Catalysts engine aging

Fig. 4.18 Product yield during the NH3 oxidation evaluation depicting N2, NO, N2O, and NO2 in a fresh SCR catalyst and b SCR catalyst engine-aged at 650 °C...

Table 18. Engine-out and tailpipe emissions of a passenger car equipped with a closed-loop three-way emission control catalyst in the three phases of the US-FTP 75 vehicle test cycle (engine aged catalyst).

Figure 59. Influence of space velocity on gas temperature needed to reach 50% and 70% conversion of CO, HC and NOjt over a fresh and an engine aged three-way catalyst (monolith catalyst with 62 cells cm, three-way formulation with Pt 1.42gl-, Rh 0.28gl->, engine bench light-off test at lambda 1.02 for CO and HC, and at lambda 0.986 for NO engine bench aging during 200 h).

Figure 63. Influence of monolith radius at fixed catalyst volume on the conversion of CO, HC and NO.v reached over fresh and engine aged three-way catalysts at fixed exhaust gas temperature, space velocity and exhaust gas composition (monolith catalyst with 62cellscm" engine bench test space velocity 60000 N11 h exhaust gas composition lambda 0.995 dynamic frequency 1 Hz amplitude 1A/F).

Figure 67. Influence of the washcoat formulation on the conversion of CO, HC and NO , reached over various engine aged three-way catalysts as a function of the exhaust gas lambda value (monolith catalyst with 62cells cm three-way formulation with Pt 1.16gC, Rh 0.23gl" engine bench test A/F scan at a space velocity of 60000 Nl 1 h exhaust gas temperature 723 K dynamic frequency 1 Hz amplitude 1 A/F engine bench high temperature aging cycle for lOOh). Sample A baseline formulation, samples B-D increasing amounts of stabilizers.

The influence of the total amount of precious metals on the conversion also depends upon the catalyst operation conditions (Fig. 72). After engine aging, the HC light-off under lean conditions is improved by about 40 K upon increasing the Pd loading from 3.5gl to 40gl , whereas the improvement is only about 20K under stoichiometric conditions. 

Figure 76. Conversion of CO, HC and NO < reached at fixed reaction conditions over model catalysts representing the different combinations between the precious metals Pt, Pd and Rh, and the wash-coat constituents alumina and ceria, after engine aging (monolith catalyst with 62 cells cm Pt, Pd or Rh at an equimolar loading of 8 mmol 1 Pt/Rh catalyst withPt 1.42gl, Rh ...

Table 27. Amount of sulfur, phosphorus and carbon on a diesel catalyst after aging on a diesel engine bench, as a function of the platinum loading, and of the composition of the fuel and the engine lubricating oil. (Reprinted with permission from ref [69], C 1992 Society of Automotive Engineers, Inc.)...

Likewise, Fig. 112 shows the conversion efficiency for diesel particulate matter reached in the US transient cycle with a diesel catalyst mounted on a heavy duty engine. Table 29 shows the conversion for CO, HC and particulate matter in the European 13-mode test performed with a heavy duty engine for a fresh and for an engine-aged catalyst. The catalyst performance at operating conditions, reflecting the lowest and the highest exhaust gas temperature in this 13-mode test, is also reported. 

Table 28. Emission of carbon monoxide, gaseous hydrocarbons, nitrogen oxides and particulate matter from a passenger car equipped with an IDI/NA diesel engine, and conversion over a diesel catalyst in the fresh and the engine aged state, in the different phases of the US-FTP 75 vehicle test procedure and of the European MVEG-A vehicle test procedure. ...

The first results on the durability of the diesel NO i reduction catalyst show that engine aging decreases the maximum NO.v conversion and shifts the onset of the conversion to higher temperatures. This deactivation was found to be caused by phenomena similar to those identified for the deactivation of diesel oxidation catalysts. 

Figure 2 Static engine sweep test results for catalyst types I and IV. (100 g Pd/ft 40 h, 1273 K engine aged SV=60000 NWh, Tw = 673 K IHz 1A/F)...

Fig. A. Static engine based selectivity test showing the.influence of barium stabiliser on catalyst performance (A) for palladium based catalysts after 300 hrs engine ageing (800°C max.) and (B) for Rh based catalysts after hydrothermal ageing for 1 hr at 950°C.

Figure 1A shows the response of an engine-aged Pt/AlgOg catalyst to S02 injection at 300°C from 60 to 130 minutes. The conversion of CgHg increases from 15% to 53%. Following removal of the SO2, the CgHg conversion declines to... 

The results obtained with the engine-aged, laboratory PbB -aged, and model catalysts all clearly indicate that Pb-poisoned Pt/A Oj catalysts can be reactivated by S02. The model experiments indicate that the reactivation mechanism involves the formation of PbSO, which removes Pb from the Pt. Additional evidence for this mechanism is found in the CO adsorption experiments, described in the next section. 

To maximise lead deposition, and to simulate the vehicle that spends its life doing city driving, two catalysts were aged on a dynamometer engine to a predominantly low temperature, low load fcycle. The cycle is summarized in Fig. 2, the ageing duration is 300 hrs. This represents 80K km on the road. 

Figure 6. Performance of engine-aged N-2 catalyst for removal of nitric oxide from a synthetic exhaust.

Composition of the gas fed to the preheat section of the reactor (Table I) was selected by averaging data from numerous sources on the composition of automobile exhaust gases. Propylene simulated all hydrocarbons in the exhaust gas. For some experiments, the catalysts were aged in a 260-in.3 converter attached to the exhaust pipe from a 350-in.3 V8 engine under a water brake dynamometer load equivalent to 50 mph. 

---