Exhaust gas treatment system and the use thereof for the treatment of an exhaust gas

Abstract

An exhaust gas treatment system (1) comprises a catalyst article (5) for the treatment of an exhaust gas, the catalyst article (5) comprising a non-metallic substrate (20) comprising a plurality of catalytically-active transition-metal-doped iron oxide magnetic particles (45), and an inductive heater (70) for inductively heating the plurality of catalytically-active magnetic particles by applying an alternating magnetic field.

Claims

1. An exhaust gas treatment system comprising a catalyst article for the treatment of an exhaust gas, the catalyst article comprising a non-metallic substrate comprising a plurality of catalytically-active transition-metal-doped iron oxide magnetic particles, and an inductive heater for inductively heating the plurality of catalytically-active magnetic particles by applying an alternating magnetic field.

2. The exhaust gas treatment system of claim 1, wherein the non-metallic substrate is a ceramic substrate.

3. The exhaust gas treatment system of claim 1, wherein the plurality of catalytically-active magnetic particles are ferromagnetic or superparamagnetic.

4. The exhaust gas treatment system of claim 1, wherein the plurality of magnetic particles have a mean particle size of from 1 nm to 10 μm.

5. The exhaust gas treatment system of claim 1, wherein the plurality of magnetic particles consist of transition-metal-doped iron oxide magnetic particles.

6. The exhaust gas treatment system of claim 1, wherein the plurality of catalytically-active magnetic particles are surface-coated with a further catalytic material.

7. The exhaust gas treatment system of claim 1, wherein the plurality of catalytically-active magnetic particles have a spinel-type microstructure.

8. The exhaust gas treatment system of claim 1, wherein the magnetic particles comprise Mn.sub.xFe.sub.3-xO.sub.4, Co.sub.xFe.sub.3-xO.sub.4, Cu.sub.xFe.sub.3-xO.sub.4 or a mixture of two or more thereof, wherein x>0 and x≤1.

9. The exhaust gas treatment system of claim 1, wherein the magnetic particles are provided only on a region extending from one end of the catalyst article.

10. The exhaust gas treatment system of claim 1 wherein the plurality of catalytically-active magnetic particles have SCR activity, ASC activity, DOC activity, Urea-hydrolysis activity, Exotherm-generation activity or TWC activity.

11. The exhaust gas treatment system of claim 1, wherein the plurality of catalytically-active magnetic particles are provided as a washcoat on the non-metallic substrate.

12. The exhaust gas treatment system of claim 1, wherein the alternating magnetic field has a frequency from 100 kHz to 1 Mhz.

13. An internal combustion engine comprising the exhaust gas treatment system according to claim 1.

14. A method for the treatment of an exhaust gas, the method comprising contacting an exhaust gas with the exhaust gas treatment system according to claim 1 and inductively heating the plurality of catalytically-active magnetic particles with an alternating magnetic field produced by the inductive heater for inductively heating the plurality of catalytically-active magnetic particles.

15. The exhaust gas treatment system of claim 1, wherein the plurality of magnetic particles have a mean particle size of from 10 to 500 nm.

16. The exhaust gas treatment system of claim 6, wherein the further catalytic material comprises one or more platinum group metals.

Description

(1) The invention will now be described in relation to the following non-limiting figures, in which:

(2) FIG. 1 shows an exhaust gas treatment system having a catalyst article, as described herein.

(3) FIG. 2 shows the apparatus employed to test the performance of the catalyst article of FIG. 1.

(4) FIG. 3 shows a plot of concentration of NO.sub.2, N.sub.2O, NO and NH.sub.3 in ppm against time in seconds over the course of Experiment 1.

(5) FIG. 4 shows a bar chart of power supplied to the induction coil 70 against conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O over the course of Experiment 1.

(6) FIG. 5 shows a plot of concentration of N.sub.2O and NO.sub.2 in ppm against power in Amps over the course of Experiment 1.

(7) FIG. 6 shows a bar chart of power supplied to the induction coil 70 against conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O over the course of Experiment 2.

(8) FIG. 7 shows a plot of concentration of N.sub.2O and NO.sub.2 in ppm against power in Amps over the course of Experiment 2.

(9) FIG. 1 shows an exhaust gas treatment system 1 comprising a catalyst article 5. An internal combustion engine 10 is in gaseous communication with the catalyst article 5. The catalyst article 1 is further in gaseous communication with the remainder 15 of the exhaust gas treatment system 1, which comprises at least an outlet to the environment, but can also comprise other catalyst articles. The catalyst article 5 is arranged downstream of the internal combustion engine 10 and upstream of the remainder 15 of the exhaust gas treatment system 1. By upstream it is meant that, in use, the catalyst article 5 is closer to the engine manifold vis-a-vis the flow of the exhaust gas leaving the engine. Similarly, the catalyst article 5 has a substrate 20, which has an end which is “upstream” since, in use, it is closer to the engine manifold. This means that the exhaust gas leaving the engine 10 first contacts the upstream end 25 of the substrate 20. The downstream end 30 of the substrate 20 is where the exhaust gas leaves the catalyst article 5 and progresses through the remainder 15 of the exhaust gas treatment system 1.

(10) The substrate 20 of the catalyst article 5 is a monolithic honeycomb flow-through filter made of cordierite. The substrate 20 has a generally cylindrical shape with upstream end 25 and downstream end 30. The substrate 20 has a plurality of channels 35 formed therein by walls 40 extending from the upstream end 25 to the downstream end 30. The channels 35 are configured to enable gas flow therethrough from the upstream end 25 to the downstream end 30. The walls 40 each have a surface for contacting exhaust gas flowing therethrough.

(11) A plurality of catalytically-active transition-metal-doped iron oxide magnetic particles 45, herein referred to as the plurality of particles 45, are applied as a washcoat on the walls 40 of a first region 50 of the catalyst article 5. The first region 50 of the catalyst article 5 extends from the upstream end 25 of the substrate 20. The plurality of catalytically-active transition-metal-doped iron oxide magnetic particles may have SCR activity, ASC activity, DOC activity, urea-hydrolysis activity, exotherm-generation activity or TWC activity.

(12) A further catalytically active composition 55 having the same type of activity as the plurality of particles 45 is applied as a washcoat on the walls 40 of a second region 60 of the catalyst article 5. The second region 60 of the catalyst article 5 extends from the downstream end 30. Although the second region 60 is shown as not overlapping the first region 50, the second region 60 may be arranged to overlap the first region. The first region 50 is shown as being shorter in length than the second region 60. The first region 50 may be of the same length as the second region 60. The first region 50 may be longer than the second region 60.

(13) The exhaust gas treatment system 1 further comprises an induction coil 70 surrounding at least the first region of the catalyst article 5. The induction coil 70 is electrically connected to a power source (not shown) capable of providing alternating electric current to the induction coil 70.

(14) In use, during cold-start, an alternating electric current is applied to the induction coil 70 by the power source thereby generating an alternating magnetic field in the first region of the catalyst article 5. The alternating magnetic field inductively heats the plurality of catalytically-active transition-metal-doped iron oxide magnetic particles 45. This heating enables the plurality of catalytically-active transition-metal-doped iron oxide magnetic particles 45 to reach their operating temperature during cold-start. The term “operating temperature” refers to the temperature at which the particles are conducive to catalytic activity.

(15) A cold exhaust gas from a combustion engine 10 passes out of the engine 10 to the catalyst article 5. The exhaust gas then contacts the inductively heated plurality of particles 45 provided on the first region 50 of the catalyst article 5. The plurality of particles 45 are able to treat the cold exhaust gas received from the engine, since the plurality of particles 45 have been inductively heated to their operating temperature.

(16) The hot exhaust gas then contacts the further catalytically active composition 55 provided on the second region 60 of the catalyst article 5. The further catalytically active composition 55 is not inductively heated by the electromagnetic field. However, the further composition may be heated by conduction of heat from the plurality of particles 45 to the further catalytically active composition 55 and by the hot exhaust gas. Accordingly, the plurality of particles 45 may accelerate the heating of the further catalytically active composition to reach its operating temperature such that the further catalytically active composition 55 can treat exhaust gas more quickly following cold-start of an engine.

(17) The exhaust gas then leaves the catalyst article 5 and enters the remainder 15 of the exhaust gas treatment system 1 for optional further treatment therein.

(18) The performance of the catalytically-active transition-metal-doped iron oxide magnetic particles 45 was tested using the apparatus 75 shown in FIG. 2. The results of the tests are discussed below. The apparatus 75 comprises a sealed enclosure (not shown) having a tube 80 formed of quartz therein. The tube 80 has an inlet 85 and an outlet 87. The inlet 85 of the tube 80 is in gaseous communication with an exhaust gas supply 90 located upstream of the tube 80 and externally to the sealed enclosure. The outlet 87 of the tube 80 is in gaseous communication with a Fourier-transform infrared (FTIR) spectroscope 100 located downstream of the tube and externally to the sealed enclosure. The tube 80 contains the plurality of the catalytically-active transition-metal-doped iron oxide magnetic particles 45 therein and quartz wool 110 configured to immobilize the plurality of particles 45. The apparatus comprises an induction coil 70 surrounding at least the portion of the tube 80 containing the plurality of particles 45. A power source (not shown) is electrically connected to the induction coil 70. The power source is capable of providing alternating electric current to the induction coil 70. The induction coil 70 is water cooled such that its temperature does not affect the measurement of temperature of the plurality of particles 45 within the tube 80, which is discussed below.

(19) FIG. 3 shows a plot of concentration of NO.sub.2, N.sub.2O, NO and NH.sub.3 in ppm against time in seconds over the course of Experiment 1. Concentration of N.sub.2O and NO.sub.2 in ppm is provided on the left-hand y-axis. Concentration of NO and NH.sub.3 in ppm is provided on the right-hand y-axis. Time in seconds is provided on the x axis. At time period 65-75 seconds, the relative peak heights of the lines shown in FIG. 3 are such that the highest peak is for N.sub.2O concentration, the second highest peak is for NH.sub.3 concentration, the third highest peak is for NO concentration and the lowest peak is for NO.sub.2 concentration.

(20) FIG. 4 shows a bar chart of power supplied to the induction coil 70 against conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O over the course of Experiment 1. Percentage of NO.sub.2, N.sub.2O and N.sub.2 is provided on the y-axis. Power in Amps is provided on the x-axis. The top part of each bar represents percentage of N.sub.2. The bottom part of each bar represents percentage of N.sub.2O. The middle part of each bar represents percentage of NO.sub.2.

(21) FIG. 5 shows a plot of concentration of N.sub.2O and NO.sub.2 in ppm against power in Amps over the course of Experiment 1. Concentration of N.sub.2O and NO.sub.2 in ppm is provided on the y-axis. Power in Amps is provided on the x-axis. The lower of the two lines at 400 Amps represents concentration of NO.sub.2, the other line represents concentration of N.sub.2O.

(22) FIG. 6 shows a bar chart of power supplied to the induction coil 70 against conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O over the course of Experiment 2. Percentage of NO.sub.2, N.sub.2O and N.sub.2 is provided on the y-axis. Power in Amps is provided on the x-axis. The top part of each bar represents percentage of N.sub.2. The bottom part of each bar represents percentage of N.sub.2O. The middle part of each bar represents percentage of NO.sub.2.

(23) FIG. 7 shows a plot of concentration of N.sub.2O and NO.sub.2 in ppm against power in Amps over the course of Experiment 2. Concentration of N.sub.2O and NO.sub.2 in ppm is provided on the y-axis. Power in Amps is provided on the x-axis. The lower of the two lines at 150 Amps represents concentration of N.sub.2O, the other line represents concentration of NO.sub.2.

EXAMPLES

(24) The invention will now be described in relation to the following non-limiting examples.

(25) Two types of catalytically-active transition-metal-doped iron oxide magnetic particles were tested for their performance in treating an exhaust gas from an internal combustion engine using the apparatus of FIG. 2, which is discussed above. Experiment 1 was performed with catalytically-active transition-metal-doped iron oxide magnetic particles formed of MnFe.sub.2O.sub.4. Experiment 2 was performed with catalytically-active transition-metal-doped iron oxide magnetic particles formed of CUFe.sub.2O.sub.4. The methodology for each experiment is provided below.

(26) Experimental Method

(27) In each experiment, the plurality of particles 45 were placing inside the tube 80 and immobilized with quartz wool 110. An exhaust gas at room temperature (approximately 25° C.) from the exhaust gas supply 90 flowed into the tube 80 via the inlet 85, contacted the plurality of particles 45 and flowed out of the tube 80 via the outlet 87 to the MKS MultiGas™ 2030 FTIR spectroscope 100 for analysis. The simulated partial diesel exhaust gas supply 90 was from a Hiden Analytical Catlab instrument comprising 400 ppm of NO, 400 ppm of NH.sub.3, 5% CO.sub.2, 10% O.sub.2 and the balance N.sub.2. The gas flow through the tube 80 during each experiment was at a rate of approximately 1 L/min. The alternating electric current was supplied by an Ambrell EasyHeat® 0224 instrument fitted with a 1.5″ length×1.5″ diameter multi-turn helical coil.

(28) Once the gas flow through the tube 80 had stabilised, the power supply was turned on such that the alternating electric current was applied to the induction coil 70 by the power source. The alternating electric current generated an alternating magnetic field in the region of the tube 80 having the plurality of particles 45 therein. The alternating electric current was applied to the induction coil 70 for five minutes. The alternating magnetic field inductively heated the plurality of particles 45 within the tube 80. This heating enabled the plurality of particles 45 to reach their operating temperature.

(29) The exhaust gas flowing through the tube 80 contacted the inductively heated plurality of particles 45. The exhaust gas then left the tube 80 via the outlet 87 and entered the FTIR spectroscope 100 for analysis. The spectra obtained by the FTIR spectroscope 100 were used to determine the concentration of the components of the exhaust gas over the course of the experiments.

Experiment 1

(30) As discussed above, Experiment 1 was performed using the above methodology with the plurality of particles within the tube 80 being formed of MnFe.sub.2O.sub.4. The exhaust gas flow through the tube 80 commenced at time 0 seconds, the supply of alternating electric current to the induction coil 70 started at time 65 seconds and the supply of alternating electric current to the induction coil 70 stopped at time 365 seconds.

(31) To measure the temperature of the particles of MnFe.sub.2O.sub.4 over the course of the experiment, the sealed enclosure was opened and an IR thermal imaging camera was placed inside the sealed enclosure after the alternating electric current had been applied to the inductive coil for 120 seconds (i.e. at time 185 seconds). The measured temperature of the MnFe.sub.2O.sub.4 particles was 200° C. thereby confirming that the MnFe.sub.2O.sub.4 particles are inductively heatable. It is noted that the temperature of the MnFe.sub.2O.sub.4 particles at time 185 seconds may be greater than 200° C., since some heat loss may have occurred on opening the enclosure to insert the thermal imaging camera. Nevertheless, this temperature measurement shows that the MnFe.sub.2O.sub.4 particles are inductively heatable.

(32) FIG. 3 comprises data obtained by the FTIR 100 over the course of the experiment performed with the plurality of particles 45 within the tube 80 being formed of MnFe.sub.2O.sub.4, herein referred to as MnFe.sub.2O.sub.4 particles, and the power supplied to the induction coil 70 being between 0-400 Amps (0-2400 Watts). FIG. 3 is a graph of concentration of NO.sub.2, N.sub.2O, NO and NH.sub.3 in ppm against time in seconds over the course of the experiment.

(33) As can be seen from FIG. 3, on commencing the induction heating at time 65 seconds, there is a spike in concentration of NO and NH.sub.3. One explanation for this observation is that on commencing flow of exhaust gas through the tube 80 before inductively heating the plurality of particles, NO and NH.sub.3 adsorbs onto the surface of the plurality of particles 45. It is considered that the spike at time 65 seconds is a consequence of desorption of NO and NH.sub.3 from the surface of the particles 45 on commencing the inductive heating. An alternative explanation is that on commencing flow of exhaust gas through the tube 80 before inductively heating the plurality of particles 45, ammonium nitride and ammonium nitrate form and adsorb onto the surface of the plurality of particles 45. On commencing the inductive heating, the decomposition of ammonium nitride and ammonium nitrate lead to N.sub.2O formation. A method of determining which of these explanations is more plausible would be to characterise the plurality of particles 45 after exposure to the exhaust gas in the absence of induction heating, using an appropriate analytical technique. A method to avoid the adsorption of NO or NH.sub.3 or the formation and adsorption of ammonium nitride or ammonium nitrate on the plurality of particles 45 would be to introduce a bypass gas flow to the experimental apparatus. The bypass gas flow would independently allow the plurality of particles 45 to be inductively heated and the exhaust gas supply to stabilise, before the exhaust gas supply contacts the plurality of particles 45.

(34) This spike in FIG. 3 would not be expected to be seen in an engine, since there would be no pre-exposure to the NO and NH.sub.3 before heating. At time 95 seconds, the concentrations of NO and NH.sub.3 decreased to 0 ppm. Accordingly, over the course of 30 seconds, for which the MnFe.sub.2O.sub.4 particles were inductively heated, 100% conversion of NO and NH.sub.3 has been performed by the plurality of particles 45. It is noted that the time period of 30 seconds also includes the time during which desorption of NO and NH.sub.3 occurs. Without such desorption, the time taken for full 100% conversion of NO and NH.sub.3 might be approximately 20 seconds. The induction heating was switched off at time 365 seconds after which the concentration of NO increased due to lack of conversion by the MnFe.sub.2O.sub.4 particles. The NO.sub.2 formation and N.sub.2O formation accordingly also decreased at this point in time.

(35) In summary, FIG. 3 together with the temperature measurement at time 185 seconds shows the particles of MnFe.sub.2O.sub.4 are inductively heatable to reach their operating temperature and have SCR activity when inductively heated.

(36) FIG. 4 is a graph of power supplied to the induction coil 70 against conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O over the course of the first experiment. From FIG. 4, it can be seen that the particles of MnFe.sub.2O.sub.4 have SCR catalytic activity once the power supplied to the induction coil 70 reaches 50 Amps. Accordingly, it can be seen that conversion of NO by the MnFe.sub.2O.sub.4 particles occurs once the MnFe.sub.2O.sub.4 particles have been sufficiently inductively heated to reach their operating temperature. The catalytic activity of the MnFe.sub.2O.sub.4 particles increases with increased supply of power to the induction coil 70. Accordingly, the catalytic activity of the MnFe.sub.2O.sub.4 particles increases as the temperature of the MnFe.sub.2O.sub.4 particles increases. The conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O reaches 95% and stabilises at that value once the power supply reaches 100 Amps.

(37) In summary, FIG. 4 shows that the particles of MnFe.sub.2O.sub.4 have SCR catalytic activity once inductively heated. The catalytic activity of the MnFe.sub.2O.sub.4 particles is maximised once the power supplied to the induction coil 70 reaches 100 Amps.

(38) The N.sub.2O and NO.sub.2 formation data of FIG. 4 is presented as a line graph in FIG. 5. From both FIG. 4 and FIG. 5, it can be seen that selectivity of the reactions of the exhaust gas changes with increasing power supplied to the induction coil 70 (and so increased temperature of the inductively heated MnFe.sub.2O.sub.4 particles). NO.sub.2 formation starts when the power supply reaches 75 Amps. A sharp increase in formation of NO.sub.2 occurs when the power supplied to the induction coil 70 is increased from 100 to 125 Amps. It is considered that on increasing the power supplied to the induction coil 70 there is an increase in temperature achieved by the plurality of particles 45, which leads to increased catalytic activity. The formation of NO.sub.2 is maximised and stabilised once the power supplied to the induction coil 70 reaches 150 Amps. The formation of N.sub.2O starts when the power supplied to the induction coil 70 reaches 50 Amps and stabilises when the power supply reaches approximately 300 Amps. Accordingly, the selectivity of the reactions of the exhaust gas depends upon the temperature of the MnFe.sub.2O.sub.4 particles.

Experiment 2

(39) As discussed above, Experiment 2 was performed using the same methodology as Experiment 1 except that the plurality of particles 45 within the tube 80 were formed of CuFe.sub.2O.sub.4, herein referred to as CuFe.sub.2O.sub.4 particles.

(40) FIG. 6 is a graph of power supplied to the induction coil 70 against conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O over the course of the second experiment. From FIG. 6, it can be seen that the particles of CuFe.sub.2O.sub.4 have SCR catalytic activity once the power supplied to the induction coil 70 reaches 75 Amps. Therefore, FIG. 6 demonstrates that conversion of NO by the CuFe.sub.2O.sub.4 particles occurs once the CuFe.sub.2O.sub.4 particles have been sufficiently inductively heated to reach their operating temperature. The conversion of NO into NO.sub.2, N.sub.2 and N.sub.2O reaches a maximum value of 72% and stabilises at that value once the power supply reaches 100 Amps. In summary, FIG. 6 demonstrates that the particles of CuFe.sub.2O.sub.4 have catalytic activity once inductively heated by supplying at least 75 Amps of power to the induction coil 70. It is noted that the CuFe.sub.2O.sub.4 particles have reduced activity compared to the MnFe.sub.2O.sub.4 particles. Nonetheless, activity was demonstrated.

(41) The N.sub.2O and NO.sub.2 formation data of FIG. 6 is presented as a line graph in FIG. 7. As shown in FIGS. 6 and 7, selectivity of the reactions of the exhaust gas changes with increasing power supplied to the induction coil 70. The proportion of NO.sub.2 formed significantly increases as the power supplied to the induction coil 70 is increased from 75 Amps. The proportion of NO.sub.2 formed stabilises when the power supplied to the induction coil 70 reaches 125 Amps. Therefore, the greater the temperature of the CuFe.sub.2O.sub.4 particles, the greater proportion of NO.sub.2 is formed. The formation of N.sub.2O starts when the power supplied to the induction coil reaches 75 Amps. The formation of N.sub.2O remains stable as the power supplied to the induction coil increases beyond 75 Amps.

(42) Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the scope of the invention or of the appended claims.

(43) For the avoidance of any doubt, the entire content of any and all documents cited herein is incorporated by reference into the present application.