Catalyst for decomposition of nitrous oxide

Abstract

The present invention relates to a catalyst for decomposition of nitrous oxide and also to its method of preparation and use.

Claims

1. A nitrous oxide decomposition catalyst comprising rhodium on a catalyst carrier, wherein the catalyst carrier is obtained by mixing zirconium dioxide powder with a silicon compound as binder, optionally a porogen, optionally an acid, water and optionally also further additives to form a kneadable composition, homogenizing the composition, shaping the composition into shaped articles, drying and calcination, wherein the binder is selected from silicon compounds of general formulae (I) to (VI)
(Hal).sub.xSiR.sub.4-x (I)
(Hal).sub.xSi(OR.sup.1).sub.4-x (II)
(Hal).sub.xSi(NR.sup.1R.sup.2).sub.4-x (III)
R.sub.xSi(OR1)4-x (IV)
R.sub.xSi(NR.sup.1R.sup.2).sub.4-x (V)
(R.sup.1O).sub.xSi(NR.sup.1R.sup.2).sub.4-x (VI) where Hal in each occurrence is independently halogen, R in each occurrence is independently H or a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, arylalkyl or aryl radical, R.sup.1 and R.sup.2 in each occurrence are each independently H or a substituted or unsubstituted alkyl, acyl, arylalkyl or aryl radical, and x is from 0 to 4 and wherein the catalyst does not contain any Pd.

2. The catalyst according to claim 1 wherein the catalyst carrier is prepared by mixing a) 50 to 98 wt % of zirconium dioxide powder, b) 2 to 50 wt % of the silicon compound as binder, c) 0 to 48 wt % of porogen, and d) 0 to 48 wt % of further additives, wherein the sum total of components a) to d) adds up to 100 wt %, in the presence of water and optionally of an acid to form a kneadable composition.

3. The catalyst according to claim 1 wherein the zirconium dioxide powder consists essentially of monoclinic zirconium dioxide.

4. The catalyst according to claim 1 wherein zirconium dioxide powder has a particle size in the range from 0.2 to 50 m.

5. The catalyst according to claim 1 wherein zirconium dioxide powder has a specific BET surface area in the range from 10 to 400 m.sup.2/g.

6. The catalyst according to claim 1 wherein the catalyst on the catalyst carrier comprises yet further elements from transition group III including the lanthanides and/or from transition groups VI and/or VIII of the periodic table.

7. The catalyst according to claim 1 wherein the catalyst on the catalyst carrier further comprises molybdenum.

8. The catalyst according to claim 1, wherein the catalyst on the catalyst carrier further comprises 0.01 to 0.5% by weight molybdenum and said rhodium is in amount from 0.01 to 1.00% by weight of the amount of the catalyst.

9. A method of preparing nitrous oxide decomposition catalysts, which comprises a catalyst carrier obtained by mixing zirconium dioxide powder with a silicon compound as binder, optionally a porogen, optionally an acid, water and optionally also further additives to form a kneadable composition, homogenizing the composition, shaping the composition into shaped articles, drying and calcination, wherein the binder is selected from silicon compounds of general formulae (I) to (VI)
(Hal).sub.xSiR.sub.4-x (I)
(Hal).sub.xSi(OR.sup.1).sub.4-x (II)
(Hal).sub.xSi(NR.sup.1R.sup.2).sub.4-x (III)
R.sub.xSi(OR.sup.1).sub.4-x (IV)
R.sub.xSi(NR.sup.1R.sup.2).sub.4-x (V)
(R.sup.1O).sub.xSi(NR.sup.1R.sup.2).sub.4-x (VI) where Hal in each occurrence is independently halogen, R in each occurrence is independently H or a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, arylalkyl or aryl radical, R.sup.1 and R.sup.2 in each occurrence are each independently H or a substituted or unsubstituted alkyl, acyl, arylalkyl or aryl radical, and x is from 0 to 4, being impregnated with a rhodium-containing solution, then dried and calcined and wherein the catalyst does not contain any Pd.

10. A method for decomposition of nitrous oxide which comprises decomposing nitrous oxide with the catalyst as claimed in claim 1 at a temperature range from 250 to 700 C.

11. The method according to claim 10 wherein the gas stream passed over the catalyst comprises up to 20 000 ppm of N.sub.2O with or without up to 2000 ppm of NO.sub.x, up to 1% of H.sub.2O and/or up to 5% of O.sub.2.

Description

EXAMPLES

Example 1

Preparation of Catalyst Carrier

(1) 3680 g of ZrO.sub.2 powder are heated at 450 C. for 3 hours and then muller mixed with 262.6 g of methoxysilane (Silres MSE 100 from Wacker), 110.4 g of polyethylene oxide (Alkox E100), 110.4 g of 65 wt % HNO.sub.3 and 1270 g of water for 20 minutes. The resulting doughy composition was screw extruded into strands of 3 mm outside diameter, and the strands were dried at 120 C. and then heated at 560 C. for 4 hours. The carrier obtained had a BET surface area of 95 m.sup.2/g and a porosity of 0.36 ml/g (measured using mercury porosimetry) and had a bimodal pore diameter distribution with maxima at 20 and 450 nm. The carrier had a cutting resistance of 35 N.

Example 2

Preparation of Catalyst (Rh/ZrO.SUB.2./SiO.SUB.2.)

(2) 3.37 g of aqueous rhodium nitrate solution (13.7 wt %, from Haereus, corresponds to 0.461 g of Rh) were made up with water to 101 ml. 230 g of carrier material (1.5 mm strands from Example 1) were initially charged to a flask, the impregnating solution was added followed by allowing to stand for 30 min with shaking every 5 min. Thereafter the supernatant solution was removed in a rotary evaporator. This was followed by vacuum drying at 125 C. for 16 hours, then calcination at 540 C./4 h/100 I(S.T.P.)/h N.sub.2 in a rotary tube furnace and a subsequent passivation with air. The strands comprised 0.20 wt % of Rh.

Examples 3 and 4

(3) Preparation similar to Example 2 using respectively 8.65 and 11.13 g of rhodium nitrate solution (34 wt %, BASF Italia). The strands comprised respectively 0.32 and 0.42 wt % of Rh.

Example 5

Preparation of Catalyst (Mo/Rh/ZrO.SUB.2./SiO.SUB.2.)

(4) 3.37 g of rhodium nitrate solution (13.7 wt %, from Haereus, corresponds to 0.461 g of Rh) and 4.61 ml of Mo-ICP solution (from ABCR 1 g of Mo in 5% HNO.sub.3, corresponds to 0.0461 g of Mo) were mixed and made up with water to 101 ml. 230 g of carrier material (1.5 mm strands from Example 1) were initially charged to a flask, the impregnating solution was added followed by allowing to stand for 30 min with shaking every 5 min. Thereafter, supernatant water was removed in a water jet pump vacuum (20 mbar) at a water bath temperature of 85 C. This was followed by vacuum drying at 125 C. for 16 hours, then calcination at 540 C./4 h/100 I(S.T.P.)/h N.sub.2 in a rotary tube furnace and a subsequent passivation with air. The strands had an Rh content of 0.20 wt % and an Mo content of 0.02 wt %.

Example 6

(5) Preparation similar to Example 5 using 0.231 g of Mo (0.39 g H.sub.2MoO4 in 10 ml of 2M HNO.sub.3) and 3.37 g of rhodium nitrate solution (13.7 wt %, from Haereus, corresponds to 0.461 g of Rh) made up to 101 ml with water. The strands had an Rh content of 0.20 wt % and an Mo content of 0.10 wt %.

Comparative Examples 1-5

(6) 110 g of carrier material were impregnated with 47 ml of precursor solution. The rest of the procedure was similar to Example 2. The precursors used were: IrCl.sub.3H.sub.2O (dissolved with 9 ml of HCl), Pd(NO.sub.3).sub.2, RuCl.sub.3H.sub.2O, Fe(NO.sub.3).sub.39H.sub.2O, Pt-A solution (an amine-diluted aqueous platinum hydroxide (H.sub.2Pt(OH).sub.6) solution.

Comparative Examples 6-11

(7) Example 2 was repeated to prepare the catalysts except that the carrier of Example 1 was replaced by the following carriers: tetragonal ZrO.sub.2 with 4.2 wt % of Si (Saint-Gobain NorPro SZ 61152, monoclinic ZrO.sub.2 with 5.0 wt % of Si (Saint-Gobain Norpro SZ31107), pure predominantly monoclinic ZrO.sub.2, SiO.sub.2, -Al.sub.2O.sub.3 and CeO.sub.2.

(8) Nitrous Oxide Decomposition:

(9) 23 g (20 ml) of catalyst were packed into a vertically upright 230 ml tubular reactor having an inside diameter of 25 mm together with a 3 mm inside tube for the thermocouple. The packing of the catalyst was in the center of the tube between 1 to 1.5 mm layers of quartz glass chips. The tubular reactor was heated using an electric oven and the temperature in the catalyst bed was measured in the center of the catalyst bed by means of a thermocouple. A gas mixture consisting of 3% O.sub.2, 1000 ppm N.sub.2O, 3000 ppm H.sub.2O, 96.6% N.sub.2 was passed over the catalyst at a pressure of 8 bar and a GHSV of 20 000 h.sup.1, and the reaction gases were analyzed using infrared spectroscopy.

(10) Table 1 comprises the results for invention catalysts as per Examples 2 to 6 (B2 to B6) and for Comparative Examples 1 to 11 (VB1 to VB11).

(11) TABLE-US-00001 TABLE 1 X = N.sub.2O conversion B2: 0.20% Rh T [ C.] 289 309 325 361 X [%] 0 1.9 5.8 25 B3: 0.32% Rh T [ C.] 289 309 327 361 X [%] 2.4 9.1 26 71.2 B4: 0.42% Rh T [ C.] 287 308 325 361 X [%] 2.9 13.6 33 73.8 B5: 0.20% Rh 0.02% Mo T [ C.] 289 308 326 360 X [%] 0 2.9 11.5 37.5 B6: 0.20% Rh 0.10% Mo T [ C.] 288 306 324 359 X [%] 0 3 9.1 32.2 VB1: 0.38% Ir T [ C.] 285 307 325 359 X [%] 0 1 1.9 6.7 VB2: 0.40% Pd T [ C.] 284 305 322 356 X [%] 0 0 3 8 VB3: 0.47% Ru T [ C.] 256 283 299 329 X [%] 0 0 2 5 VB4: 0.49% Fe T [ C.] 287 307 325 359 X [%] 0 0 0 0 VB5: 0.45% Pt T [ C.] 283 305 324 357 X [%] 0 0 0 1.6 VB6: 0.33% Rh ZrO.sub.2SiO.sub.2 T [ C.] 292 316 335 371 X [%] 1 4 10 36.5 VB7: 0.34% Rh ZrO.sub.2SiO.sub.2 tetragonal T [ C.] 278 304 321 357 X [%] 0 1 4.8 8.7 VB8: 0.33% Rh ZrO.sub.2 monoclinic T [ C.] 266 293 320 350 X [%] 0 0 1.1 5.9 VB9: 0.33% Rh SiO.sub.2 T [ C.] 266 292 319 349 X [%] 0 1 2.8 9.6 VB10: 0.33% Rh Al.sub.2O.sub.3 T [ C.] 294 315 333 368 X [%] 0 1.1 4.1 12 VB11: 0.33% Rh CeO.sub.2 T [ C.] 269 296 323 350 X [%] 0 3.6 16.6 46.8

(12) Rh on ZrO.sub.2/SiO.sub.2 carrier obtained according to the present invention gave a higher conversion than other metals on this carrier. Rh on ZrO.sub.2/SiO.sub.2 carrier obtained according to the present invention gave a higher conversion than Rh on other carriers.

(13) The nitrous oxide decomposition runs were repeated with 1000 ppm NO in the gas mixture.

(14) TABLE-US-00002 metal content [%] 0.20 0.20 Rh Rh 0.20 0.32 0.42 0.38 0.4 0.47 0.49 0.45 0.02 0.10 Rh Rh Rh Ir Pd Ru Fe Pt Mo Mo temperature 361 361 360 359 356 331 359 359 357 358 [ C.] conversion 4.8 15.4 17.5 11.5 0 3.0 0 1.0 6.3 7.1 [%]

(15) The decomposition of N.sub.2O is appreciably impaired by the presence of NO.sub.x in the gas mixture. However, the catalysts of the present invention gave a distinctly higher conversion than catalysts comprising other metals.

(16) The addition of a small amount of molybdenum also had a positive effect on catalyst performance with NO.sub.x in the gas mixture. The catalysts comprising 0.10 or 0.20 wt % of Mo gave a higher conversion, at the same temperature, than catalysts comprising Rh only.

(17) Table showing catalyst analytics:

(18) TABLE-US-00003 BET Pore volume Catalyst carrier [m.sup.2/g] [cm.sup.3/g] Si content as per invention 95 0.30 7.3% SiO.sub.2ZrO.sub.2 tetragonal 141 0.33 4.2% Saint-Gobain NorPro SZ 61152 SiO.sub.2ZrO.sub.2 monoclinic 100 0.33 5.0% Saint-Gobain NorPro SZ 31107 Al.sub.2O.sub.3 216 0.69 0%