WATER-SOLUBLE Pd(II) COMPLEX, METHOD FOR SYNTHESIZING SAME, AND USE THEREOF AS CATALYTIC PRECURSOR

Abstract

Provided are a water-soluble Pd(II) complex, a synthesis method thereof and use thereof as a catalytic precursor. The complex has a chemical name, ammonium dinitrooxalato palladium (II), and a molecular formula of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.nH.sub.2O (n is the number of crystal water). The Pd(II) complex is synthesized by using PdCl.sub.2 or [Pd(NH.sub.3).sub.2Cl.sub.2] as a starting material which is firstly converted into [Pd(NH.sub.3).sub.4]Cl.sub.2 in ammonium hydroxide, followed by a chemical reaction between [Pd(NH.sub.3).sub.4]Cl.sub.2 and excessive NaNO.sub.2 to produce trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] via ligand substitution mechanism, and finally dissolving trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] in an aqueous solution of oxalic acid leads to the formation of the target product (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.2H.sub.2O. The complex does not contain chlorine and other elements that are harmful to a catalyst, is readily soluble in water and has a low thermal decomposition temperature. A supported palladium-based catalyst prepared by using the complex as a catalytic precursor displays a very high catalytic activity.

Claims

1. A water-soluble Pd(II) complex, wherein the water-soluble Pd(II) complex has a chemical name ammonium dinitrooxalato palladium (II) and a molecular formula of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.nH.sub.2O, and has the following chemical structural formula: ##STR00005## wherein n is the number of crystal water, equal to 1 or 2 in general.

2. A synthetic method for the water-soluble Pd(II) complex of claim 1, comprising the following steps: i) dissolving PdCl.sub.2 or [Pd(NH.sub.3).sub.2Cl.sub.2] in ammonium hydroxide to produce [Pd(NH.sub.3).sub.4]Cl.sub.2; ii) adding excessive NaNO.sub.2 into [Pd(NH.sub.3).sub.4]Cl.sub.2 to produce trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2]; and iii) dissolving trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] in an aqueous solution of oxalic acid to yield the water-soluble Pd(II) complex; wherein the method is conducted according to the following reaction scheme: ##STR00006##

3. The water-soluble Pd(II) complex according to claim 1, wherein the water-soluble Pd(II) complex is used as a catalytic precursor for preparation of supported palladium-based catalysts.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1: the chemical structure of ammonium dinitrooxalatopalladium(II), a water-soluble Pd(II) complex of the present disclosure.

[0034] FIG. 2: a thermogravimetric curve (TG-DTA) of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.2H.sub.2O of the present disclosure in simulated air.

[0035] FIG. 3: a thermogravimetric curve (TG-DTA) of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.2H.sub.2O of the present disclosure in nitrogen.

[0036] FIG. 4: a preparation flow chart of a catalyst sample of Example 4.

DETAILED DESCRIPTION

Example 1: Synthesis of (NH.SUB.4.).SUB.2.[Pd(NO.SUB.2.).SUB.2.(C.SUB.2.O.SUB.4.)].Math.2H.SUB.2.O

[0037] 100 g (564 mmol) of PdCl.sub.2 was suspended in 200 mL of water and heated to 60? C., and 30% ammonium hydroxide was dropwise added under stirring until PdCl.sub.2 was completely dissolved, with about 165 mL of ammonium hydroxide being used. In this case the final pH value of the solution was 10. The solution was concentrated to nearly dry under reduced pressure at 60? C. and 200 mL of water was added again to dissolve the residue to obtain a light yellow [Pd(NH.sub.3).sub.4]Cl.sub.2 solution. To which, 200 mL of aqueous solution containing 156 g (2256 mmol) of NaNO.sub.2 was slowly added under stirring at 60? C. A yellow precipitate, trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2], was precipitated slowly from the mixture solution. The reaction was continued for 1 hour and then cooled to room temperature. The product was filtered out and washed with 60 mL of water 3 times and then with 60 mL of ethanol once, and dried at 65? C. for 4 hours. 127 g of trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] was obtained, with a yield of about 97%.

[0038] 65 g (516 mmol) of H.sub.2C.sub.2O.sub.4.Math.2H.sub.2O was dissolved in 400 mL of water at 55? C. and 122 g (526 mmol) of trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] solid was added under stirring. Reaction was allowed to continue for about 1 hour until almost all of trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] was dissolved and a red solution was formed. The solution was cooled to room temperature and a small amount of insoluble residue was removed by filtration, and the mother liquor was freeze-dried to obtain 184 g of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.2H.sub.2O, an orange-yellow product, with a yield of about 98%.

Example 2: Synthesis of (NH.SUB.4.).SUB.2.[Pd(NO.SUB.2.).SUB.2.(C.SUB.2.O.SUB.4.)].Math.2H.SUB.2.O

[0039] 50 g (237 mmol) of [Pd(NH.sub.3).sub.2Cl.sub.2] was suspended in 100 mL water at 60? C., and 30% ammonium hydroxide was dropwise added under stirring until [Pd(NH.sub.3).sub.2Cl.sub.2] was completely dissolved, with about 37 mL of ammonium hydroxide being used, and In this case the final pH value of the solution was 10. The solution was concentrated at 60? C. under reduced pressure to nearly dry, and 100 mL of water was added to dissolve the residue to obtain a light yellow [Pd(NH.sub.3).sub.4]Cl.sub.2 solution. To which, 100 mL of aqueous solution containing 65 g (948 mmol) of NaNO.sub.2 was slowly added under stirring. A yellow precipitate, trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2], was precipitated slowly from the mixture solution. The reaction was continued for 1 hour and then cooled to room temperature. The product was filtered out and washed with 30 mL of water 3 times and then with 30 mL of ethanol once, and dried at 65? C. for 4 hours. 53 g of trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] was obtained, with a yield of about 96%.

[0040] 26.5 g (211 mmol) of H.sub.2C.sub.2O.sub.4.Math.2H.sub.2O was dissolved in 150 mL water at 55? C. and 50 g (215 mmol) of trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] solid was added under stirring. Reaction was allowed to continue for about 1 hour until almost all of trans-[Pd(NH.sub.3).sub.2(NO.sub.2).sub.2] was dissolved and a red solution was formed. The solution was cooled to room temperature and a small amount of insoluble residue was removed by filtration, and the mother liquor was concentrated to dryness at 55? C. with a rotary evaporator to obtain 76 g of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.2H.sub.2O, an orange-yellow product, with a yield of about 99%.

[0041] The sample of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.2H.sub.2O was submitted for composition and structural testing, and the results were as follows:

[0042] <1> Elemental analysis: Found: Pd, 29.4%; C, 6.62%, H, 3.38%; N, 15.4% (Calcd for Pd, 29.7%; C, 6.70%; H, 3.34%; N, 15.6%);

[0043] <2> IR (cm.sup.?1, KBr): 3435 (s, v(H.sub.2O), 3232, 3177 (s, v(NH.sub.4.sup.+)), 1612 (s, vas (COO.sup.?)), 1401 (s, vs (COO.sup.?)), 1137, 1311 (s, vs (NO.sub.2.sup.?)), 558 (w, v(PdO), 527 (w, v(w, v(PdNO.sub.2);

[0044] <3> .sup.13C NMR (D.sub.2O, ppm): 167 (COO.sup.?);

[0045] <4> MS-ESI.sup.?: m/e 140 [(M-2NH.sub.4-2H.sub.2O)/2, .sup.104Pd]

[0046] The analysis results are well consistent with the chemical structure of (NH.sub.4).sub.2[Pd(NO.sub.2).sub.2(C.sub.2O.sub.4)].Math.2H.sub.2O of the present disclosure, as shown in FIG. 1.

Example 3: Preparation of Benzene Desulfurization Catalyst/Adsorbent with the Pd(II) Complex of the Present Disclosure as the Precursor and its Performance Tests

[0047] 1. Preparation of Catalyst Pd/Al.sub.2O.sub.3 [0048] (1) Industrial Reference Catalyst

[0049] 2.13 g of palladium acetate (equivalent to 1 g of Pd) was dissolved in 60 g acetone at 40? C. 100 g of ?-Al.sub.2O.sub.3 pellets with a diameter of about 2.3 mm was impregnated in the above solution for 2 h. Then the solids were filtered out, dried at 120? C. for 2 h, placed in a muffle furnace for calcinating at 400? C. for 4 hours, then reduced in an atmosphere of H.sub.2 (20 ml/min) at 150? C. for 4 h, and cooled to room temperature to obtain an industrial reference catalyst Pd/Al.sub.2O.sub.3OAc with a Pd content of 1%.

[0050] (2) Tested Catalysts

[0051] 2.8 g of tetraamminepalladium dinitrate (PdS5) or 3.33 g of ammonium bis(oxalato)palladium(II)dihydrate (PdX5) or 3.4 g of the Pd(II) complex of the present disclosure (PdX6) was dissolved in 60 ml of water. 100 g of ?-Al.sub.2O.sub.3 pellets with a diameter of about 2.3 mm was impregnated in the above solution for 2 h. Then the solids were filtered out, dried at 120? C. for 2 h, placed in a muffle furnace for calcinating at 400? C. for 4 hours, then reduced in an atmosphere of H.sub.2 (20 ml/min) at 150? C. for 4 h, and cooled to room temperature to obtain the tested catalyst/adsorbent Pd/Al.sub.2O.sub.3S5, Pd/Al.sub.2O.sub.3X5 and Pd/Al.sub.2O.sub.3X6, respectively, all with a Pd content of 1%.

2. Desulfurization Activity Testing Method

[0052] Adsorption experiment was performed on a fixed-bed reactor. The experimental procedure was as follows: 70 g of adsorbent was placed in the thermostatic zone of a tube, and air in the tube was removed by injecting nitrogen gas. Thiophene benzene (50 ppm) was preheated to 170? C. in a heater and then was introduced to the reaction tube by using a flow pump. Benzene passed through an adsorption bed at a flow rate of 4 mL/min at 150? C. The effluent benzene was collected and analyzed on Shimadzu GC-2010 Plus gas chromatography equipped with a flame photometric detector (FPD). The formula for calculating the sulfur adsorption capacity is as follows:

[00001]$q=\frac{v}{1000m}{?}_0^t\left(C_0-C_1\right)\mathrm{dt}$

[0053] where q is the adsorption sulfur capacity of the adsorbent (mg/g), v is the feed volume flow (mL/min) at any time (h), m is the weight of the adsorbent (g), Co and Ct are the initial concentration and instantaneous concentration of thiophene in benzene at a certain measured time, respectively.

3. Test Results

[0054] The fixed-bed adsorption activity test was carried out for four Pd/Al.sub.2O.sub.3 catalysts prepared by using different palladium catalytic precursors. The test results are shown in Table 1. The cumulative sulfur adsorption capacities of the four catalysts after 12 hours were measured to be 1.479, 1.518, 1.419, and 1.747 mg/g, respectively. Pd/Al.sub.2O.sub.3X6 prepared with the Pd(II) complex of the present disclosure as a precursor has the best sulfur adsorption effect, which is better than that of the industrial benzene desulfurization catalyst, and also better than the catalyst prepared by using tetraamminepalladium dinitrate or ammonium bis(oxalato)palladium(II)dihydrate as a precursor.

TABLE-US-00001 TABLE 1 Amount of sulfur adsorbed by Pd/Al.sub.2O.sub.3 prepared by using different palladium precursors (mg Sulfur/g Catal) Sample number 2 h 4 h 6 h 8 h 10 h 12 h Pd/Al.sub.2O.sub.3OAc 0.351 0.711 1.061 1.344 1.428 1.479 Pd/Al.sub.2O.sub.3S5 0.332 0.665 1.046 1.394 1.494 1.518 Pd/Al.sub.2O.sub.3X5 0.315 0.674 0.923 1.116 1.301 1.419 Pd/Al.sub.2O.sub.3X6 0.373 0.658 1.045 1.271 1.576 1.747

[0055] The catalyst samples were analyzed by XRD, XPS and TEM. The results show that compared with other three precursors, PdX6 as the catalytic precursor can enhance the interaction between Pd and Al in the Pd/Al.sub.2O.sub.3 catalyst, prevent the migration and agglomeration of Pd nanoparticles, increase the degree of dispersion, and thus improve the desulfurization activity.

Example 4: Preparation of VOCs Catalyst with Pd(II) Complex of the Present Disclosure as Precursor and Performance Evaluation

[0056] 1. Main Raw Materials and Instruments and Equipment Ceramic carrier (300-mesh), La-modified alumina, rare earth composite oxide, ethanolamine hydroxyplatinum, palladium nitrate solution, the Pd(II) complex of the present disclosure (referred to as PdX6), acetic acid, barium hydroxide, hydroxyethyl cellulose, pseudo-boehmite, nitric acid, and deionized water. Balance, agitator, oven, muffle furnace, catalyst evaluation device SGB-2 #, MKS infrared analyzer, hole punch, etc.

2. Preparation of Catalyst Sample and Test Method for Catalytic Performance

[0057] 1. Sample Preparation

[0058] As shown in FIG. 4, the preparation of catalyst samples involves mixing the substrate coating material with a precious metal solution under stirring and adjusting pH of the mixture to a certain value, drying and roasting to generate a coating material containing platinum and palladium, and then pulping and coating the pulp on the porous surface of the ceramic carrier, and finally calcinating to obtain the catalyst sample. The precious metal loading capacity in this sample was 1.8 g/L and the mass ratio of Pt to Pd was 5.

[0059] 2. Catalytic Activity Testing Method

[0060] The catalyst sample with a diameter of 1 inch and a height of 2 inch was intercepted, wrapped with asbestos cloth and loaded into a sample tube in the catalyst evaluation device SGB-2 #. The reaction chamber was heated, and the reaction gas was introduced when the temperature reached a value required for reaction. The test temperature started from 350 to 500? C. and the temperature gradient was 50? C. The flow rate of the reaction gas was calculated and determined according to a space velocity of 20,000/h, a carbon monoxide concentration of 4,000 ppm, a methane concentration of 1,000 ppm, a propane concentration of 1,000 ppm, an oxygen concentration of 5%, a water vapor concentration of 0-20%. The exhaust gas concentration level was detected in real time by using MKS infrared analyzer.

3. Test Results

[0061] The test data of the oxidative conversion of carbon monoxide, methane and propane by catalysts prepared by using two palladium precursors under the same conditions are shown in Table 2-Table 4.

[0062] (1) From the test data in Table 2, it can be seen that the catalysts prepared by using two different palladium compounds PdX6 and a palladium nitrate solution have an oxidative conversion rate of more than 99.5% for CO at different temperatures and water contents, which meets the technical requirements for industrial use.

TABLE-US-00002 TABLE 2 Oxidative conversion rate of CO over catalyst prepared by using two palladium precursors Reaction Water Conversion rate/% of CO temperature/? C. content/% Pd-X6 Palladium nitrate solution 350 0 100 100 5 100 100 10 100 100 15 100 100 20 100 100 400 0 100 100 5 100 100 10 100 100 15 100 100 20 100 100 450 0 100 100 5 100 100 10 100 100 15 100 100 20 100 100 500 0 100 100 5 100 100 10 100 100 15 100 100 20 100 100

[0063] (2) The test data in Table 3 reveal that the oxidative conversion rate of methane over the catalysts correlates positively with the temperature in the reaction chamber and negatively with the water content in the inlet gas. Under the same reaction conditions, especially at lower temperature, the oxidative conversion of methane over the catalyst prepared from PdX6 is much greater than that over the catalyst prepared from the palladium nitrate solution.

[0064] (3) The test data of the oxidative conversion rate of propane over the catalysts prepared by two different palladium compounds under the same conditions are given in Table 4. Similar to the situation of methane, the oxidative conversion rate of propane increases with the rise of the temperature and decreases with the increase of the water. But the influence of water on the oxidative conversion of propane becomes less obvious when the reaction temperature rises, and the conversion rate at 450? C. and above is up to 99.5%. From the conversion rate of propane under the same reaction conditions over the catalysts prepared by the two palladium compounds, it can be still concluded that PdX6 is superior to palladium nitrate as the catalytic precursor.

TABLE-US-00003 TABLE 3 Oxidative conversion rate of methane over catalysts prepared by using two different palladium precursors Reaction Water Conversion rate/% of Methane temperature/? C. content/% Pd-X6 Palladium nitrate solution 350 0 58.3 1.8 5 32.2 0 10 22.2 0 15 17.1 0 20 13.2 0 400 0 71.7 26 5 49.3 12.2 10 41.4 10.2 15 35.7 8.6 20 31.7 7.8 450 0 85.6 55.4 5 74 40 10 67.9 34 15 63.5 28.8 20 59.8 25.6 500 0 92.7 77.4 5 88.5 69.2 10 86.1 65.2 15 86 61 20 86.7 57.6

TABLE-US-00004 TABLE 4 Oxidative conversion rate of propane over catalysts prepared by using two different palladium precursors Reaction Water Conversion rate/% of Propane temperature/? C. content/% Pd-X6 Palladium nitrate 350 0 100 81.7 5 97.8 59.2 10 94.9 57.9 15 91.2 57.9 20 87.5 57.8 400 0 100 98.9 5 100 96.9 10 99.6 96 15 99 95.2 20 100 94.4 450 0 100 99.86 5 100 99.65 10 100 99.57 15 100 99.46 20 100 99.36 500 0 100 100 5 100 100 10 100 100 15 100 100 20 100 100

[0065] Therefore, the catalyst prepared by using the Pd(II) complex of the present disclosure as a catalytic precursor has a significantly better purification effect on VOCs than an industrial catalyst prepared with a palladium nitrate solution as a precursor.