SE504912C2 - catalyst Usage - Google Patents

Abstract

The present invention relates to the use of a catalyst in a catalytic combustion, which catalyst is produced by the coating of a carrier with a suspension of noble metal particles in a microemulsion. The carrier is distributed on a monolith. The invention also relates to a catalyst comprising an active phase which by microemulsion technique has been deposited on a carrier. The active phase comprises noble metal particles. The carrier comprises a metal oxide and is distributed on a monolith. The invention also relates to a method of producing a catalyst as defined above by microemulsion technique, wherein bimetallic particles are produced by the blending of not reduced noble metal particles in microemulsion and then the reduction thereof.

Description

* 'so4 9í2 10 15 20 25 30 35 Ethanol is already used as fuel in buses that run on trial in Stockholm. These buses are equipped with diesel engines. When burning oil and gasoline in car engines, it is well known that it is formed environmentally hazardous substances. In the same way it is formed during ethanol combustion undesirable substances, such as acetaldehyde and acetic acid.

Emissions from petrol engines are now taken care of car exhaust catalysts that convert, among other things, NO to N2 and CO to CO 2. These catalysts contain precious metals, such as Pt and Rh, consists of Al2O3.

The same type of catalysts are currently used which are deposited on a carrier as often for the purification of emissions from diesel engines containing ethanol used as fuel. The exhaust gases from ethanol vehicles contains unburned ethanol and acetaldehyde as in turn can be converted to acetic acid, which is irritating due of its special odor.

To prevent these substances from entering the exhaust gases attempts have been made to find suitable oxidation catalysts.

In the past, precious metal-based materials have been used catalysts, but also base metal oxides have been investigated.

Another area where catalytic combustion is interesting is the combustion of fuels at such y applications such as industrial boilers, gas turbine combustors and heat generation systems, ie such systems that are primarily aimed at energy recovery.

The requirements in this area on material properties and complicated chemical reaction systems, however, do this one of the most difficult applications of catalytic combustion.

Problem statement When using ethanol as fuel in diesel engines in buses, it has been shown that today's catalysts works satisfactorily while driving. Problem 10 15 20 25 30 35 Iso4 912 occurs, however, in situations when the engine is idling, such as at stops or queues. In such situations, namely the temperature of the catalyst is lowered, whereupon both activity and selectivity deteriorate substantially. Acetic acid and acetaldehyde, as well as some unburned ethanol, is thus present in the exhaust gases emitted in the urban environment.

There is thus a great need for a more specific one catalyst, which, among other things, can work effectively at low temperatures, as the exhaust gases at idle have a temperature of 250 ° C or lower.

To tailor a catalyst as on one can effectively take care of the exhaust gases formed at ethanol combustion must be identified the combustion products to find out which ones products formed at low temperatures. Then you can develop the ability of the catalyst to convert them products for more environmentally friendly exhaust gases. The exhaust gases from ethanol vehicles contain, as mentioned above, unburned ethanol and acetaldehyde and it is these substances that together with acetic acid must be removed. So far, however failed to develop a catalyst that enables this effectively at low temperatures.- When using catalysts in combustion for energy recovery, it has been shown to be a precatalyst which ignites at low temperature is of great importance.

Description of the invention The present invention solves to a very large extent above mentioned problems by providing the use of a new type of decatalyst in catalytic combustion. This catalyst is prepared by coating a support with a suspension of precious metal particles in a microemulsion, the carrier also being spread on a * “So4 9ï2 10 15 20 25 30 monolith. The invention also relates to the above-mentioned catalysts and a process for their preparation.

Some such catalysts are in themselves prior known from EP 8l900804.6, but from this one can not read out the present use and even less those outstanding results as the catalyst according to the invention has been found to give in to this.

Detailed description of the invention The invention more particularly relates to a new use of a catalyst in combustion, where the catalyst is prepared by coating a carrier with a suspension of noble metal particles in a microemulsion. The carrier is spread on one monolith as a support and to the contact surface between the active or catalytic parts of the catalyst on the carrier and the combustion gases shall maximized.

In one embodiment of the invention is used a carrier, which is coated with a monolayer of the precious metal particles. This increases the contact area against the exhaust gases significantly.

In another embodiment of the invention used a catalyst according to above, where the precious metal particles are monometallic, ie each particle is built of a kind of metal. It can also include embodiments, where the catalyst includes several metals, as long as each particle does not include more than one variety. dy In an alternative embodiment of the invention is the precious metal particles bimetallic, ie made up of two metals. 10 15 20 25 30 uï V1 V5 "504 912 In another embodiment of the invention used a catalyst, where the carrier is coated with precious metal particles The Pt group, preferably Pt and / or Pd.

In a special embodiment of the invention is as mentioned above precious metal particles Pt and Pd, which have co-reduced in the microemulsion. By the metals are reduced simultaneously, mixed with each other, surprisingly an activity is achieved, which is significantly much higher than that obtained when the metals are first reduced each and one separately and then mixed.

In one embodiment of the invention is the support is a monolith, such as Al 2 O 3, TiO 2 or SiC, preferably Al fi ß.

In another embodiment of the invention a monolith consisting of metal was used, metal alloy or inorganic oxides. Its geometric shape is such that combustion gases, or exhaust fumes, can pass without anything noticeable pressure drop. A preferred monolith is made of * cordierite (2MgO ° öSiO2 ° 2Al2O3). A preferred form is a cylinder with a large number of square channels for minimizing the above-mentioned pressure drop.

In one embodiment of the invention is the catalytic combustion combustion of alcohol-based fuels, in particular ethanol. The use of the catalyst according to the invention, the activity of which is surprising is significantly higher than the previously known ones the catalysts, not least at low temperatures, has been shown to be special advantageous in the diesel engines, such as l'5o4 9ï2 10 15 20 25 30 35 ethanol-powered inner city buses today are equipped with.

In another embodiment of the invention is the catalytic combustion combustion in gas turbines, industrial boilers or heat generation system. The low flash point at use of the catalyst according to the invention should be special in this context advantageous.

According to another aspect relates the present invention to a catalyst, which comprises an active phase, which genome microemulsion technology has been deposited on a carrier.

The active phase comprises noble metal particles and the support comprises a metal oxide. The carrier is also in this case scattered on a monolith.

The catalyst according to the invention has been found be particularly suitable for combustion reactions, especially of the kind mentioned above in in connection with the use according to the invention, e.g. combustion of alcohol-based or other organic materials; In one embodiment of this aspect of According to the invention, the carrier is coated with a monolayer of the precious metal particles.

In another embodiment of this aspect is the precious metal particles are monometallic.

An alternative to this embodiment is the precious metal particles are bimetallic.

In a particular embodiment, the catalyst is according to the invention made up of precious metal particles, which, for example, are derived from The Pt group, preferably Pt and / or Pd. In a special embodiment is the precious metal particles Pt and Pd, which are co-reduced in the microemulsion, 10 15 20 25 30 35 “A7 504 912 that is, they have been mixed before their reduction took place.

In another embodiment, the metal oxide in the carrier Al2O3, TiO2 or SiC, where Al2O3dock today is preferred due to its good properties in terms of aging.

In a special embodiment of the catalyst according to the invention is monolithic metal, metal alloy or inorganic oxides.

According to another aspect relates present invention to a method of preparation of such a catalyst, which has described above. The catalyst is manufactured by i and per se known microemulsion technique, where, however according to the invention bimetallic particles produced by unreduced Precious metal particles in microemulsion are mixed and then reduced.

According to a special embodiment of the method according to the invention belongs the noble metal particles Pt group, preferably Pt and Pd.

Exggpel Catalyst production For the experiments, three microemulsions were prepared, one Pt and a Pd microemulsion as well as a microemulsion such as contained both Pt and Pd. From a monolith, with 142.4 g / dm 3 Al2O3 carriers, test pieces were sawn out. The size of the specimens were made to fit one existing test facility. The monolith had one cell density of 62 cells / cm 2.

The metal salts were reduced and deposited on the test pieces. The volume of the monolith pieces is estimated to be 11000 mm3 or expressed in dm3 llxlOü dm3. 504 9í2 8 in 10 15 20 25 The monoliths were prepared with a metal charge according to table 1. comparison could be made with previously performed These metal contents were selected to a relevant tests of catalytic activity.

The notation Pt-Pd indicates that the metal salts was co-reduced, ie both salts were present at the reduction. By Pt + Pd is meant that the respective metal salt was reduced in its own microemulsion and that these then mixed.

Table 1 Catalyst Mbtall concentration Metal concentration on monolith, g / dm3 on monolith, mmol / dm3 Pt 1.8 9.5 Pd 1.0 9.5 Pt, Pt 0.9, 0.5 4.8, 4.8 (1.4 total) (9.5 total) The support consists of y-Al2O3 (Condea PXl40) with one specific surface area of about 140 m2 / g. These values apply to both catalysts made by impregnation technology and for catalysts prepared by microemulsion technology.

Catalytic reaction The experimental setup makes it possible catalytic tests of gas mixtures whose composition is such that it resembles the exhaust gases formed at ethanol production in a diesel engine. 10 15 20 25 ”09 i '504 912 Table 2 Subject Concentration O2 10 vol% H 2 O 10 vol% CO; 6.5 vol% N; Balance CO 300 ppm U NO 600 ppm C2H5OH 200 ppm The catalyst is tested at 100% excess air (Ä = 2) in one gas mixers whose composition is given in Table 2. The experiments performed between 75 ° 0 and 500 ° C with a space Velocity of iooooorfl.

The pretreatment means that the catalyst is heated from All catalysts were pretreated. room temperature to 500 ° C with a heating rate of 100 / minute. the reaction mixture over the catalyst in the reactor.

During the heating streams The catalyst is then cooled with a gas mixture whose 1Ü96 H20 OCh 8Û% Ng. At the cooling is the space velocity of the gas mixture Velocity 25000 h'Ü Measuring equipment The concentration of the total amount of hydrocarbon, composition is 10% 02, nitric oxide and carbon monoxide in the outgoing stream were analyzed line. For this, conventional continuous was used The total amount of hydrocarbons (FID). analytical instrument. was analyzed with a flame ionization detector Nitric oxide was analyzed with a chemiluminescent detector (CLD) infrared instrument and carbon dioxide were measured with a non-dispersive (NDIR). Detailed analysis of oxygen, nitrogen, carbon dioxide, oxidized substances and hydrocarbons were performed on-line in a semi-continuous way. This was done with a gas chromatograph equipped with thermal conductivity, flamjonisation and "far ultra Violet" detector. 504 10 15 | .1. 912 io Results Table 3 presents a summary of the catalytic experiments. Values that are usually used to characterize catalysts have been tabulated.

The light-off temperature specified refers to the temperature then you have a turnover of 50% of the current component.

Table 3 Catalysis Metal Light-off Light-off Max Max -ator temperature for temperaturu turnover turnover. ethanol r for CO of of ethanol (50% rev.), ° C (50% rev.) Ethanol to ° C to acetic acid acetal-% dehyd, % Impreg- P1; 153 (1491) 167 30 2 nerad Pd 213 (2031) 190 33 0.40 Pt, Pa 1301 (1351) - ej det.

Micro- Pt 116 166 35-45 not it. emul- Pd 164 176 55 ej det. sion Pt-Pd lll 152 45 ej det.

Pt + Pd 164 173 45 ej det. Results from catalysts deposited on TiO2 and prepared with impregnation technique. 10 15 20 25 30 I * -1 11 - 504 912 The following reaction steps take place during ethanol oxidation: C2H50H + 302 - * 2CO2 + 3H2O (1) C2H50H + 0.5 O2 - + CH3CHO + H2O (2) C2H50H - + CH3CHO + H2 (3) C2H50H + O2 -> CH3CO00H + H2O (4) CH3CHO + 0.502 - * CH3COH (5) Acetic acid or acetaldehyde is thus formed during oxidation of ethanol. It can be seen that for all catalysts acetaldehyde is formed during the reaction. However, formed no detectable amount of acetic acid. No acetic acid could nor detected when the catalysts were prepared with microemulsion technique.

Catalytic oxidation of ethanol The microemulsion prepared catalysts which are (i.e. Pt, Pt-Pd, The light-off temperatures of these catalysts most active are those that contain Pt Pt + Pd). is measurably lower than for the monolith that was coated with only Pd. Catalysts made with impregnation technology certainly shows the same mutual difference depending on metal composition, but the activity for these is generally lower than for corresponding microemulsion-prepared catalysts.

Light-off temperature for microemulsion prepared catalysts are generally seen lower than for the corresponding catalysts which prepared by impregnation.

For microemulsion-produced Pt, Pd and Pt-Pd catalysts, the light-off temperatures are 37, 39 resp 504 10 15 20 25 30 rr 912 20 ° C lower than for the corresponding impregnated catalyst (see Table 3).

If one compares impregnated catalysts with TiO2 as a support with the corresponding Y-Al 2 O 3 catalyst can be seen that an impregnated bimetallic Pt-Pd catalyst with TiO2 support gives a 25 ° C lower light-off temperature than one Y-A1203 carrier. Microemulsion-produced Pt catalysts on the A120; still gives a light-off temperature that is 37 ° C lower than impregnated Pt catalysts on TiO2.

These results show that microemulsion prepared catalysts are active at a lower temperature than the corresponding impregnated catalysts, regardless of metal composition. Pt and Pt-Pd are most active. When A120; replaced with TiO2 in those impregnated bimetallic catalysts you get a light-off temperature which is 5 ° C lower than in Pt-Pd catalysts on A120; produced by microemulsion technique.

Formation of acetaldehyde It can be seen that on all the above mentioned catalysts acetaldehyde is formed during the course of the reaction independently which method has been used to produce the catalyst. Catalysts produced in microemulsion converts larger amounts of ethanol to acetaldehyde than impregnated catalysts. Turnover is 10-15% higher than for impregnated catalysts regardless of metal composition. The Pd catalyst provides it maximum turnover of 55%.

If you compare the temperature at which the turnover of acetaldehyde begins to decrease it is seen that for microemulsion-produced Pt catalysts are decreasing acetaldehyde turnover approx. 35 ° C before the corresponding impregnated catalyst. 10 15 20 25 30 35 504 912 Formation of acetic acid Acetic acid could not be detected for microemulsion prepared catalysts. For impregnated catalysts form acetic acid with a turnover of 2% for the Pt catalyst and 0.38 for Pd. The detection limit for acetic acid with the current apparatus is about 0.5 ppm.

Sales of CO Q Of the microemulsion prepared catalysts have The Pt-Pd catalyst also has the lowest light-off temperature in the case of oxidation of CO. Light-off temperature for this catalyst, 14 ° C is lower than the best value presented for the impregnated catalysts. At comparison of the Pd catalysts it turns out that it the microemulsion-produced Pd catalyst has a light off-temperature which is 140C lower than the corresponding impregnated Pd catalyst. Light-off temperature for The PT catalysts are approximately equal for both types.

Discussion Studies of ethanol oxidation on various catalysts shows that a number of different factors affect the catalyst activity. These factors include the production method, the nature and composition of the metal. Also support material affects the activity of the catalyst.

As for the nature of the metal, it turns out that the production method does not affect the difference between Pt and Pd catalysts, ie that Pt is more active than Pd in ethanol oxidation. This may have its explanation in that Pd forms PdO at a lower temperature than Pt forms PtO.

The respective metal oxide is assumed to be less active than Pt ° and Pd °.

The catalyst of Pt + Pd, which was prepared by mixing of microemulsion-produced Pt- and Pd particles, did not show the same activity as Pt-Pd the catalyst. The Pt-Pd catalyst was prepared by lso4 9f2 10 15 20 25 30 '14 _ reduction in a microemulsion containing metal salt of both Pt and Pd. The catalytic activity of Pt + Pd- the catalyst is of the same order of magnitude as the corresponding catalyst with only Pd particles, ie it has one relatively Pt catalysts high light-off temperature. Pt- The Pd catalyst, on the other hand, has a light-off temperature such as is comparable to the corresponding Pt catalyst. This means that to get a high activity with bimetallic catalysts, the metal particles must be prepared so that there is an alloying or mixing of the metals.

It can also be stated that they are bimetallic the catalysts of Pt and Pd lower the light-off the temperature of CO oxidation, which may be off interest in other applications where catalysts used, such as three-way catalysts.

Conclusion The catalysts prepared in microemulsion have showed higher activity for ethanol oxidation than those which have produced with impregnation technology. In these studies, only the activity of catalysts prepared with Y- Al2O3 as carrier compared. Studies of catalysts_ produced by impregnation technology, however, shows that TiO2 can be an interesting alternative to Y-Al2O3.

Claims (16)

10 15 20 25 30 35 l-W 115 get 504 912 PATENT CLAIMS Use of a catalyst in the catalytic combustion of alcohol-based fuels, which catalyst is prepared by coating a support with a suspension of noble metal particles composed of two metals in a microemulsion, the support being dispersed on a monolith. Use according to claim 1, wherein the carrier is coated with a monolayer of the noble metal particles. Use according to any one of the preceding claims, wherein the support is coated with particles of noble metal belonging to the Pt group, preferably Pt and / or Pd. Use according to any one of the preceding claims, wherein the noble metal particles have been co-reduced in the microemulsion. Use according to claim 4, wherein the noble metal particles are Pt and Pd. Use according to any one of the preceding claims, wherein the carrier is selected from Al 2 O 3, TiO 2 and SiC. Use according to any one of the preceding claims, wherein the monolith is of metal, metal alloy or inorganic oxides. Use according to any one of the preceding claims, wherein the catalytic combustion is the combustion of ethanol. Use according to any one of claims 1-6, wherein the catalytic combustion is combustion in diesel engines, gas turbines, industrial boilers or heat generation systems. Catalyst, especially for combustion reactions, comprising an active phase which has been deposited on a support by microemulsion technology, the active phase comprising noble metal particles composed of two metals which are co-reduced in the microemulsion, the support being dispersed on a monolith. 5114 9:12 1116 '10 15 20 25 30 The catalyst of claim 10, wherein the support is coated with a monolayer of noble metal particles. Catalyst according to any one of claims 10-11, wherein the particles are of noble metal belonging to the Pt group, preferably Pt and / or Pd. A catalyst according to any one of claims 10-12, wherein the support is selected from Al 2 O 3, TiO 2 and SiC. A catalyst according to any one of claims 10-13, wherein the monolith is of metal, metal alloy or inorganic oxides. A process for producing a catalyst according to any one of claims 10-14 by microemulsion technique, wherein particles composed of two metals are produced by mixing and then reducing reduced noble metal particles in microemulsion. A method according to claim 15, wherein the bimetallic particles are of noble metals belonging to the Pt group, preferably Pt and Pd.