CN108927163B

CN108927163B - Preparation method of supported copper oxide catalyst with cerium oxide as carrier

Info

Publication number: CN108927163B
Application number: CN201810769925.0A
Authority: CN
Inventors: 程党国; 夏阳; 陈丰秋; 詹晓力
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2018-07-13
Filing date: 2018-07-13
Publication date: 2020-10-20
Anticipated expiration: 2038-07-13
Also published as: CN108927163A

Abstract

The invention relates to a preparation method of a supported copper oxide catalyst which utilizes ultrasonic assistance and takes cerium oxide as a carrier. An excess of base is added to the aqueous solution of the copper salt and cerium salt, the base being exothermic during dissolution. Copper salt forms copper hydroxide precipitate and is further converted into copper oxide small particles by utilizing an exothermic process; the cerium salt forms cerium hydroxide precipitate and forms cerium oxide with a cavity structure under an exothermic environment; then, carrying out ultrasonic treatment on the sample for a certain time to generate local hot spots with high temperature and high pressure, and promoting copper oxide to fill in the cavity of cerium oxide to form mixed oxide; and (4) centrifugally washing, freeze-drying and roasting at high temperature to obtain the final catalyst. Because of the close combination interaction of the copper oxide and the cerium oxide carrier, the copper oxide is partially unsaturated, so that defective copper oxide with good oxidation-reduction capability is formed, and the complete oxidation of carbon monoxide under hydrogen-rich conditions by the catalyst at a lower temperature and in a wider window range is realized.

Description

Preparation method of supported copper oxide catalyst with cerium oxide as carrier

Technical Field

The invention relates to the field of catalysts, in particular to a preparation method of a supported copper oxide catalyst taking cerium oxide as a carrier, which can remove trace carbon monoxide under a hydrogen-rich condition.

Background art:

proton Exchange Membrane Fuel Cells (PEMFCs) are attracting increasing attention, particularly in the residential and automotive power supply fields, due to their advantages of low operating temperature, high power density, and long-term operation. Although hydrogen oxidation produces only water, which is an ideal energy source, the storage and transportation of pure hydrogen limits its application. Therefore, the direct production of hydrogen-rich gas by the steam reforming reaction of hydrocarbons to supply PEMFCs has become a reliable solution. However, 0.3% -1% of CO produced by this reaction poisons the platinum electrode in the battery, which affects the efficiency of the battery. The catalyst is used for removing trace carbon monoxide (preferred Oxidation of CO Reaction PROX) under the condition of hydrogen enrichment, and the method is an effective means for solving the problem with both effect and cost.

From the current state of research, the earliest elements applied to the catalyst of PROX were platinum group metals, and Engelhard in the 60 th 20 th century supported platinum on alumina, which was the earliest patent of invention. Subsequently, more and more catalysts are developed, and good effects are achieved under a wide range of operation temperatures (80-180 ℃). Depending on the type of active metal supported, the catalysts can be divided into two classes, group VIII metal (mainly platinum group elements) catalysts and group IB metal (copper, silver, gold) catalysts. At the same time, different vectors also have different effects. The support, which merely has a structural supporting function, providing a loading location is often referred to as a "non-reducing" support. Supports that not only provide support, but also have a valence state that is altered to interact with the active metal, affecting the chemistry of the active metal, are referred to as "reducible" supports. Therefore, different kinds of active metals and different kinds of carriers are freely combined, resulting in a wide variety of catalysts. For example, a platinum group metal element supported on a reducible oxide support can achieve good catalytic effects at operating temperatures in a wide range of 60 to 150 ℃. For gold element, no matter what kind of carrier, it has good low temperature activity. Unfortunately, at the operating temperature of the PEMFC (80-180 ℃), the active metal Au is gradually sintered for a long time under the working condition, and meanwhile, the competitive reaction of hydrogen oxidation is severe, which limits the activity of the catalyst. For copper metal, the loading effect of the non-reducing carrier is poor, but the combination of the reducing carrier such as cerium oxide and copper can achieve good catalytic effect and higher selectivity at the operating temperature, and has great cost advantage. But compared with other noble metals, the operation temperature for realizing the complete conversion of the carbon monoxide is high (more than 100 ℃), the window temperature for keeping the complete conversion of the carbon monoxide is narrow (5-20 ℃), and the copper catalyst has the obvious defect. Therefore, lowering the carbon monoxide complete conversion temperature and extending the window temperature are currently major challenges facing copper catalysts.

The invention content is as follows:

the invention aims to provide a preparation method of a novel supported copper oxide catalyst taking highly dispersed cerium oxide as a carrier, aiming at the defects of the prior art.

The invention adopts the following technical scheme: a preparation method of a load type copper oxide catalyst taking cerium oxide as a carrier comprises the following steps: adding excessive alkali into the mixed solution of copper salt and cerium salt to enable copper ions and cerium ions to form oxides respectively, and enabling the cerium oxide carrier to form a cavity structure; further, through ultrasound, the copper oxide is dispersed and filled into cerium oxide cavities, the interaction between the copper oxide and a cerium oxide carrier is strengthened, a mixed oxide is formed, the unsaturated coordination structure in the copper oxide is increased, the generation of reduced copper oxide is promoted, and the redox performance of the copper oxide is enhanced.

Further, the method comprises the following steps:

(1) cerium salt and copper salt are dissolved in deionized water, the molar ratio of the copper ions to the cerium ions is 6:19, and the solution temperature is kept at 25 ℃. And (3) pouring sodium hydroxide solid at one time, wherein the molar concentration of sodium hydroxide is 3mol/L, the temperature is increased from 25 ℃ to 50 ℃, a precipitate is formed, stirring is carried out for 5min, and then ultrasonic treatment is carried out for 5-45 min under the ultrasonic frequency and power of 40KHZ and 250W.

(2) Transferring the suspension after ultrasonic treatment to a low-temperature water bath with the temperature of-2 ℃, stirring for 30min, and then centrifugally washing by deionized water until the pH value of the washing liquid is less than 9. And drying the washed solid in a freeze drying oven, and roasting at the high temperature of 500 ℃ for 2 hours to finally obtain the supported copper oxide catalyst taking cerium oxide as a carrier.

Further, the copper salt in step 1 is selected from copper nitrate and copper chloride.

Further, the cerium salt in step 1 is selected from cerium nitrate and cerium chloride.

Further, the sonication time was 35 minutes.

The invention has the beneficial effects that:

compared with the traditional deposition method, the method utilizes the solution heat of alkali in the step 1. In the excess hydroxyl solution, the copper salt forms a copper hydroxide precipitate and is further converted to copper oxide particles under a heated environment. The cerium salt generates cerium hydroxide precipitate and is converted into cerium oxide with a cavity structure under a heating environment. The ultrasonic action in the step 2 can generate local 'hot spots', and the high-temperature and high-pressure environment of the 'hot spots' promotes copper oxide to be filled into the cerium oxide cavities and form a mixed oxide structure. The unsaturated coordination structure in the copper oxide is increased, the generation of reduced copper oxide is promoted, the oxidation-reduction performance of the catalyst is obviously improved, the carbon monoxide low-temperature oxidation effect under the good hydrogen-rich condition is generated, and the wider window temperature (50 ℃) is realized on the basis that the catalyst completely converts carbon monoxide at 110 ℃.

Description of the drawings:

FIG. 1 is an XPS plot of 7 parts of catalyst, A) the binding energy spectrum of XPS and B) the auger spectrum of XPS.

FIG. 2 is a graph of H2-TPR for 7 parts of catalyst.

FIG. 3 is an EDS map of a 35min sample.

FIG. 4 shows the evaluation results of CO oxidation activity under hydrogen-rich conditions of the catalysts of examples 1 to 4.

The specific implementation mode is as follows:

the invention relates to a supported copper oxide catalyst taking cerium oxide as a carrier and a preparation method thereof by utilizing ultrasonic assistance. An excess of base is added to an aqueous solution of a copper salt and a cerium salt. Wherein the alkali is released during the dissolution process. Copper salt firstly forms copper hydroxide precipitate, and then small copper oxide particles are formed by utilizing an exothermic process; the cerium salt forms cerium hydroxide precipitate, and the cerium hydroxide forms cerium oxide with a cavity structure under the condition of excessive alkali and exothermal environment; and then, carrying out ultrasonic treatment on the sample for a certain time, wherein ultrasonic action is carried out on the suspension, and a local 'hot point' is formed in a tiny space on the surface of the suspension due to the acoustic cavitation phenomenon, so that high temperature of more than 5000K and high pressure of 50MPa are generated. After that, the hot spot is cooled down sharply. The instantaneous high-temperature and high-pressure process enables the copper oxide to be dispersed and filled into the cerium oxide cavity to form mixed oxide, and interaction between metals is promoted; and (4) centrifugally washing, freeze-drying and roasting at high temperature to obtain the final catalyst. The load substance copper oxide of the catalyst is uniformly dispersed on the carrier cerium oxide, and because of the close combination interaction of the copper oxide and the carrier, the partial position of the copper oxide is unsaturated, so that the defect copper oxide with good redox capability is formed, and the complete oxidation of carbon monoxide under the condition of low temperature and wide window is realized.

The present invention will be further described with reference to the following examples.

Example 1

(1) Weighing 0.5g of copper nitrate solid, adding 50ml of deionized water, weighing 10ml of cerium nitrate solution with the concentration of 1.16mol/L, adding, uniformly stirring, keeping the rotation speed at a low speed to ensure uniform stirring, and keeping the temperature at 25 ℃. 10.56g of solid sodium hydroxide are weighed out and poured in one portion, the temperature rising from 25 ℃ to 50 ℃. The solution turned green first and then yellow, forming a precipitate. Stirring for 5 min.

(2) Performing ultrasonic treatment on the suspension prepared in the step 1 at the frequency and power of 40KHZ and 250W, and extracting samples at the time of 0min, 5min, 15min, 30min, 35min, 45min and 60 min;

(3) and (3) respectively processing the 7 samples subjected to the ultrasonic treatment in the step (2) as follows: transferring into a low-temperature water bath at-2 deg.C, stirring for 30min, centrifuging with deionized water, and washing with water solution pH less than 9 for 8 times. And drying the washed solid in a freeze drying oven for 24 hours, and roasting at the high temperature of 500 ℃ for 2 hours to finally obtain 7 parts of the supported copper oxide catalyst taking cerium oxide as a carrier.

And (3) carrying out CO catalytic oxidation reaction performance evaluation on the 7 parts of catalyst on a normal-pressure fixed bed tubular differential reactor, wherein the raw material composition gas is as follows: 1% of CO, 1% of O2, 1% of He, 23% of H2: 75 percent. The gas flow rate was 18000 ml/g.h.

The results are as follows:

FIG. 1 is an XPS plot of 7 parts of catalyst, taken together with the binding spectrum of XPS in FIG. 1A and the Auger spectrum of XPS in 2B, showing that the increase in sonication time is in addition to representing Cu²⁺934.5eV of 2P3/2 shows the appearance of a Cu-representing⁺The peak of the low binding energy 932.8eV, and the area ratio of the peak is increased and then decreased with the increase of the ultrasonic time, and the peak area is maximum at 35 min. The Auger spectrum of FIG. 1B also illustrates Cu with the state of copper ions from 918.0eV²⁺Cu biased to 916.5eV⁺And the change rule is consistent with the change of the binding energy of Cu2 +. Both together illustrate the formation of unsaturated coordinated copper oxide with prolonged sonication time, and the maximum amount formed in 35min, and almost none in 60 min. FIG. 2 shows 7 parts of catalystH2-TPR plot of the agents. Significant shifts in peak position and shape changes occur due to the formation of mixed oxides. Alpha peak represents coordinately unsaturated high-dispersion CuO_xAnd the beta peak represents normal CuO not in contact with the support. As can be seen from the figure, the peak a obviously shifts to the left and then to the right along with the increase of the ultrasonic time, and the left shift represents CuO_xThe redox ability of (a) is significantly enhanced. It can be seen that CuOx formed in 35min has the best redox ability. 60min is CuO_xThe disappearance of the structure, the disappearance of the alpha peak, shows a peak shape clearly different from that of the other samples. FIG. 3 is an EDS chart of the 35min sample, and it can be seen that the Cu element is uniformly dispersed on the surface of the carrier, with no apparent aggregated sites, indicating good dispersion of the 35min sample. FIG. 4 shows the evaluation results of 7 parts of catalyst, and it can be seen that the effect of the catalyst and CuO_xThe redox capacity of (a) remains uniform. The sample subjected to ultrasonic treatment for 35min has the best catalytic effect.

Claims

1. A preparation method of a load type copper oxide catalyst taking cerium oxide as a carrier is characterized by comprising the following steps: adding excessive alkali into a mixed solution of copper salt and cerium salt, wherein copper salt firstly forms copper hydroxide precipitate, and then small copper oxide particles are formed by using the solution heat of the alkali; the cerium salt forms cerium hydroxide precipitate, and the cerium hydroxide forms cerium oxide with a cavity structure under the condition of excessive alkali and exothermal environment; the alkali is sodium hydroxide, and the molar concentration is 3 mol/L; further through ultrasound, the ultrasound conditions are as follows: the ultrasonic frequency is 40KHz, the power is 250W, and the ultrasonic time is 5-45 minutes, so that the copper oxide is dispersed and filled into a cerium oxide cavity, the interaction between the copper oxide and a cerium oxide carrier is strengthened, a mixed oxide is formed, an unsaturated coordination structure in the copper oxide is increased, the generation of reduced copper oxide is promoted, and the redox performance of the copper oxide is enhanced.

2. The method of claim 1, comprising the steps of:

(1) dissolving cerium salt and copper salt in deionized water, wherein the molar ratio of copper ions to cerium ions is 6:19, and keeping the temperature of the solution at 25 ℃; pouring sodium hydroxide solid at one time, wherein the molar concentration of sodium hydroxide is 3mol/L, the temperature is increased from 25 ℃ to 50 ℃, a precipitate is formed, stirring is carried out for 5min, and then ultrasonic treatment is carried out for 5-45 min under the ultrasonic frequency and power of 40KHz and 250W;

(2) transferring the suspension after ultrasonic treatment to a low-temperature water bath at the temperature of-2 ℃, stirring for 30min, and centrifugally washing with deionized water until the pH of a washing liquid is less than 9; and drying the washed solid in a freeze drying oven, and roasting at the high temperature of 500 ℃ for 2 hours to finally obtain the supported copper oxide catalyst taking cerium oxide as a carrier.

3. The method according to claim 2, wherein the copper salt in step (1) is selected from the group consisting of copper nitrate and copper chloride.

4. The method according to claim 2, wherein the cerium salt in the step (1) is selected from cerium nitrate and cerium chloride.

5. The method of claim 2, wherein the sonication time is 35 minutes.