cracking methods on fuel specifications of castor oil biodiesel

A series of NiMo/γ-Al2O3 carbides were synthesized with the temperature programmed carburization method for the tri-reforming of methane. The relationship between the catalytic behavior and the impregnation sequence was investigated by XRD, TG-DSC, XPS, SEM, and so on. It was found that Mo2C species were the active species for the tri-reforming of methane. The amounts of Mo2C species on the fresh NiMo carbides decreased in the order of co-impregnated NiMo carbide > Ni-first NiMo carbide > Mo-first NiMo carbide. In contrast, Mo2C species on the latter two carbides would continue to be formed during the tri-reforming of methane. NiMoO4 species only existed on the co-impregnated NiMo oxidic precursor, exhibiting a strong synergistic effect between Ni and Mo species. NiMoO4 species were reduced more easily than MoO3 species on the step-impregnated NiMo oxides. Ni0 species promoted the dissociation of methane, induced the reduction of molybdenum oxide and supplied active hydrogen and carbon species for the carburization process. The co-impregnation method was conducive to refine the particles.

Selective hydrogenation of acetylene in an ethylene-rich stream over silica supported Ag-Ni bimetallic catalysts

Semi-hydrogenation of acetylene in an ethylene-rich stream is an industrially important process. Recent work on the purification of ethylene mainly focuses on the modification of Pd catalysts; little attention has been paid to the development of alternative catalysts with low-cost metals. Herein, a series of Ag-Ni/SiO2 bimetallic catalysts, with varied Ni/Ag atomic ratios, were prepared by wetness co-impregnation method. Their activity for the selective hydrogenation of acetylene in an ethylene-rich stream was evaluated, which showed that the introduction of Ag decreased the formation of both ethane and methane, thus increased the ethylene selectivity. The ethylene selectivity over the AgNi0.25/SiO2 catalyst was increased by >600% when compared with the corresponding monometallic Ni0.25/SiO2 as well as the simple physical mixture of the monometallic Ag/SiO2 and Ni0.25/SiO2 catalysts. As was verified by a combination of the X-ray diffraction, high angular annular dark field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy under scanning transmission electron microscopy results, decreased Ni content induced the sintering of the bimetallic nanoparticles while with uniform dispersion. Temperature-programmed reduction results demonstrated that, compared with the corresponding monometallic catalysts, both the reduction of AgOx and NiOx were promoted in the Ag-Ni/SiO2 bimetallic catalysts. In-situ Fourier-transform infrared spectroscopy results also illustrated obvious interaction between Ag and Ni. The contact between Ag and Ni may account for the enhanced ethylene selectivity.

Phosphorus modified MoO3–Bi2SiO5/SiO2 catalyst for gas-phase epoxidation of propylene by molecular oxygen

The phosphorus (P) modified MoO3–Bi2SiO5/SiO2 catalyst was prepared by a simple co-impregnation method and investigated in the epoxidation of propylene by molecular oxygen. The catalyst was characterized by X-ray diffraction (XRD), N2 adsorption–desorption analysis, NH3-temperature-programmed desorption (NH3-TPD), transmission electron microscopy, and Raman spectroscopy. It was found that the P-modified MoO3–Bi2SiO5/SiO2 catalyst with a P/Mo molar ratio of 0.5 exhibits the best catalytic performance for epoxidation of propylene by O2, the TOFs for propylene oxide (PO) formation was four times higher than that of the unmodified one at 633 K. The modification by P could promote the dispersion of MoO3 nanoparticles and increase the number of weak and moderate acid sites with respect to the phosphorus-free MoO3–Bi2SiO5/SiO2 catalyst, which were beneficial to the formation of PO. Moreover, the introduction of P also could protect the mesoporous structure by inhibiting the formation of Bi2Mo3O12, which was beneficial to the dispersion of active species. We suppose that the phosphorus, bismuth and molybdenum species of P-modified MoO3–Bi2SiO5/SiO2 catalyst play important roles for propylene epoxidation by molecular oxygen.

Effect of impregnation sequence on the catalytic performance of NiMo carbides for the tri-reforming of methane

A series of NiMo/γ-Al2O3 carbides were synthesized with the temperature programmed carburization method for the tri-reforming of methane. The relationship between the catalytic behavior and the impregnation sequence was investigated by XRD, TG-DSC, XPS, SEM, and so on. It was found that Mo2C species were the active species for the tri-reforming of methane. The amounts of Mo2C species on the fresh NiMo carbides decreased in the order of co-impregnated NiMo carbide > Ni-first NiMo carbide > Mo-first NiMo carbide. In contrast, Mo2C species on the latter two carbides would continue to be formed during the tri-reforming of methane. NiMoO4 species only existed on the co-impregnated NiMo oxidic precursor, exhibiting a strong synergistic effect between Ni and Mo species. NiMoO4 species were reduced more easily than MoO3 species on the step-impregnated NiMo oxides. Ni0 species promoted the dissociation of methane, induced the reduction of molybdenum oxide and supplied active hydrogen and carbon species for the carburization process. The co-impregnation method was conducive to refine the particles.

Influence of different impregnation modes on the properties of CuO[sbnd]CeO2/γ-Al2O3 catalysts for NO reduction by CO

A series of ceria modified CuO/γ-Al2O3 (CuO-CeO2/γ-Al2O3) catalysts were prepared via stepwise impregnation (CuCeAl-SI) and co-impregnation (CuCeAl-CI) method and tested in the model reaction of NO reduction by CO. It was found that the influence of impregnation modes on the catalytic properties of CuCeAl samples mainly lies on the control of ceria particle sizes and modulation of the distribution of various copper species. In both impregnation modes, ceria was mainly spread on γ-Al2O3 as small particles while copper species were highly dispersed. A quantitative estimation of copper species was tentatively provided via a combined surface acid leaching experiment and H2-TPR characterization for the first time. The results showed that for CuCeAl-CI catalyst, about 55% and 25% copper species were dispersed on γ-Al2O3 and nanosized ceria, respectively, while about 20% was migrated into ceria lattice during the calcination process. In contrast, in CuCeAl-SI sample, the corresponding values changed to about 25%, 70% and 5%, respectively. The synergistic effect between copper species and ceria can promote the improvement of catalytic performance, which results in higher activity of CuCeAl-SI than that of CuCeAl-CI catalyst.

Hydroisomerization of n-octane over bimetallic Ni-Cu/SAPO-11 catalysts

Bimetallic Ni-Cu/SAPO-11 catalysts were prepared by co-impregnation method and assessed in the hydroisomerization of n-octane. Their physicochemical properties were characterized by means of powder X-ray diffraction, nitrogen adsorption-desorption, temperature-programmed desorption of ammonia, pyridine-adsorbed infrared spectroscopy, temperature-programmed reduction of hydrogen, transmission electron microscopy, energy dispersive X-ray, and X-ray photoelectron spectroscopy. The Ni-Cu alloy was formed after reduction in the H2 flow at 450°C. Copper changed the electronic interaction of nickel and diluted the nickel ensemble size in the Ni-Cu alloy. The hydrogenolysis reaction that decreases the selectivity of isomerization was effectively restrained over the bimetallic Ni-Cu/SAPO-11 catalysts. The selectivity to n-octane isomers over the bimetallic nickel (3%) and copper (1.5%) catalyst was 19% more than that over the monometallic nickel (3%) catalyst at the conversion of 70%. A possible reaction scheme was proposed to explain the catalytic properties in n-octane hydroisomerization.

Enhanced activity and stability of the monolithic Pt/SiO2–Al2O3 diesel oxidation catalyst promoted by suitable tungsten additive amount

Abstract A series of the modified Pt/SiO 2 –Al 2 O 3 diesel oxidation catalysts with different WO 3 loading were prepared through co-impregnation method. With an optimum additive loading of 2 wt% WO 3 , the catalyst significantly improved the performance and its stability. Compared to the free-tungsten sample, the catalyst increased the maximum conversion of NO by 5–10% and decreased the reaction temperature for 30% NO conversion by 7–28 °C. It was found that there exist the electron and structure interaction between platinum and tungsten species. The interactions can generate and maintain more Pt sites in metallic state for the catalytic oxidation with enhanced activity and stability.

Facile synthesis of supported copper manganese oxides catalysts for low temperature CO oxidation in confined spaces

In this work, several MxOy-supported CuO-MnO2 (MxOy=Al2O3, CeO2, TiO2 and Y2O3) composite catalysts were synthesized by the co-impregnation method using copper and manganese acetates as precursors. The catalysts were characterized by N2 adsorption-desorption at 77K, XRD, FESEM, FT-IR and XPS techniques. Low-temperature CO oxidation performances of the catalysts were evaluated using a fixed-bed reactor system. Amongst the prepared catalysts, CuO-MnO2/CeO2 exhibited excellent CO oxidation activity, good working stability after about 1h of reaction tested and superior kinetics performances. The dual synergistic effects in CuO-MnO2 and CuO-CeO2 are associated with the enhanced CO oxidation process observed over CuO-MnO2/CeO2. The catalyst shows promise for removing CO from typical confined spaces such as onboard naval submarines, space-crafts and mine refuge chambers.

Synthesis and characterization of cerium promoted Ni/SBA-16 oxygen carrier in cyclic chemical looping steam methane reforming

Abstract Chemical-looping steam methane reforming (CL-SMR) is based on oxidation–reduction cycles through a solid–gas reaction with an oxygen carrier (OC) for producing high purity hydrogen or synthesis gas. In this study, Ce promoted Ni-based OC was synthesized via co-impregnation method and applied in this process. The presence of CeO2 nanoparticles in the framework of nickel oxide doped SBA-16 oxygen carrier could significantly improve the uniformity and distribution of nickel oxide nanoparticles duo to the restrictional influence of the SBA-16 framework and the strong interaction of nickel and cerium. The reaction temperature (500–750 °C), Ce loading percentage (3.9–23.3 wt. %) and Ni loading percentage (10–30 wt. %) were studied in order to investigate and optimize the catalyst structure and process temperature with maximizing the average CH4 conversion and H2 production yield in this process. The synthesized oxygen carriers were characterized by X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The redox results revealed that 20Ni-11.6Ce/S16 oxygen carrier had the high catalytic activity of about 100% average CH4 conversion and 86.98% H2 production yield at reduction temperature of 700 °C.

Controlled pore size of ordered mesoporous Al2O3-supported Mn/Cu catalysts for CO oxidation

In this paper, by controlling the calcination temperature, ordered mesoporous Al2O3 with controllable pore diameters were rationally designed and synthesized by evaporation-induced self-assembly method. The CuMn-Al2O3 catalysts with different pores were synthesized by a co-impregnation method with ordered mesoporous Al2O3 as template. These catalysts expressed ordered mesoporous structure, possessed higher specific surface area and large pore volume, and owned more surface active sites, which were helpful for CO oxidation. When the calcination temperature of Al2O3 was 400 °C, this catalyst showed the highest catalytic activity. The reason was due to its relatively stronger redox ability and surface activity species. More Cu+ and chemisorbed oxygen concentration was very useful in achieving the highest catalytic performance.

Continuous Hydrogenolysis of Glycerol to 1,2-Propanediol Over Bi-metallic Ni–Ag Supported on γ-Al2O3 Catalysts

Continuous hydrogenolysis of glycerol was carried over bimetallic Ni–Ag supported on γ-Al2O3 catalysts. These catalysts were prepared by co-impregnation method. The catalysts surface and structural properties were derived from CO chemisorption, X-ray diffraction, temperature programmed reduction, temperature programmed desorption of NH3 and X-ray photoelectron spectroscopy. The presence of Ag led to the improvement in the dispersion, metal area and particle size of the Ni. Hydrogenolysis activity of Ni was enhanced by the synergistic effect of Ag. The catalyst with 10% Ni–5% Ag/γ-Al2O3 gave about 80% of glycerol conversion with 58% selectivity towards 1,2-propanediol. Effect of various reaction parameters on glycerol conversion and selectivity were also investigated and optimum condition were established. The time on stream analysis was carried and the catalysts exhibited stability.

Deposition of carbon species on the surface of metal: As a poison or a promoter for the long-term stability of Ni/SiO2 methanation catalyst?

The effect of carbon deposition on the long-term stability of the Ni/SiO2 catalyst during the methanation reaction was studied in this work. For a conventional Ni/SiO2 catalyst prepared by the impregnation method, it was found that the water-gas shift reaction (WGSR) as one side reaction took place on Ni(100) planes predominately and followed the carboxyl mechanism under the present condition. The inhabitation of this WGSR could produce the carboxyl and carbonyl species on surface which initiated the deactivation of this conventional impregnation derived Ni/SiO2 catalyst. Comparatively, the co-impregnation of nickel nitrate and dicyandiamide molecules on SiO2 support did not markedly change the defect sites on the metallic Ni0 particles, however, it was favorable to deposit trace pyrrolic nitrogen containing carbon on Ni(111) planes. Such carbon deposition allowed the electron transfer from pyrrolic nitrogen atoms to Ni(111) planes, leading to more active sites available for the reaction on this Ni(111). This effect facilitated the occurrence of WGSR on Ni(111) rather than Ni(100) planes and significantly reduced the deposition of carboxyl and carbonyl species on this carbon pre-deposited Ni/SiO2 catalyst. As a result, the co-impregnation method derived Ni/SiO2 catalyst has better long-term stability than the conventional Ni/SiO2 catalyst in the methanation reaction.