WO2020010646A1

WO2020010646A1 - Nano titanium dioxide composite particle and preparation method thereof

Info

Publication number: WO2020010646A1
Application number: PCT/CN2018/096387
Authority: WO
Inventors: 胡彦杰; 李春忠; 江浩; 张玲; 姜海波; 沈建华
Original assignee: 华东理工大学
Priority date: 2018-07-10
Filing date: 2018-07-20
Publication date: 2020-01-16
Also published as: CN108993532A

Abstract

Provided is a nano titanium dioxide composite particle and a preparation method thereof. An organic titanium source, a Pt salt and a Co salt are used as precursors and dissolved in an ethanol solvent. By using a spray pyrolysis process, the precursors in the form of an atomized diffusion gas are sprayed into a reactor through a feeder. In an auxiliary flame of hydrogen and oxygen, the atomized precursors react to form sub-nanometer, platinum-loaded titanium dioxide composite particles. The size of the composite particles is 10-30 nm. The mass of platinum is 0.5-2% of the mass of titanium dioxide. The sub-nanometer platinum has a size of 0.5 to 1.2 nm and is uniformly supported on the surface of the titanium dioxide composite particles. The method increases the nucleation rate of platinum by introducing a cobalt source, reduces the particle size of platinum, and obtains Pt-loaded particles having a high loading amount and a sub-nanometer size.

Description

Nano titanium dioxide composite particles and preparation method thereof

Technical field

The invention belongs to a preparation method for preparing noble metal-supported oxide nanoparticles, and particularly relates to a one-step method for preparing sub-nanoscale Pt-supported titanium dioxide composite particles.

Background technique

Precious metal-supported oxide nano-catalyst systems have been widely studied and applied to automobile exhaust treatment, proton exchange membrane fuel cells, water-gas conversion, photocatalysis, and electrocatalysis. Among them, the Pt-supported oxide system has been repeatedly explored by many researchers and used in the efficient catalytic reaction of CO oxidation in order to seek a higher activity and higher stability of the catalytic system. Studies have shown that for Pt-supported systems to catalyze CO oxidation, the catalytic mechanism has both LH and MK mechanisms (Applied Catalysis B: Environmental, 2013, 142-143, 523-532). In order to further increase the activity, reducing the size of supported Pt particles has become a major Research direction, this will not only make more interface between Pt particles and active support, which will increase the number of active sites, but also increase the portion of the precious metal Pt exposed on the surface, which will increase the utilization of Pt and ensure that With the same activity, the amount of precious metals is greatly reduced, thereby reducing costs. Therefore, a large amount of research has been carried out in the direction of reducing the size of precious metals. Through the optimization of various process methods, even the supported particles have reached the level of single atoms (Nat. Chem., 2011, 3 (8), 634-641). However, studies have shown that for Pt-based supported systems, Pt single atoms have a stronger adsorption capacity for CO than Pt particles and it is difficult to desorb during the reaction, making Pt single atoms catalyzed CO oxidation capacity is not strong ( Science, 2015, 350, 189-192). Therefore, the preparation of load particles with reasonable size has become a hot research topic.

The traditional methods for preparing noble metal-supported oxide nano-catalyst systems are mainly precipitation deposition methods (J. Am. Chem. Soc., 2013, 135 (34), 12634-12645; J. Am. Chem. Soc., 2014, 136 ( 9): 3617-3623) and impregnation method (Nat. Chem., 2011, 3 (8), 634-641), etc., but these methods usually can only reduce the size of precious metal particles by reducing the content of precious metals, which is difficult to achieve Smaller size particles are obtained at higher loadings. Although some new preparation methods such as atomic layer deposition (Chem. Cat. Chem., 2015, 7 (17): 2559-2567) method can prepare systems with higher loading and smaller loading particle size, the process The cost is high and the process is relatively complicated.

The invention adopts a spray combustion method with simple equipment, low cost, short production cycle, continuous production, and the preparation of a supported catalyst by a one-step method. Sub-nanoscale Pt is supported on a reducible active support and has a high catalytic activity for CO oxidation.

Summary of the invention

The purpose of the present invention is to provide a method for preparing sub-nanometer level Pt-supported titanium dioxide composite particles, which solves the problems existing in the prior art.

The idea of the invention is as follows:

The organic titanium source, the salt of the noble metal Pt and the Co salt are used as precursors, and they are dissolved in an ethanol solvent, diffused through a feeder at a certain rate under a certain pressure, atomized into the reactor, and assisted by a flame of hydrogen and oxygen. In the process, the atomized precursor reacts to form a Pt-supported titanium dioxide composite particle at the sub-nanometer level. In the prepared composite particles, the titanium dioxide support is first formed. Because it is performed in this unique non-equilibrium flame field and temperature field, two phases of anatase and rutile phase are generated at the same time, and they are in the form of mixed crystals. presence. Then in this high-temperature and fast-cooling flame field, the noble metal Pt has undergone a nucleation reaction and a nuclear growth process, and is deposited on the surface of the resulting titanium dioxide. Due to the characteristics and small content of Co salt, it will exist in both the bulk phase and the surface of titanium dioxide, and because Co will transfer electrons to Pt during the reaction from the low-valent state to the high-valent state, making the precious metal Pt The nucleation rate is accelerated, and more Pt particles are formed per unit time, so that sub-nanoscale Pt is supported on the titanium dioxide support.

The detailed technical solution of the present invention is as follows:

A method for preparing sub-nanometer level Pt-supported titanium dioxide composite particles includes the following steps:

(1) Configure an ethanol solution of organic titanium source with a metal concentration of 0.1-0.9mol / L, and add Pt salt and Co salt in a weight ratio of 1: 0.1 ～ 1, and disperse it in ultrasonic for 10-20min to make it uniform and stable. Solution as precursor solution;

(2) the precursor is pumped into the reactor through a feeder under an external diffusion pressure, a further combustion reaction is performed under the auxiliary flame of hydrogen and oxygen, and the nano powder is collected in the collector by a vacuum pump.

The organic titanium source is selected from one or more of tetrabutyl titanate, ethyl titanate, butyl titanate, and tetraisopropyl titanate.

The Pt salt is one or more of chloroplatinic acid hydrate or chloroplatinic acid hexahydrate.

The Co salt is cobalt (II) nitrate hexahydrate.

The percentage of the Pt content in the titanium source mole is 0.2-2%.

The Co content accounts for 0.2-2% of the titanium source mole.

The precursor feed rate is 2-6 ml / min.

The total flow of hydrogen and oxygen of the auxiliary flame is 1.2-1.8m3 / h, and the volume ratio of the hydrogen and oxygen is 1: 2-1: 4;

The external diffusion gas is oxygen or air, and the shear pressure at the shear atomizing nozzle is 0.1-0.25 MPa.

The maximum temperature of the flame zone is 2000 ° C.

The size of the composite particles is 10nm-30nm, and the mass fraction of the noble metal Pt in the titanium dioxide is 0.5-2%.

The sub-nanoscale precious metal Pt has a size of 0.5-1.2 nm, and is uniformly supported on the surface of the titanium dioxide particles.

The Pt-supported titanium dioxide composite particles at the sub-nanometer level exhibit high activity in CO-catalyzed oxidation.

Compared with the prior art, the present invention solves the difficulties encountered in the prior art and has the following beneficial effects:

(1) The present invention uses a one-step spray combustion technology to rapidly and continuously prepare sub-nanoscale Pt-supported titanium dioxide nanocomposite particles.

(2) In the present invention, the nucleation rate of Pt is increased by the method of adding a Co source, thereby reducing the particle size of Pt, which is different from the traditional method of reducing the particle size of Pt by reducing the load, and the relative load is obtained. Pt-supported particles with high and sub-nanometer size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an XRD curve of the product of Example 1. FIG.

FIG. 2 is a transmission electron microscope photograph of the product of Example 1. FIG.

FIG. 3 is an XRD curve of the product of Example 2. FIG.

FIG. 4 is a transmission electron microscope photograph of the product of Example 2. FIG.

Figure 5 Activity curves of catalyzed CO oxidation at different temperatures using a fixed bed reactor.

detailed description

The following uses the examples to further describe the content of the present invention, but the protection scope of the present invention is not limited to the examples. Other changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention are still included in the scope of protection of the present invention.

Example 1

1 g of solid H2Pt6.6H2O was dissolved in absolute ethanol and diluted with a 100 ml volumetric flask to a chloroplatinic acid ethanol solution with a Pt content of 3.76 g. Weigh 6.126g of tetrabutyl titanate, 0.0708g of Co (NO3) 2 · 6H2O, measure 3.780g of chloroplatinic acid ethanol solution into a beaker, and add 50.4ml of absolute ethanol solution to configure the precursor solution. Sonicate in ultrasound for 15 minutes to form a uniform and stable solution.

The syringe solution was used to pump the precursor solution into the capillary tube at a rate of 5 ml / min. The precursor solution was atomized into extremely small droplets by diffusing oxygen with a diffusion pressure of 0.15 MPa, and then entered the combustion reactor. The flow rate is 380L / h and the flow rate of auxiliary O2 is 1000L / h. The precursor reacts in the auxiliary flame field of hydrogen and oxygen to form sub-nanoscale Pt-loaded titanium dioxide composite particles, which are then assisted with glass fiber filter paper by a vacuum pump. The XRD curve collected in Figure 1 shows that the titanium dioxide support is a mixed crystal of anatase phase and rutile phase, and is mainly anatase phase, and no Pt or Co-related peaks appear in the XRD chart. The TEM image in Figure 2 shows that Pt is uniformly supported on the titanium dioxide matrix, and the size of the Pt particles is 0.5-1.2 nm.

Example 2

The syringe solution was used to pump the precursor solution into the capillary tube at a rate of 3 ml / min. The precursor solution was atomized into extremely small droplets by diffusing oxygen with a diffusion pressure of 0.18 MPa, and then entered the combustion reactor. The auxiliary H2 of the reactor The flow rate is 380L / h and the flow rate of auxiliary air is 1000L / h. The precursor reacts in the auxiliary flame field of hydrogen and air to form sub-nanoscale Pt-loaded titanium dioxide composite particles, which are then assisted with glass fiber filter paper by a vacuum pump. The XRD curve in Figure 1 shows that the titanium dioxide support is a mixed crystal of anatase phase and rutile phase, and is mainly anatase phase, and no Pt or Co-related peak appears in the XRD chart. The TEM image in Figure 2 shows that Pt is uniformly supported on the titanium dioxide matrix, and the size of the Pt particles is 0.5-1.2 nm.

The fixed-bed reactor was used to evaluate the catalytic oxidation performance of CO. The conversion rate at different temperatures was measured at a space velocity of 30,000 ml / (h · g). Figure 5 shows the catalytic oxidation of CO at different temperatures. Activity curve, the results show that it shows high activity at room temperature.

Claims

A nano-titanium dioxide composite particle, characterized in that an organic titanium source, a salt of Pt, and a salt of Co are used as precursors, are dissolved in an ethanol solvent, and are sprayed into a diffuser gas by a sprayer through a feeder to enter into In the reactor, in the auxiliary flame of hydrogen and oxygen, the atomized precursor reacts to generate sub-nanometer Pt-supported titanium dioxide composite particles;

The size of the composite particles is 10nm-30nm, and the mass fraction of Pt in the titanium dioxide is 0.5-2%;

The size of the sub-nanometer Pt is 0.5-1.2 nm, and the Pt is uniformly supported on the surface of the titanium dioxide particles.
A method for preparing nano titanium dioxide composite particles includes the following steps:

(1) Configure an ethanol solution of organic titanium source with a metal concentration of 0.1-0.9mol / L, and add Pt salt and Co salt in a weight ratio of 1: 0.1 ～ 1, and disperse it in ultrasonic for 10-20min to make it uniform and stable. Solution as precursor solution;

(2) The precursor is pumped into the reactor through a feeder under an external diffusion pressure, and a combustion reaction is performed under the auxiliary flame of hydrogen and oxygen to prepare sub-nanoscale Pt-supported titanium dioxide composite particles.
The nano titanium dioxide composite particles according to claim 1, wherein the organic titanium source is selected from one of tetrabutyl titanate, ethyl titanate, butyl titanate, and tetraisopropyl titanate. Species or several.
The nano titanium dioxide composite particle according to claim 1, wherein the Pt salt is one or more of chloroplatinic acid hydrate or chloroplatinic acid hexahydrate.
The nano titanium dioxide composite particle according to claim 1, wherein the Co salt is cobalt (II) nitrate hexahydrate.
The method according to claim 2, wherein the organic titanium source is selected from the group consisting of tetrabutyl titanate, ethyl titanate, butyl titanate, and tetraisopropyl titanate One or more of them.
The method according to claim 2, wherein the Pt salt is one or more of chloroplatinic acid hydrate or chloroplatinic acid hexahydrate.
The method for preparing nano titanium dioxide composite particles according to claim 2, wherein the Co salt is cobalt (II) nitrate hexahydrate.
The method for preparing nano titanium dioxide composite particles according to claim 2, wherein the percentage of the Pt content in the titanium source mole is 0.2-2%; and the Co content in the titanium source mole is 0.2-2%. The percentage is 0.2-2%.
The method for preparing nano titanium dioxide composite particles according to claim 2, wherein the precursor feed rate is 2-6 ml / min.
The method for preparing nano titanium dioxide composite particles according to claim 2, wherein the total flow of hydrogen and oxygen in the auxiliary flame is 1.2-1.8 m3 / h, and the volume ratio of the hydrogen and oxygen is 1 : 2-1: 4.
The method for preparing nano titanium dioxide composite particles according to claim 2, wherein the external diffusion gas is oxygen or air, and the shear pressure at the shear atomizing nozzle is 0.1-0.25 MPa.