BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a graph showing the desorption temperature of sulfur compounds adsorbed on zeolite powder, measured using a mass spectrograph;
FIG. 2 is a graph showing the extent of discharge of H2S by sulfur compounds adsorbed on zeolite powder in a rich condition measured using a mass spectrograph;
FIG. 3 is a graph showing the reaction of H2S gas and SO2 gas on zeolite powder measured using a mass spectrograph;
FIG. 4 is a graph showing the effect of reducing H2S based on a three-way catalyst containing no Ni or zeolite, a three-way catalyst containing Ni, and a three-way catalyst containing zeolite, measured using a mass spectrograph; and
FIG. 5 is a graph showing the efficiency of purification of HC, NOx and CO based on a three-way catalyst containing no Ni or zeolite, a three-way catalyst containing Ni, and a three-way catalyst containing zeolite, evaluated through a rapid deterioration mode in an engine bench test.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.
Hereinafter, a catalyst design process will be described by selecting the above mentioned zeolite as a component of the catalyst composition, but the present invention is not limited thereto.
First, the present inventor sought to determine whether the effect of discharging SO2, not H2S, which meets the needs of the present invention, could be obtained when sulfur compounds are adsorbed on zeolite and then desorbed therefrom.
FIG. 1 shows the desorption temperature of sulfur compounds adsorbed on zeolite powder measured using a mass spectrograph. 0.5 g of zeolite powder, exposed to sulfur by injecting 20 ppm of H2S gas and 50 ppm of SO2 gas at respective rates of 500 ml and 100 ml per minute for 5 minutes, was put into a quartz tube, and was then heated to a temperature of 850° C. while injecting N2 gas at a rate of 100 ml per minute, thereby measuring the desorption temperature of the sulfur compound. As a result, among the sulfur compounds, H2S gas was not generated, and SO2 gas started to be desorbed at a temperature of about 300° C., and was maximally desorbed at a temperature of 520° C. Accordingly, it was found that the sulfur compounds adsorbed on zeolite were discharged into SO2 gas rather than H2S gas at the time of raising a temperature.
Further, the present inventor measured the extent of discharge of H2S in a rich condition, which is shown in FIG. 2.
FIG. 2 shows the extent of discharge of H2S in a rich condition measured using a mass spectrograph by injecting SO2 gas at a temperature of 500° C. for 30 minutes in order to adsorb sulfate on zeolite powder, purging the zeolite powder having sulfate adsorbed thereon using N2 gas for 10 minutes, and then injecting H2 gas thereto. As a result, even in a rich condition, that is, a dilute oxygen condition, in which sulfur compounds are discharged into H2S, the discharge amount of H2S gas was about 30 ppm, less than that of SO2 gas, and thus the extent of discharge of H2S was slight. Accordingly, it can be seen that, when zeolite powder is used, a very small amount of the adsorbed SO2 is converted into H2S in a rich condition.
Meanwhile, FIG. 3 shows the reaction of H2S gas and SO2 gas on zeolite powder measured using a mass spectrograph. An experiment on the above reaction was performed by putting 0.5 g of pure zeolite powder in a quartz tube and injecting 20 ppm of H2S gas at a rate of 500 ml per minute, 100 ppm of SO2 gas at a rate of 100 ml per minute and N2 gas at a rate of 100 ml per minute, at a temperature of 500° C. In the above experiment, in a time range of 0˜3200 sec, H2S, SO2 and N2 gas were injected in the above condition at a temperature of 500° C., and, in a time range of 3200˜4400 sec, O2 and N2 gas were injected. Further, in a time range of 4400˜5000 sec, H2S, SO2 and N2 gas were injected in the same condition as during the time range of 0˜3200 sec at a temperature of 500° C., and, in a time range of 5000 sec or more, the quartz tube was rapidly cooled from a temperature of 500° C., while injecting H2S, SO2 and N2 gas, as the result of the above experiment, H2S and SO2 gas, which are reactant gases, were not detected. In conclusion, in the reaction of H2S gas and SO2 gas on zeolite powder, it was determined that both H2S gas and SO2 gas were discharged into SO2 gas through the reaction at a temperature of 500° C., and sulfur compounds were adsorbed on zeolite at low temperatures.
Based on the above results, the present inventor measured the effect of reducing H2S according to a three-way catalyst containing no Ni and zeolite, a three-way catalyst containing Ni and a three-way catalyst containing zeolite, using a mass spectrograph, and showed this in FIG. 4. The three-way catalyst is a catalyst including a honeycombed support, having an insulator structure, coated thereon with the catalyst composition including active alumina supporting palladium and rhodium; metals such as Ba, La, Pr and Zr; and cerium oxides. The Ni-containing three-way catalyst is a catalyst containing Ni at a ratio of 7 g per l of catalyst. The zeolite-containing three-way catalyst according to the present invention is a catalyst containing ZSM-5 powder at a ratio of 10 g per l of catalyst. In FIG. 4, as the result of experimentation on the discharge amount of H2S in an H2S test mode in consideration of the air/fuel (A/F) ratio in a real car, using a mass spectrograph, the discharge amount of H2S in the zeolite-containing three-way catalyst was 27 ppm, which was the lowest measurement value. Accordingly, the three-way catalyst according to the present invention exhibits a better effect of reducing H2S.
Based on the determination that it is difficult to apply zeolite to a three-way catalyst if the capacity of purifying exhaust gases is decreased, even if the discharge of H2S can be suppressed, by applying the zeolite to the three-way catalyst, the performances of the zeolite-containing three-way catalyst, the Ni-containing three-way catalyst, and the three-way catalyst containing no Ni or zeolite were evaluated in an engine bench test through a rapid deterioration mode. The rapid deterioration mode was performed for 50 hours by setting the maximum temperature in the catalyst to 900° C. The three-way catalyst, deteriorated in this mode, corresponds to the catalyst of a real car having traveled 80,000 km. The rapidly deteriorated three-way catalyst was mounted in a 2.0 L vehicle, and was then tested in FTP-75 mode, which is an exhaust qualification test mode in U.S.A and Korea. The test results were shown in FIG. 5. As shown in FIG. 5, it was found that the zeolite-containing three-way catalyst according to the present invention exhibits better effect of purifying HC, CO and NOx than the Ni-containing three-way catalyst.
As described above, the present invention provides a Ni-free three-way catalyst which can suppress the discharge of H2S, which causes discomfort, without using Ni, which is harmful to the human body, and which can improve the capacity of purifying exhaust gases at a ratio of 2.9% by adding zeolite in substitute for Ni.
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
Patent Application
20070238606
