DE2743031C2 - Catalytic converters for the elimination of nitrogen oxides in exhaust gases - Google Patents

Description

substance

MnPc / MnO ₂ CoPc / Co ₂ O ₃ NiPc / NiO CuPc / CuO

Metal% 10 63 10 71 10 79 11 80

Depending on the MPc used, various reactions can be selected, e.g. B. decay or reduction, be catalyzed.

The preparation and action of the new catalysts are shown in the examples below. Pure NO was used, which was mixed in pulses or continuously with a carrier gas and passed over the catalytic converters. Carrier gases were He or H ₂ to which O _{2 was} added; in this way, NO _{x was also} offered to the catalytic converters. The stated conversions are based on pure NO. The examined temperature range goes from room temperature to 425 ° C.

The action of nitrogen oxides or oxygen on the pure MPc creates new substances with a certain phase width. They clearly differ in their IR spectrum and in the temperature range of their resistance from the "intercalation compounds" or "adducts" described so far. They can best be described as bridged structures with nitrite or nitrato or oxy or peroxy groups. In the following, they are simply referred to as MPc-Oxy-Catalyst or MPc-Nitrato-Catalyst. The BET surface areas are usually between 1 and 14 mVg. They can be increased considerably by the methods customary in heterogeneous catalysis. Due to the thermal stability of the new catalysts, the new substances can be used up to temperatures of 55O ⁰ C.

Examples
Example 1 (MnPc)

Chemically pure MnPc is hardly active. The MnPc oxy catalyst is obtained by subliming MnPc in the presence of O ₂ . 5.6 mg NO are passed over 125 mg MnPc oxy catalyst in a stream of Hr at 395 ° C. (reaction time 7.5 seconds). Only decomposition of the NO occurs, the constant conversion is 4%.

After further O ₂ activation by passing a inert gas-O ₂ mixture (O ₂ content 5%) at temperatures above 20O ⁰ C (minimum contact 600 seconds) increase the sales in the H ₂ stream to 54%. The proportion of MnPc _: Oxy catalyst in MnPc and, accordingly, the activity are more than tenfold

Example 2 (MnPc)

About 25 mg of MnPc oxy catalyst, obtained according to Example 1, are added at 380 ° C. in a stream of He 5.2 mg NO passed (reaction time 5 seconds). The conversion is 3%.

The examples make it clear that the MnPc oxy catalyst, obtained by appropriate treatment of MnPc with O ₂ , has a high activity and only catalyzes the decomposition of the nitrogen oxides without the formation of ammonia

20 Example 3 (CoPc)

If over 250 mg of pure CoPc (obtained by sublimation under inert gas) at 416 ° C in the H ₂ stream 0.85 mg of NO are passed (reaction time 7.5 seconds), the conversion is only 6% o. By exposure to 85 mg NO above 300 ° C (exposure time 150 seconds), the CoPC nitrate catalyst is partially formed from CoPc. At 410 ° C, conversions of 11% are achieved in the HrStrom for 0.3, 3.0 and 30.0 mg NO (reaction time 0.5 seconds / mg NO).

Example 4 (CoPc)

Over 500 mg of CoPc treated with NO according to Example 3 are 1,0,10,0 and at 425 ° C. in a He stream 20.0 mg NO passed (reaction time 2 seconds / mg NO). NO decay occurs only in traces.

A comparison of Examples 3 and 4 shows that nitrogen oxides are effectively reduced to H ₂ O and N _{2 by the CoPc-Nitrato catalyst in the presence of H 2} , while the decomposition is only insignificant

35 Example 5 (NiPc)

Pure NiPc, obtained by sublimation under inert gas, is almost inactive, both during decay and during Reduction.

From 250 mg NiPc, the action of 95 mg NO above 250 ° C in the H ₂ -StTOm (minimum exposure time 150 seconds) produces NiPc nitrate catalyst. In the HrStrom it causes a conversion of 19.5% at 380 ° C (reaction time 0.5 seconds / mg NO), the only nitrogen product is N ₂ .

Example 6 (NiPc)

_{If 0.45 mg NO is brought to reaction in the H 2} stream on 250 mg NiPc-Nilrato catalyst (cf. Example 5) at 367 ° C. (reaction time 2 seconds / mg NO), NO is mainly _{reduced to NH 3} , which Conversion is 32%.

Example 7 (NiPc) see above

Over 500 mg of NiPc nitrate catalyst according to Example 5, 0.85 mg of NO are added at 400 ° C. in a stream of He conducted (reaction time 2 seconds / mg NO). The conversion for the NO decomposition is below 3% o.

Examples 5 to 7 show that NiPc nitrate catalyst is a very active catalyst in which the NO decay is subordinate to the reduction, but the sales are considerable.

Example 8 (CuPc)

On 500 mg of pure CuPc, the conversion at 425 ° C is when 0.9,9.0 and 18.0 mg NO are used (reaction time 4 seconds / mg NO) each only 5% o.

Example 9 (CuPc)

Chemical treatment of the pure CuPc with NO at temperatures above 300 ° C (exposure times at least 300 seconds) increases the conversion: at 425 ° C 250 mg CuPc-Nitrato-catalyst are im HrStrom when using 0.25 mg NO conversions of 2 to 3% determined (reaction time 0.5 seconds / mg NO); N H3 is not detectable.

Examples 8 and 9 show that CuPc nitrate catalyst, although not a very active one, is exclusive

Formation of N ₂ and H ₂ O is a very selective reduction catalyst

Higher efficiency and complete elimination of NO with, if necessary, simultaneous lowering of the reaction temperatures can be achieved by the usual measures of fixed bed catalysis (e.g. increasing the Amount, bed length and surface area or full utilization of the temperature stability of the catalysts up to 550 ° C) Reach 5.

Example 10 (CoPc)

4 g obtained by sublimation CoPc be brought by milling in its BET surface area five times the ίο value corresponding to Example 3, and at 350 ⁰ C and 180 mg NO-treated (a minimum contact 300 seconds). The conversion at 412 ° C. is now 98%.

Claims (2)

Patent claims: 1. Catalysts for eliminating nitrogen oxides in exhaust gases based on metal phthalocyanines, characterized in that industrially produced metal phthalocyanines have been purified by sublimation twice and treated _{with NO or O 2 at temperatures above 250 ° C.} 2. Use of the catalysts according to claim 1 for removing nitrogen oxides in exhaust gases. The invention relates to a process for the production of catalysts for eliminating nitrogen oxides in Exhaust gases based on metal phthalocyanines. They are obtained by being technically manufactured Metal phthalocyanines purified by sublimation twice and at temperatures above 250 ° C with NO or O2. With these catalysts, NO can both by decomposition and by reduction with gases such as Carbon monoxide, hydrogen, and ammonia turn into non-toxic products like water, nitrogen, and oxygen convict. Nitric oxide (NO) is formed with every combustion process and is in different concentrations contained in smoke and exhaust gases. So far, transition metals, in particular of the 4th period, or their oxides have been used as catalysts for eliminating nitrogen oxides. Disadvantages are the sharp drop in activity and the sometimes insufficient selectivity. In some cases, considerable amounts of N ₂ O are formed; catalytic reduction by _NH3 is feasible only in a limited range of temperatures because at higher temperatures the catalytic oxidation of NH3 by present O2 to NO occurs upon catalytic hydrogenation is up to now in addition to N ₂ - always found NH ₃ -Büdung, in some catalysts is NH ₃ the only product Compared to the prior art, there is the task of producing and using catalysts that avoid the disadvantages mentioned and are simpler in their manufacturing process. The object is achieved according to the invention by catalysts for eliminating nitrogen oxides in exhaust gases based on metal phthalocyanines, which are characterized in that industrially produced metal phthalocyanines have been purified by sublimation twice and treated _{with NO or O 2 at temperatures above 250 ° C.} These catalysts are used to remove nitrogen oxides in exhaust gases. Metal phthalocyanines (MPc) have so far been used as catalysts in the liquid phase, occasionally also in gas-solid reactions been used. In the liquid phase, there are oxidations or oxidative dehydrations of hydrocarbons, alcohols and aldehydes. The oxidation of Propanethiol in the liquid phase; also in the catalytic sweetening of mineral oils (oxidation of thiols to Disulfides) MPc catalysts are used In the gas phase, propanol is oxidized and decomposed, Rearrangements of aldehydes, oxidation of propanethiol and hydrogen sulfide and the decomposition of Hydrazine known In all of these reactions the MPc are used as pure compounds. The use of technically produced MPc means that the metal content is less than that of oxide catalysts reduced, as the following comparison with metal oxides of the highest oxidation state shows: