Study On Bimetallic Catalysts For P-chloronitrobenzene Hydrogenation With H₂

Because of their good monodispersity,thermal stability and other unique properties, Core-shell nanoparticles are widely used in chemical, catalysis, energy, biomedical and other fields. Among different types of core-shell nanocatalysts, the study of core-shell nanocatalysts with noble metal core is the most common. However, the cost of noble metals is very high in industrial applications despite that nanocatalysts with noble metal core exhibit excellent catalytic activity. Therefore, how to reduce the cost of nanocatalysts in industry and improve the catalytic performance of noble metal so that make the best use of noble metals attracted many researchers.Two series of core-shell nanoparticles were explored, and discussed. On the one hand, Pd@SiO2, Pd-NiO@SiO2and PdNi@SiO2core-shell nanocatalysts with-4nm nanoparticle core and-17nm thickness of silica shell were synthesized and used in p-chloronitrobenzene (p-CNB) hydrogenation in order to compare their catalytic activity by analyzing the reaction data. The design of experimental steps was summaried as follows:In aqueous system, PdNi@SiO2core-shell mesoporous nanocatalysts were successfully synthesized by a sol-gel process. PdNi alloy NPs were firstly synthesized by co-reduction of K2PdCl4and Ni(acac)2by NaBH4using TTAB as capping agents. The SiO2shells were then coated onto the PdNi NPs by hydrolysis of TEOS. In order to synthesize core-sell nanocatalysts with suitable thickness of shell, the pH value and the mole ratio of TEOS/Pd can be accordingly changed to control the silica shell.Then, the obove obtained PdNi@SiO2NPs was collected and dried and then calcined at500℃to remove TTAB surfactants in order to obtain PdO-NiO@SiO2NPs with large amout of mesoporous. At last, Pd-NiO@SiO2and PdNi@SiO2core-shell nanocatalyst separately obtained after the H2reduction of PdO-NiO@SiO2NPs at200℃and500℃. The other part is to use a similar method to synthesize Pt@SiO2, Pt-NiO@SiO2and PtNi@SiO2core-shell nanocatalysts with similar thickness of silica shell and these three kinds of nanocatalysts were also used in p-chloronitrobenzene hydrogenation for comparing their catalytic activity.Furthermore,the characterization results by FTIR, XRD, TEM and BET confirmed the core-shell structure that show high BET areas and thermal stability. In p-chloronitrobenzene hydrogenation over Pd@SiO2, Pd-NiO@SiO2and PdNi@SiO2nanocatalysts, the activity sequence of p-CNB hydrogenation over Pd@SiO2, PdNi@SiO2and Pd-NiO@SiO2is the following order:Pd-NiO@SiO2> Pd@SiO2> PdNi@SiO2. The catalytic p-CAN selectivity sequence of p-CNB hydrogenation is the following order:Pd-NiO@SiO2> PdNi@SiO2> Pd@SiO2. In p-chloronitrobenzene hydrogenation over Pt@SiO2、 Pt-NiO@SiO2、 PtNi@SiO2nanocatalysts, the activity sequence of p-CNB hydrogenation over Pt@SiO2, PtNi@SiO2and Pt-NiO@SiO2is the following order:Pt@SiO2≈Pt-NiO@SiO2≈PtNi@SiO2. The catalytic p-CAN selectivity sequence of p-CNB hydrogenation is the following order:Pt-NiO@SiO2≈PtNi@SiO2> Pt@SiO2.