A method for preparing a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst and its application in CO oxidation.

Abstract

The application discloses a preparation method of a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst and application of the catalyst in CO oxidation reaction, and relates to the technical field of industrial catalysis and waste gas treatment. The catalyst comprises a composite active component composed of noble metal and rare earth metal, a TiO2 carrier and a molecular sieve coating layer; the composite active component composed of noble metal and rare earth metal is dispersed in the TiO2 carrier, and the TiO2 carrier is coated by the molecular sieve coating layer. The catalyst provided by the application exhibits excellent catalytic performance, outstanding sulfur poisoning resistance and heavy metal poisoning resistance in the CO oxidation reaction, and simultaneously has good economy and long-term stability, thereby providing an efficient and stable CO oxidation catalyst technical scheme for flue gas treatment in the steel industry.

Description

Technical Field

[0001] This invention relates to the field of industrial catalysis and waste gas treatment technology, and in particular to a method for preparing a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst and its application in the CO oxidation reaction. Background Technology

[0002] In recent years, CO pollution from typical industrial sources, such as steel sintering processes, has become increasingly prominent, posing a key obstacle to the continuous improvement of environmental quality. CO not only directly harms human health through hemoglobin binding but also participates in photochemical reactions, exacerbating the formation of complex air pollutants such as ozone and secondary aerosols. Strengthening CO emission control has become an important task in improving the modern environmental governance system, and developing efficient and economical CO purification technologies is the core path to achieving this goal.

[0003] CO catalytic oxidation technology is widely recognized as the preferred solution for CO treatment in steel sintering flue gas due to its high reaction kinetics and strong adaptability to various operating conditions. This technology reduces the activation energy of the reaction by utilizing active sites on the catalyst surface, achieving efficient oxidation of CO and O2 at lower temperatures. In catalyst system design, noble metal-based catalysts have attracted much attention due to their excellent CO catalytic activity at low temperatures. Among them, noble metal catalysts supported on TiO2 exhibit significant advantages: the acidity, reducibility, and abundant oxygen vacancy defects of TiO2 can form strong metal-support interactions with noble metal components, thereby improving oxygen activation efficiency and reaction stability. However, the large-scale application of noble metal-supported TiO2 catalysts still faces several challenges. First, carbonyl sulfide (COS) in sintering flue gas can form a stable sulfur species adsorption layer with the active centers of noble metals, leading to irreversible deactivation of the catalyst. Second, heavy metal vapors such as Pb and Zn deposit on the catalyst surface, covering acidic sites and significantly inhibiting CO adsorption activation efficiency. In addition, to achieve industrial-grade CO conversion rates, the noble metal loading is usually high, resulting in high catalyst costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst and its application in CO oxidation, so as to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of the present invention is to provide a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst, comprising: a composite active component composed of noble metal and rare earth metal, a TiO2 support and a molecular sieve coating layer;

[0007] The composite active component composed of noble metals and rare earth metals is dispersed in the TiO2 support, and the molecular sieve coating layer coats the TiO2 support.

[0008] Furthermore, the precious metal is selected from at least one of Pt, Pd, Au and Ir, and the rare earth metal is at least one of La, Gd, Nd and Pr; the support is anatase TiO2; and the molecular sieve coating is composed of SAPO-18 or SAPO-34 molecular sieves.

[0009] Furthermore, the loading of noble metals accounts for 0.2–1.5 wt.% of the TiO2 support mass, and the loading of rare earth metals accounts for 0.2–2 wt.% of the TiO2 support mass.

[0010] The second technical solution of this invention provides a method for preparing a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst, comprising the following steps:

[0011] (1) Dissolve noble metal salts, rare earth metal salts and titanium sources in a solvent, and add a binder after hydrolysis and aging to obtain a sol system; the solvent is preferably a mixture of anhydrous ethanol and acetylacetone; wherein, acetylacetone acts as a chelating agent to stabilize metal ions, prevent them from precipitating prematurely, and slow down the hydrolysis rate of titanium sources to ensure uniform sol formation, while anhydrous ethanol provides a suitable polar environment to promote dissolution;

[0012] (2) The sol system is loaded onto a ceramic carrier, and then dried, cured and calcined to obtain a noble metal-rare earth metal / TiO2 matrix; preferably, the loading is carried out by vacuum impregnation.

[0013] (3) A molecular sieve coating layer is grown in situ on the noble metal-rare earth metal / TiO2 matrix by hydrothermal method, and then calcined in stages in an oxidizing atmosphere and a reducing atmosphere to obtain the molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst.

[0014] Furthermore, the noble metal salt is selected from at least one of chloroplatinic acid (H2PtCl6), palladium chloride (PdCl2), chloroauric acid (HAuCl4), and iridium chloride (IrCl3); the rare earth metal salt is selected from at least one of lanthanum nitrate (La(NO3)3), gadolinium nitrate (Gd(NO3)3), neodymium nitrate (Nd(NO3)3), and praseodymium nitrate (Pr(NO3)3).

[0015] Furthermore, the binder is at least one selected from silica sol, polyvinyl alcohol, polyethylene glycol, and hydroxypropyl methylcellulose.

[0016] Furthermore, the drying and curing temperature in step (2) is 80-120°C, and the calcination temperature is 400-700°C; the hydrothermal method in step (3) has a temperature of 140-200°C and a reaction time of 2-6 days.

[0017] Furthermore, in step (3) segmented calcination, the oxidizing atmosphere calcination conditions are: in an O2 / N2 mixed gas containing 3% to 25% oxygen by volume, the temperature is raised to 400 to 700°C and calcined at a constant temperature for 2 to 8 hours; the reducing atmosphere calcination conditions are: in an H2 / N2 mixed gas containing 1% to 7% hydrogen by volume, the temperature is raised to 400 to 700°C and calcined at a constant temperature for 2 to 8 hours.

[0018] Furthermore, step (3) is further detailed as follows:

[0019] A silicon source, an aluminum source, a template agent, phosphoric acid, and water were mixed in a specific molar ratio and stirred until homogeneous to prepare an initial molecular sieve gel, which was then placed into the liner of a reaction vessel. Subsequently, the noble metal-rare earth metal supported TiO2 matrix obtained in step (2) was placed in the initial molecular sieve gel for hydrothermal reaction. After the hydrothermal reaction, the resulting material was washed and dried, and then calcined in stages under oxidizing and reducing atmospheres, respectively, to finally obtain a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst.

[0020] The silicon source is selected from at least one of sodium silicate, tetraethyl orthosilicate, or silica sol; the aluminum source is selected from at least one of sodium aluminate, boehmite, or aluminum sulfate; and the template agent is selected from at least one of tetraethylammonium hydroxide (TEAOH), morpholine (MOR), triethylamine (TEA), N,N-diisopropylethylamine (DIPEA), and N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (DMPDOH).

[0021] Furthermore, the molar ratio of Si:Al:P:H2O:template is 1~5:4~14:2~16:80~200:3~10.

[0022] Furthermore, the molecular sieve material is SAPO-18 or SAPO-34.

[0023] This invention proposes an in-situ hydrothermal method for preparing molecular sieve-coated monolithic noble metal-rare earth metal / TiO2 catalysts. This technology effectively solves the problems of COS sulfur poisoning deactivation, heavy metal poisoning deactivation, and economic bottlenecks faced by noble metal / TiO2 catalysts in the purification of flue gas from steel sintering through the multi-scale synergistic effect of electronic modulation of the active components and the confinement effect of molecular sieves. Specifically, firstly, the unique pore structure and acidic properties of molecular sieves restrict the adsorption and diffusion of sulfur species through the confinement effect, effectively fixing them on the molecular sieve surface and avoiding direct contact between sulfides and the active centers of noble metals, thereby significantly improving the catalyst's resistance to sulfur poisoning. Secondly, the acidic sites on the molecular sieve surface can preferentially adsorb and fix heavy metal ions, forming a steric hindrance protective layer, reducing the coverage and poisoning effect of heavy metals on the active sites of noble metals, and effectively delaying the catalyst deactivation process. Furthermore, rare earth metals regulate the electronic structure of noble metals through electron transfer effects, optimizing their d-band central energy levels, thus enhancing the oxygen activation capacity of the noble metal surface. While reducing the amount of precious metals used, the addition of rare earth metals not only improves the low-temperature oxidation efficiency of the catalyst, but also significantly enhances the overall catalytic performance. This multi-stage synergistic strategy, while maintaining high catalyst activity, systematically solves the economic bottleneck caused by poisoning and deactivation of traditional catalysts and excessive precious metal loading, thus providing a technical solution for complex flue gas purification systems that combines long-term stability and industrial feasibility.

[0024] The third technical solution of the present invention provides the application of the above-mentioned molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst in the carbon monoxide oxidation reaction.

[0025] The fourth technical solution of the present invention provides a CO catalytic oxidizer, comprising the above-mentioned molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst.

[0026] Fifth technical solution of the present invention: Provides a tail gas treatment system for steel sintering machine, including the above-mentioned CO catalytic oxidizer.

[0027] This invention is based on a multi-scale synergistic regulation strategy: a molecular sieve coating layer is constructed on the surface of a noble metal-rare earth metal / TiO2 using an in-situ hydrothermal method. The confined pores of the molecular sieve selectively trap sulfur species and heavy metal ions, blocking their contact with the active sites. The rare earth metal optimizes the electronic structure of the noble metal through electronic modulation, enhancing oxygen activation capacity while reducing the noble metal loading. The integral support design, combined with the mass transfer optimization characteristics of the molecular sieve coating, achieves a synergistic effect of high mechanical strength and long-lasting catalytic performance in complex flue gas environments. This technology not only significantly improves the catalyst's resistance to sulfur and heavy metal poisoning but also overcomes economic bottlenecks through efficient utilization of active components, providing an efficient, stable, and low-cost solution for the synergistic purification of multiple pollutants under harsh conditions such as steel sintering flue gas.

[0028] This invention has the following technical advantages:

[0029] (1) This invention proposes a method for preparing a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst. This method is simple to operate, easy to repeat, and has good controllability and consistency, aiming to optimize the catalytic oxidation performance of CO.

[0030] Compared to Pt / TiO2 (ignition temperature T) 70 =225℃), Pt-Pr / TiO2(T 70 =220℃) and SAPO-34@Pt / TiO2(T 70 =216℃) catalyst, the ignition temperature T of the molecular sieve-coated noble metal-rare earth metal catalysts (SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2 and SAPO-18@Ir-La / TiO2) provided by the present invention is 216℃. 70 The measured values ​​of 206℃, 203℃, 210℃, and 214℃ indicate that the synergistic effect of molecular sieve coating and the bimetallic combination of noble and rare earth metals enhances the CO oxidation performance of the catalyst. This is mainly because the microporous structure of SAPO-34 and SAPO-18 molecular sieves improves the dispersion of noble metals (Pt, Pd, Au, or Ir) and rare earth metals (Pr, Nd, Gd, or La) through confinement. Furthermore, the strongly acidic sites of the molecular sieves facilitate CO adsorption and activation. Simultaneously, rare earth metals significantly enhance the redox capacity of noble metals through electronic and structural effects, while the oxygen storage capacity of rare earth metals themselves accelerates the interfacial reaction between CO and O2. Notably, the molecular sieve layer effectively inhibits the migration and aggregation of active components through physical confinement, thus maintaining high catalyst activity over a wide temperature range.

[0031] After introducing COS or catalysts into the reaction and undergoing Pb heavy metal poisoning, the ignition temperatures T of the following catalysts were observed: SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2, SAPO-18@Ir-La / TiO2, Pt / TiO2, Pt-Pr / TiO2, and SAPO-34@Pt / TiO2. 70Increasing the temperature to 222℃ or 217℃, 217℃ or 212℃, 229℃ or 224℃, 237℃ or 230℃, 281℃ or 255℃, 263℃ or 248℃, and 244℃ or 238℃ respectively indicates that the CO oxidation activity of all catalysts decreased to varying degrees. Among them, the molecular sieve-coated noble metal-rare earth metal catalysts exhibited significantly better resistance to COS and Pb poisoning than other catalysts. This is mainly due to the following synergistic mechanism: the microporous structure of SAPO-34 and SAPO-18 selectively blocks large molecular poisons (such as sulfur or Pb species) from contacting the active sites of the catalyst through size sieving effect, while allowing small molecule CO / O2 to diffuse freely, thereby reducing the direct coverage of poisons on the noble metal surface. Rare earth metals have oxygen storage-release function, which can dynamically remove adsorbed sulfur / lead species and form stable sulfates or lead oxides. These substances then migrate to the support surface, thereby avoiding clogging of the active sites of noble metals. Furthermore, the electron transfer between noble metals and rare earth metals can maintain the reduced state of noble metals, effectively inhibiting the oxidative deactivation of active sites caused by poisons. The weak hydrophobicity of SAPO-18 or SAPO-34 reduces the adsorption tendency of polar poisons on the catalyst surface; at the same time, bimetallic loading further weakens the chemisorption intensity of poisons through competitive adsorption (e.g., CO preferentially occupies active sites). In contrast, uncoated Pt / TiO2 and Pt-Pr / TiO2 catalysts lack physical barriers and chemical synergistic protection, allowing poisons to directly coat the active metal surface and leading to irreversible passivation. Although SAPO-34@Pt / TiO2 has the physical barrier of a molecular sieve, it only supports a single Pt metal and lacks the oxygen buffering effect of rare earth metals, making it unable to dynamically remove adsorbed poisons; moreover, due to the lack of sufficient electronic effects, its competitive adsorption capacity is weak, and poisons are more likely to occupy isolated Pt sites. These factors together result in its significantly weaker resistance to poisoning than bimetallic systems (such as SAPO-34@Pt-Pr / TiO2). These results further demonstrate the importance of molecular sieve coating and the synergistic design of precious and rare earth metals in enhancing resistance to poisoning. This design provides a solution for the purification of industrial sulfur- and heavy metal-containing waste gases that combines high activity with antitoxicity.

[0032] (2) This invention proposes a molecular sieve-coated monolithic catalyst of noble metal-rare earth metal / TiO2 prepared by in-situ hydrothermal method. This catalyst employs a coupled design of noble metal-rare earth metal electronic synergy and molecular sieve confinement protection to systematically solve key problems such as CO sulfur poisoning, heavy metal (Pb, Zn) poisoning, and high cost of noble metals in steel sintering flue gas. First, noble metals and rare earth metals are in-situ loaded onto the surface of TiO2 support to form a dual-active component system. Noble metals serve as the main active center for CO oxidation, while rare earth metals optimize the d-band center position of noble metals through electron transfer effects, effectively reducing the adsorption energy and dissociation barrier of CO and enhancing its reactivity. Simultaneously, oxygen vacancies in rare earth metals promote the adsorption and activation of O2. Furthermore, rare earth metals inhibit the high-temperature migration of noble metal nanoparticles through anchoring, solving the problem of activity degradation caused by sintering in traditional catalysts. Subsequently, a hydrothermal crystallization process is used to in-situ grow a SAPO-34 or SAPO-18 molecular sieve coating layer on the surface of the noble metal-rare earth metal / TiO2. The microporous structure of molecular sieves provides a size sieving effect, selectively blocking large poison molecules (such as sulfides and lead compounds) from entering the catalyst interior, allowing only small molecules (such as CO and O2) to freely diffuse to the active sites, thereby enhancing the catalyst's resistance to poisoning. Simultaneously, the abundant surface area of ​​molecular sieves... Acidic sites preferentially adsorb and immobilize heavy metal ions, forming a steric hindrance protective layer that effectively prevents them from covering the active centers of noble metals, further delaying the catalyst deactivation process. Notably, under the electronic regulation of rare earth metals, the activity of noble metals is enhanced, significantly reducing the amount of noble metal required to maintain the same CO conversion rate and significantly improving its atom utilization efficiency. Through the synergistic effect of the physical shielding provided by the molecular sieve coating layer and the structural stabilizing effect of the rare earth metals, the service life of this catalyst in simulated steel sintering flue gas is significantly extended, and the overall operating cost is reduced. In summary, the catalyst prepared in this invention combines high activity, excellent anti-poisoning performance, thermal stability, and economy, providing a highly efficient, low-consumption, and long-term stable solution for the catalytic oxidation of CO and the purification of harmful impurities in steel sintering flue gas.

[0033] The present invention discloses the following technical effects:

[0034] The molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst provided by this invention has significant technical effects in the following aspects: (1) Strong resistance to poisoning: The microporous structure of the molecular sieve blocks sulfur species, heavy metals and other poisons from contacting the active sites through size sieving; the oxygen storage-release function of rare earth metals can dynamically remove poisons; the bimetallic system can also maintain the reduced state of noble metals, weaken the adsorption of poisons, and effectively solve the problems of CO sulfur poisoning and heavy metal poisoning. (2) High catalytic activity: The confinement effect of the molecular sieve improves the metal dispersion; the rare earth metal optimizes the electronic structure of noble metals, enhances the oxygen activation ability, and reduces the CO oxidation ignition temperature. (3) Good economic efficiency: While maintaining high activity, the amount of noble metals used is reduced, thus reducing costs. (4) The molecular sieve layer can also inhibit the migration and aggregation of active components and improve the thermal stability of the catalyst.

[0035] The catalyst provided by this invention not only exhibits excellent resistance to poisoning and catalytic activity, but also possesses good economic efficiency and thermal stability, offering a highly promising technical solution for industrial applications in related fields. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 X-ray diffraction (XRD) patterns of the SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2, SAPO-18@Ir-La / TiO2, Pt / TiO2, Pt-Pr / TiO2, and SAPO-34@Pt / TiO2 catalysts prepared in Examples 1-4 and Comparative Examples 1-3.

[0038] Figure 2 The CO oxidation conversion rates of the SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2, SAPO-18@Ir-La / TiO2, Pt / TiO2, Pt-Pr / TiO2, and SAPO-34@Pt / TiO2 catalysts prepared for Examples 1-4 and Comparative Examples 1-3 are shown in the graph.

[0039] Figure 3The CO oxidation conversion rate of the SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2, SAPO-18@Ir-La / TiO2, Pt / TiO2, Pt-Pr / TiO2, and SAPO-34@Pt / TiO2 catalysts prepared for Examples 1-4 and Comparative Examples 1-3 in the presence of 500 ppm COS is shown in the graph.

[0040] Figure 4 The CO oxidation conversion rate of the SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2, SAPO-18@Ir-La / TiO2, Pt / TiO2, Pt-Pr / TiO2, and SAPO-34@Pt / TiO2 catalysts prepared for Examples 1-4 and Comparative Examples 1-3 after being poisoned with 4 wt.% Pb is shown in the graph. Detailed Implementation

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0044] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0045] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0046] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0047] In a first aspect, the present invention provides a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst, comprising: a composite active component composed of noble metals and rare earth metals, a TiO2 support, and a molecular sieve coating layer; wherein the composite active component composed of noble metals and rare earth metals is dispersed in the TiO2 support, and the molecular sieve coating layer coats the TiO2 support.

[0048] The active component of the noble metal is preferably at least one of Pt, Pd, Au and Ir, and the rare earth metal component is preferably at least one of La, Gd, Nd and Pr; the support is anatase TiO2; and the molecular sieve coating is composed of SAPO-18 or SAPO-34 molecular sieve.

[0049] In a second aspect, the present invention provides a method for preparing a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst, comprising the following steps:

[0050] (1) Dissolve the titanium source, noble metal salt, and rare earth metal salt in a mixed solvent of anhydrous ethanol and acetylacetone. Slowly add an aqueous nitric acid solution under constant temperature and stirring at 40–80°C to initiate the hydrolysis reaction, controlling the reaction time to 2–6 hours. After the hydrolysis reaction is complete, place the system at room temperature for 6–24 hours to age and form a stable sol system. Finally, add an appropriate amount of binder and continue stirring for 0.5–2 hours to obtain a homogeneous sol system with suitable viscosity.

[0051] (2) The cordierite honeycomb ceramic support (200-400 mesh) was placed in a vacuum impregnation apparatus, and the TiO2 sol prepared in step (1) was fully penetrated into the pores of the support by using negative pressure. After impregnation, the vacuum was released, and the support loaded with sol was dried at 80-120°C for 6-12 hours. Then, the temperature was increased to 400-700°C at a programmed heating rate of 2-5°C / min and calcined for 3-8 hours to obtain a monolithic catalyst of noble metal-rare earth metal supported TiO2.

[0052] (3) A silicon source (calculated as Si), an aluminum source (calculated as Al), phosphoric acid (calculated as P), water, and a template agent are mixed in a molar ratio of 1–5:4–14:2–16:80–200:3–10, and stirred thoroughly to form an initial molecular sieve gel. The mixture is then transferred to the liner of a reaction vessel. Subsequently, the noble metal-rare earth metal supported TiO2 monolithic catalyst obtained in step (2) is immersed in the initial molecular sieve gel and subjected to a hydrothermal crystallization reaction at 140–200 °C for 2–6 days. After the hydrothermal reaction, the product is washed and dried, and then calcined at 400–700 °C for 2–8 hours in an O2 / N2 mixed gas containing 3%–25% oxygen by volume; and at 400–700 °C for 2–8 hours in an H2 / N2 mixed gas containing 1%–7% hydrogen by volume. Ultimately, a molecular sieve-coated monolithic catalyst of noble metal-rare earth metal / TiO2 was obtained.

[0053] Preferably, in step (1), the noble metal salt is selected from chloroplatinic acid (H2PtCl6), palladium chloride (PdCl2), chloroauric acid (HAuCl4), or iridium chloride (IrCl3); the rare earth metal salt is selected from lanthanum nitrate (La(NO3)3), gadolinium nitrate (Gd(NO3)3), neodymium nitrate (Nd(NO3)3), or praseodymium nitrate (Pr(NO3)3); and the binder is silica sol, polyvinyl alcohol, polyethylene glycol, or hydroxypropyl methylcellulose.

[0054] Preferably, in step (2), the drying and curing temperature is 80-120°C, and the calcination temperature is 400-700°C.

[0055] Preferably, in step (3), the silicon source is selected from sodium silicate, tetraethyl orthosilicate, or silica sol; the aluminum source is selected from sodium aluminate, boehmite, or aluminum sulfate; and the template agent is selected from tetraethylammonium hydroxide (TEAOH), morpholine (MOR), triethylamine (TEA), N,N-diisopropylethylamine (DIPEA), or N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (DMPDOH). The molecular sieve is SAPO-18 or SAPO-34.

[0056] In some embodiments, the noble metal salt used in step (1) is chloroplatinic acid (H2PtCl6), palladium chloride (PdCl2), chloroauric acid (HAuCl4), or iridium chloride (IrCl3); the rare earth metal salt is lanthanum nitrate (La(NO3)3), gadolinium nitrate (Gd(NO3)3), neodymium nitrate (Nd(NO3)3), or praseodymium nitrate (Pr(NO3)3); and the binder is silica sol, polyvinyl alcohol, polyethylene glycol, or hydroxypropyl methylcellulose.

[0057] In some embodiments, the drying and curing temperature in step (2) is 80–120°C, and the calcination temperature is 400–700°C.

[0058] In some embodiments, the silicon source in step (3) is sodium silicate, tetraethyl orthosilicate, or silica sol; the aluminum source is selected from sodium aluminate, boehmite, or aluminum sulfate; the template agent is tetraethylammonium hydroxide (TEAOH), morpholine (MOR), triethylamine (TEA), N,N-diisopropylethylamine (DIPEA), or N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (DMPDOH). The molecular sieve is SAPO-18 or SAPO-34.

[0059] In a third aspect, the present invention provides the application of a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst in the carbon monoxide oxidation reaction.

[0060] In a fourth aspect, the present invention provides a CO catalytic oxidizer comprising the above-mentioned molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst.

[0061] In a fifth aspect, the present invention provides a tail gas treatment system for a steel sintering machine, comprising the above-mentioned CO catalytic oxidizer.

[0062] Example 1

[0063] A method for preparing a SAPO-34-coated Pt-Pr / TiO2 catalyst includes the following steps:

[0064] (1) Dissolve 42.7 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 60 °C, add 0.191 g of chloroplatinic acid (H2PtCl6·6H2O) and 0.222 g of praseodymium nitrate (Pr(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 4 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 12 hours to age and form a stable sol. Finally, add 2 g of silica sol as a binder and continue stirring for 1 hour to obtain a homogeneous sol system.

[0065] (2) The cordierite honeycomb ceramic support (300 mesh) and the sol system from step (1) were placed in a vacuum impregnation apparatus, and a vacuum was drawn and maintained for 5 minutes to allow the sol obtained in step (1) to fully penetrate into the pores of the support. After impregnation, the vacuum was slowly released, the support loaded with sol was removed, and dried at 100°C for 8 hours. Subsequently, the sample was heated to 550°C at a heating rate of 2°C / min and calcined at this temperature for 5 hours to obtain the Pt-Pr / TiO2 monolithic catalyst.

[0066] (3) Mix 2.24g sodium silicate, 2.15g boehmite, 4.46g tetraethylammonium hydroxide, 4.49g phosphoric acid, and 15.71g water, and stir for 2 hours to form a uniform initial gel. Transfer the gel to a reaction vessel with a polytetrafluoroethylene liner, and immerse the Pt-Pr / TiO2 monolithic catalyst prepared in step (2) into the molecular sieve initial gel. Perform a hydrothermal crystallization reaction at 180℃ for 5 days. After the reaction, wash the product repeatedly with deionized water until neutral, and dry at 80℃ for 12 hours. Finally, the dried sample was calcined at 550°C for 5 hours in a 10% O2 / N2 atmosphere at a heating rate of 5°C / min. Then, it was switched to a 3% H2 / N2 atmosphere and calcined under the same conditions for 4 hours. Finally, a SAPO-34-coated Pt-Pr / TiO2 monolithic catalyst (labeled as SAPO-34@Pt-Pr / TiO2) was obtained with a Pt loading of 0.6 wt.% of TiO2 mass and a Pr loading of 0.6 wt.% of TiO2 mass.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 is that the surface of the Pt / TiO2 monolithic catalyst was not coated with SAPO-34 molecular sieve and no Pr metal was added. All other conditions were exactly the same as in Example 1. Finally, a Pt / TiO2 monolithic catalyst (labeled Pt / TiO2) with a Pt loading of 0.6 wt.% of the TiO2 mass was obtained.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that the surface of the Pt-Pr / TiO2 monolithic catalyst is not coated with SAPO-34 molecular sieve. All other conditions are exactly the same as in Example 1. Finally, a Pt-Pr / TiO2 monolithic catalyst (labeled Pt-Pr / TiO2) with a Pt loading of 0.6 wt.% of TiO2 mass and a Pr loading of 0.6 wt.% of TiO2 mass was obtained.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that the SAPO-34-coated Pt / TiO2 monolithic catalyst was not loaded with Pr. All other conditions were exactly the same as in Example 1. Finally, a SAPO-34-coated Pt / TiO2 monolithic catalyst (labeled SAPO-34@Pt / TiO2) was obtained with a Pt loading of 0.6 wt.% of the TiO2 mass.

[0073] Example 2

[0074] A method for preparing a SAPO-18 coated Pd-Nd / TiO2 catalyst includes the following steps:

[0075] (1) Dissolve 53.4 g of tetraisopropyl titanate in a mixed solvent of 130 mL anhydrous ethanol and 60 mL acetylacetone. Under constant temperature and stirring at 70 °C, add 0.125 g palladium chloride (PdCl2) and 0.365 g neodymium nitrate (Nd(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 6 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 8 hours to age and form a stable sol. Finally, add 3 g of hydroxypropyl methylcellulose as a binder and continue stirring for 0.5 hours to obtain a homogeneous sol system.

[0076] (2) The cordierite honeycomb ceramic support (300 mesh) and the sol system from step (1) were placed in a vacuum impregnation apparatus, and a vacuum was drawn and maintained for 8 minutes to allow the sol prepared in step (1) to fully penetrate into the pores of the support. After impregnation, the vacuum was slowly released, the support loaded with the sol was removed, and dried at 90°C for 6 hours. Subsequently, the sample was heated to 600°C at a heating rate of 3°C / min and calcined at this temperature for 4 hours to obtain the Pd-Nd / TiO2 monolithic catalyst.

[0077] (3) Mix 8.33g tetraethyl orthosilicate, 5.74g sodium aluminate, 10.34g N,N-diisopropylethylamine, 5.88g phosphoric acid, and 19.21g water, and stir for 2 hours to form a uniform initial gel. Transfer the gel to a reaction vessel with a polytetrafluoroethylene liner, and immerse the monolithic Pd-Nd / TiO2 catalyst prepared in step (2) into the molecular sieve initial gel. Perform a hydrothermal crystallization reaction at 160℃ for 6 days. After the reaction, wash the product repeatedly with deionized water until neutral, and dry at 90℃ for 6 hours. Finally, the dried sample was calcined at 600℃ for 4 hours in a 15% O2 / N2 atmosphere at a heating rate of 5℃ / min. Then, it was switched to a 5% H2 / N2 atmosphere and calcined under the same conditions for 4 hours. Finally, a SAPO-18-coated Pd-Nd / TiO2 monolithic catalyst (labeled as SAPO-18@Pd-Nd / TiO2) was obtained with a Pd loading of 0.5 wt.% of TiO2 mass and an Nd loading of 0.8 wt.% of TiO2 mass.

[0078] Example 3

[0079] A method for preparing a SAPO-34-coated Au-Gd / TiO2 catalyst includes the following steps:

[0080] (1) Dissolve 63.95 g of tetraisopropyl titanate in a mixed solvent of 160 mL anhydrous ethanol and 40 mL acetylacetone. Under constant temperature and stirring at 50 °C, add 0.288 g of chloroauric acid (HAuCl4·3H2O) and 0.258 g of gadolinium nitrate (Gd(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 3 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 16 hours to age and form a stable sol. Finally, add 3.5 g of polyvinyl alcohol as a binder and continue stirring for 1.5 hours to obtain a homogeneous sol system.

[0081] (2) The cordierite honeycomb ceramic support (400 mesh) and the sol system from step (1) were placed in a vacuum impregnation apparatus, and a vacuum was drawn and maintained for 10 minutes to allow the sol obtained in step (1) to fully penetrate into the pores of the support. After impregnation, the vacuum was slowly released, the support loaded with sol was removed, and dried at 110°C for 7 hours. Subsequently, the sample was heated to 650°C at a heating rate of 4°C / min and calcined at this temperature for 3 hours to obtain the Au-Gd / TiO2 monolithic catalyst.

[0082] (3) Mix 1.82g silica sol, 20.53g aluminum sulfate, 6.11g morpholine, 7.84g phosphoric acid, and 27.13g water, and stir for 3 hours to form a uniform initial gel. Transfer the gel to a reaction vessel with a polytetrafluoroethylene liner, and immerse the Pt-Pr / TiO2 monolithic catalyst prepared in step (2) into the molecular sieve initial gel. Perform a hydrothermal crystallization reaction at 200℃ for 4 days. After the reaction, wash the product repeatedly with deionized water until neutral, and dry at 110℃ for 7 hours. Finally, the dried sample was calcined at 650°C for 3 hours in a 20% O2 / N2 atmosphere at a heating rate of 5°C / min. Then, it was switched to a 6% H2 / N2 atmosphere and calcined under the same conditions for 3 hours. Finally, a SAPO-34-coated Au-Gd / TiO2 monolithic catalyst (labeled as SAPO-34@Au-Gd / TiO2) was obtained with an Au loading of 0.8 wt.% of TiO2 mass and a Gd loading of 0.5 wt.% of TiO2 mass.

[0083] Example 4

[0084] A method for preparing a SAPO-18-coated Ir-La / TiO2 catalyst includes the following steps:

[0085] (1) Dissolve 71.20 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 80 °C, add 0.257 g of iridium chloride (IrCl3·3H2O) and 0.561 g of lanthanum nitrate (La(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 5 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 20 hours to age and form a stable sol. Finally, add 4 g of polyethylene glycol as a binder and continue stirring for 2 hours to obtain a homogeneous sol system.

[0086] (2) The cordierite honeycomb ceramic support (400 mesh) and the sol system from step (1) were placed in a vacuum impregnation apparatus, and a vacuum was drawn and maintained for 15 minutes to allow the sol obtained in step (1) to fully penetrate into the pores of the support. After impregnation, the vacuum was slowly released, the support loaded with sol was removed, and dried at 80°C for 12 hours. Subsequently, the sample was heated to 450°C at a heating rate of 5°C / min and calcined at this temperature for 7 hours to obtain the Ir-La / TiO2 monolithic catalyst.

[0087] (3) 2.44 g sodium silicate, 1.83 g boehmite, 6.96 g N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, 4.90 g phosphoric acid, and 16.22 g water were mixed and stirred for 4 hours to form a uniform initial gel. The gel was transferred to a reaction vessel with a polytetrafluoroethylene liner, and the Ir-La / TiO2 monolithic catalyst prepared in step (2) was immersed in the molecular sieve initial gel. Hydrothermal crystallization reaction was carried out at 150 °C for 6 days. After the reaction, the product was repeatedly washed with deionized water until neutral and dried at 80 °C for 12 hours. Finally, the dried sample was calcined at 450°C for 7 hours in a 25% O2 / N2 atmosphere at a heating rate of 5°C / min. Then, it was switched to a 2% H2 / N2 atmosphere and calcined under the same conditions for 7 hours. Finally, a SAPO-18-coated Ir-La / TiO2 monolithic catalyst (labeled as SAPO-18@Ir-La / Ti) was obtained with Ir loading of 0.7 wt.% of TiO2 mass and La loading of 0.9 wt.% of TiO2 mass.

[0088] XRD tests were performed on the catalysts prepared in Examples 1-4 and Comparative Examples 1-3, and the results are as follows: Figure 1As shown, SAPO-34-coated Pt-Pr / TiO2 exhibits typical diffraction peaks characteristic of anatase TiO2 and SAPO-34 molecular sieves; SAPO-18-coated Pd-Nd / TiO2 exhibits characteristic diffraction peaks characteristic of anatase TiO2 and SAPO-18 molecular sieves; SAPO-34-coated Au-Gd / TiO2 exhibits characteristic diffraction peaks characteristic of anatase TiO2 and SAPO-34 molecular sieves; SAPO-18-coated Ir-La / TiO2 exhibits characteristic diffraction peaks characteristic of anatase TiO2 and SAPO-18 molecular sieves. Pt / TiO2 and Pt-Pr / TiO2 only show diffraction peaks characteristic of anatase TiO2, while SAPO-34-coated Pt / TiO2 exhibits dual characteristic diffraction patterns characteristic of both anatase TiO2 and SAPO-34 molecular sieves. These results indicate that the molecular sieve coating layer was successfully constructed, and the coating process did not induce a phase transition in TiO2 or damage to the molecular sieve structure. This demonstrates that the in-situ hydrothermal synthesis coating process is compatible with the thermal stability of the TiO2 support. Furthermore, no characteristic diffraction peaks of noble metals such as Pt, Pd, Au, and Ir, or rare earth metals such as La, Gd, Nd, or Pr were observed in any of the catalysts, indicating that the active metal components are highly dispersed or that their nanoparticle size is smaller than the XRD detection limit.

[0089] The catalysts prepared in Examples 1-4 and Comparative Examples 1-3 were tested for their CO catalytic oxidation performance and resistance to COS poisoning. The test conditions were: catalyst dosage 0.25 g (60-80 mesh); simulated flue gas composition 1000 ppm CO, 10% H₂O, 8% O₂, 500 ppm COS (introduced if necessary); and reaction space velocity 150,000 h⁻¹. -1 .

[0090] The test results for the catalyst's CO oxidation performance, resistance to COS poisoning, and resistance to Pb (4 wt.%) poisoning are as follows: Figure 2 , Figure 3 and Figure 4 As shown.

[0091] Depend on Figure 2It is evident that, compared to Pt / TiO2, Pt-Pr / TiO2, and SAPO-34@Pt / TiO2 catalysts, SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2, and SAPO-18@Ir-La / TiO2 catalysts exhibit higher CO catalytic oxidation performance. This is primarily because the microporous structure (~0.38 nm) of the SAPO-34 and SAPO-18 molecular sieves enhances the dispersion of noble metals (Pt, Pd, Au, or Ir) and rare earth metals (Pr, Nd, Gd, or La) through confinement. Furthermore, the strongly acidic sites of the molecular sieves facilitate CO adsorption and activation. Simultaneously, rare earth metals significantly enhance the redox capabilities of noble metals through electronic and structural effects, while the oxygen storage capacity of rare earth metals themselves accelerates the interfacial reaction between CO and O2. It is worth noting that the molecular sieve layer effectively inhibits the migration and aggregation of active components through physical confinement, thereby maintaining the high activity of the catalyst over a wide temperature range.

[0092] Depend on Figure 3 and Figure 4It can be seen that after COS is introduced into the reaction or the catalyst is poisoned by Pb heavy metals, the CO oxidation activity of all catalysts decreases to varying degrees. However, the noble metal-rare earth metal catalysts coated with molecular sieves (SAPO-34@Pt-Pr / TiO2, SAPO-18@Pd-Nd / TiO2, SAPO-34@Au-Gd / TiO2 and SAPO-18@Ir-La / TiO2) show significantly better resistance to COS and Pb poisoning than other catalysts. This is mainly due to the following synergistic mechanism: (1) The physical barrier effect of the molecular sieve support: The microporous structure of SAPO-34 and SAPO-18 selectively blocks large molecular poisons (such as sulfur species or Pb species) from contacting the active sites of the catalyst through the size sieving effect, while allowing small molecular CO / O2 to diffuse freely, thereby reducing the direct coverage of poisons on the surface of noble metals. (2) Chemical resistance of bimetallic systems: Rare earth metals have oxygen storage-release functions, which can dynamically remove adsorbed sulfur / lead species and form stable sulfates or lead oxides. These substances then migrate to the surface of the support, thereby avoiding clogging of the active sites of noble metals. In addition, the electron transfer between noble metals and rare earth metals can maintain the reduced state of noble metals and effectively inhibit the oxidative deactivation of active sites caused by poisons. (3) Optimization of surface chemical properties of molecular sieves: The weak hydrophobicity of SAPO-18 or SAPO-34 reduces the adsorption tendency of polar poisons on the catalyst surface; at the same time, bimetallic loading further weakens the chemical adsorption intensity of poisons through competitive adsorption (such as CO preferentially occupying active sites). In contrast, uncoated Pt / TiO2 and Pt-Pr / TiO2 catalysts lack physical barriers and chemical synergistic protection, and poisons can directly cover the surface of the active metal, leading to irreversible passivation. It is worth noting that although SAPO-34@Pt / TiO2 possesses the physical barrier of a molecular sieve, it only loads a single Pt metal and lacks the oxygen buffering effect of rare earth metals, thus failing to dynamically remove adsorbed poisons. Furthermore, due to the lack of sufficient electronic effects, its competitive adsorption capacity is weak, and poisons are more likely to occupy isolated Pt sites. These factors combined result in its significantly weaker anti-poisoning ability compared to bimetallic systems (such as SAPO-34@Pt-Pr / TiO2). These results further demonstrate the importance of molecular sieve coating and noble metal-rare earth metal synergistic design in improving anti-poisoning capabilities.

[0093] Example 5

[0094] A method for preparing a SAPO-34-coated Au-La / TiO2 catalyst includes the following steps:

[0095] (1) Dissolve 64.05 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 50 °C, add 0.144 g of chloroauric acid (HAuCl4·3H2O) and 0.561 g of lanthanum nitrate (La(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 3 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 10 hours to age and form a stable sol. Finally, add 2.5 g of hydroxypropyl methylcellulose as a binder and continue stirring for 1 hour to obtain a homogeneous sol system.

[0096] (2) The cordierite honeycomb ceramic support (200 mesh) and the sol system from step (1) were placed in a vacuum impregnation apparatus, and a vacuum was drawn and maintained for 10 minutes to allow the sol obtained in step (1) to fully penetrate into the pores of the support. After impregnation, the vacuum was slowly released, the support loaded with the sol was removed, and dried at 90°C for 10 hours. Subsequently, the sample was heated to 500°C at a heating rate of 3°C / min and calcined at this temperature for 6 hours to obtain the Au-La / TiO2 monolithic catalyst.

[0097] (3) Mix 1.25 g silica sol, 2.44 g boehmite, 2.11 g triethylamine, 4.08 g phosphoric acid, and 15.84 g water, and stir for 2.5 hours to form a uniform initial gel. Transfer the gel to a reaction vessel with a polytetrafluoroethylene liner, and immerse the Au-La / TiO2 monolithic catalyst prepared in step (2) into the molecular sieve initial gel. Perform a hydrothermal crystallization reaction at 170 °C for 4 days. After the reaction, wash the product repeatedly with deionized water until neutral, and dry at 90 °C for 10 hours. Finally, the dried sample was heated to 500℃ for 6 hours in a 5% O2 / N2 atmosphere at a heating rate of 5℃ / min, and then switched to a 4% H2 / N2 atmosphere and calcined under the same conditions for 6 hours. Finally, a SAPO-34 coated Au-La / TiO2 monolithic catalyst with Au loading of 0.4 wt.% of TiO2 mass and La loading of 1.0 wt.% of TiO2 mass was obtained.

[0098] Example 6

[0099] The only difference from Example 5 is that the step (3) for preparing the initial gel is as follows:

[0100] Mix 3.75g silica sol, 7.32g boehmite, 6.33g triethylamine, 12.24g phosphoric acid and 47.52g water, and stir for 2.5 hours to form a uniform initial gel.

[0101] Example 7

[0102] The only difference from Example 5 is that the step (3) for preparing the initial gel is as follows:

[0103] Mix 7.5g silica sol, 14.64g boehmite, 12.66g triethylamine, 24.48g phosphoric acid and 95.04g water, and stir for 2.5 hours to form a uniform initial gel.

[0104] Example 8

[0105] A method for preparing a SAPO-18 coated Ir-Nd / TiO2 catalyst includes the following steps:

[0106] (1) Dissolve 35.58 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 40 °C, add 0.220 g of iridium chloride (IrCl3·3H2O) and 0.365 g of neodymium nitrate (Nd(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 3 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 14 hours to age and form a stable sol. Finally, add 1 g of silica sol as a binder and continue stirring for 1.5 hours to obtain a homogeneous sol system.

[0107] (2) The cordierite honeycomb ceramic support (300 mesh) and the sol system from step (1) were placed in a vacuum impregnation apparatus, and a vacuum was drawn and maintained for 7 minutes to allow the sol obtained in step (1) to fully penetrate into the pores of the support. After impregnation, the vacuum was slowly released, the support loaded with sol was removed, and dried at 105°C for 7 hours. Subsequently, the sample was heated to 600°C at a heating rate of 2°C / min and calcined at this temperature for 5 hours to obtain the Ir-Nd / TiO2 monolithic catalyst.

[0108] (3) Mix 3.19 g of tetraethyl orthosilicate, 7.86 g of aluminum sulfate, 2.33 g of N,N-diisopropylethylamine, 3.01 g of phosphoric acid, and 10.33 g of water, and stir for 2 hours to form a uniform initial gel. Transfer the gel to a reaction vessel with a polytetrafluoroethylene liner, and immerse the Ir-Nd / TiO2 monolithic catalyst prepared in step (2) into the molecular sieve initial gel. Perform a hydrothermal crystallization reaction at 190 °C for 3 days. After the reaction, wash the product repeatedly with deionized water until neutral, and dry at 105 °C for 7 hours. Finally, the dried sample was heated to 600℃ for 5 hours in a 13% O2 / N2 atmosphere at a heating rate of 5℃ / min, and then switched to a 5% H2 / N2 atmosphere and calcined for 5 hours under the same conditions. Finally, a SAPO-18 coated Ir-Nd / TiO2 monolithic catalyst with Ir loading of 1.2 wt.% of TiO2 mass and Nd loading of 1.5 wt.% of TiO2 mass was obtained.

[0109] Example 9

[0110] The only difference from Example 8 is that the step (3) for preparing the initial gel is as follows:

[0111] Mix 6.38g tetraethyl orthosilicate, 15.72g aluminum sulfate, 4.66g N,N-diisopropylethylamine, 6.02g phosphoric acid and 20.66g water, and stir for 2 hours to form a uniform initial gel.

[0112] Example 10

[0113] Mix 15.95g tetraethyl orthosilicate, 39.31g aluminum sulfate, 11.65g N,N-diisopropylethylamine, 15.05g phosphoric acid and 51.65g water, and stir for 2 hours to form a uniform initial gel.

[0114] Example 11

[0115] A method for preparing a SAPO-18 coated Pt-Gd / TiO2 catalyst includes the following steps:

[0116] (1) Dissolve 46.27 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 70 °C, add 0.069 g of chloroplatinic acid (H2PtCl6·6H2O) and 0.112 g of gadolinium nitrate (Gd(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 5 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 18 hours to age and form a stable sol. Finally, add 2 g of polyethylene glycol as a binder and continue stirring for 2 hours to obtain a homogeneous sol system.

[0117] (2) The cordierite honeycomb ceramic support (200 mesh) was placed in a vacuum impregnation apparatus, and a vacuum was drawn and maintained for 9 minutes to allow the sol prepared in step (1) to fully penetrate into the pores of the support. After impregnation, the vacuum was slowly released, the support loaded with sol was removed, and dried at 120°C for 6 hours. Subsequently, the sample was heated to 700°C at a heating rate of 4°C / min and calcined at this temperature for 3 hours to obtain the Pt-Gd / TiO2 monolithic catalyst.

[0118] (3) Mix 2.02g silica sol, 4.60g sodium aluminate, 8.24g N,N-dimethyl-3,5-dimethylpiperidinium, 6.62g phosphoric acid, and 32.24g water, and stir for 2 hours to form a uniform initial gel. Transfer the gel to a reaction vessel with a polytetrafluoroethylene liner, and immerse the Pt-Gd / TiO2 monolithic catalyst prepared in step (2) into the molecular sieve initial gel. Perform a hydrothermal crystallization reaction at 140℃ for 6 days. After the reaction, wash the product repeatedly with deionized water until neutral, and dry at 120℃ for 6 hours. Finally, the dried sample was heated to 700℃ for 3 hours in a 25% O2 / N2 atmosphere at a heating rate of 5℃ / min, and then switched to a 7% H2 / N2 atmosphere and calcined for 3 hours under the same conditions. Finally, a SAPO-18 coated Pt-Gd / TiO2 monolithic catalyst with a Pt loading of 0.2 wt.% of TiO2 mass and a Gd loading of 0.3 wt.% of TiO2 mass was obtained.

[0119] Example 12

[0120] The only difference from Example 11 is the amount of chloroplatinic acid and gadolinium nitrate added in step (1):

[0121] (1) Dissolve 46.27 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 70 °C, add 0.173 g of chloroplatinic acid (H2PtCl6·6H2O) and 0.261 g of gadolinium nitrate (Gd(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 5 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 18 hours to age and form a stable sol. Finally, add 2 g of polyethylene glycol as a binder and continue stirring for 2 hours to obtain a homogeneous sol system.

[0122] Step (3) finally yields a SAPO-18 coated Pt-Gd / TiO2 monolithic catalyst with a Pt loading of 0.5 wt.% of TiO2 mass and a Gd loading of 0.7 wt.% of TiO2 mass.

[0123] Example 13

[0124] (1) Dissolve 46.27 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 70 °C, add 0.276 g of chloroplatinic acid (H2PtCl6·6H2O) and 0.410 g of gadolinium nitrate (Gd(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 5 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 18 hours to age and form a stable sol. Finally, add 2 g of polyethylene glycol as a binder and continue stirring for 2 hours to obtain a homogeneous sol system.

[0125] Step (3) finally yields a SAPO-18 coated Pt-Gd / TiO2 monolithic catalyst with a Pt loading of 0.8 wt.% of TiO2 mass and a Gd loading of 1.1 wt.% of TiO2 mass.

[0126] Example 14

[0127] (1) Dissolve 46.27 g of tetraisopropyl titanate in a mixed solvent of 150 mL anhydrous ethanol and 50 mL acetylacetone. Under constant temperature and stirring at 70 °C, add 0.414 g of chloroplatinic acid (H2PtCl6·6H2O) and 0.597 g of gadolinium nitrate (Gd(NO3)3·6H2O). Then, slowly add 50 mL of 2M nitric acid aqueous solution and react for 5 hours to complete the hydrolysis process. After the reaction is complete, let the reaction system stand at room temperature for 18 hours to age and form a stable sol. Finally, add 2 g of polyethylene glycol as a binder and continue stirring for 2 hours to obtain a homogeneous sol system.

[0128] Step (3) finally yields a SAPO-18 coated Pt-Gd / TiO2 monolithic catalyst with a Pt loading of 1.2 wt.% of TiO2 mass and a Gd loading of 1.6 wt.% of TiO2 mass.

[0129] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. The application of a molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst in the CO oxidation reaction, characterized in that, The molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst comprises: a composite active component composed of noble metals and rare earth metals, a TiO2 support, and a molecular sieve coating layer. The composite active component composed of noble metals and rare earth metals is dispersed in the TiO2 support, and the molecular sieve coating layer coats the TiO2 support; The noble metal is selected from at least one of Pt, Pd, Au and Ir, and the rare earth metal is at least one of La, Gd, Nd and Pr; The preparation method of the molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst includes the following steps: (1) Dissolve noble metal salts, rare earth metal salts and titanium source in solvent, and add binder after hydrolysis and aging to obtain sol system; (2) The sol system is loaded onto a ceramic carrier, and then dried, cured and calcined to obtain a noble metal-rare earth metal / TiO2 matrix; (3) A molecular sieve coating layer is grown in situ on the noble metal-rare earth metal / TiO2 matrix by hydrothermal method, and then calcined in stages in an oxidizing atmosphere and a reducing atmosphere to obtain the molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst. In step (3), the material of the molecular sieve coating layer is SAPO-18 or SAPO-34.

2. The application of the molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst according to claim 1 in the CO oxidation reaction, characterized in that, The loading of precious metals accounts for 0.2 to 1.5 wt.% of the TiO2 support mass, and the loading of rare earth metals accounts for 0.2 to 2 wt.% of the TiO2 support mass.

3. The application of the molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst according to claim 1 in the CO oxidation reaction, characterized in that, The noble metal salt is selected from at least one of chloroplatinic acid, palladium chloride, chloroauric acid and iridium chloride; the rare earth metal salt is selected from at least one of lanthanum nitrate, gadolinium nitrate, neodymium nitrate and praseodymium nitrate; the binder is at least one of silica sol, polyvinyl alcohol, polyethylene glycol and hydroxypropyl methylcellulose.

4. The application of the molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst according to claim 1 in the CO oxidation reaction, characterized in that, The drying and curing temperature in step (2) is 80~120 ℃, and the calcination temperature is 400~700 ℃; the hydrothermal temperature in step (3) is 140~200 ℃, and the reaction time of the hydrothermal method is 2~6 days.

5. The application of the molecular sieve-coated noble metal-rare earth metal / TiO2 monolithic catalyst according to claim 1 in the CO oxidation reaction, characterized in that, In step (3) segmented calcination, the calcination conditions under the oxidizing atmosphere are: in an O2 / N2 mixed gas containing 3%~25% oxygen by volume, the temperature is raised to 400~700 ℃ and calcined at a constant temperature for 2~8 hours; the calcination conditions under the reducing atmosphere are: in an H2 / N2 mixed gas containing 1%~7% hydrogen by volume, the temperature is raised to 400~700 ℃ and calcined at a constant temperature for 2~8 hours.

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