Low-content Noble Metal Catalyst And Its Preparation,Characterization And Application In HC-SCR Reaction

Large quantities of pollutants are released to the environment from the combustion of biomass and fossil fuels.Among these contaminants are nitrogen oxides?NOx?which are the source of severe environmental problems.Research in the field of NOx abatement has grown significantly in the last decades.Alternatively,selective catalytic reduction of NOx using hydrocarbons as a reductant?HC-SCR?is currently attracting a great deal of interest because of the main advantage of the use of a gas mixture very similar to that found in exhausts.The noble metal catalysts have been generally regared as the most desiable catalysts.However,the high cost of the noble metal catalysts limits their widespread application.From the consideration on the economy,combining with the advantages of noble metal catalyst and the non-noble metal,adding an appropriate amount of non-noble metal content into the noble metal to prepare a complex catalyst of noble metal which has both precious and non-precious properties so that reducing the cost of the catalyst and improving the activity and stability of the catalyst.The main results of this dissertation are as follows:1?Nb-modified low-content noble metal catalystNb-modified Pd/Al₂O₃ and Pt/Al₂O₃ were prepared and tested for the NOx selective catalytic reduction,It was clear that adding Nb could significantly improve the catalytic activity.The T90 of Pd-Nb/Al₂O₃ and Pt-Nb/Al₂O₃ were 39 ? and 52 ? lower respectively than that for similar performance with the Pd/Al₂O₃ and Pt/Al₂O₃ catalyst.The results showed that the catalytic activity increased first and reduced then with the increase of Nb content and the best loading content was 5% and 10% each when the catalytic activity increased most significantly.The results showed that the addition of Nb effectively improved the activity and stability of the noble metal catalyst by increasing the dispersion of Pd and Pt active components and increasing the oxygen species concentration on the surface of catalyst.2?Mo-modified low-content noble metal catalystMo-modified Pd/Al₂O₃ and Pt/Al₂O₃ were prepared and tested for the NOx selective catalytic reduction,It was clear that adding Mo could significantly improve the catalytic activity.The T90 of Pd-Mo/Al₂O₃ and Pt-Mo/Al₂O₃ were 37 ? and 44? lower respectively than that for similar performance with the Pd/Al₂O₃ and Pt/Al₂O₃ catalyst.The results showed that the catalytic activity increased first and reduced then with the increase of Mo content and the best loading content was 5% and 10% each when the catalytic activity increased most significantly.The results showed that the addition of Mo effectively improved the activity and stability of the noble metal catalyst by increasing the dispersion of Pd and Pt active components and increasing the oxygen species concentration on the surface of catalyst.The addition of Nb and Mo effectively improved the performance of the catalyst,which could be attributed to highly dispersed active Pd and Pt components as well as the partially metallic Pd and Pt generated and the increased oxygen species concentration on the surface of catalyst.Moreover,the catalytic activity of the catalyst is higher than that of the 2% Pd/Al₂O₃ and 2% Pd/Al₂O₃ catalyst,indicating that the consumption of noble metal will be saved by more than half with the addition of Nb and Mo.