Synthesis Of Graphdiyne/Graphyne-based Dual Atomic Pd Catalyst And Its Performance For Nitrobenzene Reduction

Single-atom catalysts show great potential in catalysis because of their fully exposed active sites and maximum atomic utilization.However,single-atom catalysts have only one specific active site,and it is difficult to improve the catalytic activity to the optimal level when multi-step or multi-intermediates are involved in complex reactions.Compared with single-atom catalysts,dual-atom catalysts have more than one adsorption site,which can optimize the interaction between reactants/intermediates and the catalytic active center,so that the dual-atom as the active site can carry out synergistic catalysis,improve the reaction rate and selectivity,and thus improve the overall catalytic performance.Graphynes is a new carbon allotrope composed of sp and sp~2hybrid carbon atoms,and the ortho alkyne bonds of benzene ring have strong anchoring effect on transition metal atoms.In particular,the fixation effect of the alkyne bonds on metal atoms is much stronger than that of sp~2hybrid carbon materials.At the same time,the structure of graphdiyne material has rich tunability,which provides more possibilities for the design and synthesis of new atomic catalysts.Based on the above research background,we designed and synthesized graphdiyne（TEGDY）and graphyne（TEGY）,which have different hole sizes,through C-C coupling reaction.Based on the strong anchoring effect of ortho alkyne bonds of benzene ring to transition metal atoms,acetylene-based double-atom Pd catalysts TEGDY-Pd and TEGY-Pd were constructed with precise coordination sites and adjustable metal atom spacing.Then the effect of the distance between metal atoms in the acetylene bond holes on the catalytic activity was investigated using 4-nitrophenol（4-NP）reduction reaction as a model.The results showed that both TEGDY-Pd and TEGY-Pd demonstrated the adsorption capacity to 4-NP,and the adsorption rate of TEGY-Pd to 4-NP was 2.9 times higher than that of TEGDY-Pd.In addition,in the reduction reaction of 4-NP,the rate constant of TEGY-Pd is 2.1 times higher than that of TEGDY-Pd,and it also shows high cyclic stability.Further,TEGY-Pd displayed high catalytic activity to nitrobenzenes with different structures.DFT calculation shows that TEGY-Pd has greater binding energy to 4-NP than TEGDY-Pd.Besides,due to the closer distance between Pd atoms in TEGY-Pd（TEGY-Pd:3.8?;TEGDY-Pd:8.2?）,when one oxygen atom in 4-NP is anchored by Pd atom,the electron cloud density on the other Pd atom is affected by 4-NP and the charge change was more obvious.Compared with TEGDY-Pd,the other O atom in nitro functional group is easier to have dipole interaction with the second Pd atom in TEGY-Pd.This study shows that for the same metal species,the distance of Pd atom has an important influence on the reaction process.