Method for preparing molecular sieve SCR catalyst, and catalyst prepared therethrough

Abstract

A method for preparing a molecular sieve SCR (selective catalytic reduction) catalyst and a prepared catalyst therethrough. In the method, several molecular sieves are mixed and modified by transition metal or rare-earth metal via ion exchange, then loaded Fe by equivalent-volume impregnation, and loaded Cu by one or more liquid ion exchange. This present invention, combined with several techniques, such as modification of stable molecular sieve by transition and rare-earth metal, Fe loading by equivalent-volume impregnation and Cu loading by one or more liquid ion exchange, and after through stable and effective modification and loading control, the obtained catalyst material is coated on a carrier substrate via size mixing and coating process to be prepared into an integral catalyst.

Claims

1. A molecular sieve SCR catalyst, wherein the catalyst is prepared by the following method: (1) a molecular sieve mixing: a Beta molecular sieve and an SSZ-13 molecular sieve were taken and evenly mixed, and added deionized water for size mixing, and then dried by spraying to obtain a molecular sieve carrier material; (2) a molecular sieve modification: dissolving soluble transition metal and/or rare-earth metal salt into deionized water, and heating up to 70-90° C., wherein concentration of the solution ranges within 0.01-0.5 mol/L, adding the molecular sieve carrier material obtained in the step (1) under stirring condition, performing ion exchange in a 70-90° C. thermostatic reaction kettle for 2-12 h, filtering, washing and drying; (3) active component Fe loading by isometric equivalent-volume impregnation: weighing a molecular sieve carrier material modified in step (2) for further use, firstly testing saturated water absorption of the molecular sieve per unit mass, calculating the total water absorption, dissolving soluble Fe salt into deionized water, stirring and dissolving, wherein total volume of the solution is equal to total water absorption of the molecular sieve; adding the molecular sieve carrier material weighed for further use and stirring it on a rotary evaporator at normal temperature, afterwards, heating in water bath, and continuously stirring until the molecular sieve carrier material weighed for further use is completely dried; placing it into a muffle furnace for calcinating for 3 h at constant temperature of 500° C.; (4) active component Cu loading by ion exchange: accurately weighing a molecular sieve carrier material obtained by isometric equivalent-volume impregnation in step (3) for further use; dissolving soluble Cu salt in deionized water, wherein concentration of the solution ranges within 0.01-0.6 mol/L, heating up to 70-90° C., and adding the molecular sieve carrier material weighed for further use at the beginning of this step under stirring condition, performing ion exchange in a 70-90° C. thermostatic reaction kettle for 2-12 h, filtering, washing and drying; (5) calcinating to prepare into catalyst powder: calcinating a molecular sieve carrier material obtained by ion exchange in step (4) for 3 h at constant temperature of 500° C.; (6) size mixing and coating: adding water and a binder to a molecular sieve carrier material calcinated in step (5), performing ball milling for slurrying, coating slurry on a ceramic carrier or a metal carrier, drying and calcinating it to obtain the molecular sieve SCR catalyst.

2. A molecular sieve SCR catalyst according to claim 1, wherein in the step (2) of molecular sieve modification, the transition metal and/or rare-earth metal for modification is/are selected from the group consisting of Cr, Mn, Fe, Co, Ce, Ni, Zn, Sn, Y, Pr, Zr, Nd, W and La, and wherein a total metal ion concentration(s) of the solution is/are selected from the group consisting of 0.01 mol/L, 0.1 mol/L, 0.2 mol/L, 0.4 mol/L and 0.5 mol/L.

3. A molecular sieve SCR catalyst according to claim 1, wherein in the step (2) of molecular sieve modification, the transition metal and/or rare-earth metal for modification is/are selected from the group consisting of Fe, Ni, Y, Pr, Zr, Ce, Nd, W, and La.

4. A molecular sieve SCR catalyst according to claim 1, wherein in the step (3) of Fe loading by equivalent-volume impregnation, the Fe salt is selected from the group consisting of FeSO4, Fe(NO3)3, Fe(CH3COO)3 and FeCl3, and a water-bath temperature is selected from the group consisting of 50° C., 60° C., 70° C. and 80° C. when water-bath heating and stirring is performed in the rotary evaporator; wherein, calculated by Fe3+, the active component accounts for 1-10% of the total mass of the molecular sieve.

5. A molecular sieve SCR catalyst according to claim 1, wherein in the step (4) of active component Cu loading by ion exchange, the Cu salt is selected from the group consisting of soluble Cu(NO3)2, Cu(CH3OO)2, CuSO4 and CuCl2, the copper concentration of the solution of step (4) is selected from the group consisting of 0.01 mol/L, 0.1 mol/L, 0.2 mol/L, 0.4 mol/L and 0.6 mol/L; calculated by Cu2+, the active component accounts for 0.5-4.5% of the total mass of the molecular sieve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a contrast diagram of NO.sub.x conversion efficiency. In the figure, x-coordinate denotes temperature, y-coordinate denotes the NO.sub.x conversion efficiency, and unit is %;

(2) FIG. 2 shows the yield of a by-product N.sub.2O generated in SCR reaction of different catalysts. In the figure, x-coordinate denotes temperature, y-coordinate denotes the yield of N.sub.2O, and unit is ppm.

DETAILED DESCRIPTION OF THE INVENTION

(3) The present invention is described in detail by examples below, and the embodiment merely serves to further describe the present invention, but may not be understood to limit the protection scope of the present invention; some nonessential improvements and adjustments made by those skilled in the art belong to the protection scope of the present invention.

Embodiment 1

(4) I. Preparation of the Carrier Molecular Sieve

(5) Beta molecular sieve and SSZ-13 molecular sieve were taken and evenly mixed according to the mass ratio of 3:1, and added deionized water for size mixing, and then dried by spraying to obtain the molecular sieve carrier material.

(6) II. Modification of the Carrier Molecular Sieve Material

(7) 1000 mL of lanthanum nitrate solution was prepared and heated up to 70° C., where concentration of La.sup.3+ in the solution is 0.5 mol/L, and added 50 g of carrier, namely, the powdered molecular sieve under the condition of violent stirring for ion exchange for 10 h in a 70° C. thermostatic reaction kettle. The obtained slurry was filtered and washed by deionized water for three times; the obtained molecular sieve block was dried at 105° C. for 24 h at air atmosphere, and the dried molecular sieve block was twiddled and sieved by a 40-mesh sieve. The obtained powder was denoted La-Zeolite.

(8) III. Fe Loading by Equivalent-Volume Impregnation

(9) Specific pore volume of the modified molecular sieve material obtained in step II was detected, and the powdered La-Zeolite was placed into a rotary evaporator, the dissoluble Fe salt solid was calculated according to Fe.sup.3+: Fe.sup.3+ accounted for 2% of the total mass of the molecular sieve, then the powder was prepared into salt solution according to the specific pore volume and Fe.sup.3+ loading proportion, total volume of the solution=total mass of the molecular sieve*specific pore volume, the solution was slowly added in a spraying mode and stirred continuously, and the solution was stirred continuously for 3 h after spraying, then stirred continuously for 5 h at 70° C. The powder was removed and dried in a 105° C. oven for 24 h, then calcined for 3 h at 550° C. air atmosphere to obtain dark red powder, denoted as Fe/La-Zeolite.

(10) IV. Cu Loading by Ion Exchange

(11) 500 mL of copper nitrate solution was prepared and heated up to 70° C., wherein concentration of Cu.sup.2+ in the solution was 0.6 mol/L, then added 50 g of Fe/La-Zeolite obtained in step III under the condition of violent stirring, and then ion exchange was performed in a 70° C. thermostatic reaction kettle for 4 h. The obtained slurry was filtered and washed by deionized water for three times, then dried for 24 h at 105° C. air atmosphere, the dried molecular sieve block was twiddled and sieved by a 40-mesh sieve. Cu ion exchange was repeated for 3 times. The obtained molecular sieve powder was calcinated in air atmosphere, and the calcinating curve was as follows: room temperature.fwdarw.300° C. (1 hr).fwdarw.500° C. (3 hr).fwdarw.cooling to room temperature naturally, thus obtaining red powder.

(12) The above powder was prepared into slurry whose solid content was 30%-35% of the mass percent. The slurry was coated on a cordierite ceramic carrier with mesh number of 400 cell/in.sup.2 and volume of 38.4 ml, placed into an electric-heating blast drying oven for drying, then placed into a chamber electric furnace for calcinating by the sequence of room temperature.fwdarw.300° C. (1 hr).fwdarw.500° C. (3 hr), thus obtaining the SCR catalyst.

Comparative Example 1

(13) The commercially-available molecular sieve catalyst was cut and the catalyst having the same specification as Embodiment 1 was taken. The obtained sample was denoted as B1.

Comparative Example 2

(14) In order to perform horizontal comparison and verify the performance of the catalyst prepared by the present invention and the one prepared by a similar loading method, based upon the method of the CN103127951A patent, the catalyst with similar composition was prepared by loading Cu and Fe via equivalent-volume impregnation. The modified molecular sieve powder La-Zeolite of Embodiment 1 was taken and loaded Fe and Cu simultaneously by equivalent-volume impregnation, Fe and Cu accounted for 2.5% of the total mass of the molecular sieve powder respectively; catalyst coating and other preparation conditions were the same as those of Embodiment 1. The obtained sample was denoted as B2.

(15) Contrast of the NO.sub.x conversion efficiency among Embodiment 1 (S1), Comparative Example 1 (B1) and Comparative Example 2 (B1) is shown in FIG. 1. B1 is a commercial Cu—CHA molecular sieve catalyst, and compared with B1, S1 and B2 show better low-temperature catalyst activity; there is no obvious difference among the above three in the medium temperature region. In the high temperature region, Si and B1 show similar high temperature activity, while B2 has slightly lower high temperature activity. Thus it can be seen that the catalyst prepared by the present invention has the same activity temperature window as the commercial Cu—CHA, and has higher low-temperature activity. In addition, fresh activity of the catalyst prepared by the present invention is slightly better than that of the catalyst prepared by the patent CN103127951A.

Embodiment 2

(16) Beta molecular sieve and SSZ-13 molecular sieve were uniformly mixed according to the mass ratio of 3:1 for size mixing and spray drying, and then modified by yttrium nitrate solution (concentration: 0.2 mol/L), afterwards, loaded Fe by equivalent-volume impregnation and loaded Cu by ion exchange; other preparation parameters and conditions of the catalyst were the same as those of Embodiment 1 excepting for the type of the salt for molecular sieve modification. The obtained sample was denoted as S2.

(17) Contrast on the yield of a by-product N.sub.2O of catalysts S1, S2 and B2 generated in SCR reaction process is shown in FIG. 2; compared with that of B2, the yield of N.sub.2O generated in the catalytic reduction NO.sub.x process of the catalyst prepared by the present invention reduced by nearly 50%, obviously improving N.sub.2 selectivity of the present invention. Thus it can be seen that based upon the catalyst prepared by catalyst preparation technique, its N.sub.2O yield dropped obviously, which has an important application prospect.