Control of SI Engine Exhaust Emission Using ZSM-5 Supported Cu-Pt Bimetals as a Catalyst 2002-01-2147
Recently Cu-ion exchanged ZSM-5 have received considerable research attention as a potential, highly probable, cost effective, judicious alternative of noble metal automotive catalyst mainly because of their ability to promote the decomposition and selective hydrocarbon, reduction of nitrogen oxides (NOx) in the presence of large excess of oxygen. In recent vehicle tests it has been found that Cu-ZSM-5 catalysts indeed have much better activity toward NOx reduction under lean conditions than that of its noble metal counterparts. In our previous investigation on catalytic reduction of S I Engine emissions using Cu-ion exchanged ZSM-5, copper sites were found highly active for the simultaneous reduction of NOx and oxidation of HCs and CO. In spite of great potentiality and possibility the disadvantage associated with copper based automotive exhaust catalysts is it's comparatively more towards sulphur poisoning than that of the noble metal. Best remedy of this disadvantage may be the appropriate and successful use of bimetallic system. It is well known that bimetallic catalysts often exhibit improved catalytic activity stability and /or selectivity. The use of traces of noble metals often greatly enhances the performance of certain metal oxide catalyst. In our previous communication the catalytic potentiality of Cu-ZSM-5 as a three way automotive exhaust catalyst has been reported. The present paper reports the judicious and successful use of ZSM-5 supported Cu-Pt bimetallic system in conjunction with Cu-ion exchanged ZS-5 in separate stages for simultaneous reduction of NOx and oxidation of HCs and CO of Maruti 800 cc S.I. Engines. The effects of catalyst bed temperature, engine load, engine speed, air fuel ratio on the reduction of the auto-emissions such as NOx, HCs and CO are reported in this paper. Comparison of catalytic activities and the poison resistance characteristics of this system, with that of our previously reported Cu-ZSM-5 catalyst system are also included in this paper.
Cu-ZSM-5 (Cu-4%) in conjunction with ZSM-5 supported Cu-Pt (Cu-4%, Pt<0.1%) was found a very efficient and robust catalyst bed as compared to that of our previously reported Cu-ZSM-5 for the simultaneous reduction of NOx and oxidation of HCs and CO. The best conversion efficiency NOx, CO and HC were observed 85% at 380°C, 83% at 395°C and 78% at 390°C respectively.
Backpressure developed across the catalytic bed was found to be well within the acceptable limits and the efficiency loss of engine was only 0.2%. No diminished catalytic activity was observed even after repeated use of catalysts for 500 hours.