Palladium oxide supported zinc-based catalyst and preparation method and application thereof
阅读说明：本技术 一种氧化钯负载型锌基催化剂及其制备方法和应用 (Palladium oxide supported zinc-based catalyst and preparation method and application thereof ) 是由 左莹 魏学红 张婷 于 2021-07-22 设计创作，主要内容包括：本发明公开了一种氧化钯负载型锌基催化剂及其制备方法,属于有机气体污染物催化燃烧领域。催化剂载体为粒径在150nm-300nm的氧化锌,负载的贵金属钯以氧化物形式存在,粒径尺寸主要分布在1.5nm-2.5nm,以催化剂的质量百分数计,氧化钯负载量占0.2%～0.6%,均匀分散于氧化锌载体表面。该催化剂通过超声-焙烧两步法实现在氧化锌载体上对氧化钯的负载,相较于现有钯基甲烷催化燃烧催化剂,本发明所述催化剂具有低钯负载量、高活性及稳定性的特点,同时制备工艺简单,易于推广应用。(The invention discloses a palladium oxide supported zinc-based catalyst and a preparation method thereof, belonging to the field of catalytic combustion of organic gas pollutants. The catalyst carrier is zinc oxide with the particle size of 150nm-300nm, the loaded noble metal palladium exists in the form of oxide, the particle size is mainly distributed in the range of 1.5nm-2.5nm, the loading amount of the palladium oxide accounts for 0.2% -0.6% by mass percent of the catalyst, and the palladium oxide is uniformly dispersed on the surface of the zinc oxide carrier. The catalyst realizes the loading of palladium oxide on a zinc oxide carrier through an ultrasonic-roasting two-step method, has the characteristics of low palladium loading capacity, high activity and stability compared with the existing palladium-based methane catalytic combustion catalyst, and is simple in preparation process and easy to popularize and apply.)
1. A palladium oxide supported zinc-based catalyst characterized by: the catalyst carrier is zinc oxide, the supported noble metal palladium exists in an oxide form, and the supported amount of the palladium oxide accounts for 0.2-0.6% of the mass percent of the catalyst and is uniformly dispersed on the surface of the zinc oxide carrier.
2. The palladium oxide-supported zinc-based catalyst of claim 1, wherein: the zinc oxide carrier has a particle size of 150nm-300nm and a hexagonal wurtzite structure, noble metal palladium loaded on the surface exists in an oxide form, and the particle size is mainly distributed in the range of 1.5nm-2.5 nm.
3. A method of preparing the palladium oxide-supported zinc-based catalyst of claim 1 or 2, comprising the steps of:
the method comprises the following steps: preparation of zinc oxide support
(1) Dissolving zinc acetate and zinc nitrate in 80ml ethanol under vigorous stirring;
(2) filling the reaction solution into a stainless steel reaction kettle with a polytetrafluoroethylene lining, wherein the filling degree is 70% -90%, and the reaction is carried out for 5-10 hours after sealing;
(3) after the reaction kettle in the step (2) is naturally cooled to room temperature, washing the obtained white precipitate with deionized water for several times, and drying in an oven at 40-80 ℃ for 5-20 hours to obtain the zinc oxide carrier;
step two: deposition of active component palladium oxide
(1) Adding 1g of prepared zinc oxide carrier into 100ml of deionized water under stirring, and then dripping a palladium-containing cation precursor solution with the concentration of 0.005g/ml to obtain a suspension;
(2) carrying out ultrasonic treatment on the obtained suspension at 40 ℃ for 1-2 hours;
(3) filtering the product obtained in the step (2), fully washing the obtained precipitate, and drying in an oven to obtain an ultrasonic treatment sample;
(4) and (4) placing the ultrasonic treatment sample obtained in the step (3) in a muffle furnace for roasting to obtain the palladium oxide supported zinc-based catalyst.
4. The method of claim 3, wherein the palladium oxide-supported zinc-based catalyst comprises: the molar ratio of the zinc acetate to the zinc nitrate in the step one (1) is 8-10.
5. The method of claim 3, wherein the palladium oxide-supported zinc-based catalyst comprises: the reaction temperature in the step one (2) is 120-160 ℃.
6. The method of claim 3, wherein the palladium oxide-supported zinc-based catalyst comprises: and in the second step (1), the palladium-containing cation precursor is one of palladium nitrate, palladium chloride and potassium chloropalladate.
7. The method of claim 3, wherein the palladium oxide-supported zinc-based catalyst comprises: in the second step (2), the ultrasonic frequency is 20-30 kHz, and the ultrasonic power is 150-200W.
8. The method of claim 3, wherein the palladium oxide-supported zinc-based catalyst comprises: in the second step (3), the drying temperature is 40-80 ℃, and the drying time is 5-10 hours.
9. The method of claim 3, wherein the palladium oxide-supported zinc-based catalyst comprises: in the second step (4), the roasting temperature is 500-600 ℃, and the roasting time is 2-3 hours.
10. Use of a palladium oxide supported zinc based catalyst according to claim 1 or 2 for catalysing the combustion of methane, wherein: is carried out on a quartz tube type fixed bed reactor with the inner diameter of 4mm, the dosage of the catalyst is 50mg, and the proportion of reaction gas is 1 percent CH4+ 99% Air, reaction gas flow rate 50 ml/min, CH4The conversion rate of (A) is analyzed by a chromatograph, and the temperature of the reactor is controlled by a program temperature controller until the reaction reaches CH4And (4) complete conversion.
Technical Field
The invention relates to a palladium oxide supported zinc-based catalyst and a preparation method and application thereof, belonging to the field of catalytic combustion of organic gas pollutants.
Background
Natural gas is an important chemical raw material and clean energy, and has very wide development and application prospects. Methane, a major constituent of natural gas, has a high degree of tetrahedral symmetry and is extremely difficult to activate under mild conditions (its C — H bond energy is up to 434 KJ/mol). In the research at home and abroad, the supported palladium catalyst is one of the current methane combustion catalysts with the best performance, but sintering deactivation of palladium species can be caused at high temperature in the use process, the performance and the service life of the catalyst are reduced, in addition, the price of palladium metal is high, the consumption of active metal palladium of the current supported palladium catalyst is high, the preparation cost is high, and the application of the supported palladium catalyst in the field of methane catalytic combustion is limited, so that the development of the supported palladium catalyst for methane catalytic combustion with low load capacity and high temperature resistance has important significance.
Disclosure of Invention
Aiming at the problems of high catalyst cost and poor stability of the traditional supported palladium catalyst for methane combustion, the palladium oxide supported zinc-based catalyst which is simple in preparation process, low in palladium loading capacity, high in activity and stability is provided, and therefore excellent activity and high-temperature stability are obtained. The invention also provides a preparation method and application of the palladium oxide supported zinc-based catalyst.
In the invention, under the ultrasonic condition, a large amount of vacuoles are generated in liquid, the palladium ions can be promoted to form a palladium simple substance on the surface of zinc oxide by high temperature, high pressure and strong energy generated by the rupture of the vacuoles, the palladium simple substance is rapidly and well dispersed on a zinc oxide carrier, the particle agglomeration is prevented, the palladium simple substance can be oxidized into palladium oxide by the subsequent roasting treatment, and finally the palladium oxide supported zinc-based catalyst with smaller palladium oxide particle size and narrower particle size distribution is obtained.
The invention provides a palladium oxide supported zinc-based catalyst, wherein a catalyst carrier is zinc oxide with the particle size of 150nm-300nm, supported noble metal palladium exists in the form of oxide, the particle size is mainly distributed in the range of 1.5nm-2.5nm, the palladium oxide supporting amount accounts for 0.2% -0.6% of the mass percentage of the catalyst, and the palladium oxide supporting amount is uniformly dispersed on the surface of the zinc oxide carrier.
The zinc oxide carrier has a hexagonal wurtzite structure, and noble metal palladium loaded on the surface exists in an oxide form.
The invention provides a preparation method of a palladium oxide supported zinc-based catalyst, which comprises the following steps:
firstly, the method comprises the following steps: preparing a zinc oxide carrier; secondly, the method comprises the following steps: deposition of the active component palladium oxide.
The preparation method of the zinc oxide carrier comprises the following steps:
(1) dissolving a certain proportion of zinc acetate and zinc nitrate in 80ml of ethanol under vigorous stirring;
(2) putting the reaction solution into a stainless steel reaction kettle with a polytetrafluoroethylene lining, wherein the filling degree is 70% -90%, and the reaction is carried out for 5-10 hours at a certain temperature in a sealed manner;
(3) and (3) after the reaction kettle in the step (2) is naturally cooled to room temperature, washing the obtained white precipitate with deionized water for several times, and drying in an oven at 40-80 ℃ for 5-20 hours to obtain the zinc oxide carrier.
The molar ratio of the zinc acetate to the zinc nitrate in the step (1) is 8-10.
The reaction temperature in the step (2) is 120-160 ℃.
The deposition of the active component palladium oxide comprises the following steps:
(1) adding 1g of prepared zinc oxide carrier into 100ml of deionized water under stirring, and then dropwise adding a certain amount of palladium-containing cation precursor solution with the concentration of 0.005 g/ml;
(2) carrying out ultrasonic treatment on the suspension in the step (1) at 40 ℃ for 1-2 hours;
(3) filtering the product obtained in the step (2), fully washing the obtained precipitate, and drying the precipitate in an oven at a certain temperature for 5-10 hours to obtain an ultrasonic treatment sample;
(4) and (4) placing the ultrasonic treatment sample obtained in the step (3) in a muffle furnace for roasting at a certain temperature for 2-3 hours to obtain the palladium oxide supported zinc-based catalyst.
The palladium-containing cation precursor in the step (1) may be one of palladium nitrate, palladium chloride and potassium chloropalladate.
In the step (1), the weight of the catalyst is calculated as 100%, and the weight percentage of the palladium oxide is 0.2% -0.6%.
In the step (2), the ultrasonic frequency is 20-30 kHz, and the ultrasonic power is 150-200W.
The drying temperature in the step (3) is 40-80 ℃.
In the step (4), the roasting temperature is 500-600 ℃.
The invention provides application of the palladium oxide supported zinc-based catalyst, and the palladium oxide supported zinc-based catalyst can be used for catalytic combustion of methane. The evaluation of the combustion performance of the methane is carried out on a quartz tube type fixed bed reactor with the inner diameter of 4mm, the dosage of the catalyst is 50mg, and the proportion of the reaction gas is 1 percent CH4+ 99% Air, reaction gas flow rate 50 ml/min, CH4The conversion of (A) was analyzed by Shimadzu chromatography GC-2014, and the temperature of the reactor was controlled by a programmed temperature controller to CH4And (4) complete conversion.
The invention has the beneficial effects that:
the palladium oxide supported zinc-based catalyst material obtained by the method has the advantages of uniform particle size of active component palladium oxide, good dispersibility and low loading capacity, can be used as a methane combustion catalytic material, and solves the problems of high cost and easy inactivation at high temperature of the traditional supported palladium catalyst. And the preparation process is simple, the operation is convenient, the preparation parameters are easy to control, the repeatability is good, and the large-scale synthesis can be realized.
Drawings
FIG. 1 is an X-ray diffraction pattern of the palladium oxide supported zinc-based catalyst of example 1.
FIG. 2 is a transmission electron micrograph of the palladium oxide-supported zinc-based catalyst of example 1.
FIG. 3 is a graph showing the activity of the palladium oxide supported zinc-based catalyst in example 1 in catalyzing the combustion of methane.
FIG. 4 is a life test of the palladium oxide supported zinc-based catalyst catalyzing methane combustion in example 1.
FIG. 5 is a repeated experiment of the palladium oxide supported zinc-based catalyst in example 1 catalyzing methane combustion.
Detailed Description
The present invention is further illustrated by, but is not limited to, the following examples.
Example 1:
at room temperature, 50mmol of zinc acetate and 5mmol of zinc nitrate are completely dissolved in 80mL of absolute ethyl alcohol by stirring to obtain clear and transparent solution, the clear and transparent solution is transferred into a polytetrafluoroethylene reaction kettle, the reaction kettle is sealed by a stainless steel outer lining and then is placed in an oven 150 degreesoAnd C, reacting for 5 hours, naturally cooling to room temperature, filtering, washing and drying the obtained product to obtain the zinc oxide carrier. 1g of the prepared zinc oxide sample was added to 100ml of deionized water with stirring, and a palladium nitrate solution (0.4% by weight of palladium oxide) was added dropwise to the solution at a concentration of 0.005g/ml, to the solution at 40%oC, ultrasonic treating for 1 hour at 20kHz and 150W, filtering, washing, and baking in oven at 80 deg.CoC, drying for 5 hours, and placing in a muffle furnace for 500 hoursoAnd C, roasting for 2 hours to obtain the palladium oxide supported zinc-based catalyst.
FIG. 1 is an X-ray diffraction pattern of a palladium oxide supported zinc-based catalyst, which shows that the phase of the catalyst is hexagonal wurtzite ZnO, and no palladium related peak is observed because the supported amount of palladium is lower than the detection limit of an X-ray diffractometer. FIG. 2 is a transmission electron micrograph of a palladium oxide supported zinc oxide catalyst, which shows that the powder has a spheroidal structure, the particle diameter is 150nm-300nm, and a plurality of clearly dispersed palladium oxide nano-particles with the particle diameter of 1.9nm-2.4nm can be seen on the surface of the carrier. 50mg of catalyst are placed in a fixed bed reactor and 1% CH is introduced4Mixed gas of 99% air and 50 mL/min of flow rate, CH4The conversion of (a) was analyzed by chromatography GC-2014, and the temperature of the reactor was controlled by a programmed temperature controller until CH4And (4) complete conversion. The activity curve for a palladium oxide supported zinc-based catalyst catalyzing methane combustion is shown in FIG. 3 at 440oAnd the complete conversion of methane is realized under C, and good catalytic activity is shown. FIG. 4 is a life test of a palladium oxide supported zinc-based catalyst for catalyzing methane combustion, which shows that the catalyst has good thermal stability. Fig. 5 is a repeated experiment of methane combustion under the action of the catalyst, and the four catalytic performances can be reproduced regardless of the experimental sequence.
Example 2:
at room temperature, 50mmol of zinc acetate and 5mmol of zinc nitrate are completely dissolved in 80mL of absolute ethyl alcohol by stirring to obtain clear and transparent solution, the clear and transparent solution is transferred into a polytetrafluoroethylene reaction kettle, the reaction kettle is sealed by a stainless steel outer lining and then is placed in an oven 150 degreesoAnd C, reacting for 5 hours, naturally cooling to room temperature, filtering, washing and drying the obtained product to obtain the zinc oxide carrier. 1g of the prepared zinc oxide sample was added to 100ml of deionized water with stirring, and a palladium nitrate solution (0.2% by weight of palladium oxide) was added dropwise to the solution at a concentration of 0.005g/ml, to the solution at 40%oC, performing ultrasonic treatment for 2 hours at the ultrasonic frequency of 20kHz and the ultrasonic power of 150W, filtering and washing the obtained product, and performing 80-hour ultrasonic treatment in an ovenoC, drying for 5 hours, and placing in a muffle furnace for 500 hoursoAnd C, roasting for 2 hours to obtain the palladium oxide supported zinc-based catalyst. The phase of the zinc oxide is hexagonal wurtzite ZnO by X-ray diffraction spectrum analysis. 50mg of catalyst are placed in a fixed bed reactor and 1% CH is introduced4Mixed gas of 99% air and 50 mL/min of flow rate, CH4The conversion of (a) was analyzed by chromatography GC-2014, and the temperature of the reactor was controlled by a programmed temperature controller until CH4And (4) complete conversion. Palladium oxide supported zinc-based catalysts at 490oAnd the complete conversion of methane is realized under C, and good catalytic activity is shown.
Example 3:
at room temperature, 50mmol of zinc acetate and 5mmol of zinc nitrate are completely dissolved in 80mL of absolute ethyl alcohol by stirring to obtain clear and transparent solution, the clear and transparent solution is transferred into a polytetrafluoroethylene reaction kettle, the reaction kettle is sealed by a stainless steel outer lining and then is placed in an oven 150 degreesoAnd C, reacting for 5 hours, naturally cooling to room temperature, filtering, washing and drying the obtained product to obtain the zinc oxide carrier. 1g of the prepared zinc oxide sample was added to 100ml of deionized water with stirring, and a palladium chloride solution (0.6% by weight of palladium oxide) was added dropwise to the solution at a concentration of 0.005g/ml, to the solution at 40%oC, ultrasonic treating for 1 hour at 20kHz and 150W, filtering, washing, and baking in oven at 80 deg.CoC, drying for 5 hours, and placing in a muffle furnace for 500 hoursoAnd C, roasting for 2 hours to obtain the palladium oxide supported zinc-based catalyst. By X-ray diffraction patternThe spectral analysis shows that the phase is hexagonal wurtzite ZnO. 50mg of catalyst are placed in a fixed bed reactor and 1% CH is introduced4Mixed gas of 99% air and 50 mL/min of flow rate, CH4The conversion of (a) was analyzed by chromatography GC-2014, and the temperature of the reactor was controlled by a programmed temperature controller until CH4And (4) complete conversion. A palladium oxide supported zinc-based catalyst at 435oAnd the complete conversion of methane is realized under C, and good catalytic activity is shown.