Study On The Preparation Of Pd Nanocatalyst And Its Application For CO Oxidation

As an important component of air pollution,CO is a colorless,odorless and harmful gas to human health,and when the concentration of CO is too high,it will have adverse effects on people's life,work,science and technology,etc.Therefore,the research on the elimination of CO oxidation has attracted much attention.At present,the catalysts for CO oxidation are mainly divided into two types:precious metal catalysts and non-precious metal catalysts.The catalytic performances of non-precious metal catalysts are generally low,while those of precious metal catalyst are excellent but the cost of precious metals is high.Therefore,the preparation of precious metal catalysts with high stability is a research hotspot.We firstly focused on the modification of Al₂O₃ support in this paper,and prepared a series of Pd/Al₂O₃ catalysts by liquid phase in situ reduction method,and then the catalytic activity for CO oxidation was studied.Meanwhile,CO-TPD,XRD,IR,BET,TEM,XPS and AFM spectroscopy methods were use to investigate the adsorption characteristics,surface structure and morphology of Pd-based catalysts.The influence of Al₂O₃ support modification on the structure and catalytic activity of Pd catalyst was discussed.The specific research tasks are as follows:?1?The structural modification of cellulose on the Al₂O₃ support was studied,the effects of key factors?e.g.,pretreatment method,cellulose content,support acidity and active metal content?on the CO oxidation activity of Pd/Al₂O₃ catalyst were discussed.The experimental results showed that the highest catalytic activity for CO oxidation was achieved over the 1%Pd/6X-Al₂O₃ catalyst with 6 wt%cellulose addition,wherein the CO light-off started at 90?and CO was completely transformation at 150?.At the same time,the spectral characterization results showed that the addition of cellulose could effectively promote the formation and uniform dispersion of Pd particles in the hydrothermal crystallization process.Pd particle size in the prepared catalyst was distributed in the range of 2-5 nm,which supports a good activation ability for CO oxidation.?2?The structure of Al₂O₃ support was modified by adding Ni species,the effects of key factors?e.g.,Ni/Al molar ratio,support crystallization time,preparation method and active metal content?on the CO oxidation activity of Pd/Ni-Al₂O₃ catalyst were investigated.The experimental results showed that the highest CO oxidation activity was achieved over the 1%Pd/Ni-Al?1:40?catalyst with the 1:40 molar ratio of Ni/Al,wherein the CO light-off started at 50?and CO was completely transformation at 130?.Compared with the cellulose modified catalyst,the catalytic activity of 1%Pd/Ni-Al₂O₃catalyst for CO oxidation was significantly enhanced.Meanwhile,the results of spectral characterization showed that there was a certain interaction between Ni and Al₂O₃,which significantly improved the formation of Pd particles in the catalyst.Pd particle size in the prepared catalyst was distributed in the range of 1-4 nm,which supports an excellent activation ability for CO oxidation.?3?The catalytic activity of the catalyst for CO oxidation under different reaction condition was studied,and the size change of Pd particles in the catalyst before and after the reaction was also discussed.The experimental results showed that the catalyst prepared from Al₂O₃ support by cellulose or Ni species modification had better catalytic performance than the catalyst prepared by pure Al₂O₃,and the performance of the catalyst remained stable after repeated experiment for 6 times.The results of XPS and TEM showed that Pd particles in the catalyst remained stable before and after the reaction,and Pd species mainly existed in the form of Pd⁰.Compared with traditional calcination method,the advantages of hydrothermal crystallization and liquid phase in situ reduction method adopted in this paper are unique.