“No-Noble-Metal” Catalytic trap to remove Hydrocarbons, NOx and CO emissions from combustion engines
Basically, the catalytic trap bed is composed of a zeolite with a Si/Al ratio between 10 and 20. The zeolite is partially interchanged with cations of one or several non-noble metals. In order to achieve an optimum performance of the catalytic trap, these metals should be interchanged in the internal zeolite structure, and never on its external surface. In this way, the outflow of the exhaust gases passes through the catalytic trap bed to adsorb the HC at low temperatures. The material has been developed at laboratory scale. Different compositions of this material have been tested with simulated streams of internal combustion engines (cold starts). As a result, the material is able to reduce HC emissions in internal combustion engines operating with both mixtures almost stoichiometric and low fuel mixtures. The main difference between this invention and other existing materials is that this catalytic trap avoids any element or additional layer composed of an oxidation catalyst based on noble metals. Consequently, HC emissions could be totally removed through a single bed without using high-cost materials (noble metals) or further stream treatments. This fact allows the catalytic trap to be placed in any position according to the different control systems employed for decreasing other pollutant emissions existing in the gases stream, since the total elimination of HC takes place on the catalytic trap. Thus, this technology development results in a solid material where coexists metal(s) and protons in an optimum ratio inside of the zeolite channels, leading to a system that can act as a HC trap and as an oxidation catalyst in only a single bed, during the whole cold start cycle. The main innovative aspect of this catalytic trap is that the adsorbent material can capture the hydrocarbons in the cold start of the engine and oxidize gases during its warmed-up operating conditions without using noble metals, which are frequently used as oxidation catalyst. At high temperatures, this material is able to carry out total oxidation of both hydrocarbons retained by the catalytic trap and those present in the exhaust gas stream. Consequently, the resulting gas stream released to the atmosphere is innocuous in hydrocarbons. • Noble metals are not used. • Structural advantages, since the control systems are simplified and pollutants in internal combustion engines are reduced. • Economic benefits (The price of noble metal is approximately 100 times more expensive than the materials employed by the researchers). • The catalytic trap can be placed in any position with regard to different control systems. • Besides its hydrocarbon trapping role, the system can also act as oxidation catalyst during the cold-start cycle.