In recent years,single atom catalysts have shown great potential in heterogeneous catalysis.Precious metal catalysts,especially the palladium catalysts,have been widely used in industrial hydrogenation reactions.In this thesis,we used a novel synthetic strategy-thermal atomization to create atomically dispersed palladium atoms anchored on SBA-15 and nitrogen-doped carbon shell over SBA-15(SBA-15@N-C),respectively.The morphologies and microstructure of the catalysts were examined by a series of characterizations.Both catalysts show excellent catalytic performance in hydrogenation reactions.The main contents are as follows:1.Single atom catalyst was synthesized by thermal atomization.(Catalyst 1)The palladium salt solution was dispersed onto the nitrogen doped carbon shell over SBA-15 by sonication.Then,it was calcined at high temperature in an argon atmosphere followed by air to burn away excess nitrogen layer to give single atom catalyst Pd1/SBA-15.The high angle of annular dark field scanning transmission electron microscopy,X-ray photoelectron spectroscopy,and other means were used for characterization.The results verify that the palladium atoms were dispersed in an isolated fashion over the support.(Catalyst 2)The single atom catalyst Pd1/SBA-15@N-C was obtained by depositing Pd atoms on SBA-15@N-C.It was characterized by high angle of annular dark field scanning transmission electron microscopy,X-ray photoelectron spectroscopy,X-ray absorption fine structure and other techniques.The results show that the Pd species were atomically dispersed and coordinated with four nitrogen atoms(Pd-N4).2.Styrene and phenylacetylene hydrogenation reactions were performed with different catalysts under mild conditions.1)For styrene hydrogenation,Pd1/SBA-15 achieved 99%conversion to phenylethane within 120 min,the turnover frequency(TOF)was calculated to be632 h-1.For the semi-hydrogenation of phenylacetylene,the conversion reached 99%,and the selectivity to styrene was 78%and TOF value was 11538 h-1 after 5 min;2)Pd1/SBA-15@N-C has a high efficiency for the semi-hydrogenation of phenylacetylene,with a conversion was96%and selectivity to styrene of 93%at 10 min,along with a high TOF of up to 12060 h-1.For the hydrogenation of styrene,the conversion is merely 6%at 180 min.3.The high temperature stability of the catalysts Pd1/SBA-15 and Pd1/SBA-15@N-C was tested at 500°C under the condition of 5%H2/95%Ar atmosphere.After calcination,the catalysts maintained their original structure without Pd agglomeration.The single-atom catalyst can be reused repeatedly without significant decay in the activity.In addition,we have validated the feasibility of large-scale synthesis of the catalyst,and the catalyst’s activity was similar to the catalyst prepared in lab-scale. |