Alloy Catalyst

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Hexing Li - One of the best experts on this subject based on the ideXlab platform.

  • highly active co b amorphous Alloy Catalyst with uniform nanoparticles prepared in oil in water microemulsion
    Journal of Catalysis, 2008
    Co-Authors: Hui Li, Ming-hua Qiao, Hexing Li
    Abstract:

    Abstract Uniform Co–B nanoparticles were synthesized for the first time by chemical reduction of cobalt ion with borohydride in an oil-in-water microemulsion system comprising cyclohexane, polyethylene glycol, and water. The particle size was controlled by modulating the cyclohexane content. With the characterization of X-ray diffraction, selective area electronic diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, the resulting Co–B nanoparticles were identified to be amorphous Alloys ranging in size from 6 to 20 nm. During liquid-phase cinnamaldehyde hydrogenation, the as-synthesized Co–B Catalyst was extremely active and more selective than the regular Co–B prepared in aqueous solution. Furthermore, this Catalyst also was found to be more durable during the hydrogenation process.

  • ultrasound assisted preparation of a highly active and selective co b amorphous Alloy Catalyst in uniform spherical nanoparticles
    Journal of Catalysis, 2007
    Co-Authors: Hexing Li, Hui Li, Jing Zhang, Ming-hua Qiao
    Abstract:

    Abstract Uniform spherical Co-B amorphous Alloy nanoparticles were prepared by ultrasound-assisted reduction of Co(NH3)2+6 with BH−4 in aqueous solution, and the particle size was adjusted by changing either the ultrasound power or the ultrasonication time. During liquid-phase cinnamaldehyde (CMA) hydrogenation, the as-prepared Co-B Catalyst exhibited much higher activity and better selectivity to cinnamyl alcohol (CMO) than the regular Co-B obtained by direct reduction of Co2+ with BH−4. The higher activity can be attributed to both the higher dispersion of Co active sites ( S Co ) and the higher intrinsic activity ( R S ). The higher selectivity can be attributed to both the uniform Co-B amorphous Alloy particles and the strong electronic interaction between Co and B, which enhances the competitive adsorption of C O group against C C group in the CMA molecule. Meanwhile, the stronger adsorption for hydrogen on Co active sites was more favorable for C O hydrogenation in comparison with the C C hydrogenation.

  • liquid phase acetonitrile hydrogenation to ethylamine over a highly active and selective ni co b amorphous Alloy Catalyst
    Applied Catalysis A-general, 2004
    Co-Authors: Hexing Li, Yuedong Wu, Jing Zhang, Ming-hua Qiao
    Abstract:

    Abstract The ultrafine Ni–Co–B amorphous Alloys with Co/(Co + Ni) molar ratio ( χ Co ) varying from 0 to 1 was prepared by chemical reduction of mixed Ni 2+ and Co 2+ ions with BH 4 − in aqueous solution. During liquid phase acetonitrile hydrogenation to ethylamine, the specific activity ( R m ) and the intrinsic activity (TON) of the Ni–Co–B Catalyst first increased and then decreased with the increase of χ Co from 0 to 1. The maximum activity was obtained at χ Co = 0.5; the value of the activity was nearly twice as that of the Ni–B or the Co–B Catalyst. Treatment of the Ni–Co–B Catalyst at 873 K resulted in an abrupt decrease in the activity due both to a decrease in active surface area and, especially, to the crystallization and the decomposition of the Ni–Co–B amorphous Alloy. The selectivity to ethylamine increased rapidly with χ Co and then remained constant at χ Co ≥ 0.5. The maximum yield of ethylamine could reach 93%, showing a good potential for industrial applications. According to kinetic studies and results of various characterization methods, such as ICP, XRD, EXAFS, XPS, SAED, TEM, DSC, TPD, and hydrogen chemisorption, the correlation of the catalytic performance to both the structural and the electronic characteristics was discussed briefly. The activation of the C N and/or C N bonds, the promotion on the hydrogen adsorption, and the inhibition on the ethylamine adsorption were the decisive factors responsible for the excellent activity and selectivity of the Ni–Co–B Catalyst.

  • a ce promoted ni b amorphous Alloy Catalyst ni ce b for liquid phase furfural hydrogenation to furfural alcohol
    Materials Letters, 2004
    Co-Authors: Hexing Li, Siyong Zhang
    Abstract:

    Abstract A Ce-doped Ni–B amorphous Catalyst (Ni–Ce–B) was prepared by chemical reduction of mixed NiCl2 and CeSO4 with KBH4 in aqueous solution. During liquid-phase hydrogenation of furfural (FFR), all the as-prepared Ni–Ce–B amorphous Catalyst exhibited excellent selectivity to furfural alcohol (FFA) owing to the unique amorphous structure and the electronic interaction between the metallic Ni and the Alloying B. With the increase of the Ce dopant, the activity first increased and then decreased. The optimum Ce/(Ce+Ni) molar ratio (XCe) was determined as 1.28%. The X-ray photoelectron spectroscopy (XPS) spectra revealed that most of the Ce species in the Ni–Ce–B sample were present in the form of Ce2O3. On one hand, the Ce2O3 might serve as a support for the Ni–B amorphous Alloy particles, resulting in the higher surface areas (SBET). On the other hand, the Ce2O3 might serve as a Lewis acid which could strongly adsorb and further polarize the CO group in the FFR molecule. These two factors could successfully account for the promoting effect of the Ce dopant on the hydrogenation activity of the Ni–B amorphous Alloy. Very high content of the Ce dopant (XCe>1.28%) resulted in the decrease of the hydrogenation activity because too many Ni active sites were covered by Ce2O3 species. Treatment of the Ni–Ce–B Catalyst at high temperature also caused a decrease in activity due to the transformation from the amorphous structure to the crystalline structure and the loss of the surface area.

  • liquid phase hydrogenation of acetonitrile to ethylamine over the co_b amorphous Alloy Catalyst
    Journal of Catalysis, 2003
    Co-Authors: Hexing Li, Minghui Wang, Yuedong Wu, Yeping Xu
    Abstract:

    Abstract The CoB amorphous Alloy Catalyst was prepared by chemical reduction of Co 2+ ions with BH 4 − in aqueous solution. Its activity and selectivity were measured during the liquid phase hydrogenation of acetonitrile and the effects of various factors, such as the reaction time, acetonitrile concentration, hydrogen pressure, reaction temperature, and solvent, were investigated. The following results were obtained: (1) The maximum ethylamine yield of 69% was obtained at the total conversion of acetonitrile. (2) The acetonitrile hydrogenation was zero-order with respect to acetonitrile and first-order with respect to hydrogen. Meanwhile, the selectivity to ethylamine increased slightly with the increase of either hydrogen pressure or acetonitrile concentration. (3) Increased reaction temperature resulted in a great enhancement in the activity (the apparent activation energy was determined as 46 kJ/mol) but a slight decrease in the selectivity to ethylamine. (4) Addition of a little H 2 O may result in an increase in the activity. All these effects are discussed based on the reaction mechanism. In comparison with other Co-based Catalysts, such as Raney Co, pure Co powder Catalyst, and the crystallized CoB Catalyst, the amorphous CoB Catalyst exhibited much higher activity and better selectivity to ethylamine. Although Ni-based Catalysts had higher activity, their poorer selectivity to ethylamine suggested that they were not suitable for the title reaction under the present conditions. Based on the reaction mechanism and various characterizations, including SAED, XRD, SEM, TEM, EXAFS, XPS, hydrogen chemisorption, and DSC, the promoting effects on the activity and selectivity of the CoB amorphous Catalyst are discussed briefly by considering both the structural characteristics and the electronic interaction between the Co and the Alloying B.

Keiichi Tomishige - One of the best experts on this subject based on the ideXlab platform.

  • total hydrogenation of furfural and 5 hydroxymethylfurfural over supported pd ir Alloy Catalyst
    ACS Catalysis, 2014
    Co-Authors: Yoshinao Nakagawa, Kana Takada, Masazumi Tamura, Keiichi Tomishige
    Abstract:

    Hydrogenation of aqueous furfural was conducted with SiO2-suported palladium-based bimetallic Catalysts. The combination of palladium and iridium gave the best performance for the total hydrogenation to tetrahydrofurfuryl alcohol. Higher H2 pressure and lower reaction temperature were advantageous to suppress side reactions. The synergy between Pd and Ir in the hydrogenation catalysis is most remarkable for substituted furans as substrates. Furfural was first converted into furfuryl alcohol, which was further converted to tetrahydrofurfuryl alcohol. A small amount of tetrahydrofurfural was formed in the first step (∼20% selectivity), and the subsequent hydrogenation of tetrahydrofurfural was much slower. The combined yield of tetrahydrofurfuryl alcohol and tetrahydrofurfural reached 98%. The yield of tetrahydrofurfuryl alcohol reached 94% with larger amount of Catalyst. Total hydrogenation of 5-hydroxymethylfurfural was also possible using Pd–Ir/SiO2 Catalyst. The performance of Pd–Ir/SiO2 Catalyst was sl...

  • performance and characterization of rhenium modified rh ir Alloy Catalyst for one pot conversion of furfural into 1 5 pentanediol
    Catalysis Science & Technology, 2014
    Co-Authors: Yasushi Amada, Yoshinao Nakagawa, Masazumi Tamura, Keiichi Tomishige
    Abstract:

    One-pot selective conversion of highly concentrated furfural to 1,5-pentanediol (1,5-PeD) was carried out over Rh-added Ir–ReOx/SiO2 Catalysts through two-step reaction temperatures. Over the optimized Catalyst, Rh(0.66 wt%)–Ir–ReOx/SiO2, the maximum yield of 1,5-PeD was 71.1% from highly concentrated furfural (50 wt%) and 78.2% from diluted furfural (10 wt%). These values were higher than those obtained with Ir–ReOx/SiO2 or Pd–Ir–ReOx/SiO2 Catalysts. Rh–Ir–ReOx/SiO2 showed much higher activity in the hydrogenation of furfural to tetrahydrofurfuryl alcohol intermediate in the low temperature step than Ir–ReOx/SiO2, although the hydrogenation activity was lower than that of Pd–Ir–ReOx/SiO2. A long reaction time in the low temperature step is necessary to obtain a good 1,5-PeD yield over Rh–Ir–ReOx/SiO2 in two-step reaction of furfural. The hydrogenolysis activity of Rh–Ir–ReOx/SiO2 for tetrahydrofurfuryl alcohol to 1,5-PeD in the high temperature step was higher than that of Pd–Ir–ReOx/SiO2 and was comparable to that of Ir–ReOx/SiO2. The characterization results of TPR, XRD, XANES, EXAFS, STEM-EDX and FT-IR of adsorbed CO indicated that Rh–Ir–ReOx/SiO2 Catalysts showed the structure of Ir–Rh Alloy particles partially covered with ReOx species. The hydrogenation activity of Rh–Ir–ReOx/SiO2 for the furan ring was higher than those of the mixture of Rh–Ir/SiO2 and Ir–ReOx/SiO2 or the mixture of Rh–ReOx/SiO2 and Ir–ReOx/SiO2. Both Ir–Rh Alloy formation and ReOx modification of Alloy particles are essential for the high hydrogenation activity.

  • performance structure and mechanism of pd ag Alloy Catalyst for selective oxidation of glycerol to dihydroxyacetone
    Journal of Catalysis, 2013
    Co-Authors: Shota Hirasawa, Yoshinao Nakagawa, Hideo Watanabe, Tokushi Kizuka, Keiichi Tomishige
    Abstract:

    The mechanism of the oxidation of glycerol to dihydroxyacetone over Pd–Ag Catalysts was discussed. Characterization results suggest that the metal composition of the surface of the crystalline Pd–Ag Alloy particles is almost the same as the bulk composition. The synergetic effects of Pd and Ag appear on the oxidation of the secondary OH group of vic-diols. The reaction order with respect to glycerol concentration over Pd–Ag/C was zero, suggesting the strong interaction between glycerol and the Catalyst surface. The reaction order with respect to O2 pressure was 0.4, suggesting that the rate-determining step is the reaction involving oxygen species. These reaction trends and characterization results support the mechanism where the terminal OH group of glycerol is adsorbed on the Ag site and the neighboring secondary OH group (CH–OH) is attacked by the oxygen species dissociatively adsorbed on the Pd site.

  • total hydrogenation of furan derivatives over silica supported ni pd Alloy Catalyst
    Catalysis Communications, 2010
    Co-Authors: Yoshinao Nakagawa, Keiichi Tomishige
    Abstract:

    Abstract The Ni–Pd bimetallic Catalysts supported on silica were prepared by co-impregnation method. The Catalyst with Ni/Pd = 7 showed the best catalytic performance for the hydrogenation of 5-hydroxymethyl-2-furaldehyde (HMF). The Catalyst was more active than commercial Raney Ni and more selective than Pd/C. The yield of 2,5-bis(hydroxymethyl)tetrahydrofuran reached 96%. Hydrogenation of other furanic compounds, cyclohexanone, phenol, and alkenols also proceeded. Characterizations by TEM and XRD revealed that Ni–Pd Alloy particles were formed on Ni–Pd/SiO 2 (Ni/Pd = 7).

Ming-hua Qiao - One of the best experts on this subject based on the ideXlab platform.

  • highly active co b amorphous Alloy Catalyst with uniform nanoparticles prepared in oil in water microemulsion
    Journal of Catalysis, 2008
    Co-Authors: Hui Li, Ming-hua Qiao, Hexing Li
    Abstract:

    Abstract Uniform Co–B nanoparticles were synthesized for the first time by chemical reduction of cobalt ion with borohydride in an oil-in-water microemulsion system comprising cyclohexane, polyethylene glycol, and water. The particle size was controlled by modulating the cyclohexane content. With the characterization of X-ray diffraction, selective area electronic diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, the resulting Co–B nanoparticles were identified to be amorphous Alloys ranging in size from 6 to 20 nm. During liquid-phase cinnamaldehyde hydrogenation, the as-synthesized Co–B Catalyst was extremely active and more selective than the regular Co–B prepared in aqueous solution. Furthermore, this Catalyst also was found to be more durable during the hydrogenation process.

  • ultrasound assisted preparation of a highly active and selective co b amorphous Alloy Catalyst in uniform spherical nanoparticles
    Journal of Catalysis, 2007
    Co-Authors: Hexing Li, Hui Li, Jing Zhang, Ming-hua Qiao
    Abstract:

    Abstract Uniform spherical Co-B amorphous Alloy nanoparticles were prepared by ultrasound-assisted reduction of Co(NH3)2+6 with BH−4 in aqueous solution, and the particle size was adjusted by changing either the ultrasound power or the ultrasonication time. During liquid-phase cinnamaldehyde (CMA) hydrogenation, the as-prepared Co-B Catalyst exhibited much higher activity and better selectivity to cinnamyl alcohol (CMO) than the regular Co-B obtained by direct reduction of Co2+ with BH−4. The higher activity can be attributed to both the higher dispersion of Co active sites ( S Co ) and the higher intrinsic activity ( R S ). The higher selectivity can be attributed to both the uniform Co-B amorphous Alloy particles and the strong electronic interaction between Co and B, which enhances the competitive adsorption of C O group against C C group in the CMA molecule. Meanwhile, the stronger adsorption for hydrogen on Co active sites was more favorable for C O hydrogenation in comparison with the C C hydrogenation.

  • liquid phase acetonitrile hydrogenation to ethylamine over a highly active and selective ni co b amorphous Alloy Catalyst
    Applied Catalysis A-general, 2004
    Co-Authors: Hexing Li, Yuedong Wu, Jing Zhang, Ming-hua Qiao
    Abstract:

    Abstract The ultrafine Ni–Co–B amorphous Alloys with Co/(Co + Ni) molar ratio ( χ Co ) varying from 0 to 1 was prepared by chemical reduction of mixed Ni 2+ and Co 2+ ions with BH 4 − in aqueous solution. During liquid phase acetonitrile hydrogenation to ethylamine, the specific activity ( R m ) and the intrinsic activity (TON) of the Ni–Co–B Catalyst first increased and then decreased with the increase of χ Co from 0 to 1. The maximum activity was obtained at χ Co = 0.5; the value of the activity was nearly twice as that of the Ni–B or the Co–B Catalyst. Treatment of the Ni–Co–B Catalyst at 873 K resulted in an abrupt decrease in the activity due both to a decrease in active surface area and, especially, to the crystallization and the decomposition of the Ni–Co–B amorphous Alloy. The selectivity to ethylamine increased rapidly with χ Co and then remained constant at χ Co ≥ 0.5. The maximum yield of ethylamine could reach 93%, showing a good potential for industrial applications. According to kinetic studies and results of various characterization methods, such as ICP, XRD, EXAFS, XPS, SAED, TEM, DSC, TPD, and hydrogen chemisorption, the correlation of the catalytic performance to both the structural and the electronic characteristics was discussed briefly. The activation of the C N and/or C N bonds, the promotion on the hydrogen adsorption, and the inhibition on the ethylamine adsorption were the decisive factors responsible for the excellent activity and selectivity of the Ni–Co–B Catalyst.

  • Adsorption of sulfur on NimB2 clusters: a theoretical investigation on the mechanism of strong sulfur resistance of Ni–B Alloy Catalyst
    Journal of Molecular Catalysis A-chemical, 2002
    Co-Authors: Wenning Wang, Ming-hua Qiao
    Abstract:

    Ni–B Alloy is a novel industrial Catalyst famous for its high activity, low-cost, and strong sulfur resistance in hydrogenation reactions. To get an insight into the special properties of Ni–B Alloy Catalyst, the adsorption of sulfur on Ni mB2 (m = 1–4) clusters has been studied with the density functional theory (DFT) method. The theoretical results show that the adsorbed sulfur tends to be connected with boron, not with nickel in the Ni–B Alloy Catalyst. This adsorption site prevents active nickel from being poisoned by sulfur or even being oxidized in the practical catalytic processes. This provides a sound explanation for the strong sulfur resistance of Ni–B Alloy in the catalytic hydrogenation reactions. © 2002 Elsevier Science B.V. All rights reserved.

Tao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • hydrogenolysis of methyl glycolate to ethanol over a pt cu sio2 single atom Alloy Catalyst a further step from cellulose to ethanol
    Green Chemistry, 2018
    Co-Authors: Chaojun Yang, Zhili Miao, Fan Zhang, Lin Li, Aiqin Wang, Tao Zhang
    Abstract:

    Cellulosic ethanol can be produced via a chemocatalytic approach in which cellulose is first converted into methyl glycolate (MG) in methanol using a W-based Catalyst under an oxygen atmosphere, and the formed MG is then hydrogenated to ethanol over a supported copper Catalyst. Aiming at enhancing the ethanol selectivity for this two-step approach, we developed a 0.1Pt–Cu/SiO2 single-atom Alloy Catalyst in the present study, where Pt was isolated as single atoms, and formed a Pt–Cu Alloy phase. The characterizations of the Catalyst via in situ XRD, FTIR, CO-adsorbed DRIFTS, N2O chemisorption, and XPS revealed that the introduction of 0.1 wt% Pt into the Cu/SiO2 Catalyst resulted in an improvement in the Cu dispersion and an increase in the Cu+/Cu0 ratio. Moreover, Pt single atoms promoted the activation of hydrogen. As a consequence, the catalytic activity and selectivity of ethanol were enhanced; the maximum selectivity of ethanol (76.7%) was obtained at 503 K. Over 700 h on stream, the Catalyst did not show any deactivation, demonstrating a promising stability.

  • silica supported au cu Alloy nanoparticles as an efficient Catalyst for selective oxidation of alcohols
    Applied Catalysis A-general, 2012
    Co-Authors: Aiqin Wang, Wanjun Li, Tao Zhang
    Abstract:

    Abstract Silica-supported Au–Cu and Au–Ag Alloy nanoparticles were synthesized, characterized, and tested for the aerobic oxidation of alcohols. The results showed that Au–Cu Alloy Catalyst exhibited good activity and selectivity to aldehydes for a variety of structurally diverse alcohols and a strong synergistic effect was found between Au and Cu. In contrast, Au–Ag Alloy Catalysts were less active and selective for the oxidation of alcohols although they have very similar particle sizes to the Au–Cu Alloy Catalysts. Besides the chemical compositions, the pretreatment conditions were found to affect significantly the catalytic performances, and the reduction treatment is necessary for obtaining a high activity and selectivity, suggesting Au–Cu Alloy is the active phase. Moreover, the Catalyst could be reused if only the Catalyst after the reaction was subjected to reduction treatment.

Aiqin Wang - One of the best experts on this subject based on the ideXlab platform.

  • hydrogenolysis of methyl glycolate to ethanol over a pt cu sio2 single atom Alloy Catalyst a further step from cellulose to ethanol
    Green Chemistry, 2018
    Co-Authors: Chaojun Yang, Zhili Miao, Fan Zhang, Lin Li, Aiqin Wang, Tao Zhang
    Abstract:

    Cellulosic ethanol can be produced via a chemocatalytic approach in which cellulose is first converted into methyl glycolate (MG) in methanol using a W-based Catalyst under an oxygen atmosphere, and the formed MG is then hydrogenated to ethanol over a supported copper Catalyst. Aiming at enhancing the ethanol selectivity for this two-step approach, we developed a 0.1Pt–Cu/SiO2 single-atom Alloy Catalyst in the present study, where Pt was isolated as single atoms, and formed a Pt–Cu Alloy phase. The characterizations of the Catalyst via in situ XRD, FTIR, CO-adsorbed DRIFTS, N2O chemisorption, and XPS revealed that the introduction of 0.1 wt% Pt into the Cu/SiO2 Catalyst resulted in an improvement in the Cu dispersion and an increase in the Cu+/Cu0 ratio. Moreover, Pt single atoms promoted the activation of hydrogen. As a consequence, the catalytic activity and selectivity of ethanol were enhanced; the maximum selectivity of ethanol (76.7%) was obtained at 503 K. Over 700 h on stream, the Catalyst did not show any deactivation, demonstrating a promising stability.

  • silica supported au cu Alloy nanoparticles as an efficient Catalyst for selective oxidation of alcohols
    Applied Catalysis A-general, 2012
    Co-Authors: Aiqin Wang, Wanjun Li, Tao Zhang
    Abstract:

    Abstract Silica-supported Au–Cu and Au–Ag Alloy nanoparticles were synthesized, characterized, and tested for the aerobic oxidation of alcohols. The results showed that Au–Cu Alloy Catalyst exhibited good activity and selectivity to aldehydes for a variety of structurally diverse alcohols and a strong synergistic effect was found between Au and Cu. In contrast, Au–Ag Alloy Catalysts were less active and selective for the oxidation of alcohols although they have very similar particle sizes to the Au–Cu Alloy Catalysts. Besides the chemical compositions, the pretreatment conditions were found to affect significantly the catalytic performances, and the reduction treatment is necessary for obtaining a high activity and selectivity, suggesting Au–Cu Alloy is the active phase. Moreover, the Catalyst could be reused if only the Catalyst after the reaction was subjected to reduction treatment.

  • a novel efficient au ag Alloy Catalyst system preparation activity and characterization
    Journal of Catalysis, 2005
    Co-Authors: Aiqin Wang
    Abstract:

    Abstract We present a novel efficient Catalyst, Au–Ag Alloy nanoparticles supported on mesoporous aluminosilicate. The Catalysts were applied to the low-temperature CO oxidation reaction. The sample was prepared in one pot, in which the formation of nanoparticles was coupled in aqueous solution with the construction of mesoporous structure. Both XRD and TEM characterizations show that the Alloy particles are much larger than the monometallic gold particles and become even bigger with an increase in the amount of Ag. We shall demonstrate that such large particles with an average particle size of about 20–30 nm exhibit exceptionally high activity for CO oxidation at low temperatures. Moreover, the activity varies with the Au/Ag molar ratios and attains the best conversion when Au/Ag is 3:1. The presence of excess H2 deactivates the Alloy activity completely at room temperature. UV–vis and EXAFS confirm the Au–Ag Alloy formation. XPS results show that the Alloy Catalysts are in the metallic state, and they have a greater tendency to lose electrons than do the monometallic Catalysts. EPR results show there is an O 2 − species on the Catalyst surface, and the intensity of the O 2 − species becomes the strongest at Au/Ag = 3:1. The catalytic activity coincides with the magnitude of O 2 − EPR signal intensities. Based on the spectroscopic study and catalytic activity measurements, a reaction mechanism has been proposed.