A chlorine-free type palladium-based catalyst for vapor-phase oxo synthesis of dimethyl carbonate, a preparation method and application thereof

Abstract

The application discloses a chlorine-free type palladium-based catalyst for gas-phase carbonyl synthesis of dimethyl carbonate and a preparation method and application thereof. The catalyst comprises an active component Pd and a molecular sieve carrier; wherein the molecular sieve carrier is further loaded with structural stabilizing aids Cu, K and metal M; in the catalyst, the Pd is 0.25-2% in mass percentage, the Cu is 0.05-10% in mass percentage, the K is 0.01-5% in mass percentage, and the M is 0.01-1% in mass percentage. The catalyst is prepared by firstly loading the Cu, K and metal M on the molecular sieve carrier to obtain a skeleton-modified Cu-K-M-molecular sieve carrier, configuring the carrier into a suspension, then adding a palladium precursor solution drop by drop into the suspension for ion exchange, and finally calcining in an oxidizing atmosphere. The catalyst has high activity and high stability, and the preparation method is simple, green and environment-friendly. When applied to a CO and methyl nitrite gas-phase carbonyl synthesis process of dimethyl carbonate, the catalyst can eliminate the problems of deactivation of a chlorine-containing catalyst and corrosion of equipment, and has industrial application potential.

Description

Technical Field

[0001] This invention belongs to the field of palladium-based catalyst technology, specifically relating to a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate, its preparation method, and its application. Background Technology

[0002] Dimethyl carbonate (DMC), as a green chemical intermediate, has received widespread attention in the fields of construction, automobiles, medical devices, lithium batteries, and fuels over the past two decades. Furthermore, the DMC molecule possesses both methyl and carbonyl functional groups, thus it can replace highly toxic dimethyl sulfate and phosgene as a green methylating and carbonylating agent.

[0003] Currently, over 90% of industrially produced DMC is obtained via transesterification. This process uses propylene oxide as a raw material, reacting it with CO2 to produce a recyclable carbonate intermediate. This carbonate intermediate then undergoes transesterification with methanol to generate DMC. However, propylene oxide is produced from petroleum through a chlorohydrin process, resulting in high production costs and severe environmental pollution. With the increasing depletion of global fossil fuels and the growing demand for DMC, there is an urgent need to develop a low-cost and environmentally friendly DMC production route.

[0004] The gas-phase synthesis of dimethyl carbonate (DMC) from CO and methyl nitrite, developed by UBE Corporation of Japan, has garnered widespread attention in the industry due to its unique characteristics of operating at atmospheric pressure and low temperature (363-403 K) without water generation during the reaction. It is a highly economical and environmentally friendly process. Currently, reported catalysts for the gas-phase carbonyl synthesis of DMC are mainly classified into chlorine-containing palladium-based catalysts and chlorine-free palladium-based catalysts. In the gas-phase carbonyl synthesis of DMC, CO in the feed gas acts as a strong reducing agent. As the catalytic reaction proceeds, the active site Pd in ​​the catalyst... 2+ Reduced to Pd by CO 0 As the number of ions increases, the catalyst gradually loses its catalytic ability and becomes deactivated. Therefore, catalyst stability is the main reason limiting the industrialization of this process. Yasushi Yamamoto et al. proposed that in the gas-phase carbonyl synthesis of dimethyl carbonate, the active sites of both chlorine-containing palladium-based and non-chlorine-containing palladium-based catalysts are divalent palladium (Pd). 2+ How to ensure that palladium is distributed as uniformly as possible and that Pd is maintained during the catalytic cycling reaction? 2+The presence of the valence state is a key factor in improving catalyst stability (vapour phase carbonylation reactions using methyl nitrite over Pd catalysts, Catalysis surveys from Asia (2010) 14:103–110). For chlorine-containing catalysts with high initial catalytic performance and selectivity, HCl gas must be continuously added to the system during production to maintain the Pd valence state in the catalyst. 2+ The stable presence of chloride ions can cause corrosion of production equipment and affect the gloss of the product. In contrast, although chloride-free catalysts can solve the problem of catalyst deactivation caused by chloride ion loss and effectively reduce production costs, current chloride-free catalysts generally suffer from low activity and insufficient stability. Patent CN106179506A discloses a supported palladium-based catalyst and its preparation method. The active component of the catalyst is a palladium-based complex, and the promoter is a metal complex. The preparation method involves adding ammonia to the palladium complex and the metal complex to form a strongly alkaline solution, then adding the support and stirring to disperse it. Finally, ammonia is evaporated until the pH of the system is neutral, followed by separation, drying, and calcination to obtain the supported palladium-based catalyst. This catalyst maintains a CO conversion rate of around 80% and a DMC selectivity of over 99% within 100 hours of reaction. However, this patent does not disclose the space-time yield of dimethyl carbonate, and the catalyst preparation process uses various organic solvents, strong alkalis, and large amounts of ammonia, which will inevitably increase the difficulty of subsequent wastewater treatment and environmental protection. Patent CN111659456A discloses a catalyst specifically for the synthesis of dimethyl carbonate and its preparation method. The active metal of this catalyst is palladium, the auxiliary agent is copper, and the support is an oxide-modified molecular sieve. The preparation method involves first modifying the molecular sieve support through processes such as ion exchange, alkaline precipitation, and calcination to obtain a metal oxide-modified molecular sieve support M. x O y -Y. Then, ion exchange was used on M... x O y A chlorine-free catalyst can be obtained by loading Pd and Cu onto Y. The DMC space-time yield of this catalyst can reach about 700 (g / l˙h); however, this invention not only does not disclose the stability of the catalyst, but also requires ultrasonic assistance in the preparation process, which makes it difficult to apply in actual large-scale production.

[0005] Although significant progress has been made both domestically and internationally in the development of chlorine-free gas-phase carbonyl synthesis catalysts for dimethyl carbonate, the key factor in whether the gas-phase carbonyl synthesis of dimethyl carbonate can be industrialized remains the development of highly active and stable chlorine-free palladium-based catalysts using simple, green, economical, and safe preparation methods. Summary of the Invention

[0006] The purpose of this invention is to provide a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate, its preparation method, and its application. This catalyst has high activity and high stability, and its preparation method is simple, environmentally friendly, and has potential for industrial application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising an active component Pd and a molecular sieve support; wherein the molecular sieve support is further supported with structural stabilizing agents Cu, K and metal M; wherein, by mass percentage, Pd is 0.25-2%, Cu is 0.05-10%, K is 0.01-5%, and M is 0.01-1%.

[0009] According to the above scheme, the metal M is one or two of Zn, Fe, Ag, Mn, V, and Eu; particularly preferred are combinations of Zn and Mn, Fe and Mn, or V and Fe.

[0010] According to the above scheme, the molecular sieve support is one or a mixture of two or more of the following molecular sieves: NaX type, NaY type, Naβ, MCM-41, and ZSM-35.

[0011] According to the above scheme, the chlorine-free palladium-based catalyst uses a framework-modified Cu-KM-molecular sieve obtained by modification with Cu, K, and metallic M as a support, and undergoes ion exchange with a palladium precursor solution (palladium reacts with Na in the molecular sieve support). + It is obtained by ion exchange and calcination in an oxidizing atmosphere. Specifically, Cu, K and metal M are first loaded onto a molecular sieve support, and then calcined to obtain a framework-modified Cu-KM-molecular sieve support. The framework-modified Cu-KM-molecular sieve support is then prepared into a suspension, and a palladium precursor solution is added dropwise to the suspension for ion exchange. After separation, washing and drying, it is finally calcined in an oxidizing atmosphere to obtain the final product.

[0012] This invention also provides a method for preparing the above-mentioned chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate, wherein the structural stabilizing agents Cu, K, M and palladium are stepwise supported on a molecular sieve support, comprising the following steps:

[0013] 1) The molecular sieve support is prepared into a support suspension, and then soluble Cu salt, soluble K salt and soluble metal M salt are added to the support suspension and stirred together for loading; after loading is completed, the support is separated and washed, and finally dried and calcined to obtain the framework modified Cu-KM-molecular sieve support.

[0014] 2) Prepare a palladium precursor solution from the palladium precursor;

[0015] 3) Prepare a suspension using the Cu-KM-molecular sieve support obtained in step 1), and then add the palladium precursor solution obtained in step 2) dropwise to the suspension while stirring, so that the Na in the molecular sieve support reacts with the Na. + Ion exchange is performed; after the exchange is complete, the catalyst is separated and washed, and finally dried and calcined to obtain a chlorine-free palladium-based catalyst; the calcination is carried out under an oxidizing atmosphere.

[0016] According to the above scheme, in step 1), the mass ratio of molecular sieve carrier to deionized water in the carrier suspension is 1:20 to 1:300.

[0017] According to the above scheme, in step 1), the stirring load conditions are: temperature controlled at 10-80℃, stirring speed controlled at 300-800rpm, and time of 0.5-10h.

[0018] According to the above scheme, in step 1), the drying temperature is 60-120℃ and the drying time is 2-24h; the calcination temperature is 200-600℃ and the calcination time is 2-6h.

[0019] According to the above scheme, in step 1), the Cu salt is one or more of copper chloride, copper sulfate, or copper nitrate; the K salt is one or more of potassium chloride, potassium nitrate, potassium sulfate, or potassium carbonate.

[0020] According to the above scheme, the metal M salt is ZnCl2, Zn(NO3)2, Fe(NO3)3, Fe(NO3)2, FeCl3, FeCl2, AgNO3, MnCl2, VOSO4, or EuCl3.

[0021] According to the above scheme, in step 2), the palladium precursor is one or both of dichlorotetraamminepalladium or tetraamminepalladium nitrate.

[0022] According to the above scheme, in step 2), the Pd in ​​the palladium precursor solution 2+ The concentration is 0.001–0.05 M.

[0023] According to the above scheme, based on the total mass of molecular sieve support, Pd, Cu, K, and metal M, the palladium precursor, calculated as Pd, accounts for 0.25-2% by mass percentage; Cu salt, calculated as Cu, accounts for 0.05-10%; K salt, calculated as K, accounts for 0.01-5%; and metal M salt, calculated as M, accounts for 0.01-1%.

[0024] According to the above scheme, in step 3), the mass ratio of Cu-KMY molecular sieve support to deionized water in the suspension is 1:50 to 1:400.

[0025] According to the above scheme, in step 3), the stirring speed is controlled at 200-600 rpm, the ion exchange temperature is 10-80℃, and the exchange time is 4-48h.

[0026] According to the above scheme, in step 3), the palladium precursor solution is added over a period of 3 to 23 hours.

[0027] According to the above scheme, in step 3), the drying temperature is 60-120℃ and the drying time is 2-24h.

[0028] According to the above scheme, in step 3), the calcination temperature is 150–300℃, and the calcination time is 2–6 hours. Preferably, the heating rate is 0.5–2℃ / min.

[0029] According to the above scheme, in step 3), the roasting is completed in a muffle furnace or a tube furnace.

[0030] According to the above scheme, in step 3), the oxidizing atmosphere is a nitrogen-oxygen mixture atmosphere; preferably, the oxygen percentage in the nitrogen-oxygen mixture is in the range of 20-100%, and the equilibrium gas is N2.

[0031] According to the above scheme, in step 3), the flow rate of the oxidizing atmosphere gas during the roasting process is 100-400 ml / min.

[0032] This invention provides an application of the above-mentioned chlorine-free palladium-based catalyst in the synthesis of dimethyl carbonate from the reaction of carbon monoxide and methyl nitrite.

[0033] According to the above scheme, the reaction conditions for the application are: reaction temperature 110–130℃; reaction pressure 0.1–1 MPa; space velocity 6000–8000 h⁻¹. -1 .

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. This invention provides a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate, comprising a Pd active component and a molecular sieve support. The molecular sieve support is further supported with structural stabilizing agents Cu, K, and metal M. The addition of Cu effectively inhibits the aggregation and growth of palladium particles, while the addition of K promotes CO activation. Furthermore, a special structural stabilizing agent M is doped into the catalyst. The outer electron orbitals of this type of metal M are all in an unfilled or half-filled state, allowing it to both accept and release electrons. Therefore, it can effectively transfer electrons with Pd, preventing Pd from being absorbed in the strong reducing atmosphere of CO. 2+Excessive reduction of Pd by CO 0 This can better facilitate the long-term stable existence of divalent palladium, thereby further improving the stability of the catalyst; in addition, the empty or half-empty orbitals of the structurally stabilizing promoter M can accept electrons from CO molecules and further activate CO molecules, maintaining the long-term stable activity of the catalyst.

[0036] 2. This invention provides a method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate. First, structurally stabilizing agents Cu, K, and M are loaded onto a molecular sieve support to obtain a framework-modified Cu-KM-molecular sieve support, with Cu, K, and M uniformly distributed on the molecular sieve support. Then, a palladium precursor solution is added dropwise to the Cu-KM-molecular sieve support suspension, reacting with Na+ in the molecular sieve support. + Ion exchange is performed, with the palladium precursor uniformly distributed within suitable pores of the molecular sieve support. This ensures effective contact with the reactant molecules, guaranteeing good catalyst activity, while also suppressing deactivation caused by subsequent Pd particle agglomeration. Finally, calcination under an oxidizing atmosphere effectively ensures the conversion of palladium into Pd. 2+ It exists, the preparation method is simple, no ammonia, acid, alkali or organic solvents are required, it is environmentally friendly, and it is particularly suitable for large-scale industrial production and application. Attached Figure Description

[0037] Figure 1 The graph shows the relationship between the space-time yield of dimethyl carbonate and the reaction time when the chlorine-free palladium-based catalysts prepared in Examples 1-10 are applied to the gas-phase carbonyl synthesis of dimethyl carbonate from methyl nitrite. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Example 1

[0040] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0041] 1) Preparation of Cu-K-Zn modified NaY support: At room temperature, 10.0 g of NaY molecular sieve was weighed and dispersed in 500 g of deionized water at 400 rpm. Then, 0.4140 g of CuCl2·2H2O, 0.0981 g of KCl and 0.5574 g of ZnCl2 were weighed and added to the support dispersion. After stirring for 3 h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 80 °C for 2 h. Then, it was calcined in a muffle furnace at 500 °C for 2 h to obtain the framework modified Cu-K-Fe modified NaY support.

[0042] 2) Preparation of 0.0075M Pd solution: Weigh 0.5111g of dichlorotetraamminepalladium containing 0.05142g of palladium and dissolve it in 64.4ml of deionized water and stir well.

[0043] 3) Preparation of chlorine-free palladium catalyst: First, the Cu-K-Zn modified NaY support from step (1) was dispersed in deionized water at a solid-liquid ratio of 1:50 at a speed of 250 rpm and stirred for 30 minutes. Then, the Pd solution from step (2) was added dropwise to the dispersion for 10 hours of ion exchange, with the Pd solution being added at a uniform rate over 8 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 110°C for 2 hours. Then, it was heated to 200°C at a heating rate of 1°C / min in a tube furnace with a gas flow rate of 200 ml / min and a gas flow rate of 20% O2 + 80% N2, and calcined for 4 hours to obtain a highly active and stable chlorine-free dimethyl carbonate catalyst of 0.5% Pd·1.5% Cu·0.5% K·0.26% Zn·97.24% NaY.

[0044] Example 2

[0045] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0046] 1) Preparation of Cu-K-Fe-Mn modified NaY support: 10.0 g of NaY molecular sieve was dispersed in 1000 g of deionized water at 40 °C at 600 rpm. Then, 0.3648 g of CuCl2·2H2O, 0.3989 g of KCl, 0.0375 g of Fe(NO3)3·9H2O and 0.0076 g of MnCl2·4H2O were added to the support dispersion. After stirring for 6 h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 100 °C for 2 h. Then, it was calcined in a muffle furnace at 550 °C for 4 h to obtain the framework-modified Cu-K-Fe-Mn modified NaY support.

[0047] 2) Preparation of 0.01 MPd solution: Weigh 1.0398 g of dichlorotetraamminepalladium containing 0.1046 g of palladium and dissolve it in 98 ml of deionized water and stir well.

[0048] 3) Preparation of chlorine-free palladium catalyst: The Cu-K-Fe-Mn modified NaY support obtained in step (1) was first dispersed in deionized water at 80℃ at a solid-liquid ratio of 1:200 at 300 rpm. After stirring for 30 minutes, the Pd solution from step (2) was added dropwise to the dispersion for ion exchange for 24 hours, with the Pd solution being added at a uniform rate over 12 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 110℃ for 4 hours. Then, it was heated to 150℃ at a heating rate of 0.5℃ / min in a tube furnace with a gas flow rate of 200 ml / min and a mixture of 20% O2 and 80% N2 and calcined for 4 hours to obtain a highly active and stable chlorine-free dimethyl carbonate catalyst of 1.0% Pd·1.3% Cu·2.0% K·0.05% Fe·0.02% Mn·95.63% NaY.

[0049] Example 3

[0050] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0051] 1) Preparation of Cu-K-Ag modified mixed molecular sieve support: 8.5g of NaY and 1.5g of NaX molecular sieves were weighed and dispersed in 1500g of deionized water at 80℃ with a rotation speed of 500rpm. Then, 1.1999g of Cu(NO3)2·3H2O, 0.0902g of KCl and 0.0828g of AgNO3 were weighed and added to the support dispersion. After stirring for 5h, the suspension was separated into solid and liquid. The obtained solid was dried at 120℃ for 24h after being rinsed with deionized water and then calcined in a muffle furnace at 400℃ for 5h to obtain the framework modified Cu-K-Ag modified mixed molecular sieve support.

[0052] 2) Preparation of 0.05M Pd solution: Weigh 1.0457g of dichlorotetraamminepalladium containing 0.1052g of palladium and dissolve it in 19.6ml of deionized water and stir well.

[0053] 3) Preparation of chlorine-free palladium catalyst: At room temperature, the Cu-K-Ag modified mixed molecular sieve support obtained in step (1) was first dispersed in deionized water at a solid-liquid ratio of 1:150 at 300 rpm. After stirring for 30 minutes, the Pd solution from step (2) was added dropwise to the dispersion for 24 hours of ion exchange, with the Pd solution being added at a uniform rate over 5 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and then dried at 110℃ for 4 hours. Then, it was heated to 300℃ at a heating rate of 0.5℃ / min in a tube furnace with pure oxygen flowing through it and calcined for 4 hours to obtain a highly active and stable chlorine-free dimethyl carbonate catalyst with a 1.0%Pd·3.0%Cu·0.45%K·0.5%Ag·95.05% mixed molecular sieve support.

[0054] Example 4

[0055] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0056] 1) Preparation of Cu-KV-Ag modified NaY support: 10.0g of NaY molecular sieve was weighed and dispersed in 2000g of deionized water at 700rpm and controlled temperature at 60℃. Then, 1.3827g of CuCl2·2H2O, 0.5952g of KNO3, 0.0792g of VOSO4·3H2O and 0.0017g of AgNO3 were weighed and added to the support dispersion. After stirring for 3h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 110℃ for 3h. Then, it was calcined in a muffle furnace at 550℃ for 5h to obtain the framework modified Cu-KV-Ag modified NaY support.

[0057] 2) Preparation of 0.005 MPd solution: Weigh 0.5589 g of tetraamminepalladium nitrate containing 0.1973 g of palladium and dissolve it in 370 ml of deionized water and stir well.

[0058] 3) Preparation of chlorine-free palladium catalyst: First, the Cu-K-Zr-Nb modified NaY support obtained in step (1) was dispersed in deionized water at a temperature controlled at 40℃ at a solid-liquid ratio of 1:100 at a speed of 350 rpm. After stirring for 30 minutes, the Pd solution in step (2) was added dropwise to the dispersion for 10 h of ion exchange, with the Pd solution being added at a uniform rate over 9 h. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 80℃ for 5 h. Then, it was heated to 200℃ at a rate of 1℃ / min and calcined for 4 h in a tube furnace with a gas mixture of 100 ml / min and 20% O2 + 80% N2. This yielded a highly active and stable chlorine-free dimethyl carbonate catalyst of 1.8% Pd·4.7% Cu·2.1% K·0.17% V·0.01% Ag·91.22% NaY.

[0059] Example 5

[0060] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0061] 1) Preparation of Cu-K-Eu modified mixed molecular sieve support: 3.5g of MCM-41 and 6.5g of Naβ molecular sieve were weighed and poured into 500g of deionized water at 10℃ with a rotation speed of 400rpm. Then, 2.1599g of Cu(NO3)2·3H2O, 1.2383g of KNO3 and 0.1531g of EuCl3·6H2O were weighed and added to the support dispersion. After stirring for 4h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 90℃ for 4h. Then, it was calcined in a muffle furnace at 350℃ for 4h to obtain the framework modified Cu-K-Eu modified mixed molecular sieve support.

[0062] 2) Preparation of 0.03 MPd solution: Weigh 0.0788 g of tetraamminepalladium nitrate containing 0.0278 g of palladium and dissolve it in 9 ml of deionized water, stirring until homogeneous.

[0063] 3) Preparation of chlorine-free palladium catalyst: First, the Cu-K-Pr modified mixed-support molecular sieve carrier obtained in step (1) was dispersed in deionized water at 50℃ with a solid-liquid ratio of 1:75 at 250 rpm. After stirring for 30 minutes, the Pd solution from step (2) was added dropwise to the dispersion for 8 hours of ion exchange, with the Pd solution being added at a uniform rate over 7 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation and washed with deionized water. The resulting solid was dried at 110℃ for 6 hours and then calcined at 300℃ for 2 hours in a tube furnace with a gas flow rate of 200 ml / min and a gas flow rate of 40% O2 + 60% N2, at a rate of 1.5℃ / min. This yielded a highly active and stable chlorine-free dimethyl carbonate catalyst with a mixed molecular sieve carrier of 0.25% Pd·5.1% Cu·4.3% K·0.57% Eu·89.78%.

[0064] Example 6

[0065] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0066] 1) Preparation of Cu-KV-Fe modified ZSM-35 support: At room temperature, 10.0 g of ZSM-35 molecular sieve was weighed and dispersed in 2000 g of deionized water at 550 rpm. Then, 2.8318 g of CuSO4·5H2O, 0.6956 g of K2CO3, 0.1916 g of VOSO4·3H2O and 0.060 g of FeCl2·4H2O were weighed and added to the support dispersion. After stirring for 6 h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 110 °C for 4 h. Then, it was calcined in a muffle furnace at 450 °C for 4 h to obtain the framework modified Cu-KV-Fe modified ZSM-35 support.

[0067] 2) Preparation of 0.025M Pd solution: Weigh 0.8400g of dichlorotetraamminepalladium containing 0.0845g of palladium and dissolve it in 31ml of deionized water and stir until homogeneous.

[0068] 3) Preparation of chlorine-free palladium-based catalyst: The Cu-KV-Fe modified mixed support molecular sieve obtained in step (1) was first dispersed in deionized water at 70℃ at a solid-liquid ratio of 1:400 at 600 rpm. After stirring for 30 minutes, the Pd solution from step (2) was added dropwise to the dispersion for 16 hours of ion exchange, with the Pd solution being added at a uniform rate over 3 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 80℃ for 5 hours. Then, it was calcined in a tube furnace with 100 ml of 60% O2 + 40% N2 mixed gas at a rate of 2℃ / min to 300℃ for 4 hours to obtain a highly active and stable chlorine-free dimethyl carbonate catalyst of 0.75% Pd·6.4% Cu·3.5% K·0.40% V·0.15% Fe·88.80% ZSM-35.

[0069] Example 7

[0070] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0071] 1) Preparation of Cu-K-Mn modified MCM-41 support: 10.0 g of MCM-41 molecular sieve was weighed and dispersed in 800 g of deionized water at 35 °C at 400 rpm. Then, 0.3342 g of Cu(NO3)2·3H2O, 0.0090 g of K2CO3, and 0.3055 g of MnCl2·4H2O were weighed and added to the support dispersion. After stirring for 5 h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 90 °C for 2 h. Then, it was calcined in a muffle furnace at 400 °C for 5 h to obtain the framework modified Cu-K-Mn modified ZSM-35 support.

[0072] 2) Preparation of 0.008M Pd solution: Weigh 0.3618g of tetraamminepalladium nitrate containing 0.1277g of palladium and dissolve it in 150ml of deionized water and stir well.

[0073] 3) Preparation of chlorine-free palladium catalyst: First, the Cu-KV-Fe modified mixed support molecular sieve obtained in step (1) is dispersed in deionized water at 80℃ with a solid-liquid ratio of 1:350 at 300 rpm. After stirring for 30 minutes, the Pd solution from step (2) is added dropwise to the dispersion for ion exchange for 6 hours, with the Pd solution being added at a uniform rate over 5 hours. After the ion exchange is completed, the suspension is subjected to solid-liquid separation. The obtained solid is washed with deionized water and dried at 90℃ for 6 hours. Then, it is heated to 185℃ at a rate of 0.75℃ / min and calcined for 4 hours in a tube furnace with 400 ml of 25% O2 + 75% N2 mixed gas. This yields a highly active and stable chlorine-free dimethyl carbonate catalyst of 1.25% Pd·0.86% Cu·0.05% K·0.83% Mn·97.87% MCM-41.

[0074] Example 8

[0075] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0076] 1) Preparation of Cu-K-Zn-Mn modified NaY support: 10.0 g of NaY molecular sieve was dispersed in 200 g of deionized water at 300 rpm and controlled temperature of 50 ℃. Then, 0.5023 g of CuSO4·5H2O, 0.5943 g of K2SO4, 0.1942 g of Zn(NO3)2·6H2O and 0.0576 g of MnCl2·4H2O were added to the support dispersion. After stirring for 2 h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 100 ℃ for 18 h. Then, it was calcined in a muffle furnace at 300 ℃ for 3 h to obtain the framework modified Cu-K-Zn-Mn modified NaY support.

[0077] 2) Preparation of 0.0025M Pd solution: Weigh 0.2416g of tetraamminepalladium nitrate containing 0.0853g of palladium and 1.2742g of dichlorotetraammine and palladium containing 0.1280g of palladium, dissolve them in 800ml of deionized water, and stir well.

[0078] 3) Preparation of chlorine-free palladium catalyst: The Cu-K-Ti-Ni modified mixed support molecular sieve obtained in step (1) was first dispersed in deionized water at a solid-liquid ratio of 1:300 at 600 rpm and stirred for 30 minutes. Then, the Pd solution from step (2) was added dropwise to the dispersion for ion exchange for 48 hours, with the Pd solution being added at a uniform rate over 47 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 60°C for 24 hours. It was then introduced into a tube furnace with a gas mixture of 100 ml / min and 50% O2 + 50% N2 and heated to 200°C at a rate of 0.5°C / min and calcined for 2 hours to obtain a highly active and stable chlorine-free dimethyl carbonate catalyst of 2.0% Pd·1.2% Cu·2.5% K·0.4% Zn·0.15% Mn·93.75% NaY.

[0079] Example 9

[0080] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0081] 1) Preparation of Cu-K-Zn-Eu modified mixed molecular sieve support: 9.2g of MCM-41 molecular sieve and 0.8g of NaX molecular sieve were weighed and dispersed in 3000g of deionized water at 800rpm. Then, 0.1508g of CuCl2·2H2O, 0.0292g of KCl, 0.1160g of Zn(NO3)2·6H2O and 0.0123g of EuCl3·6H2O were weighed and added to the support dispersion. After stirring for 10h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 100℃ for 8h. Then, it was calcined in a muffle furnace at 550℃ for 2h to obtain the framework-modified Cu-K-Zn-Eu modified mixed molecular sieve support.

[0082] 2) Preparation of 0.001M Pd solution: Weigh 1.1173g of dichlorotetraamminepalladium containing 0.1124g of palladium and dissolve it in 1056ml of deionized water and stir well.

[0083] 3) Preparation of chlorine-free palladium catalyst: The Cu-K-Eu modified mixed support molecular sieve obtained in step (1) was first dispersed in deionized water at 80℃ at a solid-liquid ratio of 1:50 at 600 rpm. After stirring for 30 minutes, the Pd solution from step (2) was added dropwise to the dispersion for ion exchange for 48 hours, with the Pd solution being added at a uniform rate over 24 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water, dried at 120℃ for 2 hours, and then calcined in a muffle furnace at 300℃ for 2 hours to obtain a highly active and stable chlorine-free dimethyl carbonate catalyst of 1.1% Pd·0.55% Cu·0.15% K·0.25% Zn·0.05% Eu·97.9% mixed molecular sieve.

[0084] Example 10

[0085] A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate is provided, comprising the following steps:

[0086] 1) Preparation of Cu-KV modified mixed molecular sieve support: At room temperature, 9.5g of ZSM-35 molecular sieve and 0.5g of Naβ molecular sieve were weighed and dispersed in 600g of deionized water at 400rpm. Then, 3.0690g of Cu(NO3)2·3H2O, 0.206g of K2CO3 and 0.1460g of VOSO4·3H2O were weighed and added to the support dispersion. After stirring for 6h, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 80℃ for 2h. Then, it was calcined in a muffle furnace at 300℃ for 2h to obtain the framework modified Cu-KV modified mixed molecular sieve support.

[0087] 2) Preparation of 0.04M Pd solution: Weigh 0.1269g of tetraamminepalladium nitrate containing 0.0448g of palladium and dissolve it in 11ml of deionized water and stir well.

[0088] 3) Preparation of chlorine-free palladium-based catalyst: The Cu-K-Co-Ag modified mixed support molecular sieve obtained in step (1) was first dispersed in deionized water at 60℃ at a solid-liquid ratio of 1:200 at 200 rpm. After stirring for 30 minutes, the Pd solution from step (2) was added dropwise to the dispersion for ion exchange for 4 hours, with the Pd solution being added at a uniform rate over 3 hours. After the ion exchange was completed, the suspension was subjected to solid-liquid separation. The obtained solid was washed with deionized water and dried at 100℃ for 24 hours. Then, it was heated to 150℃ at a rate of 0.5℃ / min and calcined for 6 hours in a tube furnace with a gas flow rate of 200 ml / min and a gas flow rate of 20% O2 + 95% N2. This yielded a highly active and stable chlorine-free palladium-based catalyst with a mixed molecular sieve of 0.4% Pd·7.2% Cu·0.8% K·2.4% V·89.2%.

[0089] Example 11

[0090] Catalytic reaction performance evaluation: 1 ml of the catalyst prepared in Examples 1-10 was packed into a fixed-bed reactor with an inner diameter of 7 mm and a length of 400 mm. The feed gas composition was: 12% methyl nitrite, 6% CO, 82% N2 (high purity), and the gas space velocity was 6000 h⁻¹. -1 The reaction was carried out under atmospheric pressure and at a bed temperature of 110–130 °C for 24 h to investigate the catalyst performance. The target product, dimethyl carbonate, obtained from the catalyst evaluation reaction was absorbed by cooling with 50 ml of methanol absorbent placed in a -20 °C cold trap. The methanol absorbent was replaced every 2 h, and the concentration of dimethyl carbonate in the methanol absorbent was determined using gas chromatography. The space-time yield of dimethyl carbonate was then calculated.

[0091] The results showed that the space-time yield of DMC of the catalysts prepared in Examples 1-10 was 350-600 g / h·Lcat, and their catalytic activity did not decrease within the evaluation period of 168 h, demonstrating excellent catalytic stability.

[0092] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A chlorine-free type palladium-based catalyst for vapor-phase oxo synthesis of dimethyl carbonate, characterized by, It includes the active component Pd and the molecular sieve support; wherein: The molecular sieve support is also loaded with structural stabilizing agents Cu, K and metal M; In the catalyst, by mass percentage, Pd is 0.25-2%, Cu is 0.05-10%, K is 0.01-5%, and M is 0.01-1%. The molecular sieve support is one or a mixture of two or more of NaX-type, NaY-type, Naβ, MCM-41, and ZSM-35 molecular sieves; the metal M is a combination of Zn and Mn. The preparation of the catalyst includes the following steps: 1) The molecular sieve support is prepared into a support suspension, and then soluble Cu salt, soluble K salt and soluble metal M salt are added to the support suspension and stirred together for loading; after loading is completed, the support is separated and washed, and finally dried and calcined to obtain the framework modified Cu-KM-molecular sieve support. 2) Prepare a palladium precursor solution from the palladium precursor; 3) The Cu-KM-molecular sieve support obtained in step 1) is prepared into a suspension, and the palladium precursor solution obtained in step 2) is added dropwise to the suspension under stirring to carry out ion exchange with the molecular sieve; after the exchange is completed, the mixture is separated and washed, and finally dried and calcined to obtain a chlorine-free palladium-based catalyst; wherein the calcination is carried out under an oxidizing atmosphere and the calcination temperature is 150~300℃.

2. A method for preparing a chlorine-free palladium-based catalyst for the gas-phase carbonyl synthesis of dimethyl carbonate as described in claim 1, characterized in that, Includes the following steps: 1) The molecular sieve support is prepared into a support suspension, and then soluble Cu salt, soluble K salt and soluble metal M salt are added to the support suspension and stirred together for loading; after loading is completed, the support is separated and washed, and finally dried and calcined to obtain the framework modified Cu-KM-molecular sieve support. 2) Prepare a palladium precursor solution from the palladium precursor; 3) The Cu-KM-molecular sieve support obtained in step 1) is prepared into a suspension, and the palladium precursor solution obtained in step 2) is added dropwise to the suspension with stirring to carry out ion exchange with the molecular sieve; After the exchange is completed, the catalyst is separated, washed, and finally dried and calcined to obtain a chlorine-free palladium-based catalyst. The calcination is carried out in an oxidizing atmosphere at a temperature of 150-300℃.

3. The preparation method according to claim 2, characterized in that, In step 1), the stirring load conditions are as follows: the temperature is controlled at 10~80℃, the stirring speed is controlled at 300~800rpm, and the time is 0.5~10h; the calcination temperature is 200~600℃, and the calcination time is 2~6h.

4. The preparation method according to claim 2, characterized in that, In step 1), the Cu salt is one or more of copper chloride, copper sulfate, or copper nitrate; the K salt is one or more of potassium chloride, potassium nitrate, potassium sulfate, or potassium carbonate.

5. The preparation method according to claim 2, characterized in that, In step 2), the palladium precursor is one or both of dichlorotetraamminepalladium or tetraamminepalladium nitrate.

6. The preparation method according to claim 2, characterized in that, The Pd concentration of the palladium precursor solution in step 2) is 0.001-0.05 M 2+ The mass ratio of the Cu-K-M molecular sieve carrier to the deionized water used in the suspension in step 3) is 1:50-1:

400.

7. The preparation method according to claim 2, characterized in that, In step 3), the stirring speed is controlled at 200~600 rpm, the ion exchange temperature is 10~80℃, the exchange time is 4~48h, the dropwise addition time of the palladium precursor solution is 3~23h, and the calcination time is 2~6h.

8. The use of the chlorine-free palladium-based catalyst of claim 1 in the synthesis of dimethyl carbonate from the reaction of carbon monoxide and methyl nitrite.

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