CN111372679A

CN111372679A - Bimetallic composite catalyst for catalytic oxidation of organic pollutants

Info

Publication number: CN111372679A
Application number: CN201880071524.6A
Authority: CN
Inventors: 胡晓; 钟子宜; 王朋华; 梁颖南
Original assignee: Nanyang Technological University
Current assignee: Nanyang Technological University
Priority date: 2017-11-02
Filing date: 2018-11-02
Publication date: 2020-07-03
Also published as: WO2019088928A1

Abstract

Disclosed herein is a catalytic composite comprising: including Na₂Mo₄O₁₃And α -MoO₃A metal oxide matrix of the mixture of (a); and a deposit of elemental metal nanoparticles, wherein each elemental metal nanoparticle consists of or is an alloy of gold or palladium. Also disclosed herein are processes for preparing the sameA method for the production of a material, and the use of the composite material for the catalytic wet air oxidation of organic materials.

Description

Bimetallic composite catalyst for catalytic oxidation of organic pollutants

Technical Field

The present invention relates to a catalytic composite material comprising a metal oxide matrix and a deposit of metal nanoparticles, and to the use of said material for the catalytic wet air oxidation of organic materials under mild reaction conditions.

Background

The listing or discussion of a prior-published document in this specification should not necessarily be taken as an admission that the document is part of the state of the art or is common general knowledge.

Environmental pollution is one of the major concerns and challenges facing the world today. In the case of water pollution, a large amount of industrial wastewater and volatile organic pollutants are produced from the petrochemical, textile, pharmaceutical, chemical and automotive industries, all of which can be harmful to the environment. Therefore, these industrial waste waters and waste streams must be properly treated to remove various toxic, refractory and/or volatile organic compounds before they can be discharged into the surrounding environment. In addition, national and/or local governments have implemented increasingly stringent regulations that only allow the presence of small amounts of organic contaminants in industrial and other waste stream effluents, which inevitably motivate interest in wastewater treatment.

One of the most interesting class of compounds is organic dyes, which represent a large class of refractory organic pollutants. It is estimated that the worldwide industry used 10,000 different dyes and pigments in 2003 and produced 7x10⁵Synthetic dyes (H.Zollinger, colour chemistry: synthesis, properties and applications of organic dyes and pigments (Co)lor chemistry Synthesis, Properties and applications of organic dies and pigments), revision 3, Wiley-VCH, Weinheim, Zurich Switzerland, (2003) 637. About 1-20% of the total global dye production is discharged into the aquatic environment during application, which may cause serious damage to the photosynthetic activity and human health of aquatic plants: (http://www.food-info.net/uk/colour/azo.htm(ii) a M.vakili, et al, carbohydr.polym., 2014, 113, 115-; m.yuan, et al, appl.surf.sci., 2011, 257, 7913-.

To date, a number of processes have been developed for treating wastewater. These processes include bioprocessing, thermal decomposition, adsorption, membrane processes, and Advanced Oxidation Processes (AOPs). However, such processes have their own limitations. For example, biological processes are not suitable for the treatment of non-biodegradable and highly toxic compounds, whereas thermal decomposition is generally only used for high Chemical Oxygen Demand (COD) industrial wastewater (typical COD)>10g L^-1) Consisting of total combustion at temperatures above 1000 ℃. Furthermore, thermal decomposition is a very energy-consuming process that produces ash, solid waste and NO-containing_x、SO_xAnd toxic fumes of dioxins. Adsorption and membrane processes are very efficient but require a series of pre-and post-treatments. Although conventional chemical oxidation processes can be carried out at room temperature, the use of expensive and environmentally unfriendly oxidizing agents, such as chlorine, chlorine dioxide or potassium permanganate, is required. Most AOPs rely on the use of highly reactive radicals generated by ultraviolet activated oxygen (photocatalytic process), ozone (ozonation process), or hydrogen peroxide (wet peroxide oxidation and Fenton process). However, the cost of treating industrial wastewater with AOPs such as ozonation process and Fenton process increases in proportion to COD, and may become costly at high COD.

The Catalytic Wet Air Oxidation (CWAO) process is an AOP and has recently received much attention due to its relatively low cost of using air as an oxidant. However, most reported CWAO processes require high reaction temperatures and pressures (80-180 ℃ and 1-5MPa), which are considered undesirable (l.mingming, et al, Recent pat.chem.eng., 2013, 6, 79-86). These harsh reaction conditions not only increase capital investment and operating costs, but also cause severe leaching of the catalyst, which can lead to catalyst deactivation and further contamination of the treated wastewater.

Recently, Xu and colleagues reported the degradation of red GTL by CWAO over Mo-Zn-Al-O catalysts at room temperature and atmospheric pressure (y.xu, et Al, environ.sci.technol., 2012,46, 2856-. More active catalyst systems using Na have been reported by Zhang et al₂Mo₄O₁₃/α-MoO₃The composite catalyst degrades red GTL (z.zhang, et al, sci.rep., 2014, 4, 6797-. Although these catalysts have a high catalytic activity, they have leaching problems and appear to work only with a few dyes, which therefore limits their application.

In view of the above, there remains a need for more active and stable catalysts for the degradation of organic pollutants by CWAO. More importantly, these catalysts must be able to exhibit high catalytic activity under mild or ambient reaction conditions. In addition, the catalysts should have minimal or no leaching problems, so that they have a long service life and can be reused many times. Preferably, the desired catalyst should be suitable for use in areas where there are significant differences in climate and natural conditions (e.g., where the temperature difference between day and night temperatures and/or between different seasons is large), or in remote and less developed areas.

Disclosure of Invention

In a first aspect of the invention, there is provided a catalytic composite comprising:

including Na₂Mo₄O₁₃And α -MoO₃The metal oxide matrix of the mixture of (a), wherein the matrix is in the form of nanofibers; and

a deposit of elemental metal nanoparticles, wherein each elemental metal nanoparticle consists of or is an alloy of gold or palladium, wherein

The elemental metal nanoparticles are deposited in a total amount of from 0.1 to 1.2 wt% relative to the total weight of the metal oxide matrix; and is

The weight to weight ratio of elemental gold to elemental palladium in the composite material is from 1:3 to 3: 1.

In an embodiment of the first aspect of the invention:

(ia) elemental metal nanoparticles may be deposited in a total amount of from 0.5 to 1.1 wt%, for example from 0.75 to 1 wt%, relative to the total weight of the metal oxide matrix;

(ib) the weight to weight ratio of elemental gold to elemental palladium in the composite material may be from 0.5:1 to 2:1, e.g. 1: 1;

(ic) the metal oxide matrix nanofibers may have a length of from 500 to 5,000nm and a diameter of from 50 to 500nm, such as a length of from 800 to 4,000nm and a diameter of from 75 to 400nm, for example the metal oxide matrix nanofibers may have a length of from 900 to 3,700nm and a diameter of from 100 to 350 nm;

(id) Na in the metal oxide matrix₂Mo₄O₁₃And α -MoO₃The weight to weight ratio of (a) may be from 0.3:1 to 0.7:1, for example from 0.35:1 to 0.6: 1;

(ie) the elemental metal nanoparticles may have a diameter of from 1 to 50nm, such as from 5 to 30nm, such as from 7 to 25 nm.

In a second aspect of the invention there is provided the use of a catalytic composite material as described in the first aspect of the invention and any technically reasonable combination of embodiments thereof in the catalytic wet air oxidation of organic materials. In an embodiment of the second aspect of the present invention, the organic material may be one or more selected from the group of pharmaceutical compounds, pesticides, and more specifically organic dyes (e.g. one or more of safranin O, methylene blue and brilliant green, or other organic compounds with similar structures).

In a third aspect of the present invention there is provided a method of catalytic wet air oxidation of organic material, the method comprising the steps of: contacting an organic material with any technically reasonable combination of the catalytic composite material according to the first aspect of the present invention and embodiments thereof in an aqueous environment supplied with a gas stream comprising oxygen to oxidize the organic material.

In an embodiment of the third aspect of the invention:

(ai) the organic material may be one or more selected from the group of pharmaceutical compounds, pesticides, and more specifically organic dyes (e.g., one or more of safranin O, methylene blue, and brilliant green, or other organic contaminants having similar structures);

(aii) the weight to weight ratio of the catalytic composite to the organic material may be from 1x10^-41 to 10:1, e.g. from 1x10^-31 to 5:1, for example from 0.1:1 to 1: 1;

(aiii) the process may be carried out at a temperature of from 0 to 75 ℃, such as from 2.5 to 45 ℃, such as from 5 to 30 ℃, such as 25 ℃.

In a fourth aspect of the invention, there is provided a method of forming a catalytic composite, the method comprising the steps of:

(a) providing a solution containing Na₂Mo₄O₁₃And α -MoO₃The metal oxide matrix of the mixture of (a), wherein the matrix is in the form of nanofibers;

(b) suspending the substrate in a solvent and then adding a source of elemental metal to form a first mixture;

(c) adding a ligand and a reducing agent to the first mixture and aging for a first period of time to form a ligand coated product;

(d) collecting the ligand coated product, drying it and allowing it to be at a calcination temperature of 250 to 550 ℃ for a second period of time to form the catalytic composite, wherein:

the element metal source consists of an element gold source and an element palladium source;

the elemental metal source deposits elemental metal nanoparticles on the surface of the substrate in a total amount of from 0.1 to 1.2 wt% relative to the total weight of the metal oxide substrate; and is

In an embodiment of the fourth aspect of the invention:

the (bi) elemental metal nanoparticles may be deposited in a total amount of from 0.5 to 1.1 wt%, for example from 0.75 to 1 wt%, relative to the total weight of the metal oxide matrix;

(bii) the weight to weight ratio of elemental gold to elemental palladium in the composite material may be from 0.5:1 to 2:1, for example 1: 1;

(biii) the metal oxide matrix nanofibers may have a length of from 3,000 to 35,000nm and a diameter of from 800 to 3,100nm, such as a length of from 3,500 to 26,000nm and a diameter of from 825 to 2,700nm, for example, the metal oxide matrix nanofibers may have a length of from 3,750 to 18,000nm and a diameter of from 850 to 2,500 nm;

(biv) Na in the Metal oxide matrix₂Mo₄O₁₃And α -MoO₃The weight to weight ratio of (a) may be from 0.3:1 to 0.7:1, for example from 0.35:1 to 0.6: 1;

(bv) the elemental metal nanoparticles may have a diameter of from 1 to 50nm, such as from 5 to 30nm, such as from 7 to 25 nm;

(bvi) subjecting the metal oxide substrate to a calcination temperature of from 250 to 400 ℃, e.g., 300 ℃, prior to use in step (a).

(bvii) subjecting the ligand coated product to a calcination temperature of from 300 to 450 ℃ for a second period of time to form the catalytic composite.

Drawings

Figure 1 depicts the following XRD patterns: (a) NM substrates calcined at different temperatures; (b) Au-Pd (1:1)/NM catalyst of the invention calcined at a different temperature than the uncalcined sample; and (c) Au-Pd/NM catalysts of the invention calcined at 400 ℃ with different Au to Pd ratios.

Fig. 2 depicts FESEM images of: (a-b) NM 300; and (c-d) Au-Pd (1:1)/NM-400 of the present invention.

FIG. 3 depicts (a) TEM and (b) HRTEM images of Au-Pd (1:1)/NM-400 obtained in an initial study; (c) HRTEM image of Au-Pd (1:1)/NM-400 obtained after optimization of conditions (which corresponds to the TEM image of the inset in FIG. 4 (e)); and (d) DRS spectra of NM300, Au/NM-400, Pd/NM-400 and Au-Pd (1: 1)/NM-400.

FIG. 4 depicts TEM, FESEM images and EDX elemental mapping of Au-Pd (1:1)/NM-400 of the present invention: (a) TEM image of Au-Pd (1:1)/NM-400 obtained in the initial study; (b-d) elemental mapping corresponding to Pd, Au and Mo for the sample in (a); (e) FESEM image of Au-Pd (1:1)/NM-400 obtained after optimizing the conditions, inset shows TEM image of the sample; and (f) elemental mapping of Mo, O, Au and Pd, corresponding to the TEM image of the inset in (e).

FIG. 5 depicts XPS spectra of NM300 and Au-Pd (1:1)/NM-400 of the present invention, whose binding energies correspond to (a) Mo 3 d; (b) o1 s; (c) au 4 f; and (d) Pd3 d.

Fig. 6 depicts the effect of calcination temperature on the catalytic activity of the catalyst support (NM substrate), where (a) and (b) represent initial and optimized results, respectively. At 23 deg.C under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The experiment was carried out for a reaction time of 2 h.

FIG. 7 depicts the effect of calcination temperature on the catalytic activity of the Au-Pd (1:1)/NM catalyst of the present invention, where (a) and (b) represent initial and optimized results, respectively. At 23 deg.C under atmospheric pressure, at 100mg L^-10.5gL of initial dye concentration^-1The experiment was carried out for a reaction time of 2 h.

FIG. 8 depicts the color change of the dye using Au-Pd (1:1)/NM-400 of the present invention compared to NM 300. At 23 ℃ under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The experiment was performed with the catalyst concentration of (a).

FIG. 9 depicts the effect of Au-Pd mass ratio on the catalytic activity of the Au-Pd/NM catalyst of the present invention, where (a) and (b) represent initial and optimized results, respectively. At 23 ℃ under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The experiment was carried out for a reaction time of 2 h.

Fig. 10 depicts Au — Pd (1:1) the effect of/NM-400 concentration on dye removal efficiency, where (a) and (b) represent initial and optimized results, respectively. At 23 ℃ under atmospheric pressure, at 100mg L^-1At 0.1gL of each of the initial dye concentrations^-1、0.2g L^-1And 0.5g L^-1The experiment was carried out for a reaction time of 2 h. For a catalyst concentration of 1.0g L^-1The reaction time was 1 h.

FIG. 11 depicts: (a-c) at 300mg L each^-1、400mg L^-1And 600mg L^-1Initial studies on the catalytic activity of the inventive NM300, Au-Pd (1:1)/NM-400 and Au-Pd (1:1) NM-500 in the presence of the dye of (1); and (d-f) at 300mg L each^-1、400mg L^-1And 600mg L^-1The optimization of the catalytic activity of NM300 and Au-Pd (1:1)/NM-400 of the present invention was investigated in the presence of the dye of (1). At 23 ℃ under atmospheric pressure at 0.5g L^-1The experiment was carried out for a reaction time of 2 h.

FIG. 12 depicts the decolorization over time of BG at various concentrations using NM300 and Au-Pd (1:1)/NM-400 of the present invention. The experiment was carried out at 23 ℃ at atmospheric pressure with a catalyst concentration of 0.5g/L for a reaction time of 2 hours.

FIG. 13 depicts the catalytic activity of NM300 and Au-Pd (1:1)/NM-400 of the present invention in removing dye at reaction temperatures of 35 ℃ and 45 ℃ respectively: (a and b) initial studies at 35 ℃ and 45 ℃ respectively; and (c and d) optimization studies at 35 ℃ and 45 ℃ respectively. At atmospheric pressure, at 600mg L^-10.5g L initial dye concentration^-1The experiment was carried out for a reaction time of 2 h.

FIG. 14 depicts the catalytic activity of NM300 and Au-Pd (1:1)/NM-400 of the present invention in removing dye at reaction temperatures of 5 ℃ and 10 ℃: (a and b) initial studies were performed at 5 ℃ for 2h and 24h, respectively; (c and d) initial studies were performed at 10 ℃ for 2h and 24h, respectively; and (e-g) optimization studies were performed at 5 ℃ for 2h, 24h and 48h, respectively. Initial study (a-d) was at 100mg L^-1Was performed at an initial dye concentration of 300mg L, and the optimization study (e-g) was performed^-1Is performed at the initial dye concentration of (a). All experiments were carried out at 0.5g L at atmospheric pressure^-1Of the catalyst concentration of (a).

FIG. 15 depicts the Au-Pd (1:1)/NM-400 after regeneration in various solutions, after degradation: (a) SO; (b) MB; and (c) reusability and stability testing in BG. At 23 ℃ under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The experiment was carried out for 2 h.

Fig. 16 depicts: (a) the dye removal efficiency of Au-Pd (1:1)/NM-400 (2%) was compared to Au-Pd (1:1)/NM-400 with a metal loading of 1%. At 23 ℃ under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The experiment was carried out for 2 hours; and (b) TEM images of Au-Pd (1:1)/NM-400 (2%) samples.

FIG. 17 depicts the SO degradation kinetics of NM300, Au/NM-400, Pd/NM-400 and Au-Pd (1:1)/NM-400 of the present invention: (a) UV-Vis spectra of SO samples treated with the respective catalysts at different reaction times; (b) C/C₀As a function of reaction time, where C denotes the dye concentration at each time point, and C₀Indicates the initial dye concentration. At 23 ℃ under atmospheric pressure at 20mg L^-10.1g L initial dye concentration^-1The experiment was performed with the catalyst concentration of (a).

FIG. 18 depicts the MB degradation kinetics of NM300, Au/NM-400, Pd/NM-400 and Au-Pd (1:1)/NM-400 of the present invention: (a) UV-Vis spectra of MB samples treated with the respective catalysts at different reaction times; (b) C/C₀As a function of reaction time, where C denotes the dye concentration at each time point, and C₀Indicates the initial dye concentration. At 23 ℃ under atmospheric pressure at 20mg L^-10.1g L initial dye concentration^-1The experiment was performed with the catalyst concentration of (a).

FIG. 19 depicts the BG degradation kinetics of NM300, Au/NM-400, Pd/NM-400 and Au-Pd (1:1)/NM-400 of the present invention: (a) UV-Vis spectra of BG samples treated with the respective catalysts at different reaction times; (b) C/C₀As a reactionPlot of time as a function of time, where C represents the dye concentration at each time point, and C₀Indicates the initial dye concentration. At 23 ℃ under atmospheric pressure at 20mg L^-10.1g L initial dye concentration^-1The experiment was performed with the catalyst concentration of (a).

FIG. 20 depicts the proposed catalytic mechanism for dye degradation by using Au-Pd (1: 1)/NM-400: degradation of (a) SO, (b) MB and (c) BG in the presence of a quencher. At 23 ℃ under atmospheric pressure at 20mg L^-10.1g L initial dye concentration^-1The experiment was conducted with the catalyst concentration of (a); (d) schematic diagram of the mechanism of dye degradation on the proposed bimetallic composite catalyst.

FIG. 21 depicts a schematic of the introduction of a bimetallic composite catalyst (40) into a wastewater treatment system using: (a) a suspension of catalyst; and (b) a catalyst immobilized on the porous support (100).

Detailed Description

It was surprisingly found that a catalyst with improved activity can be obtained by adding small amounts of two noble metals (gold and palladium) as nanoparticles to the surface of the catalytic system. Accordingly, there is provided a catalytic composite comprising:

Surprisingly, the inclusion of only 0.1 to 1.2 wt% of elemental metal relative to the total weight of the matrix material provides surprising catalytic activity. In contrast, conventional systems use higher weight percentages of metals (e.g., 2 to 3 wt%), but it is shown herein that using such high metal loadings in current systems results in a significant loss of catalytic activity (see examples section).

In the embodiments herein, the term "comprising" may be interpreted as requiring the presence of the stated features but not limiting the presence of other features. Alternatively, the term "comprising" may also refer to the presence of only the listed components/features (e.g., "comprising" may be replaced by the phrase "consisting of or" consisting essentially of). It is expressly contemplated that broader and narrower interpretations may apply to all aspects and embodiments of the invention. In other words, the word "comprising" and its synonyms may be replaced by the phrase "consisting of … … (consests of)" or the phrase "consisting essentially of … … (consensulacency of)" or its synonyms, and vice versa.

As used herein, the term "nanofiber" refers to a material provided in the form of a fiber having a diameter in the nanometer range.

The metal oxide matrix is composed of Na in the form of nanofibers₂Mo₄O₁₃And α -MoO₃May be obtained by any suitable method, for example by subjecting a molybdenum oxide precursor (e.g., (NH) under hydrothermal reaction conditions₄)₆Mo₇O₂₄·4H₂O) with a suitable sodium source (e.g. NaNO)₃) Reacted and then calcined. Any suitable Na may be used in the metal oxide matrix₂Mo₄O₁₃And α -MoO₃Weight to weight ratio of (a). For example, Na in the metal oxide matrix₂Mo₄O₁₃And α -MoO₃May be from 0.3:1 to 0.7:1 or from 0.35:1 to 0.6: 1. the calcination temperature applied to the intermediate material may affect α -MoO in the matrix material₃For example, a 300 ℃ calcination temperature for 5 hours may provide a catalyst having a lower α -MoO₃The use of the specific materials, while a calcination temperature of 600 ℃ for 5 hours, can provide a material with much higher α -MoO₃The material of the ratio.

As discussed in more detail below, the metal oxide matrix material is then subjected to a second calcination step in forming the catalytic composite defined above. This second calcination step can further alter the physical properties (i.e., length and diameter) of the composite. For example, the freshly prepared metal oxide matrix may have a length of from 3,000 to 35,000nm and a diameter of from 800 to 3,100nm, such as a length of from 3,500 to 26,000nm and a diameter of from 825 to 2,700nm, (e.g., a length of from 3,750 to 18,000nm and a diameter of from 850 to 2,500 nm), prior to use in forming the catalytic composite. However, when the material has been subjected to subsequent calcination and/or reduction steps to provide the desired catalytic composite, the size of the nanofibers is reduced. For example, the resulting metal oxide matrix nanofibers may have a length of from 500 to 5,000nm and a diameter of from 50 to 500nm, such as a length of from 800 to 4,000nm and a diameter of from 75 to 400nm, for example the metal oxide matrix nanofibers may have a length of from 900 to 3,700nm and a diameter of from 100 to 350 nm.

Unless expressly stated otherwise, as used herein, the endpoints of the relevant ranges can be combined together in any suitable manner to form other ranges that are also specifically contemplated. For example, in the newly prepared metal oxide matrix described above, the following length ranges can be obtained: 3,000 to 3,500nm, 3,000 to 3,750nm, 3,000 to 18,000nm, 3,000 to 26,000nm, 3,000 to 35,000nm, 3,500 to 3,750nm, 3,500 to 18,000nm, 3,500 to 26,000nm, 3,500 to 35,000nm, 3,750 to 18,000nm, 3,750 to 26,000nm, 3,750 to 35,000nm, 18,000 to 26,000nm, 18,000 to 35,000nm, and 26,000 to 35,000 nm. Furthermore, any of these length ranges may be combined with any of the correspondingly derived diameter ranges-the same applies to any grouping of the link ranges mentioned herein.

As used herein, "elemental metal" means that the metal is provided as the element itself. Thus, "elemental gold" refers to gold in elemental form, which may be substantially pure (e.g., > 90% pure, e.g., > 95% pure, e.g., > 99.999% pure), and "elemental palladium" may be construed accordingly. Elemental metal nanoparticles may be formed substantially from one metal or another (i.e., gold or palladium), but nanoparticles formed from alloys of gold and palladium may also be formed. Nanoparticles formed from an alloy of gold and palladium may comprise any suitable amount of gold and palladium, for example from 0.5 wt% gold and 99.5 wt% palladium to 99.5 wt% gold and 0.5 wt% palladium.

As described above, the elemental metal nanoparticles may be deposited in a total amount of from 0.1% to 1.2 wt% relative to the total weight of the metal oxide matrix. For example, the elemental metal nanoparticles may be deposited in a total amount of from 0.5% to 1.1 wt% relative to the total weight of the metal oxide matrix. In particular embodiments of the present invention, the elemental metal nanoparticles may be deposited in a total amount of from 0.75% to 1 wt% relative to the total weight of the metal oxide matrix. As noted above, it has been surprisingly found that the use of such small amounts of elemental metal nanoparticles of gold and/or palladium provides a significant improvement in catalytic performance.

Any suitable weight to weight ratio of elemental gold to elemental palladium may be used in the composites disclosed herein. For example, the weight to weight ratio of elemental gold to elemental palladium in the composite material may be from 0.5:1 to 2:1, such as 1: 1. The elemental metal nanoparticles can have any suitable nanoparticle diameter. For example, the elemental metal nanoparticles may have a diameter of from 1 to 50nm, such as from 5 to 30nm, such as from 7 to 25 nm.

The catalytic composite disclosed herein is suitable for use in the decomposition of organic materials. For example, pharmaceutical compounds, pesticides and especially organic dyes. In certain embodiments, the decomposable organic material comprises at least one aromatic or heteroaromatic ring (e.g., at least one benzene ring). Thus, the use of a catalytic composite material as described above in the catalytic wet air oxidation of organic materials is disclosed.

As used herein, the term "at least one aromatic or heteroaromatic ring" will be understood to cover a monocyclic or fused ring system comprising a ring component having 4n +2 pi-electrons. Each ring or ring system may contain from 5 to 20 atoms, for example from 5 to 10 atoms or 6 atoms. Examples of aromatic ring systems include benzene and naphthalene. Examples of aromatic heterocycles include pyridine and quinoline. In particular embodiments of the invention that may be mentioned herein, the organic material may be an organic material comprising at least one aromatic ring, such as benzene.

Also disclosed is a method of catalytic wet air oxidation of an organic material, the method comprising the steps of: contacting an organic material with any technically reasonable combination of the catalytic composite and embodiments thereof described above in an aqueous environment supplied with a gas stream comprising oxygen to oxidize the organic material.

Wet Air Oxidation (WAO) is a process that uses oxygen in air (or an oxygen-rich stream) to oxidize organic matter at high temperatures (200-. Under these severe reaction conditions, the organic waste is decomposed into intermediates (e.g., carboxylic acids and other low molecular weight organic compounds) and end products (e.g., CO) by a free radical mechanism₂And water). At about 250 c, almost all organic compounds can be eliminated, except for acetic acid and propionic acid, which require temperatures of about 320 c to decompose. It will be appreciated that WAO requires the use of specialized equipment, resulting in a large capital investment in suitable plants and a large ongoing operating cost. Catalytic Wet Air Oxidation (CWAO) overcomes these problems by reducing the temperature to more moderate levels (typically 125 to 200 ℃, with a maximum pressure of 5 MPa). Ideally, the CWAO would be able to operate at ambient (or sub-ambient) temperature and pressure.

The uses and methods described herein achieve desirable conditions because the CWAO can be performed at ambient pressure and at temperatures substantially lower than required for the WAO. For example, the process may be operated at a temperature of from 0 to 75 ℃, such as from 2.5 to 45 ℃, for example from 5 to 30 ℃, such as 25 ℃. Notably, the composite materials disclosed herein are capable of performing a CWAO process at a temperature of about 0 ℃ or about 25 ℃ at standard pressure, thereby allowing the process to be operated without significant capital investment costs and minimizing the ongoing costs associated with operating the process.

It will be noted from the above that the use and method described above can be used for the oxidation of any organic material. For example, the organic material may be an organic dye-but the process is not limited to organic dyes. Examples of organic dyes that may be mentioned herein include, but are not limited to, safranin O, methylene blue, brilliant green and other organic dyes having similar structures (e.g., having at least one aromatic or heteroaromatic ring, such as a benzene ring). Examples of other organic materials that can be oxidized by the methods disclosed herein include, but are not limited to, pharmaceutical compounds and pesticide compounds, such as pharmaceutical compounds and pesticide compounds containing at least one benzene ring.

As used herein, the term "aqueous environment" with respect to the CWAO process means that the organic material and the catalytic composite are in a solvent consisting essentially of water (e.g., water comprises from 90 to 100 wt%, such as greater than 95 wt%, greater than 99 wt%, such as greater than 99.999 wt% of the solvent). If present, the organic solvent is not considered to be part of the solvent, but is considered to be part of the organic material.

The CWAO process discussed herein requires that a gas stream comprising oxygen is supplied to a mixture of solvent, organic material and catalytic composite material to achieve the desired oxidation. The gas may be any gas containing oxygen, such as air or pure oxygen (e.g. from a gas cylinder). The amount and flow rate of gas required can be readily determined by those skilled in the art using their knowledge and trial and error.

It will be appreciated that the catalytic composite may be used in suitable amounts to carry out the reaction. As used herein, "catalyst" as used in general terms refers to a material that causes or accelerates a chemical reaction without itself being affected. In other words, the catalytic composite may be used multiple times, but may be present in a sub-stoichiometric amount relative to the organic material to be oxidized, or it may be present in excess. For example, the weight to weight ratio of catalytic composite to organic material may be from 1x10 ^-41 to 10:1, e.g. from 1x10 ^-31 to 5:1, for example from 0.1:1 to 1: 1.

It will be appreciated that a catalytic composite must be prepared to function as a catalyst. This may be achieved by any suitable means, such as a method of forming a catalytic composite comprising the steps of:

(d) collecting the ligand coated product, drying it and subjecting it to a calcination temperature of from 250 to 550 ℃ for a second period of time to form the catalytic composite, wherein:

the elemental metal source deposits elemental metal nanoparticles on the surface of the substrate in a total amount of from 0.1 to 1.2 wt% relative to the total weight of the metal oxide substrate; and

In certain embodiments that may be mentioned herein, in step (d), the ligand coated product may be subjected to a calcination temperature of from 300 to 450 ℃.

The physical properties of the metal oxide matrix provided in step (a) (i.e., the freshly prepared metal oxide material) and its preparation are discussed above and in the examples section below. As described above, the metal oxide substrate provided in step (a) above may be prepared using a process comprising a first calcination step. The first calcination step may be carried out at a calcination temperature of from 250 to 400 ℃, for example 300 ℃, prior to use in step (a).

It will be appreciated that the physical properties and amounts of the component materials forming the catalytic composite described herein are the same as those described above. For example:

(ci) the elemental metal nanoparticles may be deposited in a total amount of from 0.5 to 1.1 wt%, for example from 0.75 to 1 wt%, relative to the total weight of the metal oxide matrix; the weight to weight ratio of elemental gold to elemental palladium in the composite material may be from 0.5:1 to 2:1, e.g., 1: 1;

(cii) Na in the Metal oxide matrix₂Mo₄O₁₃And α -MoO₃The weight to weight ratio of (a) may be from 0.3:1 to 0.7:1, for example from 0.35:1 to 0.6: 1;

(ciii) the elemental metal nanoparticles may have a diameter of from 1 to 50nm, for example from 5 to 30nm, for example from 7 to 25 nm.

In step (b) of the above process, any suitable solvent, any source of elemental gold, and any source of elemental palladium may be used. Examples of suitable solvents include, but are not limited to, water and compatible organic solvents, although the use of water alone is preferred. Examples of suitable elemental gold sources include, but are not limited to, AuCl₃Or more specifically HAuCl₄And hydrates thereof. Examples of suitable elemental palladium sources include, but are not limited to, Pd (NO)₃)₂、H₂PdCl₄、Na₂PdCl₄Or more specifically PdCl₂、PdBr₂And the like.

In step (c) of the above process, any suitable ligand and reducing agent may be used to form the ligand coated product. The ligand should be one that can form a complex with the gold metal ion and palladium metal ion present in the respective elemental metal sources. Examples of suitable ligands include, but are not limited to, citrates (e.g., potassium citrate or more specifically sodium citrate), and the like. The reducing agent should be capable of reducing the gold and palladium ions to their respective elemental metals. Examples of suitable reducing agents include, but are not limited to, hydroiodic acid, or more specifically, sodium borohydride. The first period of time can be any suitable period of time to ensure formation of the ligand-coated product (i.e., elemental metal nanoparticles deposited on the substrate but coated with the ligand). Examples of suitable time periods include, but are not limited to, time periods from 30 minutes to 24 hours, such as from 45 minutes to 1.5 hours, such as about 1 hour.

In step (b)In step (d), the calcination temperature may be controlled to maintain Na in the calcined substrate₂Mo₄O₁₃The ratio of (a) to (b) is in accordance with the above ratio. Thus, a suitable temperature range for calcination may be from 250 to 550 ℃, e.g., from 300 to 450 ℃. The calcination time may be a sufficient period of time to ensure substantial removal of the ligand coating. Examples of suitable time periods include, but are not limited to, time periods from 30 minutes to 1.5 hours, such as from 45 minutes to 1.25 hours, such as about 1 hour, at the calcination temperatures discussed immediately above.

Further aspects and embodiments of the invention will now be discussed with respect to the following non-limiting examples.

Examples

Material

Ammonium molybdate tetrahydrate ((NH) from Sigma-Aldrich₄)₆Mo₇O₂₄·4H₂O, 99%), sodium nitrate (NaNO)₃99%), palladium chloride (PdCl)₂99%), trisodium citrate dihydrate (Na)₃C₆H₅O₇·2H₂O, 99%), sodium hydroxide (NaOH, 98%), hydrochloric acid (HCl, 37%), acetone (CH)₃COCH₃99.9%), 1, 4-Benzoquinone (BQ), sodium azide (NaN)₃99.5%), dimethyl sulfoxide (DMSO, 99.7%) and Brilliant Green (BG). Tetrachloroauric acid trihydrate (HAuCl) from VWR Singapore personal Co., Ltd₄·3H₂O, 99%), sodium borohydride (NaBH)₄98%), Safranin O (SO), and Methylene Blue (MB). All chemicals were used as received without further purification. Millipore co.milliq (MQ) water with a resistivity of 18.2M Ω cm was used throughout the study unless otherwise noted.

General procedure

On a Bruker D8 ADVANCE X-ray diffractometer, in the 2 theta range of 5-80 DEG, with radiation of Cu K α

An X-ray diffraction (XRD) pattern was measured. With JSM 7200F Field Emission Scanning Electron Microscope (FESEM) and JEOL-2100F transmission electron microscope X-ray energy spectrometer (TEM-EDX)The micro-morphology and structure of the nanocomposite was observed. Using a gas-liquid mixture equipped with BaSO₄Perkin Elmer Lambda 35UV-Vis Spectrophotometer for integrating sphere assemblies for reflectance standards UV-Vis Diffuse Reflectance Spectra (DRS) was obtained using the Brunauer-Emmett-Teller (BET) equation, using a Quantachrome Autosorb-1 instrument, at 77K, calculating the specific surface area the catalyst surface chemistry and bonding state was analyzed by X-ray photoelectron Spectroscopy (XPS) on a Kratos AXIS Supra spectrometer using a monochromated Al K α (1486.71eV) X-ray source, all spectra were calibrated with indeterminate carbon at 284.8 eV.

Synthesis of catalyst support substrate

In principle, stable metal oxides and their composites with other stable materials can be used as matrices for bimetallic composite catalysts. Due to its reported catalytic activity, Na₂MO₄O₁₃/α-MoO₃(NM) was chosen as an example substrate for the composite catalyst and therefore also can be used as a benchmark for comparison. NM matrices were synthesized using a hydrothermal method modified from the reported method (z. zhang, et al, sci. rep.2014, 4, 6797-.

Generally, 5.296g (NH)₄)₆Mo₇O₂₄·4H₂O was dissolved in 30mL MQ water to form a clear solution at 50 deg.C, then 0.408g NaNO was added₃And mixed for 30 minutes under magnetic stirring. Subsequently, the resulting solution was transferred to a 50mL stainless steel autoclave lined with polytetrafluoroethylene and subjected to hydrothermal treatment at 120 ℃ for 18 h. The resulting precipitate was separated by centrifugation, washed thoroughly with MQ water, and then dried in an oven at 60 ℃ overnight. After grinding the precipitate into a fine powder, the obtained samples were calcined in a muffle furnace under an air atmosphere at 300 ℃, 400 ℃,500 ℃ and 600 ℃ for 5h, respectively, to obtain final products, which are denoted as NM300, NM400, NM500 and NM600, respectively.

Another example of a metal oxide substrate that can be used as a catalyst support is a FeMgAl mixed oxide catalyst. The mixed oxide of FeMgAl is synthesized by an auto-combustion method (

M.h., et al, j.mol.catal.a-chem.2015, 398, 358-. Typically, the metal oxide precursors (iron (III) nitrate, magnesium nitrate and aluminum nitrate) and glycine were dissolved in 20mL of water and mixed for 30 min. The mixture was then evaporated at 90-100 ℃ to form a gel. The gel was then heated at 500 ℃ for 2h and then at 700 ℃ for 4h to produce a FeMgAl mixed oxide. However, preliminary studies have shown that the catalytic activity of the mixed oxides is not good, since the dye color removal is not significant.

General method for evaluating the catalytic activity of a synthesized catalyst

The catalytic activity of the synthesized catalysts was evaluated with three dyes (SO, MB and BG) as target contaminants. In a glass reactor with a capacity of 250mL, at ambient conditions, at 1.2L min^-1Air was pumped into the bottom of the suspension and the degradation of the dye on the synthesized catalyst was studied.

In a typical experiment, the catalyst concentration was 0.5g L in MQ water^-1And an initial single initial dye concentration of 100 to 600mg L^-1In the meantime. For dye degradation kinetics studies, 0.1g L was used^-1Catalyst concentration and 20mg L^-1The initial single original dye concentration. During catalysis, sample aliquots were collected at appropriate time intervals and filtered for analysis. The dye concentration was measured at the dye's absorption maximum wavelength (625 nm for BG, 517nm for SO, and 664nm for MB) using a UV-2600UV-Vis spectrophotometer. Changes in Total Organic Carbon (TOC) were measured with a Shimadzu ASI-V TOC analyzer. In addition, N is used before adding catalyst₂The dye solution was purged for 30min and N was added after the catalyst was added₂Continuously injecting into the bottom of the suspension to adsorb the dye on the catalyst to prevent dissolution in H₂O of O₂The influence of (c).

To investigate the reusability of the synthesized catalyst, the suspension obtained after the reaction was centrifuged and treated with MQ water; HCl solution; NaOH solution; or three times with acetone. The regenerated catalyst was collected and dried at 105 ℃ for 2h before being reused.

Study showing the Effect of calcination temperature on the catalytic Activity of NM substrate

The CWAO of various NM matrices (NM300, NM400, NM500 and NM600) prepared at different calcination temperatures versus three dyes (SO, MB and BG) was evaluated under ambient conditions (room temperature at 23 ℃ and atmospheric pressure) with an original dye concentration of 100mg L^-1And a catalyst concentration of 0.5g L^-1The results of the initial and subsequent optimization studies (shown in fig. 6a and 6b, respectively) show that NM300 shows the highest catalytic activity for the degradation of three dyes compared to NM400, NM500 and NM600, which is probably due to α -MoO in NM300₃And Na₂MO₄O₁₃The coexistence of the two. XRD results (FIG. 1a) show that as the calcination temperature is increased, MoO₃In the amount ratio of Na₂Mo₄O₁₃Higher because of Na at higher temperatures₂Mo₄O₁₃To MoO₃The conversion rate of (a) is higher. High proportion of MoO₃/Na₂Mo₄O₁₃The catalytic performance of the catalyst was reduced, which is consistent with the report (z.zhang, et al, sci.rep.2014, 4, 6797-. Therefore, NM300 was selected as a matrix support for preparing the bimetallic composite catalyst in example 1, and as a reference catalyst in the subsequent examples.

Example 1 by Metal particles in Na₂MO₄O₁₃/α-MoO₃Deposition on (NM) substrates to prepare bimetallic composite catalysts

The wet solution route was chosen to prepare the bimetallic composite catalyst of the present invention by depositing metal particles onto the NM substrate. Using simple one-pot deposition reduction method with NM300 as carrier and HAuCl₄·3H₂O and PdCl₂Respectively as a gold source and a palladium source, and a series of NM catalysts loaded with Au-Pd and with the total metal loading of 1 wt% are synthesized.

Typically, 500mg of NM300 is dispersed in 10-20mL MQ water under sonication for holdingAnd continuing for 30 min. Then, 520. mu.L of HAuCl was added under magnetic stirring₄·3H₂O solution (24.28mM) and 2090. mu.L of PdCl₂Solution (11.28mM) was added to the above suspension and the reaction mixture was allowed to stir for 10 min. Subsequently, 5mL of sodium citrate solution (0.05M) was added with continuous stirring and stirring was continued for 30 min. Followed by rapid addition of 5mL of freshly prepared NaBH under continuous stirring₄Solution (0.05M) and the reaction mixture was stirred for 60 min. The catalyst suspension was obtained by centrifugation and washed with MQ water. The samples obtained were dried under vacuum overnight and then calcined in a muffle furnace at 300 deg.C, 400 deg.C and 500 deg.C, respectively, for 1h under air to obtain the final products, which are expressed as Au-Pd (1:1)/NM-300, Au-Pd (1:1)/NM-400 and Au-Pd (1:1)/NM-500, respectively.

For reference, by adjusting HAuCl₄·3H₂O solution and PdCl₂The amount of solution added Au-Pd loaded NM catalyst was prepared at a total metal loading of 1 wt% according to the one-pot deposition reduction method described above with different Au-Pd mass ratios (1:3, 1:2, 2:1, 3: 1). In addition, Au/NM and Pd/NM were prepared with the same total metal loading of 1 wt%, respectively.

For clarity, various metal composite catalysts that have been synthesized and different conditions are summarized in table 1.

Table 1. metal composite catalysts prepared using different conditions.

Example 2 with Na₂Mo₄O₁₃/α-MoO₃Characterization of (NM) substrate-compared, synthesized bimetallic composite catalysts

Characterization by X-ray diffraction (XRD)

From FIG. 1a of NM300, diffraction peaks at about 12.70 °, 19.38 °, 23.33 °, 25.77 °, 27.28 °, 33.67 °, 38.86 °, 46.07 °, 49.34 °, and 58.75 ° were observed and can be assigned to α -MoO₃(JCPDS No.35-0609) inDiffraction peaks of about 11.75 °, 15.96 °, 22.50 °, 28.36 °, 29.72 °, and 32.18 ° may be assigned to Na₂Mo₄O₁₃(JCPDS No. 28-1112.) this indicates that NM300 contains α -MoO₃And Na₂MO₄O₁₃A composite material of the two (Z.Zhang, et al, Sci.Rep., 2014, 4, 6797-. For NM400, NM500 and NM600, Na, in contrast to NM300₂Mo₄O₁₃The intensity of the diffraction peak of (a) slowly decreases, which is probably due to Na as the calcination temperature increases₂Mo₄O₁₃To α -MoO₃Transformation of (1 a).

Use of TOPAS software for Na in various NM matrices in XRD spectra₂Mo₄O₁₃And α -MoO₃The ratios of (c) were quantified (table 2). It was observed that more Na was present with increasing calcination temperature₂MO₄O₁₃Is converted into α -MoO₃. For catalysts with Au-Pd deposits, the peaks are affected by the presence of Au-Pd. Therefore, the exact scale cannot be directly quantized. However, it was deduced that the ratio should be in the same range as the corresponding NM substrate calcined at the same temperature.

TABLE 2 for NM substrates calcined at different temperatures, Na₂MO₄O₁₃And α -MoO₃The ratio of (a) to (b).

In addition, MoO was observed in the Au-Pd (1:1)/NM samples before and after calcination₃And Na₂Mo₄O₁₃Diffraction peaks of both (FIG. 1 b). A similar phenomenon was also observed for catalysts with different Au-Pd mass ratios after calcination at 400 ℃, indicating no change in the structure of the support after loading with both Au and Pd (fig. 1 c).

However, for all Au-Pd supported catalysts, no diffraction peaks were observed for both Au and Pd, which should be at about 38.2 and 44.4 and at about 40.1 and 46.7, respectively (A. Cybula, et al, appl. Catal., B: Environ, 2014, 152, 202-211). This is probably due to the high dispersion and low loading of both Au and Pd in the catalyst.

By Field Emission Scanning Electron Microscope (FESEM), transmission electron microscope X-ray energy spectrometer (TEM-EDX) and and (5) performing characterization by using a UV-Vis Diffuse Reflectance Spectrum (DRS).

The synthesized NM300 and Au-Pd (1:1)/NM-400 catalysts were characterized by FESEM. FESEM images of NM300 show nanofiber morphology (fig. 2a and 2b), confirming the same morphology as reported in z.zhang, et al, sci.rep., 2014, 4, 6797-. Furthermore, FESEM images of Au-Pd (1:1)/NM-400 showed similar morphology of nanofibers to NM300, indicating that Au-Pd deposits had little effect on the morphology of the catalyst (FIG. 2c, FIG. 2d and FIG. 4 e).

In addition, TEM images of Au-Pd (1:1)/NM-400 samples obtained during the initial study showed that Au nanoparticles and Pd nanoparticles were not deposited on the substrate to some extent (FIG. 3 a.) As shown in HRTEM images (FIG. 3b), the spacing between lattice fringes of about 0.366 and 0.385NM was assigned to α -MoO, respectively₃And (001) plane (z.zhang, et al, sci.rep., 2014, 4, 6797-. Further, the inter-fringe distances of 0.224nm and 0.232nm may be allocated to (111) planes of Pd nanoparticles and Au nanoparticles, respectively (w.fang, et al, j.colloid interface sci., 2017, 490, 834. sub. 843), and the inter-fringe distance of 0.228 is also in the range of 0.224nm to 0.232 nm. Fringe-to-fringe distances of 0.201 and 0.206nm can be assigned to the (200) plane of the Au nanoparticles (r.h. padilla, et al, ultrason. sonochem., Part B, 2017, 35, 631-.

In the samples in which Au-Pd (1:1)/NM-400 was characterized using the optimized conditions, it was observed from the HRTEM image of FIG. 3c that the inter-fringe distance of 0.231NM was located between the lattice distances of the respective Au (111) plane (0.236NM) and Pd (111) plane (0.225NM), confirming that Au-Pd alloy particles (G.Zhan, et al, Mater.Lett., 2011, 65, 2989-.

In addition, the formation of Au-Pd alloy particles in Au-Pd (1:1)/NM-400 was also verified by DRS analysis (FIG. 3 d). A maximum Surface Plasmon Resonance (SPR) band at about 560NM was found in Au/NM-400. So-called Localized Surface Plasmons (LSPs) with extensive optical resonances are found in Pd/NM-400. However, no SPR peak was observed in the Au-Pd (1:1)/NM-400 spectrum, indicating that Pd inhibited the plasma band of Au, probably due to the strong interaction between Au and Pd and the formation of Au-Pd alloy particles in Au-Pd (1:1)/NM-400 (R.H.Padella, et al, ultrason.Sonochem., Part B, 2017, 35, 631-639).

The deposition of Au and Pd nanoparticles in Au-Pd (1:1)/NM-400 generated in the initial study was further confirmed by TEM-EDX elemental mapping as shown in FIGS. 4 a-d. With further improvements in the catalyst preparation method, the uniform deposition of Au nanoparticles and Pd nanoparticles on the surface was optimized to produce Au-Pd (1:1)/NM-400 samples with the elemental mapping shown in fig. 4e and 4 f. Supported by the above XRD results, it can be concluded that the catalyst support on which the metal nanoparticles are deposited has been successfully prepared.

The ranges of values for the length and width of the nanofibers and the diameter of the metal nanoparticles are listed in table 3.

Table 3. length and width of the nanofibers used for the catalyst and the range of values of the diameter of the metal nanoparticles.

^aWith a total metal loading of 1 wt%.

^bData from FESEM.

^cData from TEM.

Characterization by X-ray photoelectron spectroscopy (XPS)

XPS analysis was performed to investigate the surface chemical composition and chemical base state of the support and catalyst. FIGS. 5a-d show XPS spectra for Mo 3d, O1s, Au 4f, and Pd3d in NM300 and Au-Pd (1: 1)/NM-400. Two peaks at 232.2eV and 235.4eV are observed in the Mo 3dXPS spectrum of NM300, while peaks at 232.3eV and 235.5eV are observed in the Mo 3d spectrum of Au-Pd (1: 1)/NM-400. Watch with a watch bodyIn the two catalysts, Mo is mainly Mo⁶⁺Exists (W.Li, et al, appl.Catal., B: environ, 2009, 92, 333-.

For the O1s XPS spectrum as shown in FIG. 5b, the peak at 530.1eV in NM300 and the peak at 529.9eV in Au-Pd (1:1)/NM-400 are attributed to the O of the metal oxide^2-Ions (lattice oxygen). The peak at 531.7eV in NM300 and the peak at 531.9eV in Au-Pd (1:1)/NM-400 are assigned to O in the oxygen vacancy region^2-Ions, while the peak at 534.2eV in NM300 and the peak at 534.0eV in Au-Pd (1:1)/NM-400 are assigned to loosely bound surface O₂(Z.Zhang, et al, Sci.Rep.2014, 4, 6797-.

Loosely bound surface O in Au-Pd (1:1)/NM-400₂And O in the oxygen vacancy region^2-The percentage of ions is higher than in NM300 (6% versus 4%; and 27% versus 24%, respectively). These results indicate that the adsorption and activation of molecular oxygen is enhanced after Au-Pd (1:1) deposition, which may result in a higher catalyst activity for Au-Pd (1:1)/NM-400 than for NM 300. Considering that the reaction is carried out at ambient conditions, the probability of lattice oxygen participation in the Catalytic Wet Air Oxidation (CWAO) reaction should be small, and thus the adsorbed oxygen species should be the primary reactive oxygen species participating in the CWAO reaction.

FIG. 5c shows Au 4f XPS spectra of Au-Pd (1: 1)/NM-400. Peaks at 84.5eV and 88.1eV are assigned to Au⁰Au 4f of_7/2And Au 4f_5/2While peaks at 86.2eV and 89.8eV are assigned to Au³⁺Au 4f of_7/2And Au 4f_5/2(W.Fang, et al, J.colloid Interface Sci., 2017, 490, 834-843; G.Fu, et al, CrystEngComm, 2014, 16, 1606-1610; S.M.Kim, et al, ACS Nano, 2011, 5, 1236-1242).

The Pd3d XPS spectrum of Au-Pd (1:1)/NM-400 is shown in FIG. 5d and consists of four sub-peaks. The peaks at 336.3eV and 341.6eV are attributed to Pd⁰Pd3d of_5/2And Pd3d_3/2While peaks at 338.8eV and 344.2eV are assigned to Pd²⁺(w.fang, et al,colloid Interface Sci, 2017, 490, 834-843). Surface Pd²⁺The presence of the species may be due to calcination of the catalyst in air. In addition, it was observed that Au was compared to the standard values for bulk Au and Pd metals⁰And Pd⁰The binding energy of both peaks shifts to higher binding energies, indicating electron deficiency or electron loss for both Au and Pd (h.zhang, et al, nat. mater, 2011, 11, 49). The electrons of the Au-Pd bimetallic particles seem to be in Au-Pd and MoO₃Is transferred to MoO at the interface between₃And these O-vacancy points may serve as sites for adsorption of molecular oxygen (h.zhang, et al, nat. mater, 2011, 11, 49).

Brunauer-Emmett-Teller (BET) surface area of catalyst

The specific area of the catalyst is very small, e.g. about 5.4 and 8.5m for Au-Pd (1:1)/NM-400 and NM300, respectively²(ii) in terms of/g. Prior to catalytic evaluation, adsorption experiments were performed which showed that BG adsorbed less than 10% on Au-Pd (1:1)/NM-400 and NM300 in 30 min. This indicates that the dye molecules are not adsorbed predominantly on these samples, which supports a small specific surface area of the catalyst. In addition, this also indicates that the dye removal in subsequent dye degradation experiments was primarily due to catalytic oxidation rather than adsorption of the dye.

Example 3 Effect of calcination temperature on the catalytic Activity of Au-Pd (1:1)/NM catalyst

NM300 substrates loaded with Au-Pd in a 1:1 mass ratio calcined at different temperatures were prepared according to example 1 to investigate the effect of calcination temperature on dye removal efficiency. At 23 ℃ under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The experiment was carried out for a reaction time of 2 h.

Initial study

In initial studies, as shown in FIG. 7a, uncalcined Au-Pd (1:1)/NM showed negligible catalytic activity, and the catalytic activity was enhanced after calcination, probably due to the burning-off of citrate ligands. The Au-Pd (1:1)/NM-400 catalyst exhibits higher catalytic activity than NM300 due to the catalytic function of Au nanoparticles and Pd nanoparticles.

However, with further increase in the calcination temperature, the dye removal efficiency becomes slightly lower. It is noted in FIG. 7a that the enhanced catalytic effects of Au and Pd are not clearly observed, since the TOC removal efficiency of NM300 and Au-Pd (1:1)/NM-400 has reached nearly 90%. This was more clearly observed in the initial studies of example 6 and example 7, where higher dye concentrations and a wider reaction temperature range were used.

Subsequent optimization study

Similarly, the optimization results shown in FIG. 7b indicate that the catalytic activity of Au-Pd (1:1)/NM is enhanced after calcination due to the burning-off of the citrate ligand. The Au-Pd (1:1)/NM-400 catalyst was observed to be the most active catalyst because the ligands covering the Au nanoparticles and Pd nanoparticles could only be completely removed above 400 ℃ (Z.Bai, et al, J.of Power Sources, 2010, 195, 2653-2658). However, due to Na₂Mo₄O₁₃To MoO₃Is higher, so calcination at temperatures above 400 ℃ results in MoO₃With Na₂Mo₄O₁₃Is higher. Therefore, the dye removal efficiency of Au-Pd (1:1)/NM-500 was observed to be lower than that of Au-Pd (1: 1)/NM-400.

Furthermore, even though NM300 has higher Na₂Mo₄O₁₃In this amount, Au nanoparticles and Pd nanoparticles still have a strong catalytic function, so Au-Pd (1:1)/NM-400 also shows a higher catalytic activity than NM300 (compare Au-Pd (1:1)/NM-400 in FIG. 7b with NM300 in FIG. 6 b).

As shown in fig. 8, the degradation of the dye was more clearly observed from the color change. For both NM300 and Au-Pd (1:1)/NM-400 catalysts, the solution containing SO was degraded in the shortest time, while the solution containing BG took the longest of the three dye solutions to degrade. It was also clearly observed that the BG-containing solution decolorized much faster with Au-Pd (1:1)/NM-400 than with NM300 (see FIG. 6b and FIG. 7 b). However, after a reaction time of 2h, all three dyes were effectively degraded (fig. 7a and 7 b).

Example 4 influence of Au-Pd mass ratio on the catalytic Activity of Au-Pd/NM catalyst

A series of NM300 loaded with different Au-Pd mass ratios (total metal loading of 1 wt%) calcined at 400 ℃ were prepared according to example 1 and evaluated for catalytic activity for SO, MB and BG removal. At 23 ℃ under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The experiment was carried out for a reaction time of 2 h.

Fig. 9a and 9b show initial and optimized results, respectively, for the catalytic activity of the catalyst. Both studies show that more effective SO, MB and BG removal is achieved using Au-Pd (1:1)/NM-400 compared to catalysts with other Au-Pd mass ratios and monometallic Au/NM-400 and monometallic Pd/NM-400. This indicates that the optimal Au-Pd ratio is 1:1, and that the double metal combination of both Au and Pd is better than using only a single Au or Pd metal, probably due to the synergistic effect of Au and Pd.

EXAMPLE 5 Effect of catalyst concentration on the catalytic Activity of Au-Pd/NM-400 catalyst

The effect of catalyst concentration on the dye removal efficiency of the catalyst (prepared according to example 1) was also investigated. In both the initial and optimization studies, 0.1g L was used^-1、0.2g L^-1And 0.5g L^-1At a catalyst concentration of 100mg L at 23 ℃ under atmospheric pressure^-1The experiment was carried out for a reaction time of 2 h. For a catalyst concentration of 1.0g L^-1The reaction time was 1 h.

As shown in fig. 10a and 10b, respectively, an increase in dye removal efficiency with increasing catalyst concentration was observed. After 2h of reaction, 0.5g L was used^-1Au-Pd (1:1)/NM-400 can remove more than 90% of SO, MB and BG. Furthermore, 1.0gL was used^-1Similar removal efficiencies were achieved with Au-Pd (1:1)/NM-400 for a reaction time of 1 h. This may be due to the presence of more catalytic sites with higher catalyst concentrations.

Example 6 Effect of dye concentration on the dye removal efficiency of NM300, Au-Pd (1:1)/NM-400 and Au-Pd (1:1)/NM-500 catalysts

The catalyst activity was studied at fixed catalyst concentrations using NM300, Au-Pd (1:1)/NM-400 and Au-Pd (1:1)/NM-500 prepared according to example 1, with different dye concentrations. In both the initial and optimization studies, 300mg L was used^-1、400mg L^-1And 600mg L^-1At a dye concentration of 0.5g L at 23 ℃ under atmospheric pressure^-1The experiment was carried out for a reaction time of 2 h.

Initial study

At a fixed 0.5g L^-1The catalyst activity was investigated at different dye concentrations. Found at 300mg L^-1At three dye concentrations of Au-Pd (1:1)/NM-400, showed higher catalytic activity than Au-Pd (1:1)/NM-500 and NM300 (FIG. 11 a). When the dye concentration increased to 400mg L^-1While, Au-Pd (1:1)/NM-400 still showed high TOC removal for the three dyes: (>90%) and when NM300 is used, TOC is removed for MB and BG<80% (fig. 11 b). When the dye concentration was further increased to 600mg L^-1In this case, the catalytic activity of Au-Pd (1:1)/NM-400 (SO-90%, MB-75% and BG-55%) was still higher than that of NM300 (SO-75%, MB-40% and BG-30%) (FIG. 11 c). These results indicate that deposition of Au-Pd on the support can significantly improve the catalytic performance of NM300 at high dye concentrations.

Subsequent optimization study

For subsequent use 300 and 400mg L^-1(FIG. 11d and FIG. 11e), SO removal efficiencies of Au-Pd (1:1)/NM-400 and NM300 are similar: (>90%) and the MB and BG removal efficiencies of Au-Pd (1:1)/NM-400 (1%>90%) is much higher than NM 300. With increasing dye concentration to 600mg L^-1The Au-Pd (1:1)/NM-400 catalyst still showed high TOC removal efficiency for these three dyes (FIG. 11 f). This shows that Au-Pd (1:1)/NM-400 has higher catalytic activity compared to NM300 with high dye concentration due to the deposition of Au-Pd. Furthermore, it is visually observed in FIG. 12, where for 300mg L^-1And 400mg L^-1BG concentration of (2) using Au-Pd (1:1)/NM-400 produced a more vigorous decolorization of BG than with NM 300.

Example 7 Effect of reaction temperature on Au-Pd (1:1)/NM-400 catalytic Activity compared to NM300

The experiment was performed at reaction temperatures of 5 deg.C, 10 deg.C, 35 deg.C and 45 deg.C, respectively, to evaluate the effect of the reaction temperature on the catalytic activity of Au-Pd (1:1)/NM-400 (prepared according to example 1) and NM 300.

For experiments conducted at 35 ℃ and 45 ℃ (both initial and optimization studies, fig. 13a-d), at atmospheric pressure, at 600mg L^-10.5g L initial dye concentration^-1The experiment was carried out for a reaction time of 2 h.

For experiments carried out at 5 ℃ and 10 ℃, at 100mg L under atmospheric pressure^-10.5mgL of the initial dye concentration of^-1The initial study (fig. 14a-d) was carried out for 2h and 24 h. For the optimization study (FIGS. 14e-g), at 5 ℃ at 300mg L under atmospheric pressure^-10.5mg L of the initial dye concentration of^-1The optimization study was carried out for 2h, 24h and 48 h.

Initial study

From the initial results, it was observed that the catalytic activity of Au-Pd (1:1)/NM-400 was generally higher than that of NM300 at 35 ℃ and 45 ℃ (FIGS. 13a and 13 b). The dye removal efficiency increases as the reaction temperature increases from 35 ℃ to 45 ℃.

At reaction temperatures of 5 ℃ and 10 ℃ respectively, at 100mg L^-1Further study of dye removal efficiency. Fig. 14a-d show the increasing catalytic activity from 5 to 10 ℃ and the dye removal is enhanced with increasing reaction time from 2 to 24 h. This indicates that Au-Pd (1:1)/NM-400 can operate at temperatures below room temperature and has potential for use in areas with significant differences in climatic and natural conditions. For example, in areas where the temperature varies greatly, both day and night, and during different seasons.

Subsequent optimization study

Similar to the initial results, it was observed in the optimized results that the catalytic activity of Au-Pd (1:1)/NM-400 was higher than that of NM300 at 35 ℃ for the removal of MB and BG (FIG. 13 c). The dye removal efficiency increased on NM300 as the operating temperature increased to 45 deg.C, which is similar to the dye removal efficiency increased on Au-Pd (1:1)/NM-400 (FIG. 13 d). In short, this indicates that the higher the operating temperature, the higher the catalytic activity.

The catalytic activity of Au-Pd (1:1)/NM-400 and NM300 at 5 ℃ was further investigated in view of the temperature variation with time, region and season of the day. As shown in FIG. 14e, at 5 deg.C, at 300mg L^-1The dye removal efficiency after 2h for Au-Pd (1:1)/NM-400 (61%, 52% and 45% for SO, MB and BG, respectively) was higher than that of NM300 (40%, 19% and 10% for SO, MB and BG, respectively). After extending the reaction time to 48h, the dye removal efficiencies of SO, MB and BG reached more than 92%, more than 88% and more than 85% for Au-Pd (1:1)/NM-400, respectively, and 68%, 39% and 26% for NM300, respectively (FIG. 14 g). This shows that Au-Pd (1:1)/NM-400 is still effective and able to remove the dye even at a low reaction temperature of 5 ℃. In this regard, Au-Pd (1:1)/NM-400 has the potential to be used in areas where the temperature difference is significant.

Example 8 reusability and stability of Au-Pd (1:1)/NM-400 catalyst

Inactivation test was performed to investigate the durability of Au-Pd (1:1)/NM-400 (prepared according to example 1) for dye removal. Figures 15a-c show that after five reuses of the catalyst, high dye removal efficiency was achieved for all three different dyes. It was also observed that the catalytic activity was not affected by the choice of the solution used for regenerating or washing the catalyst (water, acetone, HCl, NaOH), thus indicating the general use and high stability of the catalyst. In addition, the Au released from Au-Pd (1:1)/NM-400 after the dye was oxidized for 10h³⁺And Pd²⁺The weight percentages of (A) and (B) are respectively 3.3% and 1.5%. Therefore, it can be concluded that Au-Pd (1:1)/NM-400 has good reusability and catalytic stability.

Example 9 Effect of Metal loading (% by weight) on the catalytic Performance of Au-Pd (1:1)/NM-400 catalyst

As a comparative study, Au-Pd (1:1)/NM-400 (2%) loaded with 2 wt% of a metal (Au-Pd at a mass ratio of 1:1) was prepared according to a similar method to Au-Pd (1:1)/NM-400 in example 1. At 23 ℃ under atmospheric pressure, at 100mg L^-10.5g L initial dye concentration^-1The catalytic study was carried out for 2 h.

As shown in FIG. 16a, Au-Pd (1:1)/NM-400 (2%) degraded the catalytic activity of three different dyes lower than that of Au-Pd (1:1)/NM-400, which had a metal loading of 1 wt%. This is probably due to the aggregation of Au-Pd nanoparticles at a higher metal loading of 2 wt% (as shown in the TEM image of FIG. 16 b), which therefore reduced the catalytic activity of Au-Pd (1:1)/NM-400 (2%).

Example 10 degradation kinetics of SO, MB and BG on NM300, Au/NM-400, Pd/NM-400 and Au-Pd (1:1)/NM-400

To further understand the catalytic performance of the catalyst, 20mg L was used^-1Low dye concentrations of SO, MB and BG the degradation kinetics on NM300, Au/NM-400, Pd/NM-400 and Au-Pd (1:1)/NM-400 (prepared according to example 1) were investigated.

For SO degradation (FIG. 17), a higher rate of degradation of Au-Pd (1:1)/NM-400 for SO than for NM300, Au/NM-400 and Pd/NM-400 was observed. Furthermore, SO degradation follows quasi-first order reaction kinetics with reaction rate constants of 0.20, 0.24, 0.23, and 0.46min for NM300, Au/NM-400, Pd/NM-400, and Au-Pd (1:1)/NM-400, respectively^-1. Similar degradation kinetics were also observed for MB and BG, which also follow quasi-first order reaction kinetics, as shown in fig. 18 and 19. The reaction rate constants for each catalyst used to degrade each dye are summarized in table 4.

TABLE 4 reaction rate constants for NM300, Au/NM-400, Pd/NM-400 and Au-Pd (1:1)/NM-400 in the degradation of SO, MB and BG, respectively.

Example 11 proposed catalytic mechanism for dye degradation on Au-Pd (1:1)/NM-400

It is concluded that Reactive Oxygen Species (ROS) play a role in the catalytic degradation of dyes by the catalysts of the present invention. To further understand the role of ROS in the mechanism of dye degradation in Au-Pd (1:1)/NM-400, 1, 4-Benzoquinone (BQ), NaN₃And dimethyl sulfoxide (DMSO) as superoxide radical (. O)₂ ^-) Singlet oxygen (a)¹O₂) And quenchers of hydroxyl radicals (. OH) (P.Wang, T. -T.Lim, Water Res.,2012,46, 1825-1837).

As shown in FIG. 20a, SO degradation is inhibited in the presence of ROS quenchers, in the order of significance BQ>NaN₃>DMSO. A similar phenomenon was observed for MB and BG degradation (FIG. 20b and FIG. 20c, respectively), where O₂ ^-And¹O₂both significantly promote dye degradation while OH was found to be less significant. Therefore, O is inferred by the superoxide radical mechanism and the single oxygen mechanism₂ ^-And¹O₂are the primary active oxidizing species during CWAO of the dye.

As described above, XPS analysis confirmed that, after Au-Pd was deposited on the catalyst support, the oxygen species adsorbed on the surface of the catalyst increased, and that with respect to Pd⁰With a slight loss of electrons (fig. 5). Furthermore, traces of O vacancies should be formed on the support surface, which are possibly distributed in the Au-Pd and MoO₃At the interface therebetween.

Based on the quenching experiments and XPS analysis above, the proposed catalytic mechanism for dye degradation by using Au-Pd (1:1)/NM-400 is shown in FIG. 20 d. In general, electrons on the surface of Au-Pd alloy particles can be partially transferred to Au-Pd and MoO₃At the interface therebetween₃Then through the O adsorbed on the O vacant site (h.zhang, et al, nat. mater, 2011, 11, 49)₂Trapping the electrons to form-O₂ ^-And¹O₂(H.Masatake, et al, chem.Lett., 1987, 16(1987) 405-; M.R.Hoffmann, et al, chem.Rev., 1995, 95, 69-96). Produced O₂ ^-And¹O₂has potential for degradation of organic compounds.

EXAMPLE 12 possible modes of introducing the bimetallic composite catalyst into a wastewater treatment System

The bimetallic composite catalyst system may be introduced into the water treatment process by various means. One way is to have the catalyst freely suspended in the waste stream, as shown in fig. 21 a. The waste influent 20 will be added with a free-floating bimetallic composite catalyst 40. With air or O₂(60) Together, the wastewater is purified to produce product water 80, and the dispersed catalyst 40 is separated from the product water 80 and recovered for reuse.

In other forms, as shown in fig. 21b, the bimetallic composite catalyst 40 may be in a fixed or immobilized state on a range of porous materials 100 (e.g., meshes, fibers, fabrics, and membranes). In air or O₂(60) The wastewater 20 may be purified to produce purified water 80. This structure can facilitate easy separation of the catalyst from the purified water by removing the porous support 100 containing the catalyst 40.

Claims

1. A catalytic composite comprising:

2. The catalytic composite of claim 1, wherein the elemental metal nanoparticles are deposited in a total amount of from 0.5 to 1.1 wt% relative to the total weight of the metal oxide matrix.

3. The catalytic composite of claim 1 or claim 2, wherein the elemental metal nanoparticles are deposited in a total amount of from 0.75 to 1 wt% relative to the total weight of the metal oxide matrix.

4. Catalytic composite according to any of the previous claims, wherein the weight to weight ratio of elemental gold to elemental palladium in the composite is from 0.5:1 to 2: 1.

5. Catalytic composite according to any of the previous claims, wherein the weight to weight ratio of elemental gold to elemental palladium in the composite is 1: 1.

6. The catalytic composite of any of the previous claims, wherein the metal oxide matrix nanofibers have a length of from 500 to 5,000nm and a diameter of from 50 to 500 nm.

7. The catalytic composite of claim 6, wherein the metal oxide matrix nanofibers have a length of from 800 to 4,000nm and a diameter of from 75 to 400nm, optionally wherein the metal oxide matrix nanofibers have a length of from 900 to 3,700nm and a diameter of from 100 to 350 nm.

8. Catalytic composite according to any of the preceding claims, wherein Na is in the metal oxide matrix₂Mo₄O₁₃And α -MoO₃Is from 0.3:1 to 0.7:1, such as from 0.35:1 to 0.6: 1.

9. Catalytic composite according to any of the preceding claims, wherein the elemental metal nanoparticles have a diameter of from 1 to 50nm, such as from 5 to 30 nm.

10. The catalytic composite of claim 9, wherein the elemental metal nanoparticles have a diameter of from 7 to 25 nm.

11. Use of a catalytic composite material according to any one of claims 1 to 10 in the catalytic wet air oxidation of organic materials.

12. Use according to claim 11, wherein the organic material can be one or more selected from the group of pharmaceutical compounds, pesticides and organic dyes.

13. Use according to claim 11 or claim 12, wherein the organic dye is selected from one or more of the group consisting of safranin O, methylene blue and brilliant green.

14. A method of catalytic wet air oxidation of organic material comprising the steps of: contacting an organic material with a catalytic composite as claimed in any one of claims 1 to 10 in an aqueous environment supplied with a gas stream comprising oxygen to oxidise the organic material.

15. The method of claim 14, wherein the organic material can be one or more selected from the group of pharmaceutical compounds, pesticides, and organic dyes.

16. The method of claim 14 or claim 15, wherein the organic dye is selected from one or more of the group consisting of safranin O, methylene blue and brilliant green.

17. The method of any one of claims 14 to 16, wherein the weight to weight ratio of the catalytic composite to organic material is from 1x10^-41 to 10: 1.

18. The method of claim 17, wherein the weight to weight ratio of the catalytic composite to the organic material is from 1x10^-31 to 5: 1.

19. The method of claim 18, the weight to weight ratio of the catalytic composite to the organic material is from 0.1:1 to 1: 1.

20. The process according to any one of claims 14 to 19, wherein the process is carried out at a temperature of from 0 to 75 ℃.

21. The process according to claim 20, wherein the process is carried out at a temperature of from 2.5 to 45 ℃, such as from 5 to 30 ℃, such as 25 ℃.

22. A method of forming a catalytic composite comprising the steps of:

23. The method of claim 22, wherein the elemental metal nanoparticles are deposited in a total amount of from 0.5 to 1.1 wt% relative to the total weight of the metal oxide matrix.

24. The method of claim 22 or claim 23, wherein the elemental metal nanoparticles are deposited in a total amount of from 0.75 to 1 wt% relative to the total weight of the metal oxide matrix.

25. The method of any one of claims 22 to 24, wherein the weight to weight ratio of elemental gold to elemental palladium in the composite material is from 0.5:1 to 2: 1.

26. The method of any one of claims 22 to 25, wherein the weight to weight ratio of elemental gold to elemental palladium in the composite material is 1: 1.

27. The method of any one of claims 22 to 26, wherein the metal oxide matrix nanofibers have a length of from 3,000 to 35,000nm and a diameter of from 800 to 3,100 nm.

28. The method of claim 27, wherein the metal oxide matrix nanofibers have a length from 3,500 to 26,000nm and a diameter from 825 to 2,700nm, optionally wherein the metal oxide matrix nanofibers have a length from 3,750 to 18,000nm and a diameter from 850 to 2,500 nm.

29. The method of any one of claims 22 to 28, wherein Na is in the metal oxide matrix₂Mo₄O₁₃And α -MoO₃Is from 0.3:1 to 0.7:1, such as from 0.35:1 to 0.6: 1.

30. The method according to any one of claims 22 to 29, wherein the elemental metal nanoparticles have a diameter of from 1 to 50nm, such as from 5 to 30nm, such as from 7 to 25 nm.

31. The process of any one of claims 22 to 30, wherein the metal oxide substrate is subjected to a calcination temperature of from 250 to 400 ℃, for example 300 ℃, prior to use in step (a) of claim 22.

32. The method of any one of claims 22 to 31, wherein the ligand coated product is subjected to a calcination temperature of from 300 to 450 ℃ for a second period of time to form the catalytic composite.