Selective Hydrogenation Over Intermetallic Compound Catalysts Prepared By Lithium-Naphthalenide-Driven Reduction

Intermetallic compounds?IMCs?have attracted much attention in recent years due to their long-range ordering of atoms,separation of active sites and specific stoichiometric ratio.Rational design and controllable synthesis of IMCs nanomaterials to adjust the catalytic reaction environment and improve the catalytic reaction efficiency as well as selectivity of target products have attracted wide attention.In this paper,bulk Ni-^intAl_x alloy,Pt-M,and supported Pt-M/CNTs?M=Sn,Cu,Ni?IMCs were prepared by chemical reduction with LiNaPh as strong reductant.Their catalytic performance was detected by hydrogenation of naphthalene and cinnamaldehyde.Ni-^intAl_x catalysts with excellent catalytic activity and high selectivity for hydrogenation of naphthalene had been synthesized by chemical reduction with LiNaPh.Nanoparticles were uniformly dispersed on the support Al₂O₃ and a dense oxide film formed by Al in the presence of air which could protect Ni material from severe oxidation.Among them,Ni-^intAl catalyst with an average particle size of 7.5 nm had purer FCC crystalline phase of Ni and more suitable Al doping amount than other samples.In the selective hydrogenation of naphthalene,the electronic effect between Ni and Al adjusted the adsorption performance of the intermediate tetraline to a certain extent to avoid excessive hydrogenation.The separation of active sites could effectively prevent carbon deposition,and had high catalytic activity and selectivity?The catalytic efficiency for naphthalene was up to 98%and the selectivity for tetraline was 99%?.PtCu,PtNi,Pt₃Sn and other bulk Pt-M IMCs were synthesized using LiNaPh as strong reducing agent.XRD,TEM and other characterizations showed that bulk Pt-M IMCs were mostly pure single phase with uniform particle size and an average particle size of about 2.5nm.LiNaPh was used to modify CNTs to prepare a variety of Pt-M/CNTs intermetallic compound catalysts with theoretical loading of 1 wt.%.The nanoparticles were evenly distributed on CNTs.In the selective hydrogenation of cinnamaldehyde catalyzed by prepared Pt-M/CNTs intermetallics and Pt/CNTs,the highest yield of cinnamic alcohol was obtained by Pt-Sn/CNTs.When Sn content increasesd to 25%,Sn polarized positively which enhanced the adsorption capacity of C=O and enhanced the catalytic activity of catalysts on cinnamaldehyde because of the electronic effect of Sn on Pt?Substrate could be completely converted within 3 h,and the selectivity for cinnamic alcohol was 53%?.With the increase of Sn content,the hydrogenation activity followed a volcano shape with Pt-Sn bimetallic nanoparticles.Due to the electronic effect of Sn on Pt and the attraction of CNTs and Sn,Pt₃Sn/CNTs intermetallic compound catalysts still maintained a high C=O selectivity after 8cycles.The loss of active metals from spent Pt/CNTs catalysts was serious,which proves that the introduction of Sn could effectively avoid the loss of nanoparticles and enhanced the anchoring of Pt-based intermetallic compound nanoparticles.