Acetylene Mediated Synthesis Of Au/Graphene Composite For Hydrogenations

Graphene is a two-dimensional allotrope of carbon in which sp~2-hybridized carbon atoms are arranged in a honey-comb lattice.Its unique properties such as high specific surface area,excellent stability and mechanical features make graphene an attractive substrate for deposition of gold nanoparticles(Au NPs).However,graphene does not have sufficient functional groups to anchor Au nanoparticles.Although,most of which have focused on the chemical modification of graphitic surface in order to introduce anchoring sites,the chemical treatment of graphene usually involves complicated procedures and sometimes harsh reaction conditions,which could lead to the cleavage of graphene backbone,and the loss of the inherent properties of graphene.Furthermore,the available procedures usually provided Au NPs with size of 5 to 20 nm.It is not sufficient enough to meet the requirement for catalytic purposes.Thus,a simple and efficient approach to prepare ultrasmall Au NPs immobilized on unmodified graphene is highly desired.In this work,we attempted to in situ synthesize Au/unmodified graphene nanocomposite using acetylene as a reducing agent.Au/graphene composite was characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Ultraviolet–visible spectroscopy(UV-Vis),fourier transform infrared spectroscopy(FT-IR),nuclear magnetic resonance analysis,contact angle measurement and electrochemical analysis.Selective hydrogenation reactions were employed to evaluate catalytic performances.It is found that Au/graphene catalyst had excellent selectivity and activity.Furthermore,recycling test indicated that the catalyst showed an excellent stability without loss of catalytic efficiency.After reaction,the product could be very easily separated via centrifuging to greatly simplify the separation process.Its activity in hydrogenation of halogenated nitrobenzene and the deactivation mechanism in the presence of O2 were also investigated.NH3?BH3 reacts spontaneously with ethanol under N2 or O2,generating active hydrogen species.It's worth noting that Au catalyst is not required at this step.Then the active hydrogen is transferred and adsorbed at the surface of gold to give Au-[H].Finally,halogenated nitrobenzene was hydrogenated by Au-[H] species.In this step,O2 would fast consume the hydrogen species on Au surface,resulting in a poor yield of the desired aniline.