CN107626317B - A kind of Ce-based oxide catalyst and its preparation and application - Google Patents

Abstract

The invention discloses a Ce _- based oxide catalyst and its preparation and application. It uses CeO2 as a carrier, and controls the shape of the catalyst by controlling the type and amount of the added reducing agent and the temperature of the hydrothermal reaction. A Co/CeO ₂ catalyst was obtained. The preparation process of the present invention is simple, easy to operate, low in cost, and high in conversion rate. The obtained catalyst exhibits high catalytic oxidation activity in a wide temperature range, can be used for catalytic oxidation of toluene and propane, etc., and exhibits high catalytic oxidation activity. Thermal stability, with obvious industrial application value.

Description

A kind of Ce-based oxide catalyst and its preparation and application

technical field

The invention belongs to the field of nanotechnology, and in particular relates to a Ce-based oxide catalyst and its preparation and application.

Background technique

Human survival and development are inseparable from a suitable environment. With the development of industry, environmental pollution is becoming more and more serious, and even threatens the survival and development of human beings. Therefore, it is urgent to protect the environment. Aromatic hydrocarbons are highly toxic to humans and animals. If they are exposed to high concentrations for a long time, they will cause nausea, headache, dizziness and other symptoms. In addition, polycyclic aromatic hydrocarbons in petroleum have a strong triple effect. Leaked crude oil and other hydrocarbons will cause a fire accident if exposed to an open flame; if the leaked hydrocarbons enter a confined space, it is very easy to explode, and even cause catastrophic accidents that cause mass death and mass injury. Therefore, the removal of hydrocarbons is of great significance to both the human body and the environment. Catalytic oxidation is one of the effective methods for hydrocarbon elimination, and noble metal-based catalysts such as Pt, Pd, Au, and Ag all exhibit low-temperature hydrocarbon elimination performance. However, due to the high price of noble metals, high temperature sintering and limited reserves of noble metals, the wide application of noble metal-based catalysts in industry is limited. In recent years, CeO ₂ has been favored by many researchers due to its good oxygen storage capacity and redox performance, as well as abundant surface oxygen vacancy sites, which are beneficial to the reoxidation process of Ce ³⁺ through the Mars-van Krevelen pathway. However, due to the lack of acid sites on the surface of pure CeO2, the low _- temperature catalytic activity and selectivity are far from meeting the practical requirements.

Contents of the invention

The object of the present invention is to provide a kind of Ce base oxide catalyst and its preparation method and application, and this catalyst is a kind of cheap catalyst of low temperature, high activity, high thermal stability and high selectivity, and it is stable in wide temperature range. It exhibits high catalytic oxidation activity, and can be applied to the elimination of hydrocarbons such as toluene and propane.

To achieve the above object, the present invention adopts the following technical solutions:

A Ce-based oxide catalyst prepared by loading _1-10wt % Co on CeO2. The morphology and structure of the obtained catalyst include any one of nanorods, nanocubes, nanospheres and nanocones.

The preparation method of the Ce-based oxide catalyst is to carry out the hydrothermal reaction of the precursor of Ce in a solvent containing a reducing agent, and then roast the obtained product to obtain the catalyst. It specifically includes the following steps:

1) Dissolve and mix the precursor of Ce, cobalt nitrate and reducing agent in a certain amount of solvent;

2) The resulting mixed solution is subjected to a hydrothermal reaction in a reactor;

3) Centrifuge the reacted solution, wash the product alternately with water and ethanol several times, and dry it in vacuum;

4) Calcining the dried product to prepare the catalyst.

The precursor of Ce is cerium nitrate.

The molar ratio of Ce precursor to reducing agent used is 1:1.05-1:2.67.

The reducing agent is urea or NaOH, and its concentration in the solvent is 6-9 mol/L; the solvent is one or both of water and ethanol.

The temperature of the hydrothermal reaction is 100-180° C., and the time is 10-24 h.

The heating rate during calcination is 1-3 ℃/min, the calcination temperature is 500-550 ℃, and the calcination time is 2-6 h.

An accelerator can also be added to the mixed solution in step 2) to regulate the synthesis of nanocones and nanospheres; the accelerator is hydrochloric acid, and its addition amount is 12 mol/L.

The obtained Ce-based oxide catalyst can be used to catalyze the catalytic oxidation of hydrocarbons such as methane, propane and organic toluene emitted from coal combustion flue gas. In its specific application, it can be used in the form of particles, or it can be loaded on a honeycomb carrier such as cordierite as a coating to prepare a monolithic porous catalyst.

_The present invention uses CeO2 as a carrier, and combines Ce with transition metal element Co to significantly change the surface of Ce to form more surface oxygen vacancies, thereby improving the redox ability of the catalyst and forming more accepting lone pairs of electrons. Empty orbitals facilitate the adsorption of hydrocarbons. At the same time, due to the unsaturated 3d electronic structure of Co oxides, the unsaturated electrons on the d orbitals are easy to migrate to the CH bonds, which is beneficial to improve the low-temperature catalytic activity.

Significant advantage of the present invention is:

(1) The present invention regulates the morphology and structure of the catalyst by controlling the type and concentration of the reducing agent used and the temperature of the hydrothermal reaction, thereby realizing the regulation and control of the catalyst activity. For example, when the reducing agent is NaOH, by adjusting its concentration and hydrothermal reaction temperature, Ce-based oxide catalysts with nanorod and nanocube structures can be prepared; when the reducing agent is urea, by adding accelerator HCl and controlling water Ce-based oxide catalysts with nanosphere and nanocone structures can be prepared under thermal reaction temperature. At the same time, when the morphology of catalysts is different, the exposed crystal planes are also different.

(2) The catalyst obtained in the present invention exhibits high catalytic oxidation activity in a wide temperature range. For example, the catalytic conversion rate of Co/CeO _{2 nanocubes to toluene reached 90% at 237 °C, while the catalytic conversion rate of Co/CeO 2 nanorods} to propane reached 90% at 254 °C, which is better than traditional toluene. and propane catalytic oxidation catalysts.

(3) The preparation process of the catalyst of the present invention is simple, convenient to operate, low in cost, high in catalytic conversion rate, and has obvious industrial application value.

Description of drawings

Fig. 1 is the scanning electron micrograph of the catalyst that embodiment 1-4 makes, and wherein (A) is CeO ₂ nano cubes, (B) is CeO ₂ nano balls, (C) is CeO ₂ nano cones, (D) is _CeO2 nanorods.

Fig. 2 is the conversion rate of toluene at different temperature points of the catalyst prepared in Examples 1-4.

Fig. 3 is the conversion rate of propane at different temperature points of the catalyst prepared in Examples 1-4.

Detailed ways

In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

Example ₁ Preparation of Co/CeO2 nanocubes

Dissolve 1.736 g Ce(NO ₃ ) ₃ 6H ₂ O (molecular weight 434.12) and 0.034 g Co(NO ₃ ) ₂ 6H ₂ O (molecular weight 291.03) in 10 mL of deionized water, and add 70 mL, 6 mol/L NaOH solution, stirred at room temperature for 1 h, then transferred to a hydrothermal kettle, reacted at 100 °C for 24 h, centrifuged, and the obtained product was washed 3 times with deionized water and ethanol, and then vacuum-dried at 60 °C for 12 h , and then in a muffle furnace, the temperature was raised to 500°C at a rate of 3°C/min, and fired for 3h.

Example ₂ Preparation of Co/CeO2 nanospheres

Add 0.434 g Ce(NO ₃ ) ₃ ·6H ₂ O (molecular weight 434.12), 0.010 g Co(NO ₃ ) ₂ ·6H ₂ O (molecular weight 291.03) and 8 g urea (molecular weight 60) to a 70 mL In a mixed solvent composed of ionic water and 10 mL ethanol, stir at room temperature for 1 h, then add 0.1 mL of HCl (12M), stir vigorously at room temperature for 1 h, then transfer to a hydrothermal kettle, and react at 160 °C for 12 h. After centrifugation, the obtained product was washed three times with deionized water and ethanol, and then vacuum-dried at 60 °C for 12 h, then heated in a muffle furnace to 550 °C at a rate of 3 °C/min, and roasted for 2 h.

Example 3 Preparation of Co/CeO ₂ nanocones

Dissolve 1.042 g Ce(NO ₃ ) ₃ 6H ₂ O (molecular weight 434.12), 0.033 g Co(NO ₃ ) ₂ 6H ₂ O (molecular weight 291.03) and 0.384 g urea (molecular weight 60) in 80 mL of deionized water, stirred at room temperature for 1 h, then transferred to a hydrothermal kettle, reacted at 120 °C for 8 h, centrifuged, and the obtained product was washed with deionized water and ethanol three times, and then vacuum-dried at 60 °C for 12 h, and then placed in a horse In a Furnace, the temperature was raised to 500 °C at a rate of 3 °C/min, and roasted for 6 h.

Example ₄ Preparation of Co/CeO2 nanorods

Dissolve 1.736 g Ce(NO ₃ ) ₃ 6H ₂ O (molecular weight 434.12) and 0.069 g Co(NO ₃ ) ₂ 6H ₂ O (molecular weight 291.03) in 10 mL of deionized water, and add 70 mL of 9 mol/L NaOH solution, stirred at room temperature for 1 h, then transferred to a hydrothermal kettle, reacted at 180 °C for 24 h, centrifuged, and the obtained product was washed with deionized water and ethanol three times, and then vacuum-dried at 60 °C for 12 h , and then in a muffle furnace, the temperature was raised to 500°C at a rate of 3°C/min, and calcined for 3 h.

Fig. 1 is the scanning electron micrograph of embodiment 1-4 obtained catalyst.

Performance Testing

Adopt each 0.1g of the catalysts prepared in Examples 1-4 respectively, carry out toluene and propane conversion rate measurement on the miniature fixed bed of continuous flow, mass space velocity 90000 mL/(g h), the variation of toluene and propane concentration in the tail gas by Gas chromatography detection, reaction gas composition: 1000 ppm toluene or propane, 20vol% O ₂ and N ₂ as balance gas. The conversion effect of the catalyst on toluene and propane was measured at 200-400°C.

Fig. 2 is the conversion rate of toluene at different temperature points of the catalyst prepared in Examples 1-4. It can be seen from Fig. ₂ that the toluene conversion of the Co/CeO2 nanocube catalyst reached 90% at 237 °C, comparable to that of noble metal-based catalysts.

Fig. 3 is the conversion rate of propane at different temperature points of the catalyst prepared in Examples 1-4. It can be seen from Fig. ₃ that the Co/CeO2 nanocubes exhibited excellent low-temperature oxidation activity of propane, and the conversion of propane reached 80% at 246 °C.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (3)

1. a kind of preparation method of Ce base oxide catalyst, it is characterised in that: by the presoma of Ce and cobalt nitrate containing also Hydro-thermal reaction is carried out in the solvent of former agent, then roasts products therefrom, and the catalyst is made；Co's is negative in the catalyst Carrying capacity is 1-10 wt%；

The presoma of the Ce is cerous nitrate；The presoma of Ce and the molar ratio of reducing agent are 1:1.05-1:2.67；

The concentration of reducing agent is 6-9 mol/L in solvent；Wherein, the reducing agent is urea or NaOH, and the solvent is water, second One or both of alcohol；

The temperature of the hydro-thermal reaction is 100-180 DEG C, and the time is 10-24 h；

Heating rate when roasting is 1-3 DEG C/min, and maturing temperature is 500-550 DEG C, and calcining time is 2-6 h；

The appearance structure of gained catalyst includes nanometer rods, nano cubic block, nanosphere, any one in nanocone.

2. the preparation method of Ce base oxide catalyst according to claim 1, it is characterised in that: hydro-thermal reaction it is anti- Answering further includes promotor in system；The promotor is hydrochloric acid, and dosage is 12 mol/L.

3. a kind of application of Ce base oxide catalyst made from method as described in claim 1, it is characterised in that: be used for hydro carbons Catalysis oxidation；

The hydro carbons includes organic toluene of alkane or coal-fired flue-gas discharge.