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 cat alysts with high and low Ce content were prepared and tested in conversion of gas mixtures simulating the emissions from natural gas (NG) driven vehic les and biofuel combustion, The test procedure contained lean and rich ligh t-off activity tests, stationary and oscillating lambda sweeps, space veloc ity tests as well as runs with sulphur poisoning. The catalysts exhibited h igh conversion of the model pollutants. In the oscillating lambda sweep exp eriments, the Pd-Ce/Al2O3 with high Ce loading showed high activities in co nversion of CH4 and CO at lean lambda values up to 1.04. Ageing under the r eactants flow as well as hydrothermal treatment of the catalysts resulted i n improved catalytic activities in terms of light-off temperatures of the m odel pollutants. This activation was believed to be a result of both Cl-rel ease from the surface as well as restructuring of the Pd-particles. Interac tion of Pd-Ce or Al-Ce induced at high temperature was also believed to aff ect the activation. Addition of 5 ppm of SO2 into the gas mixture of simula ted emissions from biofuel combustion raised the T-50% of CH4 by approximat ely 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 Els evier Science B.V. All rights reserved.