Patent ID: 12220658

EXAMPLES WITH CATALYTICALLY PRECOATED FILTERS

Cordierite wall-flow filters with a diameter of 11.8 cm and a length of 13.5 cm were in-wall coated in order to produce the VGPF, GPF1, GPF2, and GPF3 particulate filters described in the examples and comparative examples. The wall-flow filters had a cell density of 46.5 cells per square centimeter at a wall thickness of 0.203 mm. The average pore size of the filters was 20 μm, with the porosity of the filters being about 65%.

First, a coating suspension containing noble metal was applied to these wall-flow filters. After application of the coating suspension, the filters were dried and then calcined at 500° C. The amount of coating after calcination corresponded to 50 g/l based on the volume of the substrate. This corresponds to the preparation of the VGPF.

According toFIG.1, 3 filters were coated with different amounts of aluminum oxide powder in the pores by means of the apparatus.

Example 1

GPF1: The open pores of an in-wall-coated filter were coated according to the invention with 3.3 g/l, based on the total filter volume, of a dry aluminum oxide. An aluminum oxide having an average particle diameter (d50) of 3.5 μm was used as the powder. This corresponds to a ratio of the average particle size of the powder used to the average pore size of the filter of 0.175.

Example 2

GPF2: The open pores of an in-wall-coated filter were coated according to the invention with 5.6 g/l, based on the total filter volume, of a dry aluminum oxide. An aluminum oxide having an average particle diameter (d50) of 3.5 μm was used as the powder. This corresponds to a ratio of the average particle size of the powder used to the average pore size of the filter of 0.175.

Example 3

GPF3: The open pores of an in-wall-coated filter were coated according to the invention with 8.6 g/l, based on the total filter volume, of a dry aluminum oxide. An aluminum oxide having an average particle diameter (d50) of 3 μm was used as the powder. This corresponds to a ratio of the average particle size of the powder used to the average pore size of the filter of 0.15.

The particulate filters GPF1, GPF2, and GPF3 according to the invention were investigated in comparison with the VGPF produced. After powder coating, the particulate filters were measured for their back pressure; as described below, filtration measurement was then carried out on the dynamic engine test bench. The back-pressure increase of the filters according to the invention is shown inFIG.3.

The VGPF, GPF1, GPF2, and GPF3 filters described were investigated for their fresh filtration efficiency on the engine test bench in the real exhaust gas of an engine operating with an on average stoichiometric air/fuel mixture. A globally standardized test procedure for determining exhaust emissions, or WLTP (Worldwide harmonized Light vehicles Test Procedure) for short, was used here. The driving cycle used was WLTC Class 3. The respective filter was installed close to the engine immediately downstream of a conventional three-way catalyst. This three-way catalyst was the same one for all filters measured. Each filter was subjected to a WLTP. In order to be able to detect particulate emissions during testing, the particle counters were installed upstream of the three-way catalyst and downstream of the particulate filter.FIG.4shows the results of the filtration efficiency measurement in the WLTP.

FIG.4shows the results of the filtration efficiency measurement. Depending on the amount of powder applied and the particle size distribution of the powder used, an improvement in the filtration efficiency by up to 20% at a maximum back-pressure increase (FIG.3) of only about 9% can be achieved.

The measured data demonstrate that the selective coating of the open pores of an already in-wall-coated filter leads to a significant improvement in filtration efficiency with only slightly increased back pressure.

Catalytic Characterization:

The particulate filters VGPF2 as well as GPF4, GPF5 were used for catalytic characterization. The wall-flow filters had a cell density of 46.5 cells per square centimeter at a wall thickness of 0.203 mm. The average pore size of the filters was 18 μm, with the porosity of the filters being about 65%. First, a coating suspension containing noble metal was applied to these wall-flow filters. After application of the coating suspension, the filters were dried and then calcined at 500° C. The amount of coating after calcination corresponded to 75 g/l, the concentration of Pd being 1.06 g/l and concentration for Rh being 0.21 g/l. All concentrations are based on the volume of the substrate.

Example 4

GPF4: The open pores of an in-wall-coated filter were coated with 10 g/l, based on the total filter volume, of a dry aluminum oxide. An aluminum oxide having an average particle diameter (d50) of 3.5 μm was used as the powder. This corresponds to a ratio of the average particle size of the powder used to the average pore size of the filter of 0.194.

Example 5

GPF5: The open pores of an in-wall-coated filter were coated with 15.8 g/l, based on the total filter volume, of a dry aluminum oxide. An aluminum oxide having an average particle diameter (d50) of 3.5 μm was used as the powder. This corresponds to a ratio of the average particle size of the powder used to the average pore size of the filter of 0.194.

The catalytically active particulate filters VGPF2, GPF4, and GPF5 were first tested in the fresh state and were then aged together in an engine test bench aging process. The latter consists of an overrun cut-off aging process (Aging 1) with an exhaust gas temperature of 900° C. upstream of the catalyst inlet (maximum bed temperature of 970° C.). The aging time was 19 hours. After the first aging process, the filters were examined for their catalytic activity and then subjected to a further engine test bench aging process (Aging 2). This time, the latter consists of an overrun cut-off aging process with an exhaust gas temperature of 950° C. upstream of the catalyst inlet (maximum bed temperature of 1030° C.). The filters were then tested repeatedly.

In the analysis of catalytic activity, the light-off behavior of the particulate filters was determined at a constant average air ratio λ on an engine test bench, and the dynamic conversion was checked when λ changed. In addition, the filters were subjected to a “lambda sweep test.”

The following tables contain the temperatures T50at which 50% of the component under consideration are respectively converted. In this case, the light-off behavior with stoichiometric exhaust gas composition (λ=0.999 with ±3.4% amplitude) was determined. The standard deviation in this test is ±2° C.

Table 1 contains the “light-off” data for the fresh filters, Table 2 the data after Aging 1, and Table 3 the data after Aging 2.

TABLE 1T50HCT50COT50NOxstoichiometricstoichiometricstoichiometricVGPF2279277278GPF4279275277GPF5278274277

TABLE 2T50HCT50COT50NOxstoichiometricstoichiometricstoichiometricVGPF2347351355GPF4350353356GPF5349352355

TABLE 3T50HCT50COT50NOxstoichiometricstoichiometricstoichiometricVGPF2396421422GPF4398413419GPF5394406412

The dynamic conversion behavior of the particulate filters was determined in a range for λ of 0.99 to 1.01 at a constant temperature of 510° C. The amplitude of λ in this case was ±3.4%. Table 3 shows the conversion at the intersection of the CO and NOx conversion curves, along with the associated HC conversion of the aged particulate filters. The standard deviation in this test is ±2%.

Table 4 contains the data for the fresh filters, Table 5 the data after Aging 1, and Table 6 the data after Aging 2.

TABLE 4HC conversion at the λCO/NOx conversionof the CO/NOxat the intersectionintersectionVGPF299%99%GPF499%99%GPF599%99%

TABLE 5HC conversion at the λCO/NOx conversionof the CO/NOxat the intersectionintersectionVGPF298%97%GPF498%97%GPF598%97%

TABLE 6HC conversion at the λCO/NOx conversionof the CO/NOxat the intersectionintersectionVGPF279%94%GPF480%94%GPF583%95%

In comparison to VGPF2, particulate filters GPF4 and GPF5 according to the invention show no disadvantage in catalytic activity in either the fresh or the moderately aged states. In a highly aged state, the powder-coated filters GPF4 and GPF5 even have an advantage in both CO conversion and NOx conversion and also in the dynamic CO/NOx conversion.

Examples with Non-Catalytically Precoated Filters:

Cordierite wall-flow filters with a diameter of 15.8 cm and a length of 14.7 cm were used to produce the VGPF, GPF1, and GPF2 particulate filters described in the examples and comparative examples. The wall-flow filters had a cell density of 31 cells per square centimeter at a wall thickness of 0.203 mm. The average q3 pore size (d50) of the filters was 18 μm, with the porosity of the filters being about 50%.

For coating the filters according to the invention, an air/powder aerosol of a dry aluminum oxide with a d10 value of the q3 particle size of 0.8 μm, a d50 value of the q3 particle size of 2.9 μm, and a d90 value of the q3 particle size of 6.9 μm was used. This corresponds to a ratio of the average particle size of the powder used to the average pore size of the filter of 0.16 and a ratio of d10 to d50 of 28%.

As comparative example, VGPF, an untreated filter as described above was used. The coating was carried out with an apparatus as described inFIG.1.

Example 1

GPF1: The open pores of a filter were coated with 6 g/l, based on the total filter volume, of the dry aluminum oxide.

Example 2

GPF2: The open pores of a filter were coated with 11.7 g/l, based on the total filter volume, of the dry aluminum oxide.

The particulate filters GPF1 and GPF2 according to the invention were investigated in comparison with the conventional VGPF. After coating, the particulate filters were measured for their back pressure, after which filtration measurement was then carried out on the highly dynamic engine test bench. The increase in back pressure of the filters according to the invention, measured on a back-pressure test stand (Superflow ProBench SF1020) at room temperature with an air throughput of 600 m3/h, is shown inFIG.6.

The VGPF, GPF1, and GPF2 filters described were investigated for their fresh filtration efficiency on the engine test bench in the real exhaust gas of an engine operating with an on average stoichiometric air/fuel mixture. A globally standardized test procedure for determining exhaust emissions, or WLTP (Worldwide harmonized Light vehicles Test Procedure) for short, was used here. The driving cycle used was WLTC Class 3. The respective filter was installed 30 cm downstream of a conventional three-way catalyst. This three-way catalyst was the same one for all filters measured. Each filter was subjected to a WLTP. In order to be able to detect particulate emissions during testing, the particle counters were installed upstream of the three-way catalyst and downstream of the particulate filter.FIG.7shows the results of the filtration efficiency measurement in the WLTP.

FIG.7shows the results of the filtration efficiency measurement. Depending on the amount of powder applied, an improvement in filtration efficiency up to 10% is already observed in the first WLTP cycle with a slight back-pressure increase (FIG.6).

The measured data demonstrate that the selective coating of the open pores of a conventional ceramic wall-flow filter leads to a significant improvement in filtration efficiency with only slightly increased back pressure.