Palladium based catalysts for exhaust aftertreatment of natural gas powered vehicles and biofuel combustion

Hydrothermally aged (1000/850 degreesC, 12/16h) Pd-Ce-supported alumina catalysts with high and low Ce content were prepared and tested in conversion of gas mixtures simulating the emissions from natural gas (NG) driven vehicles and biofuel combustion, The test procedure contained lean and rich light-off activity tests, stationary and oscillating lambda sweeps, space velocity tests as well as runs with sulphur poisoning. The catalysts exhibited high conversion of the model pollutants. In the oscillating lambda sweep experiments, the Pd-Ce/Al2O3 with high Ce loading showed high activities in conversion of CH4 and CO at lean lambda values up to 1.04. Ageing under the reactants flow as well as hydrothermal treatment of the catalysts resulted in improved catalytic activities in terms of light-off temperatures of the model pollutants. This activation was believed to be a result of both Cl-release from the surface as well as restructuring of the Pd-particles. Interaction of Pd-Ce or Al-Ce induced at high temperature was also believed to affect the activation. Addition of 5 ppm of SO2 into the gas mixture of simulated emissions from biofuel combustion raised the T-50% of CH4 by approximately 100 degreesC. SO2-TPD experiments were used to correlate the catalytic activity to S-poisoning. The catalysts were characterised by H-2-adsorption, XPS, FTIR, SO2-/NO-/O-2-TPD, XRD, XRF and N-2-physisorption. (C) 2001 Elsevier Science B.V. All rights reserved.