Synthesis Of Single Atom Catalysts Based On SBA-15 Molecular Sieve And Investigation Of Their Hydrogenation Performance

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.