Supported bimetallic core-shell structure catalyst and its preparation method

Abstract

The purpose of the invention is to provide a supported bimetallic core-shell structure catalyst and its preparation method. Supporter, metal salt and reducing agent solution are mixed to synthesize the catalyst M@PdM/ZT by using a one-step synthesis method, wherein the active metal particle M@PdM as core-shell structure, M Is the core representing one of the Ag, Pt, Au and Ir. ZT is the supporter, representing one of hydrotalcite (Mg.sub.2Al-LDH), alumina (Al.sub.2O.sub.3) and silica (SiO.sub.2). By changing the temperature and the reaction time to control the kinetic behavior of the reduction of two kinds of metal ions to realize the construction of core-shell structure. Active metal particle composition and shell thickness are regulated by controlling metal ion concentration. The bimetallic core-shell catalyst prepared by this method showed excellent selectivity and stability in acetylene selective hydrogenation and anthraquinone hydrogenation.

Claims

1. A preparation method of supported bimetallic core-shell catalyst comprising: adding M salt and Pd salt to a reducing solution to obtain a mixed salt solution after ultrasonic irradiation for 4-5 min; wherein a total concentration of M and Pd ions is 0.01-20 mmol/L, a molar ratio of M:Pd ions is 0.1 to 10; M is one of Ag, Pt, Au and Ir; M salt is one of AgNO.sub.3, HPtCl.sub.6, Pt(C.sub.5H.sub.7O.sub.2).sub.2, H.sub.2IrCl.sub.6.6H.sub.2O, Ir(C.sub.5H.sub.7O.sub.2).sub.3 and HAuCl.sub.4.4H.sub.2O; Pd salt is one of the PdCl.sub.2, Pd(NO.sub.3).sub.2, Pd(C.sub.5H.sub.7O.sub.2).sub.2, Pd(CH.sub.3COO).sub.2; the reducing solution is a mixture of reducing agent and deionized water, wherein, a mass ratio of the deionized water is 0-20%; the reducing agent is one of ethylene glycol, isopropanol, N, n-dimethyl acetamide, N, n-dimethyl formamide and glyceraldehyde; stirring and heating the mixed salt solution for 10-30 min under 40-50 C., adding a supporter and continuing to stir for 10-20 min; raising temperature to 100-160 C. and keeping the temperature for 0.5-24 h to obtain a black precipitate suspension; dropping to room temperature to obtain gray or black powders after centrifuging, washing and drying; wherein the gray or black powders are catalyst M@PdM/ZT containing metal active ingredient particles dispersed on the supporter; the metal active ingredient particles are of a core-shell structure with M being the core and PdM alloy being the shell; the supporter is one of alumina (Al.sub.2O.sub.3), silica (SiO.sub.2) and hydrotalcite (Mg.sub.2Al-LDH).

2. A supported bimetallic core-shell catalyst M@PdM/ZT comprising metal active ingredient particles dispersed on a supporter, wherein the active metal ingredient particles contain M and PdM alloy and are of a core-shell structure; M is the core with a diameter of 5-15 nm, and selected from the group consisting of Ag, Pt, Au and Ir; PdM alloy is the shell with a thickness of 1-10 nm; ZT is the supporter, and selected from the group consisting of hydrotalcite (Mg.sub.2Al-LDH), alumina (Al.sub.2O.sub.3) and silica (SiO.sub.2).

Description

APPENDED DRAWINGS

(1) FIG. 1 is the electron microscope image of catalyst Ag@PdAg/Mg.sub.2Al-LDH prepared by embodiment 1.

(2) FIG. 2 is the EDX linear sweep results of metal Pd and Ag in metal particles of catalyst Ag@PdAg/Mg.sub.2Al-LDH prepared by embodiment 1.

(3) FIG. 3 is the X-ray photoelectron spectroscopy of Pd in catalyst Ag@PdAg/Mg.sub.2Al-LDH prepared by embodiment 1.

(4) FIG. 4 is the changing curve of ethylene selectivity with temperature in selective hydrogenation of acetylene when using the catalyst Ag@PdAg/Mg.sub.2Al-LDH prepared by embodiment 1.

(5) FIG. 5 is the changing curve of acetylene conversion and ethylene selectivity with time in selective hydrogenation of acetylene when using the catalyst Ag@PdAg/Mg.sub.2Al-LDH prepared by embodiment 1.

(6) FIG. 6 is the electron microscope image of catalyst Ag@PdAg/Mg.sub.2Al-LDH prepared by embodiment 1 after 48 h selective hydrogenation of acetylene.

(7) FIG. 7 is the scanning transmission electron microscope (STEM) photo of metal particles of catalyst Au@PdAu/SiO.sub.2 prepared by embodiment 2.

(8) FIG. 8 is the changing curves of hydrogenation efficiency of the catalyst prepared by embodiment 1 and embodiment 2 in the hydrogenation of anthraquinone.

(9) FIG. 9 is the changing curves of effective anthraquinone selectivity with time of the catalyst prepared by embodiment 1 and the embodiment 2 in the hydrogenation of anthraquinone.

PREFERRED EMBODIMENTS

(10) The present invention is further described in detail in combination with the appended drawings.

Embodiment 1

(11) Add 0.008 mmol Pd(C.sub.5H.sub.7O.sub.2).sub.2, 0.08 mmol AgNO.sub.3 into 100 ml N,N-Dimethylformamide to obtain mixed salt solution after 5 min ultrasonic irradiation. Pure the mixed solution in a flask and put it on an oil bath for stirring and heating for 10 min under 50 C., add 1 g Mg.sub.2Al-LDH and continue to stir for 10 min, heat up the temperature to 130 C. and keep it for 2 h to obtain black precipitate suspension, drop to room temperature to obtain black powder after centrifuging, washing and drying. It is proved as catalyst Ag@PdAg/Mg.sub.2Al-LDH by characterization; its metal active ingredient particles are core-shell structure, wherein PdAg alloy is the shell.

Embodiment 2

(12) Add 0.01 mmol Pd(CH.sub.3COO).sub.2, 0.04 mmoln HAuCl.sub.4.4H.sub.2O into 100 ml Eethylene glycol aqueous solution (the mass ratio of deionized water is 20%) to obtain mixed salt solution after 5 min ultrasonic irradiation with stirring. Pure the mixed solution in a flask and put it on an oil bath for stirring and heating for 0.5 h under 50 C., add 0.5 g amorphous silica powder and continue to stir for 10 min, heat up the temperature to 110 C. and keep it for 12 h to obtain black precipitate suspension, drop to room temperature to obtain black powder after centrifuging, washing and drying. It is proved as catalyst Au@PdAu/SiO.sub.2 by characterization; its metal active ingredient particles are core-shell structure, wherein PdAu alloy is the shell.

Embodiment 3

(13) Add 0.002 mmol Pd(NO.sub.3).sub.2, 0.06 mmolAgNO.sub.3 into 100 ml N,N-dimethylformamide aqueous solution (the mass ratio of deionized water is 10%) to obtain mixed salt solution after 5 min ultrasonic irradiation with stirring. Pure the mixed solution in a flask and put it on an oil bath for stirring and heating for 1 h under 40 C., add 1 g Al.sub.2O.sub.3 powder and continue to stir for 10 min, heat up the temperature to 130 C. and keep it for 2 h to obtain black precipitate suspension, drop to room temperature to obtain gray powder after centrifuging, washing and drying. It is proved as catalyst Ag@PdAg/Al.sub.2O.sub.3 by characterization; its metal active ingredient particles are core-shell structure, wherein PdAg alloy is the shell.

Embodiment 4

(14) Add 0.005 mmol Ir(C.sub.5H.sub.7O.sub.2).sub.3, 0.001 mmolPdCl.sub.2 into 100 ml isopropanol aqueous solution (the mass ratio of deionized water is 10%) to obtain mixed salt solution after 5 min ultrasonic irradiation with stirring. Pure the mixed solution in a flask and put it on an oil bath for stirring and heating for 0.5 h under 40 C., add 2 g Mg.sub.2Al-LDH powder and continue to stir for 10 min, heat up the temperature to 100 C. and keep it for 1 h to obtain black precipitate suspension, drop to room temperature to obtain gray powder after centrifuging, washing and drying. It is proved as catalyst Ir@PdIr/Mg.sub.2Al-LDH by characterization; its metal active ingredient particles are core-shell structure, wherein PdIr alloy is the shell.

Embodiment 5

(15) Add 0.01 mmol Pd(CH.sub.3COO).sub.2, 0.004 mmolHPtCl.sub.6 into 100 ml N,N-dimethylacetamide solution to obtain mixed salt solution after 5 min ultrasonic irradiation with stirring. Pure the mixed solution in a flask and put it on an oil bath for stirring and heating for 0.5 h under 45 C., add 2 g Al.sub.2O.sub.3 powder and continue to stir for 10 min, heat up the temperature to 160 C. and keep it for 12 h to obtain black precipitate suspension, drop to room temperature to obtain black powder after centrifuging, washing and drying. It is proved as Pt@PdPt/Al.sub.2O.sub.3 catalyst by characterization; its metal active ingredient particles are core-shell structure, wherein PdPt alloy is the shell.

Application Example 1

(16) Evaluate the performance of acetylene selective hydrogenation of the catalyst in embodiment 1-5 and the comparison sample.

(17) The evaluation device is WFS-3015 microreactor of Tianjin xianquan instrument co. LTD. The operation steps are as follows:

(18) 0.1 g catalyst samples are weighed, mixed with 1.9 g quartz sand (40-80 mesh) and placed in quartz reaction tubes. Before the reaction, raise the temperature of reaction bed to 150 C. and process the catalyst pretreatment with nitrogen for 1 hour. The nitrogen flow rate is 50 ml/min. After the pretreatment and the reaction bed temperature drops to room temperature, feed nitrogen, ethylene acetylene mixture and hydrogen with the flow rate of 111, 55.5 and 1.0 ml/min respectively. The percentage of acetylene in ethylene-acetylene mixture is 0.947%, and the ratio of hydrogen acetylene is about 2. Control the reaction temperature is 100 C., the reaction airspeed is 10050 h.sup.1, and the relative pressure of the reaction system is 0.4 MPa. The concentrations of reactants and products are analyzed by online gas chromatography, capillary column is 0.53*50 mm and the detector adopts hydrogen flame detector. Normalization method is adopted for data processing. The results of acetylene conversion and ethylene selectivity of catalyst under 100 C. are shown in table 1:

(19) TABLE-US-00001 TABLE 1 Catalyst Embodiment Embodiment Embodiment Embodiment Embodiment sample 1 2 3 4 5 comparison Acetylene 100 94 87 100 100 86 conversion (%) Ethylene 94 91 100 74 91 72 selectivity (%)

(20) Wherein, the comparison is catalyst PdPtAg/Mg.sub.2Al-LDH which is disclosed in CN103977794B, this catalyst is specially designed for selective hydrogenation of acetylene.

Application Example 2

(21) Evaluate the performance anthraquinone hydrogenation of the catalyst in embodiment 1-5 and the comparison sample.

(22) The evaluation device is PTFE internal tank reactor with magnetic stirring and heating device, 25 g catalyst and 60 ml anthraquinone working solution (100 g/L anthraquinone working solution is composed of 100 g 2-ethyl anthraquinone, 1,3, 5-tritoluene and 400 mL trioctyl phosphate) are added to the reactor and sealed, injecting hydrogen into the reactor through a cylinder to replace the air, repeat 5 times. Heat up the reactor to 50 C., fill with hydrogen, make the pressure reach 0.3 MPa and adjust the stirring speed to 1200 rpm/min, then start to timing. After the 1.5 h reaction, the reaction samples are collected from the reaction gas outlet valve for activity and selectivity evaluation and the yield of H.sub.2O.sub.2 is calculated. The yield of H.sub.2O.sub.2 and spatio-temporal yield of catalyst are shown in table 2.

(23) TABLE-US-00002 TABLE 2 Catalyst Embodiment Embodiment Embodiment Embodiment Embodiment sample 1 2 3 4 5 comparison yield of 14.30 13.58 13.09 14.10 12.69 11.00 H.sub.2O.sub.2(g/mL) Spatio- 2884 2715 2618 2618 2538 2200 temporal yield (gH.sub.2O.sub.2/ (gPd .Math. h))

(24) Wherein, the comparison is catalyst Pd/Al.sub.2O.sub.3 which is disclosed in CN103172097A, this catalyst is specially designed for anthraquinone hydrogenation.