CN1403377A - Cerium-base ternary nano level composite RE oxide and its prepn process - Google Patents

Abstract

A ternary nanoscale rare earth composite oxide based on cerium and its preparation method. The rare earth composite oxide provided by the invention is a solid solution of cerium oxide, zirconium oxide and lanthanum oxide, and its chemical composition is: CeO ₂ : 20- 40wt%, ZrO ₂ : 50-70wt%, La ₂ O ₃ : 1-10wt%. The present invention uses inorganic salts as raw materials, adopts sol-gel method and co-precipitation method to complete together or through coating method and co-precipitation method, no three wastes are generated, and the reactions are all carried out at room temperature, so the preparation method is simple and the production cost lower; the provided CeO ₂ -ZrO ₂ -La ₂ O ₃ composite oxide, after low temperature (650°C) or high temperature (1000°C) heat treatment, shows that its specific surface area and high temperature thermal stability are comparable to those of the prior art There is a significant improvement. It can be applied to the catalytic process of various reactions, and is especially suitable for the purification treatment of automobile exhaust gas.

Description

A kind of cerium-based ternary nanoscale rare earth composite oxide and preparation method thereof

technical field

The invention relates to a rare earth composite oxide and its preparation method, in particular to a cerium-based ternary nanoscale rare earth composite oxide and its preparation method; it can be applied to the catalytic process of various reactions, such as hydrosulfurization , Hydrodenitrogenation, dehydrohalogenation, exhaust gas treatment of internal combustion engines, dehydrocyclization of hydrocarbons or other organic substances, especially suitable for automobile exhaust purification treatment.

Background technique

Automobile is a symbol of modern civilization, and its appearance has greatly promoted the development and progress of human society. However, while bringing convenience to people's lives, it also brings many serious problems to humans, such as noise, harmful gas emissions, etc. Automobile exhaust has become the main source of urban air pollution. With the requirements of sustainable development and the enhancement of people's awareness of environmental protection, the control of automobile pollution is imperative, and the catalytic purification of automobile exhaust is one of the most effective ways to reduce harmful exhaust emissions. An effective way to control the pollution of automobile exhaust to the environment is to use an automobile exhaust catalytic purification device. At present, the single tetragonal cerium-zirconium oxide compound is the main raw material for the catalytic conversion device of automobile exhaust gas, and it mainly acts as a catalytic assistant.

Cerium oxide is an important component in the three-way catalyst (TWC) for automobile exhaust purification, mainly because of the reversible conversion between cerium Ce ³⁺ and Ce ⁴⁺ , which has a good oxygen storage capacity (OSC). Cerium oxide easily releases oxygen under reducing conditions to oxidize CO and _CHx ; stores oxygen under oxidizing conditions to reduce _NOx ; thereby controlling the fluctuation of the atmosphere near the noble metal and maintaining the purification activity of the catalyst. This function requires CeO ₂ and the noble metal synergistic effect, if CeO ₂ particles increase will lead to CeO ₂ surface noble metal grains increase and thus reduce the oxygen storage capacity (OSC) of CeO ₂ . FomasieroP et al found that the thermal stability of Ce-Zr solid solution is higher than that of pure CeO ₂ , and adding Zr ⁴⁺ can increase the activity of oxygen in CeO ₂ , reduce the reduction activation energy of Ce ⁴⁺ , and reduce the initial reduction of the bulk phase. temperature, so that Ce-Zr has higher oxygen storage/release capacity (see Fomasiero P, Di Monte R, Ranga Rao G.Rh-loaded CeO ₂ -ZrO ₂ solid solutions as highly efficient oxygen exchangers:dependence of the reduction behavior and theoxygen storage capacity on the structural properties[J]. J Catal, 1995, 151(1): 168-177). ChristineB et al., adding ZrO ₂ to CeO ₂ , the specific surface area of CeO ₂ -ZrO ₂ is significantly higher In CeO ₂ , after aging at 700°C for 6 hours, its specific surface area is 70m ² /g, and after aging at 1000°C for 6 hours, its specific surface area is 8m ² /g (see ChristineB, Francois G.Characterisation of ceria-zirconia for details solid solutions after hydrothermal ageing [J]. Applied Catalysis A, 2001, 220: 69-77).

However, since the oxidation-reduction reaction of the three-way catalyst mainly occurs on the surface of the catalyst. High specific surface area and high temperature thermal stability are prerequisites for high oxygen storage capacity (OSC) of cerium oxide. Therefore, it is necessary to further improve the specific surface area and high temperature thermal stability of cerium oxide on the basis of previous studies.

Contents of the invention

The purpose of the present invention is to provide a ternary nano-scale rare earth oxide based on cerium and its preparation method, and prepare the cocatalyst cerium oxide (CeO ₂ ) as an ultrafine powder, thereby improving the catalytic performance and storage capacity of cerium oxide. Oxygen capacity, while adding other Zr ⁴⁺ and La ³⁺ ions to refine CeO ₂ grains and prepare nano-rare earth composite oxides; in order to obtain high specific surface area and good thermal stability under high temperature conditions co-catalyst.

Technical scheme of the present invention is as follows:

A ternary nanoscale rare earth composite oxide based on cerium, the rare earth composite oxide is a solid solution of cerium oxide, zirconium oxide and lanthanum oxide, and its molecular expression is: CeO ₂ -ZrO ₂ -La ₂ O ₃ ; chemical composition:

CeO ₂ : 20-40wt%, ZrO ₂ : 50-70wt%, La ₂ O ₃ : 1-10wt%;

The present invention provides a method for preparing the above-mentioned cerium-based ternary nanoscale rare earth composite oxide, which is jointly completed by a sol-gel method and a co-precipitation method, and its specific preparation steps are as follows:

(1) under room temperature conditions, dissolve cerium salt, zirconium salt, lanthanum salt respectively with dilute nitric acid, prepare respectively cerium nitrate, zirconium nitrate and lanthanum nitrate solution;

(2) According to the composition ratio, take the above solution and prepare it into a mixed nitric acid solution containing Ce ³⁺ , Zr ⁴⁺ and La ³⁺ ions. Under continuous stirring, the surfactant that accounts for 1-5vol% of the mixed nitric acid solution added to the mixed solution;

(3) Then the precipitant is added to the mixed solution, or the mixed solution is added to the precipitant, the pH value is controlled at 4.5-11 during the reaction, the reaction time is 40-80 minutes, and a white precipitate is obtained;

(4) The white precipitate is washed with deionized water, and then calcined at 400-700° C. for 1-3 hours.

The present invention also provides another method for preparing the above-mentioned cerium-based ternary nano-scale rare earth composite oxide. The method is jointly completed by the coating method and the co-precipitation method. The specific preparation steps are as follows: (1) Under room temperature conditions, dilute nitric acid is used to dissolve zirconium salt and lanthanum salt respectively to prepare zirconium nitrate and lanthanum nitrate solutions;

(1) according to composition ratio, get above-mentioned each solution, be prepared into the mixed nitric acid solution that contains ^Zr and La ^ion ;

(2) Add cerium carbonate solid to the precipitant at room temperature, then add surfactants accounting for 1-5 vol% of the mixed nitric acid solution, and stir for 30-60 minutes;

(3) under stirring conditions, the mixed nitric acid solution in step (2) is added in the solution in step (3), the pH value is controlled at 5.5-10 in the reaction process, and the reaction time is 40-80 minutes; Obtain white Precipitate,

(4) The white precipitate is washed with deionized water, and then calcined at 400-700° C. for 1-3 hours.

The cerium salt described in the present invention is any one of cerium carbonate, cerium ammonium nitrate, and cerium nitrate, and the zirconium salt is any one of zirconyl dichloride, zirconium nitrate, and zirconyl nitrate; the lanthanum The salt is lanthanum nitrate; the prepared cerium nitrate solution has a concentration of 0.3-0.5M, the zirconium nitrate solution has a concentration of 0.3-0.5M and the lanthanum nitrate solution has a concentration of 0.5M.

The precipitation agent described in the present invention is soluble hydroxide, soluble carbonate or ammonia water.

The surfactant added among the present invention can adopt any one in Tween 20, Tween 60, Span 80, polyvinyl alcohol 20000, sodium dodecylsulfonate or cetyl ammonium chloride.

Since the present invention uses inorganic salts as reaction raw materials, no three wastes are produced, and the reactions are all carried out at room temperature, so the preparation method is simple and the production cost is low; the provided CeO ₂ -ZrO ₂ -La ₂ O ₃ composite oxide After heat treatment at 650°C for 4 hours, the specific surface area is 90-110m ² /g, and their primary particle size is in the range of 10-20nm; after heat treatment at 1000°C for 4 hours, the specific surface area is 25-35m ² /g; The primary particle size is in the range of 20-30nm

Description of drawings

Fig. 1 is an XRD pattern of CeO ₂ -ZrO ₂ -La ₂ O ₃ (the weight ratio of each oxide is 30/60/10) composite oxide after heat treatment at 1000°C for 4 hours.

Detailed ways

In the present invention, cerium ions can be obtained from any one of cerium carbonate, cerium ammonium nitrate, and cerium nitrate; zirconium ions can be obtained from any one of zirconium oxychloride, zirconium nitrate, and zirconyl nitrate; lanthanum ions can be obtained from any one of lanthanum nitrate Obtain.

The selected precipitant can be soluble carbonate or ammonia water. The added surfactant can be Tween 20, Tween 60, Span 80, polyvinyl alcohol 20000, sodium dodecylsulfonate, cetyl ammonium chloride.

The sources of the above materials are all commercially available commodities.

Embodiment 1: (method 1)

Concentration is respectively 0.3M cerium nitrate, 0.3M zirconium nitrate and 0.5M lanthanum nitrate mixed solution (respectively according to the weight ratio of oxide is 30/60/10) add the Tween 60 of 1vol% in above-mentioned mixed solution, in Under the condition of stirring, the mixed solution was added into the ammonium bicarbonate solution, the pH value was controlled at 7.5, the reaction time was 60 minutes, and a white precipitate was formed; the precipitate was filtered, and then calcined at 600°C for 2 hours, and its specific surface area was 130.5 m ² /g. Then calcined at 650°C and 1000°C for 4 hours respectively, the specific surface areas were 98.3m ² /g and 28m ² /g respectively.

Fig. 1 is an XRD pattern of CeO ₂ -ZrO ₂ -La ₂ O ₃ (the weight ratio of each oxide is 30/60/10) composite oxide after heat treatment at 1000°C for 4 hours. It can be seen from the figure that the obtained oxide exists in the form of a pure solid solution without other impurity phases, indicating that this oxide has good thermal stability at high temperature. Small angle X-ray diffraction analysis of the sample after calcination at 650°C for 4 hours, its central particle diameter d ₅₀ was 12.4nm, and after calcination at 1000°C for 4 hours, d ₅₀ was 26.5nm.

Embodiment 2: (method 1)

To concentration is 0.3M cerium nitrate, 0.3M zirconium nitrate and 0.5M lanthanum nitrate mixed solution (respectively according to the weight ratio of oxide is 40/55/5), add 5vol% Span 80 in above-mentioned mixed solution, stir Under certain conditions, the mixed solution was added to concentrated ammonia water, the pH value was controlled at 11, the reaction time was 40 minutes, and a white precipitate was formed; the precipitate was filtered, and then calcined at 600°C for 2 hours, and its specific surface area was 130m ² /g . Calcined at 650°C and 1000°C for 4 hours respectively, the specific surface areas are 101.1m ² /g and 26.5m ² /g.

X-ray diffraction analysis shows that the obtained oxide exists in a pure solid solution phase (the X-ray diffraction pattern is consistent with Figure 1, so it is omitted). Small angle X-ray diffraction analysis of the sample after calcination at 650°C for 4 hours, its central particle diameter d ₅₀ was 13.8nm, and after calcination at 1000°C for 4 hours, d ₅₀ was 29.5nm.

Embodiment 3: (method 2)

Under stirring conditions, add 0.5M lanthanum nitrate solution to the 0.5M zirconium nitrate solution to prepare a mixed solution (the weight ratio of cerium oxide, zirconium oxide and lanthanum oxide is 30/60/10); then the cerium carbonate solid Add it into the ammonium carbonate solution, and add 5vol% sodium dodecylsulfonate into the solution, and stir for 30 minutes; under the condition of stirring, add the nitric acid mixture into the above-mentioned precipitant suspension, and the pH value is controlled at 8.5, the reaction time was 80 minutes, and a white precipitate was formed; the precipitate was filtered, and then calcined at 600°C for 2 hours. Calcined at 650°C and 1000°C for 4 hours respectively, the specific surface areas are 108m ² /g and 32.5m ² /g.

X-ray diffraction analysis shows that the obtained oxide exists in a pure solid solution phase (the X-ray diffraction pattern is consistent with Figure 1, so it is omitted). Small angle X-ray diffraction analysis of the sample after calcination at 650°C for 4 hours, its central particle diameter d ₅₀ was 18.2nm, and after calcination at 1000°C for 4 hours, d ₅₀ was 28.8nm.

Embodiment 4: (method 2)

Under stirring conditions, add 0.5M lanthanum nitrate solution to the 0.5M zirconium nitrate solution to prepare a mixed solution (the weight ratio of cerium oxide, zirconium oxide and lanthanum oxide is 20/70/10); then the cerium carbonate solid Add it to the ammonium carbonate solution, and add 5vol% polyvinyl alcohol 20000 to the solution, and stir for 50 minutes; under the condition of stirring, add the zirconium lanthanum nitrate mixture to the above-mentioned precipitant suspension, and the pH value is controlled at 10 , the reaction time was 40 minutes, and a white precipitate was generated; the precipitate was filtered, and then calcined at 400° C. for 3 hours. Calcined at 650°C and 1000°C for 4 hours respectively, the specific surface areas are 101.25m ² /g and 28.5m ² /g.

X-ray diffraction analysis shows that the obtained oxide exists in a pure solid solution phase (the X-ray diffraction pattern is consistent with Figure 1, so it is omitted). Small angle X-ray diffraction analysis of the sample after calcination at 650°C for 4 hours, its central particle diameter d ₅₀ was 15.6nm, and after calcination at 1000°C for 4 hours, d ₅₀ was 26.5nm.

Embodiment 5: (method 2)

Under stirring conditions, add 0.5M lanthanum nitrate solution to the 0.4M zirconium nitrate solution to prepare a mixed solution (the weight ratio of cerium oxide, zirconium oxide and lanthanum oxide is 40/59/1); then the cerium carbonate solid Add it to the ammonium carbonate solution, and add 1vol% cetyl ammonium chloride to the solution, and stir for 60 minutes; under the condition of stirring, add the zirconium lanthanum nitrate mixture to the above precipitant suspension, the pH value The temperature is controlled at 5.5, the reaction time is 60 minutes, and a white precipitate is formed; the precipitate is filtered, and then calcined at 700° C. for 1 hour. Calcined at 650°C and 1000°C for 4 hours respectively, the specific surface areas are 95.3m ² /g and 25.5m ² /g.

X-ray diffraction analysis shows that the obtained oxide exists in a pure solid solution phase (the X-ray diffraction pattern is consistent with Figure 1, so it is omitted). Small angle X-ray diffraction analysis of the sample after calcination at 650°C for 4 hours, its central particle diameter d ₅₀ was 19.6nm, and after calcination at 1000°C for 4 hours, the d ₅₀ was 29.8nm.

Comparative examples:

Christine B et al. studied that adding excess ammonia water to the mixture of cerium nitrate and zirconium oxynitrate (the weight ratio of each oxide was 67/33), after aging at 700°C for 6 hours, the specific surface area of CeO ₂ -ZrO ₂ After aging at ⁹⁰⁰ °C for 6 hours, its specific surface area is 26m ² /g, and after aging at 1000°C for 6 hours, its specific surface area is 8m ² /g (see ChristineB, Francois G.Characterisation of ceria -zirconia solid solutions after hydrothermal ageing [J]. Applied Catalysis A, 2001, 220: 69-77).

The composite oxide prepared by using the embodiment of the present invention was calcined at 600° C. for 2 hours, and its specific surface area was 130 m ² /g. Calcined at 700°C and 1000°C for 6 hours respectively, the specific surface areas are 90.5m ² /g and 15.5m ² /g.

It can be seen from this example that by changing the composition and adding lanthanum ions, the specific surface area of the composite oxide can be improved at both low and high temperatures compared with the research results of Christine B et al.

Claims (8)

1. the ternary nano level complex rare-earth oxidate containing valuable metal of a cerium-based, it is characterized in that: this complex rare-earth oxidate containing valuable metal is the sosoloid of cerium oxide, zirconium white and lanthanum trioxide, its developed by molecule formula: CeO ₂-ZrO ₂-La ₂O ₃Its chemical ingredients:

CeO ₂：20-40wt％，ZrO ₂：50-70wt％，La ₂O ₃：1-10wt％。

2. one kind prepares the method for complex rare-earth oxidate containing valuable metal according to claim 1, it is characterized in that this method carries out as follows:

(1) at ambient temperature, dissolve cerium salt, zirconates, lanthanum salt respectively, be prepared into cerous nitrate, zirconium nitrate and lanthanum nitrate hexahydrate respectively with rare nitric acid;

(2) according to proportioning components, get above-mentioned solution, be prepared into and contain Ce ³⁺, Zr ⁴⁺And La ³⁺Ionic mixed nitrate solution under lasting the stirring, is added to the tensio-active agent that accounts for mixed nitrate solution 1-5vol% in the described mixing solutions;

(3) then precipitation agent is added in the mixing solutions, or mixing solutions is added in the precipitation agent, the pH value is controlled at 4.5-11 in the reaction process, and the reaction times is 40-80 minute, obtains white depositions;

(4), calcined 1-3 hour down at 400-700 ℃ then with the white depositions deionized water wash.

3. according to the preparation method of the described complex rare-earth oxidate containing valuable metal of claim 2, it is characterized in that: prepared cerous nitrate solution concentration is that 0.3-0.5M, zirconium nitrate solution concentration are that 0.3-0.5M and lanthanum nitrate hexahydrate concentration are 0.5M.

4. according to the preparation method of the described complex rare-earth oxidate containing valuable metal of claim 2, it is characterized in that: the cerium salt described in the step (1) is any in cerous carbonate, cerium ammonium nitrate, the cerous nitrate, and described zirconates is any in zirconium oxychloride, zirconium nitrate, the Zircosol ZN; Described lanthanum salt adopts lanthanum nitrate.

5. according to the preparation method of the described complex rare-earth oxidate containing valuable metal of claim 2, it is characterized in that: the precipitation agent described in the step (3) is soluble carbon hydrochlorate or ammoniacal liquor.

6. according to the preparation method of the described complex rare-earth oxidate containing valuable metal of claim 2, it is characterized in that: described tensio-active agent can be any in polysorbas20, polysorbate60, span 80, polyvinyl alcohol 20000, sodium laurylsulfonate or the cetyl chloride ammonia.

7. one kind prepares the method for complex rare-earth oxidate containing valuable metal according to claim 1, and it is characterized in that: this method is carried out as follows:

(1) at ambient temperature, dissolve zirconates, lanthanum salt respectively, make zirconium nitrate and lanthanum nitrate hexahydrate respectively with rare nitric acid;

(2) according to proportioning components, get above-mentioned each solution, be prepared into and contain Zr ⁴⁺And La ³⁺Ionic mixed nitrate solution;

(3) at ambient temperature, the cerous carbonate solid is added in the precipitation agent, adds the tensio-active agent that accounts for mixed nitrate solution 1-5vol% then, stirred 30-60 minute;

(4) under agitation condition, the mixed nitrate solution in the step (2) is joined in the solution of step (3), the pH value is controlled at 5.5-10 in the reaction process, and the reaction times is 40-80 minute, obtains white depositions;

(5), calcined 1-3 hour down at 400-700 ℃ then with the white depositions deionized water wash.

8. according to the preparation method of the described complex rare-earth oxidate containing valuable metal of claim 7, it is characterized in that: the zirconium nitrate solution concentration described in the step (1) is 0.3-0.5M, and lanthanum nitrate hexahydrate concentration is 0.5M.