Synthesis of zeolite with the CHA crystal structure, synthesis process and use thereof for catalytic applications

Abstract

Disclosed is a synthesis process of a crystalline material with the CHA structure, which comprises the following steps: i) Preparation of a mixture that comprises one source of water, one source of a tetravalent element Y, one source of an alkaline or alkaline earth cation (A), one source of a trivalent element X, and one organic molecule (OSDA1) with the structure [R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+]Q.sup., being the molar composition: n X.sub.2O.sub.3:YO.sub.2:a A:m OSDA1:z H.sub.2O, ii) crystallisation of the mixture obtained in i) in a reactor, iii) recovery of the crystalline material obtained in ii).

Claims

1. A mixture comprising at least one source of water, at least one source of a tetravalent element Y, at least one source of an alkaline or alkaline earth cation A, at least one source of a trivalent element X, and at least one organic molecule (OSDA1) with the structure [R.sup.1R.sup.2R.sup.3R.sup.4N.sup.+]Q.sup., wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are selected from linear alkyl groups, and wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each have between 1 and 4 carbon atoms, but at least two of them must have at least two carbon atoms, and wherein Q.sup. is an anion, being the molar composition:
nX.sub.2O.sub.3:YO.sub.2:aA:mOSDA1:zH.sub.2O wherein n ranges between 0 and 0.1; a ranges between 0 and 2; m ranges between 0.01 and 2; z ranges between 1 and 200.

2. The mixture according to claim 1, wherein the source of the tetravalent element Y is selected from silicon, tin, titanium, germanium, and combinations thereof.

3. The mixture according to claim 2, wherein the source of the tetravalent element Y is a source of silicon selected from silicon oxide, silicon halide, colloidal silica, fumed silica, tetraalkyl orthosilicate, silicate, silicic acid, a previously synthesised crystalline material, a previously synthesised amorphous material, and combinations thereof.

4. The mixture according to claim 3, wherein the source of silicon is selected from a previously synthesised crystalline material, a previously synthesised amorphous material and combinations thereof.

5. The mixture according to claim 4, wherein the previously synthesised materials contain other heteroatoms in their structure.

6. The mixture according to claim 3, wherein the previously synthesized material is a faujasite-type zeolite (FAU).

7. The mixture according to claim 1, wherein the source of the trivalent element X is selected from aluminium, boron, iron, indium, gallium, and combinations thereof.

8. The mixture according to claim 7, wherein the source of the trivalent element X is aluminium.

9. The mixture according to claim 1, wherein the OSDA1 is selected from tetraethylammonium, methyl triethylammonium, propyl triethylammonium, diethyl dipropylammonium, diethyl dimethylammonium, and combinations thereof.

10. The mixture according to claim 9, wherein said OSDA1 is tetraethylammonium.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the diffraction pattern of the material obtained in Example 1 of the present invention.

(2) The present invention is illustrated by means of the following examples, which are not intended to limit the scope of the invention.

EXAMPLES

Example 1: Synthesis of CHA Using Tetraethylammonium as the OSDA

(3) 1037.2 mg of an aqueous solution of tetraethylammonium hydroxide (TEAOH, Sigma Aldrich, 35% by weight in water) are mixed with 477.1 mg of a 20%-by-weight aqueous solution of sodium hydroxide (NaOH, Sigma-Aldrich, 98%) and 34 mg of Milli-Q water. The mixture is homogenised by being kept under stirring. Finally, 791.0 mg of zeolite Y (CBV-720, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=21) are added, and the mixture is kept under stirring until the desired concentration is achieved. The composition of the final gel is SiO.sub.2/0.047Al.sub.2O.sub.3/0.2 TEAOH/0.2NaOH/5H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 160 C. for 7 days. Once this time has elapsed, the product obtained is recovered by means of filtration and washed abundantly with water. By means of X-ray diffraction, it is observed that the solid obtained presents the characteristic peaks of the CHA structure (see FIG. 1). The solid yield obtained is greater than 85%.

(4) The material is calcined at 550 C. for 4 h in an air atmosphere in order to eliminate the organic matter retained inside it.

Example 2: Synthesis of CHA Using Tetraethylammonium as the OSDA

(5) 4494.4 mg of an aqueous solution of tetraethylammonium hydroxide (TEAOH, Sigma Aldrich, 35% by weight in water) are mixed with 2047.1 mg of a 20%-by-weight aqueous solution of sodium hydroxide (NaOH, Sigma-Aldrich, 98%) and 9525.0 mg of Milli-Q water. The mixture is homogenised by being kept under stirring. Finally, 3670.2 mg of zeolite Y (CBV-712, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=12) are added, and the mixture is kept under stirring until the desired concentration is achieved. The composition of the final gel is SiO.sub.2/0.083Al.sub.2O.sub.3/0.2 TEAOH/0.2NaOH/15H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 160 C. for 7 days. Once this time has elapsed, the product obtained is recovered by means of filtration and washed abundantly with water. By means of X-ray diffraction, it is observed that the solid obtained presents the characteristic peaks of the CHA structure. The solid yield obtained is greater than 85%.

(6) The material is calcined at 550 C. for 4 h in an air atmosphere in order to eliminate the organic matter.

Example 3: Synthesis of Triethylpropylammonium Hydroxide

(7) 12.8 ml of triethylamine (C.sub.6H.sub.15N, Sigma Aldrich, 99%) are dissolved in 250 ml of acetonitrile (CH.sub.3CN, Scharlau, 99%). This solution is kept under stirring whilst 44 ml of 1-iodopropane (C.sub.3HI, Sigma Aldrich, 99%) are added drop by drop. After the addition is completed, the mixture is heated under reflux at 80 C. for 3 days. Once this time has elapsed, the mixture is partially concentrated in the rotary evaporator and an excess of diethyl ether (C.sub.4H.sub.10O, Scharlau, 99.5%) is added in order to precipitate the final product triethylpropylammonium iodide, which is vacuum filtered and washed with diethyl ether, to obtain a yield of 88%.

(8) Finally, ion exchange of the triethylpropylammonium halide is performed with the corresponding hydroxide. To this end, a solution of 10 g of triethylpropylammonium iodide in 73.7 g of water is prepared, and 37 g of the ion-exchange resin Amberlite (Amberlite IRN78, hydroxide form, Supelco) are added to this mixture. The mixture is kept under stirring overnight and, once this time has elapsed, it is vacuum filtered in order to separate the final product, triethylpropylammonium hydroxide, from the resin. The solution obtained is titrated with hydrochloric acid (HCl, Sigma Aldrich, 0.1 M), resulting in a concentration of 7.1% by weight and 75% exchange.

Example 4: Synthesis of CHA Using Triethyl Propylammonium as the OSDA

(9) 3064.5 mg of a solution of triethylpropylammonium hydroxide (TEPrOH, 7.1% by weight, prepared according to Example 3 of the present invention) are mixed with 274.0 mg of a 20%-by-weight solution of sodium hydroxide (NaOH, 98%) in water. The mixture is homogenised by being kept under stirring. Finally, 435.0 mg of zeolite Y (CBV-720, SiO.sub.2/Al.sub.2O.sub.3 molar ratio=21) are added, and the mixture is kept under stirring until the desired concentration is achieved. The composition of the final gel is SiO.sub.2/0.047Al.sub.2O.sub.3/0.2 TEPrOH/0.2NaOH/5H.sub.2O. This gel is transferred to a teflon-lined steel autoclave and heated at 160 C. for 7 days. Once this time has elapsed, the product obtained is recovered by means of filtration and washed abundantly with water. By means of X-ray diffraction, it is observed that the solid obtained primarily presents the characteristic peaks of the CHA structure.

(10) The material is calcined at 550 C. for 4 h in an air atmosphere in order to eliminate the organic matter.

Example 5: Preparation of the Cu-Exchanged Zeolite CHA (Cu-CHA)

(11) The sample synthesised and calcined according to the method explained in Example 1 is washed with 150 g of a 0.04 M aqueous solution of sodium nitrate (NaNO.sub.3, Fluka, 99% by weight) per gram of zeolite.

(12) 33.63 mg of copper acetate [(CH.sub.3COO).sub.2Cu.H.sub.2O, Probus, 99%] are dissolved in 30 g of water, and 303.3 mg of the previously washed zeolite are added. The suspension is kept under stirring for 24 h. Once this time has elapsed, the product obtained is recovered by means of filtration and washed abundantly with water. Finally the material is calcined in air at 550 C. for 4 h.

Example 6: Catalytic Assay of the SCR Reaction of NOx

(13) The catalytic activity of the Cu-CHA sample synthesised according to Example 5 of the present invention in the selective catalytic reduction of NOx is studied using a fixed-bed tubular quartz reactor 1.2 cm in diameter and 20 cm long. In a typical experiment, the catalyst is compacted into particles with a size ranging between 0.25-0.42 mm; these are introduced into the reactor and the temperature is increased until 550 C. are reached (see the reaction conditions in Table 1); subsequently, this temperature is maintained for one hour under a flow of nitrogen. Once the desired temperature has been reached, the reaction mixture is fed. The SCR of NOx is studied using NH.sub.3 as the reducing agent. The NOx present in the reactor outlet gas is continuously analysed by means of a chemiluminiscent detector (Thermo 62C).

(14) TABLE-US-00001 TABLE 1 Reaction conditions for the SCR of NOx Total gas flow (ml/min) 300 Catalyst load (mg) 40 NO concentration (ppm) 500 NH.sub.3 concentration (ppm) 530 O.sub.2 concentration (%) 7 H.sub.2O concentration 5 Tested temperature range ( C.) 170-550

(15) The catalytic results of the Cu-CHA catalyst prepared according to Example 5 of the present invention are summarized in Table 2.

(16) TABLE-US-00002 TABLE 2 Conversion (%) of NOx at different temperatures (200 C., 250 C., 300 C., 350 C., 400 C., 450 C., 500 C.) using the Cu-CHA catalyst prepared according to Example 5 of the present invention Conversion (%) of NOx at different temperatures 210 C. 250 C. 300 C. 350 C. 400 C. 450 C. 500 C. 550 C. Example 5 94.9 100.0 100.0 100.0 100.0 99.7 95.5 90.8