Study On Fullerene Electronic Buffered Copper-based Catalysts For Selective Conversion Of C-O Bonds

The development of new and efficient catalysts with excellent performance and mild operating conditions is one of the goals of chemical industry,and is also conducive to the realization of carbon peaking and carbon neutrality.Copper-based catalysts are widely used in heterogeneous catalysis such as C-O bond hydrogenation,alcohol reforming,CO oxidation,NOx reduction and many other reactions,due to their advantages of cheap,harmless,and simple-structured.However,there are still many problems in the industrial application of Cu-based catalysts,such as harsh and sensitive reaction conditions,valence imbalance,and easy sintering.The addition of elements or second metal promoters to improve the activity and stability has been widely studied,and most of the promoters achieve performance improvement by irreversibly changing the surface electron density of Cu.On the other hand,fullerene materials represented by C60 and C70 have unique structures and exotic electronic properties of reversible electrons reception and release,which have been demonstrated in many fields such as electrochemistry and photovoltaic devices.However,there are few reports on the use of this electronic property of fullerenes as catalyst promoters.In this thesis,in order to modify the structure and performance of copper-based catalysts,fullerene-based materials such as C60 were innovatively introduced into Cu/SiO2 catalyst(C60-Cu/SiO2).Reactions involving the selective conversion of C-O bonds,such as the hydrogenation of dimethyl oxalate(DMO)to ethylene glycol(EG)and methanol steam reforming(MSR),were taken to investigate the catalytic performance of C60-Cu/SiO2.In addition,various characterization methods were used to investigate the influence of fullerene-based materials such as C60 on the catalyst structure and chemical environment.Reasonable structure-activity correlations were proposed,and the following main results were obtained.The C60-Cu/SiO2 catalyst was used in the hydrogenation of DMO to EG,and the ambient-pressure reaction can be realized.Compared with the conventional Cu/SiO2 catalyst,the EG yield was increased by nearly 10 times,and the performance remained stable in the 1000-hour test.The catalyst structure after the reaction also maintained stable,and the recovery of C60 can be realized.A series of spectroscopic characterization results showed that most of C60 were adsorbed on the surface of Cu nanoparticles,and d-π interaction was formed with between C60 and Cu,which inhibited the reduction of Cu species and significantly increased the content of Cu+in the catalyst.Supported by electrochemical cyclic voltammetry and charge transfer theoretical calculations,it was confirmed that C60 can act as "electronic buffer" to stabilize Cu+ in the system.And the electronic buffered Cu+ can keep balance during the reaction process and enhance the adsorption and activation of DMO substrates,thereby greatly improving the catalytic activity and stability.In addition,the Cu species bound by C60 can also enhance the chemisorption of H2,and it is beneficial to improve the hydrogenation catalytic performance of C60-Cu/SiO2 catalyst.The C60-Cu/SiO2 catalyst was used in the MSR reaction and the results showed that compared with the Cu/SiO2 catalyst,the hydrogen activity was increased by 37-58%,and the by-product CO selectivity was reduced by 32～56%.Performance and structural stability were maintained during 100-hour stability test.The structure-activity correlation study of the catalyst showed that the electronic buffered Cu+ sites by C60 in this system play a key role in the adsorption and activation of oxygen-containing groups and the inhibition of CO by-product formation.Combined with the results of in situ MSR-DRIFTS and other characterizations,the reaction route of methyl formate intermediate for MSR reaction over the C60-Cu/SiO2 catalyst was proposed.On the basis of the above work,further attempts have been taken to expand the catalytic promotion effect of other fullerene-based materials(fullerene C70,fullerenol and fullerene polymer)on the Cu/SiO2 catalyst in this thesis.The experimental results show that C70 also possesses the characteristics of reversible receiving and releasing electrons and excellent thermal stability.The C70-Cu/SiO2 catalysts also showed great catalytic activity and stability in DMO hydrogenation and MSR reaction.The combination of characterization and theoretical calculation showed that C70 can also act as "electronic buffer" similar to C60,and can stabilize Cu+ in the catalyst,thereby improving its catalytic activity.The Cu/SiO2 catalysts with Fullerenol(FO)and fullerene polymer(FP)also showed a certain catalytic promotion effect,but they were difficult to achieve the promotion effect like C60 and C70.It is speculated that due to the destruction of the fullerene conjugated structure in FO and FP to a certain extent,it was difficult for them to fully inherit the electronic buffering properties of C60.What’s more,they have losed the good thermal stability of C60.