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

摘要

Hydrothermally aged (1000/850°C, 12/16h) Pd-Ce-supported alumina catalysts with high and low Ce content were pre- pared and tested in conversion of gas mixtures simulating the emissions from natural gas (NO) driven vehicles and biofuel combustion. The test procedure contained lean and rich light-off activity tests, stationary and oscillating lambda sweeps, space velocity tests ~s well as runs with sulphur poisoning. The catalysts exhibited high ~nversion of the model pollutants. In the oscillating lambda sweep experiments, the Pd-Ce/AI203 with high Ce loading showed high activities in conversion of C~ and CO at lean A 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 be- lieved to be a result of both Cl-release from the surface as well as restructuring of the Pd-particles. Interaction of Pd-Ce or AI-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 Tso% of CH4by approximately 100°C. SO2-TPD experiments were used to correlate the catalytic activity to S-poisoning. The catalysts were characterised by H2 -adsorption, XPS, FfIR, SO2-/NO-/02-TPD, XRD, XRF and N2-physisorption.